Diagnostic Genesis Features of Au-Ag Selenide-Telluride Mineralization of Western Java Deposits

Abstract

-The ore mineralogy of the westernmost part of West Java such as Pongkor, Cibaliung, Cikidang, Cikotok, and Cirotan are characterized by the dominance of silver-arsenic-antimony sulfosalt with silver selenides and rarely tellurides over the argentite, whereas the eastern part of West Java including Arinem and Cineam deposits are dominated by silver-gold tellurides. Mineralogy of Se-type deposits at Pongkor, Cikidang, Cibaliung, Cisungsang, and Cirotan and Te-type deposits at Arinem and Cineam shows their different geochemical characteristics. Mineralogical and geochemical differences can be explained by variation of physico-chemical conditions that existed during gold-silver deposition by applying the phase relation among sulfide, telluride, and selenide mineral association in the deposits. The relative values of ƒSe 2(g) , ƒTe (g) , and ƒS 2(g) control the actual presence of selenide or telluride minerals within the West Java deposits, which also depend on their concentrations in the hydrothermal fluid. Even though the concentration of selenium in the hydrothermal fluid of Te-type deposits might have been similar or even higher than that in the Se-type, early substitution of selenium in the sulfide minerals prevents its concentration in the hydrothermal fluid to the levels for precipitating selenide minerals. Therefore, early sulfide mineral deposition from reduction fluids will not increase the ƒSe 2(g) /ƒS 2(g) ratio to form selenide minerals in Te-type deposits of Arinem and Cineam, other than selenium-bearing sulfide mineral such as Se-bearing galena or Se-bearing pyrargyrite-proustite.

Conditions of formation of Au–Se–Te mineralization in the Gaching ore occurrence (Maletoyvayam ore field), Kamchatka, Russia

“…The formation of selenide minerals (AuSe) is only possible in solution with extremely high / ratios so some transition metal may form selenide minerals. Oxidation-reduction conditions are important controls on the presence of selenide minerals as well as the relative values of , and Reducing conditions will not lead to an increase in selenium activity and Se/S ratios to form selenide minerals (Yuningsih et al , 2016). Twenty two kinds of complexes of Au with oxygen, sulfur and tellurium are known in the oxygen–sulfur–selenium–tellurium group system, but the complexing of Au with Se has not been previously reported (Liu et al ., 2000).…”

Auroselenide, AuSe, a new mineral from Maletoyvayam deposit, Kamchatka peninsula, Russia

“…The primary source of organic compounds and selenium could be bacteria and algae that were modified into organic matter of low maturity and then saturated the ore-forming fluids in Se and Au. The crystallisation of selenides is regulated by the H 2 Se/H 2 S ratio or at very high ratios of f Se 2 / f S 2 in aqueous fluids (Hustor et al , 1995; Yuningsih et al , 2016; Tolstykh et al , 2018). If this ratio is low, selenium enters sulfides as an isomorphic impurity replacing sulfur in minerals.…”

Au-Ag-Se-Te-S Mineralization in the Maletoyvayam High-Sulfidation Epithermal Deposit, Kamchatka Peninsula

“…Selenium minerals may be found in sandstones, skarn, uranium deposits, and at epithermal deposits, where Se-rich parageneses occur in association with Te-rich minerals. However, tellurium and selenium do not form mixtures or compounds, due to the fact that the geochemical behavior of tellurium and selenium is different [17]. In nature, tellurides are more common than selenides, with the former tending to produce its own minerals in epithermal deposits, owing to its incompatibility with selenium in the structure of minerals.…”

“…They require a highly oxidizing environment with a high pH to form, which is controlled by the H 2 Se/H 2 S ratio in aqueous fluids [17][18][19]. A substantial increase of these ratios contributes to the successive substitution of Au-S by Au-Se complexes [20].…”

“…Recently obtained mineralogical data also revealed the presence of an Ag-bearing association, in a few samples, in addition to the Au-rich (Ag-free) assemblage. Hence, the aim of this study is to reveal the correlation of Au/Ag and Se/S ratios in mineral parageneses, due to the fact that selenium activity increases when the acidity of solutions is increased [17][18][19]. Furthermore, a detailed description of the reference mineralogical collection of the Maletoyvayam deposit (Gaching occurrence), characterizing the products of acidic hydrothermal solutions, is also of great scientific importance to understand the ore genesis of epithermal deposits.…”