Alteration Characteristics of Ore-forming Cr-spinel in the Sartokay Chromite Ore District, Xinjiang
新疆萨尔托海铬铁矿造矿铬尖晶石蚀变特征及指示意义

The altered Cr-spinel in disseminated ore is composed of three parts,namely,unaltered core(gray),early altered middle zone(gray)and late altered edge(light gray).Electron microprobe analyses of these three parts show that the altered Cr-spinel experienced loss of Al and enrichment of Fe in early alteration,and enrichment of Al,Cr,Mg and loss of Fe in late alteration relative to early alteration.A comparison with chromium spinel in metamorphic ultrabasic rocks abroad has led the authors to believe that the early alteration corresponds to low-amphibolite facies metamorphism with the temperature being 550～600℃,the late alteration corresponds to greenschist facies metamorphism characterized by the temperature of 350～500℃,and the unaltered core is equal to metamorphism between the low amphibolite facies and the amphibolite facies,with the stable temperature higher than 600℃,hence resulting in no alteration.Based on an analysis of the characteristics of regional metamorphism in combination with the location of altered Cr-spinel,it is considered that the late alteration might have resulted from regional tectonic activity after the location of Dalabute ophiolite,whereas the eady alteration was probably related to ophiolite tectonic emplacement.