青海省夏日哈木铜镍矿床岩石地球化学特征及其意义

新发现的青海省夏日哈木超大型镍矿床,在国内是仅次于金川岩浆铜镍矿床的第二大矿床。矿区发育5个镁铁-超镁铁岩体,目前仅Ⅰ号镁铁-超镁铁岩体内发现了具有经济价值的超大型矿体,其他4个岩体多为镁质橄榄岩及榴辉岩,是多种构造体制叠加岩浆活动的结果。分析发现Ⅰ号岩体所有岩石的SiO2含量为34.11%~54.28%,其m/f值为2.01~4.93,属铁质系列的镁铁-超镁铁岩石。通过对橄榄石Fo值与Ni含量研究表明,存在多期次的岩浆成矿作用,橄榄石Fo值与Ni含量正相关和负相关的协变关系,说明存在早期硫化物不混溶作用。结合区域年代学综合分析认为,夏日哈木超大型岩浆铜镍硫化物矿床的形成,是早泥盆世早期岩浆活动于柴达木盆地边缘东昆仑造山带夏日哈木地区具体的成矿表现。在其Ⅰ号和Ⅱ号岩体的深部,仍具有较大的找矿潜力,而其他3个镁铁-超镁铁质多以镁质橄榄岩为主,不具备镍矿成矿条件,可能没有发现铜镍矿的经济价值。

Petrogeochemical Characteristics of the Xiarihamu Magmatic Ni-Cu Sulfide Deposit in Qinghai Province and Its Study for Olivine

Located in eastern Kunlun orogenic belt in Qinghai Province, the super-large Xiarihamu magmatic Ni-Cu sulfide deposit is the second ones after Jinchuan Ni-Cu sulfide deposit.Totally, 5 mafic-ultramafic intrusionswere developed 1n this mining area, in which some super-large economic ore-bodies have been found only in No.Ⅰintrusive rocks, but other 4 ones belong to basicto magnesium peridotite and eclogite, these maybe the results of at least two tectonic systems superimposed with magmatic activities. For the No.Ⅰintrusive rocks in the Xiarihamu deposit, their SiO2 contentsvary from 34.11% to 54.28%, and m/f ratios range from 2.01 to 4.93, belonging to ferruginous basic-ultrabasic rocks.The Fo and Ni valuesof olivine show that the Xiarihamu Ni-Cu deposit had experienced multiple stage of magmatic mineralization, the positive and negative correlations between Fo value and Ni content from olivine stand for the immiscibility of sulfide in the early mineralization stage. Combined with regional chronology and other geological information, it's believed that the Xiarihamu super-large magmatic Ni-Cu sulfide deposit was the result of early lower Devonian magmatism and mineralization in the margin of Qaidam basin, eastern Kunlun orogenic belt. By the way, there maybe have better metallogenic conditions and prospecting potentiality in the depth of No.ⅠandⅡ intrusions, especially the place of magmatic origin or flowing direction, but the other three mafic-ultramafic intrusions that mainly belonged to magnesium peridotite have bad metallogenic condition on Ni-Cu sulfide deposit, and no economic value.