The Frenchman Springs Member is the most voluminous member of the Wanapum Basalt, Columbia River Basalt Group. We have revised the distribution maps and estimates of the areas and volumes for the units of the Frenchman Springs based on mapping and fieldwork that have been conducted since the previous compilation in 1989. The revised estimates indicate that many of the Frenchman Springs flows are significantly larger than previously believed. The total area underlain by Frenchman Springs flows is now estimated to be ~72,595 km 2 ; the revised volume is estimated to be ~7628 km 3 . Based on the new data, the Basalts of Palouse Falls, Ginkgo, Sand Hollow, and Sentinel Gap are significantly more voluminous than previously indicated, while the Basalt of Silver Falls is significantly smaller. We have also reduced the number of units within the Frenchman Springs Member to five. The Basalt of Lyons Ferry has been combined with the Basalt of Sentinel Gap based on the similarity of their geochemistries and paleomagnetism and the lack of an identified dike/vent system. Geochemical variations in Frenchman Springs Member flows (as well as those in the Roza and Priest Rapids Members, Wanapum Basalt) are consistent with being produced by open magma system processes.

Many structural domes and anticlines rise from undeformed surroundings; the general crust of the earth is neither shortened nor extended by these local swells or blisters, but the area of the plate upfolded is increased. With plastic material the increase is effected largely by flow; with brittle material, largely by fracture. Many mining districts are associated with upfolds of this type. Districts here described fall into two categories: (1) those whose structural frame is a dome, and (2) those whose structural frame is an anticline. Domes may show fractures which radiate from the apex, or concentric fractures which are segments of circles, of varying diameters but with a common center, the apex of the dome. Both types may appear on the same dome; the fractures of each type aid enlargement of the plate during doming. Sunlight and Kirwin, Wyoming, are minor districts with dominant radial fracture patterns. Vein matter was deposited while the walls of the vein fractures were being pulled apart. With a radial vein system the only way in which all the vein walls could be simultaneously pulled apart is by stretching of the fabric of an expanding dome. The structural setting of the Ophir, Utah, lead-silver district, and of the Matehuala, Mexico, copper district is that of a half dome truncated by a normal fault with downthrow away from the domical apex. Displacement on the fault is greatest opposite the apex and decreases progressively in both directions, becoming zero at the spring line. No part of the dome ever existed on the down-thrown side of the fault, which was a fracture before doming. Maximum uplift was centered on one side of the fault and there produced the half dome; but the pre-existing fracture offered locally an easier mode of uplift by rise of the foot-wall block. At Ophir ore shoots followed intersections on the half dome of radial fractures with limestone beds. At Matehuala stretching during doming was effected largely by flow of limestone, but a monzonite stock intruded in the half dome was too brittle to flow. The limestone pulled away from the unyielding stock; fractures concentrated around the periphery of the stock localized the Dolores copper ore bodies. In the Silverton-Telluride district, Colorado, fractures radiate from a relatively large, roughly circular graben, along whose margin monzonitic stocks were intruded. Evidence suggests that this fracture pattern resulted from domical uplift, with the graben at the apex. Transfer of volcanic material from depth to the surface in the central area produced a sag which has eliminated the upward bulge of the dome. Mineralization advanced outward from the graben step by step with the outward growth of the radial fractures. Copper-silver pipes within the fault zone bounding the graben were formed first, followed successively outward by base-metal deposits as veins, which were reopened to admit gold and silver, and by precious-metal vein deposits in the outermost zone. The structural setting of La Plata, Colorado, is that of a dome, truncated, south of its apex, by a zone of high-angle faults striking eastward. Displacements on the faults are greatest opposite the domical apex. The doming is accentuated by a horseshoe-shaped hinge fold, open on the south. Along the fold dips of the strata steepen sharply; outside it, dips are gentle, whereas inside it, they are nearly flat. Several stocks were intruded along the fold, and others inside it. The steep flexural fold and abundant intrusions suggest upward shove of a flat-topped piston, perhaps a magma column congealed in its upper part, but fluid and under pressure below. Fractures are abundant along the horseshoe fold, and, with respect to the dome, fall into two classes, radial and concentric. Gold-silver deposits were concentrated chiefly within or near the horseshoe fold, and in the eastward-trending fault zone. Doming, which began during the intrusive epoch, persisted through the period of metallization, because at that time older fractures were reopened, new radial and concentric fractures were created, and fractures of both generations became loci for ore bodies. The structure at Rico, Colorado, is that of a dome with eastern elongation. Superimposed upon the major dome, toward its eastern end, is a doubly plunging anticline, also with easterly trend, cut by fractures which parallel its axis, and by fractures normal to the axis. Rich ore bodies were localized at a stratigraphic horizon originally occupied by a bed of gypsum which was dissolved, leaving silty material which the ores replaced. Ribbon-shaped mantos lay directly above fractures, both of the longitudinal and transverse sets. Ore solutions ascended these fractures to form the mantos during late stages of the doming. The Goldfield, Nevada, district lies on the southwest flank of a dome encircled by a belt of intense alteration, and of complex fracturing, which probably coalesces at depth into one or more persistent faults concentric with respect to the domical apex, and which formed the channel for altering and metallizing solutions. The volcanic rocks were brittle when first fractured by doming, but solutions rising along the fractures of the circular belt softened the rock by alunitization and kaolinization. Silica-bearing solutions then created the irregular silica “ledges” at horizons close to the then surface. The soft rock encasing the ledges flowed, as doming persisted, but the brittle ledges fractured. Ledges which had no “keel” below them were inaccessible to gold-bearing solutions; those with keels extending down to the main ore channel received the rich ore bodies. Many mining districts are associated with doubly plunging anticlines, which with brittle rock are broken by fractures which strike parallel or normal to the axis. At Creede, Colorado, older extrusive rocks were flexed into a north-trending anticline. Younger extrusive rocks do not share in the folding, but faults which strike parallel to the anticlinal axis and dip toward it cut and displace both older and younger rocks; they form a graben along the crest of the buried anticline. These faults originated as tension fissures, the result of arching of the older volcanic rocks. After extrusion of the younger volcanic rocks, renewed uplift was concentrated along the abutments of the arch, in the footwalls of the graben faults. These faults were propagated upward through the younger volcanic rocks. The eastern graben fault, the Amethyst, fingers out at its southern end. Most of the silver ore of the district came from the southern segment of the Amethyst vein. Here intense local uplift in the footwall, unable to utilize the split-up fault as a lubricated plane of movement, tore apart the walls to permit entry of the silver-bearing solutions. The structure at Bodie, California, is that of an irregular anticline upon which are superimposed several domes. The country rock is volcanic. Most of the faults and veins strike parallel to the anticlinal axis and dip toward it; but the Fortuna fracture, which carried the richest ore body, lies in anomolous relation to the anticline, for it is neither a longitudinal nor a cross fracture. It seems to have resulted from an earlier deformation, but to have been utilized by the uplift which formed the anticline in such a way that its flat segment gaped open to admit rich silver- and gold-bearing solutions. Guanajuato, Mexico, lies on the northeast flank of a major anticline which plunges southeast. The anticline carries a crestal graben. The graben fault on the northeast flank is the Veta Madre, with maximum displacement on the northwest; displacement decreases progressively southeastward, in the direction of plunge of the anticline. Like the Amethyst fault at Creede, the Veta Madre originated as a tension fissure, but became an antithetic fault when the arch broke into segments under continued uplift. Major silver-ore bodies on the Veta Madre were localized where differential movement of the walls brought shallow cups in the footwall surface opposite planar areas in the hanging-wall surface. At El Oro, Mexico, the attitudes of remnants of an andesite flow overlying shale, together with the fracture pattern, indicate deformation to form a broad anticline trending north-northwestward. The San Rafael vein lies along a normal fault striking parallel to the anticlinal axis, with downthrow on the west, toward the axis. Faulting had been completed by the time of mineralization. Early, low-grade vein matter welded the fault, but arching continued and with it an urge toward resumption of faulting, prevented by the welding. The resulting strong shearing strain produced a number of vertical feather-joint branches in the hanging wall of the fault. These were mineralized by solutions rich in gold and silver. The Mogollon, New Mexico, district lies on the west flank of a large anticline trending and plunging north-northeastward. The Pacific-Great Western and Queen faults strike parallel to the anticlinal axis and dip eastward toward the axial plane. The block between these faults contains a local bulge truncated on the east by the Queen fault. Displacement on the fault is greatest opposite the crest of the bulge and decreases progressively in either direction. The local uplift in the footwall increased the displacement on the Queen fault, but it took place in the hanging wall of the Pacific-Great Western fault. The original displacement was reversed in the segment affected by the bulge. The bulge has the form of a doubly plunging anticline trending northward, parallel to the Queen and Pacific-Great Western faults. The chief productive veins of the district occupy cross fractures normal to the anticlinal axis. Most of those north of the highest point on the up-bowed axis dip southward, whereas most of those south of that point dip northward. These fractures gaped open, under continued bulging, in time to receive the richest surge of silver-gold solutions. The following generalizations appear valid. Uplift in these districts was accompanied by development of tension fissures. Uplift and consequent stretching of the arching plate persisted through the period of mineralization, but by this time stretching in many areas had reached a stage at which Assuring could no longer facilitate it; Assuring was succeeded by graben and antithetic faulting. Ore deposition sometimes preceded this faulting but more often followed it. The fracture pattern on these domes and anticlines developed as uplift progressed. Solutions deposited vein matter in those fractures which were permeable at the time and accessible from the main solution channel. Mesothermal deposits associated with domes and anticlines fall into groups defined by age of mineralization and by metallographic provinces, but epithermal deposits are scattered from one end of the Cordilleran region to the other. They show, however, a preference for major uplifts. Silverton, Rico, La Plata, and Creede lie on a tectonic element marked by recurrent uplift from the close of the Paleozoic to the Pleistocene. Epithermal deposits in Mexico are concentrated on the site of the persistently positive Occidental geanticline. The crystalline basement lies deep throughout much of Nevada, but Goldfield, Tonopah, and other epithermal districts lie above or close to relative highs in the basement which are much larger than the local uplifts with which these districts are associated. These major uplifts were developing while epithermal metallization was taking place. The whole Cordilleran region was fast assuming its present shape. The local phenomena of uplift, Assuring, intrusion, and metallization were satellitic features superimposed on the uplift of the Cordilleran region as a whole. Because of this fact, a deep-seated origin for epithermal ores is suggested.

Cenozoic deposits of the Silver Peak region, western Nevada, and adjacent California consist principally of continental sedimentary and pyroclastic rocks of the Esmeralda Formation and lavas and tuffs of the Silver Peak volcanic center. The sedimentary rocks comprise several thick sequences of tuffaceous volcanic sandstone and siltstone and interbedded air-fall tuff. These rocks were deposited in basins that coincide in a general way with the present valleys. Thick wedges of conglomerate and sandstone occur along the basin margins and reflect source areas. Most of the sedimentary rocks were deposited under fluctuating fluviatile and lacustrine conditions, but paludal conditions prevailed locally. Abrupt facies changes and numerous local unconformities indicate that deposition was not uniform within a given basin. The sedimentary rocks range in age from late Miocene to late Pliocene. The oldest reliably dated rocks in the Esmeralda Formation are 13.1 m.y. by K-Ar (Barstovian), and all sedimentary strata are younger than an ash-flow sheet dated at 21.5 m.y. by K-Ar. An air-fall tuff in the upper part of the section has a K-Ar age of 4.3 m.y. Rocks of the Silver Peak volcanic center, 4.8 to 6.1 m.y. by K-Ar, crop out principally in the central part of the Silver Peak Range. Along the margins of the range, they overlie and interfinger with the various sedimentary sequences. The volcanic rocks are mostly rhyolite and trachyandesite tuffs and flows with subordinate basalts and andesites. Basin and Range faulting began in late early to middle Miocene time and has continued intermittently to the present, but present topography was largely established by late Pliocene time.

Abstract The Leadville district has yielded gold, silver, and base metals for more than 125 years, principally from dolostone-hosted massive sulfide replacement bodies (mantos). The carbonate host rocks were deposited on a Paleozoic shallow marine shelf overlying a Proterozoic (1.4 Ga) granitic basement, and subsequent diagenetic processes converted the shelf rocks to do-lostones. Multiple stages of dissolution with infilling generated paleokarst units within the uppermost dolostone, the Leadville Dolomite. The ore host rocks lie in the Mosquito Range on the eastern flank of the Laramide Sawatch uplift. Southwest-directed, east-dipping, low-augle thrust faults offset by high-angle reverse faults characterized the compressional environment in the Leadville district during the Laramide orogeny. The first Phanerozoic igneous eveut in the area, emplacement of the Pando Porphyry, occurred contemporaneously with low-angle thrusting. The Pando Porphyry was emplaced along thrust planes and along an unconformity at the top of the Leadville Dolomite. Six igneous events resulting in sills, dikes, and a small stock followed during Tertiary time, culminating with the emplacement of the Breece Hill stock in the eastern part of the Leadville district. All of the preore igneous rocks are latite to quartz monzonite in composition: Four genetic types of ore deposits are present within the Leadville district: (1) contact-related magnetite-serpeutine bodies, (2) dolostone-hosted barite-silver-minor base metal replacement and open-space filliugs termed “Sherman-type ore,” (3) dolostone-hosted zinc-lead-silver-gold massive sulfide replacement bodies with associated veins, referred tg as “Leadville-type ore,” and (4) placer gold. The contact-related magnetite-serpentine bodies replace dolostone aud formed during emplacement of the Breece Hill stock as well as locally around the margin of au older stock southeast of Breece Hill. These ores were used sporadically as smelting flux. The main Leadville district ore deposits are principally massive sulfide replacement bodies in dolostone, but there are related quartz-pyrite-gold veins, disseminated quartz-pyrite-gold in porphyry, and quartz-base metal veins. These are zoned spatially about the Breece Hill stock with central-most quartz-pyrite-gold veins and local disseminations surrounded by quartz-base metal veins and mautos. Mantos closer to Breece Hill have higher gold coutent (Ag/Au = 20), as do those localized along an east-dipping low-angle thrust fault west of Breece Hill; with increasing distance from Breece Hill silver/gold ratios of ores within mantos increase to>75. Manganese in gangue and alteration products increases away from the stock as well. Leadville orebodies in dolostone are dominated by pyrite with lesser marmatite, galena, chalcopyrite, tetrahedrite, pyrrhotite, marcasite, eleetrum, and late-stage veinlets with elevated silver, gold, bismuth, and tellurium contents. Late golden barite, dolomite, and rare fluorite are found in veinlets or vugs within ore. The sulfide coutent of ores in dolostone is>65 vol perceut. The ores are massive and commonly exhibit banding due to textural, size, or min-eralogical differences between bands. The bands parallel sedimentary layering or fracture ‘ planes cutting the dolostones. Diffusion-controlled replacement resulted in ores that locally exhibit concentric banding about unreplaced dolostone bodies, reflecting the stratigraphic and structural controls on ore fluid movement. Local sulfide replacement of paleokarst results in complete preservation of finely laminated cave fill with soft sediment impact features due to rock falls in the paleocaves; however, Leadville ores replaced principally massive dolostone with paleokarst localizing only miuor amouuts of ore. Hydrothermal alteration of the Breece Hill stock is extensive with both sericitic and argillic products common. Adjacent to veins and mantos more intense sericitic alteration is friuged by argillic and propylitic assemblages, extending as much as 100 m from ore. All assemblages contain abundant siderite or manganosiderite. The carbonate host rocks exhibit limited visible alteration exteuding uo more than 5 m from ore. Thermal effects on dolostone insoluble residue phyllosilicates is more extensive. Potassium-argon dates on sericite in Johnson Gulch Porphyry yield an average age on the Leadville ore event of 39.6 ± 1.7 Ma or early Oligocene. Fission-track dates on apatite and zircon from altered preore Johnson Gulch Porphyry indicate that cooling of the hydrothermal system occurred over a 6-m.y. period. The Leadville orebodies are cut by rhyolite porphyry dikes and plugs; these, in turn, have been broken by fragmental porphyry, a fluidized breccia system of tabular to irregular bodies around the perimeter of the Breece Hill stock. Late-stage quartz-base metal sulfide veins cut the fragmental porphyry and yield similar fluid inclusion data as found in the main Leadville-type orebodies. The rhyolite and fragmental porphyries were apparently derived from an intrusive system centered beneath the Breece Hill stock. As the fragmental porphyry bodies were emplaced, the downdropped block, a large triangular-shaped graben in the southeastern part of the district, subsided. Postmineral normal faulting (east side up) associated with development of tbe Rio Grande-Upper Arkansas rift exposed the ores in several blocks up the western flank of the Mosquito Range, leading to oxidation and supergene enrichment of the Leadville-type orebodies and the development of placer gold in California Gnlch, the site of initial discovery.

Abstract The characteristics of five explored hot spring systems are reviewed, focusing attention on features that may be preserved after the activity has ceased. Four systems, including the Upper Basin and Norris Basin of Yellowstone Park, Steamboat Springs, Nevada, and Wairakei, New Zealand have relatively high temperatures at the surface and at depth. They are volcanic in origin, deriving heat, much mineral matter, and part of their water from a volcanic source. Surficial acid leaching related to oxidation of H 2 S occurs above the water table in three of the four areas. Kaolinite and alunite are characteristic of mild acid alteration immediately below the water table, if the environment is favorable. Where acid alteration is absent, fresh rock may occur near the surface. Alteration minerals formed at depth include adularia, montmorillonite, illite, sericite, kaolinite, chlorite, pyrite, calcite, zeolites, and sodic plagioclase. All have been found at Steamboat Springs, most were described from the Upper Basin and Wairakei, but only a few occur at Norris. Tridymite and “orthoclase” (sandine), previously described in welded tuffs at Norris by Fenner, are related to pneumatolitic alteration when the tuffs were deposited, and are not related to present activity. Chalcedony, quartz, and calcite are typical vein minerals. Opal is dominant near the surface in sinter and in veins, but it seldom occurs below 100 feet. Where the temperature is much above 100° C., opal may form if deposition is sufficiently rapid, but it is generally converted to chalcedony. Cinnabar and stibnite occur at Steamboat and orpiment and realgar in Norris Basin, restricted to shallow depths. Sinter at Steamboat and Wairakei contains gold and silver. In many respects, the four high-temperature spring systems are similar to epithermal gold-silver deposits. The fifth explored system, Sulphur Bank, California, is the only one that has been mined extensively for its metal content, having produced 126,000 flasks of quicksilver. Rock alteration and present temperatures differ notably from the other systems. Most alteration is of the superficial acid type but some replacement calcite, pyrite, and argillic minerals occur in deeper workings. Cinnabar and opal are intimately associated and persist to depths of at least 260 feet, probably because temperatures of the past and present are relatively low. The water as well as the quicksilver may be derived from sedimentary rather than volcanic rocks. The near-surface activity of the spring systems is dependent on many factors, including structure, topography, ground-water relations, compositions of the waters, temperature relations, and rates of discharge. The waters of all five hot spring systems are believed to be near-neutral at depth, but those of the Upper Basin are somewhat more alkaline than the others. The possible existence of deep acid water in Norris Basin is also recognized. As the near-neutral waters approach the surface they may become more alkaline because of boiling and relative loss of CO 2 , or under favorable conditions, more acid because of surficial oxidation of H 2 S. Thermal springs may form siliceous sinter, travertine, other special types of deposits, or no significant deposit at all. Four of the five well-explored systems are of the high temperature, sinter-depositing type. Most other types, unfortunately, have not been explored at depth, or the associated vein and alteration minerals have not been studied. Nearly all epithermal ore deposits that show a relatively close relationship to thermal springs fall into four major groups: Quicksilver (and antimony), manganese (and tungsten), gold-silver, and fluorite. A significant number of quicksilver deposits are associated with thermal springs, and some others are characterized by abnormally high temperatures and gases (principally CO 2 and CH 4 ). Some quicksilver has probably been derived from a volcanic source but much may have come from sedimentary rocks, with connate water as the transporting agent. Some manganese deposits are clearly of hot-spring origin, and a few contain notable tungsten. Most bedded deposits in marine and non-marine sediments overlie basic and intermediate volcanic rocks that have been altered or albitized. The volcanic rocks appear to be the source of the manganese, which was probably transported by circulating ocean water or saline meteoric water of the non-marine sedimentary basins. Silver and gold deposits of the epithermal type appear to be closely related to the high-temperature volcanic hot springs; mineralogy of the veins and altered rocks are strikingly similar except for the scarcity of precious metals in Quaternary hot springs systems. Fluorite deposits are not well known but they may be related to travertine-depositing spring waters that contain volcanic components, and have also been influenced by contact with carbonate rocks. In summary, some ore epithermal deposits were formed by solutions closely related to volcanism, but others were probably deposited from circulating meteoric and connate waters. Much additional study is needed, particularly concerning criteria that distinguish waters of different origin.

Abstract The year 1895 marked a climax in the Penrose career. In January he reached the peak of his academic life, when a letter from William R. Harper, president of the University of Chicago, notified him that he had been promoted to a full professorship in economic geology in that institution. In December, the partners, Penrose and Barringer, together with John M. Brock-man began mining operations at what later became Pearce, Arizona, and Penrose was elected president of the company, known as the Common-Wealth Mining and Milling Company, which mined gold and silver in Cochise County, some 25 miles from the old town of Tombstone.Barringer had known Brockman as far back as the fall of 1891, and perhaps even earlier. In a report which Barringer made for Henry C. Butcher, of Philadelphia, dated September 18, 1891, he says, “As prearranged, I met Mr. R. L. Heflin at Deming, and with him went to Silver City, eight or nine miles south east of which the mine is situated. In company with Mr. Heflin and Mr. John Brockman, I spent three days upon the property and in the immediate neighborhood of the same.” He speaks of the exploratory work having been done by Heflin and Brockman, and in conclusion recommends the purchase of the property. This may, or may not, have been Barringer’s introduction to Brockman. In any event, Penrose was in Silver City in March and April of the following year and undoubtedly saw Brockman at that time, if not before.

ABSTRACT Riverfront Park in Spokane, Washington, USA, hosts a wide range of sites that highlight the interplay between prominent geologic features and the cultural development of Spokane. Stops in this field guide illustrate such topics as the impacts of historic Silver Valley mining, extraordinary fluvial incisions in Miocene Columbia River Basalt Group flows, cataclysmic alterations to the Spokane River valley from Pleistocene megafloods, earthquake hazards, hydroelectric generation, stormwater management solutions, and fascinating historical tidbits. Human interactions with the land began with the Interior Salish-speaking tribes, who have inhabited this region for thousands of years and historically gathered at the falls to fish. After European American influx, the Spokane River has been harnessed for many uses, including mills, water supply, irrigation, flood control, and hydropower. Today, Riverfront Park is the core of downtown Spokane, providing community access to the river and the largest urban waterfall in the United States.