哈拉乔拉岩体橄榄石与辉石成分对阿尔泰造山带铜镍成矿潜力的指示

Mineral Composition of the Halaqiaola Mafic-ultramafic Intrusion and Implications for Ni-Cu Exploration in the Altay Orogenic Belt

哈拉乔拉基性-超基性岩体于431 Ma侵位于阿尔泰造山带南缘,以辉长岩和橄榄辉长岩为主,类比于基性岩含矿的喀拉通克和黄山东矿床。本文通过哈拉乔拉岩体的矿物成分探讨该岩体的硫化物熔离过程。哈拉乔拉橄榄辉长岩中橄榄石Fo值为75~83 mol%,类似于黄山东与喀拉通克,但Ni含量更为亏损(小于100×10^-6~840×10^-6),明显低于这两个矿床Fo值相近的橄榄石。单斜辉石成分(Mg^#为0.75~0.81)对比也表明哈拉乔拉岩体与喀拉通克岩体具有相似的母岩浆成分与演化过程。哈拉乔拉橄榄石和单斜辉石的成分指示岩浆侵位之前曾经历橄榄石分异结晶作用,Ni严重亏损指示深部橄榄石分异过程中还伴随着硫化物熔离作用。但目前地表及有限的钻孔并未见大量硫化物,暗示硫化物可能堆积在岩体深部或深部岩浆房。经以上分析,认为志留-石炭纪侵位的基性-超基性岩也具形成铜镍矿床的潜力,其成矿潜力评价可综合地球化学-地质-地球物理-成矿过程研究等多方面信息。

The Ni-Cu mineralization potential of the mafic-ultramafic complexes in this Altay area is still unclear.The Halaqiaola mafic-ultramafic complex is located in the southern margin of the Altay region,with an age of about 431 Ma.Gabbro and olive gabbro are the dominated rocks in the outcrops,which is analogous to the rocks from the Kalatongke and Huangshandong deposits.The Fo value in olivine in the Halaqiaola olivine gabbro vary from 75 to 83 mol%,similar to that of the Huangshandong and Kalatongke,but the Ni content of olivine(100×10^-6~800×10^-6)is significantly lower than that of the two deposits.The comparison of the Mg^# in clinopyroxene in the same rocks also indicates that the Halaqiaola rock mass is relatively evolved(Mg#is 75~83),similar to the Kalatongke rocks.The composition of olivine and clinopyroxene compositions indicate the olivine crystallization before magma emplacement at the Halaqiaola chamber,probably accompanied by sulfide segregation and removal from the magma,but the current surface and borehole show that no large amounts of sulfide enrichment were observed,suggesting that sulfides may accumulate in the deep of the current intrusion or at deeper magma chambers.Although the age of the mafic-ultramafic rocks in the Altay region is earlier than the ore-forming age of the Kalatongke deposit in the adjacent area,the mineral composition of the Halaqiaola rocks indicates the complexes earlier than the Permian regionally still have the potential for Ni-Cu mineralization.