Mineralogy of Gold, Tellurides and Sulfides from Lianzigou Gold Deposits in the Xiaoqinling Region, Central China: Implications for Ore-Forming Conditions and Processes

The Lianzigou deposit, which has an Au-Te paragenetic association, is hosted in plagioclase gneiss of the Qincanggou Formation in the Taihua Group in the Xiaoqinling region, central China. This quartz vein-type Au deposit comprises native Au and a variety of tellurides. The latter include calaverite (AuTe2), krennerite (Au3AgTe8), petzite (Au3AgTe2), hessite (Ag2Te), melonite (NiTe2), and altaite (PbTe). Four stages have been recognized in this deposit: stage I consists of K-feldspar and quartz; stage II is of milky quartz veins accompanied by coarse-grained disseminated and lumps of pyrite with weak Au mineralization; stage III is composed mainly of Au, tellurides, and sulfides; and stage IV is characterized by abundant carbonate and quartz. Based on mineral assemblage and thermodynamic data, we estimated the physicochemical conditions of the main metallogenic stages. Based on thermodynamic modelling, the physicochemical conditions of Au-Ag-Te mineral associations were estimated. The Au-Ag-Te minerals from stage III formed mainly under conditions of logfO(2) = -43.15 to -33.31, logfH(2)S = similar to-9.29, pH < 7, logfTe(2) = -10.6 to -9.8 and log alpha Au+/alpha Ag+ = -7.2 to -6.5. In contrast, the physicochemical conditions of stage II were higher, specifically pH (8.3-8.5) and logfO(2) (-34.90-31.96). In the ore-forming fluids of the Lianzigou deposit, the dominant Au species was Au(HS)(2)(-) while the dominant Te species were HTe- (aq) and Te-2(2-) (aq). Moreover, the Au-Ag-Te metal associations in the Lianzigou Au deposit were derived from mantle materials related to lithospheric thinning of the eastern North China craton in the Early Cretaceous under an extensional tectonic system.