山东五莲七宝山铅锌多金属矿床硫化物微量元素分布特征及地质意义

为探讨五莲七宝山铅锌多金属矿中主要硫化物的微量元素分布特征,对矿床成因类型进行约束,在矿床地质研究的基础上,以不同成矿阶段形成的闪锌矿和方铅矿为研究对象,开展矿相学和矿物LA-ICPMS微量元素组成研究。结合野外地质调查和室内矿相学研究,将五莲七宝山铅锌多金属矿床的成矿过程划分为3个成矿阶段,分别是多金属硫化物+碎裂岩阶段(Ⅰ)、多金属硫化物+石英+白云石阶段(Ⅱ)和石英+白云石阶段(Ⅲ)。LA-ICP-MS分析结果表明,主要硫化物中闪锌矿富集Fe、Co、Mn和Cd元素,贫Ge、Se、Te、Re和Tl元素,方铅矿则主要富集Ag和Cd元素;闪锌矿中Cu、Cd、Fe、Mn、Co和In元素以类质同象的方式赋存在矿物中,偶见方铅矿显微包体,方铅矿中Ag元素以类质同象的形式赋存在矿物中,Cu、Zn和As元素则以显微包体的形式赋存在碳酸盐岩化矿石方铅矿中。闪锌矿微量元素成矿温度研究表明,Ⅰ阶段形成的碎裂—角砾岩化矿石以中温为主,Ⅱ阶段形成的碳酸盐岩化矿石则形成于低温环境。结合矿床地质和微量元素分布特征,认为七宝山铅锌多金属矿床属于与岩浆热液作用相关的中—低温热液脉型矿床。

Cooling History of Mesozoic Magmatism and Implications for Large-Scale Gold Mineralization in the Jiaodong Peninsula, East China: Constraints from T-t Paths Determined by U-Pb Thermochronology of Zircon and Apatite

The Mesozoic intrusions of the Jiaodong Peninsula,eastern China,host giant gold deposits.Understanding the genesis of these deposits requires the determination of the source of the parental auriferous fluid and the timing of gold mineralization,which are strongly influenced by the cooling/uplift histories of the hosting intrusions.We performed an integrated U-Pb geochronology study on both zircon and apatite from four major magmatic episodes of the Jiaodong Peninsula.The zircon and apatite U-Pb ages are 156.9±1.2 and 137.2±2.4 Ma for the Linglong intrusion,129.9±1.0 and 125.0±3.8 Ma for the Qujia intrusion,119.5±0.7 and 117.2±1.8 Ma for the Liulinzhuang intrusion,118.6±1.0 and 111.6±1.6 Ma for the Nansu intrusion,respectively.The coupled zircon and apatite data of these granitoids indicate a slow cooling rate(11.9°C/Ma)in the Late Jurassic,and rapid uplift and cooling(35.8-29.2°C/Ma)in the Early Cretaceous.The dramatically increased uplift and cooling period in the Early Cretaceous are contemporaneous with large-scale gold mineralization in the Jiaodong Peninsula.This implies that thermal upwelling of asthenosphere and related tectonic extension played an important role in gold remobilization and precipitation.

Exhumation history and preservation of the Jiaojia giant gold deposit, Jiaodong Peninsula

The Jiaojia giant gold deposit is the largest gold deposit in China, with a total gold reserve of approximately 1200 t.Until now, the knowledge of the exhumation history of post-mineralization period is limited, in particular for the low-temperature thermochronology studies of samples below-1000 m. In this work, we combined zircon fission-track(ZFT) and apatite fission-track(AFT) dating of samples between-1100 and-2000 m to determine the post-mineralization cooling and exhumation history of the Jiaojia giant gold deposit. The ZFT ages ranged from 144.2±6.3 to 124.4±5.5 Ma, representing the cooling period and the disturbance of ore-forming fluid. The AFT ages ranged from 28.1±2.6 to 16.2±1.0 Ma, recording the exhumation and cooling processes. With reference to previous low-temperature thermochronology studies in the Jiaojia goldfield, we estimated the exhumation rate and amount of the Jiaojia giant gold deposit and reconstructed its exhumation and preservation history. The exhumation history was divided into four stages, rapid exhumation(~120–95 Ma), relatively slow exhumation(~95–50 Ma),slow exhumation(~50–30 Ma) and relatively rapid exhumation(since 30 Ma). Each stage corresponds to geological events related to the basin-mountain coupling that have occurred since the Cretaceous in the Jiaodong area, namely, a strong tectonic extension and volcanic eruption in the Jiaolai Basin, subsidence of the Jiaolai Basin and Wangshi Group molasse sedimentary,tectonic quiescence, and the Linqu Group basalt eruption of the Jiaobei uplift. Our results show that the exhumation of the Jiaojia giant gold deposit is ~5.2±1.2 km and the orebody erosion degree is relatively low, indicating huge prospecting potential deep in the Jiaojia giant gold deposit. These findings have significance and practical value for deep prospecting in the Jiaodong area.