The Carpentaria province (McArthur basin and Mount Isa inlier) in northern Australia is one of the most important districts for clastic-dominated (CD-type) massive sulfide deposits. The George Fisher Zn-Pb-Ag deposit, located in this province, is hosted by the carbonaceous Urquhart Shale Formation (ca. 1654 Ma) in a region that has an active history of metamorphism and tectonism. In this study, paragenetically constrained pyrite in samples from the George Fisher deposit and unmineralized Urquhart Shale have been analyzed in situ using secondary ion mass spectrometry (SIMS) of sulfur isotopes (δ³⁴S values). Samples were taken from four drill cores through the main orebodies at George Fisher and one drill core through correlative, unmineralized Urquhart Shale (Shovel Flats area). Five generations of pyrite were identified at George Fisher and record a protracted history of sulfate reduction under diagenetic and subsequent hydrothermal conditions: (1) fine-grained, subhedral-spheroidal pyrite (Py-0), (2) coarse-grained, anhedral pyrite (Py-1) associated with ore-stage 1 sphalerite and galena, (3) coarse-grained, euhedral pyrite (Py-2) associated with ore-stage 2 sphalerite, galena, and pyrrhotite, (4) massive subhedral to euhedral pyrite (Py-3) associated with ore-stage 3 chalcopyrite, pyrrhotite, galena, and sphalerite, and (5) coarse-grained euhedral pyrite (Py-euh), which occurs only in unmineralized rocks. In the unmineralized Shovel Flats drill core, only Py-0 and Py-euh are present. Whereas pre-ore pyrite (Py-0) preserves negative δ³⁴S values (–8.1 to 11.8‰), the ore-stage pyrites (Py-1, Py-2, and Py-3) have higher δ³⁴S values (7.8–33.3, 1.9–12.7, and 23.4–28.2‰, respectively). The highest δ³⁴S values (7.2–33.9‰) are preserved in Py-euh. In combination with petrographic observations, the δ³⁴S values of pyrite provide evidence of three different processes responsible for the reduction of sulfate at George Fisher. Reduced sulfur in fine-grained pyrite (Py-0) formed via microbial sulfate reduction (MSR) under open-system conditions prior to the first generation of hydrothermal pyrite (Py-1) in ore-stage 1, which most likely formed via thermochemical sulfate reduction (TSR). During deformation, previously formed sulfide phases were then recycled and replaced during a second hydrothermal event (ore-stage 2), resulting in intermediate sulfur isotope values. Another syndeformational hydrothermal Cu event, involving a sulfate-bearing fluid, formed ore-stage 3 via TSR. This study demonstrates that the fine-grained pyrite formed pre-ore under conditions open to sulfate and outlines the role of multiple stages of sulfide formation in producing high-grade Zn-Pb-Ag orebodies in the Mount Isa inlier.

中文翻译：

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北元古元古代Urquhart页岩层和George Fisher Zn-Pb-Ag矿床硫铁矿形成条件下的硫同位素约束

澳大利亚北部的卡彭塔里亚省（麦克阿瑟盆地和伊萨山外围地区）是碎屑为主的（CD型）大型硫化物矿床的最重要地区之一。位于该省的George Fisher Zn-Pb-Ag矿床由碳质的Urquhart页岩层（约1654 Ma）所控制，该地区具有活跃的变质和构造历史。在这项研究中，paragenetically约束黄铁矿在使用硫的同位素的二次离子质谱法（SIMS）从乔治费舍尔存款和未矿化厄克特页岩样品中原位进行了分析（δ ³⁴S值）。样品是通过George Fisher的主要矿体从四个钻孔岩心中采集的，而从相关的，未矿化的Urquhart页岩（铲子平坦区）中采集了一个钻孔岩心。在乔治费舍尔发现了五代黄铁矿，并记录了在成岩作用和随后的热液条件下硫酸盐还原的悠久历史：（1）细粒，亚面体球状黄铁矿（Py-0），（2）粗粒，亚面体黄铁矿（Py-1）与矿石阶段1的闪锌矿和方铅矿相关，（3）与矿石阶段2闪锌矿，的方铅矿和黄铁矿相关的粗粒，正矿黄铁矿（Py-2），（4）块状至正圆形的黄铁矿（Py-3）与矿石阶段3的黄铜矿，黄铁矿，方铅矿和闪锌矿有关，以及（5）粗粒全黄铁矿（Py-euh），仅在未矿化的岩石中发生。在未矿化的“铲平”钻芯中，仅存在Py-0和Py-euh。前矿黄铁矿（Py-0）保留负δ^34个价值观（-8.1至11.8‰），矿石级黄铁矿（PY-1，PY-2，和PY-3）具有较高的δ ^34个价值观（7.8-33.3，1.9-12.7，和23.4-28.2‰ ， 分别）。最高δ ³⁴价值观（7.2-33.9‰）被保留在PY-EUH。与岩相观察，δ组合³⁴黄铁矿的S值提供了乔治·费舍尔负责硫酸盐还原的三种不同过程的证据。矿石阶段1中第一批热液黄铁矿（Py-1）生成之前，在开放系统条件下通过微生物硫酸盐还原（MSR）形成的细粒黄铁矿（Py-0）中的还原硫硫酸盐还原（TSR）。在变形过程中，先前形成的硫化物相随后被循环利用，并在第二次水热事件中发生替代（阶段2），从而得到中等的硫同位素值。另一个含硫酸盐流体的同形热液铜事件通过TSR形成了矿石阶段3。