Tourmaline is a common mineral in granites and metamorphic rocks in collisional orogens. This paper describes graphite-bearing, metasomatic tourmalinites in sillimanite-zone schists of the Proterozoic Black Hills Orogen, South Dakota. The tourmalinites bound quartz veins and beyond about 1 m grade into schists with disseminated tourmaline, and ultimately tourmaline becomes only a trace, intrinsic phase in the schists. Next to the quartz veins, tourmaline has almost completely replaced schist minerals, including biotite, muscovite, and plagioclase. The tourmaline is generally anhedral and follows the original foliation direction of the schist. However, tourmaline is euhedral in quartz veinlets cutting through the tourmalinites. Tourmaline is compositionally zoned from having about 22 to 2% of apparent Al occupancy on the Y sites. There are very good negative correlations of Y(Fe2++Mg2+), XCa2+, and YTi4+ with YAl3+, and a very good positive correlation of X-site vacancies with YAl3+. Mg# [molar Mg2+/(Mg2++Fe2+)] is fairly invariant at approximately 0.5, which is somewhat higher than that in the precursor biotite. This is in contrast to tourmaline in the neighboring peraluminous Harney Peak leucogranite where the range of Y site occupancy of Al is small at about 20%, but the Mg# ranges from 0.12 to 0.5.The compositional trends in the metasomatic tourmaline are dominated by the exchange X☐ + 4 YAl3+ = XCa2+ + 3 Y(Fe2++Mg2+) + YTi4+. Mass-balance calculations suggest the metasomatizing fluid brought in H+ and B(OH)3 and removed K+, SiO2, and some Fe2+ during tourmalinization. Other elements in the tourmaline largely reflect the bulk composition of the replaced schist. The calculations show that silica in the quartz veins was locally derived, not brought in by the metasomatizing fluid. Interstitial graphite in the tourmalinites shows precipitation of carbon from the methane-bearing fluid. The study demonstrates an important effect of boron transfer by fluids during metamorphism and magmatism in the Earth's crust.

中文翻译：

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南达科他州布莱克希尔斯造山运动中减少片岩中交代托马硅酸盐的形成

电气石是花岗岩和碰撞造山带中变质岩中的常见矿物。本文描述了南达科他州元古代的Black Hills Orogen硅线石带片岩中的含石墨，交代的托马硅酸盐。电气石将石英脉和超过约1 m的坡度与散布的电气石结合成片岩，最终电气石仅成为片岩中的痕量固有相。在石英脉旁，电气石几乎已完全取代片岩矿物，包括黑云母，白云母和斜长石。电气石通常是反面的，并且遵循片岩的原始叶面方向。然而，碧玺中的石英细矿中的电气石是天然的。电气石在Y部位的组成占Al的表观Al占有率约为22％至2％。Y（Fe2 ++ Mg2 +），XCa2 +和YTi4 +与YAl3 +有很好的负相关，X位空位与YAl3 +有很好的正相关。Mg＃[摩尔Mg2 + /（Mg2 ++ Fe2 +）]大致不变，约为0.5，略高于黑云母中的Mg＃。这与邻近的高铝哈尼峰白云石中的电气石相反，Al的Y位占有率范围很小，约为20％，但Mg＃的范围从0.12至0.5。交换X☐+ 4 YAl3 + = XCa2 + + 3 Y（Fe2 ++ Mg2 +）+ YTi4 +。质量平衡计算表明，在电气化过程中，交代化流体引入了H +和B（OH）3，并去除了K +，SiO2和一些Fe2 +。电气石中的其他元素在很大程度上反映了被替换的片岩的整体组成。计算表明，石英脉中的二氧化硅是局部衍生的，而不是由交代流体引入的。电气石中的间隙石墨显示出含甲烷流体中碳的沉淀。这项研究表明，在地壳的变质和岩浆作用过程中，流体对硼的转移具有重要作用。