埃达克岩研究及斑岩铜矿找矿新方向

REVIEW ON ADAKITE AND NEW DIRECTION FORFINDING PORPHYRY COPPER DEPOSIT

埃达克岩是一种成因方式特殊的钙碱性系列岩浆岩 ,其典型特征是 :SiO2 ≥ 5 6 % ,Al2 O3 ≥ 1 5 % ,MgO通常小于 3% ,贫Y和Yb(Y≤ 1 8× 1 0 -6,Yb≤ 1 .9× 1 0 -6) ,高Sr(多数大于 4 0 0× 1 0 -6) ,LREE富集 ,无Eu异常或仅有轻微的负Eu异常。其成因主要有两类 :一类由俯冲板片的部分熔融成因 (O型 ) ;另一类由玄武质岩浆底侵下地壳时发生部分熔融或下地壳拆沉作用成因 (C型 )。两类埃达克岩都与斑岩铜矿的成矿作用存在着密切的关系。世界上大多数超大型的斑岩铜矿与O型埃达克岩有关 ,而我国的斑岩铜矿则大多数与C型埃达克岩有关。埃达克岩可作为一种重要的找矿标志 。

Adakite is a kind of acid-intermediate and calc-alkaline igneous rock. Its typal characteristics are: SiO2≥56%,Al2O3≥15%,MgO>3%,relatively poor Y and Yb(Y≤18×10-6,Yb≤1.9×10-6),high Sr(>400×10-6),rich LREE,absent or slightly negative Eu anomaly. There are two types of adakites (C-type and O-type) with different petrogenesis. The O-type adakite is formed by the partially melting of subducted slab. The C-type adakite is formed by the partially melting of basaltic lower crust under the continental accretion setting or the delamination of lower crust. They are all closely associated with the mineralization of porphyry copper deposits. The super large porphyry copper deposits are usually related to the O-type adakites in the world. However, porphyry copper deposits in China are mainly associated with the C-type adakites. It is concluded that a new direction for prospecting of porphyry copper deposits can be supplied because adakite would be used as a new exploration indication to find large-size or superlarge-size porphyry copper deposits.