Epithermal Gold‐Silver Mineralization of the Asachinskoe Deposit in South Kamchatka, Russia

Abstract

The Asachinskoe epithermal Au-Ag deposit is a representative low-sulfi dation type of deposit in Kamchatka, Russia. In the Asachinskoe deposit there are approximately 40 mineralized veins mainly hosted by daciteandesite stock intrusions of Miocene -Pliocene age. The veins are emplaced in tensional cracks with a north orientation. Wall-rock alteration at the bonanza level (170 -200 m a.s.l.) consists of the mineral assemblage of quartz, pyrite, albite, illite and trace amounts of smectite. Mineralized veins are well banded with quartz, adularia and minor illite. Mineralization stages in the main zone are divided into stages I -IV. Stage I is relatively barren quartz -adularia association formed at 4.7 ± 0.2 Ma (K-Ar age). Stage II consists of abundant illite, Cu-bearing cryptomelane and other manganese oxides and hydroxides, electrum, argentite, quartz, adularia and minor rhodochrosite and calcite. Stage III, the main stage of gold mineralization (4.5 -4.4 ± 0.1 -3.1 ± 0.1 Ma, K-Ar age), consists of a large amount of electrum, naumannite and Se-bearing polybasite with quartz -adularia association. Stage IV is characterized by hydrothermal breccia, where electrum, tetrahedrite and secondary covellite occur with quartz, adularia and illite. The concentration of Au+Ag in ores has a positive correlation with the content of K 2 O + Al 2 O 3 , which is controlled by the presence of adularia and minor illite, and both Hg and Au also have positive correlations with the light rare-earth elements. Fluid inclusion studies indicate a salinity of 1.0 -2.6 wt% NaCl equivalent for the whole deposit, and ore-forming temperatures are estimated as approximately 160 -190°C in stage III of the present 218 m a.s.l . and 170 -180°C in stage IV of 200 m a.s.l. The depth of ore formation is estimated to be 90 -400 m from the paleo-water table for stage IV of 200 m a.s.l., if a hydrostatic condition is assumed. An increase of salinity ( ⌬ C NaCl ≈ 0.2 wt%) and decrease of temperature ( ⌬ T ≈ 30°C) within a 115-m vertical interval for the ascending hydrothermal solution is calculated, which is interpreted as due to steam loss during fl uid boiling. Ranges of selenium and sulfur fugacities are estimated to be log f Se 2 = −17 to −14.5 and log f S 2 = −15 to −12 for the ore-forming solution that was responsible for Au-Ag-Se precipitation in stage III of 200 m a.s.l. Separation of Se from S-Se complex in the solution and its partition into selenides could be due to a relatively oxidizing condition. The precipitation of Au-Ag-Se was caused by boiling in stage III, and the precipitation of Au-Ag-Cu was caused by sudden decompression and boiling in stage IV.

Ore‐forming Ages and Sulfur Isotope Study of Hydrothermal Deposits in Kamchatka, Russia

“…The Nokleberg et al (1997a, b); Ispolatov et al (2004); Kirmasov et al (2004);Solov'ev et al (2006). Ore-forming ages are from Takahashi et al (2002Takahashi et al ( , 2006Takahashi et al ( , 2007; Okrugin et al (2007a, b, c) and this study. CKY: Central Koryak, CK: Central Kamchatka, and EK: East Kamchatka metallogenic belts (Nokleberg et al, 2005).…”

“…Nokleberg et al (2005) summarized the mineralogical description of ore deposits in Kamchatka, and then categorized the Cenozoic hydrothermal deposits into the Central Koryak, Central Kamchatka, and East Kamchatka metallogenic belts. Ore-forming ages and physicochemical conditions for the epithermal ore deposits in East and Central Kamchatka belts have been reported by Takahashi et al (2002Takahashi et al ( , 2004Takahashi et al ( , 2006Takahashi et al ( , 2007 and Okrugin et al (2007a, b, c), respectively. These age data are summarized as Pliocene to Pleistocene in the East Kamchatka belt (Rodnikovoe, Mutnovskoe and Asachinskoe ore deposits), and Miocene (Zolotoe, Ostantsovoe and Aginskoe) and Pliocene to Pleistocene (Baranievskoe) in the Central Kamchatka metallogenic belt.…”

“…Ore forming ages of hydrothermal deposits in Kamchatka had been reported in previous studies; c. 20.4 Ma for the Zolotoe deposits (Okrugin et al ., 2007a), c. 8.9 Ma for the Ostantsovoe prospect (Okrugin et al ., 2007b), and c. 2.9–2.4 Ma for the Baranievskoe deposit (Okrugin et al ., 2007c) in the Central Kamchatka metallogenic belt; and 4.7–3.1 Ma for the Asachinskoe deposit (Takahashi et al ., ), 1.1–0.9 Ma for the Rodnikovoe deposit (Takahashi et al ., ), and 1.3 and 0.7 Ma for the Mutnovskoe deposit (Takahashi et al ., ) in the East Kamchatka metallogenic belt (Figs , ).…”

“…Ore‐forming ages and physicochemical conditions for the epithermal ore deposits in East and Central Kamchatka belts have been reported by Takahashi et al . (, , , ) and Okrugin et al . (2007a, b, c), respectively.…”

Geochemistry and Fluid Inclusions Analysis of Vein Quartz in the Multiple Hydrothermal Systems of Mankayan Mineral District, Philippines

“…a) indicate the correlation of Al 3+ substitution to Si 4+ and the incorporation of K + as charge compensators (e.g. Takahashi et al, ). In Carmen, the porphyry‐type stockwork veinlet quartz (030817‐04C) and the epithermal‐type vein quartz (030817‐04A and 0308‐17‐04B) show a slight deviation from linearity, which may indicate that other cations are present as substitute or charge compensators.…”