祁连山蛇绿岩型超镁铁岩铬铁矿床成矿的主要特征

祁连山造山带目前已发现不同规模的超镁铁岩体（群）1000余个,产有铬铁矿床（点）和矿化点80余处,这些岩体及其矿产主要产在北祁连优地斜增生地体边部的海沟带中,少数产在祁连中间地块的边部。岩体成因类型为蛇绿岩组合中的超镁铁质单元,铬铁矿的富集部位是地幔橄榄岩和堆积杂岩带底部的纯橄榄岩。岩石多为铝过饱和系列,岩体的平均化学成分接近于斜辉橄榄岩;Cr₂0₃的平均含量大于0.40％,Al₂0₃的平均含量近于或者大于1％。铬尖晶石的化学参数特征反映出低铁富镁的介质对形成富铬尖晶石是有利的。富铬岩体中Cr、Co、Ti、V的含量较高。

THE MAIN CHARACTERISTIC OF MINERALIZATION FOR OPHIOLITETYPE ULTRAMAFITE IN QILIAN MOUNTAIN

More than 80 chromite mineralizations or mineralized spots in different size have been found in Qil-ianshan orogenic belt. And they mainly occur in the marginal trench zone of eugeocline accretion terrane of the north Qilian mountain and only a few were found in margin of Qi-lian mountain median mass. On the basis of the genetic type ,the ultramafic bodies are part of ultramafic unit of ophiolite and the positions where the chromite enriched are mantle peridotite or bottom dunite of cumulate complex zone . Mostly the rocks are series of aluminium supersaturated, mean chemical composition of the ultramafic bodies is approaching to harzburgite and Cr2O3 average content is more than 0. 40% ,Al2O3 average content is approaching to or mroe than 1 %. The chemical parameters of chrome -spinel shown that is low-iron and rich-magnesium medium and it is favorable to form rich-chrome spinel. There is the higher content of Cr,Co,Ti,V in the rich-chrome ultramafic bodies.