This work investigates the ultra-large Huize Pb-Zn deposit, based on the results of preceding studies and detailed field geological surveys. The existing findings were reorganized and reinterpreted and supplemented with C-H-O isotopic measurements, which resulted in the identification of two different metallogenic fluids: a high temperature, low salinity, and acidic Fluid A, which originates from deep-seated fluids and is enriched in lighter C and O isotopes (−3‰ < 13 C‰ < −4‰; 10‰ < 18 O‰ < 17‰; −92‰ < D‰ < −50‰), and a low temperature, high salinity Fluid B, which is a subsurface brine formed by atmospheric precipitation. Fluid B is characterized by heavier C-O-H isotopic compositions (−2‰ < 13 C‰ < 1‰; 2‰ < 18 O‰ < 24‰; −66‰ < D‰ < −43‰) than Fluid A and cycles continuously within the strata. We hypothesize that the Huize Pb-Zn deposit is the result of large-scale fluid migration from deep regions of the crust. These upward-moving fluids extracted metallic elements from carbonate strata of various ages, forming a metal-rich metallogenic fluid (Fluid A). After higher-grade ores were precipitated from the fluid following decompression boiling, it then mixed with Fluid B and continued to precipitate sulfides.

The Chuxiong basin, located in southwest China, is well known as a mineralization area of red-bed type copper deposits in China. These deposits are characterized by mineral zoning, which is especially true for the Dayao deposits. The mineral zoning is consistent for both horizontal and vertical zoning; from the base (center) of the ore body to the top (outermost), the mineral zones are from hematite, chalcocite, chalcocite + bornite, and bornite + chalcopyrite to pyrite. We studied the mineral zoning in detail using a thermodynamic phase diagram method, such as log O 2 -log S 2 , pH-log O 2 , and pH-Eh, and discussed the constraints on the order of the minerals precipitation under different physiochemical conditions. It is indicated that changes in temperature have little effect on pH and Eh in the formation of minerals. S 2− is stable only below 473 K, and the forming temperature of chalcocite must be below 473 K. In this paper, we also explain the mineral zoning formation mechanism and propose that the main controlling factor of mineral zoning is pH. Because this mineral zoning is widespread in sediment-hosted deposits, studies on this mechanism can considerably promote better understanding of the genesis of ore deposits in order to guide the exploration.

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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.