辽宁第Ⅳ金刚石成矿带东部潘家沟辉绿岩中铬铁矿的矿物化学特征及其意义

Mineralogical chemical characteristics of chromite from diabase in Panjiagou area of the eastern fourth diamond metallogenic belt and its significance in Liaoning Province

辽宁省永宁地区因发现原生金刚石而被划分为辽宁第Ⅳ金刚石成矿带,但尚未厘定出金刚石的来源,有必要加强对与金刚石伴生的指示矿物的研究。对该成矿带东部潘家沟地区辉绿岩中选获的铬铁矿开展电子探针成分分析,并与辽宁典型金伯利岩管中的铬铁矿成分进行对比,以探讨该地区铬铁矿的成因及其与金刚石的关系。根据铬铁矿样品电子探针背散射图像显示的粒径、形态及熔蚀特征,以及铬铁矿电子探针成分测试显示的高Cr、富Mg、低Al及贫Ti的特征,推测该地区的铬铁矿来自地幔捕掳晶,属于镁铬铁矿亚类,主要为镁铁-铬铝铁亚种和镁铁-铬铝亚种。计算得到铬铁矿的形成温度为1 252~1 307℃,与前人报道的瓦房店典型金伯利岩中铬铁矿的形成温度基本一致,也接近金刚石的形成温度,表明潘家沟地区辉绿岩中铬铁矿的成因与金刚石关系密切,该地区具有良好的金刚石成矿潜力和找矿前景。研究成果对潘家沟地区金刚石原生矿的勘查及探明该地区金刚石的来源具有指导意义。

Yongning area has been classified as the fourth diamond metallogenic belt in Liaoning Province due to the discovery of primary diamond.However,the diamond source has not yet been determined so far,and it is necessary to reinforce the study of the indicator minerals associated with the diamond.The compositions of chromite selected from the diabase in Panjiagou area in the eastern Yongning area were analyzed by electron microprobe,and they are compared with the chromite from typical kimberlite pipes in Liaoning Province to explore chromite genesis and the relationship with diamonds.According to the particle sizes,morphology,and melting erosion characteristics in the back-scattered electron images of chromite samples and the composition feature of high Cr,rich Mg,low Al and poor Ti through electron probe micro analysis,the authors speculated that the chromite come from mantle xenocryst,belonging to chromite subclass,which is mainly mafic-chromium-aluminium-ferrum subspecies and mafic-chromium-aluminium subspecies.The calculated formation temperatures of the chromite are 1252~1307℃,which is consistent with the reported formation temperatures of the chromite in Wafangdian kimberlite,and is also closed to the formation temperature of diamonds.It indicates an affinity relationship between chromites and diamonds,and great potential for diamond prospecting in the diabases of Panjiagou area.This study is significant for the exploration of primary diamond deposits and the identification of the diamond sources in Panjiagou area.