胶东大庄子金矿微量元素及Pb-S同位素地球化学研究

Trace Elemental and Pb-S Isotopic Geochemistry of the Dazhuangzi Gold Deposit, East Shandong, China

报道了大庄子金矿Pb、S同位素 ,稀土和微量元素等地球化学特征 ,并讨论了其地质意义 .大庄子金矿Pb同位素组成与胶东群和荆山群相似 ,而S同位素组成 (δ34Scdt=1 1 .9‰±0 .4‰ )与荆山群更为相近 ,Pb、S同位素组成与胶东主要金矿基本一致 ,研究显示其成矿物质可能主要来源于胶东群和荆山群 .对蚀变岩和较新鲜原岩的稀土 (REE)和微量元素含量研究发现 ,钾化蚀变过程中两者都从流体中带入围岩 ;而绢英岩化蚀变过程中 ,REE从围岩中带出 ,微量元素既有带入也有带出 ;Cu、Pb、Zn等主要金属元素在两蚀变过程中主要是带入 .围岩及黄铁矿的稀土元素分配曲线特征 ,揭示了成矿物质的沉淀明显受微观环境的制约 ,浸染状黄铁矿的沉淀伴随着成矿流体与围岩之间的蚀变作用而发生 ,此时水 /岩反应进程导致的成矿流体PH值和Eh值等因素的变化 ,可能是成矿物质沉淀的主导因素 ;而脉状黄铁矿则直接从成矿流体中沉淀而出 ,围岩的影响不明显 ,成矿流体演化过程中温度、压力的变化 。

This paper geochemically studies the general features of the Dazhuangzi gold deposit in the east Shandong peninsula. It is revealed that the Pb and S isotopic compositions of the deposit are similar to the other gold deposits in this area. Pb isotopic compositions could be correlated with the Jiaodong and Jingshan Groups and S isotopes (δ^(34)Scdt=11.9 ‰±0.4 ‰) are related to Jingshan Groups. Therefore, its ore_forming materials have been mainly derived from the two groups. The regular variation of the REE and trace elements of different wall rocks shows that the two group elements were immigrated from hydrothermal fluids into the wall rocks during potassic alteration stage, while the REE were lost from wall rocks in the sericite_quartz alteration stage. In contrast, elements Cu, Pb and Zn were always immigrated from the fluid into the wall rocks in the two alteration processes, it is supposed that the ore_forming elements were got into the fluid before the wall rocks alteration. The characteristics of the REE distribution of the different wall rocks and pyrites reveal that the precipitation of sulfides could be controlled by the micro_environmental conditons of the ore_forming system. The disseminated pyrites deposited along with the interaction between the ore_forming fluid and the wall rocks when the pH and Eh values of the aqueous solutions changed. On the other hand, the vein pyrites could be directly precipitated from the ore_forming fluid just because the temperature and pressure of the ore_forming system decreased.