Abstract

A new Sc-bearing variety of tusionite has been found in the Eastern Pamirs, in the near-miarolitic Dorozhny granite pegmatite complex at the Kukurt pegmatite field (left bank of the Kukurt River, 45 km east of the settlement of Murghab, Gorno-Badakhshan Autonomous Oblast, Tajikistan). Miarolitic pegmatites are related to the alpine leucocratic granites of the Shatput intrusive complex and occur in rocks of the Sarydzhilga Formation (PR₃?) metamorphosed under amphibolite and epidote–amphibolite facies. Tusionite occurs in association with quartz, K-feldspar, albite, elbaite, Sc-bearing spessartine (up to 0.2 wt % Sc₂O₃) and accessory fluorapatite, Y-bearing fluorite, Sn-bearing titanite, magnetite, polycrase-(Y), B-rich gadolinite-(Y), ixiolite, manganocolumbite, pyrochlore, chernovite-(Y), cassiterite, varlamoffite, lepidolite, and Hf-rich zircon (up to 17.0 wt % HfO₂). Tusionite forms thin lamellae (0.05–0.25 mm) and fanlike aggregates. It is yellow and transparent with a vitreous luster. It has weak pleochroism, N_o (orange–yellow) > N_e (light yellow). It is a uniaxial negative mineral, n_o = 1.870(5), n_e = 1.760(3). The Raman spectrum has been reported for tusionite for the first time (laser excitation 532 nm); main bands: 228, 305, 379, 466, 661, 733, 750, 942, 1218, and 1458 cm^–1. Its X-ray diffraction pattern is similar to tusionite from the Southwestern Pamirs. Hexagonal unit cell parameters: a = 4.772(3), c = 15.28(3) Å. Chemical composition (electron microprobe, wt %, average of 14 analyses): 0.06 (0.00–0.31) Ta₂O₅; 50.28 (49.43–51.03) SnO₂; 0.02 (0.00–0.19) TiO₂; 1.02 (0.62–1.53) Sc₂O₃; 0.03 (0.00–0.19) CaO; 0.21 (0.16–0.46) FeO; 24.06 (23.59–24.34) MnO; 24.51 (calc. 23.90) B₂O₃; total 99.62 (99.08–100.79). The substitution mechanism involving Sc is not clear. Substitution of Sc⁺³ for Sn⁺⁴ with partial replacement of Mn⁺² by Mn⁺³ is possible; however, Sc negatively correlates not only with Sn, but also with (Fe + Mn), which may result from the location of Sc in both octahedral positions with Sn⁺⁴ and Mn⁺².

中文翻译：

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东帕米尔高原（塔吉克斯坦）的一种新的含sion榴辉岩品种

摘要

在帕米尔高原东部，在库库特伟晶岩田（库库尔河左岸，库尔纳河定居点以东45公里的库库特河左岸）的近半橄榄岩多罗日尼花岗岩伟晶岩复合体中，发现了一种新的含Sc的辉长岩变种。塔吉克斯坦自治州）。微硅质伟晶岩与Shatput侵入复合体的高山白垩纪花岗岩有关，并发生在变质岩和闪石－闪石岩相下变质的Sarydzhilga组（PR ₃？）的岩石中。球墨石与石英，钾长石，钠长石，钠长石，含Sc的Spessartine结合使用（最高0.2 wt％Sc ₂ O ₃）及其副萤石，含Y的萤石，含Sn的钛土，磁铁矿，多裂纹-（Y），富B的ado石-（Y），异黄铁矿，锰锰矿，烧绿石，钙锰矿-（Y），锡石，硅锰矿，锂云母，和富含H的锆石（最高17.0 wt％的HfO ₂）。球状长石形成薄薄片（0.05-0.25毫米）和扇状聚集体。它是黄色透明的，具有玻璃光泽。它具有弱的多相性，N _o（橙黄色）> N _e（浅黄色）。它是单轴负矿物，n _o = 1.870（5），n _e= 1.760（3）。首次报道了堇青石的拉曼光谱（激光激发532 nm）；主乐队：228、305、379、466、661、733、750、942、1218和1458 cm ^–1。它的X射线衍射图样类似于西南帕米尔高原的球墨石。六角形晶胞参数：a = 4.772（3），c = 15.28（3）。化学成分（电子探针，wt％，平均14次分析）：0.06（0.00–0.31）Ta ₂ O ₅；50.28（49.43–51.03）SnO ₂；0.02（0.00–0.19）TiO ₂；1.02（0.62-1.53​​）Sc ₂ O ₃；0.03（0.00–0.19）CaO；FeO 0.21（0.16-0.46）；24.06（23.59–24.34）MnO；24.51（计算23.90）B ₂O ₃ ; 总计99.62（99.08–100.79）。涉及Sc的替代机制尚不清楚。可以用Sc ⁺³取代Sn ⁺⁴，而用Mn ⁺³部分取代Mn ⁺²；但是，Sc不仅与Sn负相关，而且还与（Fe + Mn）负相关，这可能是由于Sc在Sn ⁺⁴和Mn ^+2的两个八面体位置上都具有负相关关系。