Abstract The supergiant Olympic Dam Cu-U-Au-Ag deposit in South Australia is a type example of the iron-oxide copper–gold (IOCG) deposit family. Hosted entirely within heterogeneous breccia in 1.59 Ga granite, the deposit contains a volumetrically substantial and mineralogically diverse component of carbonate minerals. Carbonate minerals are always associated with ore minerals (sulfides, uraninite), implying a genetic relationship and providing an opportunity to use gangue carbonates to better understand ore formation. This study provides the first detailed and comprehensive petrographic and chemical/isotopic study of Olympic Dam carbonates, with a particular emphasis on petrography and texture, and an attempt is made to relate carbonate formation to local and regional events that have affected Olympic Dam. Based on a set of 196 carbonate-bearing samples, carbonate minerals are observed in all lithologies present at Olympic Dam. Carbonates occur as cement in breccia and conglomerates, as breccia clasts, in veins crosscutting ore-rich breccia and other rock types, in pores and ooids, and in the form of laminated carbonate. Siderite and siderite-rhodochrosite-magnesite solid solution are by far the most common carbonate types, whereas calcite, dolomite-ankerite solid solution and REE-fluorocarbonates are locally abundant. Single carbonate grains typically show compositional zones (simple or oscillatory) and replacement textures (including mutual replacement of carbonates with other carbonates and with hematite) are common. In the absence of consistent, deposit-wide paragenetic relationships, the carbonates were placed in seven associations based on host rock, mineralogy and texture: (1) coarse-grained calcite veins in weakly brecciated granite and rhyolite, (2) carbonates in strongly brecciated granite, (3) carbonate veins in bedded clastic facies, (4) carbonates in mafic and ultramafic igneous rocks, (5) massive barite-fluorite-dominated veins with minor carbonate, (6) laminated siderite, and (7) carbonate matrix in conglomerate-breccia-sandstone above the unconformity. Some of these associations can be related to regional tectonic events based on local context and relationships with dated assemblages. δ13C (−6.5‰ to −2‰) values for the carbonates show a relatively limited range whereas δ18O is more variable (+9.4‰ to + 20.9‰). C-O isotopic compositions for the various carbonate associations tend to overlap, suggestive of mixed fluid sources, recycling of older carbonate and perhaps other fractionation processes. The C-O isotope data overlap the compositional fields of several major carbon–oxygen reservoirs (magmatic, sedimentary) and carbon sources in local granite, felsic volcanics, older BIF and sedimentary rocks are all possible at different stages of carbonate deposition.

中文翻译：

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南澳大利亚州奥林匹克大坝 Cu-U-Au-Ag 矿床的碳酸盐岩。第 1 部分：分布、纹理、关联和稳定同位素 (C, O) 特征

摘要 南澳大利亚的特大奥林匹克坝 Cu-U-Au-Ag 矿床是氧化铁铜金 (IOCG) 矿床系列的典型例子。该矿床完全位于 1.59 Ga 花岗岩中的异质角砾岩内，含有大量体积大且矿物成分多样的碳酸盐矿物成分。碳酸盐矿物总是与矿石矿物（硫化物、铀矿）相关联，暗示着一种亲缘关系，并提供了使用脉石碳酸盐更好地了解矿石形成的机会。本研究首次对奥林匹克坝碳酸盐岩进行了详细而全面的岩相学和化学/同位素研究，特别强调了岩相学和质地，并尝试将碳酸盐岩的形成与影响奥林匹克坝的地方和区域事件联系起来。根据一组 196 个含碳酸盐样品，在奥林匹克大坝存在的所有岩性中都观察到了碳酸盐矿物。碳酸盐以角砾岩和砾岩中的胶结物、角砾碎屑、横切富含矿石的角砾岩和其他岩石类型的脉、孔隙和鲕粒以及层状碳酸盐的形式存在。菱铁矿和菱铁矿-菱锰矿-菱镁矿固溶体是迄今为止最常见的碳酸盐类型，而方解石、白云石-铁橄榄石固溶体和稀土-氟碳酸盐在当地较为丰富。单个碳酸盐颗粒通常表现出成分带（简单或振荡），并且置换结构（包括碳酸盐与其他碳酸盐和赤铁矿的相互置换）是常见的。在缺乏一致的、全矿床共生关系的情况下，根据主岩、矿物学和质地，将碳酸盐分为七个组合：(1) 弱角砾岩和流纹岩中的粗粒方解石脉，(2) 强角砾岩中的碳酸盐，(3) 层状碎屑相中的碳酸盐脉， (4) 基性和超基性火成岩中的碳酸盐，(5) 块状重晶石-萤石为主的脉，含少量碳酸盐，(6) 层状菱铁矿，(7) 不整合面上方砾岩-角砾岩-砂岩中的碳酸盐基质。其中一些关联可能与基于当地背景和与年代久远组合关系的区域构造事件有关。碳酸盐的 δ13C（-6.5‰ 至 -2‰）值显示出相对有限的范围，而 δ18O 的变化更大（+9.4‰ 至 +20.9‰）。各种碳酸盐组合的 CO 同位素组成倾向于重叠，暗示了混合流体来源、旧碳酸盐的再循环和可能的其他分馏过程。CO 同位素数据与几个主要碳氧储层（岩浆、沉积）的组成场重叠，局部花岗岩、长英质火山岩、较老的 BIF 和沉积岩中的碳源都可能处于碳酸盐沉积的不同阶段。