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ABSTRACT: Mineralogical and Genetic Features of Volcanic Gold-Silver Deposits of the Pacific Ore Belt

Ivan Y. Nekrasov

Five mineral types are distinguished among Au-Ag deposits of the volcanic formation common in Mexico, Peru, Philippines, China, South Korea, and the USSR: low-sulfide adularia-quartz, sulfide-sulfosalt, telluride, telluride-selenide, and cassiterite-telluride-selenide. In low-sulfide deposits, kustelite, electrum, and native gold accumulated Au and Ag, with subordinate role of acanthite and gold-silver sulfides (petrovskaite, aithenbogaardite, and penginite). These epithermal deposits are related to acidic subvolcanic rocks. In sulfide-sulfosalt deposits, genetically related to porphyry-dioritic extrusions, Au is associated with galena, sphalerite, chalcopyrite, and Ag, Pb, Sb, As, and Bi sulfosalts. They were formed at 150 to 200°C under high fS2 (10-4 to 10-7 Pa). Gold-telluride deposits are related to central-type volcanoes, cauldrons of which are filled with dacites and andesite-dacites, and have undergone alunitization and propylitization. About 30% Au is accumulated in tellurides, and 70% as native gold. Telluride-selenide minerals (goldfieldite, hessite, krennerite, sylvanite, and bohdanowiczite) were produced by polycomponental hydrothermal solutions of combined andesitic and rhyolitic complexes. Combined tin-gold-silver deposits are associated with polygenetic differentiated subvolcanic granitic intrusives. Differences in metallogenic specialization of Au-Ag deposits are due to the composition and inhomogeneity of crustal and mantle material producing melts, degree of their differentiation, and nat re of fluid regime.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990