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.

中文翻译：

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秘鲁东南部圣拉斐尔锡（铜）矿床在初始花岗岩侵入体不到 1 米内沉积了 >1.5 吨锡

San Rafael 锡 (-Cu) 矿床位于秘鲁东南部的东科迪勒拉山脉，是世界上最大的含锡石矿脉系统之一（自 1969 年以来生产了超过 1 吨锡）。该矿床由石英-锡石-绿泥石-硫化物矿脉系统组成，在空间上与上渐新世（约 24 Ma）S 型花岗岩岩体相关。^{根据修改后的矿床共生序列，我们解释了通过40} Ar/ ³⁹ Ar 逐步加热和 U-Pb 激光分析的岩浆（黑云母、钾长石）和热液（白云母、铁矿、锡石）矿物的时间背景烧蚀电感耦合等离子体质谱 (LA-ICP-MS) 地质年代学。来自巨晶二长花岗岩的扰动最少的黑云母样品产生了24.10 ± 0.26 Ma (2σ) 的⁴⁰ Ar/ ³⁹ Ar 平台年龄，这将岩体上部的冷却时间限制在 300°C 以下。云英岩在花岗岩冲天炉顶部发育，其直接变质光环的年代为 24.24 ± 0.24 Ma（2σ；⁴⁰ Ar/ ³⁹ Ar 白云母平均高原年龄），被解释为与前矿石石英电气石脉和角砾岩的侵位同时发生。锡石（包括石英绿泥石脉和角砾岩中的葡萄状锡石（“木锡”）和粗粒锡石）的原位 U-Pb 测年将主要锡矿石阶段的时间限制在 24.10 ± 0.37 和 23.47 ± 0.53 之间马（2σ）。葡萄状锡石和粗粒锡石的特征是具有相似的微量元素组成，且金属浓度在生长带上波动，这表明锡石沉淀过程中热液系统的物理化学条件发生了显着变化，这可能是由岩浆流体和大气地下水之间的快速和反复混合引起的。^{根据阿杜拉利亚40} Ar/ ³⁹ Ar 高原年龄，富含多金属硫化物的矿脉和石英碳酸盐矿脉的形成时间为 22.72 ± 0.11 至 22.29 ± 0.24 Ma (2σ)。后者重叠部分重置了主体花岗岩中钾长石巨晶的⁴⁰ Ar/ ^{39 Ar 年龄光谱，从而反映了热液的普遍蚀变。}总的来说，结果显示岩浆-热液系统跨越了至少 2 my，其中主要锡矿石阶段代表矿床寿命<1 my。最新的多金属阶段比主要的锡矿阶段晚了大约 10 年。1 我反映了热液系统的减弱，同时伴随着大气地下水的额外入侵。这项研究提供了进一步的证据，表明目前暴露的圣拉斐尔花岗岩是锡矿化的被动宿主，并且只为来自岩浆系统更深部分的矿化流体提供了结构聚焦。