Abstract The strata-bound Century zinc-lead-silver deposit is located approximately 250 km north-northwest of Mount Isa in northwestern Queensland, Australia. High-grade mineralization at Century occurs mostly in black shales of the Middle Proterozoic Lawn Hill Formation, dominantly as fine-grained sphalerite and galena lamellae with siderite and minor pyrite. An intricate network of associated, but paragenetically later, strata-bound microfractures overprints these lamellae, mineralized with progressively more discordant sphalerite, galena, and siderite. The black shale units are separated by less mineralized, siderite-rich, silt-stone horizons. The deposit is unmetamorphosed, only weakly deformed, and displays excellent lateral stratigraphic and grade continuity apart from small-scale fault dislocations. Century lies within a 20-km-diam cluster of relatively small quartz-siderite-galena-sphalerite veins. These lodes are for the most part confined to a distinctive stratigraphic interval in the lower to middle Lawn Hill Formation, several hundred meters beneath the mineralized strata at Century. The lodes formed relatively late in the deformational and mineralization history of the district but have a strong kinship to the earlier, deep-level diagenetic mineralization at Century. A major strata-bound district-scale siderite-ferroan dolomite-ankerite-illite alteration system partly overlaps the major vein cluster and is roughly centered on the Century deposit. The deposit, the regional lodes, and the strata-bound alteration are genetically linked and were products of a single district-scale fluid system. The Century ores were emplaced in the relatively early stages of the system and correlate with the first-stage basin inversion event (D 1 ). The regional lodes are the products of continuing but less voluminous fluid migration during a regional D 2 fold event. The regional alteration has textural aspects suggestive of both early- and late-stage burial diagenesis and per-haps developed intermittently throughout the entire life of the system in subtly changing lithostructural environments that were not conducive to sulfide mineral deposition. The discovery and subsequent development of an economic resource at Century is the result of explo-ration persistence and conceptual flexibility in an area with a greater than 100-yr history of exploration and mining. The Century orebody was discovered by drilling a zinc, lead, and silver soil geochemical anomaly. Surface expression of mineralization was visually subtle. Only a small part of the mineralization had an out-crop expression because of the synclinal structure of the orebody and later postmineral Cambrian lime-stone cover. These outcrops lacked a classic iron-rich gossan profile because of the low iron sulfide content of the ore. The soil anomaly was not drill tested for 3 yr because of its unpromising visual appearance and lack of a conductive geophysical response. Key concerns that remain unresolved at Century include the absolute timing of different phases of the system, detailed controls on sulfide-rich versus sulfide-deficient alteration assemblages, the geometry of major fluid conduits, and the definition of boundary conditions for ore fluid compositions. A better under-standing of these characteristics will provide critical insights for the generation of new targets in alternative stratigraphic and/or structural positions.

Abstract The Carbonate and Ragged Top mining districts, located about 5 miles northwest and west of Lead respectively, are the only two areas in the northern Black Hills where significant replacement deposits of silver-lead and gold-silver occur in the Mississippian Pahasapa Limestone (Fig. 1). There is an additional occurrence of weakly- mineralized Pahasapa Limestone in the Vanocker area, SE of Lead (Fig. 1). Following discovery of high grade silver- lead ores in 1881, Carbonate became a flourishing mining camp from 1885 to 1891 with a total production of at least 2.6 kg (83 oz) of gold; 525 kg (18,511 oz) of silver; and 5,193 kg (183,191 lbs) of lead (Shapiro and Gries, 1970). At Ragged Top (Fig. 1), after gold was discovered in 1896, mining operations were continuous until 1917, producing a total of 1,879 kg (60,598 oz) of gold (Shapiro and Gries, 1970). From 1937 to 1958, the deposit was sporadically exploited and was finally abandoned. Current mining and heap-leach processes make the Carbonate and Ragged Top areas favorable for renewed exploration. In the Carbonate district, the Pahasapa Limestone has been intruded extensively by early Tertiary sills and dikes. The principal ore bodies are of two types: fissure veins and solution cavity-filling. Fissure veins consist of Au- bearing ferruginous gouge in the center and Pb-Ag rich (galena, cerussite, and cerargyrite) jasperoids along the margins (Irving, 1904). The solution cavity-filling ores are usually close to igneous intrusions, are less siliceous than jasperoid and are rich in lead, silver with minor gold

Abstract Massive sulfide deposits of the Vermont copper belt yielded approximately 3.6 Mt of ore during intermittent production from 1793 to 1958. The deposits consist of stratabound and generally stratiform pyrrhotite, chalcopyrite, and minor sphalerite and pyrite within metasedimentary rocks and minor mafic metavolcanic rocks of Silurian to Early Devonian age. At the largest deposits (Elizabeth, Ely, Pike Hill), massive sulfides are generally associated with metabasaltic amphibolite. The deposits are structurally complex, and have been deformed together with their host rocks during two stages of nappe-related, largely isoclinal folding, and during a later stage of dome-related folding; syntectonic shears and thrust faults commonly mark the contacts between massive sulfide bodies and silicate wall rocks. Postore re-gional metamorphism took place under amphibolite-grade conditions, producing locally abundant kyanite and staurolite in pelitic country rocks during peak prograde events. Geochemical studies of clastic metasedimentary host rocks in the district indicate a significant mafic component that suggests a continental island-arc provenance. The amphibolites, in contrast, have immobile trace element and rare earth element (REE) geochemical signatures similar to that of midocean ridge basalt (MORB). Lithologically unusual wall rocks at the Elizabeth deposit, including coarse garnet-mica schist, laminated plagioclase-rich granofels, quartz-mica-carbonate schist, tremolite-phlogopite schist, and quartz-albite tourmalinite, have high contents of Cr and MORB-type REE patterns that suggest protoliths of tholeiitic basalt. Massive sulfide, metachert, Mn-rich garnet-quartz rocks (coticule), and magnetite iron formation in the district are believed to have formed as exhalative chemical precipitates on the sea floor. Chemical analyses of unoxidized massive sulfide from the Elizabeth, Ely, and Pike Hill mines show that in addition to very high Cu (to 23.6 %) and in rare cases very high Zn (to 26.2 %), some ore samples contain minor Ag (to 100 ppm), Au (to 0.85 ppm), Cd (to 1500 ppm), Co (to 1469 ppm), Mn (to 5600 ppm), Mo (to 420 ppm), and Se (to 87 ppm). The ores have uniformly low As, Ba, Bi, Cr, Hg, Ni, Pb, REEs, Sb, Sn, Te, Th, Tl, U, and W. The overall geologic and geochemical features of the Vermont copper belt ores are similar to those of the Besshi deposits in Japan. Possible modern analogs include the actively forming massive sulfides of Guaymas Basin in the Gulf of California, Escanaba Trough on the Gorda Ridge, and Middle Valley on the Juan de Fuca Ridge.

Abstract The Purpose of this trip is to examine relations of the economic geology and mining history of the Vermont copper belt to the environmental behavior of these deposits and their potential future reclamation. In contrast, the 1993 Society of Economic Geologists field trip focused on the regional and economic geology of the copper belt (Slack etal., 1993). The Vermont copper belt, like many other mining districts, has had a long and colorful history (Abbott, 1973). This history spans the period of active mining from the discovery of the Elizabeth deposit in 1793 through its closure in 1958, to the present, as plans to reclaim the site are being made. Like other districts, the history is intimately intertwined with the economic development and early settlement of the region. Production was dominated by three main mines: Elizabeth, near South Strafford; Ely, near West Fairlee; and Pike Hill, near Corinth. In addition, several other smaller mines and prospects are found in the belt. All mines exploited copper-rich massive sulfide deposits, or their weathered equivalents. The earliest mining from Elizabeth was for iron from the gossan zone, followed by mining of pyrrhotite for the manufacture of copperas (hydrated ferrous sulfate). Copperas was produced by roasting the ores to oxidize the pyrrhotite. Resulting ferrous sulfate was leached from the roast beds with water, and concentrated in evaporating vats. During the late 18th and early 19th centuries, copperas was used for curing and setting colors in hides and pelts, and for making dyes, treating timbers and

Abstract The Homestake mine in the northern Black Hills, South Dakota is the largest iron-formation-hosted gold deposit known (Fig. 1), and has produced 1,113 tonnes (35.8 million oz.) of gold from 128 million tonnes of ore milled. In 1989 the mine produced 11.9 tonnes of gold. The deposit was discovered in 1876, and the mine has operated continuously to the present day (Fig. 2). Ore is currently mined from depths to 2,438 meters. Gold is the major commodity produced along with a minor silver by-product. The gold/silver ratio averages 5:1; base metal content is negligible. The Homestake gold deposit is hosted within quartz-veined, sulfide-rich segments of an early Proterozoic, carbonate-facies iron-formation in a sequence of originally calcareous, pelitic, and quartzose rocks (Fig. 3). Strata that contain the Homestake deposit were complexly deformed by a series of tight isoclinal and sheath fold events, and synchronous, extensive ductile and ductile-brittle shearing. Mine area rocks have been subjected to upper greenschist-lower amphibolite facies metamorphism. Early-stage ductile shearing appears to have controlled fluid movement in the system thereby controlling thermal energy and metamorphic processes. Observed prograde metamorphism in the district is therefore characterized as dynamothermal. Intrusion of a 1.72 Ga Harney Peak-type granite in an area northeast of the mine post -dated regional prograde metamorphism, and appears to be contemporaneous with later stages of semi-brittle deformation (Bachman et al., 1990).

Abstract Huron-Montezuma prospect south of Iron King mine. Turn south on Arizona Highway 69 toward Mayer. 0.5 Highway makes gentle turn to the left. Large, dark hill on the right contains bouldery outcrops of Laramide stock that intrudes metabasaltic rocks. Dumps of the Henrietta mine, a copper-rich Laramide vein, on the skyline at 3:00. 0.8 Mount Elliott, elev. 6,980 ft, on the skyline at the right. Bold cliffs of Mount Elliott are composed of the undated (probably ~1740 Ma) Crooks Canyon Granodiorite, an Early Proterozoic pre-tectonic leucocratic pluton (Anderson and Blacet, 1972a; DeWitt, in press) that forms extensive outcrops in the southwestern part of the Prescott area. In the foreground are bouldery weathering outcrops of the Laramide stock at Poland Junction (fig. 43). 0.9 Roadcut exposes meta-andesite and metabasalt flows of the Iron King Volcanics. 1.1 Poland Junction. Road to Walker leads to the right and follows the route of a 1900's narrow gauge railroad bed. The Poland-Walker Tunnel cut through the crest of Eugene Ridge and connected the Walker district with the smelter at Humboldt (Lindgren, 1926). This drainage divide is capped by Quaternary to Tertiary gravel that locally conceals the metavolcanic strata. Ridges of ferruginous metachert and iron-formation protrude above the gravel, especially near the Boggs (Hurlbut, 1986) and Iron Queen mines to the left at about 10:00. Behind and to the right at 5:00 are the dumps of the Henrietta mine. View straight ahead in the far distance is of the New River Mountains. The jagged peaks are