Most of the world's Zn and Pb is extracted from sediment-hosted Zn-Pb deposits. The Zn-Pb deposits hosted in carbonate rocks are hypothesized to form by mixing of acidic metal-bearing brines with reduced sulfur-bearing fluids while dissolving sedimentary carbonate. To test the role of carbonate in this process, we conducted hydrothermal experiments simulating ore formation by reacting Zn ± Pb ± Ba–bearing brines with H2S and SO42– produced by native sulfur, with and without carbonate minerals (calcite or dolomite crystals), at 200 °C and water-saturated pressure. Sphalerite, galena, and barite (or anhydrite) crystals formed only when carbonate was present in the experiment, accompanied by carbonate dissolution. The textures of sphalerite clusters are similar to those observed in ancient and modern hydrothermal deposits. Thermodynamic modeling at 150 °C and 250 °C demonstrates that mixing of metal-rich brines and H2S causes most of the Zn in solution to precipitate as sphalerite only when carbonate dissolution occurs to buffer the pH, consistent with the experimental observations. The need for a pH buffer increases with increasing temperature, and different pH buffers may play a role for different deposit types. We propose that carbonate-buffered fluid mixing is a critical process for forming post-sedimentary Zn ± Pb ± Ba deposits in sedimentary carbonate rocks.Sediment-hosted Zn-Pb deposits, such as Mississippi Valley–type (MVT), Irish-type, and sedimentary exhalative (SEDEX) (e.g., Large et al., 2005; Leach et al., 2005; Wilkinson, 2014), are the most important Zn and Pb resources globally. Different ore-genesis models have been proposed for different classes of these deposits: Large et al. (1998, 2005) proposed a syn-sedimentary–exhalative origin for the giant HYC deposits (McArthur River, Australia), while Perkins and Bell (1998) and Spinks et al. (2021) identified key features of post-sedimentary mineralization and carbonate replacement by metal sulfide minerals. A carbonate replacement model is proposed for the Irish-type (e.g., Wilkinson, 2014; Wilkinson and Hitzman, 2015) and MVT-type deposits (e.g., Corbella et al., 2004). Kelley et al. (2004) also argued that sphalerite and barite in the giant Anarraaq Zn deposit in the Red Dog district, Alaska (USA), also formed via carbonate replacement.Ore-genesis models for Zn-Pb deposits in sedimentary carbonate rocks have been proposed for many decades (e.g., Jackson and Beales, 1967; Anderson, 1975, Anderson and Garven, 1987; Cooke et al., 2000) and have been used to explain field observations (e.g., Leach et al., 2005; Wilkinson, 2014) and as a basis for reactive transport modeling (e.g., Garven et al., 1999; Corbella et al., 2004); however, experimental studies have mainly focused on the solubility of Zn-Pb sulfide minerals and stability of aqueous Zn and Pb complexes (e.g., Ruaya and Seward, 1986; Bourcier and Barnes, 1987; Barrett and Anderson, 1988; Tagirov and Seward, 2010; Mei et al., 2015, 2016; Etschmann et al., 2018, 2019; Sanz-Robinson and Williams-Jones, 2019). Recently, room-temperature titration experiments by Zhang et al. (2019a, 2019b) suggested that hydrolysis is the key factor for Zn-Pb sulfide precipitation, and Zhang et al. (2021) emphasized that pH change is the primary mechanism for Zn-Pb sulfide deposition up to 150 °C; however, the role of carbonate replacement has not yet been closely examined experimentally.Our study elucidates the chemical processes that control the formation of Zn-Pb deposits in carbonate rocks using experimental and thermodynamic modeling techniques, focusing on the role of carbonate in the deposition of Zn-Pb sulfide minerals from hydrothermal fluids.Sodium-chloride brines with different pH and concentrations of Zn, Pb, Ba, Ca, and Mg were reacted with native sulfur with and without carbonate (calcite or dolomite) crystals at 200 °C (for solution composition, see Table S1 in the Supplemental Material1). We chose native sulfur (S) because it disproportionates to H2S and SO42– in water at elevated temperatures (Ellis and Giggenbach, 1971), providing reduced sulfur and also conveniently buffering the redox state of the solution near the sulfate-sulfide boundary. The solid reaction products were characterized using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), electron backscatter diffraction (EBSD), and cathodoluminescence (CL; e.g., MacRae et al., 2013). We investigated experimental reactions and fluid mixing of metal-bearing brine with H2S using thermodynamic modeling. Details of the experimental and modeling methods are described in the Supplemental Material.The backscattered electron (BSE), EPMA, CL, and EBSD images of solid reaction products for representative samples are shown in Figures 1–3. Solutions of Zn2+ + NaCl reacted with sulfur, calcite (samples R5-3, R5-4; Figs. 1A and 1B), and dolomite (sample R3; Fig. 1C) to produce sphalerite and anhydrite with coincident dissolution of carbonate. The sphalerite grew in spheroidal clusters tens to hundreds of micrometers in diameter (Fig. 1A), with angular crystals as large as 2 µm in size (Fig. 1B).Solutions of Zn2+ + Mg2+ + Ca2+ + NaCl reacted with S and calcite (sample R11-1) to produce sphalerite and anhydrite as well as Mg-calcite crystals with partial dissolution of the calcite. The Mg-calcite and sphalerite crystals grew in a shell around the dissolving calcite crystal (Figs. 1D and 1E). Sphalerite clusters and galena also grew on the anhydrite crystals when Pb2+ was added (Fig. 1F). Adding Ba2+ to the initial solution caused barite formation instead of anhydrite, with sphalerite clusters growing on larger, angular barite crystals (sample R16-1; Fig. 2A).Solutions of Zn2+ + Ba2+ + Pb2+ + Mg2+ + Ca2+ + NaCl, when reacted with S and calcite (samples R12-5 and R17-1) and dolomite (sample R17-3) also caused carbonate dissolution and sulfide and barite precipitation. Some barite redissolved as the sphalerite clusters grew on and around the crystals (Figs. 2A and 2E). Cubic and octahedral galena crystals grew among the barite and sphalerite clusters (Figs. 2C and 2F). Some galena and barite crystals dissolved and seeded the growth of sphalerite (Figs. 2C–2E and 3).Close examination of the sphalerite clusters showed fine structural zonation from the center of the cluster to the rim, as shown in Figures 3A–3F. Major mineral phases indicated in these figures are identified using EPMA (Fig. 3A), quantitative spot microanalysis (Table S2; spots marked in Figs. 3A and 3B), and EBSD (Fig. 3F). The globular sphalerite clusters showed ring-like growth zones (BSE in Fig. 3B; CL in Fig. 3C). These zones contain nanocrystals of a globular, equiaxed-type morphology with nanoporosity (Figs. 3D and 3E). The coarse crystals around the rim of the cluster showed the strongest CL emission. By contrast, the growth zones in the center of the clusters showed some CL emission indicating a crystalline phase but at a reduced level, suggesting that the crystal size is extremely small (<~100 nm). The EBSD phase map (Fig. 3F) shows that sphalerite clusters have diffraction patterns only in the coarser crystals around the rim of the clusters.The experimental products of a non-acidified solution (sample R11-1; Table S1) are like the acidified ones. Comparison experiments with identical starting compositions of metal-bearing brines were reacted with S but did not contain carbonates. No Zn or Pb sulfide precipitation was observed in those experiments, and the inductively coupled plasma–optical emission spectrometry (ICP-OES) analysis showed most of the Zn stayed in solution (Table S4). The solution also turned more acidic (pH = 0.6–1) than the initial solution (Table S1).Thermodynamic modeling of the reaction products for the experimental systems is generally consistent with the observed mineral assemblages, pH, and composition of the resultant solutions (Table S4). An example (sample R12-5) is demonstrated in the Supplemental Material (Fig. S1).The globular textures of the sphalerite clusters observed in our experiments are very similar to those observed in seafloor hydrothermal systems (Hu et al., 2019; Glenn et al., 2020) as well as the colloform textures observed in MVT ores (Roedder, 1968; Leach et al., 2005, 2010) and Irish-type ores (Hitzman et al., 2002). In those ores, there are multiple depositional layers and more replacement features than in our experimental products, which most likely indicates multiple episodes of carbonate dissolution and ore deposition within a compact subsurface environment. While sulfide deposition occurred in our experiments in a closed and spatially unrestricted system, complexity in mineralogy, grain size, and mineral chemistry still develops (Figs. 1–3).Sphalerite nanocrystals in the center of the sphalerite clusters (Fig. 3D), causing poor EBSD pattern quality (Fig. 3F) and low CL emission (Fig. 3C), likely reflect an easy nucleation and rapid deposition due to the supersaturation of Zn in solution at the initial stage of the fluid reacting with H2S. Over time, the Zn concentration in solution decreased, causing the nucleation rate to decrease, so large crystals had time to grow around the outer rims of sphalerite globules. This mimics the ore paragenesis sequence suggested by Hu et al. (2019) for modern seafloor hydrothermal sphalerite.Etching of anhydrite, barite, and galena during sphalerite growth (Figs. 1 and 2), in addition to intergrowth of these minerals, indicates dynamic interactions during their crystal growth. These observations indicate that some reduced sulfur can be derived from sulfate dissolution, e.g., anhydrite and barite dissolution to produce H2S (Anderson and Garven, 1987; Magnall et al., 2020).Different carbonate species (dolomite or calcite) do not affect this fundamental process because Zn-Pb ± Ba mineral assemblages always formed in our experiments with similar features, which indicates that the role of carbonate is a simple process of dissolution to take up H+ produced by sulfide precipitation (Equations 1 and 2). The equilibrium constants (logK) of Zn-Pb sulfide deposition (Equations 1 and 2) notably decrease with increasing temperatures (Table S3; logK values were calculated based on Mei et al. [2015] and Etschmann et al. [2018]): e.g., from 5.3 at 25 °C to −3.5 at 250 °C for Equation 1, and from 6.0 at 25 °C to −2.4 at 250 °C for Equation 2. This trend indicates that although the sphalerite may precipitate by reacting with reduced sulfur without carbonate at room temperature (Zhang et al., 2019a), the need for a pH buffer to enhance Zn-Pb sulfide precipitation (Equations 1 and 2) increases vastly with increasing temperatures.To further test the role of carbonate in the deposition of Zn-Pb sulfide minerals, we modeled fluid mixing of a Zn-Pb-Ba–bearing, sulfur-poor brine (1000 ppm Zn, 200 ppm Pb, and 500 ppm Ba) with H2S at two pH values of 2 and 5.5, and with and without dolomite, at 150 °C and 250 °C (Figs. 4A–4D). These two temperatures were chosen to be the same as in the log fO2–pH (fO2—oxygen fugacity) diagrams of Cooke et al. (2000). See the Supplemental Material for the choice of ore fluid composition, thermodynamic models, and result data (Table S5).All the mixing reactions that start from point 1 and point 2 in the sulfate-stable region proceed to the sulfide-stable area (Figs. 4B and 4D). Without carbonate, the reaction paths (marked red) reach acidic pH (point 3 in Figs. 4B and 4D) independent of the starting pH of 2 or 5.5 after 0.2 m H2S being reacted. Figures 4A and 4C show that most of the Zn and Ba remain in solution with the final concentration increasing with temperature. At 150 °C, 88% of Zn, 99% of Ba, and 15% of Pb remain in solution when the starting pH is 2; and 65% of Zn, 99% of Ba, and 11% of Pb remain in solution when the starting pH is 5.5 (Fig. 4A). At 250 °C and starting pH of 2, 99% of Zn, Pb, and Ba remain in solution, and when starting pH is 5.5, 99% of Zn and Ba and 39% of Pb remain in solution (Fig. 4C).In contrast, when carbonate is present, most of the Zn and Pb in solution precipitates in all scenarios (Fig. 4, blue reaction paths toward point 4), with the final concentrations of 0.01–0.5 ppm Zn and 0.2–0.9 ppm Pb left in solution. At 250 °C, a significant concentration of Ba stays in solution due to a lack of sulfate when the reaction path proceeds toward reduced conditions. The reaction paths from point 3 to point 4 in Figures 4B and 4D indicate that under reducing conditions, carbonate also enhances metal-sulfide precipitation.The modeling results show that a simple mixing of Zn-bearing (~1000 ppm Zn) brines with H2S of as much as 0.2 m under acid or near-neutral pH conditions would not effectively precipitate sphalerite at 150–250 °C. This is because the partial precipitation of sphalerite decreases the fluid pH and stops the ore deposition due to the high solubility of sphalerite in acidic solutions, as shown in Cooke et al. (2000) and Spinks et al. (2021). The much higher degree of galena precipitation in the carbonate-free experiments is due to the lower solubility of galena compared to sphalerite (e.g., Etschmann et al., 2018). Thus, galena deposition is likely to be less dependent on a pH buffer than sphalerite. Also, metal hydrolysis (Zhang et al., 2019a, 2019b) is unnecessary because reaction paths are wholly within the predominant field of Zn and Pb chloride complexes and sulfide minerals (Figs. 4B and 4D).Our results verify the long-standing hypothesis of Zn-Pb ore-formation via fluid-mixing of metal-bearing brine and reduced sulfur by Jackson and Beales (1967) and Anderson (1975). Further, we have demonstrated how sphalerite, galena, and barite form from the interaction of a single metal-rich ore fluid with reduced sulfur when facilitated by the dissolution of carbonate buffering the pH of the solution.There are limitations in applying our experimental and modeling results to ore deposits. Firstly, at high ratios of H2S/metal concentrations and/or at low temperatures (ambient to ~100 °C) where solubility of sphalerite is low, the precipitation of metal-sulfide minerals without a carbonate buffer is likely. The logK values for sphalerite deposition (Equation 1) indicate this, and it has been observed by Zhang et al. (2019a, 2019b). Secondly, the acidic fluids generated by sulfide deposition may be continually replaced by newly arriving ore fluid, negating the need for a pH buffer. Thirdly, this study does not consider other chemical processes for ore formation (e.g., cooling, fluid mixing with pore water, and ore fluids reacting with organic matter) that can operate in different geological settings where carbonate rock is absent (e.g., some sandstone-hosted Pb-Zn deposits), or that several factors could play in concert to cause ore deposition. Nevertheless, carbonate-buffered fluid mixing is likely a critical mechanism for the formation of post-sedimentary Zn-Pb ± Ba deposits in carbonate rocks and in carbonate-hosted polymetallic sulfide deposits (e.g., Knorsch et al., 2020). These findings demonstrate the importance of the presence of carbonate in sediment-hosted base-metal mineral systems, showing that accounting for carbonate should be an essential part of any mineral systems–based exploration targeting approach.Research funding is from the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Australian Research Council (grant LE130100087). We thank S. Schmid and C. Siegel for their helpful comments. Special thanks to J. Menuge, two anonymous reviewers, and editor G. Dickens for their constructive reviews.

中文翻译：

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碳酸盐溶解如何促进沉积物承载的 Zn-Pb 矿化

世界上大部分锌和铅是从沉积物中的锌铅矿床中提取的。假设碳酸盐岩中的锌铅矿床是由酸性含金属盐水与含硫量减少的流体混合，同时溶解沉积碳酸盐而形成的。为了测试碳酸盐在该过程中的作用，我们进行了热液实验，通过使含 Zn ± Pb ± Ba 的盐水与天然硫产生的 H2S 和 SO42（有或没有碳酸盐矿物（方解石或白云石晶体））反应来模拟矿石形成，在200 °C 和水饱和压力。闪锌矿、方铅矿和重晶石（或硬石膏）晶体仅在实验中存在碳酸盐时形成，伴随着碳酸盐溶解。闪锌矿簇的结构与在古代和现代热液矿床中观察到的结构相似。150 °C 和 250 °C 下的热力学模型表明，只有当碳酸盐溶解以缓冲 pH 值时，富金属盐水和 H2S 的混合才会导致溶液中的大部分锌沉淀为闪锌矿，这与实验观察结果一致。对 pH 缓冲液的需求随着温度的升高而增加，不同的 pH 缓冲液可能对不同的沉积物类型起作用。我们认为碳酸盐缓冲流体混合是在沉积碳酸盐岩中形成沉积后 Zn ± Pb ± Ba 沉积物的关键过程。和沉积喷出物 (SEDEX)（例如，Large 等，2005；Leach 等，2005；Wilkinson，2014）是全球最重要的锌和铅资源。已经为这些不同类别的矿床提出了不同的成矿模型：Large 等。(1998, 2005) 提出了巨大的 HYC 矿床（澳大利亚麦克阿瑟河）的同沉积-喷出成因，而 Perkins 和 Bell (1998) 以及 Spinks 等人。(2021) 确定了沉积后成矿和金属硫化物矿物替代碳酸盐的关键特征。为爱尔兰型（例如，Wilkinson，2014；Wilkinson 和 Hitzman，2015）和 MVT 型矿床（例如，Corbella 等，2004）提出了碳酸盐替代模型。凯利等人。(2004) 还认为，美国阿拉斯加州 Red Dog 地区的巨大 Anarraaq Zn 矿床中的闪锌矿和重晶石也是通过碳酸盐置换形成的。几十年（例如，Jackson 和 Beales，1967 年；安德森，1975，安德森和加文，1987；Cooke et al., 2000) 并已被用于解释野外观察（例如，Leach 等人，2005 年；Wilkinson，2014 年）并作为反应性输运建模的基础（例如，Garven 等人，1999 年；Corbella 等人., 2004); 然而，实验研究主要集中在 Zn-Pb 硫化物矿物的溶解度和水性 Zn 和 Pb 配合物的稳定性（例如，Ruaya 和 Seward，1986 年；Bourcier 和 Barnes，1987 年；Barrett 和 Anderson，1988 年；Tagirov 和 Seward，2010 年） ；Mei 等人，2015 年，2016 年；Etschmann 等人，2018 年，2019 年；Sanz-Robinson 和 Williams-Jones，2019 年）。最近，Zhang 等人的室温滴定实验。(2019a, 2019b) 表明水解是 Zn-Pb 硫化物沉淀的关键因素，Zhang 等人。(2021) 强调 pH 变化是 Zn-Pb 硫化物沉积高达 150 °C 的主要机制；然而，碳酸盐置换的作用尚未通过实验进行仔细研究。我们的研究利用实验和热力学建模技术阐明了控制碳酸盐岩中 Zn-Pb 沉积物形成的化学过程，重点关注碳酸盐在沉积物沉积中的作用。来自热液流体的 Zn-Pb 硫化物矿物。 具有不同 pH 值和 Zn、Pb、Ba、Ca 和 Mg 浓度的氯化钠盐水与天然硫在 200 °C 下反应，有或没有碳酸盐（方解石或白云石）晶体（对于溶液组成，参见补充材料中的表 S1)。我们选择天然硫 (S)，因为它在高温下与水中的 H2S 和 SO42– 不成比例（Ellis 和 Giggenbach，1971），提供减少的硫并方便地缓冲硫酸盐 - 硫化物边界附近溶液的氧化还原状态。使用扫描电子显微镜 (SEM)、电子探针微量分析 (EPMA)、电子背散射衍射 (EBSD) 和阴极发光 (CL；例如 MacRae 等人，2013) 表征固体反应产物。我们使用热力学模型研究了含金属盐水与 H2S 的实验反应和流体混合。补充材料中描述了实验和建模方法的详细信息。代表性样品的固体反应产物的背散射电子 (BSE)、EPMA、CL 和 EBSD 图像如图 1-3 所示。Zn2+ + NaCl 溶液与硫、方解石（样品 R5-3、R5-4；图 1A 和 1B）和白云石（样品 R3；图 1B）反应。1C) 生产闪锌矿和硬石膏，同时碳酸盐溶解。闪锌矿以直径数十至数百微米的球状团簇生长（图 1A），角状晶体的大小可达 2 微米（图 1B）。 Zn2+ + Mg2+ + Ca2+ + NaCl 溶液与 S 和方解石反应（样品 R11-1) 以生产闪锌矿和硬石膏以及部分溶解方解石的镁方解石晶体。镁方解石和闪锌矿晶体在溶解的方解石晶体周围的壳中生长（图 1D 和 1E）。当添加 Pb2+ 时，闪锌矿簇和方铅矿也在硬石膏晶体上生长（图 1F）。在初始溶液中加入 Ba2+ 导致重晶石而不是硬石膏形成，闪锌矿簇生长在更大的、有棱角的重晶石晶体上（样品 R16-1；图 2A）。Zn2+ + Ba2+ + Pb2+ + Mg2+ + Ca2+ + NaCl 的溶液与 S 和方解石（样品 R12-5 和 R17-1）和白云石（样品 R17-3）反应时，也会引起碳酸盐溶解以及硫化物和重晶石沉淀。随着闪锌矿簇在晶体上和周围生长，一些重晶石重新溶解（图 2A 和 2E）。立方和八面体方铅矿晶体在重晶石和闪锌矿簇中生长（图 2C 和 2F）。一些方铅矿和重晶石晶体溶解并促进了闪锌矿的生长（图 2C-2E 和 3）。对闪锌矿簇的仔细检查显示从簇中心到边缘的精细结构分带，如图 3A-3F 所示。这些图中显示的主要矿物相是使用 EPMA（图 3A）、定量点微量分析（表 S2；图 3A 和 3B 中标记的点）和 EBSD（图 3F）确定的。球状闪锌矿簇显示出环状生长区（图 3B 中的 BSE；图 3C 中的 CL）。这些区域包含具有纳米孔隙率的球状等轴型纳米晶体（图 3D 和 3E）。簇边缘周围的粗晶体显示出最强的 CL 发射。相比之下，簇中心的生长区显示出一些 CL 发射，表明结晶相但水平降低，表明晶体尺寸非常小（<~100 nm）。EBSD 相图（图 3F）显示闪锌矿簇仅在簇边缘周围较粗的晶体中具有衍射图案。那些。使用相同的含金属盐水起始成分的比较实验与 S 反应但不含碳酸盐。在这些实验中没有观察到 Zn 或 Pb 硫化物沉淀，电感耦合等离子体发射光谱 (ICP-OES) 分析显示大部分 Zn 留在溶液中（表 S4）。溶液也变得比初始溶液更酸（pH = 0.6-1）（表 S1）。 实验系统反应产物的热力学模型通常与观察到的矿物组合、pH 值和所得溶液的组成一致（表 S4)。补充材料中展示了一个示例（样品 R12-5）（图 S1）。在我们的实验中观察到的闪锌矿簇的球状结构与在海底热液系统中观察到的结构非常相似（Hu 等人，2019 年；Glenn 等人，2020 年）以及在 MVT 矿石中观察到的胶状结构（Roedder，1968 年） ; Leach 等人，2005 年，2010 年）和爱尔兰型矿石（Hitzman 等人，2002 年）。在这些矿石中，与我们的实验产品相比，存在多个沉积层和更多的置换特征，这很可能表明在致密的地下环境中发生了多次碳酸盐溶解和矿石沉积。虽然在我们的实验中硫化物沉积发生在一个封闭且空间不受限制的系统中，但矿物学、晶粒尺寸和矿物化学的复杂性仍在发展（图 1-3）。闪锌矿簇中心的闪锌矿纳米晶体（图 3D），导致较差的 EBSD 图案质量（图 3F）和低 CL 发射（图 3C），可能反映了由于在流体与 H2S 反应的初始阶段溶液中 Zn 的过饱和，容易成核和快速沉积。随着时间的推移，溶液中的 Zn 浓度降低，导致成核速率降低，因此大晶体有时间在闪锌矿球的外缘周围生长。这模仿了 Hu 等人提出的矿石共生序列。(2019) 用于现代海底热液闪锌矿。在闪锌矿生长过程中硬石膏、重晶石和方铅矿的蚀刻（图 1 和 2），以及这些矿物的共生，表明它们在晶体生长过程中的动态相互作用。这些观察结果表明，一些还原的硫可以源自硫酸盐溶解，例如，硬石膏和重晶石溶解产生 H2S（Anderson 和 Garven，1987 年；Magnall 等人，2020 年）。不同的碳酸盐种类（白云石或方解石）不影响这一基本过程，因为在我们的实验中总是形成 Zn-Pb ± Ba 矿物组合类似的特征，这表明碳酸盐的作用是一个简单的溶解过程，以吸收硫化物沉淀产生的 H+（方程式 1 和 2）。Zn-Pb 硫化物沉积的平衡常数 (logK)（方程式 1 和 2）随着温度的升高而显着降低（表 S3；logK 值根据 Mei 等人 [2015] 和 Etschmann 等人 [2018] 计算）：例如，对于公式 1，从 25 °C 时的 5.3 到 250 °C 下的 -3.5，以及对于公式 2，从 25 °C 下的 6.0 到 250 °C 下的 -2.4。这一趋势表明，虽然闪锌矿可能通过在室温下与没有碳酸盐的还原硫反应而沉淀（Zhang 等人，2019a），但需要 pH 缓冲液来增强 Zn-Pb 硫化物沉淀（方程式 1 和 2）温度升高。为了进一步测试碳酸盐在 Zn-Pb 硫化物矿物沉积中的作用，我们模拟了含 Zn-Pb-Ba 的贫硫盐水（1000 ppm Zn、200 ppm Pb 和 500 ppm Ba) 在两个 pH 值分别为 2 和 5.5，以及有和没有白云石的情况下，在 150 °C 和 250 °C 下使用 H2S（图 4A-4D）。选择这两个温度与 Cooke 等人的 log fO2-pH（fO2-氧逸度）图中的相同。(2000)。有关矿石流体成分、热力学模型和结果数据的选择，请参阅补充材料（表 S5）。从硫酸盐稳定区域中的点 1 和点 2 开始的所有混合反应都进行到硫化物稳定区域（图 4B 和 4D）。在没有碳酸盐的情况下，反应路径（标记为红色）在 0.2 m H2S 反应后达到酸性 pH（图 4B 和 4D 中的点 3），与 2 或 5.5 的起始 pH 无关。图 4A 和 4C 显示大部分 Zn 和 Ba 保留在溶液中，最终浓度随温度增加。在 150 °C 时，当起始 pH 值为 2 时，88% 的 Zn、99% 的 Ba 和 15% 的 Pb 保留在溶液中；当起始 pH 值为 5.5 时，65% 的 Zn、99% 的 Ba 和 11% 的 Pb 保留在溶液中（图 4A）。在 250 °C 和起始 pH 值为 2 时，99% 的 Zn、Pb 和 Ba 保留在溶液中，当起始 pH 值为 5.5 时，99% 的 Zn 和 Ba 以及 39% 的 Pb 保留在溶液中（图 4C）。相反，当存在碳酸盐时，在所有情况下，溶液中的大部分 Zn 和 Pb 都会沉淀（图 4，指向点 4 的蓝色反应路径），最终浓度为 0.01-0.5 ppm Zn 和 0.2-0.9 ppm Pb 留在溶液中。在 250 °C 时，当反应路径朝着还原条件进行时，由于缺乏硫酸盐，大量浓度的 Ba 留在溶液中。图 4B 和 4D 中从点 3 到点 4 的反应路径表明，在还原条件下，碳酸盐还增强了金属硫化物的沉淀。建模结果表明，含锌 (~1000 ppm Zn) 盐水与 H2S 的简单混合在酸性或接近中性的 pH 条件下，多达 0.2 m 不会在 150–250 °C 下有效地沉淀闪锌矿。这是因为闪锌矿的部分沉淀降低了流体 pH 值并由于闪锌矿在酸性溶液中的高溶解度而停止了矿石沉积，如 Cooke 等人所示。(2000) 和 Spinks 等人。(2021)。在无碳酸盐实验中，方铅矿沉淀的程度要高得多，这是由于方铅矿的溶解度低于闪锌矿（例如，Etschmann 等，2018）。因此，与闪锌矿相比，方铅矿沉积可能对 pH 缓冲液的依赖性较小。此外，金属水解 (Zhang et al., 2019a, 2019b) 是不必要的，因为反应路径完全在 Zn 和 Pb 氯化物络合物和硫化物矿物的主要领域内（图 4B 和 4D）。我们的结果证实了杰克逊和比尔斯 (1967) 和安德森 (1975) 通过含金属盐水和还原硫的流体混合形成 Zn-Pb 矿的长期假设。此外，我们还展示了在缓冲溶液 pH 值的碳酸盐溶解的促进下，单一富含金属的矿石流体与还原硫的相互作用如何形成闪锌矿、方铅矿和重晶石。 在应用我们的实验和建模方面存在局限性结果到矿床。首先，在高 H2S/金属浓度比和/或在闪锌矿溶解度低的低温（环境至~100°C）下，金属硫化物矿物可能在没有碳酸盐缓冲的情况下沉淀。闪锌矿沉积的 logK 值（方程 1）表明了这一点，并且已被 Zhang 等人观察到。（2019a，2019b）。其次，硫化物沉积产生的酸性流体可能会不断被新到达的矿石流体取代，从而不需要 pH 缓冲液。第三，本研究没有考虑可以在不存在碳酸盐岩的不同地质环境（例如，一些砂岩-托管铅锌矿床），或者几种因素可能共同作用导致矿石沉积。然而，碳酸盐缓冲流体混合可能是在碳酸盐岩和碳酸盐岩多金属硫化物矿床中形成沉积后 Zn-Pb ± Ba 矿床的关键机制（例如，Knorsch 等，2020）。这些发现证明了沉积物承载的贱金属矿物系统中存在碳酸盐的重要性，表明碳酸盐的计算应该是任何基于矿物系统的勘探目标方法的重要组成部分。研究资金来自澳大利亚联邦科学与工业部研究组织 (CSIRO) 和澳大利亚研究委员会（授予 LE130100087）。我们感谢 S. Schmid 和 C. Siegel 的有益评论。特别感谢 J. Menuge、两位匿名审稿人和编辑 G. Dickens 的建设性审稿。研究经费来自澳大利亚联邦科学与工业研究组织 (CSIRO) 和澳大利亚研究委员会（资助 LE130100087）。我们感谢 S. Schmid 和 C. Siegel 的有益评论。特别感谢 J. Menuge、两位匿名审稿人和编辑 G. Dickens 的建设性审稿。研究经费来自澳大利亚联邦科学与工业研究组织 (CSIRO) 和澳大利亚研究委员会（资助 LE130100087）。我们感谢 S. Schmid 和 C. Siegel 的有益评论。特别感谢 J. Menuge、两位匿名审稿人和编辑 G. Dickens 的建设性审稿。