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,每一旋回均表现出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橄岩-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,明显地区别于地幔橄榄岩中的豆荚状铬铁矿。大道尔吉铬铁矿床为我国一个与蛇绿岩堆晶杂岩有关的典型铬铁矿床。
The Dadao Erji rock body is a depleted ophiolitic relic slice and consists of two suites called cumulates and mantle peridotite respectively. The cumulates 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 Cr_2O_3-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 on the bottom of the third cycle cumulates, and only a few lean orebodies of chromite are seen in the mantle peridotite. The orebodies 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 cumulus deposit formed in the orthomagmatic stage. The genetic mechanism of the cumulus chromite deposit is characterized by fractional crystallization of an uitramafic magma. The authors hence hold the opinion that the Dadao Erji chromite deposit is a typical chromite deposit related to the cumulates of ophi-olite in China and that it is distinctly different from the chromite deposit occurring in the mantle peridotites.
出处
《矿床地质》
CAS
CSCD
北大核心
1989年第1期3-18,共16页
Mineral Deposits
