A magmatic‐hydrothermal origin of the Xinfang gold deposit, Liaodong Peninsula, China, revealed by in‐situ S–Pb isotopes and trace element analyses of pyrite

Abstract

The Xinfang deposit is a large gold deposit (>20 t of Au) on the southern edge of the Liaodong Peninsula, China. A total of 37 gold‐bearing orebodies are identified along NS‐ and NW‐striking faults and are mainly hosted by the Archean and Neoproterozoic metamorphic rocks. Three stages of hydrothermal mineralization are distinguished, including Stage I of dominant quartz ± pyrite (Py1), Stage II of quartz‐polymetallic sulfide (Py2), and Stage III of quartz‐calcite ± pyrite (Py3). Gold primarily occurs at the Stage II in association with intensive silicification, pyritization, and sericitization. Here, we report on high‐precision in‐situ LA‐MC‐ICP‐MS analyses of S and Pb isotopic compositions of the sulfide minerals and LA‐ICP‐MS analyses of trace element signature of the pyrite from the Xinfang gold deposit. The δ34S values of the sulfides range from 1.3 to 5.3‰, which is consistent with a magmatic origin of S. The sulfides yield 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb ratios of 37.497–37.773, 15.323–15.410, and 17.004–17.229, respectively, which deviate from the values of the wall rocks, suggesting an external Pb source. The in‐situ LA‐ICP‐MS spot analyses of the pyrite reveals that gold occurs in two generations of pyrite (Py2 and Py3) but at low concentrations (≤0.06 ppm for Py2, ≤0.24 ppm for Py3). Visible gold, however, only occurs in the Stage II assemblage as inclusions in pyrite and quartz, and is distributed along the margins or within the fractures of the sulfides. The Py2 shows high Co, Ni, and As concentrations and is depleted in other trace elements typical of a magmatic‐hydrothermal derivation. In contrast, Py3 exhibits low concentrations in most trace elements. Trace element mapping of Py2 revealed correlations between Fe and Co, as well as Ni and As, indicating their couped substitution in the pyrite structure. The available geological, petrographic and geochemical data consistently suggest that the Xinfang gold deposit formed during the Early Cretaceous by hydrothermal fluids of magmatic contribution.

The genesis of Xindian gold deposit, Liaodong Peninsula, NE China: Constraints from zircon U–Pb ages, S–Pb isotopes, and pyrite trace element chemistry

“…Later mixing with meteoric water (Peng & Yang, 1996;Shen & Pei, 1994) changed the physical and chemical conditions of the mineralizing fluid, resulting in the formation of vein-type gold deposits within the metamorphic rocks of the Gaixian Formation. Compared with other Early Cretaceous gold deposits (such as the Wulong and Xinfang deposits, [Yu et al, 2018[Yu et al, , 2021) in the Liaodong Peninsula, which are mainly derived from Early Cretaceous magmatichydrothermal fluids, our study highlights the Xindian gold mineralization is closely related to fluid-wall rock interaction. This study expands the proposed metallogenic models of the Early Cretaceous gold deposits in the Liaodong Peninsula, and highlights the importance of the Gaixian Formation to the Early Cretaceous gold mineralization, in particular, those associated with the Early Cretaceous magmatic-hydrothermal activity.…”

“…(a) Diagram showing range of δ 34 S values for Xindian sulfides from the main mineralization stage (in‐situ LA‐MC‐ICP‐MS analysis in this study), late Triassic porphyritic biotite granite, and biotite schist of Gaixian Formation (bulk analysis from Shen & Pei, 1994). (b) Comparison of δ 34 S values from the Xindian gold deposit with other representative gold deposits in the Liaodong Peninsula (Sidaogou from Feng et al (2019); Wulong from Yu et al (2018); Xinfang from Yu et al (2021); Maoling from Liu et al (2018) and Liu et al (1990); Xiaotongjiapuzi from Liu et al (2020); Baiyun from Zhang et al (2019) and Sun et al (2020)), typical orogenic gold deposits (Goldfarb et al, 2005), and Gaixian Formation (Feng et al, 2019; Peng & Yang, 1996; Sun et al, 2020)…”

“…It is interesting to note that the unique Baiyun gold deposit hosted by the Gaixian Formation has negative δ 34 S values (−12.5‰–1.9‰; Zhang et al, 2019; Sun et al, 2020), and the interpretation is that the sulfur there was derived from oxidized magmatic fluids (Sun et al, 2020). In contrast to the gold system hosted by the Gaixian Formation, the Xinfang gold deposit is mainly hosted by the Archean Anshan Group which has δ 34 S values (1.3‰–5.3‰; Yu et al, 2021) more akin to a magmatic source. In that case, Archean Anshan Group would have added little sulfur to the fluid system.…”

“…The analyzed masses include 53 Cr, 59 Co, 60 Ni, 63 Cu, 66 Zn, 75 As, 77 Se, 107 Ag, 121 Sb, 124 Sn, 125 Te, 197 Au, and 208 Pb. The detailed analytical techniques followed those described by Yu et al (2021).…”

“…(a) Tectonic location of the Liaodong peninsula (modified after Zhu et al, 2015); (b) regional geological map of the Liaodong peninsula, showing the distribution of three major ore fields and Xindian gold deposit (modified after Yu et al, 2021). CAOB, central Asian Orogenic Belt, NCC–North China craton; YC, Yangtze craton.…”