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首页> 外文期刊>Economic geology and the bulletin of the Society of Economic Geologists >Geology, Alteration, and Origin of Archean. Au-Ag-Cu Mineralizatior. Associated with the Synvolcanic Chibougamau Pluton: The Brosman Prospect, Abitibi Greenstone Belt, Canada
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Geology, Alteration, and Origin of Archean. Au-Ag-Cu Mineralizatior. Associated with the Synvolcanic Chibougamau Pluton: The Brosman Prospect, Abitibi Greenstone Belt, Canada

机译：太古代的地质，蚀变和起源。金银铜矿化。与同火山的Chibougamau岩体有关：加拿大阿比蒂比绿石带的布罗斯曼展望

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摘要

The Au-Ag-Cu Brosman prospect is located in the Line Lake area on the northern limb of the Chibougamau anticline, in the northeast part of the Archean Abitibi greenstone belt. This prospect comprises a broad N-S, subvertical mineralized envelope formed in a synvolcanic fault-related environment. This envelope is at least 300 m long, up to 30 m wide, and is known to a depth of 950 m, where it remains open. It exhibits two contrast ing mineralized zones that are representative of the varying styles of mineralization in the area. The Auriferous zone consists of both ubiquitous pyrite disseminations and Au-bearing silicate-sulfide veins in strongly fractured intrusive, effusive, and volcaniclastic rocks showing propylitic and chloritic alteration assemblages. The Polymetallic zone, on the other hand, is characterized by discrete, Cu-Ag-Au-rich magnetite-sulfide veins and lesser pyrite disseminations within distal propylitic and proximal potassic to sodic alteration zones. The Polymetallic zone is hosted by a chaotic assemblage of gabbro and tuff bodies interpreted as a talus megabreccia. Several lines of evidence, including the spatial distribution pattern and nature of the alteration and mineralization assemblages, metal associations, mass-balance calculations, pyrite composition, and crosscutting relationships are indicative of a preregional deformation, synvolcanic origin for the hydrothermal activity. Crosscutting relationships, alteration characteristics as well as whole-rock and LA-ICP-MS pyrite analyses reveal two stages of hydrothermal alteration and mineralization. Stage I consists of both ubiquitous disseminated pyrite, found in the Polymetallic and Auriferous zones, and contemporaneous magnetite-sulfide veins, restricted to the Polymetallic zone. Stage II is restricted to the Auriferous zone and corresponds to Au-bearing silicate-sulfide veins with characteristic vein-halo chloritic alteration overprinting Stage I alteration and mineralization. This hydrothermal activity is interpreted to have occurred concurrently with the development of the fertile, deeper magmatic-hydrothermal system related to the Chibougamau Pluton. Stage I hydrothermal activity, related to the early build-up of the volcanic sequence, formed a continuum of mineralization from discrete massive magnetite-sulfide veins to ubiquitous pyrite disseminations in a submarine talus megabreccia generated along synvolcanic faults. Afterward, a late Au-rich contribution to the hydrothermal fluids, possibly related to intermediate to felsic magmatism (the 2707.6 ± 1.4 Ma Line Lake stock), produced Stage II silicate-sulfide veins overprinting mineralization and alteration in favorably oriented and sustainably permeable fracture zones of the Auriferous zone. Overall, this study suggests that the Brosman prospect is a rare example of Archean polymetallic mineralization produced by a shallow subaqueous epithermal-style subsystem developed in a broader, fertile magmatichydrothermal arc setting.
机译：Au-Ag-Cu Brosman勘探区位于基布加高背斜北缘的Line Lake地区，位于太古代阿比提比绿岩带的东北部。该前景包括在与火山断层有关的环境中形成的宽阔的N-S，亚垂直矿化包膜。该封套的长度至少为300 m，最大宽度为30 m，已知深度为950 m，并保持打开状态。它显示了两个对比的矿化带，代表了该地区不同的矿化方式。含金矿带既有遍及黄铁矿的散布，又有强烈断裂的侵入性，喷出性和火山碎屑岩中的含金的硅酸盐-硫化物脉，显示出质变和质变的组合。另一方面，多金属带的特征是，富Cu-Ag-Au的磁铁矿-硫化物矿脉离散且在远距离的丙炔质和近钾质至苏打蚀变区中散布的黄铁矿较少。多金属带是由辉长岩和凝灰岩体（被解释为距骨巨角砾岩）的混沌组合所占据。包括空间分布模式和蚀变和矿化组合的性质，金属缔合，质量平衡计算，黄铁矿成分和横切关系在内的几条证据表明，该区域存在变形，是热液活动的合火山成因。横切关系，蚀变特征以及全岩和LA-ICP-MS黄铁矿分析揭示了热液蚀变和成矿的两个阶段。第一阶段包括在多金属和金铁矿区普遍存在的弥散性黄铁矿，以及仅限于多金属带的同期磁铁矿-硫化物脉。第二阶段仅限于金质带，并对应于含金的硅酸盐-硫化物脉，具有特征性的脉-卤氯蚀变套印，覆盖了第一阶段的蚀变和矿化作用。这种热液活动被解释为与与Chibougamau岩体有关的肥沃，深层的岩浆热液系统同时发生。与火山序列早期形成有关的第一阶段热液活动，形成了一个连续的矿化过程，从离散的块状磁铁矿-硫化物矿脉到沿顺伏断层产生的海底距骨巨型角砾岩中普遍的黄铁矿扩散。之后，晚期富金对热液的贡献，可能与中等岩浆作用有关（2707.6±1.4 Ma Line Lake储量），产生了II期硅酸盐-硫化物矿脉，覆盖了成矿作用和方向有利且可持续渗透的裂隙带的蚀变。金耳区。总体而言，这项研究表明Brosman矿床是由较浅的水下超热型子系统产生的太古宙多金属矿化的罕见例子，该子系统在较宽的肥沃岩浆热液弧环境中发展而成。

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