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Electrum showing crystal outlines associated with quartz and sulphides. The argentite was very probably formed by the replacement of galena, but all the other minerals are believed to be alpha hypo gene. Photomicrograph of polished surface of ore from 1,260- foot level, Murray vein, Tonopah Extension mine. Nye County, Nevada. 1915. Plate 5- B, with graphics, in U.S. Geological Survey. Professional paper 104. 1918.
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Album caption and index card: Photomicrograph of gold-tungsten ore from Keklonga mine, Magnolia district. Sylvanite (s) in vuggy quartz (q3) which contains a little pyrite (py). Quartz (q3) and ferberite (fe) cut in early quartz. Boulder County, Colorado. Notes: Published as figure LXXIV-B in U.S.Geological Survey. Professional Paper 223. 1950.
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Photomicrograph of vein rock shown in photo 37, with plain light, showing orthoclase, or, fractured and veined by quartz q. Bartow County, Georgia. Circa 1944. Plate 12-C, in U.S.Geological Survey Professional paper 224. 1950.
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Irregular intergrowth of polybasite, probably alpha hypo gene, with quartz and pyrite; photomicrograph of polished surface of ore just above 500-foot level, West End vein, West End mine. Nye County, Nevada. 1915. Plate 4-A, with graphics, in U.S. Geological Survey. Professional paper 104. 1918.
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Photomicrograph of polished sections of ore: subgraphic pattern of calaverite and sylvanite in hessite, Calaverite, sylvanite and hessite. These textures may indicate replacement of hessite by gold tellurides, but owing to its rarity, such replacement is not believed to be important in La Plata ores. Reflected light 250 x. Gold King mine. Photo by F.W. Galbraith. La Plata County, Colorado. Circa 1936. Plate 10-C, in U.S.Geological Survey Professional paper 219. 1949.
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Album caption and index card: Photomicrograph of gold-tungsten ore from west end of 280-foot level of Keklonga mine, Magnolia district. Sylvanite (s) in crustified quartz (q₁ and q₂) associated with early coarse-grained ferberite. Fine-grained ferberite with a little quartz lies on the earlier quartz and is in turn incrusted and veined by late quartz (q3) containing some ferberite of three generations (f1, f2, and f3). py, Pyrite. Boulder County, Colorado. Notes: Published as figure LXXIV-A in U.S.Geological Survey. Professional Paper 223. 1950.
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Photomicrograph of andesine-augite gneiss, showing texture of the rock and association of minerals; the andesine shows strong twinning. Other minerals are augite, a, marginally altered to uralite; biotite, b; orthoclase, o; black areas are ilmenite. Crossed nicols. Bartow County, Georgia. Circa 1944. Plate 6-D, in U.S.Geological Survey Professional paper 224. 1950.
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Photomicrograph of polished sections of ore: hypogene chalcopyrite replaced by supergene bornite; Chalcopyrite, bornite; reflected light 175 x.
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Sphalerite traversed by minute veinlets of chalcopyrite and polybasite; some of the veinlets in sphalerite are continuous with areas of the same minerals replacing galena this feature does not show in the picture. The veinlets are in the main formed by replacement, though possibly in small part fracture fillings. Photomicrograph of polished surface of ore from hanging-wall branch of Belmont vein, 1,200-foot level, Tonopah-Belmont mine. Nye County, Nevada. 1915. Plate 8-A, with graphics, in U.S. Geological Survey. Professional paper 104. 1918.
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Possible presence of hydrocarbons (?) in Nanushuk Group rocks. Migration apparently occurred during or after compaction of the sandstones. Possible hydrocarbon (?) migration is facilitated along solution seams probably formed during compaction. Sample 78ACh34, Marmot syncline; magnification, 2.5 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 51A in U.S. Geological Survey. Bulletin 1614. 1985.
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Photomicrograph of polished sections of ore: subgraphic pattern of calaverite and sylvanite in hessite, Calaverite, sylvanite and hessite. These textures may indicate replacement of hessite by gold tellurides, but owing to its rarity, such replacement is not believed to be important in La Plata ores. Reflected light 250 x. Gold King mine. Photo by F.W. Galbraith. La Plata County, Colorado. Circa 1936. Plate 10-D, in U.S.Geological Survey Professional paper 219. 1949.
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Partial replacement of galena by fine aggregate of a light-colored carbonate, argentite and some chalcopyrite; there has been a slight replacement of the quartz. Photomicrograph of polished surface of ore from Favorite vein, Tonopah-Belmont mine, depth uncertain. Nye County, Nevada. 1915. Plate 9-A in U.S. Geological Survey. Professional paper 104. 1918.
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Peripheral replacement of galena by an association of argentite and electrum (stippled); note the smoothness of the galena border in passing from contact with argentite to contact with electrum. Photomicrograph of polished surface of ore from 1,250-foot level Murray vein, Tonopah Extension mine. Nye County, Nevada. 1915. Plate 9-B in U.S. Geological Survey. Professional paper 104. 1918.
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Replacement of galena by polybasite; between these two minerals occur narrow bands of an unidentified transition mineral (not visible in the picture), and the very narrow light colored bands that mark the initiation of the replacement process along the contacts between galena crystals consist of this mineral. Photomicrograph of polished surface of ore from Favorite vein, Tonopah-Belmont mine, depth uncertain. Nye County, Nevada. 1915. Plate 7-B, with graphics, in U.S. Geological Survey. Professional paper 104. 1918.
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Possible presence of hydrocarbons (?) in Nanushuk Group rocks. Migration apparently occurred during or after compaction of the sandstones. Possible hydrocarbon (?) migration into intergranular pore spaces and into a grain cracked by compaction. Dissolution pore (P) unfilled by hydrocarbon indicates that migration may have occurred prior to creation of dissolution porosity. Sample 78ACh25, Marmot syncline; magnification, 2.5 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 51B in U.S. Geoloqical Survey. Bulletin 1614. 1985.
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Photomicrograph of vein rock shown in photo 37, with crossed nicols, showing strain twinning in orthoclase and strain shadows in quartz. Bartow County, Georgia. Circa 1944. Plate 12-D, in U.S.Geological Survey Professional paper 224. 1950.
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Polybasite (light gray) with bladelike outlines, inclosed by pyrargyrite (white); the dark gray is quartz. The polybasite has been made visible by brief treatment with mercuric chloride solution. Photomicrograph of polished surface of ore, Tonopah Extension mine, exact location uncertain. Nye County, Nevada. 1915. Plate 4-B in U.S. Geological Survey. Professional paper 104. 1918.
    map background search result map search result map Gold-tungsten ore from west end of 280-foot level of Keklonga mine. Boulder County, Colorado. 1932. Photomicrograph of gold-tungsten ore from Keklonga mine. Boulder County, Colorado. 1932. Gold-tungsten ore from west end of 280-foot level of Keklonga mine. Boulder County, Colorado. 1932. Photomicrograph of gold-tungsten ore from Keklonga mine. Boulder County, Colorado. 1932.