| 冰长石——大厂锡一多金属矿床同生 |
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| 引用本文：.1993.Adularia-an important indicator mineral of syngenetic origin for stratiform mineralization at the Dachang tin-polymetallic deposit[J].Mineral Deposits,12(4):330~337 |
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| 基金项目:地质行业基金会资助项目 |
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| 中文摘要:钾长石在大厂锡-多金属矿床分布广泛，与成矿关系密切。长期以来，对其成因有种种不同看法。本文最新研究证明，该矿床中的钾长石属于冰长石和钡冰长石，系钾长石的低温变种。这种低温钾长石是在成岩期形成的，而不是岩浆期后热液交代作用的产物。无疑，这项新发现为大厂锡-多金属矿床同生成因提供了重要新证据。 |
| 中文关键词:(钡)冰长石 成岩作用 大厂锡矿床 |
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| Adularia-an important indicator mineral of syngenetic origin for stratiform mineralization at the Dachang tin-polymetallic deposit |
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| Abstract:K-feldspars are widespread i n rocks of the Dachang tin-polymetallic ore field and occur in the stratiform, bedded ores. Current data indicate that the K-feldspars are a low-temperature variety, corresponding to adularia or hyalophane. Microscopic studies show that many of these K-feldspar grains have the distinctive lozenge shapes, characteristic of adularia. Their longer diagonal corresponds to the optical orientation of Ng, like that of typical adularia. Studies of five grains on the Fedorov Stage indicate that this adularia has smaller optical angles, (-)2V ranging from 10 to 14 degrees, thus is obviously different from orthoclase. X-ray analyses show it to be monoclinic, and its powder diffraction data are similar to those of adularia as described in the literature. Two samples were studied to determine its structural state. The results show that the site occupancies of aluminum in the lattice are t1(o)= t1 (m)=0.330 and 0.365, and degrees of Si-AI ordering are S=0.25 and 0.40, respectively. Its paragenetic relationships and spatial and temporal distribution in the ore-bearing strata indicate that it may have formed during a digenetic stage of deposition. Microprobe analyses of adularia coexisting with sulfide and cassiterite in thin mineralized layers of the stratiform ores reveal that the former contain high contents of BaO, up to 4.75％, thus indicating hyalophane, and the latter have no significant BaO content. These data, including the identification of very low-temperature K-feldspars, their optical and crystallographic characteristics and high barium content provide important new evidence favoring a sedimentary exhalative-diagenetic origin for stratiform mineralization in the Dachang tin-polymetallic field. |
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