Genesis of the Changba–Lijiagou Giant Pb‐Zn Deposit, West Qinling, Central China: Constraints from S‐Pb‐C‐O isotopes

Abstract

The extensive Changba‐Lijiagou Pb‐Zn deposit is located in the north of the Xihe–Chengxian ore cluster in West Qinling. The ore bodies are mainly hosted in the marble, dolomitic marble and biotite‐calcite‐quartz schist of the Middle Devonian Anjiacha Formation, and are structurally controlled by the fault and anticline. The ore‐forming process can be divided into three main stages, based on field geological features and mineral assemblages. The mineral assemblages of hydrothermal stage I are pale‐yellow coarse grain, low Fe sphalerite, pyrite with pits, barite and biotite. The mineral assemblages of hydrothermal stage II are black‐brown cryptocrystalline, high Fe shalerite, pyrite without pits, marcasite or arsenopyrite replace the pyrite with pits, K‐feldspar. The features of hydrothermal stage III are calcite‐quartz‐sulfide vein cutting the laminated, banded ore body. Forty‐two sulfur isotope analyses, twenty‐five lead isotope analyses and nineteen carbon and oxygen isotope analyses were determined on sphalerite, pyrite, galena and calcite. The δ34S values of stage I (20.3 to 29.0‰) are consistent with the δ34S of sulfate (barite) in the stratum. Combined with geological feature, inclusion characteristics and EPMA data, we propose that TSR has played a key role in the formation of the sulfides in stage I. The δ34S values of stage II sphalerite and pyrite (15.1 to 23.0‰) are between sulfides in the host rock, magmatic sulfur and the sulfate (barite) in the stratum. This result suggests that multiple S reservoirs were the sources for S2– in stage II. The δ34S values of stage III (13.1 to 22‰) combined with the structure of the geological and mineral features suggest a magmatic hydrothermal origin of the mineralization. The lead isotope compositions of the sulfides have 206Pb/204Pb ranging from 17.9480 to 17.9782, 207Pb/204Pb ranging from 15.611 to 15.622, and 208Pb/204Pb ranging from 38.1368 to 38.1691 in the three ore‐forming stages. The narrow and symmetric distributions of the lead isotope values reflect homogenization of granite and mantle sources before the Pb‐Zn mineralization. The δ13CPDB and δ18OSMOW values of stage I range from –0.1 to 2.4‰ and from 18.8 to 21.7‰. The values and inclusion data indicate that the source of fluids in stage I was the dissolution of marine carbonate. The δ13CPDB and δ18OSMOW values of stage II range from –4 to 1‰ and from 12.3 to 20.3‰, suggesting multiple C‐O reservoirs in the Changba deposit and the addition of mantle‐source fluid to the system. The values in stage III are –3.1‰ and 19.7‰, respectively. We infer that the process of mineralization involved evaporitic salt and sedimentary organic‐bearing units interacting through thermochemical sulfate reduction through the isotopic, mineralogy and inclusion evidences. Subsequently, the geology feature, mineral assemblages, EPMA data and isotopic values support the conclusion that the ore‐forming hydrothermal fluids were mixed with magmatic hydrothermal fluids and forming the massive dark sphalerite, then yielding th...

Measurements of Sulfur Isotope Composition on Ultrasmall (80 Nanomole) Sulfide and Sulfate Samples by a Modified EA‐IRMS

“…It occurs in nature with varied chemical valences and in diverse forms. Sulfur isotope analysis is usually used to investigate the origin and behavior of S-bearing materials and has been broadly applied in studies of igneous, sedimentary, hydrothermal and biological processes on Earth (Ohmoto, 1972;Ohmoto et al, 1993;Ono, 2008;Partridge et al, 2008;Wei et al, 2020).…”

Ore Genesis of the Changkeng–Fuwan Au-Ag Deposit in Central Guangdong, South China: Evidence from Fluid Inclusions and C-H-O-S-Pb-He-Ar Isotopes

“…The diagram of 207 Pb/ 204 Pb versus 206 Pb/ 204 Pb (Figure 16) indicates that all the Pb isotopic data were plotted above or near the upper crust curve, which was consistent with the previous studies. Zhu (1998) [109] proposed that the ratios of 207 [109] and Wei (2020) [110]. The diagram of Δβ-Δγ (Figure 17) further shows that the Pb isotopic data were distributed in the upper crust field or near fields between the upper crust and the mantle.…”

“…It can more effectively trace the origin of metals than global patterns of evolution. The values of Δβ and Δγ can be calculated by the equation of Zhu (1998) [109] and Wei (2020) [110]. The diagram of Δβ-Δγ (Figure 17) further shows that the Pb isotopic data were distributed in the upper crust field or near fields between the upper crust and the mantle.…”

Trace elements of sulfides in the Dengjiashan Pb–Zn deposit from West Qinling, China: Implications for mineralization conditions and genesis

“…It is bordered by the southern margin of the North China Plate to the north, and the northern margin of the Yangtze Plate to the south, while the northeastern front of the Tibetan Plateau lines its western border (Figure 1). The West Qinling region has experienced the formation and evolution stages of the Neoarchean-Paleoproterozoic Precambrian basement, the Neoproterozoic-Palaeozoic tectonic plate evolution, as well as the evolution process of the intracontinental orogenic stage since the Mesozoic, which have resulted in the current tectonic framework (Dong et al, 2011;Wei, Wang, Mei, et al, 2022;Zhang et al, 1997Zhang et al, , 2004.…”

“…The thickness of this formation exceeds 300 m. In the mud and calcite veins between the layers, small amounts of galena, sphalerite, pyrite, or chalcopyrite mineralization have been identified. The main Pb-Zn F I G U R E 1 Simplified geological map of the Xicheng ore field, Gansu Province, China (after Wei et al, 2020). (Hao et al, 2021).…”