中文摘要：

岗上超镁铁质岩主要由纯橄岩和石榴橄榄岩组成,主要组成矿物有橄榄石、铬尖晶石、石榴子石、单斜辉石和斜方辉石等。铬尖晶石的Cr#[Cr/（Cr＋Mg）×100]从51到89变化,铬尖晶石矿物表现为4期次演化的特点,反映了从岩浆期向榴辉岩相、角闪岩相和绿片岩相演化特征。随着超镁铁质岩的演化,铬尖晶石中Cr#不断增大（51增大到89）,而铬尖晶石Mg#[Mg×100/（Mg＋Fe2＋）]不断减少,氧逸度不断增加。在绿片岩相—绿片角闪岩相退变质过程中,铬尖晶石中Cr、Mg和Al减少,Fe相对增加,产生富Cr尖晶石变质作用样式。晚期剪切变形等次生变化有利于富铬铬尖晶石矿物的形成和铬尖晶石的富集。同时,角闪岩相和绿片岩相变质作用使铬尖晶石富集呈现容易开采的条带状,降低了铬尖晶石与其他硅酸盐矿物的结合强度,降低了开采强度和成本,使原本不易于开采的铬铁矿矿体变得可以开采。这些意味着铬铁矿矿体展布要结合后期变质作用进行综合分析。

英文摘要：

Gangshang ultramafic rocks are mainly composed of garnet peridotites and dunite,which contain olivine,chrome-spinel,diopside,endiopside,and/or garnet,orthopyroxene,amphibole and phlogopite.Chrome-spinels in Gangshang ultramafic rocks are varied in composition,with Cr#[100Cr/（Cr＋Al）] ranging from 51 to 89,and its variation in composition is related to the four stages of the evolution of ultramafic rocks.Along with the evolution of ultramafic rocks,Cr# of chrome-spinels was increasing,Mg#[100Mg/（Mg＋Fe2＋）] of chrome-spinels was decreasing and the oxygen fugacity was increasing.In the course of amphibole facies and greenschist facies retrometamorphism,Cr,Mg and Al of chrome-spinels were reducing,but Fe was relatively increasing.The shearing deformation of the Gangshang ultramafic rocks in the late stage was also helpful to the enrichment of chromium and to the formation of chrome-spinel.