The Mesoproterozoic Rondônia Tin Province of the Amazonian craton records a protracted history of about 600 m.y. of successive rare-metal granite intrusions and hosts the youngest known event of tin-granite emplacement of the craton—a rare-metal granite suite known as the Younger Granites of Rondônia intrusive suite. The ~1 Ga suite is currently interpreted as intracratonic magmatism resulting from a Grenvillian-age orogeny during the assembly of Rodinia. The Santa Bárbara massif is a tin-granite system of the Younger Granites of Rondônia intrusive suite that hosts Sn-Nb-Ta-W–bearing endogreisen and stockwork, as well as important placer deposits. The Santa Bárbara mine produces about 800 to 1,000 t Sn/year from placers and weathered greisen and represents about 20% of the tin mine output of the Rondônia Tin Province. Here, we report laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) cassiterite U-Pb ages of 989 ± 3 and 987 ± 6 Ma for the Santa Bárbara greisen and the cassiterite-quartz vein system, respectively. Alluvial cassiterite from placer mining has a U-Pb age of 995 ± 4 Ma, which is, within uncertainty, indistinguishable from those of primary cassiterite. These ages agree well with the previously published zircon and monazite U-Pb ages for the Santa Bárbara granite (978 ± 13 and 989 ± 13 Ma), which indicate a coeval relationship between hydrothermal tin mineralization and granite magmatism. The previously suggested 20- to 30-m.y. time span between granite magmatism and hydrothermal tin mineralization, which was based on mica K-Ar and Ar-Ar age data, is likely due to younger thermal disturbance of the isotopic systems.

中文翻译：

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巴西朗多尼亚锡区圣巴巴拉锡区的锡石 U-Pb 地球年代学

亚马逊克拉通中元古代朗多尼亚锡省记录了约 600 米连续稀有金属花岗岩侵入的漫长历史，并举办了已知最年轻的克拉通锡-花岗岩就位事件——一种被称为年轻花岗岩的稀有金属花岗岩组朗多尼亚侵入式套房。~1 Ga 套件目前被解释为在罗迪尼亚组装期间由格伦维尔时代的造山运动产生的克拉通内岩浆作用。Santa Bárbara 地块是朗多尼亚年轻花岗岩侵入岩组的锡花岗岩系统，该岩体包含含 Sn-Nb-Ta-W 的内灰岩和网状结构，以及重要的砂矿床。Santa Bárbara 矿每年从砂矿和风化 greisen 生产约 800 至 1,000 吨锡，约占朗多尼亚锡矿省锡矿产量的 20%。这里，我们报告了 Santa Bárbara greisen 和锡石-石英脉系统的激光烧蚀电感耦合等离子体质谱 (LA-ICP-MS) 锡石 U-Pb 年龄分别为 989 ± 3 和 987 ± 6 Ma。砂矿开采的冲积锡石的 U-Pb 年龄为 995 ± 4 Ma，在不确定范围内，与原生锡石的年龄无法区分。这些年龄与之前公布的 Santa Bárbara 花岗岩的锆石和独居石 U-Pb 年龄（978 ± 13 和 989 ± 13 Ma）非常吻合，这表明热液锡矿化和花岗岩岩浆作用之间存在同时代的关系。先前基于云母 K-Ar 和 Ar-Ar 年龄数据提出的花岗岩岩浆作用和热液锡矿化之间 20 到 30 米的时间跨度可能是由于同位素系统的较年轻的热扰动。