| 对大道尔吉铬铁矿床成因的新认识 |
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| 引用本文：.1989.Some new ideas on the genesis of the Dadao Erji chromite deposit[J].Mineral Deposits,8(1):3~18 |
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| 中文摘要:大道尔吉岩体为一肢解的蛇绿岩残片，由两个单元组成，一为堆晶杂岩，另一为地幔橄榄岩。堆晶杂岩包括三个岩浆旋回，每一旋回均表现比由超镁铁质向镁铁质演化的特点。工业铬铁矿产于堆晶杂岩第三旋回底部的纯澉岩—含辉纯橄岩中，而产于地幔橄榄岩中的铬铁矿为数甚微。矿体主要由各种浸染状的铬铁矿石组成。矿体的围岩为纯橄岩且两者逐渐过渡。副矿物铬尖晶石与造矿铬尖晶石的成分相似。上述特征表明大道尔吉铬铁矿床系堆积成因，明显地区别于地幔徽榄岩中的豆荚状铬铁矿。大道尔吉铬铁矿为我国一个与蛇绿岩堆晶杂岩有关的典型铬铁矿床。 |
| 中文关键词:蛇绿岩 堆晶杂岩 堆积铬铁矿分离结晶作用 大道尔吉 |
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| Some new ideas on the genesis of the Dadao Erji chromite deposit |
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| Abstract:The Dadao Erji body is a depleted ophiolitic relic slice and consists of two suites called cumulates and mantle peridotite respectively. The cummulates include three magma cycles, each showing a magmatic evolution trend from ultramafic to mafic, and are composed of dunite, diopsidite, wehrlite and gabbro. The cumulus sequence of the major minerals is Ol(olivine) +Sp(spinel)→Ol+Cpx(clinopyroxene)+ minor Opx(orthopyroxene)→ Cpx+Pl(plagioclase), and the repetition of this cumulus sequence exhibits distinct cyclothems. The petrochemistry and mineralogy of the cumulates indicate that they were formed by crystal accumulation of the MgO- and Cr2O3- rich tholeiitic magma in an opening system under a higher pressure. The industrial chromite deposit in the Dadao Erji rock body occurs in the dunite-pyroxene-bearing dunite oll the bottom of the third cycle cumulates, and only a few lean orebodies of chromite are seen in the mantle peridotite. The ore-bodies of chromite consist mainly of various disseminated ores, while their country rocks are all dunite, with a gradual contact between them. The accessory spinel is similar to ore-forming spinel in composition. All of these features suggest that the chromite deposit in Dadao Erji rock body is part of the cumutus deposit formed in the orthomagmatic stage. The genetic mechanism of the cumulus chromite deposit is characterized by fractional crystallization of an ultramafic magma. The authors hence hold the opinion that the Dadao Erji chromite deposit is a typical chromite deposit related to the cumulates of ophimite in China and that it is distinctly different from the chromite deposit occurring in the mantle peridotites. |
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