Genesis of the gold deposits in the Kunlun River area, East Kunlun, Qinghai Province: Constraints from geology, fluid inclusions and isotopes

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

“…may continue to migrate upward, become a special ore-forming metamorphic fluid, and periodically deposit quartz veins within shallow subsidiary faults, likely because of a sudden change of physico-chemical conditions rather than strong water-rock reactions between ore-forming fluids and wall rocks. A similar filling mineralization of quartz veins in subsidiary faults could be found in other gold deposits, such as the Heicigou gold deposit [29] in the KLRA, and the Hongqigou gold deposit [18] in the MKL, etc. During the predominant filling of quartz veins in subsidiary faults in the Heihaibei gold deposit, minor water-rock interactions may also occur in the granitic wall rocks and contribute to weak hydrothermal alterations within brecciated granitic wall rocks, minor ores of stockwork quartz veinlets, or breccias in such altered granites.…”

“…In the KLHA, compared with the high and invariable δ 34 S values of sulfides for the Heihaibei gold deposit, the Dazaohuo gold deposit has more variable δ 34 S values of sulfides (Figure 8d, [29]), which are consistent with its phyllic rock-type ores, rather than the quartz 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.…”

“…Meanwhile, the Pb isotope compositions of sulfides in the Heihaibei gold deposit are also different from the Dazaohuo gold deposit, which has predominant phyllic rock ores [29] in the KLRA, or other gold deposits in the EKO (Figure 9a,b), also showing they have different Pb sources among them. The variable Pb isotope compositions in the Heihaibei gold deposit have more uranogenic and thorogenic Pb isotope compositions than other gold deposits, which have predominant phyllic rock ores, i.e., Shenshuitan [4,7,9], Guoluolongwa [16,17] in the MKL, and Kaihuangbei [20] in the SKL, also suggesting that Pb sources are distinctive for the Heihaibei gold deposit.…”

“…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.…”

“…Because the dominant ore types are auriferous quartz veins, it was thought that the Heihaibei gold deposit belongs to a hydrothermal-vein-type gold deposit [22], a magmatic hydrothermal gold deposit [24], or an orogenic gold deposit [25]. Based on the geological characteristics and a few stable isotope compositions, some other gold deposits in the KLRA such as the Heihainan, Heicigou, and Dazaohuo gold deposits were also considered to belong to orogenic gold deposits [28,29] or altered-rock-type gold deposits [30], and the ore-forming fluids and materials were derived predominantly from metamorphic water and wall rocks, respectively [28,29]. However, Yu et al (2022) argued that the Heihaibei gold deposit was a granitic intrusion-related gold deposit rather than an orogenic gold deposit, and the ore-forming fluids and materials were derived from a magmatic hydrothermal source that was closely related to the Heihaibei granites, according to their three sets of H, O, S, and Pb isotope compositions [23].…”