红柳沟北镁铁-超镁铁质岩体矿物学特征及矿石成因分析

Mineralogical characteristics and ore genesis of the Hongliugoubei mafic-ultramafic intrusion

红柳沟北镁铁-超镁铁质岩体位于柴达木陆块北部的欧龙布鲁克微陆块东北缘,呈岩墙状,出露面积约0.1km^2,由方辉橄榄岩、橄榄二辉岩、含长单辉橄榄岩、橄榄辉长苏长岩、暗色橄榄辉长岩、苏长岩、辉长岩等组成,各岩相带在空间上呈渐变过渡关系。电子探针分析结果显示,岩体的主要造岩矿物为贵橄榄石、古铜辉石、普通辉石和斜长石,并且各矿物的结晶温度为1 307~1 122℃。岩体钛铁矿化明显,主要金属矿物为钛铁矿、钛磁铁矿和磁铁矿。利用橄榄石Fo最高值反演出原生岩浆MgO含量为8.49%,FeO含量为10.03%,TiO_2含量为1.63%,为普通玄武质岩浆。通过综合研究各矿物形成的温度和氧逸度条件,认为岩浆从橄榄石结晶到普通辉石结晶,其氧逸度是缓慢升高的,并且氧逸度是控制红柳沟北岩体Ti-Fe氧化物结晶的主要因素。

Located in the northeast of Olongbuluck block on the northern margin of Qaidam Basin, the Hongliugoubei maficultramafic intrusion is composed of harzburgite, olivine websterite, plagioclasebearing clinopyroxene peridotite, olivine gabbronorite, melaolivinegabbro, norite and gabbro and belongs to a dikeshaped intrusion, with an exposed area of about 0.1 km2. Various lithofacie belts show gradual transition relationship. Electron microprobe analyses show that the rock-forming minerals are composed of chrysolite, augite and plagioclase and their crystallization temperatures vary between 1 307 and 1 122℃. The intrusion is characterized by obvious mineralization of ilmenite, with main ore minerals being ilmenite, titanomagnetite and magnetite. The inversion of primary magma composition based on the compositions of most Forich olivines indicates that the parental magma of Hongliugoubei intrusion belonged to common basalt magma containing about 8.49 % MgO, 10.03 % FeO and 1.63 % TiO2. Studies of temperature and oxygen fugacity conditions of rock-forming minerals reveal that oxygen fugacity of magma gradually increased from olive crystallization to augite crystallization and this seems to be the main factor that controlled the crystallization of Ti-Fe oxide.