新疆北部蛇绿岩型铬铁矿床铬尖晶石的类型及其矿物化学成分

The Category and Mineral Chemical Composition of chrome spinelin Ophiolite-type Chromite Deposits in north of Xinjiang

作为蛇绿岩型铬铁矿的重要产区,新疆北部地区发育多处中小型铬铁矿矿床。铬尖晶石一直以来是作为研究地幔橄榄岩成因与铬铁矿形成过程的重要载体之一。本文在对萨尔托海、鲸鱼、阿克塔斯和清水等地区的造矿铬尖晶石与副矿物铬尖晶石进行了形态学与矿物化学成分的研究,发现造矿铬尖晶石产出特征以中粗粒半自形-自形结构为主,自形程度较好,Cr#值较高;副矿物铬尖晶石自形程度较差,多表现为中细粒半自形-他形结构,呈粒状-蠕虫港湾状,边缘蚀变程度很强烈,Cr#值较低。造矿铬尖晶石成分相对均一,副矿物铬尖晶石成分变化较大,暗示铬铁矿的形成,并不是地幔橄榄岩中副矿物铬尖晶石的简单聚集,而是复杂多期次多阶段熔融的结果。

As one of the majormining areas ofophiolite-type chromite deposits,there are many middle/small size chromite depos-its in Northern Xinjiang.The chromium spinel has been always as a carrier for studying the origin of mantle peridotite and the formationof chromite. In this contribution,we have studied the morphology and mineral chemistry of the chromium spinel and theaccessory miner-al chromium spinelin Sartohay,Jingyu,Aketasi and Qingshui deposits. Through investigation,we found that the mineralized chromiumspinel is characterized by itsmedium-grainded orcoarse-grainedeuhedral-hypidiomorphic structures and high Cr# values,whereas theaccessory mineral chromium spinel exhibits as medium-grainded or fine-grained hypidiomorphic-xenomorphic structure,lower Cr# val-ues and strongly alteration at edges. The mineralized chromium spinel has a relatively homogeneous composition,and the composition ofaccessory mineral chromium spinel varies in a large range. These data indicate that the formation of chromite resulted from the compli-cated and multi-stage melting processes,rather than simple aggregation of accessory mineral chromium spinel in mantle peridotite.