重庆东南部彭水地区重晶石-萤石矿床的成矿物质来源探讨:地球化学证据

Geochemical Evidence for Sources of Ore-forming Material of Barite-Fluorite Deposits in Pengshui Area, Southeast Chongqing

重庆东南部重晶石-萤石矿床主要赋存于早奥陶世碳酸盐岩地层中,层控特征明显,NW向断裂为主要的含矿控矿构造。为了探讨重庆东南部重晶石-萤石矿的成矿机理、成矿物质来源与演化,本文选取了彭水地区冯家、朗溪两个具有代表性的重晶石-萤石矿床,对其地质特征和微量元素、稀土元素地球化学特征进行了研究。微量元素和稀土元素特征均显示,重晶石-萤石矿床与下寒武统牛蹄塘组在成矿物质来源上有着密切的联系。稀土元素分析结果则表明,重庆东南部重晶石-萤石成矿带上的矿床(点)为同期形成的;矿石的δEu、δCe异常证明成矿环境是高氧逸度的开放体系,Tb/Ca-Tb/La关系图与La/Yb-?REE关系图显示,研究区重晶石-萤石矿床为热液成因,且与岩浆活动无直接成因上的联系,成矿物质来自沉积岩地层。封存的地层水及大气降水通过水/岩反应将成矿物质汇聚于热流体场中,构造运动和地层温压梯度致使成矿热液沿构造带上涌至早奥陶世碳酸盐岩地层中成矿,矿床类型为中-低温热液成因-断裂带充填交代型层控矿床。

The barite-fluorite deposits in Southeast Chongqing are mainly hosted in the Lower Ordovician carbonate rocks, and the orebodies are obvious stratabound and primarily controlled by the NW trend structure. Two representative barite-fluorite deposits were studied in purpose of understanding their ore-forming mechanism. Trace element geochemistry of ores show that the Lower Cambrian Niutitang Formation is likely the source of ore-forming material for the barite–fluorite deposits. REE geochemical analysis results indicate that many deposits have contemporaneous characteristics, δEu and δCe anomaly suggest a high oxygen fugacity and open system environment for the ore-forming processes. Tb/Ca-Tb/La and La/Yb-？REE plots display that the barite-fluorite deposits are hydrothermal origin. The ore-forming fluid was possibly formation brine and meteoric water, which is irrelevant to magmatic activity. We suggest that the barite-fluorite deposits in the study area are strata-bound deposits of mid-low temperature hydrothermal origin.