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  • 1990-1994  (1)
  • 1975-1979  (4)
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  • 1
    Digitale Medien
    Digitale Medien
    The Milluachaqui epithermal silver district of northern Peru (1977)
    Springer
    Mineralium deposita 12 (1977), S. 235-238 
    Details
    ISSN: 1432-1866
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract The mines in the Milluachaqui district, located near Salpo in the northern part of Peru, show a vertically zoned, epithermal silver-gold mineralization. Colonial production was obtained from oxidized, high-grade ores, consisting mostly of native silver and cerargyrite. More modern development exposed, from the top of ore shoots to their base, the "bonanza" ores (the pyrargyrite-polybasite-acanthite zone), silver-copper ores (the tetrahedrite zone), silver-lead ores (the galena-sphalerite zone), and the basal zone ores (the sphalerite zone). The ratio of gold to silver in the "bonanza" ores was about 1 to 100, by weight. Interpretation of mineralogical textures and the composition of minerals in the sulfide zone suggests that supergene movement and enrichment of silver at Milluachaqui was not a significant factor. Silver tended to be fixed in place during weathering as the chloride and native mineral. The "bonanza" ores are interpreted to be hypogene sulfide accumulations. These findings contrast to hypotheses proposed for some epithermal districts in the U.S. which assume supergene activity to have been significant in the accumulation of high grade, near-surface silver ores.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00206029
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Discussion for the manuscript of J. A. Noble: “Metallogenic provinces of the Cordillera of Western North and South America” Mineralium Deposita, volume 11, p. 219–233 (1976) (1977)
    Springer
    Mineralium deposita 12 (1977), S. 239-240 
    Details
    ISSN: 1432-1866
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00206030
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    The porphyry molybdenum deposit of Compaccha, Peru, and its geologic setting (1975)
    Springer
    Mineralium deposita 10 (1975), S. 141-151 
    Details
    ISSN: 1432-1866
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract Compaccha, in Peru, is a zoned molybdenum, copper, zinc, lead, antimonyarsenic district which has historically been important because of tungsten production derived from all zones. Wolframite, the principal tungsten mineral, is zoned compatibly with the sulfides. Manganese tungstate occurs in the molybdenum zone, while iron replaces the manganese increasingly importantly as distance is gained away from this zone. The alteration zoning in and around the molybdenum zone is typical of that of a porphyry copper deposit, in that fluorite, topaz or other fluorine rich silicates are not common. The molybdenum zone does include a porphyry molybdenum deposit, however, and this is characterized by intense silicification and quartz veining (stockworks). Within the area of the deposit, east of the coastal batholith, no Mesozoic arc type or basic volcanics can be inferred. A cratonic setting is postulated for the deposit.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00206529
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    The North Fork porphyry copper deposit of the Washington Cascades (1978)
    Springer
    Mineralium deposita 13 (1978), S. 191-199 
    Details
    ISSN: 1432-1866
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract The North Fork porphyry copper deposit in the Cascade volcanic arc of Washington displays copper mineralization confined to the potassic (biotite) and phyllic (sericite) alteration zones. No secondary potassium feldspars have been found in either alteration zone; moreover, chemical analyses indicate the potassic alteration zone contains a low K2O content. Argillic and propylitic zones are also recognized, but these are barren of hypogene copper mineralization. Biotite-chalcopyrite intergrowths in the deposit have been given a 9.9 K-Ar age. Thus it is not only one of the youngest deposits dated in the western Cordillera, but it is associated with a volcanic arc which has no current Benioff zone seismic array or accompanying trench. The deposit appears to have developed during the period when coupling of the North American and Juan de Fuca plates probably inhibited subduction under the Cascade volcanic arc.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00204642
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  • 5
    Digitale Medien
    Digitale Medien
    Relationship between low-grade gold disseminations and high-grade veins in the Quartz Mountain district, Oregon (1993)
    Springer
    Natural resources research 2 (1993), S. 284-291 
    Details
    ISSN: 1573-8981
    Schlagwort(e): Gold and mercury mineralization ; Epithermal veins ; Mineral exploration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract Gold and mercury mineralization related to epithermal hot springs occurs spatially associated with rhyolite dome complexes in the Quartz Mountain district, Lake County, Oregon. Drilling of over 800 holes from 1983 to 1991, mostly by Quartz Mountain Gold Corp., has resulted in a mineral inventory of at least 100,000,000 tons, averaging 0.0255 ounce gold per ton in two near-surface, disseminated gold ore bodies, Quartz Butte and Crone Hill. Extensive gold disseminations are underlain by and include rare, higher-grade veins that could be feeders for the near-surface, quasi-horizontal, pervasively mineralized gold dissemination. The veins contain about 2,000,000 tons of ore, aver-aging 0.29 ounce gold per ton. Approximately 750,000 tons of this underlie Quartz Butte, and the remainder is included in the Crone Hill low-grade dissemination. With a mineral inventory of about 3,000,000 ounces, Quartz Mountain is currently the largest known gold deposit in Oregon. As now known, the veins seem too few in number and too sporadically positioned to account for the volume of near-surface gold disseminations. We offer hypotheses to explain the apparent anomaly between the volume of disseminated gold ore and the paucity of feeders. Quartz Mountain has numerous alteration and mineralization similarities with the well-studied Steamboat Springs district (White and others, 1964). Coincidences between the two districts are noted.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02257539
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