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首页> 外文期刊>Economic geology and the bulletin of the Society of Economic Geologists >Evolution of the Breccia-Hosted Porphyry Cu-Mo-Au Deposit at Agua Rica, Argentina: Progressive Unroofing of a Magmatic Hydrothermal System
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Evolution of the Breccia-Hosted Porphyry Cu-Mo-Au Deposit at Agua Rica, Argentina: Progressive Unroofing of a Magmatic Hydrothermal System

机译：阿根廷阿瓜里卡角砾岩斑岩型斑岩型铜钼金矿床的演化：岩浆热液系统的渐开顶

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摘要

Detailed geologic mapping has been used to show that Agua Rica is a porphyry-style Cu-Mo-Au deposit that was first overprinted by polystage brecciation associated with a high sulfidation epithermal event and then by a barren surface-venting phreatomagmatic diatreme, prior to a final stage of supergene enrichment. It was emplaced in the Miocene (approx 8-5 Ma) as an outlier of the Farallon Negro volcanic Complex in northwestern Argentina. The Agua Rica deposit lies next to the contact between Precambrian or lower Paleozoic metasedimentary rocks and coarse-grained Ordovician granites. In a first pulse of Miocene magmatism, equigranular to porphyritic intrusions were emplaced, with minor potassic alteration and weak Cu-Mo mineralization. Subsequent intrusion of feldspar porphyries was associated with intense porphyry-style stockwork veining, potassic and propylitic alteration, and disseminated Cu-Mo-Au mineralization (molybdenite, chalcopyrite +- bornite +- pyrite). The present alteration and mineralization pattern is dominated by an almost pervasive overprint of high sulfidation epithermal assemblages (phyllic and advanced argillic alteration and Cu-Au-Ag-As-Pb-Zn mineralization) in breccia cements and as void fillings. Covellite is the dominant copper mineral in the ore and seems to have partly or completely replaced chalcopyrite and bornite of the earlier porphyry events. The high sulfidation epithermal assemblages are closely related to the emplacement of a largely clast-supported hydrothermal breccia. Three major bodies of this breccia have been mapped on the basis of clast lithology, clast shape and size, degree of alteration, and composition of breccia matrix. Igneous breccia with a fine-grained porphyritic matrix is intimately associated and interfingers with the base of the hydrothermal breccia columns. A final phase of magmatic hydrothermal activity formed a matrix-supported and commonly bedded crater infill breccia. It formed by a surface-venting phreatomagmatic emption, as shown by a continuous downward transition from bedded breccias to clast-supported breccias with sandy or pumiceous matrix to a solid igneous breccia with a fine-grained porphyritic matrix in the lower core of the conical crater infill breccia body. Graded, matrix-rich epiclastic sediments subsequently filled the crater. Magmatic activity was terminated by a dike of unmineralized biotite porphyry; which intruded the crater infill breccia. Talus breccia was shed into the crater from the rim. Supergene leaching and enrichment, which replaced covellite, pyrite, chalcopyrite, and bornite by chalcocite and secondary covellite, formed an enrichment blanket that was dissected by the present-day, steeply incised topography. The distinctive feature of the Agua Rica hydrothermal system is the occurrence of early, weakly mineralized intrusions, later feldspar porphyries with stockwork-hosted chalcopyrite-bornite-molybdenite mineralization, hydrothermal breccias with an epithermal pyrite-covellite overprint, and barren surface-venting breccias-all exposed at one location within 1,000 m of vertical exposure. Reconstruction of the time sequence of these geologic elements indicates that Agua Rica is the result of a protracted history of magmatic hydrothermal activity with superposition of several intrusion events that probably extended over several million years during progressive regional uplift, erosion, and explosive unroofing.
机译：详细的地质图已经显示出阿瓜里卡是斑岩型的铜-钼-金矿床，首先是与高硫化超热事件有关的多阶段析，然后是贫瘠的表面通透的岩浆透热，然后叠印。超基因富集的最后阶段。它被放置在中新世（约8-5 Ma）中，是阿根廷西北部的Farallon Negro火山群的离群点。阿瓜里卡（Agua Rica）矿床毗邻前寒武纪或更早古生代沉积岩与粗粒奥陶纪花岗岩之间的接触。在中新世岩浆作用的第一个脉冲中，发生了从粒状到斑状的侵入，钾的蚀变较小，Cu-Mo矿化作用较弱。长石斑岩的随后侵入与斑岩型强烈的脉状脉动，钾和丙炔的蚀变，弥散的铜钼金矿化（辉钼矿，黄铜矿+-斑铜矿+-黄铁矿）有关。当前的蚀变和矿化模式主要由角砾岩水泥中的高硫化超热组合的几乎无处不在的叠印（页岩和晚期的阿尔吉尔蚀变以及Cu-Au-Ag-As-Pb-Zn矿化）和作为空隙填充物。 Covellite是矿石中主要的铜矿物，似乎已部分或完全替代了早期斑岩事件中的黄铜矿和斑铜矿。高度硫化的超热组合与很大程度上由碎屑支撑的热液角砾岩的位置密切相关。根据角砾岩的岩性，角砾的形状和大小，蚀变程度和角砾岩基质的组成，绘制了角砾岩的三个主要主体。火成角砾岩具有细粒斑状基质，与热液角砾岩柱的底部紧密相连。岩浆热液活动的最后阶段形成了基质支撑的且通常成岩的火山口填充角砾岩。它是由表面喷出的岩浆空洞形成的，表现为从层状角砾岩到含砂质或浮质基质的碎屑支撑角砾岩的连续向下过渡，到圆锥形火山口下部核中具有细粒斑状基质的固态火成角砾岩。填充角砾岩体。渐变的富含基质的表生碎屑沉积物随后充满了火山口。岩浆活动被未矿化的黑云母斑岩的堤坝终止。它侵入了火山口填充角砾岩。 Talus角砾岩从边缘掉入火山口。表观浸出和富集作用被球晶石和次生的富铝石取代了鹅卵石，黄铁矿，黄铜矿和堇青石，形成了被当今陡峭的地形所剖析的富集层。阿瓜里卡热液系统的显着特征是早期出现矿化程度较弱的侵入岩，后期长石斑岩伴有储藏的黄铜矿-钙铁矿-辉钼矿成矿作用，热液角砾岩有超热黄铁矿-铜铁矿叠印，以及贫瘠的表面通风角砾岩-全部暴露在垂直暴露1,000 m以内的一个位置。对这些地质元素的时间序列的重建表明，阿瓜里卡是岩浆热液活动历史悠久的结果，是几次侵入事件叠加的结果，这些事件可能在区域渐进式隆起，侵蚀和爆炸性顶顶过程中延续了数百万年。

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