Mineral association and mechanism of mineral precipitation of Lianzigou gold_telluride deposit in Xiaoqinling gold orefield,Shaanxi Province
WANG Lei;LIU JiaJun;ZHU WenBing;DAI HongZhang;LIU ChongHao;LIU HuaNan;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences;School of the Earth Sciences and Resources,China University of Geosciences;
The Lianzigou gold deposit is an important gold deposit in the Jialu gold orefield within the Xiaoqinling region.The deposit is hosted in the highly metamorphic gneiss which is the main rock type of the Qincanggou Formation of the Archean Taihua Group. Ores mainly occur as quartz_vein type. Detailed petrographic and electron microprobe analysis of ore minerals was carried out. Numerous tellurium minerals were identified,such as calaverite,krennerite,petzite,hessite,altaite,melonite and native tellurium. In addition,large amounts of native gold were recognized in the fractures in quartz and pyrite,coexisting with sulfides and tellurides. Physicochemical phase diagrams were established according to mineral assemblages,temperature and pressure conditions of different metallogenic stages in this study. Physicochemical conditions for the formation of tellurides and other minerals are as follows: f( O_2) = 10~(-34.00)~ 10~(-31.00),f( H_2S) = 10~(-1.42)~ 10~(-0.9) and pH = 6 ~ 6. 8 for stage Ⅱ( 300℃),and f(S_2) =10~(-16.56)~ 10~(-12.30) and f(Te_2) = 10~(-13.70)~ 10~(-9.44) for stage Ⅲ( 200℃). Mineralogical investigation in this study indicates that tellurides formed later than sulfides,and high f(Te_2) values and f(Te_2) /f(S_2) ratios were the two key factors that controlled the precipitation of tellurides.