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Abstract

The Gold King mine water release that occurred on 5 August 2015 near the historical mining community of Silverton, Colorado, highlights the environmental legacy that abandoned mines have on the environment. During reclamation efforts, a breach of collapsed workings at the Gold King mine sent 3 million gallons of acidic and metal-rich mine water into the upper Animas River, a tributary to the Colorado River basin. The Gold King mine is located in the scenic, western San Juan Mountains, a region renowned for its volcano-tectonic and gold-silver-base metal mineralization history. Prior to mining, acidic drainage from hydrothermally altered areas was a major source of metals and acidity to streams, and it continues to be so. In addition to abandoned hard rock metal mines, uranium mine waste poses a long-term storage and immobilization challenge in this area. Uranium resources are mined in the Colorado Plateau, which borders the San Juan Mountains on the west. Uranium processing and repository sites along the Animas River near Durango, Colorado, are a prime example of how the legacy of mining must be managed for the health and well-being of future generations. The San Juan Mountains are part of a geoenvironmental nexus where geology, mining, agriculture, recreation, and community issues converge. This trip will explore the geology, mining, and mine cleanup history in which a community-driven, watershed-based stakeholder process is an integral part. Research tools and historical data useful for understanding complex watersheds impacted by natural sources of metals and acidity overprinted by mining will also be discussed.

Introduction and Purpose

An accidental release of ~3 million gallons of contaminated water, which occurred at the Gold King mine on 5 August 2015 near the historic mining community of Silverton, Colorado, has heightened awareness throughout the United States of the ongoing geoenvironmental impacts from abandoned mines (Fig. 1). Largely as a result of this event, Silverton residents and Colorado Governor John Hickenlooper asked the U.S. Environmental Protection Agency (EPA) for Superfund cleanup designation of the Bonita Peak mining area, which includes the Gold King mine and 45 other mines in the Animas River watershed. Abandoned mines have been and continue to be sources of contaminants to surface water and groundwater, in the form of draining mine adits, mine waste piles, fluvial tailings, and tailings impoundments. This contamination has occurred for decades to centuries. The water quality is due in part to mining, but also to naturally occurring altered and mineralized rocks in unmined areas that weather to produce acidic drainage.

Figure 1.

Photos taken on 5 August 2015 after Gold King mine water release. (A) View south below Silverton, Colorado, of Cement Creek (river right) and upper Animas River confluence (7:00 p.m.). Kendall Mountain Rd. in distance (upper right); stop 3, Day 3. (B) View east toward North Fork Cement Creek (6:27 p.m.). Debris fan formed during the Gold King mine water release. Photos courtesy of Ken Balleweg.

Figure 1.

Photos taken on 5 August 2015 after Gold King mine water release. (A) View south below Silverton, Colorado, of Cement Creek (river right) and upper Animas River confluence (7:00 p.m.). Kendall Mountain Rd. in distance (upper right); stop 3, Day 3. (B) View east toward North Fork Cement Creek (6:27 p.m.). Debris fan formed during the Gold King mine water release. Photos courtesy of Ken Balleweg.

This trip will include: (1) a review of current and new U.S. Geological Survey (USGS) techniques used to identify and characterize the concentrations and transport of toxic materials (both natural and anthropogenic) in abandoned mine areas; (2) a review of the “Stakeholder Process,” which seeks input from private landowners, local communities, academia, and state and federal agencies in developing remediation plans; and (3) cleanup strategies used for contaminants derived from hard rock metal mining and the storage and containment of radionuclide-bearing mine and mill waste. The reader is referred to USGS Professional Paper 1651 (von Guerard et al., 2007) for a more comprehensive discussion of many methods and techniques used to address geoenvironmental issues in historically mined watersheds.

Our trip will visit the historic mining communities of Creede and Silverton, located in the San Juan Mountains of southwest Colorado (Fig. 2). In Creede (Fig. 3), we will visit the Nelson Tunnel Superfund site and Commodore mine reclamation area. These sites are in the Central San Juan caldera cluster. Intracaldera ash-flow tuffs at Creede are host to epithermal polymetallic veins that were mined extensively from the late 1880s to the 1980s. The trip route will traverse the historical mining district north of Creede along northerly trending veins that formed within the intracaldera fill. We will also visit reclaimed areas below historical metallic mill sites in the Willow Creek floodplain south of the Creede mining district.

Figure 2.

(A) Index map showing field-trip area in southwest Colorado (green box). Animas River watershed (ARW) shown in mint green, major rivers (italics) are shown in blue. (B) Enlargement of green box in A showing major roads and counties (tan); days of trip corresponding to road log shown adjacent to each city (1–4). See Figures 3, 4, and 5 for detailed trip route.

Figure 2.

(A) Index map showing field-trip area in southwest Colorado (green box). Animas River watershed (ARW) shown in mint green, major rivers (italics) are shown in blue. (B) Enlargement of green box in A showing major roads and counties (tan); days of trip corresponding to road log shown adjacent to each city (1–4). See Figures 3, 4, and 5 for detailed trip route.

Figure 3.

Numbered stops for Day 1 (Creede area) correspond to field-trip log in this guide. Field-trip route (solid black line); faults and veins (solid yellow-orange lines). County source of faults and veins is from Steven and Ratté (1965). BVS—Bull Dog Mountain vein system; AV— Amethyst vein; SHV—Solomon—Holy Moses vein system. Solid red line is road CO-149. Terrain hill-shaded relief map from ArcGIS online.

Figure 3.

Numbered stops for Day 1 (Creede area) correspond to field-trip log in this guide. Field-trip route (solid black line); faults and veins (solid yellow-orange lines). County source of faults and veins is from Steven and Ratté (1965). BVS—Bull Dog Mountain vein system; AV— Amethyst vein; SHV—Solomon—Holy Moses vein system. Solid red line is road CO-149. Terrain hill-shaded relief map from ArcGIS online.

Figure 4.

Field-trip route for Silverton area. Gold King mine #1 and #7 refer to mine adit levels. Numbered stops for Days 3 and 4 correspond to field-trip log in this guide. Terrain hill-shaded relief map from ArcGIS online. Streams (in blue) and mine site locations are from Sole et al. (2007).

Figure 4.

Field-trip route for Silverton area. Gold King mine #1 and #7 refer to mine adit levels. Numbered stops for Days 3 and 4 correspond to field-trip log in this guide. Terrain hill-shaded relief map from ArcGIS online. Streams (in blue) and mine site locations are from Sole et al. (2007).

Figure 5.

Field-trip route for Durango area. Numbered stops for Day 2 correspond to field-trip log in this guide. Animas River (blue); major roads U.S.-160 and S. Camino del Rio (labeled).

Figure 5.

Field-trip route for Durango area. Numbered stops for Day 2 correspond to field-trip log in this guide. Animas River (blue); major roads U.S.-160 and S. Camino del Rio (labeled).

Sites visited in Silverton (Fig. 4) include Cement Creek basin and the proposed Bonita Peak Superfund area. Cement Creek traverses the core of the San Juan and nested Silverton calderas. Ancient ferricrete (iron-oxyhydroxide-cemented surficial deposits) and natural iron springs in Cement Creek, which we will visit and discuss on this trip, are strong visual indicators of the naturally occurring sources of acidity and metals that were present prior to mining. The area of the Gold King mine in upper Cement Creek will also be visited. The field-trip route will traverse regionally propylitically altered volcanic rocks that are host to the majority of base and precious-metal mineralization, an acid sulfate hydrothermal system, and epithermal polymetallic vein systems of the Gold King and Sunnyside mines. We will also be visiting the historical Mayflower tailings and metal mill sites at Eureka town site east of Silverton. Lake Emma, the site of an accidental mine water release that occurred in 1978, will also be visited, highlighting the ongoing legacy of mining impacts on the Animas River watershed.

These areas are excellent examples of how multiple sources of contaminants from both natural weathering and mining processes have affected water quality. These two areas were chosen because they have been the sites of focused geologic study since the early 1900s. Mineral deposits in these mining areas formed in similar Paleogene caldera environments. However, there are differences in the geologic, mineralogic, hydrothermal alteration, and mineral deposit types, which offer insights into the current environmental impacts of each area.

A third area affected by uranium milling in the community of Durango, Colorado, will also be visited (Fig. 5).

New Perspectives—Post-Usgs, Animas Abandoned Mine Lands Study

The Silverton mining area within the Animas River watershed (ARW) has been the site of intensive Animas Abandoned Mine Lands (AML) study by the USGS from 1996 to present. This work had multiple goals. One goal was to determine pre-mining geochemical background conditions. Another goal was to evaluate sources of acidity and metals to surface water derived from the weathering of hydrothermally altered rocks in non-mining-affected areas compared with areas impacted by mining (von Guerard et al., 2007). The AML study produced one of the most comprehensive data sets available for a geologically complex area that was impacted by historical hard-rock mining, and it generated many reports that document collaborative studies on the geology, hydrology, geochemistry, remote sensing, geophysics, and biology of this system (von Guerard et al., 2007). One role of the USGS is to provide the science to federal land managers to aid in making science-based decisions for environmental cleanup. The historical data sets produced during the USGS AML studies and how these data can be currently applied to abandoned mine land issues will be explored.

Watershed-Based and Collaborative Science Approach

A watershed approach was used as part of the AML study because the watershed units provide a manageable scale (sub-watersheds covering tens of km2 to basins covering ~100 km2) in which to assess water quality impacts from natural and mining sources of contaminants. The watershed scale can be used to effectively categorize an area that may be geologically and mineralogically complex, into logical units that can be more easily interpreted and managed in a larger basin context. Reclamation efforts commonly are mine site or mine feature based, so the subwatershed comprises an area that land managers think about when allocating resources to prioritize and mitigate the impacts of mining-related issues (Yager et al., 2013).

Watersheds are defined based on terrain boundaries (topographic divides) and hydrography. The surface hydrology of a watershed controls where water flows and how sediment is transported across the landscape. This is important because the hydrologic areas defined by watersheds can have varying geology, alteration, and mining impacts. Water interacting with bedrock, sediments and soils, and mine-related deposits can either neutralize or generate acidity. If resulting waters are acidic, they can leach metals from sulfide minerals disseminated in bedrocks and in veins, thereby contributing metals to surface water and groundwater (Bove et al., 2007a, 2007b; Yager, 2008; Yager et al., 2008a, 2008b). Where sulfide minerals such as pyrite (FeS2) are abundant, water interacts to produce sulfuric acid, which leaches metals from rocks, sediment, and colloids. The leached metals are toxic to aquatic life (Besser and Brumbaugh, 2007).

Within the AML study, collaboration occurred between geologists, geochemists, hydrologists, geophysicists, remote sensing specialists, biologists, and database experts. Such collaboration is necessary in geologically complex mining areas, because a holistic approach is needed to understand the natural weathering, hydrologic, and mining-related processes that impact water quality. A quick solution to complex issues involving mine land cleanup, while desirable, is unlikely given the complexity and magnitude of the mine cleanup issues facing many western mining communities. A collaborative approach that evaluates mining impacts within the larger geologic framework can be very useful to address both short- and long-term watershed cleanup goals.

Concepts of Geochemical Background and Baselines

The concepts of geochemical background and baselines are important for understanding life cycles of mineral deposits, including deposit discovery, pre-mining permitting and planning, active mining, mine closure, and mine cleanup. Geochemical background and baselines have been defined in multiple ways (Reimann et al., 2005). Geochemical background analyses provide information on the elements present and their concentrations that will be encountered during mining and after mining ceases. The specific elements that weather from rocks, sediments, and mining sources are unique to the hydrothermal alteration assemblages and mineralized systems from which they are sourced (du Bray, 1995). The collection and analysis of background and baseline samples unaffected by mining helps to establish a context in which to compare mining impacted samples.

Two definitions of geochemical background particularly relevant to this field trip are ambient and natural background. The ambient background is defined as the geochemical signature that is no longer pristine and has been impacted by human activity. The second definition is natural background, which can be used when natural processes can still be discriminated in the data (Reimann et al., 2005). In heavily mined areas, the “natural background” can only be determined with careful sample collection in areas known not to be impacted by mining.

A geochemical baseline is defined as the present concentration of a chemical substance in a contemporary environmental sample (Galuszka and Migaszewski, 2011). The geochemical baseline, either at a reclaimed mine site or in a stream impacted by mining, for example, can be used to gauge the effectiveness of mine cleanup once reclamation has been completed. Reclamation success is commonly determined by analyzing surface water quality downstream from reclaimed sites (Church et al., 2007c). Evaluation of the attenuation of toxic metal concentrations and/ or metal loads over time is a useful reclamation benchmark that requires repeated, long-term monitoring.

The Effect of Scale on Processes Affecting the Environment

Geochemical background and baseline can vary at regional and/or watershed scales. Figure 6 is a conceptual model of a hydrothermally altered, mineralized, and mined system that highlights point sources and diffuse sources of contaminants. The term “point source” refers to a source of contaminants originating from a single identifiable point such as a draining mine or linear fault plane. “Diffuse source” refers to contaminants that are derived from an area, such as an altered bedrock slope where sources of contaminants could originate along multiple flow paths in the fractured bedrock mass or surficial deposits. Water quality in entire basins can be impacted by diffuse sources of contaminants from hydrothermal systems that have introduced pervasive alteration, and associated sulfide minerals that generate acid-rock drainage. Depending on the size of the mineralized system, sources of naturally occurring contaminants may be restricted to individual subbasins that contain discrete contaminant sources from mineralized faults and/or diffuse sources from altered bedrock. Weathering processes at the subwatershed scale form deposits that derive minerals from upslope bedrock sources that can be either acid generating or acid neutralizing. Geochemi-cal signatures of water sampled at watershed outlets represent an integrated geochemical signature of all upstream processes, including natural weathering processes of altered and mineralized bedrocks and surficial material, as well as mine-related deposits (Yager et al., 2013).

Figure 6.

Conceptual model of diffuse and point sources of metals to surface and groundwater. Alteration assemblages from Bove et al. (2007a) draped on 3D terrain for area of upper Cement Creek. Alteration types: p—propylitic; qsp—quartz-sericite-pyrite; vqsp—vein-quartz-sericite-pyrite; arg—argillic; as—acid-sulfate; and sil—silicic. Alteration is a large and diffuse source of metals and acidity. Lower right of model shows the types of geologic and mining-related features that affect surface water (not to scale). Other diffuse sources of contaminants are mine waste and fluvial mill tailings; large point sources of contaminants are from mine adit discharge.

Figure 6.

Conceptual model of diffuse and point sources of metals to surface and groundwater. Alteration assemblages from Bove et al. (2007a) draped on 3D terrain for area of upper Cement Creek. Alteration types: p—propylitic; qsp—quartz-sericite-pyrite; vqsp—vein-quartz-sericite-pyrite; arg—argillic; as—acid-sulfate; and sil—silicic. Alteration is a large and diffuse source of metals and acidity. Lower right of model shows the types of geologic and mining-related features that affect surface water (not to scale). Other diffuse sources of contaminants are mine waste and fluvial mill tailings; large point sources of contaminants are from mine adit discharge.

The Stakeholder Process

Because mining at Creede and Silverton has waned due to depletion of ore reserves and economic factors, the current communities of Creede and Silverton formed stakeholder groups in the 1990s to understand and mitigate the impacts of historical mining on water quality. A stakeholders group is a membership of concerned, engaged, and or interested public and private entities representing community, business, land management, regulatory, as well as scientific and educational institutions. The stakeholder process in Silverton was established in lieu of a Superfund designation and at the urging of the Colorado Water Quality Control Division (Animas River Stakeholders Group, 2016). The possible impacts to the community of a Superfund designation are unclear to residents, especially in Silverton (Thompson, 2016). The 1980 federal law, Superfund, is also named the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (Switzer and Bulan, 2002). The law is designed for cleanup of sites contaminated with hazardous substances. Provisions under Superfund allow for federal resources to be applied for mine waste removal and for long-term remedial actions such as treating mine water to reduce acidity and attenuate metal loading.

The Animas River Stakeholders Group (ARSG) of Silverton and the Willow Creek Reclamation Committee (WCRC) of Creede are led by designated coordinators responsible for leading meetings, writing grants for reclamation projects, and interfacing with all stakeholders. Membership participation is possible through open meetings. The meetings involve a public forum to discuss, analyze, and interpret data; plan for implementing remedial measures; and vet decisions regarding proposed cleanup actions. The question frequently arises about who can participate in the stakeholders’ process. The ARSG answers this question in the following statement on their website: “Anyone. There is no official membership. Meetings and participation are open to anyone with a ‘stake’ or interest in the Animas River” (ARSG, 2016, http://animasriverstakeholdersgroup.org/). Experts in the fields of mine land reclamation, habitat restoration, biology, geology, geophysics, geochemistry, and water quality among other disciplines are frequently called on to provide science to help guide decisions. The USGS does not make recommendations regarding reclamation decisions, but scientists involved in the Animas AML project participate with both the ARSG and WCRC to provide data and scientific interpretations to help guide decisions. Over the course of this field trip, the parallel processes used by the ARSG and WCRC to address impacts of mining on watersheds will be discussed.

In addition to the challenges of mine cleanup, the citizens of the remote mountain towns of Creede and Silverton were required to find sources of income other than from mining to sustain their local economies. It should be noted that mining may again be economically viable in the future. However, although mineral exploration has continued in both the Creede and Silverton areas, mining in these areas remains uneconomical today.

The San Juan Mountains are renowned for their scenic beauty and recreational opportunities. Creede and Silverton depend on tourism and outdoor enthusiasts as a principal source of revenue. Historical mining structures and mine waste piles are also a tourism draw. Significant efforts have been made to preserve historically important mining structures and sites that would be lost if restoration projects were not implemented (Rich, 2000). Real or perceived environmental issues from mining, however, can also be a deterrent to tourists, especially when water quality is affected. The stakeholders’ process involves discussions of historical preservation measures as part of an integrated approach to reclamation decisions.

Geologic and Mining-Related Summaries for Field-Trip Areas

San Juan Volcanic Field

This field trip traverses the San Juan volcanic field, which is located in southwest Colorado and is part of the southern Rocky Mountains (Fig. 7). Basement rocks underlying the younger volcanic rocks consist of Precambrian schist, gneiss, quartzite, metavolcanics, and plutonic rocks (Gonzales and Van Schmus, 2007). The basement rocks have been proposed as a source of precious metals that were leached and remobilized by hydrothermal fluids during the Neogene (Koch, 1990). A sequence of Paleozoic through Paleogene sedimentary rocks overlies the Pre-cambrian rocks except in areas of basement block uplifts centered near Silverton, where the sedimentary section has been eroded or where the basement has been downdropped during Paleogene to Neogene caldera formation.

Figure 7.

Generalized, regional geologic map showing area of the San Juan volcanic field in Colorado. Figure modified from Casadevall and Ohmoto (1977) and Lipman and Bachmann (2015).

Figure 7.

Generalized, regional geologic map showing area of the San Juan volcanic field in Colorado. Figure modified from Casadevall and Ohmoto (1977) and Lipman and Bachmann (2015).

Volcanism in the San Juan volcanic field commenced at ca. 35 Ma with eruption of 25,000 km2 of intermediate composition lavas (Lipman et al., 1973). Igneous rocks of the San Juan volcanic field are comprised of an erosional remnant of lava flows, flow breccias, lahars, volcaniclastic rocks, and igneous intrusions. Between 30 Ma and 22 Ma, multiple silicic magma bodies ascended into shallow (<5 km) levels of the crust. Multiple calderas formed during this time throughout the San Juan volcanic field, when felsic magmas were erupted and overlying roof rocks collapsed into the voids created from the partially evacuated magma chambers. Eruptive products from the calderas blanket the area with dacitic to rhyolitic ash-flow tuffs. Intermediate to felsic composition lavas commonly were erupted along the periphery of the calderas and sometimes infill the areas of caldera collapse with intracaldera lava. Resurgent intrusions within the calderas caused doming of the central caldera cores. The caldera structures and those structures formed during resurgent doming were structural flow paths for mineralizing fluids. Two caldera systems will be visited on this trip. The Creede area is in the central San Juan caldera cluster (Lipman, 2006). The Silverton area is located in the western San Juan Mountains (Fig. 7).

Creede

Intermediate composition volcanic rocks that pre-date caldera formation in this area are known as the Conejos Formation. The Conejos lavas erupted from central vent volcanoes, and lava flows are overlain by the multiple ash-flow sheets that blanket the area (Ratté and Steven, 1967; Lipman, 2000). The Creede mining area is centered in the central San Juan caldera cluster (Lipman, 2006). The central San Juan caldera cluster was the locus of multiple caldera-forming events between 28.3 and 26.5 Ma, and resulted in deposition of nine ash-flow sheets (Lipman, 2006). The largest ash-flow sheet erupted from the massive (from 10–75 km maximum dimension) La Garita caldera, which was the source of an estimated 5000 km3 of dacitic ash-flow tuff (Lipman and Bachmann, 2015). Younger (27.35 Ma to 26.7 Ma) calderas in the central San Juan caldera cluster, with eruptive volumes of ash-flow tuff ranging from 100 to 1000 km3, formed within or adjacent to the La Garita caldera (Fig. 7) (Lipman, 2006).

The calderas that are most relevant to this field trip in the central San Juan caldera cluster are the 27.35 Ma Bachelor and 26.7 Ma Creede calderas. The Bachelor caldera formed in response to the eruption of >1000 km3 of rhyolite to dacite composition Carpenter Ridge ash-flow tuff (Lipman, 2000). Intracaldera subunits of the Bachelor caldera have been historically named the Willow Creek (Tbw), Campbell Mountain (Tbc), and Windy Gulch Members (Tbwg) (Steven and Ratté, 1965). Lipman (2000) reinterpreted the intracaldera fill not as separate ash-flow cooling units but as different welding zones of the Bachelor Mountain Member of the Carpenter Ridge Tuff. The reinterpretation by Lipman (2000) has economic exploration implications, because prior mapping had used the previous Tbw, Tbc, and Tbwg unit designations as mappable, separate units within the intracaldera fill. Steven and Ratté (1965) describe the contact between units Tbw and Tbc as one of the only consistent changes in the intracaldera tuffs that can be consistently mapped. Unit Tbw at the base of the intracaldera section has a very fluidal structure. The overlying unit Tbc has a densely welded eutaxitic structure and is host to most of the vein mineralization.

The intracaldera Snowshoe Mountain Tuff, a crystal-rich dacite, forms the picturesque resurgent core of the Creede caldera. The Creede caldera is estimated to have produced >500 km3 of crystal-rich dacite. Unlike the core of the Bachelor caldera, the Creede caldera is largely unmineralized. Faults that formed during resurgence within the Creede caldera are shown in Figure 8.

Figure 8.

(A) Faults and veins within the resurgent core of the Bachelor caldera, B; non-mineralized faults in the resurgent core of the Creede caldera, C. (B) Faults and veins of the Bachelor caldera (area shown indicated by white box in A. BVS—Bull Dog Mountain vein system; AV—Amethyst vein; SHV—Solomon—Holy Moses Vein system; NT—Nelson Tunnel. Trip route (Fig. 3) is focused in area north of Creede. Source of faults and veins is from Steven and Ratté (1965). Base maps are from Google Earth.

Figure 8.

(A) Faults and veins within the resurgent core of the Bachelor caldera, B; non-mineralized faults in the resurgent core of the Creede caldera, C. (B) Faults and veins of the Bachelor caldera (area shown indicated by white box in A. BVS—Bull Dog Mountain vein system; AV—Amethyst vein; SHV—Solomon—Holy Moses Vein system; NT—Nelson Tunnel. Trip route (Fig. 3) is focused in area north of Creede. Source of faults and veins is from Steven and Ratté (1965). Base maps are from Google Earth.

Structures and Veins of the Creede and Bachelor Calderas

Areas of caldera resurgence are important structural features that are the locus of mineralization. Resurgent doming produced faults, which in the case of the Bachelor caldera, were later mineralized with base and precious metals (Fig. 8). Upwelling of new magma within the central cores of these calderas caused doming of intracaldera ash-flow tuff. As doming proceeded, northerly trending dilatational fractures formed that permitted the central cores of the domes to be down-dropped as “keystone” blocks.

Outward from the resurgent core along the topographic margin of the Creede caldera, a caldera moat lake developed and was filled with a 1-km-thick accumulation of lacustrine sediments (Barton et al., 2000). Lake Creede is the focus of another 2016 GSA field trip “Exploring the Ancient Volcanic and Lacustrine Environments of the Oligocene Creede Caldera and Environs, San Juan Mountains, Colorado” (see Larsen and Lipman, this volume). Because lacustrine sediments are preserved west of the Creede margin, a structure known as the Clear Creek graben (Fig. 8A) is thought to have controlled sedimentation prior to caldera formation (Heiken et al., 2000). Lacustrine sedimentation continued after caldera formation in the area of the Creede caldera topographic margin outward from the resurgent dome. The present-day course of the Rio Grande River near Creede, Colorado, is along the northern margin of the Creede caldera, where it is established in Lake Creede sediments. Lake Creede brines are proposed to have formed in the lake moat sedimentary fill (Bethke and Rye, 1979), and are thought to have been the source of meteoric water that was heated by a magma body of uncertain depth. Brine that percolated beneath Lake Creede was heated and boiled, transporting metal-rich solutions northward into the faults that had developed during resurgent doming. As the brine cooled, metals were precipitated along veins in the Creede mining district (Barton et al., 1977).

The Bachelor caldera is host to rich epithermal deposits mined primarily for silver, lesser gold, and abundant base metals lead and zinc. Several phases of mineralization were identified by Plumlee and Whitehouse-Veaux (1994) in the Bulldog Mountain vein systems. Minerals that occur in abundance include: phase (A) rhodochrosite (MnCO3); phase (B) barite (BaSO4), sphalerite (ZnS), galena (PbS), and native silver; phase (C) barite, quartz (SiO2), and fluorite (CaF2); phase (D) sphalerite and galena; phase (E) pyrite (FeS2) and marcasite (FeS2); phase (F) native silver. Other trace minerals are also present including chalcopy-rite (CuFeS2), bornite (Cu5FeS4), acanthite (Ag2S), and stibnite (Sb2S3) (Plumlee and Whitehouse-Veaux, 1994). These phases are either acid generating or contain elements (copper, zinc, lead, manganese, silver, antimony) that when leached by acidic solutions can be toxic to aquatic life.

Alteration Types

Intense potassium metasomatism has altered Bachelor caldera intracaldera rocks near Creede, with resulting potassium contents of as much as 12 wt% potassium (Ratté and Steven, 1967; Bethke et al., 1985). Veins that are hosted and best developed in the Tbc welding zone range in width from 1 cm to 3 m. Veins are in some places capped by tongues of intense wall-rock alteration and consist of chlorite, chlorite-smectite, minor silici-fication, sericitization of sanidine feldspars, and pyritization of biotite (Plumlee and Whitehouse-Veaux, 1994). Hydrothermal alteration in the Creede district greatly contrasts with the many alteration types represented in the Silverton caldera area. These differences will be discussed during this trip.

Creede Mining History

Mining development began in 1889 in the Creede mining district with the discovery of the Solomon—Holy Moses vein (Steven and Ratté, 1965). The Solomon—Holy Moses vein is along the eastern margin of the graben structures of the Bachelor caldera (Steven and Ratté, 1965). In the 1890s, the Last Chance, Amethyst, and New York claims along the Amethyst vein became the most productive in the district. Initial production was mainly from near surface oxidized ores in the southern part of the vein system with silver representing 70–94% of the ore produced and reportedly reaching grades as high as 80 oz per ton (Steven and Ratté, 1965). In the early 1900s, several mills (Emperius, Humphreys, Amethyst, Solomon, and Ridge) were constructed to process ores having higher sulfide contents (Fig. 9). Sulfide ore production spiked between 1946 and 1949 with lead and zinc representing a high percentage of the ore mined as silver production declined (Steven and Ratté, 1965). Mining activity is reported to have continued along the Solomon—Holy Moses vein zone until the late 1950s (Twitty, 2002). Discovery of the Bulldog Mountain vein system in 1965 was a result of the geologic investigations by Steven and Ratté (1965) that identified structures similar to those that are host to the Amethyst and Solomon—Holy Moses vein systems to the east. Between 1965 and its closure in 1985, the Bulldog mine produced 25 M oz of silver, which is ~30% of the 79 M oz of silver mined in the district. The district as a whole also produced 150,000 oz of gold. Base metal production for the district included 2500 metric tons of copper; 139,000 metric tons of lead; and 40,000 metric tons of zinc (Barton et al., 2000).

Figure 9.

(A) Humphreys mill and Commodore mine in distance in West Willow Creek (~1903). (B) Emperius mill and trestle in Creede along Willow Creek (~1936). Photos courtesy of Creede Historical Society; used with permission.

Figure 9.

(A) Humphreys mill and Commodore mine in distance in West Willow Creek (~1903). (B) Emperius mill and trestle in Creede along Willow Creek (~1936). Photos courtesy of Creede Historical Society; used with permission.

In 1892, the Nelson Tunnel Company began work on the Nelson Tunnel along the Amethyst vein (Twitty, 2002). The tunnel was engineered to intersect the workings of many other mines and to facilitate access to vein systems, dewatering, ore haulage, and ventilation. The Nelson Tunnel, which eventually spanned two miles, was constructed to provide more extensive and efficient access to mine workings compared to traditional mining methods using shafts, adits, and rises. While the Nelson Tunnel proved effective for its intended purpose at the time, it also exposed large surface areas of sulfide minerals to oxidation and weathering, and became one of the largest sources of metals (especially zinc) to West Willow Creek and to the Rio Grande River (Kimball et al., 2004). In 2005, the Nelson Tunnel was designated as a Superfund cleanup site. Similar mine haulage tunnels were constructed around the 1900s at other mines in Colorado including the American Tunnel, Silverton; Reynolds Adit, Summitville; and Argo Tunnel, Idaho Springs, which all eventually became large point sources of metals to surface water and sites of environmental cleanup and treatment issues today (Yager et al., 2010).

Day 1 (Denver to Creede)

Cum. distance
km(mi)TimeDirections
0(0)0700Depart from Colorado Convention Center
(700 14th St., Denver, CO 80202) southeast
on 14th St. to California St.
Right (southwest) to Glenarm St.
Right (west) to W. Colfax Ave.
Right exit ramp to I-25 south.
Right exit 209B, west to U.S.-6.
Right exit to I-70 west.
Right exit 260 to CO-470 east.
25.58(15.9)Right exit U.S.-285 south.
186.52(115)0915Right (north) exit to County Rd. 304 to rest area. Arrive at Buena Vista, Arkansas Valley overlook (38.817001°N, 106.086559°W).
Cum. distance
km(mi)TimeDirections
0(0)0700Depart from Colorado Convention Center
(700 14th St., Denver, CO 80202) southeast
on 14th St. to California St.
Right (southwest) to Glenarm St.
Right (west) to W. Colfax Ave.
Right exit ramp to I-25 south.
Right exit 209B, west to U.S.-6.
Right exit to I-70 west.
Right exit 260 to CO-470 east.
25.58(15.9)Right exit U.S.-285 south.
186.52(115)0915Right (north) exit to County Rd. 304 to rest area. Arrive at Buena Vista, Arkansas Valley overlook (38.817001°N, 106.086559°W).

Stop 1: Buena Vista, Arkansas Valley Overlook

The Buena Vista valley overlook affords spectacular views to the west across the Arkansas River valley to the Sawatch Range. The Arkansas River originates near the historic hard rock mining community of Leadville, Colorado, 55.36 km (34.4 mi) to the north. The flat-floored valley is a down-dropped fault block bordered to the east by the Mosquito Range and to the west by the Sawatch Range. The Sawatch Range includes several 4267 m (14,000 ft) peaks referred to as the Collegiate peaks (Mount Harvard, Mount Yale, Mount Princeton). These peaks mark the continental drainage divide and have a high average elevation (peak elevation: 4343 m [14,249 ft]).

The geology represents a long sequence of uplifts interspersed by marine sedimentation, volcanism, glaciation, and erosion. Pro-terozoic basement rocks are composed of ca. 1.7–1.05 Ga granites, metamorphic rocks, meta-arc volcanics and Paleo- and Mesopro-terozoic rift sediments (Uncompahgre Formation) that accreted to the Archean North American continent in a series of NE-trending collisions referred to as the Colorado orogeny. The Precambrian platform is unconformably overlain by Cambrian Sawatch Quartz-ite, Permian conglomerates equivalent in part to the Fountain Formation, followed by a thick sequence of Paleozoic shales, sandstones, and limestones. Minor Mesozoic redbeds with interbedded sandstones disconformably overlie the Paleozoic sequence. Cap rocks are erosional remnants of (1) Laramide volcanics, intrusions, volcaniclastic and minor basalts; (2) Eocene erosion surface sediments and gravels; (3) mid- to upper Paleogene volcanics, intrusions, and minor basaltic andesites; and (4) Rio Grande rift—related lavas, as preserved among basement uplifts or younger extension-related structures.

The light-hued rocks exposed at the base of Mount Princeton (due west) are quartz monzonite that is hydrothermally altered, principally to kaolinite. Hydrothermal fluids leached the quartz monzonite along range front faults of the Sawatch Range. Mount Antero, just south of Mount Princeton, is a well-known gem-quality beryl (aquamarine) locality. Mount Antero aquamarine is found in granitic pegmatites.

Cum. distance
km(mi)TimeDirections
0945Depart from Buena Vista, Arkansas Valley overlook (lunch in route), from County Rd. 304, west on U.S.-285 (1.8 mi).
189.74(117.9Right (south) at intersection of U.S.-24 W and U.S.-285 south.
196.34(122)Ruby Mountain 28 Ma Topaz rhyolite, Nathrop (38.74980°N, 106.06988°W).
236.57(147)Poncha Pass Summit (38.4222°N, 106.08694°W) divide between Arkansas River Valley (north) and San Luis Valley (south), northern part of the Rio Grande rift.
329.92(205)Right (west) to CO-112 west(Center, Colorado).
350.84(218)
376.58(234)Right (west) on CO-160 to CO-149 N.
Right (west) on CO-149.
410.38(255)1230Arrive at Creede.
Reset odometer to 0.
0(0)1245Junction of 7th St. and CO-149 in Creede.West on 7th St. to Loma St.
0.64(0.4)Right on County Rd. 504 (Bachelor Rd.).
3.22(2.0)Right on Bachelor Mine Rd.
4.02(2.5)Stop 2 (Bachelor mine overlook).
Cum. distance
km(mi)TimeDirections
0945Depart from Buena Vista, Arkansas Valley overlook (lunch in route), from County Rd. 304, west on U.S.-285 (1.8 mi).
189.74(117.9Right (south) at intersection of U.S.-24 W and U.S.-285 south.
196.34(122)Ruby Mountain 28 Ma Topaz rhyolite, Nathrop (38.74980°N, 106.06988°W).
236.57(147)Poncha Pass Summit (38.4222°N, 106.08694°W) divide between Arkansas River Valley (north) and San Luis Valley (south), northern part of the Rio Grande rift.
329.92(205)Right (west) to CO-112 west(Center, Colorado).
350.84(218)
376.58(234)Right (west) on CO-160 to CO-149 N.
Right (west) on CO-149.
410.38(255)1230Arrive at Creede.
Reset odometer to 0.
0(0)1245Junction of 7th St. and CO-149 in Creede.West on 7th St. to Loma St.
0.64(0.4)Right on County Rd. 504 (Bachelor Rd.).
3.22(2.0)Right on Bachelor Mine Rd.
4.02(2.5)Stop 2 (Bachelor mine overlook).

Stop 2: Bachelor Mine Overlook (Private Site, Permission Required for Future Field Trips)

Discovered in the early 1960s, the Bachelor mine and vein system is the western expression of veins that formed along faults in the resurgent core of the Bachelor caldera. The mine was one of the richest silver producers in Colorado and closed in 1985. This site provides a panoramic view of the Creede caldera resurgent dome and a caldera moat. A 1-km-thick section of lacustrine sediments accumulated in the caldera moat. The Rio Grande River follows the northern margin of the Creede caldera resurgent dome, and is incised in easily eroded lake moat sediments of the Creede Formation.

Cum. distance
km(mi)TimeDirections
1300Depart Bachelor mine. West on Bachelor Mine Rd. Left (south) on County Rd. 504 (Bachelor Rd.).
5.6(3.5)Left (north) on CO-149. Immediate left (north) on Loma St.
6.44(4.0)Creede Community Center and Mining Museum.
6.84(4.25)1315Arrive at Humphreys Mill.
Cum. distance
km(mi)TimeDirections
1300Depart Bachelor mine. West on Bachelor Mine Rd. Left (south) on County Rd. 504 (Bachelor Rd.).
5.6(3.5)Left (north) on CO-149. Immediate left (north) on Loma St.
6.44(4.0)Creede Community Center and Mining Museum.
6.84(4.25)1315Arrive at Humphreys Mill.

Stop 3: Historical Humphreys Mill

North of Creede, the trip route traverses the intracaldera Carpenter Ridge Tuff, which is host to the epithermal poly-metallic vein mineralization in the mining district. Excellent exposures along the road provide opportunities to study the welding zones within the intracaldera fill. Stop 3 is the site of the historical Humphreys Mill (Fig. 9A). Several mills were constructed in the early twentieth century to process metallic ore mined in the district. Rail lines were also built during this time to transport processed ore. Mill tailings from this and other mills produced fluvial tailings that were deposited in the Willow Creek floodplain. Since its formation in 1999, the Willow Creek Reclamation Committee has been working toward remediating parts of the Willow Creek floodplain impacted by historical mill tailings.

Cum. distance
km(mi)TimeDirections
1315Depart from Humphreys Mill for Nelson Tunnel.
8.05(5)1330Arrive at Nelson Tunnel and Commodore mine (37.870045°N, 106.92951°W).
Cum. distance
km(mi)TimeDirections
1315Depart from Humphreys Mill for Nelson Tunnel.
8.05(5)1330Arrive at Nelson Tunnel and Commodore mine (37.870045°N, 106.92951°W).

Stop 4: Nelson Tunnel Superfund Site and Commodore Mine (Private Site, Permission Required for Future Field Trips)

The Nelson Tunnel, construction of which began in 1892, has been a source of metal loading (especially zinc) to West Willow Creek. The site was designated as a Superfund cleanup site in 2005. The section on “Tracer-Dilution Synoptic Sampling” documents the metal loading that is attributed to the Nelson Tunnel.

The linear, northwest-trending Amethyst vein and the Commodore mine workings can be seen on the East flank of Bachelor Mountain. The peak on the east side of the vein is composed of the Willow Creek welding zone; ash-flow tuff of the Campbell Mountain welding zone is down-dropped to the west along a graben fault. This vein system formed along intracaldera graben faults after resurgence of the Bachelor caldera. From 1891 to 1899, near-surface oxidized ores in the southern part of the Amethyst vein system were the most productive silver producers in the district. Amethyst from this vein is very characteristic, having a light-purple hue, and is often finely banded with milky-white quartz. In high-grade zones, amethyst nodules can contain dendritic silver.

Cum. distance
km(mi)TimeDirections
1400Depart from Nelson Tunnel and Commodoremine.
8.05(6)1415Arrive at Amethyst mine (37.883958°N, 106.932098°W).
Cum. distance
km(mi)TimeDirections
1400Depart from Nelson Tunnel and Commodoremine.
8.05(6)1415Arrive at Amethyst mine (37.883958°N, 106.932098°W).

Stop 5: Amethyst Mine (Private Site, Permission Required for Future Field Trips)

Amethyst vein and gangue material can be observed on the Amethyst mine waste pile. Banded, light-purple amethyst and milky-white quartz, light-brown sphalerite, and argentiferous galena are some of the species that may be collected on the waste pile (if permission has been obtained).

Cum. distance
km(mi)TimeDirections
1445Depart from Amethyst mine.
11.26(7)1500Arrive at Midwest mine (37.894035°N, 106.930108°W).
Cum. distance
km(mi)TimeDirections
1445Depart from Amethyst mine.
11.26(7)1500Arrive at Midwest mine (37.894035°N, 106.930108°W).

Stop 6: Midwest Mine (Private Site, Permission Required for Future Field Trips)

The Midwest mine operated sporadically between 1923 and 1984. The Willow Creek Reclamation Committee has worked on improving water quality in this area by moving and consolidating the mine waste. Waste pile material was capped with excavated material and amended with limestone and new soil. The 1 acre site was revegetated. French drains were installed to capture surface runoff and to divert flow away from the waste pile.

Cum. distance
km(mi)TimeDirections
1515Depart from Midwest mine on County Rd. 503.
14.48(9)Right (north) on Equity Mine Rd. (37.906846°N, 106.954418°W).
17.70(11)1545Arrive at Equity mine.
Cum. distance
km(mi)TimeDirections
1515Depart from Midwest mine on County Rd. 503.
14.48(9)Right (north) on Equity Mine Rd. (37.906846°N, 106.954418°W).
17.70(11)1545Arrive at Equity mine.

Stop 7: Equity Mine (Private Site, Permission Required for Future Field Trips)

The Equity mine is the site of recent exploration activity by Rio Grande Silver. Exploration in this area has investigated the extension of mineralization along vein systems within Bachelor caldera graben faults in the northern Creede mining district. An experimental drilling program in the late 1980s had proposed a 5-km-deep drill hole near the “Equity block.” The Equity block consists of Tbcw (Willow Creek welding zone) bounded by downfaulted, younger Nelson Mountain Tuff derived from the San Luis caldera complex just north of the Bachelor caldera. The “block” is defined by the downfaulted margins (on all sides) that have an estimated 300 m of displacement in some places. The deep drill hole near the Equity block was not completed; however, two experimental drill holes were completed in Creede caldera moat sediments. Researchers can view the core at the USGS Core Research Center located at the Denver Federal Center.

Cum. distance
km(mi)TimeDirections
1600Depart from Equity mine (south) on County Rd. 503.
20.92(13)Right on County Rd. 504 (Bachelor Rd.).
22.53(14)Park Regent mine on left.
24.14(15)1640Arrive at Bachelor City.
Cum. distance
km(mi)TimeDirections
1600Depart from Equity mine (south) on County Rd. 503.
20.92(13)Right on County Rd. 504 (Bachelor Rd.).
22.53(14)Park Regent mine on left.
24.14(15)1640Arrive at Bachelor City.

Stop 8: Bachelor City

This site was the once bustling community of Bachelor City. During the early 1890s, it had a reported population of ~1000; Creede is reported to have had a population of nearly 10,000 at this time. A silver crash occurred in 1893 when Congress enacted the Silver Act, which resulted in the price of silver dropping from $1.30 to 0.50 cents per oz. This caused hardship to the towns of Bachelor City and Creede and is a reminder of the episodic and cyclic nature of mining. Remnants of structures are all that remain of Bachelor City.

Cum. distance
km(mi)TimeDirections
1650Depart Bachelor City (south) on County Rd. 503.
28.97(18)Intersection with Bulldog Mine road.
29.37(18.25)Creede Formation lacustrine sedimentary rocks on left.
30.57(19)1700End of traverse at intersection of County Rd. 504 and CO-149.
1800Dinner and presentations at the Creede Community Center.
Cum. distance
km(mi)TimeDirections
1650Depart Bachelor City (south) on County Rd. 503.
28.97(18)Intersection with Bulldog Mine road.
29.37(18.25)Creede Formation lacustrine sedimentary rocks on left.
30.57(19)1700End of traverse at intersection of County Rd. 504 and CO-149.
1800Dinner and presentations at the Creede Community Center.

Day 2: Creede to Silverton Via Durango and Historical Uranium Mill and Disposal Sites

Cum. distance 
km (mi) Time Directions 
0800 Arrive at Creede Community Center for underground mine museum tour. Depart Creede on CO-149 to CO-160. 
33.79 (21)  Right (west) on CO-160 W at South Fork. 
156.27 (97.1)  Intersection with CO-550 south on left, stay on CO-160 W. 
162.54 (101) 1200 West on South Camino Del Rio, which is also CO-550 N and CO-160 W. 
   Arrive at Durango and stop at rest area that overlooks the historical uranium mill site along the Animas River (river right) (37.266020°N, 107.883977°W), stop 1 onFigure 5. 
Cum. distance 
km (mi) Time Directions 
0800 Arrive at Creede Community Center for underground mine museum tour. Depart Creede on CO-149 to CO-160. 
33.79 (21)  Right (west) on CO-160 W at South Fork. 
156.27 (97.1)  Intersection with CO-550 south on left, stay on CO-160 W. 
162.54 (101) 1200 West on South Camino Del Rio, which is also CO-550 N and CO-160 W. 
   Arrive at Durango and stop at rest area that overlooks the historical uranium mill site along the Animas River (river right) (37.266020°N, 107.883977°W), stop 1 onFigure 5. 

Stop 1: Historical Uranium Mill Site

This mill site has a varied history. It was the original site of the American Smelting and Refining Company discussed in the “Silverton Mining History” section. Base and precious-metal ore from the Silverton mining district was processed here in the late ninteenth century. In the mid-twentieth century, the Vanadium Corporation of America milled uranium ore that was mined in deposits in the Colorado Plateau to the west and southwest of the San Juan Mountains. The U.S. Department of Energy (DOE) was authorized under the Uranium Mill Tailings Remedial Action (UMTRA) to move radioactive mill tailings to a disposal cell site located south of Durango.

Cum. distance
km(mi)TimeDirections
1315Depart from mill site.
163.56(101.63)Right (south) on South Camino Del Rio to CO-210 exit on right (west).
166.34(103.36)Right on CO-212.
167.40(104.02)1330Arrive at uranium disposal cell site on right (37.247830°N, 107.908014°W), stop 2 in Figure 5.
Cum. distance
km(mi)TimeDirections
1315Depart from mill site.
163.56(101.63)Right (south) on South Camino Del Rio to CO-210 exit on right (west).
166.34(103.36)Right on CO-212.
167.40(104.02)1330Arrive at uranium disposal cell site on right (37.247830°N, 107.908014°W), stop 2 in Figure 5.

Stop 2: Uranium Disposal Cell—Uranium Milling and Storage, Durango, Colorado

This stop is a uranium mill tailings disposal cell managed and monitored by the DOE. Durango is geographically situated at the southwest margin of the San Juan Mountains and the northern San Juan basin. We will visit the Durango processing and disposal sites (Fig. 5). The processing site is a former uranium-ore processing facility located a quarter of a mile (0.4 km) southwest of the city of Durango. The source for processed uranium is sandstone-hosted, Mesozoic rocks of the Morrison Formation in the Colorado Plateau country to the west. The facility was constructed on the site of a former smelter operated by the American Smelting and Refining Company (discussed in the “Silverton Mining History” section, below) that processed ore from Silverton between 1880–1930. Vanadium Corporation of America constructed and operated a mill from 1942 to 1946 to produce vanadium. Between 1949 and 1963, the mill processed uranium ore for U.S. Government national defense programs. From 1986 to 1991, the DOE removed tailings and other contaminated materials from the Durango processing site and local contaminated properties (known as vicinity properties), and stabilized them in a disposal cell located southwest of Durango. Information, reports, and data on the processing and disposal sites can be found at www.lm.doe.gov/Durango/, and a fact sheet that discusses the two sites can be found at www.lm.doe.gov/Durango/DisposalSites.aspx.

This site offers the opportunity to discuss life cycle processes that can evolve over time. Sites can involve cleanup and mitigation of metallic elements as well as radionuclides that require containment for decades. Historical information about legacy mill and disposal areas enables communities to be aware of the multiple and sometimes varied risks that such sites may pose.

Cum. distance
km(mi)TimeDirections
1430Depart from uranium disposal cell.
168.47(104.68)South on CO-212 to CO-210.
171.25(106.41)Left (east) on CO-210 to South Camino Del Rio and go left (north) on South Camino Del Rio (CO-160 W and CO-550 N).
172.26(107.04)Intersection with South Camino Del Rio (CO-550) north and U.S.-160 on left. Merge right to CO-550 (north).
240.92(149.7)1530Arrive at Molas Lake.
249.93(155.34)1545Depart from Molas Lake (37.752426°N, 107.682599°W).
258.94(160.9)1610Arrive at Silverton.
1800Dinner and presentations at Silvertontown hall.
Cum. distance
km(mi)TimeDirections
1430Depart from uranium disposal cell.
168.47(104.68)South on CO-212 to CO-210.
171.25(106.41)Left (east) on CO-210 to South Camino Del Rio and go left (north) on South Camino Del Rio (CO-160 W and CO-550 N).
172.26(107.04)Intersection with South Camino Del Rio (CO-550) north and U.S.-160 on left. Merge right to CO-550 (north).
240.92(149.7)1530Arrive at Molas Lake.
249.93(155.34)1545Depart from Molas Lake (37.752426°N, 107.682599°W).
258.94(160.9)1610Arrive at Silverton.
1800Dinner and presentations at Silvertontown hall.

Stop 3: Molas Lake

This stop affords spectacular views of the Precambrian rocks exposed in the Needle Mountains and Grenadier Ranges to the south. Excellent exposures of Paleozoic rocks composed of inter-bedded sandstone and limestone of Pennsylvanian Hermosa Formation and overlying Permian Cutler Formation are seen in the slopes of the highly glaciated peaks to the west. These rocks represent some of the existing basement rocks in which the Paleogene caldera systems and later mineralization formed.

Silverton

The Animas River watershed study area stratigraphy consists of a Proterozoic crystalline basement overlain by Paleozoic, Mesozoic, and Eocene sedimentary rocks, and a 1- to 2-km-thick, Oligocene- to Miocene-age volcanic cover (Yager and Bove, 2007). This field trip will mainly focus on igneous units within or adjacent to the 27.8 Ma San Juan and nested 27.6 Ma Silverton calderas (Bove et al., 2001). For a discussion of the regional geology, the reader is referred to Baars and Ellingson (1984).

Pre-Caldera Volcanic Rocks

Late Paleogene volcanism in the San Juan Mountains commenced between 35 and 30 Ma with the eruption and deposition of voluminous calc-alkaline, intermediate-composition (52–63% SiO2) lava flows, flow breccias, volcaniclastics, minor mafic tuffs, and abundant mudflows of the San Juan Formation (Lipman et al., 1973; Steven and Lipman, 1976). These rocks cover an area of 25,000 km2.

San Juan-Uncompahgre Caldera and Silverton Caldera Rocks

Between 30–23 Ma, numerous calderas formed throughout the San Juan volcanic field and associated ash flows were deposited on the early, intermediate composition volcanic rocks (Lanphere, 1988; Lipman et al., 1997; Bove et al., 2001). Two caldera-forming events took place in the Silverton field-trip area: the 28.35 Ma San Juan—Uncompahgre caldera and the younger, nested 27.6 Ma Silverton caldera (Lipman and Bachmann, 2015). The San Juan caldera is the southwest half of the roughly dumbbell-shaped San Juan—Uncompahgre caldera. Tertiary calderas in the western San Juan Mountains produced more than 1000 km3 of ash-flow tuff. San Juan caldera eruptives consist of the rhyolitic to dacitic outflow, Sapinero Mesa Tuff, and intracaldera Eureka Member of the Sapinero Mesa Tuff.

Intermediate composition Silverton Volcanics lavas have infilled the San Juan caldera to a thickness exceeding 1 km. The Silverton Volcanics intermediate composition rocks include the basal Burns Member and overlying Henson and pyroxene andesite members. The Burns Member is economically important because it is host to the majority of epithermal, polymetallic veins in the area. The Burns Member is generally characterized by propylitically altered lavas and minor dacite to rhyolite tuffs. The pyroxene andesite member overlies the Burns Member and tends to be less altered compared with underlying members. The volcaniclastic sedimentary rocks of the Henson Member interfinger with both the Burns and the pyroxene andesite members (Lipman et al. 1973). The Henson Member is commonly unmineralized.

Deposition of the Silverton volcanics lavas was closely followed by eruption of the Crystal Lake Tuff, which resulted in formation of the Silverton caldera. The Crystal Lake Tuff is a crystal-poor, low-silica rhyolite (72% SiO2) (Lipman et al., 1973).

Postcaldera Igneous Rocks

Postcaldera granitic stocks (monzonite, monzodiorite, grano-diorite, and monzogranite) were intruded along the southern part of the Silverton caldera ring fracture at ca. 26.6 Ma (Lipman et al., 1976; Ringrose, 1982; Bove et al., 2001). This late-stage igneous activity was accompanied by hydrothermal alteration and formation of a low-grade, molybdenum-copper porphyry deposit and cogenetic polymetallic vein deposits (Ringrose, 1982; Musgrave and Thompson, 1991).

Late-stage, 23–10 Ma dacitic to rhyolitic intrusions emplaced along the north and northwest structural margin of the Silverton caldera were contemporaneous with hydrothermal alteration and related mineralization (Bove et al., 2007a, 2007b). Silver-copper-lead breccia pipe and fault-hosted mineralization in the Red Mountain mining district is closely associated with some of the later stage silicic intrusions (Fisher and Leedy, 1973; Nash, 1975; Bove et al., 2007b). The youngest episode of volcanism occurred at ca. 10 Ma and is represented by rhyolitic plugs and dikes.

Structures and Veins of the San Juan-Uncompahgre and Silverton Calderas

Structures that developed concurrently with volcanic activity were utilized as flow paths by later mineralizing solutions, and the resulting mineralized areas were economically mined for base-metal sulfides and precious metals (Varnes, 1963; Casa-devall and Ohmoto, 1977; Bove et al., 2007b). The structures related to the San Juan—Uncompahgre and Silverton calderas are pervasive features that reflect the complex volcanotectonic history of the study area (Fig. 10). Five dominant structural elements are related to formation of the San Juan—Uncompahgre and Silverton calderas: (1) circular and overlapping caldera ring fault zones, (2) a topographic margin associated with the San Juan caldera that is characterized by megabreccia blocks and Paleozoic limestone in contact with intracaldera tuff along its southern margin, (3) a northeast-trending graben (Eureka graben) and northwest-trending Bonita fault, formed during resurgent doming of the central core of the San Juan—Uncompahgre caldera, (4) radial faults and vein structures located principally near the northwest and southeast periphery of the San Juan and Silverton calderas, and (5) thousands of mineralized and barren veins and vein structures, many of which lack surface expressions.

Figure 10.

Major Silverton caldera vein structures from Yager and Bove (2007a) and geographic features discussed in text. Abbreviations for vein structures: B—Bonita; RB—Ross basin; S—Sunnyside; SV—Silverton caldera structural margin; T—Toltec. Other abbreviations: RM—Red Mountain mining area; SSM—South Silverton mining area;

Figure 10.

Major Silverton caldera vein structures from Yager and Bove (2007a) and geographic features discussed in text. Abbreviations for vein structures: B—Bonita; RB—Ross basin; S—Sunnyside; SV—Silverton caldera structural margin; T—Toltec. Other abbreviations: RM—Red Mountain mining area; SSM—South Silverton mining area;

Collapse of the San Juan—Uncompahgre caldera complex was followed closely by resurgence. Contemporaneous with resurgence, an elliptical dome 15 km wide by 30 km long formed between the two calderas, and extensional fracturing over the resurgent dome resulted in Eureka graben formation. The Sunnyside and Toltec faults define the central and northeastern part of the Eureka graben; the Ross Basin and Bonita faults, which formed in the southwestern part of the graben, border the westnorthwest—trending part of the graben. The northwest-trending Bonita fault cross-cuts North Fork Cement Creek near the Gold King mine, and should be evaluated for its hydrologic conductivity and as a source of groundwater in the Gold King mine. Historical mine reports document groundwater inflows within the Gold King mine that were so high, an area on the #7 level had to be abandoned (Kinney, 1932).

Structures related to the Eureka graben had a strong influence in controlling ore deposition in the Sunnyside mine (Casadevall and Ohmoto, 1977). Each of the Eureka graben faults has lateral and vertical extents of thousands of meters. The workings of the Sunnyside vein deposits were mined through a lateral and vertical extent of 2100 m and 610 m, respectively. Sunnyside mine vein systems are focused near the intersection of the Sunnyside and Ross Basin faults. The Sunnyside mine workings beneath Eureka Gulch exposed mineralized vein structures that are parallel to the Eureka graben, which contain strongly developed northeast-northwest—trending mineralized veins. Common vein minerals identified in vein systems of the Sunnyside mine workings are listed in Table 1; vein minerals of the Sunnyside mine workings that occur with less than 0.5 vol% abundance are listed in Table 2 (Casadevall and Ohmoto, 1977). Northeast-trending structures of the Gold King vein in the Gold King mine parallel vein systems of the Sunnyside veins (Koch, 1990).

Major Vein Minerals of the Sunnyside Mine Workings From Casadevall and Ohmoto (1977)

Table 1.
Major Vein Minerals of the Sunnyside Mine Workings From Casadevall and Ohmoto (1977)
MineralVol%
Quartz (SiO2)30–35
Sphalerite (ZnS)10–15
Galena (PbS)10–15
Pyroxmangite (MnSiO3)10–15
Pyrite (FeS2)6–8
Rhodochrosite (MnCO3)5–8
Chalcopyrite (CuFeS2)3–5
Tetrahedrite (Cu12Sb4S13)1–4
Fluorite (CaF2)1
Calcite (CaCO3)1
MineralVol%
Quartz (SiO2)30–35
Sphalerite (ZnS)10–15
Galena (PbS)10–15
Pyroxmangite (MnSiO3)10–15
Pyrite (FeS2)6–8
Rhodochrosite (MnCO3)5–8
Chalcopyrite (CuFeS2)3–5
Tetrahedrite (Cu12Sb4S13)1–4
Fluorite (CaF2)1
Calcite (CaCO3)1

Minor (<0.5 vol%) Vein Minerals of the Sunnyside Mine Workings (From Casadevall and Ohmoto, 1977)

Table 2.
Minor (<0.5 vol%) Vein Minerals of the Sunnyside Mine Workings (From Casadevall and Ohmoto, 1977)
Hematite (Fe2O3)Gold (Au)
Petzite (AuAg3Te2)Calaverite (AuTe2)
Alabandite (MnS)Huebnerite (MnWO4)
Tephroite (Mn2–SiO4)Friedelite (Mn8Si6O18)
Helvite (Mn4(Be3Si3O12)S)Anhydrite (CaSO4)
Sericite (KAl2)(AlSi 3O10)(OH2)Aikinite (PbCuBiS3)
Bornite (Cu5FeS4)Barite (BaSO4)
Gypsum (CaSO4(2H2O))
Hematite (Fe2O3)Gold (Au)
Petzite (AuAg3Te2)Calaverite (AuTe2)
Alabandite (MnS)Huebnerite (MnWO4)
Tephroite (Mn2–SiO4)Friedelite (Mn8Si6O18)
Helvite (Mn4(Be3Si3O12)S)Anhydrite (CaSO4)
Sericite (KAl2)(AlSi 3O10)(OH2)Aikinite (PbCuBiS3)
Bornite (Cu5FeS4)Barite (BaSO4)
Gypsum (CaSO4(2H2O))

Alteration Types

Silverton area alteration types listed in increasing order of alteration intensity are: (1) propylitic, (2) weak sericite-pyrite, (3) argillic, (4) quartz-sericite-pyrite, and (5) acid sulfate (Bove et al., 2007a) (Fig. 11). For a detailed description of alteration types, the reader is referred to Bove et al. (2007a, 2007b).

Figure 11.

Generalized alteration map of the upper Animas River watershed after Bove et al. (2007). Abbreviations for alteration types are: P—propylitic; wsp—weak sericite pyrite; qsp—quartz-sericite-pyrite; vqsp—vein quartz-sericite-pyrite; arg—argillic; and as—acid sulfate. Base map from Arc Globe, 2016.

Figure 11.

Generalized alteration map of the upper Animas River watershed after Bove et al. (2007). Abbreviations for alteration types are: P—propylitic; wsp—weak sericite pyrite; qsp—quartz-sericite-pyrite; vqsp—vein quartz-sericite-pyrite; arg—argillic; and as—acid sulfate. Base map from Arc Globe, 2016.

Figure 12.

(A) View south of Cement Creek pre-mining alluvial terrace. Dendrochronology of pine tree (top left) indicates it has grown since 1858 (Fey et al., 2000; figure 3 in Blair et al., 2002). Geochemical profiles represent complete sample collection (bottom to top) of terrace. Compared with average crustal abundances in Fortescue (1992), all element concentrations exceed crustal abundance values as follows: Fe 1.5 Xs; Pb 8 Xs; Zn 1.5 Xs; Cu 1.5 Xs, As > 15 Xs. Ag and Cd abundances are too low to show at this scale. (B) Fluvial tailings (bedded, gray and brown layers; sledge hammer for scale) from a tailings impoundment below Sunnyside mill at Eureka during flotation milling era (1918–1930) (Fey et al., 2000; figure 6 in Blair et al., 2002). Element concentrations exceed crustal abundance values as follows: Fe to 1.5 Xs; Pb, Zn, Cu, As, Ag, and Cd all > 16 Xs. Elevated base metals (Cu, Pb, Zn) are characteristic of Sunnyside mine, epithermal polymetallic base metals processed at the Sunnyside Eureka mill.

Figure 12.

(A) View south of Cement Creek pre-mining alluvial terrace. Dendrochronology of pine tree (top left) indicates it has grown since 1858 (Fey et al., 2000; figure 3 in Blair et al., 2002). Geochemical profiles represent complete sample collection (bottom to top) of terrace. Compared with average crustal abundances in Fortescue (1992), all element concentrations exceed crustal abundance values as follows: Fe 1.5 Xs; Pb 8 Xs; Zn 1.5 Xs; Cu 1.5 Xs, As > 15 Xs. Ag and Cd abundances are too low to show at this scale. (B) Fluvial tailings (bedded, gray and brown layers; sledge hammer for scale) from a tailings impoundment below Sunnyside mill at Eureka during flotation milling era (1918–1930) (Fey et al., 2000; figure 6 in Blair et al., 2002). Element concentrations exceed crustal abundance values as follows: Fe to 1.5 Xs; Pb, Zn, Cu, As, Ag, and Cd all > 16 Xs. Elevated base metals (Cu, Pb, Zn) are characteristic of Sunnyside mine, epithermal polymetallic base metals processed at the Sunnyside Eureka mill.

In the Silverton area, country rocks experienced deuteric, propylitic alteration as the caldera-forming magmatic system cooled and degassed. Regional propylitic alteration affected large areas of older intermediate composition volcaniclastic rocks. Ash-flow tuffs and postcaldera andesitic lavas that infilled the caldera were also propylitzed. Lavas in the caldera degassed water and CO2, altering the primary minerals of the lavas and developing a secondary acid-neutralizing assemblage of chlorite, epidote, and calcite (Burbank, 1960). Excellent exposures of propylitically altered intermediate composition lavas are exposed east of Cement Creek and along the upper Animas River east of Silverton.

Pervasive, quartz-sericite-pyrite alteration is associated with large hydrothermal systems adjacent to intrusions in the study area, and is characterized by total replacement of original country rocks by fine-grained quartz, sericite, and finely disseminated pyrite (Bove et al., 2007a). Large areas of pervasive quartz-sericite-pyrite alteration are exposed in upper Topeka and Ohio Gulches and at the head of Prospect Gulch, and formed adjacent to acid sulfate alteration (Fig. 11).

Vein-related quartz-sericite-pyrite alteration affects only the margins adjacent to vein structures altering host rocks within a few meters adjacent to the vein. Veins of this type include the Sunnyside vein formed along structures of the Eureka graben. These veins were the main focus of mining in the Sunnyside, Gold King, and many other mines in the Silverton area. Despite the host rocks not being highly altered, the veins can be laterally extensive for thousands of meters along strike and contain high grades of base- and precious-metal ore minerals.

The acid sulfate alteration type is characterized by original volcanic host rocks being replaced by acidic, sulfate-rich solutions. The solutions were focused along faults and hydrothermal breccia zones, such as those in upper Prospect Gulch. The acid sulfate system is zoned outward from quartz-alunite (KAlSO4), pyrophyllite (AlSiO3), and massive silicification to argillic alteration. Feldspars and groundmass in some areas of quartz-alunite-pyrophyllite alteration are entirely replaced by alunite. Feldspars and fracture fillings in the argillic zone are altered to a high-temperature, alumino-silicate clay (dickite). Quartz-ser-icite-pyrite alteration occurs adjacent to some areas of argillic and quartz-alunite-pyrophyllite alteration (Bove et al., 2007a, 2007b). Regional propylitically altered rocks occur on the margins of the intensely altered acid sulfate system. Examples of acid sulfate alteration include the Red Mountain mining district (upper Prospect Gulch), and the Ohio Peak and Anvil Mountain areas north of Silverton.

Natural weathering processes involving hydrothermally altered rocks produce acidic and metal-rich leachate that is toxic to aquatic life (Besser and Brumbaugh, 2007; Schmidt et al., 2012). The composition of leachate that forms during weathering is a function of surface water and groundwater interactions with soils, sediments, and rocks having variable mineralogy (Miller and McHugh, 1994; Miller, 1998, 1999; Bove et al., 2007b; Neubert et al., 2011). Those assemblages having moderate to high net acid production (NAP) include the weak sericite-pyrite, argillic, quartz-sericite-pyrite, and acid-sulfate assemblages. The propylitic assemblage can have significant acid neutralizing capacity (ANC) (Fig. 8) (Jambor, 2003; Yager et al., 2008a, 2008b, 2013). ANC of propylitized rocks is obliterated where overprinted by more intense hydrothermal alteration (Yager et al., 2008a).

Pyrite is often a ubiquitous primary acid-generating mineral in hydrothermal systems. Entire mountain blocks in the study area are highly altered and contain pervasive pyrite and other sulfide minerals, including chalcopyrite (CuFeS2), galena (PbS), and sphalerite (ZnS) occurring at the surface to > 1 km depth (Casadevall and Ohmoto, 1977; Bove et al., 2007b). The total watershed area of hydrothermally altered rock subjected to weathering is therefore an important factor to investigate. This is because the environmental response that has or will result from historical or new mining will be largely influenced by mineralogy of the bedrock and surficial deposits exposed to weathering at the surface, where there is an abundant oxygen concentration and water available to drive weathering reactions.

Silverton Mining History

Developments of mining and milling technology strongly controlled the quantity of ore that could be mined as well as processed. Geoenvironmental impacts were directly related to ore milling technology and how mill waste was managed after processing. Mining operations in the ARW evolved from small “high-grade” mines with limited processing capability to large mines having lower-grade ore but with a higher processing capability (Jones, 2007). A brief summary of mining and milling history helps to interpret the impacts to the watershed that may be observed in geochemical background samples collected in the watershed today. Much of this summary is derived from the paper by Jones (2007).

Lode gold mining began with the development of the Little Giant mine in Arrastra Gulch, southwest of Silverton. Hand methods were used at this time to mine a few tons of ore per day. Short tunnels and shafts accessed high-grade silver vein mineralization directly from surface exposures. Ore was seldom processed on site and was commonly shipped to distant smelters, even outside the United States. The Greene and Company smelter operating between 1875–1880 was constructed at the outlet of Cement Creek to process ore into metallic bullion. Construction of a narrow gauge railroad between Durango and Silverton in 1881 resulted in reduced production costs for ore processing and supplies. Ore processing capacity increased as ore was transported by rail and processed at what became the American Smelting and Refining Company in Durango, Colorado (visited near stop 1 of Day 2 of this trip). Five stamp mills capable of processing 10–70 tons per day operated in the ARW between 1871 and 1889. By the end of 1889, >100 tons of ore could be mined per day at the larger mines and accessed by hundreds of feet of interconnected tunnel and surface shafts (Jones, 2007).

During 1890–1913, new mining technology was developed involving the construction of aerial trams that could transport workers, machinery, and supplies to remote mine sites. The trams could also transport ore to rail lines. Advances in mining methods also evolved as hand steel mining methods gave way to compressed-air powered machine drills. Electricity also arrived at many of the mines, which further increased mining and milling efficiencies. In addition, three new railroad lines were constructed that served new milling facilities and also were integrated with aerial trams. Advances in technology, increased efficiency, and infrastructure enabled 200–400 tons of ore per day to be mined and processed. Mines could be worked year-round due to better access by trams and rail lines. Some mine tunnels attained lengths spanning thousands of linear feet. The production of higher tonnages of lower-grade ore accessed along extensive vein systems was now possible. The advent of gravity milling using Wilfley tables allowed minerals with different specific gravity to be separated more efficiently (see Jones, 2007, p. 61). Slurry waste from gravity mills, consisting of sand- to clay-sized fractions was sometimes disposed of near streams, where they were reworked by fluvial processes and deposited along the riparian zone. Long haulage tunnels were also constructed during this time to drain groundwater and dewater higher elevation workings. Total tonnage of ore processed during this time was 4.3 M tons.

The period 1914–1935 was marked by use of a ball milling and a chemical froth-flotation process that enabled the recovery of zinc. Mining of lower-grade ores continued to progress toward mining of higher tonnage, low-grade ores. A method known as “shrinkage stoping” was developed, and it became the dominant mining method throughout the twentieth century (Jones, 2007). Shrinkage stoping permitted an entire vein zone to be mined. The open stope was subsequently backfilled with waste rock allowing only the rock mined to be milled, which further increased efficiency. Mine workings increased in lateral and vertical extent and in 1916, the Sunnyside mine became the largest ore producer in the ARW. By 1928, daily production at the Sunnyside mine reached 1000 tons per day. A state-of-the-art flotation mill built in 1917–1918 at Eureka was the first large lead-zinc flotation mill in the state, and was able to process 600 tons of ore per day. Due to efficient recovery of metals by flotation milling, gravity stamp mills became obsolete in the ARW. Flotation milling produced large quantities of fine-grained mill materials that were disposed along the upper Animas River, in a section of the basin having a lower gradient that is known today for a multi-channel braided stream reach (Blair et al., 2002; Vincent and Elliott, 2007). Long haulage tunnels (such as the Gold King mill level near Gladstone, which later was extended in 1959 and renamed the American Tunnel) became sources of acidity and metal loading to surface water (Jones, 2007). Total ore tonnage produced between 1914 and 1935 was 4.2 M tons.

Between 1936 and 1991, an improvement in flotation mill chemistry using xanthate reagents allowed more efficient zinc recovery. Legal actions in the 1930s began to prevent direct disposal of mill tailings into streams. Several tailings impoundments were constructed along the upper Animas River. Early tailings impoundments were constructed near the Sunnyside Eureka mill in the braided stream reach below Eureka town site. Work by the Sunnyside Gold Corporation in collaboration with the ARSG during the 1990s moved the Eureka tailings to the Mayflower mill tailings impoundment. The Mayflower mill tailings near the outlet of Boulder Gulch are the major repository for mill waste in the ARW. Tailings impoundments constructed at this time were unlined, and this permitted percolation of water through the tailings and seepage of acidic water containing metals into the Animas River (Jones, 2007). Long haulage tunnels and underground workings were further expanded to tens of thousands of linear feet. Mine water drainage from these extensive tunnels was discharged directly into the stream. Over the duration of mining, no systematic inventory tracked how the mine workings throughout the ARW may have been interconnected.

On Sunday, 4 June 1978, the former Lake Emma (visited on Day 4 of this trip) and site of the initial discovery of the Sun-nyside mine, located at the head of Eureka Gulch above timber-line at 12,300 ft (3749 m), was breached when mining occurred too close to the surface. Heat generated from the mine is thought to have melted permafrost and glacial till that had formed along a fault beneath Lake Emma. When the frozen surficial material melted, it released lake water into the mine (Jones, 2007). This Sunnyside mine event is estimated to have sent 5–10 million gallons of mine water into the Cement Creek basin. Fortunately, because the event occurred on a Sunday, the mine was not occupied by miners. The mine water was collected and analyzed at Durango, Colorado, and was found to contain 12.6 mg/L zinc, and 4 mg/L lead (Jones, 2007). During the time period from 1936 to 1991, 9.5 M tons of ore were processed with 200,000 tons of mill waste being impounded in the Mayflower mill tailings impoundment adjacent to the Mayflower mill.

Total metal production of mines in San Juan County between 1871 and 1991 include 2.2 M oz gold; 51.3 M oz silver; 112.2 M oz copper; 765.6 M oz lead; and 604.2 M oz zinc (Jones, 2007).

Day 3: Silverton, Geologic Overview, Cement Creek, and Gold King Mine Area

Reset odometer to 0.

Cum. distance 
km (mi) Time Directions 
0.42 (0.26)   
4.10 (2.55) 0730  
  0800 Depart Silverton (intersection of Greene St. and East 14th St.). 
   South on East 14th St. to intersection of County Rd. 32 and 33. 
   Right (southwest) to Kendall Mountain Rd. (County Rd. 33). 
   Arrive at topographic margin of San Juan caldera. 
Cum. distance 
km (mi) Time Directions 
0.42 (0.26)   
4.10 (2.55) 0730  
  0800 Depart Silverton (intersection of Greene St. and East 14th St.). 
   South on East 14th St. to intersection of County Rd. 32 and 33. 
   Right (southwest) to Kendall Mountain Rd. (County Rd. 33). 
   Arrive at topographic margin of San Juan caldera. 

Stop 1: San Juan Caldera, Topographic Margin

The trip route traverses the southern margin of the San Juan and nested Silverton calderas that are discussed in the “San Juan— Uncompahgre Caldera and Silverton Caldera Rocks” section. At this stop, trip participants can walk along the southern topographic margin of the San Juan caldera. Outcrops exposed on the road have textures of intermingled Eureka Member of Sapinero Mesa Tuff and wall rock. A short walk to the south of the road reveals Leadville-Ouray Limestone. To the west across the Animas River, limestone megabreccia blocks are visible that formed during San Juan caldera collapse. A thick sequence of Silverton Volcanics, intermediate composition lavas infill the San Juan caldera north of Silverton. The arcuate drainage of Mineral Creek and the upper Animas River define the younger nested, Silverton caldera margin.

Cum. distance
km(mi)TimeDirections
0830Depart from San Juan caldera topographic margin.
8.21(5.1)Return to intersection of Greene St. and East 14th St.
9.75(6.06)Left (west) on Green St. to County Rd. 31).
Right (southeast) on County Rd. 31.
11.44(7.11)0915Arrive at hydrologic gauge A-72 (37.790277°N, 107.666944°W).
Cum. distance
km(mi)TimeDirections
0830Depart from San Juan caldera topographic margin.
8.21(5.1)Return to intersection of Greene St. and East 14th St.
9.75(6.06)Left (west) on Green St. to County Rd. 31).
Right (southeast) on County Rd. 31.
11.44(7.11)0915Arrive at hydrologic gauge A-72 (37.790277°N, 107.666944°W).

Stop 2: Hydrologic Gauge A-72 (09359020)

This is a key hydrologic gauge, discussed in the section on “The Importance of Data Collected at Hydrologic Gauges,” that is used to record flow from the main tributary basins of Mineral Creek, Cement Creek, and the upper Animas River. Data collected here are important in that they document that water is integrated from all the upstream basins, and represent the collective water quality of all upstream impacts from natural weathering processes and mining. As is pointed out in the “Tracer Studies (Silverton)” section, the data collected at this gauge, while important to evaluate watershed water quality as a whole, do not show those specific subwatershed areas that are the principal metal loaders to streams. Tracer-dilution studies are able to locate specific locations that are sources of metal loading.

Cum. distance
km(mi)TimeDirections
0945Depart from hydrologic gauge A-72.
13.13(8.16)Return to intersection of Greene St. and East 14th St.
13.42(8.34)Right (south) on 14th St. to Cement St.
Right (west) on Cement St.
13.57(8.43)1000Arrive near confluence of upper Animas River and Cement Creek (walk 0.07 mi southwest) to mixing zone.
Cum. distance
km(mi)TimeDirections
0945Depart from hydrologic gauge A-72.
13.13(8.16)Return to intersection of Greene St. and East 14th St.
13.42(8.34)Right (south) on 14th St. to Cement St.
Right (west) on Cement St.
13.57(8.43)1000Arrive near confluence of upper Animas River and Cement Creek (walk 0.07 mi southwest) to mixing zone.

Stop 3: Mixing Zone at Confluence of Upper Animas River and Cement Creek

This stop is visually important for showing the effect of mixing tributaries with different water quality. The upper Animas River is sourced from areas with abundant propylitically altered rock having some acid-neutralizing capacity and the water has a near neutral pH. Cement Creek is acidic and iron-rich, and has been this way prior to mining as evidenced by abundant ancient ferricrete deposits. Iron colloids form (precipitation) where near neutral pH water of the upper Animas River intersects the Cement Creek tributary. Iron, aluminum, and manganese precipitation is strongly controlled by pH. This is the site shown in Figure 1.

Cum. distance
km(mi)TimeDirections
1030Depart upper Animas River and Cement Creek mixing zone.
14.00(8.7)Return to intersection of Greene St. and East 14th St.
14.72(9.15)Right (east) on Greene St. to intersection with CO-34.
Left (north) on CO-110 (Cement Creek Rd.).
15.59(9.69)1045Arrive at alluvial ferricrete.
Cum. distance
km(mi)TimeDirections
1030Depart upper Animas River and Cement Creek mixing zone.
14.00(8.7)Return to intersection of Greene St. and East 14th St.
14.72(9.15)Right (east) on Greene St. to intersection with CO-34.
Left (north) on CO-110 (Cement Creek Rd.).
15.59(9.69)1045Arrive at alluvial ferricrete.

Stop 4: Alluvial Ferricrete

Cement Creek is aptly named due to the abundant ferricrete deposits that cement surficial materials along the course of the creek and in subwatersheds. These deposits have been radiocarbon dated between modern time and ~9000 yr B.P., and are evidence for the acidic conditions that have existed in the watershed for millennia. It is highly unlikely that trout species ever survived in Cement Creek basin due to the naturally occurring sources of acidity and metals.

North of the ferricrete deposit, Cement Creek Rd. traverses propylitically altered intermediate composition lavas of the Burns Member of the Silverton Volcanics. Waters draining from the east side of Cement Creek basin, where flowing across propylitically altered lavas, have near neutral pH. Hydrothermally altered rocks (quartz-sericite-pyrite; acid sulfate alteration types) along Ohio Peak and Anvil Mountain as well as in Prospect Gulch and North Fork Cement Creek overprint the older propylitic assemblage. Weathering of the highly altered areas introduces acidity and metals to surface water and groundwater.

Cum. distance
km(mi)TimeDirections
1110Depart alluvial ferricrete, north on CO-110.
17.01(10.57)Hancock Gulch fan on river left diverts flow of Cement Creek.
18.84(11.71)1120Arrive at Topeka Gulch outlet (37.846185°N, 107.678755°W). 1140 Depart fom Topeka Gulch outlet.
19.52(12.13)Ohio Gulch outlet west of road (37.852121°N, 107.677237°W).
Cum. distance
km(mi)TimeDirections
1110Depart alluvial ferricrete, north on CO-110.
17.01(10.57)Hancock Gulch fan on river left diverts flow of Cement Creek.
18.84(11.71)1120Arrive at Topeka Gulch outlet (37.846185°N, 107.678755°W). 1140 Depart fom Topeka Gulch outlet.
19.52(12.13)Ohio Gulch outlet west of road (37.852121°N, 107.677237°W).

Stop 5: Topeka Gulch, May Day Mine Reclamation

As discussed in the “Natural Events Impacting Water Quality” section, Topeka and Ohio Gulches are a large source of suspended sediment loads to Cement Creek during heavy thunderstorms. Storms that stall over areas of easily eroded quartz-sericite-pyrite altered rock at the head of this (Topeka Gulch) and Ohio Gulch transport large quantities of suspended sediment into Cement Creek. This adds to the metal loads from mining-related sources.

Cum. distance
km(mi)TimeDirections
22.74(14.13)1150Arrive at upper iron spring (37.879694°N, 107.669716°W),
Cum. distance
km(mi)TimeDirections
22.74(14.13)1150Arrive at upper iron spring (37.879694°N, 107.669716°W),

Stop 6: Upper Bog (Active Iron Spring)

In addition to the ancient ferricrete deposits mentioned in the “Tracer Studies (Silverton)” section, active iron springs continue to precipitate iron along Cement Creek. This iron spring, perched above creek level on river right, is just downstream from Prospect Gulch (Stop 7) and is a natural feature formed where groundwater transported reduced, ferrous iron that interacts with oxygen and causes ferric iron precipitation in terraces. Time permitting, we will walk to another iron spring upslope a few hundred meters from the experimental well (Stop 7). Water quality from the spring indicates high copper and arsenic concentrations that reflect an upslope source from the acid sulfate mineralized system of the Red Mountain mining district.

Cum. distance
km(mi)TimeDirections
23.13(14.37)1210
1215Depart from upper iron spring. Arrive at Prospect Gulch outlet and alluvial fan (37.882570°N, 107.667343°W) (lunch).
Cum. distance
km(mi)TimeDirections
23.13(14.37)1210
1215Depart from upper iron spring. Arrive at Prospect Gulch outlet and alluvial fan (37.882570°N, 107.667343°W) (lunch).

Stop 7: Lower Prospect Gulch Experimental Well (Private Site, Permission Required)

This is a site of an experimental drill hole completed by Dr. Raymond Johnson as part of his groundwater flow modeling study in the early 2000s. Empirical data are rarely available in subalpine watersheds to develop groundwater flow models. Data collected at this site and from two other drill holes in middle and upper Prospect Gulch provide information on the hydrology of this mountain watershed. Field parameters (temperature, dissolved oxygen, pH, and specific conductance) measured from water collected at cased intervals reveal different water quality at varying depths. The water quality determined from different well depths is indicative of the natural sources of acidity and metals that can originate from surficial and bedrock flowpaths.

Cum. distance
km(mi)TimeDirections
1330Depart from Prospect Gulch outlet.
24.83(15.43)1335Arrive at Gladstone town site (37.890491°N, 107.652107°W)
Cum. distance
km(mi)TimeDirections
1330Depart from Prospect Gulch outlet.
24.83(15.43)1335Arrive at Gladstone town site (37.890491°N, 107.652107°W)

Stop 8: Historical Gladstone Town Site

This is the site of the original Gold King mill level tunnel. According to Colorado Historical Society archives, the tunnel was excavated in 1897 by the American Tunnel and Mill Company at the site of the former Harrison mill. In 1959, the tunnel was renamed the American Tunnel and extended to access the Sunnyside mine workings beneath mineralized veins in the Sun-nyside mine. Treatment ponds were established at Gladstone to add lime to discharge from the American Tunnel. Between 1996 and 2002, three bulkheads were installed in the American Tunnel.

The foundation remnant of the historical Gold King mill is visible on the west side of the road.

Cum. distance
km(mi)TimeDirections
1400Depart from Gladstone town site.
24.94(15.5)Right at intersection of CO-110 and CO-52.
25.30(15.72)Right at intersection of CO-52 and CO-51. Trend left (northeast) at road forks (37.893592°N,107.644176°W).
27.00(16.78)1445Arrive at Gold King mine #7 level (37.894579°N,107.638371°W)
Cum. distance
km(mi)TimeDirections
1400Depart from Gladstone town site.
24.94(15.5)Right at intersection of CO-110 and CO-52.
25.30(15.72)Right at intersection of CO-52 and CO-51. Trend left (northeast) at road forks (37.893592°N,107.644176°W).
27.00(16.78)1445Arrive at Gold King mine #7 level (37.894579°N,107.638371°W)

Stop 9: North Fork Cement Creek, Gold King Mine #7 Level (Private Site, Permission Required)

Between 1999 and 2002 after sealing the first two bulkheads installed in the American Tunnel, an increase in adit discharge was observed upgradient in upper Cement Creek basin at the Mogul and Gold King, and Red and Bonita mines. Much of the discussion by the ARSG in the past few years has involved treating the draining adit discharge in this area. At this site, we will discuss events leading up to the 5 August 2015 Gold King mine water release event, current treatment methods of the Gold King #7 tunnel discharge, and water quality and analysis done by Thomas Chapin of the USGS (“Tools to Investigate Mining Impacts in Geologically Complex Watersheds” section).

Possible influences of major structural elements (Bonita fault) that may provide insight into water-bearing features within the Gold King mine will also be discussed. For example, historical records retrieved from the Colorado Historical Society dating from 1932 suggest that some parts of the Gold King mine #7 level had to be abandoned, because pumps could not keep pace with incoming water. The mineralogical assemblage at the Gold King mine differs from the Sunnyside mine workings, with the Gold King mine being a gold-rich system and having gold telluride mineralization.

Cum. distance
km(mi)TimeDirections
1545Depart from Gold King mine #7 level.
28.93(17.98)Descend road to intersection of CO-51 and CO-53.
Right (north) on CO-53.
Arrive Red and Bonitamine (37.897479°N, 107.644682°W).
Cum. distance
km(mi)TimeDirections
1545Depart from Gold King mine #7 level.
28.93(17.98)Descend road to intersection of CO-51 and CO-53.
Right (north) on CO-53.
Arrive Red and Bonitamine (37.897479°N, 107.644682°W).

Stop 10: North Fork Cement Creek, Red and Bonita Mine (Private Site, Permission Required)

Reclamation had begun at the Red and Bonita mine prior to the 2015 Gold King mine water release event. A bulkheading project managed by the Environmental Protection Agency had been designed to stem the increase in discharge that occurred from the Red and Bonita mine, after the bulkheads were sealed in the American Tunnel. Bog iron deposits may be observed in the North Fork, Cement Creek valley below the mine, although the age of these deposits is unknown. The Mogul mine is at the head of the valley to the north, which also experienced an increase in discharge following plugging of the American Tunnel.

Cum. distance
km(mi)TimeDirections
1700Depart Red and Bonita mine for Silverton.
1800Dinner and presentations at Silverton town hall.
Cum. distance
km(mi)TimeDirections
1700Depart Red and Bonita mine for Silverton.
1800Dinner and presentations at Silverton town hall.

Tools to Investigate Mining Impacts in Geologically Complex Watersheds

Pre-Mining Background (Silverton)

Streambed Sediments

To determine pre-mining background of sediments, Church et al. (2007a) collected pre-mining sediments from cores, or from trenches on preserved terraces along the Animas River and its tributaries (Fig. 12A). More than 25 localities were sampled, 15 from the upper Animas River, five from Cement Creek, and six from Mineral Creek. The terrace localities were selected based on geomorphological mapping of unconsolidated deposits. Dating methods to determine the age of terraces sampled included dendrochronology, historical records, and 14C and 210Pb dating. Wherever possible, a site was located near an Engelmann or Blue spruce to provide dendrochronological control; the trees were cored if live or sampled if dead. Table 3 shows the low, high, and mean concentration of selected metals in background pre-mining sediments grouped by subbasin. These differences in streambed chemical signatures clearly show the impact from historical mining and milling along the upper Animas River basin. This is an area that has less intense hydrothermal alteration, and yet it has higher concentrations of metals derived from the mill waste, which prior to 1930 had been deposited in the upper Animas River floodplain. The stream chemistry demonstrates that using background concentration values as a gauge for attainable remediation goals is dependent on multiple variables, including the sometimes high, ambient background geochemical signature that was overprinted by deposits from historical mining operations.

High, Low, and Mean Concentrations for Selected Elements for Background Pre-Mining Sediments Sites for Mineral Creek, Cement Creek, and Upper Animas River Basins
Table 3.
High, Low, and Mean Concentrations for Selected Elements for Background Pre-Mining Sediments Sites for Mineral Creek, Cement Creek, and Upper Animas River Basins
BasinAs (ppm)Cu (ppm)Zn (ppm)Pb (ppm)Mn (ppm)Mo (ppm)Ba (ppm)Sr (ppm)V (ppm)
Mineral Creek
High value3880410450230010800285120
Low value153212058210126018056
Average value305121317011665666235102
Cement Creek
High value6915040042012007870400220
Low value1821802305501615240150
Average value48821922978383.8779288174
Upper Animas
High value681901350750550010850260170
Low value21403007518001620160110
Average value4212867432433145.2737194133
BasinAs (ppm)Cu (ppm)Zn (ppm)Pb (ppm)Mn (ppm)Mo (ppm)Ba (ppm)Sr (ppm)V (ppm)
Mineral Creek
High value3880410450230010800285120
Low value153212058210126018056
Average value305121317011665666235102
Cement Creek
High value6915040042012007870400220
Low value1821802305501615240150
Average value48821922978383.8779288174
Upper Animas
High value681901350750550010850260170
Low value21403007518001620160110
Average value4212867432433145.2737194133

In an area as complex as the upper ARW, and given the variability in geology and mining impacts, it is not possible to assign a single background concentration value for each element, due to changing geology and alteration patterns throughout and across the basins. Indeed, Reimann et al. (2005) suggest that background should be a range and not a single value.

Water Quality Samples

The determination of background water quality in an area as geologically complicated as the Silverton area is particularly challenging. Each mineralized system can have specific mineral species that weather to produce a particular water quality. Mineralized systems may only impact small geographic areas such as a subwatershed, and hence scale plays an important role in water quality. In addition to natural sources of metals, including sediment derived from upslope sources of altered and mineralized rock, draining mine adits and weathering of mine-related deposits add to ambient geochemical background water quality signatures. Incomplete knowledge about the lateral and vertical extent of mine tunnels and shafts and how mine workings may be interconnected compounds the complexity. Lack of information is due in part to the age of mines, sometimes dating back to the late 1870s. Mine tunnels can intersect natural geologic features (faults and fracture systems) that in addition to mine workings can serve as groundwater flow paths. All of these issues can make interpretations about the water chemistry particularly challenging.

Background water quality of the upper Animas River basin was investigated by Mast et al. (2007). They collected samples from surface water, springs, and mines and grouped them into four categories: category I having no evidence of mining activity; category II appearing unaffected, but not unequivocally; category III not directly affected but having mining activity upgradient of site; and category IV having direct discharge from a mining site. Results for categories I and II for specific conductance, pH, dissolved oxygen, alkalinity, sulfate, and selected major and minor elements are shown in Table 4. The median values for the listed constituents are low, with 90 mg/L sulfate, 28 mg/l calcium, 3.2 mg/L magnesium, and 5.8 mg/L silica. Elements occurring at mildly elevated concentrations are iron, 46 μg/L; aluminum, 359 μg/L; manganese, 192 μg/L; and zinc, 28 μg/L. The high concentrations within these ranges indicate that some waters were apparently mining impacted with maximum values of 1,300 mg/L sulfate, 550 mg/L calcium, 34 mg/L magnesium, 71,400 μg/L aluminum, 117,000 μg/L iron, 141 μg/L lead, 74,700 μg/L manganese, 71 μg/L molybdenum, and 14,400 μg/L zinc.

Geochemical Parameters Determined for Category I and II, Undifferentiated Surface Water and Groundwater Samples From Mast et al. (2007, their Table 2)

Table 4.
Geochemical Parameters Determined for Category I and II, Undifferentiated Surface Water and Groundwater Samples From Mast et al. (2007, their Table 2)
ParameterMinimumMediumMaximum
pH2.64.98.5
Specific conductance122702,180
Alkalinity (mg/L, as CaCO3)<0.5<0.569
Sulfate (mg/L)1.0901,300
Ca (mg/L)1.028550
Mg (mg/L)0.13.234
SiO2 (mg/L)0.85.853
Al (μg/L)<4035971,400
Cu (μg/L)<4<4372
Fe (μg/L)<3046117,000
Zn (μg/L)<202814,400
Pb (μg/L)<30<30141
Mn (μg/L)<319274,700
Mo (μg/L)<10<1071
Ba (μg/L)<222101
Sr (μg/L)6.02365,700
V (μg/L)<4<411
ParameterMinimumMediumMaximum
pH2.64.98.5
Specific conductance122702,180
Alkalinity (mg/L, as CaCO3)<0.5<0.569
Sulfate (mg/L)1.0901,300
Ca (mg/L)1.028550
Mg (mg/L)0.13.234
SiO2 (mg/L)0.85.853
Al (μg/L)<4035971,400
Cu (μg/L)<4<4372
Fe (μg/L)<3046117,000
Zn (μg/L)<202814,400
Pb (μg/L)<30<30141
Mn (μg/L)<319274,700
Mo (μg/L)<10<1071
Ba (μg/L)<222101
Sr (μg/L)6.02365,700
V (μg/L)<4<411

Category III and IV sites of Mast et al. (2007) had higher median and maximum concentrations for most constituents compared to category I and II sites. Results for categories III and IV for specific conductance, pH, dissolved oxygen, alkalinity, sulfate, and selected major and minor elements are shown in Table 5. Maximum concentrations include the following: sulfate, 2,720 mg/L; calcium, 460 mg/L; aluminum, 71,400 μg/L; iron, 686,000 μg/L; lead, 1,379 μg/L; copper, 98,600 μg/L; and the maximum concentration for zinc was 228,000 μg/L. Importantly, several trace metals, including zinc, copper, and manganese, were present at concentrations that exceed aquatic-life standards at many of the background sites (Mast et al., 2007).

Geochemical Parameters Determined for Category III and IV, Mine Drainage Samples from Mast et al. (2007, Their Table 5)

Table 5.
Geochemical Parameters Determined for Category III and IV, Mine Drainage Samples from Mast et al. (2007, Their Table 5)
ParameterMinimumMediumMaximum
pH2.355.747.77
Specific conductance1807413,520
Alkalinity (mg/L, as CaCO3)<0.56.5137
Sulfate (mg/L)453092,720
Ca (mg/L)2.080460
Mg (mg/L)0.76.342
SiO2 (mg/L)2.01030
Al (μg/L)<4061671,400
Cu (μg/L)<4698,600
Fe (μg/L)<304,650686,000
Zn (μg/L)<20621228,000
Pb (μg/L)<30<301,379
Mn (μg/L)<31,36023,700
Mo (μg/L)<10<1042
Ba (μg/L)<21062
Sr (μg/L)378096,080
V (μg/L)<4<45
ParameterMinimumMediumMaximum
pH2.355.747.77
Specific conductance1807413,520
Alkalinity (mg/L, as CaCO3)<0.56.5137
Sulfate (mg/L)453092,720
Ca (mg/L)2.080460
Mg (mg/L)0.76.342
SiO2 (mg/L)2.01030
Al (μg/L)<4061671,400
Cu (μg/L)<4698,600
Fe (μg/L)<304,650686,000
Zn (μg/L)<20621228,000
Pb (μg/L)<30<301,379
Mn (μg/L)<31,36023,700
Mo (μg/L)<10<1042
Ba (μg/L)<21062
Sr (μg/L)378096,080
V (μg/L)<4<45

Remote Sensing Supported with Field-Based Mapping

Alteration mapping in the ARW has been aided using Advanced Visible Infrared Imaging Spectrometer (AVIRIS) remote sensing techniques. AVIRIS allows identification of acid-generating and acid-neutralizing assemblages. Field-based mapping augmented with laboratory X-ray diffractometry analysis of field samples enable ground-truth verification of AVIRIS mineral spectra and more complete mapping of alteration types in vegetated areas (Fig. 11) (Bove et al., 2007b). Other remote sensing spectrometers including Advanced Spaceborne Thermal Emission and Reflection Radiometer and Landsat Thematic Mapper have been shown effective in mapping various alteration types in the ARW (Rockwell, 2012; Yager et al., 2013). Intense alteration that overprints propylitically altered rocks that are mapped by remote sensing methods represents only ~12% of the ARW study area (Yager et al., 2013).

Importance of Data Collected at Hydrologic Gauges

Determination of the sources, concentrations, and loads of contaminants was an important aspect of the AML study. With a limited reclamation budget, it is critical to prioritize resources. Water quality data from hydrologic gauges allow an understanding of the basins that provide the most abundant and widest variety of contaminants. Repeat measurements at the gauges provide information on reclamation success and determine how additional resources should be allocated.

The hydrologic stream gauge A-72 (visited on Day 3 of this trip) located downstream from Silverton is important because it represents an integrated sample from multiple upstream basins with varying water quality. The A-72 gauge is comprised of surface water and groundwater sourced from Mineral Creek, Cement Creek, and the upper Animas River basins. The ARSG is interested in data collected at A-72 gauge because changes in water quality at this site can be used to evaluate the success of upstream reclamation activities. Element load determinations at A-72 are informative because they quantify the amount of contaminants entering the Animas Canyon as it flows toward Durango and other downstream neighbors along the San Juan River system. Element loads in kg/d are calculated by multiplying the discharge by a constituent concentration in a filtered water sample. However, this information is not detailed enough to determine the specific upstream parts of the watersheds that are producing the loads, and where to specifically target remediation efforts.

There are additional gauges at the mouth of Cement Creek (CC-48) and Mineral Creek (M-34) and the upper Animas above Silverton (A-68), where discharges can be measured, water quality samples taken, and loads calculated. However, load determinations at the mouth of these basins still do not provide enough resolution regarding sources of metal loading. Due to the issue of scale and the differences in intensity and extent of mining as well as natural sources of metals and acidity, sampling at the subwatershed outlet is commonly required to determine which areas should be prioritized for remediation (Yager et al., 2013). Tracer-dilution studies discussed below provide high resolution data, which can be used to better delineate the actual point and diffuse sources of contaminants along a stream.

Tracer-Dilution Synoptic Sampling

Tracer Studies (Silverton)

One tool that has seen increasing application over the past 30 yr is tracer-dilution synoptic sampling (Rantz et al., 1982; Kilpatrick and Cobb, 1985; Bencala and McKnight, 1987; Kimball et al., 1994), although the concept goes as far back as 1863 (Spencer and Tudhope, 1958). Over the course of the five years of the ARW study, 13 tracer studies were performed in the three subbasins, 10 of which were summarized in Kimball et al. (2007).

The basic principle of a tracer-dilution study is to inject a dye or salt tracer into a stream, measure the dilution of the tracer as it moves downstream, and thereby calculate downstream discharge from the amount of dilution (Kimball, 1997). A typical salt tracer is lithium bromide or sodium chloride. This method is used in place of the traditional method of measuring stream velocity and cross-sectional area over numerous small increments across the stream at each sampling point. The traditional method can miss hyporheic flow (flow along and through the streambed), and is difficult to perform in steep, rocky, uneven sections. The tracer dye or salt is not affected by these difficulties. Once the tracer system is in steady-state over the course of the stream reach being studied (which may take hours), a team walks the entire length of the tracer and collects many water samples from the main stem of the stream, and from tributaries and small inflows. These samples are then analyzed by inductively coupled plasma—mass spectrometry (ICP-MS) for many constituents, including the cation of the tracer. The anion of the tracer is also analyzed, as a check on tracer dilution (the cation, for example lithium, can be non-conservative under certain pH conditions).

Once the discharge on the mainstem of the stream has been calculated, and the discharges from known tributaries are added, there may be sections where the mainstem discharge has increased by more than has been accounted for. This implies that unsampled groundwater or other unsampled inflow has entered the stream in that reach. For each discharge calculated, the concentration of analyzed elements is multiplied by that discharge to get instantaneous loads at each point. The cumulative loads generally increase downstream, but in some reaches, the cumulative load for a particular element, for example copper, may decrease. This is a result of instream reactions, where copper may have sorbed to colloidal iron or otherwise precipitated out of the water column, and become part of the colloidal load or even the bed load (Fey and Wirt, 2007). The calculated loads from the side tributaries and unsampled inflows may identify sources of metal loading and their magnitudes.

Kimball et al. (2007) summarized the loads contributed by the three subbasins. At base flow, Mineral Creek dominates the total copper load: Mineral Creek contributes 60%, Cement Creek contributes 30%, and the upper Animas River contributes 4% of the cumulative instream load in the watershed. Cement Creek contributed the greatest percentage of cumulative instream load of zinc at the A-72 gauge. Mineral Creek contributed 24% of the zinc, and the upper Animas River provided 31% of the zinc. Mass-loading calculations indicated that 43% of the aluminum load was from Cement Creek, 42% from Mineral Creek, and only 9% was from the upper Animas River. The streambed and cobbles of Cement Creek are dominantly orange colored; this is reflected by its contribution of 49% of the iron load. Mineral Creek contributed 43% of the iron and the upper Animas River contributed only 4%. An indication of the high iron concentrations, especially in Mineral and Cement Creek subbasins, is fer-ricrete deposits. Ferricretes are iron-cemented surficial deposits that have formed when dissolved iron derived from sulfide oxidation and weathering, precipitates in alluvium and colluvium. Ferricretes in the ARW are dated from modern to > 9000 yr B.P., and are a strong indicator of acid-rock drainage that occurred in the area prior to mining (Yager et al., 2003; Wirt et al., 2007; Verplank et al., 2007). The upper Animas River contributed the most dissolved manganese at 49%; Cement Creek and Mineral Creek contributed 32% and 15%, respectively. Manganocrete, the manganese-rich form of ferricrete, formed in areas adjacent to the Sunnyside vein system, which has abundant manganese mineralization (Yager et al., 2003; Verplanck et al., 2007). Mill tailings produced at the Sunnyside Eureka mill and other mills upstream in Placer and California Gulches are a source of manganese to the upper Animas River.

Along Cement Creek, the tributary known as Prospect Gulch provided large percentages of the total sulfate, aluminum, iron, copper, and zinc for the entire Cement Creek basin (Wirt et al., 1999). Other, more specific sources of loading (Kimball et al., 2007) include aluminum from the Middle Fork Mineral Creek (280 kg/d), the Anvil Mountain area (100 kg/d), and the Minnesota Gulch area (~90 kg/d). High iron-loading areas include the Middle Fork Mineral Creek (~420 kg/d), and Prospect Gulch (210 kg/d). High copper loads were identified from Porphyry Gulch in upper Mineral Creek (12 kg/d), the Mogul mine (8 kg/d), and the Junction mine (8 kg/d). High zinc loads came from Porphyry Gulch (35 kg/d), the Mogul mine (60 kg/d), and the Junction mine (~20 kg/d). Much of the metal loading can be traced to 23 specific areas. Chemical reactions due to rising pH in streams in mixing zones below the confluence with higher pH streams cause flocculation (precipitation) of iron. Iron flocculent is chemically reactive, has a high surface area, and is effective at sorbing other dissolved metals. When this material coats cobbles on the streambed, it is toxic to aquatic organisms.

Tracer-Dilution Studies in Creede

The following summary of tracer work in the Creede area is from Kimball et al. (2004). Three tracer studies were accomplished in the Willow Creek basin. One tracer study was done to evaluate metal-loading inputs along the Amethyst vein system that was mined along West Willow Creek. Another tracer investigated metal inputs along the Solomon—Holy Moses vein system in the East Willow Creek subbasin. A final tracer study was in a hydrologically complex area of sediment aggradation, in a multichannel braided stream reach below the confluence of West and East Willow Creeks and extending to the Rio Grande River south of Creede.

Upper West Willow Creek is a calcium bicarbonate—calcium sulfate type water and is slightly alkaline (pH ~7.8 and ~30 mg/L CaCO3). The discharge of the Nelson Tunnel is acidic (pH 4.5) and contains high sulfate (650 mg/L) and metal concentrations. Below the inflow of the Nelson Tunnel (Fig. 3), West Willow Creek becomes a calcium sulfate type water, the pH decreases to ~7.3, and the alkalinity decreases to near zero. Downstream just below the confluence with East Willow Creek, the pH increases and both calcium and sulfate are diluted. Iron was found to be in the colloidal fraction, which is effective in sorbing metals including zinc and copper and transferring them to streambed sediments. However, zinc tended to remain in the dissolved fraction; this may be because total iron concentrations in the water were low, commonly lower than the zinc concentrations, which thus limited the amount of zinc and copper sorption.

In the upper reach of West Willow Creek, zinc concentrations were initially low (below detection) and then increased to over 200 μg/L below the Amethyst mine (stop 5, Day 1). Zinc concentrations increased to over 10,000 μg/L below the Nelson Tunnel. The zinc load just below the Nelson Tunnel was 158 kg/d. This compares with the zinc load at the Animas River gauge A-72 at low flow, which is typically around 100 kg/d and is sourced from multiple mines in the ARW and not just a single source (Church et al., 1997; Fey et al., 2002). The cumulative instream loads included 9.2 kg/d aluminum, 1.8 kg/d cadmium, 9.7 kg/d iron, 45 kg/d manganese, 4.9 kg/d lead, 269 kg/d zinc, and 2540 kg/d sulfate. Concentrations for copper and nickel were too low to calculate loads. For some constituents, the Nelson Tunnel contributed ~10x the load of any other stream reach, and generally provided at least 50% of all loads. In the two segments downstream from the Nelson Tunnel, there were also substantial loads of cadmium, manganese, lead, zinc, and sulfate, which can be attributed to Nelson Tunnel discharge flowing through the waste pile of the Commodore mine. Substantial aluminum, iron, lead, and sulfate loads were added to the stream below the confluence of West and East Willow Creeks. Much of these added loads were the result of unsampled inflow, however, and whether the source(s) were West Willow Creek, East Willow Creek, or both, is unclear.

The second tracer-dilution study addressed East Willow Creek. At the head of the study reach of East Willow Creek, the principal ions were calcium, sodium, and bicarbonate. Sulfate concentrations were very low, indicating that the water chemistry was mostly a result of the weathering of non-ore minerals. There were no major inflows to East Willow Creek, although discharge and loads increased due to unsampled diffuse inflow and mine tunnel drainage. The Solomon mine provided the bulk of the mine drainage entering East Willow Creek; these drainage waters had high metal concentrations, but not enough discharge to affect concentrations or loads in East Willow Creek. The discharge from the adit, a spring discharge from the Solomon Tunnel, and drainage from ponds along the road near the Solomon Tunnel together only added 1 kg/d of zinc.

The metal concentrations and loads in East Willow Creek were substantially lower than those of West Willow Creek. Dissolved zinc concentrations were the highest of the metals, with a maximum concentration of 4100 μg/L and a median of 110 μg/L. However, the zinc load of East Willow Creek just before it joins West Willow Creek is less than 10 kg/d. The other metal loads are similarly low compared to those of West Willow Creek.

The third tracer study was along the braided channel below Creede. The channel braiding caused the flow to reach the Rio Grande River by several different channels. This prevented construction of simple loading curves, because element loads were in some places split and partitioned into different stream branches. The overall result of the load calculations for the lower Willow Creek tracer indicated a net loss of iron, manganese, and zinc and a net gain of aluminum and sulfate over the reach between Creede and the Rio Grande River. There were some high-concentration low-pH inflows from seeps emanating from the Emperius tailings and contributing sulfate, manganese, and zinc, but the discharge was very small, and so the loadings were also small. Lower Willow Creek enters the Rio Grande River at two different locations, ~200 m (656 ft) apart, and there was a net gain of aluminum, iron, manganese, zinc, and sulfate between the two sites, which was likely caused by unsampled groundwater from the Willow Creek watershed.

Reactive Transport Modeling

Tracer-dilution studies and synoptic sampling along with reactive transport modeling are effective tools for determining the effect of remediation (Church et al., 2007c). This allows investigators to use the measured and calculated data from the synoptic sampling as input into various test-case scenarios. For example, reactive transport modeling can be used to test the hypothetical case of remediating a subbasin to the point of having low metal inputs and subsequently calculating what effect this would have on downstream surface water quality (Runkel and Kimball, 2002). Many different scenarios can be tested by adjusting input parameters, and this can help guide decisions about where and how to best apply resources.

The Mountain Hydrograph—Effect on Stream Water Quality

Discharge rates, concentrations, and loads are continuously changing in mountain drainage systems. The San Juan Mountains region receives much of its precipitation in the form of winter snow. Winter discharge in streams is typically low due to low average temperatures. The timing and duration of warming temperatures in the spring control the rate at which the winter snow-pack thaws. With the increase in discharge during spring, element concentrations and loads increase. In order to evaluate seasonal effects on metal concentrations and loads, a water sample was collected at gauge A-72 during base flow on 16 October 1995. Subsequent samples were taken on 9 May, 21 May, and 19 June 1996 when snowmelt runoff had begun. The fourth sample, collected on 19 June 1996, was on the declining part of the hydrograph and had lower discharge. The four water samples were categorized as low-flow, and early, middle, and late runoff (Church et al., 1997). Figure 13 shows how discharge with the onset of the spring snowmelt corresponds with an increase in metal loads.

Figure 13.

Element loads (Kg/day) for total (dissolved + colloidal) Cu, Fe, Al, and Zn determined for base flow, low, medium, and high flow (ft3/s). Sample collection in spring (May—June) 1996 corresponds with snowmelt following winter snowpack accumulated after base flow conditions sampled in fall (October) 1995. Key for symbols and corresponding sample dates shown in Cu graph (inset). R2 value adjacent to regression line. Data from Church et al. (1997).

Figure 13.

Element loads (Kg/day) for total (dissolved + colloidal) Cu, Fe, Al, and Zn determined for base flow, low, medium, and high flow (ft3/s). Sample collection in spring (May—June) 1996 corresponds with snowmelt following winter snowpack accumulated after base flow conditions sampled in fall (October) 1995. Key for symbols and corresponding sample dates shown in Cu graph (inset). R2 value adjacent to regression line. Data from Church et al. (1997).

Fey et al. (2002) attempted to measure element concentrations and loads upon the first indication of the spring runoff. The year 2002 was a drought year, and therefore snowpack was less than during more normal precipitation years. In addition, the first spring runoff came early that year. Fey et al. were able to sample the rising limb of the hydrograph at the first increase in discharge at the A-72 gauge over a 4-day period. Results for increases in concentrations and loads were similar to those of the 1995–1996 samples, but of lower magnitude, owing to the low discharge and to only the earliest part of the rising limb being sampled.

Fey et al. (2002) also included toxicity tests using Animas River water collected at gauge A-72. The tests indicated little difference in toxicity between pre-snowmelt and early snowmelt periods. Toxicity tests conducted using fathead minnows showed a decrease in toxicity over time, with low toxicity observed during the late snowmelt period. These results provide little evidence to support the hypothesis that turbid water from the early snow-melt period has greater toxicity from typical low-flow winter conditions. However, greater metal loads for 1995–1996 samples (Fig. 13) that were determined over the entire spring runoff, and not just the initial snowmelt discharge as was the case in 2002, may have a higher toxicity.

Natural Events Impacting Water Quality

An example of a high-flow event occurred on 26 August 1997, when a thunderstorm stalled over the Ohio Gulch—Topeka Gulch area in the Cement Creek basin. These gulches both contain a large areal percentage of hydrothermally altered rock, with loose, unstable slopes, and large areas of sparse vegetation (Fig. 14). By late afternoon, a torrent of yellow-ochre water had made its way down to the town of Silverton and joined the Animas River. A sample of the water was taken from the footbridge in Memorial Park in Silverton, above the confluence with the upper Animas River south of town. The sample contained ~50 g/L suspended sediment. Based on historical discharge data for the stream gauge at the mouth of Cement Creek, we conservatively estimate that the discharge for that peak event was 200 ft3/s (5660 L/s).

Figure 14.

26 August 1997 storm event. (A) Easily erodible hydrothermally altered bedrock exposed in upper Topeka Gulch. Light-colored slopes consist of illite (clay) with disseminated pyrite; (B) San Juan County road crew clearing debris deposited on Cement Creek during storm event. Up to boulder-sized material deposited on Cement Creek Rd. (C) Confluence of turbid Cement Creek (left) and upper Animas River (right). High dissolved-sediment load in Cement Creek caused by erosion during storm event. (D) Debris flow material deposited during storm event and sampled on 28 August 1997. Light-colored debris flow deposit in channel is about 0.5 m (1.6 ft) thick. Greenish-gray rock (photo center) is competent, propylitically altered intermediate composition lava.

Figure 14.

26 August 1997 storm event. (A) Easily erodible hydrothermally altered bedrock exposed in upper Topeka Gulch. Light-colored slopes consist of illite (clay) with disseminated pyrite; (B) San Juan County road crew clearing debris deposited on Cement Creek during storm event. Up to boulder-sized material deposited on Cement Creek Rd. (C) Confluence of turbid Cement Creek (left) and upper Animas River (right). High dissolved-sediment load in Cement Creek caused by erosion during storm event. (D) Debris flow material deposited during storm event and sampled on 28 August 1997. Light-colored debris flow deposit in channel is about 0.5 m (1.6 ft) thick. Greenish-gray rock (photo center) is competent, propylitically altered intermediate composition lava.

The suspended sediment collected from Cement Creek at the Memorial Park bridge represents an integrated mixture of all solids transported into Cement Creek above Silverton. The metal constituents do not necessarily reflect only the material derived from Ohio and Topeka Gulches. The sediment mixture, however, is representative of material transported from these subwater-sheds, and sediment scoured from the Cement Creek streambed or eroded from overbank deposits. The lead concentration in the analyzed suspended sediment sample is high (862 ppm). For comparison, a sample collected from Memorial Park at low flow in 1995 contained 370 ppm lead and 1200 ppm zinc. It is possible that high lead concentrations could be due to suspended sediment having settled out as colloidal material on the streambed, and then being remobilized during the storm event.

Mine Waste as a Potential Contaminant Source

Tracer-dilution studies indicate that most of the contaminant loading originates from draining adits. However, another potential major source of contaminants is the numerous waste and tailings piles exposed to weathering. Sampling these waste piles and exposing them to weak leach tests can give an idea of which elements are present in high concentrations and are potentially mobile (EPA method 1312, U.S. Environmental Protection Agency, 1994; Hageman and Briggs, 2000; Hageman, 2007).

Hageman and Briggs (2000) developed a simple field leach test. This test uses a statistically representative sample of mine waste material that can be leached onsite. Leachate information that can be immediately collected includes field parameters such as pH and specific conductance. Filtered and acidified leachate can later be submitted for laboratory analysis of metal cations and anions. The advantage of the field leach test is that it can be done rapidly; while not directly comparable to more rigorous EPA method 1312 protocols, the results are similar (Hageman and Briggs, 2000).

In studies of acid mine drainage, Ficklin diagrams are used that depict NAP versus the sum of metals (zinc + copper + cadmium + cobalt + nickel + lead). The Ficklin diagram is useful for comparing compositions of different acid mine waters. Fey et al. (2000) developed an analogous plot to the Ficklin diagram to categorize mine waste by chemistry. The NAP of each sample material is determined by boiling (with sufficient hydrogen peroxide) to oxidize the pyrite and other acid-producing phases and to create a slurry. This slurry is then titrated with sodium hydroxide to determine its acid content. The NAP is subsequently plotted versus the sum of elements (Fig. 15). In the ARW, Fey et al. (2000) empirically divided the NAP into four groupings. Group 1 samples contain relatively low amounts of acidity (less than 10 kg/ton CaCO3 equivalent) and summed metals (less than 1000 μg/L). Group 2 samples also contain less than 10 kg/ton net acidity, but between 1000 and 5000 μg/L summed metals. Group 3 samples have relatively low acidity but between 10,000 and 40,000 μg/L summed metals. Group 4 samples have acidity between 10 and 167 kg/ton CaCO3 and summed metals up to 58,000 μg/L. The high metal sums are generally dominated by zinc, even at low NAP. Group 1 and Group 2 are fairly innocuous, and both Group 3 and Group 4 are problematic because they represent a source of soluble metals. Nash and Fey (2007) used this chemical ranking scheme and added an additional dump size component. The modified scheme permitted ranking of waste piles based on the potential risk that they posed to the environment. These data were useful for prioritizing mine waste sites for cleanup.

Figure 15.

Plot showing net acid production (NAP) versus sum of metals (As, Cd, Cu, Pb, Zn) for mine waste materials collected near Silverton, Colorado. Figure modified from Fey et al. (2000).

Figure 15.

Plot showing net acid production (NAP) versus sum of metals (As, Cd, Cu, Pb, Zn) for mine waste materials collected near Silverton, Colorado. Figure modified from Fey et al. (2000).

Geophysical Techniques

Critical questions about the subsurface can be addressed using ground-based and airborne geophysical methods. Table 6 shows geophysical techniques and their application to geoenvironmental issues related to mining. Ground and airborne geophysical studies provide data that can be used to interpret subsurface heterogeneities and predict the origin and flow of acidic groundwater (Smith et al., 2007). The electromagnetic geophysical survey shows a conductive arcuate feature that coincides with the Silverton caldera ring fracture (Yager and Stanton, 2000; Smith et al., 2007). The importance of veins, lineaments, and structures as pathways for conductive, metal-rich waters, along with the correlation with geophysical signatures, is discussed in McDougal et al. (2007).

Potential Uses of Geophysical Methods in Mine-Waste Characterization (Modified From Campbell and Fitterman, 2000)

Table 6.
Potential Uses of Geophysical Methods in Mine-Waste Characterization (Modified From Campbell and Fitterman, 2000)
MethodMeasuresCaused byMine-waste application
EM (Frequency-Domain Electromagnetics)Electrical conductivity (mS/m)Groundwater, lithologyTracing acid mine drainage plumes
DC (Direct-Current Resistivity)Electrical resistivity (Ohm-m)Groundwater, lithologyShallow (<10 m) water tables in, and bottoms of, shallow (<20 m) waste dumps
TEM (Time-Domain Electromagnetics)Electrical conductivity (mS/m)Groundwater, lithologyDeeper (10-30 m) water tables in waste dumps
CSAMT (Controlled Source Audio MagnetotelluricsElectrical resistivity (Ohm-m)Groundwater, lithologyDeeper (10-50 m) bottoms of waste dumps
IP (Induced Polarization)Electrical chargeability (usually mV-s/V)Electrochemical reactions at grain surfacesConcentrations of sulfides in waste dumps
SP (Spontaneous Polarization)Ground voltages (mV)Redox and streaming potentialsExperimental
GPR (Ground Penetrating Radar)Speed of electromagnetic radiation (cm/ns)Ground textures and included pore waterPossibly monitoring plume remediation
MagneticsMagnetic field (nT)MagnetizationFerrous material (e.g., rebar) in mine dumps (other mine-waste applications unproven)
SeismicAcoustic wave velocity (m/s)Compaction and groundwater contentTracing bottoms and edges of waste dumps, and basement under plume areas (all mine-waste applications are still in experimental stages)
MethodMeasuresCaused byMine-waste application
EM (Frequency-Domain Electromagnetics)Electrical conductivity (mS/m)Groundwater, lithologyTracing acid mine drainage plumes
DC (Direct-Current Resistivity)Electrical resistivity (Ohm-m)Groundwater, lithologyShallow (<10 m) water tables in, and bottoms of, shallow (<20 m) waste dumps
TEM (Time-Domain Electromagnetics)Electrical conductivity (mS/m)Groundwater, lithologyDeeper (10-30 m) water tables in waste dumps
CSAMT (Controlled Source Audio MagnetotelluricsElectrical resistivity (Ohm-m)Groundwater, lithologyDeeper (10-50 m) bottoms of waste dumps
IP (Induced Polarization)Electrical chargeability (usually mV-s/V)Electrochemical reactions at grain surfacesConcentrations of sulfides in waste dumps
SP (Spontaneous Polarization)Ground voltages (mV)Redox and streaming potentialsExperimental
GPR (Ground Penetrating Radar)Speed of electromagnetic radiation (cm/ns)Ground textures and included pore waterPossibly monitoring plume remediation
MagneticsMagnetic field (nT)MagnetizationFerrous material (e.g., rebar) in mine dumps (other mine-waste applications unproven)
SeismicAcoustic wave velocity (m/s)Compaction and groundwater contentTracing bottoms and edges of waste dumps, and basement under plume areas (all mine-waste applications are still in experimental stages)

Near-surface high conductivity anomalies associated with mine waste piles may indicate groundwater with high dissolved solids or a source of metal loading to the ground-water (Fig. 16). Other areas that are hydrothermally altered and mineralized can be a near-surface source for acidic and conductive groundwater in bedrock and in associated sur-ficial deposits. Electromagnetically conductive vein structures and faults may be evidence that these features have a high hydrologic conductivity. Where these structures intersect mine workings, they may be a source of groundwater inflow into a mine.

Figure 16.

Groundwater inflows determined by tracer injection studies along Mineral Creek (Kimball et al., 2007). Height of vertical lines are proportional to quantity of groundwater inflows ranging from 0.9 to 7 ft3/s. Bright colors (yellow-orange-red) correlate with increasing conductivity along the stream. White arrow points to low-conductivity groundwater inflow (left), and higher conductivity groundwater inflows (right). Iron concentrations (in micro-grams per liter) shown for corresponding surface water and groundwater inflows.

Figure 16.

Groundwater inflows determined by tracer injection studies along Mineral Creek (Kimball et al., 2007). Height of vertical lines are proportional to quantity of groundwater inflows ranging from 0.9 to 7 ft3/s. Bright colors (yellow-orange-red) correlate with increasing conductivity along the stream. White arrow points to low-conductivity groundwater inflow (left), and higher conductivity groundwater inflows (right). Iron concentrations (in micro-grams per liter) shown for corresponding surface water and groundwater inflows.

Self-potential geophysical techniques were used effectively to investigate subsurface conductivity of mine waste (Yager and Stanton, 2000). This type of analysis is useful for site prioritization when mine waste removal is an option and managing waste with variable metal concentrations is an issue. For example, the part of a waste pile containing high metal concentrations, if identified prior to removal, could be managed separately from part of a pile that did not have high metal concentrations.

New Technologies for Low-Cost, Automated, High-Resolution Environmental Sampling and Monitoring

Long-term, high-frequency monitoring of more easily measured water quality parameters such as streamflow, conductivity, and temperature clearly demonstrates that water chemistry changes can occur on time scales ranging from seconds to years. However, monitoring high-frequency hydrologic processes in remote locations can be very difficult and costly. The USGS has long been focused on developing new field deployed instruments that increase the temporal or spatial density of water quality information.

Currently available water conductivity sensors with data logging capability typically cost >US$1000. These instruments work well for high-resolution, extended deployments, but the high cost usually limits the number of conductivity sensors that can be deployed in a study area. The USGS has developed the STIC (Stream Temperature, Intermittency, and Conductivity logger), an easy-to-build instrument that provides high-resolution temperature and relative conductivity monitoring for the low cost of US$70 (Fig. 17). This low-cost instrument provides the opportunity for deploying a number of conductivity loggers for both spatial and temporal surveys or reconnaissance of water temperature and conductivity.

Figure 17.

Components of Stream Temperature, Intermittency, and Conductivity (STIC) logger. Comparison of $70 STIC with $850 conductivity logger.

Figure 17.

Components of Stream Temperature, Intermittency, and Conductivity (STIC) logger. Comparison of $70 STIC with $850 conductivity logger.

Water sampling for toxic metals in acid mine drainage studies typically involves hand collection of a grab sample, and results in the collection of a few water samples per yr at times when the site is more easily accessed (for example, summer). Hand-collected water samples for metal analysis are often preserved by onsite sample filtration with 0.45 mm filters and acidification to pH 2 (USGS, 2006). Advances in high-sensitivity analytical instruments such as ICP-MS now provide routine ppb or less detection of over 60 elements with only a few mL of sample. Our understanding of biogeochemical processes is greatly enhanced when analytes with differing reaction pathways are detected. For example, in acid mine drainage locations where pH may fluctuate between acidic and neutral conditions, the geochemical cycling and eco-toxicity of pH-sensitive metals (e.g., aluminum, lead, copper) may be completely different from less pH-sensitive metals (e.g., zinc, cadmium).

However, hand-collected sampling rarely captures the details of episodic events such as snow melt runoff and the effects of rainstorms, especially during inaccessible periods. Grab sampling can also be very labor intensive and expensive, with costs for salary, safety equipment, field vehicles and sampling equipment ranging from hundreds to several thousand US$ to collect a single sample. Many abandoned mine sites are particularly difficult to access (for example, underground or in snowbound high alpine areas), and documenting temporal changes in toxic mine water concentrations with traditional grab sampling is commonly very difficult, expensive, and rarely possible.

Automated water samplers (e.g., Teledyne-Isco, Sigma, Hach, Sirco, etc.) have been developed for urban storm water runoff sampling and work well within their design limitations. These auto-samplers are located out of water on the streambank and use a peristaltic pump to pull water from the stream to fill 24 1-L sample bottles. However, these auto-samplers are not well suited for remote or difficult-to-access field sites since these instruments are large, heavy, subject to vandalism, do not operate in freezing conditions, and require large batteries with solar panels for extended deployments. In addition, commercially available auto-samplers do not have the capability for sample filtration and acidification, and sample bottles are open to the atmosphere and allow gas exchange that could affect sample pH and metal solubilities or introduce airborne contamination to the collected samples.

In an effort to address some of the limitations of currently available automated water sampling technologies, the USGS developed a new small volume water sampler, the MiniSipper, which is shown in Figure 18 (Chapin and Todd, 2012; Chapin, 2015). The MiniSipper is a low-cost, submersible water sampler that automatically collects up to 250 acidified and filtered 5 mL samples during deployments lasting up to 12 months and can operate in freezing conditions. The high sample capacity and long deployment duration of the MiniSipper greatly reduce fieldwork costs, especially in areas that are difficult or dangerous to access or are snowbound for many months of the year. MiniSippers have been used for high-resolution sampling for underground tracers, 24 h (diel) metal cycling studies, and automated daily water sampling over the course of a yr to capture the details of snowmelt runoff and summer storm events (Fig. 19).

Figure 18.

Components of the MiniSipper automated water sampler.

Figure 18.

Components of the MiniSipper automated water sampler.

Figure 19.

MiniSipper Zn concentrations (n = 90), conductivity, flow, and Zn-grab samples during snowmelt runoff (April to July 2013) in the Animas River near Silverton.

Figure 19.

MiniSipper Zn concentrations (n = 90), conductivity, flow, and Zn-grab samples during snowmelt runoff (April to July 2013) in the Animas River near Silverton.

Data Mining of Legacy Databases (Historical Data to Address Current Issues)

An extensive relational database was completed as part of AML studies in Silverton, Colorado. Figure 20 shows the relational database tables and attributes that store data acquired during Animas AML investigations. The database has a wealth of historical background and baseline information, and stores 144,522 entries that include quantitative, qualitative, and descriptive measurements from 69 distinct media types and amassed from 2389 sites. Results in the database record information on 1898 water, 1885 earth material (sediment, rock, and mine waste), and 190 biotic material (fish tissue, invertebrate tissue, vegetation, and biofilm) samples (Sole et al., 2007).

Figure 20.

USGS Animas Abandoned Mine Lands study relational database schema. Relational database design described in Sole et al. (2007). Parameter code database fields highlighted in “Parameter table” allow database selection of specific geochemical parameters (e.g., zinc, filtered water from seeps and springs). An extensive list of water quality parameters is stored in the database. Element concentration values are stored in the “Result” table. “Sample” and “Site” tables provide additional information recorded at each sample site. Common table relationship fields permit information between different tables to be selected and retrieved using database queries.

Figure 20.

USGS Animas Abandoned Mine Lands study relational database schema. Relational database design described in Sole et al. (2007). Parameter code database fields highlighted in “Parameter table” allow database selection of specific geochemical parameters (e.g., zinc, filtered water from seeps and springs). An extensive list of water quality parameters is stored in the database. Element concentration values are stored in the “Result” table. “Sample” and “Site” tables provide additional information recorded at each sample site. Common table relationship fields permit information between different tables to be selected and retrieved using database queries.

Examples of the types of information that can be retrieved using Animas AML database queries are shown in Figures 2123. The database is a powerful tool and the examples shown are relevant to addressing questions that are often asked in watersheds impacted by mining. These questions include: (1) What are the pre-mining geochemical signatures of groundwater sourced in bedrock that is hydrothermally altered? (2) How many draining adits are present and what is the water quality at these sites? And (3) what is the geochemical baseline of streambed geochemistry and can subsequent sampling identify mine-related or storm events that are recorded in streambed geochemistry? New ways of thinking about a watershed can develop when interacting with the database, analyzing results in a geographical information system (GIS), and interpreting the spatial relationships of data displayed in a geologic context. In each of the following examples, results from database queries were loaded into a GIS for analysis and display.

Figure 21.

Zinc in non-mining-affected seeps and springs; site category “1” stored in database (Sole et al., 2007). Symbol size is proportional to Zn concentrations.

Figure 21.

Zinc in non-mining-affected seeps and springs; site category “1” stored in database (Sole et al., 2007). Symbol size is proportional to Zn concentrations.

Figure 22.

(A) Draining mine sites (solid yellow dots) sampled as part of a mine inventory completed by Church et al. (2007b). (B) GIS selection query of data in A with mine water sites (large red dots) having: pH < 3; specific conductance > 1000 μS/cm; and Cu, Pb, and Zn > 100 μg/liter. Data source: Sole et al. (2007). Base map imagery is from ESRI Inc., ArcGlobe accessed on 16 April 2016.

Figure 22.

(A) Draining mine sites (solid yellow dots) sampled as part of a mine inventory completed by Church et al. (2007b). (B) GIS selection query of data in A with mine water sites (large red dots) having: pH < 3; specific conductance > 1000 μS/cm; and Cu, Pb, and Zn > 100 μg/liter. Data source: Sole et al. (2007). Base map imagery is from ESRI Inc., ArcGlobe accessed on 16 April 2016.

Figure 23.

(A) Arsenic in streambed sediments. Sampling methods described in Church et al. (2007a). (B) Zinc in streambed sediments. Symbol size proportional to concentration. Natural break used to select data concentration range groups. Data source: Sole et al., (2007). Base map imagery is from ESRI Inc., ArcGlobe accessed on 16 April 2016.

Figure 23.

(A) Arsenic in streambed sediments. Sampling methods described in Church et al. (2007a). (B) Zinc in streambed sediments. Symbol size proportional to concentration. Natural break used to select data concentration range groups. Data source: Sole et al., (2007). Base map imagery is from ESRI Inc., ArcGlobe accessed on 16 April 2016.

Water quality of seeps and springs represents water-rock interactions that have occurred along a groundwater flow path. A database site attribute “site category number” was assigned to seep and spring samples with a “1” being nonmine impacted and those assigned a “4” likely being mine impacted. This information highlights where local geology irrespective of mining can control water quality (Fig. 21). Results from another database query display draining adit samples dispersed throughout the Silverton area (Fig. 22A). There are over 300 draining mine adit geochemical analyses in the Animas AML database. GIS query of adit water sites reveals where samples are acidic with high specific conductance and have base metal concentrations (copper, lead, zinc) that exceed 100 μg/L (Fig. 22B).

The relational database also stores streambed sediment geochemistry (Church et al., 2007a). The database can be used to determine where selected contaminants may be dispersed by fluvial processes. The example shown in Figures 23A and 23B are for arsenic and zinc, respectively. Arsenic concentrations are also high along the upper Animas River and may be attributed to milling operations at Eureka (Fig. 23A). Relatively high zinc concentrations are observed in the upper Animas River downstream from the base metal rich (copper-lead-zinc) Sunnyside vein system (Fig. 23B).

Day 4: Silverton to Eureka Gulch, Lake Emma

The trip route will traverse the structural margin of the Silverton caldera. The road will roughly follow the arcuate drainage pattern of the upper Animas River east of Silverton. Rocks to the north of the upper Animas River are largely propylitically altered Burns Member lavas. The Silverton mining area southeast of Silverton is mainly composed of propylitically altered lavas cut by narrow, southeast-trending mineralized veins. Alteration along these veins is not pervasive as is the case in parts of Cement Creek. While not pristine, water quality is near neutral pH and does supply some alkalinity. Some subwatersheds southeast of Silverton support brook trout.

Set odometer to 0.

Cum. distance 
km (mi) Time Directions 
  0730 Depart from Silverton for Eureka Gulch. Right (east) intersection of Greene St. and East 14th St. 
0.32 (0.2)  Right (east) on CO-2. 
1.42 (0.88) 0740 Arrive at Mayflower mill tailings. 
  0800 Depart from Mayflower mill tailings. 
3.70 (2.30)  Mayflower mill on left (37.828172°N, 107.627544°W). 
Cum. distance 
km (mi) Time Directions 
  0730 Depart from Silverton for Eureka Gulch. Right (east) intersection of Greene St. and East 14th St. 
0.32 (0.2)  Right (east) on CO-2. 
1.42 (0.88) 0740 Arrive at Mayflower mill tailings. 
  0800 Depart from Mayflower mill tailings. 
3.70 (2.30)  Mayflower mill on left (37.828172°N, 107.627544°W). 

Stop 1: Mayflower Mill Tailings

The construction of mill tailings impoundments during the mid-1930s is discussed in the “Silverton Mining History” section. The Mayflower mill tailings impoundments are the largest in the watershed and were established in the 1930s. Their construction was initially designed to prevent direct discharge of tailings into the Animas River. These tailings store waste material from milling operations between the mid-1930s and 1991. The Mayflower mill operated until the Sunnyside mine closed in 1991.

Cum. distance
km(mi)TimeDirections
12.54(7.79)0845Arrive Eureka at town site and Sunnyside Eureka mill (37.880504°N, 107.566919°W).
Cum. distance
km(mi)TimeDirections
12.54(7.79)0845Arrive Eureka at town site and Sunnyside Eureka mill (37.880504°N, 107.566919°W).

Stop 2: Sunnyside Eureka Mill and Eureka Town Site

The historical Sunnyside Eureka mill and Eureka town site is located at an important area in the watershed. The upper Animas River below Eureka becomes a multi-channel braided stream reach. Mill tailings produced here and upslope in other historical mills were deposited in the floodplain where there is a change from high to low gradient, where the river flows out of the canyons above Eureka to the flat-floored braided reach of the upper Animas River valley floor.

From Eureka town site, the trip route traverses Burns Member lavas and structures that define the northeast-trending Eureka graben. The southeast and northwest part of the graben are bounded by the Toltec and Sunnyside faults, respectively. Massive silicification along the faults marks the trend of the extensive veins that can be traced for hundreds of meters along strike.

Cum. distance
km(mi)TimeDirections
0915Depart from Eureka town site and Sunnyside Eureka mill.
17.32(10.76)0945Cross Eureka graben, Toltec fault (37.893480°N, 107.603383°W).
19.18(11.92)1010Arrive at Lake Emma (37.902573°N, 107.614381°W).
Cum. distance
km(mi)TimeDirections
0915Depart from Eureka town site and Sunnyside Eureka mill.
17.32(10.76)0945Cross Eureka graben, Toltec fault (37.893480°N, 107.603383°W).
19.18(11.92)1010Arrive at Lake Emma (37.902573°N, 107.614381°W).

Stop 3: Former Lake Emma

This is the site of the original discovery of the Sunnyside mine. Gold was discovered along the massive, manganese-stained Sunnyside vein exposed to the west of Lake Emma. The vein systems below this area were mined for base metals (copper, lead, and zinc) as well as gold and silver from ~1900–1991 when the Sunnyside mine closed operations. The American Tunnel portal located at Gladstone is 524 m (1719 ft) below this site. The American Tunnel served as an ore access, haulage tunnel, and drain for the Sunnyside mine workings. Water draining from the mineral deposits associated with the Sunnyside mine has a characteristic signature due to the base metals and gangue minerals associated with the deposit. The Sunnyside vein system has abundant sphalerite. This system also contains manganese (carbonates and silicates) as well as fluorite. Waters draining this area tends to contain high fluoride and manganese.

Cum. distance
km(mi)TimeDirections
1045Depart from Lake Emma.
38.32(23.84) 1130Stop at Memorial Park, Silverton (lunch).
558(347)1215Depart from Silverton for Denver to return to the Colorado Convention Center.
Cum. distance
km(mi)TimeDirections
1045Depart from Lake Emma.
38.32(23.84) 1130Stop at Memorial Park, Silverton (lunch).
558(347)1215Depart from Silverton for Denver to return to the Colorado Convention Center.

Discussion and Conclusions

Communities impacted by historical mining such as those visited in the San Juan Mountains on this trip offer insights into the long-term environmental cleanup issues that must be addressed after mining ceases. In order to understand how contaminants are transported from source rocks, sediments, and mining features, it is necessary to employ a holistic analytical approach. A holistic approach involves collaborative efforts by scientists with expertise in geology, geochemistry, hydrology, remote sensing, biology, and geophysics. The multiple tools discussed in this field guide demonstrate the multidisciplinary skills that are required to fully understand watersheds impacted by mining.

The Gold King mine event on 5 August 2015 is also a reminder of the need to consider the entire life cycle of new mining from initial discovery to mine closure. Prior to mining, it is essential to have a thorough understanding of the geologic and structural setting, mineral deposit and alteration types, and hydrologic conditions. The mineralogy of deposits in new mining areas will ultimately be a major factor in controlling water quality. Knowledge of the historical developments in mining and milling operations will be useful for determining where mining already impacts water quality. Analysis of historical mine maps and records could aid in determining where mines may be connected, and where new workings may encroach on existing mines. An understanding of the geochemical background attributed to weathering of mineralized and altered rocks, sediments, and soils can be used to determine what cleanup standards are achievable. Remediation activities may not be able to achieve lower element concentration than existed prior to mining. Baseline water quality conditions determined prior to mining could also be used to monitor changes during mining and after mining ceases.

The communities visited on this trip provide excellent opportunities to bring to light the many aspects of geographic setting, geology, hydrology, and mining that converge to impact the environment. Current and future scientists, land managers, and the public can benefit from revisiting what has been learned in these areas in the past and what is needed in the future to better address the geoenvironmental issues associated with mining.

Acknowledgments

The authors wish to thank the Willow Creek Reclamation Committee and Animas River Stakeholders Group for participating in this trip and sharing their knowledge. Presentations by Jan Jacobs (Creede Historical Society), Beverly Rich (San Juan County Historical Society), and geologist Scott Fetchenhier are greatly appreciated. We thank geologist Randy McClure for sharing his insights on the Creede mining district. We are grateful to Rob Runkel and Katie Walton-Day (USGS) for participating in this trip and for discussing their and colleagues’ extensive water quality investigations. Field assistance in Creede by Rebecca Browning is also greatly appreciated. Reviews by Karen D. Kelley and Matt Granitto of the USGS and reviews by the Geological Society of America guidebook editors greatly improved this report.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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Proceedings from the Fifth International Conference on Acid Rock Drainage (ICARD2000)
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, May 21–24, 2000: Littleton, Colorado, Society for Mining, Metallurgy and Exploration, Inc., v.
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301
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Yager
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D.B.
Church
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S.E.
Verplanck
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P.L.
Wirt
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L.
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, Ferricrete, Manganocrete, and Bog Iron Occurrences with Selected Sedge Bogs and Active Iron Bogs and Springs in the Upper Animas River Watershed, San Juan County,
Colorado
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Field Studies Map MF-2406, scale 1:24, 000.
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L.
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, Net Acid Production, Acid Neutralizing Capacity, and Associated Mineralogical and Geochemical Characteristics of Animas River Watershed Igneous Rocks near Silverton,
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D.B.
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, Using a geographic information system (GIS) to determine the physical factors that affect water quality in the western San Juan Mountains, Silverton, Colorado, Chapter M: in
Verplanck
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, ed., Understanding Contaminants Associated with Mineral Deposits: U.S. Geological Survey Circular 1328, p.
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83
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Morgan
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Figures & Tables

Figure 1.

Photos taken on 5 August 2015 after Gold King mine water release. (A) View south below Silverton, Colorado, of Cement Creek (river right) and upper Animas River confluence (7:00 p.m.). Kendall Mountain Rd. in distance (upper right); stop 3, Day 3. (B) View east toward North Fork Cement Creek (6:27 p.m.). Debris fan formed during the Gold King mine water release. Photos courtesy of Ken Balleweg.

Figure 1.

Photos taken on 5 August 2015 after Gold King mine water release. (A) View south below Silverton, Colorado, of Cement Creek (river right) and upper Animas River confluence (7:00 p.m.). Kendall Mountain Rd. in distance (upper right); stop 3, Day 3. (B) View east toward North Fork Cement Creek (6:27 p.m.). Debris fan formed during the Gold King mine water release. Photos courtesy of Ken Balleweg.

Figure 2.

(A) Index map showing field-trip area in southwest Colorado (green box). Animas River watershed (ARW) shown in mint green, major rivers (italics) are shown in blue. (B) Enlargement of green box in A showing major roads and counties (tan); days of trip corresponding to road log shown adjacent to each city (1–4). See Figures 3, 4, and 5 for detailed trip route.

Figure 2.

(A) Index map showing field-trip area in southwest Colorado (green box). Animas River watershed (ARW) shown in mint green, major rivers (italics) are shown in blue. (B) Enlargement of green box in A showing major roads and counties (tan); days of trip corresponding to road log shown adjacent to each city (1–4). See Figures 3, 4, and 5 for detailed trip route.

Figure 3.

Numbered stops for Day 1 (Creede area) correspond to field-trip log in this guide. Field-trip route (solid black line); faults and veins (solid yellow-orange lines). County source of faults and veins is from Steven and Ratté (1965). BVS—Bull Dog Mountain vein system; AV— Amethyst vein; SHV—Solomon—Holy Moses vein system. Solid red line is road CO-149. Terrain hill-shaded relief map from ArcGIS online.

Figure 3.

Numbered stops for Day 1 (Creede area) correspond to field-trip log in this guide. Field-trip route (solid black line); faults and veins (solid yellow-orange lines). County source of faults and veins is from Steven and Ratté (1965). BVS—Bull Dog Mountain vein system; AV— Amethyst vein; SHV—Solomon—Holy Moses vein system. Solid red line is road CO-149. Terrain hill-shaded relief map from ArcGIS online.

Figure 4.

Field-trip route for Silverton area. Gold King mine #1 and #7 refer to mine adit levels. Numbered stops for Days 3 and 4 correspond to field-trip log in this guide. Terrain hill-shaded relief map from ArcGIS online. Streams (in blue) and mine site locations are from Sole et al. (2007).

Figure 4.

Field-trip route for Silverton area. Gold King mine #1 and #7 refer to mine adit levels. Numbered stops for Days 3 and 4 correspond to field-trip log in this guide. Terrain hill-shaded relief map from ArcGIS online. Streams (in blue) and mine site locations are from Sole et al. (2007).

Figure 5.

Field-trip route for Durango area. Numbered stops for Day 2 correspond to field-trip log in this guide. Animas River (blue); major roads U.S.-160 and S. Camino del Rio (labeled).

Figure 5.

Field-trip route for Durango area. Numbered stops for Day 2 correspond to field-trip log in this guide. Animas River (blue); major roads U.S.-160 and S. Camino del Rio (labeled).

Figure 6.

Conceptual model of diffuse and point sources of metals to surface and groundwater. Alteration assemblages from Bove et al. (2007a) draped on 3D terrain for area of upper Cement Creek. Alteration types: p—propylitic; qsp—quartz-sericite-pyrite; vqsp—vein-quartz-sericite-pyrite; arg—argillic; as—acid-sulfate; and sil—silicic. Alteration is a large and diffuse source of metals and acidity. Lower right of model shows the types of geologic and mining-related features that affect surface water (not to scale). Other diffuse sources of contaminants are mine waste and fluvial mill tailings; large point sources of contaminants are from mine adit discharge.

Figure 6.

Conceptual model of diffuse and point sources of metals to surface and groundwater. Alteration assemblages from Bove et al. (2007a) draped on 3D terrain for area of upper Cement Creek. Alteration types: p—propylitic; qsp—quartz-sericite-pyrite; vqsp—vein-quartz-sericite-pyrite; arg—argillic; as—acid-sulfate; and sil—silicic. Alteration is a large and diffuse source of metals and acidity. Lower right of model shows the types of geologic and mining-related features that affect surface water (not to scale). Other diffuse sources of contaminants are mine waste and fluvial mill tailings; large point sources of contaminants are from mine adit discharge.

Figure 7.

Generalized, regional geologic map showing area of the San Juan volcanic field in Colorado. Figure modified from Casadevall and Ohmoto (1977) and Lipman and Bachmann (2015).

Figure 7.

Generalized, regional geologic map showing area of the San Juan volcanic field in Colorado. Figure modified from Casadevall and Ohmoto (1977) and Lipman and Bachmann (2015).

Figure 8.

(A) Faults and veins within the resurgent core of the Bachelor caldera, B; non-mineralized faults in the resurgent core of the Creede caldera, C. (B) Faults and veins of the Bachelor caldera (area shown indicated by white box in A. BVS—Bull Dog Mountain vein system; AV—Amethyst vein; SHV—Solomon—Holy Moses Vein system; NT—Nelson Tunnel. Trip route (Fig. 3) is focused in area north of Creede. Source of faults and veins is from Steven and Ratté (1965). Base maps are from Google Earth.

Figure 8.

(A) Faults and veins within the resurgent core of the Bachelor caldera, B; non-mineralized faults in the resurgent core of the Creede caldera, C. (B) Faults and veins of the Bachelor caldera (area shown indicated by white box in A. BVS—Bull Dog Mountain vein system; AV—Amethyst vein; SHV—Solomon—Holy Moses Vein system; NT—Nelson Tunnel. Trip route (Fig. 3) is focused in area north of Creede. Source of faults and veins is from Steven and Ratté (1965). Base maps are from Google Earth.

Figure 9.

(A) Humphreys mill and Commodore mine in distance in West Willow Creek (~1903). (B) Emperius mill and trestle in Creede along Willow Creek (~1936). Photos courtesy of Creede Historical Society; used with permission.

Figure 9.

(A) Humphreys mill and Commodore mine in distance in West Willow Creek (~1903). (B) Emperius mill and trestle in Creede along Willow Creek (~1936). Photos courtesy of Creede Historical Society; used with permission.

Figure 10.

Major Silverton caldera vein structures from Yager and Bove (2007a) and geographic features discussed in text. Abbreviations for vein structures: B—Bonita; RB—Ross basin; S—Sunnyside; SV—Silverton caldera structural margin; T—Toltec. Other abbreviations: RM—Red Mountain mining area; SSM—South Silverton mining area;

Figure 10.

Major Silverton caldera vein structures from Yager and Bove (2007a) and geographic features discussed in text. Abbreviations for vein structures: B—Bonita; RB—Ross basin; S—Sunnyside; SV—Silverton caldera structural margin; T—Toltec. Other abbreviations: RM—Red Mountain mining area; SSM—South Silverton mining area;

Figure 11.

Generalized alteration map of the upper Animas River watershed after Bove et al. (2007). Abbreviations for alteration types are: P—propylitic; wsp—weak sericite pyrite; qsp—quartz-sericite-pyrite; vqsp—vein quartz-sericite-pyrite; arg—argillic; and as—acid sulfate. Base map from Arc Globe, 2016.

Figure 11.

Generalized alteration map of the upper Animas River watershed after Bove et al. (2007). Abbreviations for alteration types are: P—propylitic; wsp—weak sericite pyrite; qsp—quartz-sericite-pyrite; vqsp—vein quartz-sericite-pyrite; arg—argillic; and as—acid sulfate. Base map from Arc Globe, 2016.

Figure 12.

(A) View south of Cement Creek pre-mining alluvial terrace. Dendrochronology of pine tree (top left) indicates it has grown since 1858 (Fey et al., 2000; figure 3 in Blair et al., 2002). Geochemical profiles represent complete sample collection (bottom to top) of terrace. Compared with average crustal abundances in Fortescue (1992), all element concentrations exceed crustal abundance values as follows: Fe 1.5 Xs; Pb 8 Xs; Zn 1.5 Xs; Cu 1.5 Xs, As > 15 Xs. Ag and Cd abundances are too low to show at this scale. (B) Fluvial tailings (bedded, gray and brown layers; sledge hammer for scale) from a tailings impoundment below Sunnyside mill at Eureka during flotation milling era (1918–1930) (Fey et al., 2000; figure 6 in Blair et al., 2002). Element concentrations exceed crustal abundance values as follows: Fe to 1.5 Xs; Pb, Zn, Cu, As, Ag, and Cd all > 16 Xs. Elevated base metals (Cu, Pb, Zn) are characteristic of Sunnyside mine, epithermal polymetallic base metals processed at the Sunnyside Eureka mill.

Figure 12.

(A) View south of Cement Creek pre-mining alluvial terrace. Dendrochronology of pine tree (top left) indicates it has grown since 1858 (Fey et al., 2000; figure 3 in Blair et al., 2002). Geochemical profiles represent complete sample collection (bottom to top) of terrace. Compared with average crustal abundances in Fortescue (1992), all element concentrations exceed crustal abundance values as follows: Fe 1.5 Xs; Pb 8 Xs; Zn 1.5 Xs; Cu 1.5 Xs, As > 15 Xs. Ag and Cd abundances are too low to show at this scale. (B) Fluvial tailings (bedded, gray and brown layers; sledge hammer for scale) from a tailings impoundment below Sunnyside mill at Eureka during flotation milling era (1918–1930) (Fey et al., 2000; figure 6 in Blair et al., 2002). Element concentrations exceed crustal abundance values as follows: Fe to 1.5 Xs; Pb, Zn, Cu, As, Ag, and Cd all > 16 Xs. Elevated base metals (Cu, Pb, Zn) are characteristic of Sunnyside mine, epithermal polymetallic base metals processed at the Sunnyside Eureka mill.

Figure 13.

Element loads (Kg/day) for total (dissolved + colloidal) Cu, Fe, Al, and Zn determined for base flow, low, medium, and high flow (ft3/s). Sample collection in spring (May—June) 1996 corresponds with snowmelt following winter snowpack accumulated after base flow conditions sampled in fall (October) 1995. Key for symbols and corresponding sample dates shown in Cu graph (inset). R2 value adjacent to regression line. Data from Church et al. (1997).

Figure 13.

Element loads (Kg/day) for total (dissolved + colloidal) Cu, Fe, Al, and Zn determined for base flow, low, medium, and high flow (ft3/s). Sample collection in spring (May—June) 1996 corresponds with snowmelt following winter snowpack accumulated after base flow conditions sampled in fall (October) 1995. Key for symbols and corresponding sample dates shown in Cu graph (inset). R2 value adjacent to regression line. Data from Church et al. (1997).

Figure 14.

26 August 1997 storm event. (A) Easily erodible hydrothermally altered bedrock exposed in upper Topeka Gulch. Light-colored slopes consist of illite (clay) with disseminated pyrite; (B) San Juan County road crew clearing debris deposited on Cement Creek during storm event. Up to boulder-sized material deposited on Cement Creek Rd. (C) Confluence of turbid Cement Creek (left) and upper Animas River (right). High dissolved-sediment load in Cement Creek caused by erosion during storm event. (D) Debris flow material deposited during storm event and sampled on 28 August 1997. Light-colored debris flow deposit in channel is about 0.5 m (1.6 ft) thick. Greenish-gray rock (photo center) is competent, propylitically altered intermediate composition lava.

Figure 14.

26 August 1997 storm event. (A) Easily erodible hydrothermally altered bedrock exposed in upper Topeka Gulch. Light-colored slopes consist of illite (clay) with disseminated pyrite; (B) San Juan County road crew clearing debris deposited on Cement Creek during storm event. Up to boulder-sized material deposited on Cement Creek Rd. (C) Confluence of turbid Cement Creek (left) and upper Animas River (right). High dissolved-sediment load in Cement Creek caused by erosion during storm event. (D) Debris flow material deposited during storm event and sampled on 28 August 1997. Light-colored debris flow deposit in channel is about 0.5 m (1.6 ft) thick. Greenish-gray rock (photo center) is competent, propylitically altered intermediate composition lava.

Figure 15.

Plot showing net acid production (NAP) versus sum of metals (As, Cd, Cu, Pb, Zn) for mine waste materials collected near Silverton, Colorado. Figure modified from Fey et al. (2000).

Figure 15.

Plot showing net acid production (NAP) versus sum of metals (As, Cd, Cu, Pb, Zn) for mine waste materials collected near Silverton, Colorado. Figure modified from Fey et al. (2000).

Figure 16.

Groundwater inflows determined by tracer injection studies along Mineral Creek (Kimball et al., 2007). Height of vertical lines are proportional to quantity of groundwater inflows ranging from 0.9 to 7 ft3/s. Bright colors (yellow-orange-red) correlate with increasing conductivity along the stream. White arrow points to low-conductivity groundwater inflow (left), and higher conductivity groundwater inflows (right). Iron concentrations (in micro-grams per liter) shown for corresponding surface water and groundwater inflows.

Figure 16.

Groundwater inflows determined by tracer injection studies along Mineral Creek (Kimball et al., 2007). Height of vertical lines are proportional to quantity of groundwater inflows ranging from 0.9 to 7 ft3/s. Bright colors (yellow-orange-red) correlate with increasing conductivity along the stream. White arrow points to low-conductivity groundwater inflow (left), and higher conductivity groundwater inflows (right). Iron concentrations (in micro-grams per liter) shown for corresponding surface water and groundwater inflows.

Figure 17.

Components of Stream Temperature, Intermittency, and Conductivity (STIC) logger. Comparison of $70 STIC with $850 conductivity logger.

Figure 17.

Components of Stream Temperature, Intermittency, and Conductivity (STIC) logger. Comparison of $70 STIC with $850 conductivity logger.

Figure 18.

Components of the MiniSipper automated water sampler.

Figure 18.

Components of the MiniSipper automated water sampler.

Figure 19.

MiniSipper Zn concentrations (n = 90), conductivity, flow, and Zn-grab samples during snowmelt runoff (April to July 2013) in the Animas River near Silverton.

Figure 19.

MiniSipper Zn concentrations (n = 90), conductivity, flow, and Zn-grab samples during snowmelt runoff (April to July 2013) in the Animas River near Silverton.

Figure 20.

USGS Animas Abandoned Mine Lands study relational database schema. Relational database design described in Sole et al. (2007). Parameter code database fields highlighted in “Parameter table” allow database selection of specific geochemical parameters (e.g., zinc, filtered water from seeps and springs). An extensive list of water quality parameters is stored in the database. Element concentration values are stored in the “Result” table. “Sample” and “Site” tables provide additional information recorded at each sample site. Common table relationship fields permit information between different tables to be selected and retrieved using database queries.

Figure 20.

USGS Animas Abandoned Mine Lands study relational database schema. Relational database design described in Sole et al. (2007). Parameter code database fields highlighted in “Parameter table” allow database selection of specific geochemical parameters (e.g., zinc, filtered water from seeps and springs). An extensive list of water quality parameters is stored in the database. Element concentration values are stored in the “Result” table. “Sample” and “Site” tables provide additional information recorded at each sample site. Common table relationship fields permit information between different tables to be selected and retrieved using database queries.

Figure 21.

Zinc in non-mining-affected seeps and springs; site category “1” stored in database (Sole et al., 2007). Symbol size is proportional to Zn concentrations.

Figure 21.

Zinc in non-mining-affected seeps and springs; site category “1” stored in database (Sole et al., 2007). Symbol size is proportional to Zn concentrations.

Figure 22.

(A) Draining mine sites (solid yellow dots) sampled as part of a mine inventory completed by Church et al. (2007b). (B) GIS selection query of data in A with mine water sites (large red dots) having: pH < 3; specific conductance > 1000 μS/cm; and Cu, Pb, and Zn > 100 μg/liter. Data source: Sole et al. (2007). Base map imagery is from ESRI Inc., ArcGlobe accessed on 16 April 2016.

Figure 22.

(A) Draining mine sites (solid yellow dots) sampled as part of a mine inventory completed by Church et al. (2007b). (B) GIS selection query of data in A with mine water sites (large red dots) having: pH < 3; specific conductance > 1000 μS/cm; and Cu, Pb, and Zn > 100 μg/liter. Data source: Sole et al. (2007). Base map imagery is from ESRI Inc., ArcGlobe accessed on 16 April 2016.

Figure 23.

(A) Arsenic in streambed sediments. Sampling methods described in Church et al. (2007a). (B) Zinc in streambed sediments. Symbol size proportional to concentration. Natural break used to select data concentration range groups. Data source: Sole et al., (2007). Base map imagery is from ESRI Inc., ArcGlobe accessed on 16 April 2016.

Figure 23.

(A) Arsenic in streambed sediments. Sampling methods described in Church et al. (2007a). (B) Zinc in streambed sediments. Symbol size proportional to concentration. Natural break used to select data concentration range groups. Data source: Sole et al., (2007). Base map imagery is from ESRI Inc., ArcGlobe accessed on 16 April 2016.

Cum. distance
km(mi)TimeDirections
0(0)0700Depart from Colorado Convention Center
(700 14th St., Denver, CO 80202) southeast
on 14th St. to California St.
Right (southwest) to Glenarm St.
Right (west) to W. Colfax Ave.
Right exit ramp to I-25 south.
Right exit 209B, west to U.S.-6.
Right exit to I-70 west.
Right exit 260 to CO-470 east.
25.58(15.9)Right exit U.S.-285 south.
186.52(115)0915Right (north) exit to County Rd. 304 to rest area. Arrive at Buena Vista, Arkansas Valley overlook (38.817001°N, 106.086559°W).
Cum. distance
km(mi)TimeDirections
0(0)0700Depart from Colorado Convention Center
(700 14th St., Denver, CO 80202) southeast
on 14th St. to California St.
Right (southwest) to Glenarm St.
Right (west) to W. Colfax Ave.
Right exit ramp to I-25 south.
Right exit 209B, west to U.S.-6.
Right exit to I-70 west.
Right exit 260 to CO-470 east.
25.58(15.9)Right exit U.S.-285 south.
186.52(115)0915Right (north) exit to County Rd. 304 to rest area. Arrive at Buena Vista, Arkansas Valley overlook (38.817001°N, 106.086559°W).
Cum. distance
km(mi)TimeDirections
0945Depart from Buena Vista, Arkansas Valley overlook (lunch in route), from County Rd. 304, west on U.S.-285 (1.8 mi).
189.74(117.9Right (south) at intersection of U.S.-24 W and U.S.-285 south.
196.34(122)Ruby Mountain 28 Ma Topaz rhyolite, Nathrop (38.74980°N, 106.06988°W).
236.57(147)Poncha Pass Summit (38.4222°N, 106.08694°W) divide between Arkansas River Valley (north) and San Luis Valley (south), northern part of the Rio Grande rift.
329.92(205)Right (west) to CO-112 west(Center, Colorado).
350.84(218)
376.58(234)Right (west) on CO-160 to CO-149 N.
Right (west) on CO-149.
410.38(255)1230Arrive at Creede.
Reset odometer to 0.
0(0)1245Junction of 7th St. and CO-149 in Creede.West on 7th St. to Loma St.
0.64(0.4)Right on County Rd. 504 (Bachelor Rd.).
3.22(2.0)Right on Bachelor Mine Rd.
4.02(2.5)Stop 2 (Bachelor mine overlook).
Cum. distance
km(mi)TimeDirections
0945Depart from Buena Vista, Arkansas Valley overlook (lunch in route), from County Rd. 304, west on U.S.-285 (1.8 mi).
189.74(117.9Right (south) at intersection of U.S.-24 W and U.S.-285 south.
196.34(122)Ruby Mountain 28 Ma Topaz rhyolite, Nathrop (38.74980°N, 106.06988°W).
236.57(147)Poncha Pass Summit (38.4222°N, 106.08694°W) divide between Arkansas River Valley (north) and San Luis Valley (south), northern part of the Rio Grande rift.
329.92(205)Right (west) to CO-112 west(Center, Colorado).
350.84(218)
376.58(234)Right (west) on CO-160 to CO-149 N.
Right (west) on CO-149.
410.38(255)1230Arrive at Creede.
Reset odometer to 0.
0(0)1245Junction of 7th St. and CO-149 in Creede.West on 7th St. to Loma St.
0.64(0.4)Right on County Rd. 504 (Bachelor Rd.).
3.22(2.0)Right on Bachelor Mine Rd.
4.02(2.5)Stop 2 (Bachelor mine overlook).
Cum. distance
km(mi)TimeDirections
1300Depart Bachelor mine. West on Bachelor Mine Rd. Left (south) on County Rd. 504 (Bachelor Rd.).
5.6(3.5)Left (north) on CO-149. Immediate left (north) on Loma St.
6.44(4.0)Creede Community Center and Mining Museum.
6.84(4.25)1315Arrive at Humphreys Mill.
Cum. distance
km(mi)TimeDirections
1300Depart Bachelor mine. West on Bachelor Mine Rd. Left (south) on County Rd. 504 (Bachelor Rd.).
5.6(3.5)Left (north) on CO-149. Immediate left (north) on Loma St.
6.44(4.0)Creede Community Center and Mining Museum.
6.84(4.25)1315Arrive at Humphreys Mill.
Cum. distance
km(mi)TimeDirections
1315Depart from Humphreys Mill for Nelson Tunnel.
8.05(5)1330Arrive at Nelson Tunnel and Commodore mine (37.870045°N, 106.92951°W).
Cum. distance
km(mi)TimeDirections
1315Depart from Humphreys Mill for Nelson Tunnel.
8.05(5)1330Arrive at Nelson Tunnel and Commodore mine (37.870045°N, 106.92951°W).
Cum. distance
km(mi)TimeDirections
1400Depart from Nelson Tunnel and Commodoremine.
8.05(6)1415Arrive at Amethyst mine (37.883958°N, 106.932098°W).
Cum. distance
km(mi)TimeDirections
1400Depart from Nelson Tunnel and Commodoremine.
8.05(6)1415Arrive at Amethyst mine (37.883958°N, 106.932098°W).
Cum. distance
km(mi)TimeDirections
1445Depart from Amethyst mine.
11.26(7)1500Arrive at Midwest mine (37.894035°N, 106.930108°W).
Cum. distance
km(mi)TimeDirections
1445Depart from Amethyst mine.
11.26(7)1500Arrive at Midwest mine (37.894035°N, 106.930108°W).
Cum. distance
km(mi)TimeDirections
1515Depart from Midwest mine on County Rd. 503.
14.48(9)Right (north) on Equity Mine Rd. (37.906846°N, 106.954418°W).
17.70(11)1545Arrive at Equity mine.
Cum. distance
km(mi)TimeDirections
1515Depart from Midwest mine on County Rd. 503.
14.48(9)Right (north) on Equity Mine Rd. (37.906846°N, 106.954418°W).
17.70(11)1545Arrive at Equity mine.
Cum. distance
km(mi)TimeDirections
1600Depart from Equity mine (south) on County Rd. 503.
20.92(13)Right on County Rd. 504 (Bachelor Rd.).
22.53(14)Park Regent mine on left.
24.14(15)1640Arrive at Bachelor City.
Cum. distance
km(mi)TimeDirections
1600Depart from Equity mine (south) on County Rd. 503.
20.92(13)Right on County Rd. 504 (Bachelor Rd.).
22.53(14)Park Regent mine on left.
24.14(15)1640Arrive at Bachelor City.
Cum. distance
km(mi)TimeDirections
1650Depart Bachelor City (south) on County Rd. 503.
28.97(18)Intersection with Bulldog Mine road.
29.37(18.25)Creede Formation lacustrine sedimentary rocks on left.
30.57(19)1700End of traverse at intersection of County Rd. 504 and CO-149.
1800Dinner and presentations at the Creede Community Center.
Cum. distance
km(mi)TimeDirections
1650Depart Bachelor City (south) on County Rd. 503.
28.97(18)Intersection with Bulldog Mine road.
29.37(18.25)Creede Formation lacustrine sedimentary rocks on left.
30.57(19)1700End of traverse at intersection of County Rd. 504 and CO-149.
1800Dinner and presentations at the Creede Community Center.
Cum. distance
km(mi)TimeDirections
1315Depart from mill site.
163.56(101.63)Right (south) on South Camino Del Rio to CO-210 exit on right (west).
166.34(103.36)Right on CO-212.
167.40(104.02)1330Arrive at uranium disposal cell site on right (37.247830°N, 107.908014°W), stop 2 in Figure 5.
Cum. distance
km(mi)TimeDirections
1315Depart from mill site.
163.56(101.63)Right (south) on South Camino Del Rio to CO-210 exit on right (west).
166.34(103.36)Right on CO-212.
167.40(104.02)1330Arrive at uranium disposal cell site on right (37.247830°N, 107.908014°W), stop 2 in Figure 5.
Cum. distance
km(mi)TimeDirections
1430Depart from uranium disposal cell.
168.47(104.68)South on CO-212 to CO-210.
171.25(106.41)Left (east) on CO-210 to South Camino Del Rio and go left (north) on South Camino Del Rio (CO-160 W and CO-550 N).
172.26(107.04)Intersection with South Camino Del Rio (CO-550) north and U.S.-160 on left. Merge right to CO-550 (north).
240.92(149.7)1530Arrive at Molas Lake.
249.93(155.34)1545Depart from Molas Lake (37.752426°N, 107.682599°W).
258.94(160.9)1610Arrive at Silverton.
1800Dinner and presentations at Silvertontown hall.
Cum. distance
km(mi)TimeDirections
1430Depart from uranium disposal cell.
168.47(104.68)South on CO-212 to CO-210.
171.25(106.41)Left (east) on CO-210 to South Camino Del Rio and go left (north) on South Camino Del Rio (CO-160 W and CO-550 N).
172.26(107.04)Intersection with South Camino Del Rio (CO-550) north and U.S.-160 on left. Merge right to CO-550 (north).
240.92(149.7)1530Arrive at Molas Lake.
249.93(155.34)1545Depart from Molas Lake (37.752426°N, 107.682599°W).
258.94(160.9)1610Arrive at Silverton.
1800Dinner and presentations at Silvertontown hall.

Major Vein Minerals of the Sunnyside Mine Workings From Casadevall and Ohmoto (1977)

Table 1.
Major Vein Minerals of the Sunnyside Mine Workings From Casadevall and Ohmoto (1977)
MineralVol%
Quartz (SiO2)30–35
Sphalerite (ZnS)10–15
Galena (PbS)10–15
Pyroxmangite (MnSiO3)10–15
Pyrite (FeS2)6–8
Rhodochrosite (MnCO3)5–8
Chalcopyrite (CuFeS2)3–5
Tetrahedrite (Cu12Sb4S13)1–4
Fluorite (CaF2)1
Calcite (CaCO3)1
MineralVol%
Quartz (SiO2)30–35
Sphalerite (ZnS)10–15
Galena (PbS)10–15
Pyroxmangite (MnSiO3)10–15
Pyrite (FeS2)6–8
Rhodochrosite (MnCO3)5–8
Chalcopyrite (CuFeS2)3–5
Tetrahedrite (Cu12Sb4S13)1–4
Fluorite (CaF2)1
Calcite (CaCO3)1

Minor (<0.5 vol%) Vein Minerals of the Sunnyside Mine Workings (From Casadevall and Ohmoto, 1977)

Table 2.
Minor (<0.5 vol%) Vein Minerals of the Sunnyside Mine Workings (From Casadevall and Ohmoto, 1977)
Hematite (Fe2O3)Gold (Au)
Petzite (AuAg3Te2)Calaverite (AuTe2)
Alabandite (MnS)Huebnerite (MnWO4)
Tephroite (Mn2–SiO4)Friedelite (Mn8Si6O18)
Helvite (Mn4(Be3Si3O12)S)Anhydrite (CaSO4)
Sericite (KAl2)(AlSi 3O10)(OH2)Aikinite (PbCuBiS3)
Bornite (Cu5FeS4)Barite (BaSO4)
Gypsum (CaSO4(2H2O))
Hematite (Fe2O3)Gold (Au)
Petzite (AuAg3Te2)Calaverite (AuTe2)
Alabandite (MnS)Huebnerite (MnWO4)
Tephroite (Mn2–SiO4)Friedelite (Mn8Si6O18)
Helvite (Mn4(Be3Si3O12)S)Anhydrite (CaSO4)
Sericite (KAl2)(AlSi 3O10)(OH2)Aikinite (PbCuBiS3)
Bornite (Cu5FeS4)Barite (BaSO4)
Gypsum (CaSO4(2H2O))
Cum. distance
km(mi)TimeDirections
0830Depart from San Juan caldera topographic margin.
8.21(5.1)Return to intersection of Greene St. and East 14th St.
9.75(6.06)Left (west) on Green St. to County Rd. 31).
Right (southeast) on County Rd. 31.
11.44(7.11)0915Arrive at hydrologic gauge A-72 (37.790277°N, 107.666944°W).
Cum. distance
km(mi)TimeDirections
0830Depart from San Juan caldera topographic margin.
8.21(5.1)Return to intersection of Greene St. and East 14th St.
9.75(6.06)Left (west) on Green St. to County Rd. 31).
Right (southeast) on County Rd. 31.
11.44(7.11)0915Arrive at hydrologic gauge A-72 (37.790277°N, 107.666944°W).
Cum. distance
km(mi)TimeDirections
0945Depart from hydrologic gauge A-72.
13.13(8.16)Return to intersection of Greene St. and East 14th St.
13.42(8.34)Right (south) on 14th St. to Cement St.
Right (west) on Cement St.
13.57(8.43)1000Arrive near confluence of upper Animas River and Cement Creek (walk 0.07 mi southwest) to mixing zone.
Cum. distance
km(mi)TimeDirections
0945Depart from hydrologic gauge A-72.
13.13(8.16)Return to intersection of Greene St. and East 14th St.
13.42(8.34)Right (south) on 14th St. to Cement St.
Right (west) on Cement St.
13.57(8.43)1000Arrive near confluence of upper Animas River and Cement Creek (walk 0.07 mi southwest) to mixing zone.
Cum. distance
km(mi)TimeDirections
1030Depart upper Animas River and Cement Creek mixing zone.
14.00(8.7)Return to intersection of Greene St. and East 14th St.
14.72(9.15)Right (east) on Greene St. to intersection with CO-34.
Left (north) on CO-110 (Cement Creek Rd.).
15.59(9.69)1045Arrive at alluvial ferricrete.
Cum. distance
km(mi)TimeDirections
1030Depart upper Animas River and Cement Creek mixing zone.
14.00(8.7)Return to intersection of Greene St. and East 14th St.
14.72(9.15)Right (east) on Greene St. to intersection with CO-34.
Left (north) on CO-110 (Cement Creek Rd.).
15.59(9.69)1045Arrive at alluvial ferricrete.
Cum. distance
km(mi)TimeDirections
1110Depart alluvial ferricrete, north on CO-110.
17.01(10.57)Hancock Gulch fan on river left diverts flow of Cement Creek.
18.84(11.71)1120Arrive at Topeka Gulch outlet (37.846185°N, 107.678755°W). 1140 Depart fom Topeka Gulch outlet.
19.52(12.13)Ohio Gulch outlet west of road (37.852121°N, 107.677237°W).
Cum. distance
km(mi)TimeDirections
1110Depart alluvial ferricrete, north on CO-110.
17.01(10.57)Hancock Gulch fan on river left diverts flow of Cement Creek.
18.84(11.71)1120Arrive at Topeka Gulch outlet (37.846185°N, 107.678755°W). 1140 Depart fom Topeka Gulch outlet.
19.52(12.13)Ohio Gulch outlet west of road (37.852121°N, 107.677237°W).
Cum. distance
km(mi)TimeDirections
22.74(14.13)1150Arrive at upper iron spring (37.879694°N, 107.669716°W),
Cum. distance
km(mi)TimeDirections
22.74(14.13)1150Arrive at upper iron spring (37.879694°N, 107.669716°W),
Cum. distance
km(mi)TimeDirections
23.13(14.37)1210
1215Depart from upper iron spring. Arrive at Prospect Gulch outlet and alluvial fan (37.882570°N, 107.667343°W) (lunch).
Cum. distance
km(mi)TimeDirections
23.13(14.37)1210
1215Depart from upper iron spring. Arrive at Prospect Gulch outlet and alluvial fan (37.882570°N, 107.667343°W) (lunch).
Cum. distance
km(mi)TimeDirections
1330Depart from Prospect Gulch outlet.
24.83(15.43)1335Arrive at Gladstone town site (37.890491°N, 107.652107°W)
Cum. distance
km(mi)TimeDirections
1330Depart from Prospect Gulch outlet.
24.83(15.43)1335Arrive at Gladstone town site (37.890491°N, 107.652107°W)
Cum. distance
km(mi)TimeDirections
1400Depart from Gladstone town site.
24.94(15.5)Right at intersection of CO-110 and CO-52.
25.30(15.72)Right at intersection of CO-52 and CO-51. Trend left (northeast) at road forks (37.893592°N,107.644176°W).
27.00(16.78)1445Arrive at Gold King mine #7 level (37.894579°N,107.638371°W)
Cum. distance
km(mi)TimeDirections
1400Depart from Gladstone town site.
24.94(15.5)Right at intersection of CO-110 and CO-52.
25.30(15.72)Right at intersection of CO-52 and CO-51. Trend left (northeast) at road forks (37.893592°N,107.644176°W).
27.00(16.78)1445Arrive at Gold King mine #7 level (37.894579°N,107.638371°W)
Cum. distance
km(mi)TimeDirections
1545Depart from Gold King mine #7 level.
28.93(17.98)Descend road to intersection of CO-51 and CO-53.
Right (north) on CO-53.
Arrive Red and Bonitamine (37.897479°N, 107.644682°W).
Cum. distance
km(mi)TimeDirections
1545Depart from Gold King mine #7 level.
28.93(17.98)Descend road to intersection of CO-51 and CO-53.
Right (north) on CO-53.
Arrive Red and Bonitamine (37.897479°N, 107.644682°W).
Cum. distance
km(mi)TimeDirections
1700Depart Red and Bonita mine for Silverton.
1800Dinner and presentations at Silverton town hall.
Cum. distance
km(mi)TimeDirections
1700Depart Red and Bonita mine for Silverton.
1800Dinner and presentations at Silverton town hall.

High, Low, and Mean Concentrations for Selected Elements for Background Pre-Mining Sediments Sites for Mineral Creek, Cement Creek, and Upper Animas River Basins

Table 3.
High, Low, and Mean Concentrations for Selected Elements for Background Pre-Mining Sediments Sites for Mineral Creek, Cement Creek, and Upper Animas River Basins
BasinAs (ppm)Cu (ppm)Zn (ppm)Pb (ppm)Mn (ppm)Mo (ppm)Ba (ppm)Sr (ppm)V (ppm)
Mineral Creek
High value3880410450230010800285120
Low value153212058210126018056
Average value305121317011665666235102
Cement Creek
High value6915040042012007870400220
Low value1821802305501615240150
Average value48821922978383.8779288174
Upper Animas
High value681901350750550010850260170
Low value21403007518001620160110
Average value4212867432433145.2737194133
BasinAs (ppm)Cu (ppm)Zn (ppm)Pb (ppm)Mn (ppm)Mo (ppm)Ba (ppm)Sr (ppm)V (ppm)
Mineral Creek
High value3880410450230010800285120
Low value153212058210126018056
Average value305121317011665666235102
Cement Creek
High value6915040042012007870400220
Low value1821802305501615240150
Average value48821922978383.8779288174
Upper Animas
High value681901350750550010850260170
Low value21403007518001620160110
Average value4212867432433145.2737194133

Geochemical Parameters Determined for Category I and II, Undifferentiated Surface Water and Groundwater Samples From Mast et al. (2007, their Table 2)

Table 4.
Geochemical Parameters Determined for Category I and II, Undifferentiated Surface Water and Groundwater Samples From Mast et al. (2007, their Table 2)
ParameterMinimumMediumMaximum
pH2.64.98.5
Specific conductance122702,180
Alkalinity (mg/L, as CaCO3)<0.5<0.569
Sulfate (mg/L)1.0901,300
Ca (mg/L)1.028550
Mg (mg/L)0.13.234
SiO2 (mg/L)0.85.853
Al (μg/L)<4035971,400
Cu (μg/L)<4<4372
Fe (μg/L)<3046117,000
Zn (μg/L)<202814,400
Pb (μg/L)<30<30141
Mn (μg/L)<319274,700
Mo (μg/L)<10<1071
Ba (μg/L)<222101
Sr (μg/L)6.02365,700
V (μg/L)<4<411
ParameterMinimumMediumMaximum
pH2.64.98.5
Specific conductance122702,180
Alkalinity (mg/L, as CaCO3)<0.5<0.569
Sulfate (mg/L)1.0901,300
Ca (mg/L)1.028550
Mg (mg/L)0.13.234
SiO2 (mg/L)0.85.853
Al (μg/L)<4035971,400
Cu (μg/L)<4<4372
Fe (μg/L)<3046117,000
Zn (μg/L)<202814,400
Pb (μg/L)<30<30141
Mn (μg/L)<319274,700
Mo (μg/L)<10<1071
Ba (μg/L)<222101
Sr (μg/L)6.02365,700
V (μg/L)<4<411

Geochemical Parameters Determined for Category III and IV, Mine Drainage Samples from Mast et al. (2007, Their Table 5)

Table 5.
Geochemical Parameters Determined for Category III and IV, Mine Drainage Samples from Mast et al. (2007, Their Table 5)
ParameterMinimumMediumMaximum
pH2.355.747.77
Specific conductance1807413,520
Alkalinity (mg/L, as CaCO3)<0.56.5137
Sulfate (mg/L)453092,720
Ca (mg/L)2.080460
Mg (mg/L)0.76.342
SiO2 (mg/L)2.01030
Al (μg/L)<4061671,400
Cu (μg/L)<4698,600
Fe (μg/L)<304,650686,000
Zn (μg/L)<20621228,000
Pb (μg/L)<30<301,379
Mn (μg/L)<31,36023,700
Mo (μg/L)<10<1042
Ba (μg/L)<21062
Sr (μg/L)378096,080
V (μg/L)<4<45
ParameterMinimumMediumMaximum
pH2.355.747.77
Specific conductance1807413,520
Alkalinity (mg/L, as CaCO3)<0.56.5137
Sulfate (mg/L)453092,720
Ca (mg/L)2.080460
Mg (mg/L)0.76.342
SiO2 (mg/L)2.01030
Al (μg/L)<4061671,400
Cu (μg/L)<4698,600
Fe (μg/L)<304,650686,000
Zn (μg/L)<20621228,000
Pb (μg/L)<30<301,379
Mn (μg/L)<31,36023,700
Mo (μg/L)<10<1042
Ba (μg/L)<21062
Sr (μg/L)378096,080
V (μg/L)<4<45

Potential Uses of Geophysical Methods in Mine-Waste Characterization (Modified From Campbell and Fitterman, 2000)

Table 6.
Potential Uses of Geophysical Methods in Mine-Waste Characterization (Modified From Campbell and Fitterman, 2000)
MethodMeasuresCaused byMine-waste application
EM (Frequency-Domain Electromagnetics)Electrical conductivity (mS/m)Groundwater, lithologyTracing acid mine drainage plumes
DC (Direct-Current Resistivity)Electrical resistivity (Ohm-m)Groundwater, lithologyShallow (<10 m) water tables in, and bottoms of, shallow (<20 m) waste dumps
TEM (Time-Domain Electromagnetics)Electrical conductivity (mS/m)Groundwater, lithologyDeeper (10-30 m) water tables in waste dumps
CSAMT (Controlled Source Audio MagnetotelluricsElectrical resistivity (Ohm-m)Groundwater, lithologyDeeper (10-50 m) bottoms of waste dumps
IP (Induced Polarization)Electrical chargeability (usually mV-s/V)Electrochemical reactions at grain surfacesConcentrations of sulfides in waste dumps
SP (Spontaneous Polarization)Ground voltages (mV)Redox and streaming potentialsExperimental
GPR (Ground Penetrating Radar)Speed of electromagnetic radiation (cm/ns)Ground textures and included pore waterPossibly monitoring plume remediation
MagneticsMagnetic field (nT)MagnetizationFerrous material (e.g., rebar) in mine dumps (other mine-waste applications unproven)
SeismicAcoustic wave velocity (m/s)Compaction and groundwater contentTracing bottoms and edges of waste dumps, and basement under plume areas (all mine-waste applications are still in experimental stages)
MethodMeasuresCaused byMine-waste application
EM (Frequency-Domain Electromagnetics)Electrical conductivity (mS/m)Groundwater, lithologyTracing acid mine drainage plumes
DC (Direct-Current Resistivity)Electrical resistivity (Ohm-m)Groundwater, lithologyShallow (<10 m) water tables in, and bottoms of, shallow (<20 m) waste dumps
TEM (Time-Domain Electromagnetics)Electrical conductivity (mS/m)Groundwater, lithologyDeeper (10-30 m) water tables in waste dumps
CSAMT (Controlled Source Audio MagnetotelluricsElectrical resistivity (Ohm-m)Groundwater, lithologyDeeper (10-50 m) bottoms of waste dumps
IP (Induced Polarization)Electrical chargeability (usually mV-s/V)Electrochemical reactions at grain surfacesConcentrations of sulfides in waste dumps
SP (Spontaneous Polarization)Ground voltages (mV)Redox and streaming potentialsExperimental
GPR (Ground Penetrating Radar)Speed of electromagnetic radiation (cm/ns)Ground textures and included pore waterPossibly monitoring plume remediation
MagneticsMagnetic field (nT)MagnetizationFerrous material (e.g., rebar) in mine dumps (other mine-waste applications unproven)
SeismicAcoustic wave velocity (m/s)Compaction and groundwater contentTracing bottoms and edges of waste dumps, and basement under plume areas (all mine-waste applications are still in experimental stages)
Cum. distance
km(mi)TimeDirections
12.54(7.79)0845Arrive Eureka at town site and Sunnyside Eureka mill (37.880504°N, 107.566919°W).
Cum. distance
km(mi)TimeDirections
12.54(7.79)0845Arrive Eureka at town site and Sunnyside Eureka mill (37.880504°N, 107.566919°W).
Cum. distance
km(mi)TimeDirections
0915Depart from Eureka town site and Sunnyside Eureka mill.
17.32(10.76)0945Cross Eureka graben, Toltec fault (37.893480°N, 107.603383°W).
19.18(11.92)1010Arrive at Lake Emma (37.902573°N, 107.614381°W).
Cum. distance
km(mi)TimeDirections
0915Depart from Eureka town site and Sunnyside Eureka mill.
17.32(10.76)0945Cross Eureka graben, Toltec fault (37.893480°N, 107.603383°W).
19.18(11.92)1010Arrive at Lake Emma (37.902573°N, 107.614381°W).
Cum. distance
km(mi)TimeDirections
1045Depart from Lake Emma.
38.32(23.84) 1130Stop at Memorial Park, Silverton (lunch).
558(347)1215Depart from Silverton for Denver to return to the Colorado Convention Center.
Cum. distance
km(mi)TimeDirections
1045Depart from Lake Emma.
38.32(23.84) 1130Stop at Memorial Park, Silverton (lunch).
558(347)1215Depart from Silverton for Denver to return to the Colorado Convention Center.

Contents

GeoRef

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