Formation of a giant Zn–Pb deposit from hot brines injecting into a shallow oil–gas reservoir in sandstones, Jinding, southwestern China

Abstract

The association between mineralisation and hydrocarbons in sedimentary basins is widely recognised, but the nature and significance of their relationships are not fully understood. This paper provides an example of metalliferous brines injecting into a palaeo‐oil–gas reservoir to form a world‐class Zn–Pb deposit (Jinding, China). Petrographic and microthermometric studies of oil inclusions and PVT simulations suggest that oil and gas were charged in a shallow (<1300 m) environment before mineralisation. This environment favoured bacterial sulphate reduction (BSR), which produced large amounts of H2S that accumulated in the gas cap. Forceful injection of hot brines penetrated the oil zone to reach the H2S‐rich gas cap and precipitated sulphide ores. Individual fluid injection events were short‐lived, and the reservoir was only partly and briefly heated to beyond the bacterial survival temperature. Episodic injection of metalliferous brines and sustained supply of H2S through BSR resulted in the formation of a large Zn–Pb deposit.

Nature and Evolution of the Ore-Forming Fluids from Nanmushu Carbonate-Hosted Zn-Pb Deposit in the Mayuan District, Shaanxi Province, Southwest China

“…The 34 S values of sulfides in the Nanmushu deposit are characterized by positive values with a peak around +18‰, and the reduced sulfur may have derived from reduction of SO 4 2− from seawater and/or evaporitic sulfates. Thermochemical sulfate reduction (TSR) is the likely key factor for sulfur isotope fractionation during the ore-forming processes.…”

“…The coexistence of gas (CH 4 ), gas-aqueous, and liquid-only inclusions was also observed ( Figure 9). Such phenomenon provides evidence that the fluid system of the Nanmushu Zn-Pb deposit consisted of an aqueous-salt solution and an immiscible hydrocarbon phase (e.g., [3,4,48] Figures 10 and 12). Salinities of stage I (4.3 to 13.3 wt.% NaCl equivalent), stage II (2.0 to 14.3 wt.% NaCl equivalent), and stage III (2.1 to 19.0 wt.% NaCl equivalent) are similar (Figures 10 and 12).…”

“…(Figures 10(e) and 10(f)). When the temperature deceases to −100 ∘ C, the liquid phase of some type I inclusion was yellowish in color, which is characteristic for the eutectic composition of the H 2 ONaCl-CaCl 2 system (e.g., [4,17]). The m (-51.6…”

“…The close relationship between carbonate-hosted Zn-Pb deposits and hydrocarbon reservoirs in a sedimentary basin has been widely noted [1][2][3][4], but the detailed metallogenic mechanism remains poorly understood.…”

Hydrodynamic Links between Shallow and Deep Mineralization Systems and Implications for Deep Mineral Exploration

“…The Jinding Zn-Pb deposit, located in the Meso-Cenozoic Lanping Basin in southwestern China, is the largest sandstone-hosted Zn-Pb deposit in the world and has been the subject of numerous studies, including those related to hydrodynamics of mineralization (Kyle and Li, 2002;Xue et al, 2003Xue et al, , 2006Xue et al, , 2007Xue et al, , 2015Chi et al, 2006bChi et al, , 2007Chi et al, , 2012Chi et al, , 2017Leach et al, 2017;Song et al, 2020;Mu et al, 2021). The deposit is hosted in a structural dome consisting of Mesozoic sandstone and limestone thrusted over Tertiary sandstone that is located near the reginal Pijiang fault (Figs.…”