The Carlin-type gold deposits of the “golden triangle” of SW China: Pb and S isotopic constraints for the ore genesis

Abstract

The Yunnan–Guizhou–Guangxi “golden triangle” is considered as one of the important regions for Carlin-type (or Carlin-like) gold deposits in China. Gold deposits in this region can be grouped into lode type controlled by faults and layer-like type controlled by host strata. Arsenopyrite is one of the major gold-bearing minerals in these deposits. Here we report the S and Pb isotopic composition of arsenopyrites from the fault-controlled Lannigou and Jinya gold deposits and the stratabound Shuiyindong gold deposits, with a view to trace the sources of sulfur and lead, and to evaluate the genetic aspects of gold mineralization. The average δ34S values of arsenopyrites are 11.7‰ for Lannigou, 6.7‰ for Shuiyindong and −5.3‰ for Jinya, which are slightly lower to that of diagenetic pyrite in the host rocks of each deposit. The δ34S values of arsenopyrites show significant variation among the different deposits (−9.0‰ to +17.1‰), which indicate a sedimentary origin for sulfur, followed by local fluid–rock interaction. The Pb isotopic composition of arsenopyrites from these deposits shows a narrow range (206Pb/204Pb=18.494–18.813, 207Pb/204Pb=15.630–15.748, 208Pb/204Pb=38.559–38.884), indicating that the different deposits have the same source of lead. Based on a comparison with Pb isotopic ratios of diagenetic pyrite, arsenopyrite and Late Cretaceous magmatic rocks from this region reported in previous studies, we infer that the lead was sourced from the sediments rather than from magmatic intrusions. The formation of the Carlin-type gold deposits are therefore correlated with the evolution of the Youjiang basin from rifting to closure, and involved four distinct stages leading to the concentration of the gold ores.