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首页> 外文期刊>Economic geology and the bulletin of the Society of Economic Geologists >Physicochemical Evolution of a Porphyry-Breccia System: A Laser Ablation ICP-MS Study of Fluid Inclusions in the Mount Leyshon Au Deposit, Queensland, Australia
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Physicochemical Evolution of a Porphyry-Breccia System: A Laser Ablation ICP-MS Study of Fluid Inclusions in the Mount Leyshon Au Deposit, Queensland, Australia

机译：斑岩-角砾岩系统的物理化学演化：澳大利亚昆士兰州莱森山金矿床中流体包裹体的激光烧蚀ICP-MS研究

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摘要

The evolution of magmatism, brecciation, alteration, and mineralization is described for the Mount Leyshon intrusive complex, Queensland, Australia, using P-T-V-X analysis and major to trace element analysis of single fluid inclusions using laser ablation ICP-MS. The ～290 Ma Mount Leyshon intrusive complex is a subvolcanic porphyry-breccia system mined for ～97 metric tons (t) Au (70 Mt at ～1.4 g/t Au) between 1986 and 2000. The Mount Leyshon intrusive complex is characterized by several generations of genetically related breccias and magmatic intrusions. Both alteration and mineralization can be traced to specific intrusive events. The earliest phase of brecciation was followed by widespread biotite-magnetite alteration (stage 1). Fluid inclusions associated with stage 1 were trapped at >350℃ and >145 bars and were anomalously K and Fe rich. This stage was followed by the emplacement of rhyolite to dacite stocks and coeval breccia pipes (stage 2). Fluids exsolved from these magmas simultaneously exsolved Na-K-Fe-Mn-rich brine (～60 wt % NaCl equiv) and dilute vapor at ～500 bars (～2-km paleodepth) and >600℃. Pressures likely oscillated between lithostatic and sublithostatic conditions in response to the transient rupture and sealing of intrusions and wall rocks. Hydrothermal fluids infiltrating breccia pore space produced base metal mineralization (stage 3). Stage 3 fluid inclusions contain 2 to 10 wt percent NaCl equiv and were trapped at 300° to 400℃ below 500 bars. Stage 3 fluids were depleted in K, Fe, and Mn, and enriched in Ca, Sr, and Ba relative to stage 2 brines. This trend is consistent with the transition from potassic alteration in stage 2 to feldspar-destructive phyllic alteration in stage 3. Cu, Zn, and Pb were conservative elements above 350℃ and precipitated nonselectively as sulfides below 350℃ in a bulk ratio very similar to that measured in fluid inclusions. Subsequent emplacement of andesite to rhyodacite dikes (stage 4) was marked by Au and additional base metal sulfide mineralization in veins and breccia cavities. Stage 4 fluids are chemically similar to stage 3 but contain several mol percent CO_2, perhaps suggesting a more mafic, CO_2-charged magma source relative to earlier intrusive pulses. In addition to fluid cooling, the destabilization of Au bisulfide complexes attending phase separation of H_2O-CO_2-NaCl fluids below 400℃ and 400 bars was the likely cause for Au precipitation. Mount Leyshon appears to indicate that CO_2 can play a crucial role in the transport of gold-bearing solutions from a magmatic source at depth into much shallower hydrothermal environments.
机译：使用P-T-V-X分析以及使用激光烧蚀ICP-MS对单个流体包裹体进行痕量元素分析的方法，描述了澳大利亚昆士兰州的Leyshon侵入复合体的岩浆作用，角砾岩化，蚀变和成矿作用的演化。 〜290 Ma的Leyhonhon侵入复合体是一个亚火山岩斑岩角砾岩系统，在1986年至2000年之间开采了约97公吨（t）的金（70 Mt，约1.4 g / t Au）。与世代相传的角砾岩和岩浆侵入。蚀变和矿化都可以追溯到特定的侵入事件。角砾岩化的最早阶段是随后的黑云母-磁铁矿大范围蚀变（阶段1）。与阶段1相关的流体夹杂物在> 350℃和> 145 bar的条件下被捕获，并且异常富含K和Fe。在此阶段之后，将流纹岩放置在dacite浆液中和流传的角砾岩管道中（阶段2）。从这些岩浆中溶解出的流体在〜500 bar（古深度〜2 km）和> 600℃的温度下同时溶解了富含Na-K-Fe-Mn的盐水（〜60 wt％NaCl当量）和稀蒸汽。岩性和亚岩性之间的压力可能会因侵入体和围岩的瞬时破裂和封闭而发生振荡。渗入角砾岩孔隙空间的热液使贱金属矿化（阶段3）。第3阶段的流体夹杂物含有2至10 wt％的NaCl当量，并在300 bar至500 bar以下的温度下被捕集。相对于第2阶段盐水，第3阶段的流体贫乏了K，Fe和Mn，并富含Ca，Sr和Ba。这种趋势与从第2阶段的钾化蚀变到第3阶段的长石破坏性的蚀变变化相一致。Cu，Zn和Pb在350℃以上是保守元素，在350℃以下作为硫化物以非选择性方式沉淀，其堆积率与流体包裹体中的测量值。随后将安山岩置于流纹岩堤上（第4阶段），其特征是金和脉脉和角砾岩腔中额外的贱金属硫化物矿化。第4阶段的流体在化学上与第3阶段相似，但包含几摩尔百分比的CO_2，这可能表明相对于较早的侵入性脉冲而言，镁铁质岩浆来源更为镁铁质。除流体冷却外，在低于400℃和400 bar的压力下，H_2O-CO_2-NaCl流体相分离引起的二硫化金Au络合物的失稳可能是Au沉淀的原因。莱顺山似乎表明，CO_2在将含金溶液从深部岩浆源输送到较浅的热液环境中起着至关重要的作用。

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