广东大降坪硫(铅锌)矿床岩浆热液叠加作用——来自闪锌矿Rb-Sr年龄及硫同位素的证据

Magmatic hydrothermal superimposition in Dajiangping S(Pb-Zn) deposit,Guangdong Province: Rb-Sr isochron age and sulfur isotope evidence

广东大降坪硫(铅锌)矿床位于与岩浆作用有关的大绀山多金属矿田的中部,主矿体为赋存在震旦纪变质岩中的层状、透镜状黄铁矿矿体,最近在两个不同产状的黄铁矿矿体下部又新发现了脉状及层状铅锌矿体。文章通过对铅锌矿体的年龄及硫同位素研究,探讨其与主矿体的成因关系,获得了脉状铅锌矿体中闪锌矿的Rb-Sr等时线年龄为(88.5±3.9)Ma,即晚白垩世,与上部黄铁矿矿体的年龄(约630 Ma)相差较大,而与整个大绀山多金属矿田的成矿作用时限一致。三种不同产状的矿体硫同位素组成差异明显:层状黄铁矿矿体富集硫的轻同位素(δ34S=-10.90‰^-25.55‰),且与围岩的硫同位素范围一致,说明硫来自生物的细菌还原硫;透镜状黄铁矿矿体δ34S组成范围较宽(-9.38‰~22.69‰),具多源性硫的特征;铅锌矿体的δ34S在-7.1‰~6.4‰之间变化,硫可能来自深源岩浆,并受围岩成分混染。多方面的证据表明,大降坪黄铁矿矿体下部的铅锌矿体形成于晚白垩世的岩浆热液成矿作用,透镜状黄铁矿矿体受到岩浆热液的叠加。

Dajiangping deposit, Located in the central part of the Daganshan magmatic-related polymetalic orefield, is the largest pyrite deposit in China. The pyrite orebodies occur in the Sinian metamorphic rocks in laminated and lenticular forms. Recently, new veins and layered Pb-Zn orebodies underlying the pyrite orebodies were discovered. The age of sphalerite from the lead-zinc orebody was determined by the Rb-Sr isochron method, which yielded a Rb-Sr isochron age of （88.5 ±3.9） Ma, completely different from that the pyrite orebody （ - 630 Ma）, but consistent with the metallogenic age of the Daganshan orefield. The sulfur isotope compositions of sulfides from three orebodies were analyzed. The results show that the layered orebody has the δ^34S values of （ -10.90%～ -25.55‰）, suggesting the reduction of the bacteria sulfate. The lenticular orebody has broad δ^34S values, ranging from - 9.38‰ to 22.69‰, implying that it had complicated sulfur sources, including the mixture of magmatic source. The δ^34S values of the lead-zinc orebody are - 7.1‰-6.4%, showing the charac- teristics of deep source sulfur. These data indicate that the lead-zinc orebody was formed by magmatic hydrothermal mineralization in Cretaceous, and the lenticular pyrite orebody might have been superimposed by it.