新疆哈密黄山东铜镍硫化物矿床成岩成矿作用

黄山东铜镍硫化物矿床赋存于橄榄岩、苏长岩、辉长岩和闪长岩组成的镁铁-超镁铁质杂岩体中,赋矿岩体包含至少4套岩石组合。不同类型岩石微量元素和稀土元素原始地幔标准化配分模式指示,该矿床明显亏损Nb、Ta、Zr、Hf等高场强元素和Cr元素,富集Sr及大离子亲石元素;(La/Yb)N=1.08～2.70,δEu=0.50～2.57;含矿岩石Cu/Pd比值和Ti/Pd比值大于原始地幔值,表明不同类型岩石是高镁玄武质岩浆在深部分异结晶演化的产物。根据橄榄石和全岩化学组成可估算出母岩浆MgO含量约为12%。成矿岩浆深部演化过程中,富硅的地壳混染组分和外来流体的加入可能促成了岩浆中的硫饱和;深部熔离的不混溶硫化物珠滴被上升岩浆携带,富集在橄榄岩和苏长岩的底部。

Petrogenetic and ore_forming processes of Huangshandong Cu-Ni sulfide depo sit in Hami, Xinjiang

The Huangshandong Cu-Ni sulfide deposit is hosted by mafic-ultramafic rocks composed of peridotite, norite, gabbro and diorite in at least four intrusive rock assemblages. Mineral chemistry and whole-rock major and minor elements, REE and PGE compositions suggest that primitive mantle-normalized trace element pattems show significant depletion of such high field strength elements as Nb,Ta, Zr and Th as well as Cr, and enrichment of Sr and some large ion lithophile elements; ( La/Yb)_N = 1.08～2.70 and δEu = 0.50 ～2.57. The Cu/Pd and Ti/Pd ratios of ore-bearing rocks are higher than the values of primitive mantle. The above evidence indi-cates that different types of rocks were produced by fractional crystallization of a MgO Mg0 basaltic magma at depth. The MgO con-tent of the parental magma is estimated to be 12% on the basis of olivine and whole-rock compositions. Sulfide saturation in the ore-forming magma might have been induced in the deep chamber by Si-rich crustal contamination and exotic fluids. Immiscible sulfide droplets segregated at depth were carried by ascending magma and concentrated at the bottom of peridotite and norite.