Coupling relationship of the Mississippi Valley-type zinc‑lead deposit and hydrothermal dolostone: Its role in metallogeny

Abstract

The deposition, diagenesis, and subsequent evolution of dolostones are vital geological processes in basin sedimentary history, recording processes of evaporite formation, the Mississippi Valley–type (MVT) zinc–lead (Zn–Pb) deposit, and hydrocarbon accumulation. This review provides a comprehensive investigation and discussion on the tectonic framework of the MVT Zn–Pb deposits, the processes of dolostone formation, the spatiotemporal relationships between hydrothermal dolostone and MVT Zn–Pb deposits, and potential fluid migration mechanisms. These findings elucidate the coupling relationship between host dolostone and MVT Zn–Pb deposits, ultimately leading to the establishment of a metallogenic model.

In the Earth's geological system, nearly all basins or platforms bearing the MVT Zn–Pb deposits have undergone a sequence of distinct geological processes across different burial environments. These include the coexistence of penecontemporaneous dolostone and evaporites in the near-surface, shallow burial setting; the formation of burial dolostone and oil or gas reservoirs in deeper burial environment; and the development of hydrothermal dolostone and MVT Zn–Pb deposits in tectonic uplift setting.

The Zn–Pb ore-bearing dolostone originates from the interaction of carbonate rocks with hydrothermal fluids, as evidenced by the development of mineralised alteration zones at both the orebody and mineral scales. Orebodies are typically associated with columnar or tabular bodies of hydrothermal dolostone, or a mixture of both, or intersect the tabular body of the hydrothermal dolostone. Sulphides precipitation was likely to have occurred during the transition of dolomite from the replacement to saddle form. During the metallogenic stage, elevated fluid temperatures and high ion concentrations facilitate hydrothermal dolomitisation and thermochemical sulphate reduction processes, which were the primary factor controlling the spatiotemporal coexistence of dolostone and MVT Zn–Pb deposits. The lattice structure and chemical composition of hydrothermal dolomite can provide valuable insights into the sources of material, fluid migration pathways, and the transport mechanisms of reduced sulphur within related basins. Globally, in-situ thermochemical sulphate reduction is recognized as the dominant pathway for reduced sulphur generation in typical MVT Zn–Pb deposits.

The cogenetic model of MVT Zn–Pb deposits and dolostone formation can be divided into three distinct stages. In this model, the the first stage is thought to potentially generate abundant sulphur sources for the third stage, while the second stage provides rich reducing agents necessary for subsequent mineralisation. The coupling relationship between MVT Zn–Pb deposit and dolostone is primarily governed by the complex interactions of diverse fluids within the ore-bearing basins. This refined model not only enhances our understanding of the mineralisation processes of MVT Zn–Pb deposits and the associated dolomitization but also offers valuable insights for guiding future mineral prospecting and exploration efforts.