Isotope Geochemistry of the Shenshuitan Gold Deposit within the Wulonggou Gold Field in the Eastern Kunlun Orogen, Northwest China: Implications for Metallogeny

Abstract

The Shenshuitan gold deposit is located within the Eastern Kunlun Orogen in northwest China. The gold mineralization here occurs primarily within the ductile fault XI. The sulfide mineral assemblage is dominated by pyrite and arsenopyrite, with minor pyrrhotite, chalcopyrite, galena, and sphalerite. Host rocks predominantly consist of Ordovician silicic slate and late Silurian granites, and their alterations include silicification and sericitization. The measured δD and δ18O values of quartz and sericite range from −113.9‰ to −93.1‰ and from 4.6‰ to 12.0‰, respectively. Bulk and in situ δ34S values of sulfides range from −7.3‰ to +9.6‰ and from −3.92‰ to 11.04‰, respectively. Lead isotope compositions of sulfides show 206Pb/204Pb ratios from 18.071 to 19.341, 207Pb/204Pb ratios from 15.530 to 15.67, and 208Pb/204Pb ratios from 37.908 to 38.702. Collectively, the isotope (H, O, S, and Pb) geochemistry suggests that the ore-forming fluids were of a metamorphic origin mixed with meteoric water and that the sulfur and lead were sourced from a mixture of host rocks and original ore-forming metamorphic fluids. Lastly, this deposit can be classified as an orogenic gold deposit associated with the final collision between the Bayan Har–Songpanganzi Terrane and the Eastern Kunlun Orogen during the Later Triassic.

Isotope Geochemistry of the Heihaibei Gold Deposit within the Kunlun River Area in the Eastern Kunlun Orogen in Northwest China and Its Metallogenic Implications

“…The Dazaohuo and Heicigou gold deposits in KLRA have relatively different H and O isotope compositions compared to each other [29], and both are totally different from those of the Heihaibei gold deposit (Figure 7a), suggesting a different source of ore-forming fluids for these gold deposits in the KLHA. However, other gold deposits, i.e., Shenshuitan [4,[8][9][10], Guoluolongwa [19] in the MKL, and Kaihuangbei [14] in the SKL, in which there are both quartz veins and phyllic rock-type ores, have relatively variable H and O isotope compositions relative to gold deposits which have predominant quartz vein ores, such as the Heihaibei gold deposit (this study), as well as the Hongqigou gold deposit [60], perhaps due to higher degrees of water-rock reaction/mixing, and more meteoric water mixing during their mineralization. By the way, the H and O isotope compositions (Figure 7b) for sample K1 are slightly different from other ore samples, perhaps because sample K1 (Qv1 plus Heihaibei granitic wall rock) had experienced a greater extent of water-rock reaction than ore samples in the QV1 or QV2 veins.…”

“…As we know, an apparent water-rock reaction which formed phyllic rock-type ores and related hydrothermal alterations possibly resulted in widespread sulfur mixing and exchange, as well as sulfur isotope fractionations in different ores. Therefore, other gold deposits which have predominant phyllic rock-type-ores, i.e., Shenshuitan [4,7,8,15,16], Guoluolongwa [15][16][17] in the MKL, and Kaihuangbei [20] in the SKL, likely have more variable δ 34 S values of sulfides than those in the Heihaibei gold deposit (Figure 8d). Additionally, the Hongqigou gold deposit, which has predominant quartz vein ores, has relatively invariable heavy δ 34 S values of sulfides that are similar to this study, indicating an original metamorphic S-bearing fluid [4].…”

“…Therefore, other gold deposits which have predominant phyllic rock-type-ores, i.e., Shenshuitan [4,7,8,15,16], Guoluolongwa [15][16][17] in the MKL, and Kaihuangbei [20] in the SKL, likely have more variable δ 34 S values of sulfides than those in the Heihaibei gold deposit (Figure 8d). Additionally, the Hongqigou gold deposit, which has predominant quartz vein ores, has relatively invariable heavy δ 34 S values of sulfides that are similar to this study, indicating an original metamorphic S-bearing fluid [4]. So, once more, the relatively high and invariable δ 34 S values of sulfides suggest that the sulfur source is derived directly from a deep metamorphic origin itself, which is consistent with the filling mineralization by the quartz vein, rather than an apparent water-rock reaction.…”

“…The EKO, which is bounded by the Qaidam block (QDM) on the north and the Bayan Har-Songpanganzi Terrane (BH-SG) on the south, is usually considered to be composed of three sub-parallel tectonic belts from north to south, the North Kunlun belt (NKL), the Middle Kunlun belt (MKL), and the South Kunlun belt (SKL), separated by the North Kunlun fault (N. KLF), the Middle Kunlun fault (M. KLF), and the South Kunlun-Aryan Maqin fault (S. KLF-AMF), respectively [3]. Since 1999, numerous ore prospecting projects within the EKO have been deployed by the China Geology Survey [4]. So far, the EKO has become an important ore belt in which ca.…”

“…26 of them have become different sizes of mineral deposits in the EKO and the adjacent BH-SG (Figure 1b) [5,6]. Especially, the EKO hosts numerous gold deposits, as best represented by those in the Wulonggou gold field [4,[7][8][9][10][11][12][13], Gouli gold field [14][15][16][17][18][19], and Kaihuangbei gold field [14,20]. [21]; (b) schematic geological map of the EKO, simplified and modified after [2].…”