东沟坝多金属矿床喷流沉积成矿特征的稀土元素地球化学示踪

The characteristics of exhalation-sedimentary deposit of Donggouba polymetal deposit: evidence from ore' s REE composition.

为了进一步研究东沟坝矿床的喷流沉积成矿特征,对东沟坝矿床矿石及围岩的稀土元素进行了ICP-MS测定。东沟坝矿床矿石普遍显示明显的Eu正异常和弱的Ce负异常,说明成矿热液为温度较高(250℃及其以上)、相对还原的流体。Eu正异常和弱Ce负异常同时在矿石中发育,说明矿石沉淀时较高温度的热流体与少量的海水发生了对流混合。根据矿石与围岩的稀土配分模式的相似性及矿石铅、硫同位素组成特征,推断成矿金属元素主要来自赋矿围岩。根据矿石中大量发育重晶石和矿石普遍具有的LREE富集、明显的Eu正异常和弱Ce负异常的事实,推断同生成矿流体中大量SO_4^(2-)的出现与岩浆脱气作用有关。

The REE compositions of ore and its host rocks in Donggouba mineral deposit have been determined by ICP-MS. The ores possess obvious Eu positive anomalies and weak Ce negative anomalies indicating that ore-forming hydrothermal fluid is reductive relatively and of higher temperature than 250℃. Both visible Eu positive anomaly and Ce negative anomaly developed in ores at the same time indicate that the convective mixing of a little amount of seawater with hydrothermal fluid had happened while ores were deposited on ancient seafloor. Based on the similar REE distribution patterns between ore and host rocks, the characteristics of ore Pb, S isotopic compositions, the conclusion was suggested that the ore metals come from host rocks. Due to abundant barite in ores the S02-4 maybe is a dominant anion in metallogenic fluid. Moreover, according to the enriched LREE, Eu positive anomaly and Ce negative anomaly appearing in barites and other ores we conclude that the ore-forming hydrothermal fluid contains the component of magmatic fluid.