Precipitation Reaction Mechanisms of Mineral Deposits Simulated with a Fluid Mixing Model

Yan Zhang,Pingtang Wei,Yurong Wang,Runsheng Han,Xing Ding,Giovanni Mongelli

doi:10.1155/2021/8881677

Abstract

Nonmagmatic, carbonate-hosted epigenetic hydrothermal Pb–Zn deposits similar to those at the Huize Pb–Zn Mine are widespread across the Sichuan–Yunnan–Guizhou (SYG) polymetallic province. The precipitation mechanisms of these geologically intriguing deposits are an area of interest for many researchers. To simulate the underlying precipitation reaction mechanisms and dynamics of each aspect, a fluid mixing model for metal sulfide precipitation was used in a series of experiments, where solutions that contain Pb/Zn chloride complexes and sulfide were subjected to pH changes, water-rock reactions, and dilutions. Based on the results of these experiments, thermodynamic phase diagrams, and other experimental findings, a fluid mixing genetic model was developed for SYG Pb–Zn deposits, and this model was used to analyze the mechanisms of metal sulfide precipitation. The results indicate that acidic fluids in the form of chloride complexes transported Pb and Zn, whereas sulfide exists in the form of H2S within these fluids. The precipitation of metal sulfides occurs when these fluids undergo changes in pH, water-rock reactions, or isothermal dilution. The pH changes were found to be the most effective method for the induction of sulfide precipitation, followed by dilution and then water-rock reactions. The formation of sulfide precipitates due to pH changes, water-rock reactions, and dilution can be attributed to a single mechanism, i.e., changes in the pH of the fluid. Therefore, changes in pH are the primary mechanism of sulfide precipitation.

Highlights

Since the 1990s, there have been numerous studies on the Pb–Zn deposits in the Sichuan–Yunnan–Guizhou (SYG) polymetallic region, which are typified by the Huize Pb–Zn deposit
The electron probe microanalyzer (EPMA) used in these experiments was a Shimadzu EPMA-1600 (Japan), which was equipped with an EDAX Genesis energy-dispersive spectrometer (USA)
The results of this study indicate that, within a fluid whose Pb/Zn and sulfide contents exist as chloride complexes and H2S, respectively, sulfide precipitation can be induced by subjecting this fluid to pH changes, water-rock reactions, or isothermal dilution

Summary

Introduction

Since the 1990s, there have been numerous studies on the Pb–Zn deposits in the Sichuan–Yunnan–Guizhou (SYG) polymetallic region, which are typified by the Huize Pb–Zn deposit. Luo et al [22] proposed that fluid mixing is the main mechanism for metal precipitation; these insights were based on the findings of previous fluid inclusion studies. By analyzing Sr isotopic compositions and fluid inclusions, Zhang et al [23,24,25] concluded that fluid mixing and boiling are the primary causes of sulfide precipitation

Methods

Findings

Discussion

Conclusion