Depositing >1.5 Mt of Tin Within <1 m.y. of Initial Granitic Intrusion in the San Rafael Tin (-Copper) Deposit, Southeastern Peru

IF 5.5 1区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
M. Harlaux, D. Kontak, Alan H. Clark, K. Kouzmanov, Christopher S. Holm-Denoma, Stefano Gialli, Oscar Laurent, R. Spikings, A. Chauvet, Andrea Dini, Miroslav Kalinaj, L. Fontboté
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引用次数: 0

Abstract

The San Rafael Sn (-Cu) deposit, located in the Eastern Cordillera of southeast Peru, is one of the world’s largest cassiterite-bearing vein systems (>1 Mt Sn produced since 1969). The deposit consists of a quartz-cassiterite-chlorite-sulfide lode system spatially associated with an upper Oligocene (ca. 24 Ma) S-type granitic pluton. Based on a revised paragenetic sequence for the deposit, we interpret the temporal setting of both magmatic (biotite, K-feldspar) and hydrothermal (muscovite, adularia, cassiterite) minerals analyzed by 40Ar/39Ar step-heating and U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) geochronology. The least-disturbed biotite sample from the megacrystic monzogranite yielded a 40Ar/39Ar plateau age of 24.10 ± 0.26 Ma (2σ), which constrains the time of cooling of the upper part of the pluton to below 300°C. Greisen developed on top of the granitic cupola and its immediate metamorphic aureole dated at 24.24 ± 0.24 Ma (2σ; 40Ar/39Ar muscovite average plateau age) is interpreted to be contemporaneous with the emplacement of pre-ore quartz-tourmaline veins and breccias. In situ U-Pb dating of cassiterite, including both botryoidal cassiterite (“wood tin”) and coarse-grained cassiterite in quartz-chlorite veins and breccias, constrains the timing of the main Sn ore stage to between 24.10 ± 0.37 and 23.47 ± 0.53 Ma (2σ). Botryoidal and coarse-grained cassiterite are characterized by similar trace element compositions with fluctuating metal concentrations across growth banding, suggesting significant changes of physicochemical conditions of the hydrothermal system during cassiterite precipitation, likely caused by rapid and repeated mixing between magmatic fluids and meteoric groundwaters. Polymetallic sulfide-rich veins and quartz-carbonate veins are constrained to have formed between 22.72 ± 0.11 and 22.29 ± 0.24 Ma (2σ), based on adularia 40Ar/39Ar plateau ages. The latter overlap partially reset 40Ar/39Ar age spectra for K-feldspar megacrysts in the host granite and thus reflect pervasive alteration by hydrothermal fluids. Collectively, the results show the magmatic-hydrothermal system spanned at least 2 m.y. with the main Sn ore stage representing <1 m.y. in the lifetime of the deposit. The latest polymetallic stages postdate the main Sn ore stage by ca. 1 m.y. and reflect the waning of the hydrothermal system, accompanied by additional incursion of meteoric groundwaters. This study provides further evidence that the present-day exposed level of the San Rafael granite was a passive host for the Sn mineralization and only provided the structural focusing for the mineralizing fluids derived from a deeper part of the magmatic system.
秘鲁东南部圣拉斐尔锡(铜)矿床初始花岗质侵入岩<1米内沉积>1.5 Mt锡
圣拉斐尔锡(铜)矿床位于秘鲁东南部的东科迪勒拉,是世界上最大的锡石矿脉系统之一(自1969年以来生产了超过100万吨的锡)。矿床由石英-锡石-绿泥石-硫化物矿脉系统组成,空间上与渐新统上(约24 Ma) s型花岗岩体有关。利用40Ar/39Ar分步加热和U-Pb激光烧蚀-电感耦合等离子体质谱(LA-ICP-MS)年代学方法,对该矿床岩浆矿物(黑云母、钾长石)和热液矿物(白云母、钾长石、锡石)的时间背景进行了解释。微晶二长花岗岩中扰动最小的黑云母样品的40Ar/39Ar平台年龄为24.10±0.26 Ma (2σ),这限制了岩体上部冷却的时间在300℃以下。Greisen发育于花岗质冲天炉顶部,其直接变质光晕年龄为24.24±0.24 Ma (2σ;40Ar/39Ar白云母平均高原年龄)被解释为与成矿前石英-电气石脉和角砾岩侵位同时期。锡石的原位U-Pb定年(包括石英绿泥石脉和角砾岩中的粗粒锡石(“木锡”)和壶状锡石)将锡石主阶段的时间限制在24.10±0.37 ~ 23.47±0.53 Ma (2σ)之间。矿脉状锡石和粗粒锡石的微量元素组成相似,金属浓度在生长带上波动,表明锡石降水过程中热液系统的物理化学条件发生了显著变化,可能是岩浆流体与大气地下水快速反复混合所致。根据40Ar/39Ar的高原年龄,富硫化物多金属脉和石英-碳酸盐脉形成于22.72±0.11 ~ 22.29±0.24 Ma (2σ)之间。后者的重叠部分重置了成矿岩体中钾长石巨晶的40Ar/39Ar年龄谱,从而反映了热液流体的普遍蚀变。结果表明,岩浆-热液系统的跨度至少为2 m.,其中主锡矿期在矿床生命周期中占比小于1 m.。最新的多金属阶段比主要的锡矿阶段晚约1亿年,反映了热液系统的减弱,伴随着大气地下水的额外入侵。该研究进一步证明了圣拉斐尔花岗岩现今暴露水平是锡成矿的被动宿主,仅为岩浆系统深部的成矿流体提供了构造聚焦。
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来源期刊
Economic Geology
Economic Geology 地学-地球化学与地球物理
CiteScore
10.00
自引率
6.90%
发文量
120
审稿时长
6 months
期刊介绍: The journal, now published semi-quarterly, was first published in 1905 by the Economic Geology Publishing Company (PUBCO), a not-for-profit company established for the purpose of publishing a periodical devoted to economic geology. On the founding of SEG in 1920, a cooperative arrangement between PUBCO and SEG made the journal the official organ of the Society, and PUBCO agreed to carry the Society''s name on the front cover under the heading "Bulletin of the Society of Economic Geologists". PUBCO and SEG continued to operate as cooperating but separate entities until 2001, when the Board of Directors of PUBCO and the Council of SEG, by unanimous consent, approved a formal agreement of merger. The former activities of the PUBCO Board of Directors are now carried out by a Publications Board, a new self-governing unit within SEG.
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