Sr and Pb isotopic feature and ore-forming material source of the Yangshan gold deposit.

The Yangshan gold deposit, located in the western Qinling Orogen, is the largest Carlin-like or Carlin gold deposit in China. Given that the ores resulted from interaction between host-rocks and ore-fluids, this paper reports Sr and Ph isotopic composition of ore-hosting strata, magmatites and ores as well as the Bikou Group of the Bikou terrane to constrain sources of ore-forming material and fluid. I-Sr ratios of sulfides, ore-hosting Sanhekou Group, Mesozoic granite porphyry and the Bikou Group are 0.70798 similar to 0.71697, 0.71382 similar to 0.72005, 0.70918 similar to 0.71168 and 0.70344 similar to 0.71009, respectively. This indicates that the initial ore-fluids should have I-Sr ratios lower than those of sulfides, ore-hosting Sanhekou Group and Mesozoic granite porphyry, and must be originated from metamorphic devolatilization of the Bikou Group. The ore-fluid increased its 1, values during its upward migration due to the interaction with high-Is, ore-hosting strata. This causes higher I-Sr values of most sulfides than those of the Mesozoic granite porphyry. Sulfides yield wider variation ranges of Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-208 ratios (17.552 similar to 18.759, 15.576 similar to 15.928 and 37.894 similar to 39.293, respectively) than those of both the ore-hosting strata and granite porphyry, but similar to those of the Bikou Group. This suggests that the Pb-isotope signatures of sulfides are mainly inherited from the Bikou Group and the ore-forming elements were partly originated from the Bikou Group. Hence, it is reasonable to Suggest the Bikou Group as an indispensable source to provide ore-forming elements and fluids for the Yangshan giant gold system. In Mesozoic, the Bikou Group was northwardly underthrust along the Mian-Lue suture, metamorphosed and devolatilized beneath the Yangshan ore-field and, thereby the ore-fluid were generated and migrated upwards, providing ore-metals, fluids and beat for the Yangshan gold-mineralizing system.