冀北中生代高Sr低Y和低Sr低Y型花岗岩:地球化学、成因及其与成矿作用的关系

Mesozoic high-Sr, low-Y and low-Sr, low-Y types granitoids in the northern Hebei province: Geochemistry and petrogenesis and its relation to mineralization of gold deposits.

冀北是我国重要的金矿成矿区,冀北金矿有不同的类型,但大多与中生代中酸性侵入岩有关。本文的研究表明,冀北与金矿有关的中酸性侵入岩大体可划分为两类:一类为高Sr低Y型岩体,具有埃达克质岩的地球化学特征,推测可能是加厚的下地壳部分熔融形成的,其残留相为榴辉岩或角闪榴辉岩;另一类为低Sr低Y型岩体,以较低的Sr、Al和具明显的负铕异常而区别于埃达克质岩,又因其低Y和HREE而类似于埃达克质岩,推测源岩残留相中有斜长石存在,相当于高压麻粒岩相的环境,可能也形成于加厚下地壳底部。冀北金矿的S、Pb、H、O和C同位素大多显示深源的特点,且在时空分布上与上述两类中酸性侵入岩存在密切的关系,表明冀北金矿床的成矿物质和流体可能是幔源的,与中生代高Sr低Y和低Sr低Y型岩浆的成因有关。这一认识对于理解冀北金矿的成因和找矿可能是有益的。

North Hebei is one of important gold-producing areas in China. Most gold deposits in the northern Hebei are related to Mesozoic intermediate -acid intrusions, although they are different in genetic types. Based on the studies of this paper, these intrusions can proximately be divided into two types: a high-Sr and low-Y type and a low-Sr and Y type. The first type of intrusions has the geochemical features of adakite, and therefore it is inferred to be a possible product of partial melting of the over-thickened continental lower crust with a residual phase of eclogite or amphibole eclogite. The second type, ontke one hand, is different from the first one by its low Sr and Al contents and obviously negative Eu anomaly; on the other hand, it is similar to adakite by its low Y and HREE contents. Therefore, it is suggested that the low-Sr, low-Y type intrusions were generated by partial melting of relatively thick lower crust under high pressure granulite facies conditions with plagioclase to be the dominant residual phase. Considering that the gold deposits are spatio-temporally associated with the two types of intrusions and previous S, Pb, H, O and C isotopic data of the gold deposits in the North Hebei, which indicate that the mineralizing fluids and/or materials are most likely derived from mantle-lower crustal source, we concluded that the gold deposits have genetic relationships with high-Sr, low-Y type and- low-Sr, low-Y type intrusions. This will be helpful in understanding the genesis and exploring mineral deposits in the northern Hebei Province.