岩浆铜镍矿与钒钛磁铁矿的过渡类型——新疆哈密香山西矿床

A Intermediate Type of Cu-Ni Sulfide and V-Ti Magnetite Deposit:Xiangshanxi Deposit,Hami,Xinjiang,China

铜镍硫化物矿床与钒钛磁铁矿矿床虽然同属与镁铁-超镁铁质岩有关的岩浆型矿床范畴,但在一般情况下,二者是不共生的。新疆东天山地区的香山西矿床则是一个铜镍矿与钛铁矿共生的实例。香山地区为一复式含矿杂岩体,最早期形成辉长岩(如角闪辉长岩、灰白色细粒辉长岩等)为主体的侵入;第二期侵入的是以辉橄岩、单辉橄榄岩、二辉橄榄岩等为主的超镁铁质岩,含铜镍硫化物矿化;第三期则为岩浆期后残余岩浆形成的含钛铁矿化的辉长岩(脉)。香山西铜镍-钛铁矿床含矿岩石的碱度、镁铁指数、岩浆酸度、钙碱富集指数等地球化学参数,氧逸度和硫逸度等物理化学参数均介于独立的典型铜镍硫化物和典型钒钛磁铁矿矿床之间。矿床中磁铁矿较其他钒钛磁铁矿矿床(尾亚)具较高的V和Ti含量,同时黄铁矿和黄铜矿具较高的Co、Ni和Cu含量,反映出成矿过程中,Cu-Ni-Co系列与V-Ti-Fe系列的分离不够彻底。形成本区CuNi-VTi复合型矿床的原因,可能在于矿床所处独特的构造环境——产于造山带,而不是克拉通(边缘)。

Both copper-nickel sulfide （CNS） deposit and vanadic titianomagnetite （VTM） deposit are related to maficultramafic rocks and belong to the orthomagmatic mineral deposit, but they rarely coexist on one deposit. The Xiangshanxi deposit is a case of CNS and VTM paragenetic deposit. There exist a complex ore-bearing mafic-ultramafic rockmass in the Xiangshan area with three intrusive stages： gabbro types including green and gray hornblende gabbro and gray hornblende gabbro in the first stage, CNS-bearing ultramafic rocks including pyrolite, Cpx-pyrolite （clinopyroxene pyrolite）, lherzolite in the second stage, and Ti-Fe mineralized gabbro dyke （VTM orebody） formed by residual magma in the third stage. All lithochemiCal indexes and parameters of the Xiangshanxi host mafic-ultramafic rocks such as alkalinity （or alkaline contents）, femic ratio （FeO^＊/MgO） or marie index （m/f）, magmatic acidity （αsi）, calc-alkaline enrichment index （calk/m）, and oxygen and sulfur fugacity exhibit dualism and transitional features of typical CNS deposits and VTM deposits. Comparing with other VTM deposits （e. g. Weiya deposit, Xinjiang）, magnetite yields higher V and Ti contents while pyrite and chalcopyrite yield higher Co, Ni and Cu contents from the Xiangshanxi deposit, which indicates that fractionation of Cu-Ni-O） series and VTi Fe series is inadequacy. It is suggested that the controlling factor to form the special composite CNS-VTM deposit could owe to its tectonic setting： orogenic belt but not （margin of） craton.