Age and metal source of orogenic gold deposits in Southeast Guizhou Province, China: Constraints from Re-Os and He-Ar isotopic evidence

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 Re-Os dating and the He-Ar 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 Os-187/Os-188 ratio of 1.24 +/- 0.57 (MSWD = 0.96). An identical isochron age of 400 +/- 11 Ma with an initial (18)7Os/Os-188 ratio of 1.55 +/- 0.14 (MSWD = 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 Os-187 ratios suggest that the Os was derived from crustal rocks. Combined with previous rare earth element (REE), trace elements, Nd-Sr-S-Pb 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 He-3/He-4 ratios ranging from 5.3 x 10(-4) Ra to 2.5 x 10(-2) Ra (Ra = 1.4 x 10(-6), the He-3/He-4 ratio of air), Ar-40*/He-4 ratios from 0.64 x 10(-2) to 15.39 x 10(-2), and Ar-40/Ar-36 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 He-4 generated should not be ignored, even when Th and U are present at levels of only a few ppm in host minerals. (C) 2018, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND licens