Mineralizations of Base Metal Deposits of Acid‐Sulfate Type Coexisting with Adularia‐Sericite Type

Abstract

Abstract: Two types of ores are recognized in the Huanzala mine, Peru. Zinc and lead ore of adularia‐sericite type, is accompanied by pyrite body and skarn. Orthoclase (adularia), sericite and calcite are found in the skarn and altered country rocks. On the other hand, copper and silver (tin) ore of acid‐sulfate type, is characterized by enargite, luzonite and bornite, accompanied by tin, silver and tellurium minerals. Although sericite and calcite are found only at the earlier stage in the mineralization of acid‐sulfate type, kaolinite appears in the country rocks at a subsequent stage. It is interpreted that the ore‐forming fluid of the acid‐sulfate type separated from the adularia‐sericite type by boiling in the early stage of mineralization. The separated fluid was nearly neutral just after boiling and changed into acidic by the oxidation of H2S into HSO4‐. Both types of mineralizations are studied in terms of fo2‐fs2‐pH‐temperature diagrams. The adularia‐sericite type might correspond to the hot‐water system of a geothermal area, and the acid‐sulfate type to the vapor‐dominated system.The copper ores from the Teine mine, Hokkaido, Japan and the Chinkuashih mine, Taiwan are acid‐sulfate type, characterized by the occurrence of enargite and luzonite. However, zinc and lead ores of the adularia‐sericite type are also present in these deposits. Both types in the Teine and Chinkuashih deposits are supposed to have formed in the similar relation as in the Huanzala deposits. The enargite and luzonite ores in the Hokuetsu mine, Japan are closely associated with native sulfur of solfataric origin.