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首页> 外文期刊>Current Science: A Fortnightly Journal of Research >Re-examination of quartz-sillimanite-hypersthene-cordierite gneisses fromthe Vijayanagaram district: Does surinamite occur in the Eastern GhatsBelt?
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Re-examination of quartz-sillimanite-hypersthene-cordierite gneisses fromthe Vijayanagaram district: Does surinamite occur in the Eastern GhatsBelt?

机译：重新检查维贾亚纳加拉姆地区的石英-硅线石-高云杉-堇青石片麻岩：苏打石发生在东部高止山脉吗？

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摘要

Ramesh Kumar et al.(1) reported a boron- and gallium-bearing variety of the rare beryllosilicate surinamite in quartzofeldspathic gneisses from 7 localities near Vizianagaram, the first report of surinamite in India. These surinamite-bearing gneisses are unusually enriched in beryllium compared to other pelitic gneisses, and few non-pegmatitic silicate minerals simultaneously contain significant amounts of beryllium and boron, so the report of surinamite in the Vizianagaram gneisses is of special geochemical and mineralogical interest. In samples from two of the localities studied by Ramesh Kumar et al.(1), including four chips of their original specimens, no surinamite was found. Instead, we identified abundant hypersthene. Petrographic study and electron microprobe analyses of minerals in the original samples show these to contain quartz, K-feldspar, aluminum-rich hypersthene (7.92-10.18 wt% Al2O3), garnet (on average Alm(0.58)Prp(0.39)Sps(0.01)Grs(0.01)), zinc- and chromium-poor hercynite, sillimanite (1.47-1.75 wt% Fe2O3), magnetite and ilmenite-hematite intergrowths. Secondary cordierite is poor in alkalis and calcium, whereas biotite is rich in titanium and fluorine. Mineral compositions indicate that these gneisses crystallized under relatively oxidizing and very dry conditions near 1000 degreesC and 7 kbar. No evidence was found for beryllium, boron or gallium enrichments, but a new occurrence of the borosilicate prismatine indicates the presence of a boron-enriched layer in the gneisses.
机译：Ramesh Kumar等人（1）报道了来自Vizianagaram附近7个地区的石英长石片麻岩中稀有的铍和硼硅化苏里南粉，这是印度苏里南粉的首次报道。与其他胶质片麻岩相比，这些含苏里铝土的片麻岩中的铍含量异常丰富，并且很少有非定形硅酸盐矿物同时含有大量的铍和硼，因此关于Vizianagaram片麻岩中苏里南石的报道具有特殊的地球化学和矿物学意义。在Ramesh Kumar等人（1）研究的两个地方的样本中，包括其原始样本的四片碎屑，未发现苏里南石。取而代之的是，我们确定了丰富的高硫醚。原始样品中矿物的岩石学研究和电子微探针分析表明，这些矿物包含石英，钾长石，富含铝的超高硫（7.92-10.18 wt％Al2O3），石榴石（平均Alm（0.58）Prp（0.39）Sps（0.01） Grs（0.01）），锌和铬贫乏的锂铁矿，硅线石（1.47-1.75 wt％Fe2O3），磁铁矿和钛铁矿-赤铁矿共生。次生堇青石的碱金属和钙含量较低，而黑云母的钛和氟含量较高。矿物成分表明，这些片麻岩在相对氧化和非常干燥的条件下（接近1000摄氏度和7 kbar）结晶。没有发现富集铍，硼或镓的证据，但是新出现的硼硅酸三氮嗪表明在片麻岩中存在富硼层。

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