矿床地球化学国家重点实验室知识库

The orogenic gold deposits in Southeast Guizhou are an important component of the Xuefeng polymetallic ore belt and have significant exploration potential, but geochronology research on these gold deposits is scarce. Therefore, the ore genetic models are poorly constrained and remain unclear. In the present study, two important deposits (Pingqiu and Jinjing) are investigated, including combined ReeOs dating and the HeeAr isotope study of auriferous arsenopyrites. It is found that the arsenopyrites from the Pingqiu gold deposit yielded an isochron age of 400
24 Ma, with an initial 187Os/188Os ratio of 1.24
0.57 (MSWD ¼ 0.96). An identical isochron age of 400
11 Ma with an initial 187Os/188Os ratio of 1.55
0.14 (MSWD ¼ 0.34) was obtained from the Jinjing deposit. These ages correspond to the regional Caledonian orogeny and are interpreted to represent the age of the main stage ore. Both initial 187Os ratios suggest that the Os was derived from crustal rocks. Combined with previous rare earth element (REE), trace elements, NdeSreSePb isotope studies on scheelite, inclusion fluids with other residues of gangue quartz, and sulfides from other gold deposits in the region, it is suggested that the ore metals from Pingqiu and Jinjing were sourced from the Xiajiang Group. The He and Ar isotopes of arsenopyrites are characterized by 3 He/4 He ratios ranging from 5.3 104 Ra to 2.5 102 Ra (Ra ¼ 1.4 106 , the 3 He/4 He ratio of air), 40Ar*/4 He ratios from 0.64 102 to 15.39 102 , and 40Ar/36Ar ratios from 633.2 to 6582.0. Those noble gas isotopic compositions of fluid inclusions also support a crustal source origin, evidenced by the Os isotope. Meanwhile, recent noble gas studies suggest that the amount of in situ radiogenic 4 He generated should not be ignored, even when Th and U are present at levels of only a few ppm in host minerals.