西坝岩体的成因及其在陕西双王金矿中的成矿作用

Genesis of Xiba intrusion and its role in the gold mineralization in Shuangwang gold deposit,Shaanxi

在花岗岩原地重熔成因理论的基础上,对双王金矿的地质、地球化学和成矿学资料重新分析,认为西坝岩体的形成是该区地壳原地熔融或重熔的结果。微量元素和稀土元素配分特征表明,蚀变围岩残留了地层岩石的信息,而新生方解石、铁白云石等矿物则显示的是热液信息。双王金矿总体成矿过程是富金(亲硫元素)地层被卷入印支期地壳熔融事件,经重新分异后排出岩浆系统形成含矿热液,热液在运移过程中压裂地层形成角砾岩带容矿构造,而后在燕山早期—中期沉淀形成金矿床。从形成时间来看,若不考虑误差因素,燕山早期的金矿"成矿壳层"或已基本剥蚀殆尽,在目前的剥蚀深度上,出露的主要是燕山中期的"成矿壳层"中的金矿体。若考虑误差因素,现今金矿体测年时代可能并非由某一期岩浆热液的含金量的多寡引起,而是与两期持续过程的剥蚀深度有关。即在目前的剥蚀深度上,出露的是两期"成矿壳层"中的金矿体。

Based on the genetic theory of the in-situ granite re-melting, the authors re-analyzed the geological, geochemical and metallogenic data. It was found that the Xiba complex intrusion was formed by repeated crustal melting in the earlier Mesozoic peri- od. Characteristics of trace elements and REE distribution pattern shows that the altered wall rock reservered stratum information and the new-formed minerals such as calcite and ankerite indicated that hydrothermal information involved. The mineralization process of Shuangwang gold deposit is summarized as followings： the high gold-bearing strata was involved in melting process of Indosinian peri- od, and discharged from the magmatic system by the magmatic differentiation and resulted in formation of ore-bearing hydrothermal fluids, formed brecciaed structure in the compressive strata, and finally the Shuangwang gold orebodies were formed in early and middle Yanshanian period by the hydrothermal precipitation.