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

Abstract

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 H 2 S that accumulated in the gas cap. Forceful injection of hot brines penetrated the oil zone to reach the H 2 S‐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 H 2 S through BSR resulted in the formation of a large Zn–Pb deposit.