Quartz dioritic impact melt dikes around the 1.85 Ga Sudbury Igneous Complex, locally referred to as offset dikes, are well endowed with respect to Ni-Cu-platinum group elements (PGE). However, only those dikes proximal (<6 km) to the main mass of the Sudbury Complex are mineralized at an economic grade and, in places, host world-class deposits. We report on a new discovery of such heavily mineralized offset dike at Rathbun Lake, about 15 km east of the currently known extent of the Sudbury Igneous Complex. There, a segment of amphibole quartz diorite is exposed at the contact between Huronian metasedimentary rocks and gabbro of the 2.22 Ga Nipissing Suite, xenoliths of which are abundant throughout the diorite and record textural evidence of partial melting. The mafic inclusion-bearing quartz diorite is the host of the Rathbun Lake showing, a small but high-grade PGE-Cu(-Ni) sulfide occurrence of hitherto controversial origin.A detailed petrographic and mineralogical characterization of this occurrence revealed a two-stage mineralization history. Disseminated to semimassive (net-textured) chalcopyrite ± loop-textured pentlandite ± magnetite containing Pd-bismuthotellurides and, more rarely, sperrylite and native gold—all of which are closely associated with base metal sulfides—are interpreted as magmatic. The semimassive sulfide averages ~40 g/t Pd + Pt + Au at a Cu/(Cu + Ni) of >0.9 and a Pd/Ir of >100,000. Mineralogy, ore textures, and mantle-normalized PGE + Au patterns match a specific type of Cu-rich mineralization in the Sudbury Igneous Complex known as footwall mineralization. By analogy with these footwall deposits, the occurrence is interpreted as having formed by downward percolation of a highly fractionated sulfide melt toward the bottom of a now largely eroded offset dike. The magmatic paragenesis was hydrothermally overprinted at lower greenschist-facies conditions to pyrite-chalcopyrite-violarite ± covellite ± millerite. This involved also local remobilization into pyrite-chalcopyrite veinlets and the liberation of precious metal minerals from their sulfide hosts. In contrast to base metal sulfides, most precious metal minerals were resistant to hydrothermal alteration, although corrosion of some grains is noted as well as their truncation by chlorite and epidote. Micron-scale X-ray mapping revealed a progressive replacement of magmatic Pd-Bi-Te minerals, where in contact with hydrous silicates, by Sb- and Hg-bearing Pd minerals such as temagamite, Pd₃HgTe₃. The timing and nature of this hydrothermal overprint remains uncertain, but a connection to later regional metamorphism and faulting seems most plausible.Our finding of magmatic PGE-base metal sulfide at Rathbun Lake suggests a new subtype of distal offset dike-hosted mineralization in an area so far not known for offset dikes. It opens up new opportunities in the search for unconventional ore deposits around the Sudbury impact structure and improves our understanding on the distribution of impact melt-derived dikes around complex craters.

中文翻译：

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与萨德伯里火成岩复合体的Rathbun补偿堤有关的高级岩浆铂族元素-Cu（-Ni）硫化物矿化作用（加拿大安大略省）

相对于镍-铜-铂族元素（PGE），在1.85 Ga萨德伯里火成岩周围的石英二方晶系冲击熔岩（在当地被称为偏置堤防）具有很好的赋能。但是，只有那些靠近萨德伯里综合体主要部分（<6公里）的堤防才被开采为经济等级的矿藏，并且在某些地方拥有世界一流的矿藏。我们报告了一个新发现的矿床，该矿床位于拉德邦湖（Rudbun Lake），距离目前已知的萨德伯里火成岩复杂范围以东约15公里。在那里，Huronian沉积沉积岩与2.22 Ga Nipissing Suite的辉长岩之间的接触处暴露出一部分闪石石英闪长岩，这些闪长岩的异岩在整个闪长岩中都很丰富，并记录了部分熔融的质地证据。镁铁质包裹体石英闪长岩是Rathbun湖的主人，迄今有争议的一个小但高品位的PGE-Cu（-Ni）硫化物事件。对该事件的详细岩石学和矿物学特征揭示了两阶段的成矿历史。散布到半质量（网状）黄铜矿–环状纹理的方铁矿–含Pd-bismuthotellurides的磁铁矿，以及很少有锂闪石和原生金-所有这些都与贱金属硫化物密切相关-被认为是岩浆。在Cu /（Cu + Ni）> 0.9和Pd / Ir> 100,000时，半块状硫化物的平均含量约为40 g / t Pd + Pt + Au。矿物学，矿石质地和地幔归一化的PGE + Au模式与萨德伯里火成岩复杂的一种富含铜的矿化类型相称，即底盘矿化。类似于这些底盘沉积物，该现象被解释为是由高度分馏的硫化物熔体朝着现在已严重侵蚀的胶印堤坝的底部向下渗滤形成的。岩浆共生作用在较低的绿片岩相条件下被热液叠印成黄铁矿-黄铜矿-堇青石±陨石±千粒岩。这还涉及局部迁移到黄铁矿-黄铜矿脉中以及从其硫化物宿主中释放出贵金属矿​​物。与贱金属硫化物相比，大多数贵金属矿物都耐水热蚀变，尽管已注意到某些晶粒的腐蚀以及它们被绿泥石和附子截断的结果。微米级X射线测绘表明，与含水硅酸盐接触的岩浆Pd-Bi-Te矿物质逐渐被含Sb和Hg的Pd矿物质（例如，钛铁矿，Pd）替代 岩浆共生作用在较低的绿片岩相条件下被水热套印成黄铁矿-黄铜矿-堇青石±玄武岩±千粒岩。这还涉及到局部迁移到黄铁矿-黄铜矿细矿中以及从其硫化物宿主中释放出贵金属矿​​物。与贱金属硫化物相比，大多数贵金属矿物都耐水热蚀变，尽管已注意到某些晶粒的腐蚀以及它们被绿泥石和附子截断的结果。微米级X射线测绘表明，与含水硅酸盐接触的岩浆Pd-Bi-Te矿物质逐渐被含Sb和Hg的Pd矿物质（例如，钛铁矿，Pd）替代 岩浆共生作用在较低的绿片岩相条件下被热液叠印成黄铁矿-黄铜矿-堇青石±陨石±千粒岩。这还涉及到局部迁移到黄铁矿-黄铜矿细矿中以及从其硫化物宿主中释放出贵金属矿​​物。与贱金属硫化物相比，大多数贵金属矿物都耐水热蚀变，尽管已注意到某些晶粒的腐蚀以及它们被绿泥石和附子截断的结果。微米级X射线测绘表明，与含水硅酸盐接触的岩浆Pd-Bi-Te矿物质逐渐被含Sb和Hg的Pd矿物质（例如，钛铁矿，Pd）替代 这还涉及局部迁移到黄铁矿-黄铜矿脉中以及从其硫化物宿主中释放出贵金属矿​​物。与贱金属硫化物相比，大多数贵金属矿物都耐水热蚀变，尽管已注意到某些晶粒的腐蚀以及它们被绿泥石和附子截断的结果。微米级X射线测绘表明，与含水硅酸盐接触的岩浆Pd-Bi-Te矿物质逐渐被含Sb和Hg的Pd矿物质（例如，钛铁矿，Pd）替代 这还涉及局部迁移到黄铁矿-黄铜矿脉中以及从其硫化物宿主中释放出贵金属矿​​物。与贱金属硫化物相比，大多数贵金属矿物都耐水热蚀变，尽管已注意到某些晶粒的腐蚀以及它们被绿泥石和附子截断的结果。微米级X射线测绘表明，与含水硅酸盐接触的岩浆Pd-Bi-Te矿物质逐渐被含Sb和Hg的Pd矿物质（例如，钛铁矿，Pd）替代 尽管已注意到某些谷物的腐蚀以及它们被绿泥石和附子截断的现象。微米级X射线测绘表明，与含水硅酸盐接触的岩浆Pd-Bi-Te矿物质逐渐被含Sb和Hg的Pd矿物质（例如，钛铁矿，Pd）替代 尽管已注意到某些谷物的腐蚀以及它们被绿泥石和附子截断的现象。微米级X射线测绘表明，与含水硅酸盐接触的岩浆Pd-Bi-Te矿物质逐渐被含Sb和Hg的Pd矿物质（例如，钛铁矿，Pd）替代₃汞₃。这种热液叠印的时间和性质仍不确定，但与后来的区域变质作用和断层的联系似乎是最合理的。到目前为止，还不以抵消堤防闻名。它为寻找萨德伯里冲击构造周围的非常规矿藏开辟了新的机会，并增进了我们对复杂的陨石坑周围冲击熔岩堤防分布的理解。