赣南隆坪萤石矿床成矿流体特征及成矿模式

Characteristics of ore-forming fluids and ore-forming model of the Longping fluorite deposit in southern Jiangxi Province

赣南兴国县隆坪大型萤石矿床位于大余-南城深大断裂西侧兴国-宁都萤石成矿带内,呈板状、似层状、脉状产于永丰复式岩体外接触带北东向硅化破碎带中。本文划分了兴国县隆坪萤石矿床的成矿阶段,通过流体包裹体岩相学、显微测温、激光拉曼成分分析和H-O同位素研究,讨论了该矿床成矿流体性质、来源、演化与成矿模式。根据矿物穿插关系和矿相学特征,将隆坪萤石矿床划分为3个成矿阶段,即成矿早阶段(萤石-石英阶段)、成矿主阶段(石英-萤石阶段)和成矿晚阶段(萤石-方解石阶段)。流体包裹体类型主要为富液相两相包裹体,均一温度变化范围在111~374℃之间,盐度变化于0.53%~3.55%NaCleq之间,密度变化于0.58~1.02 g/cm^(3)之间。包裹体成分以H_(2)O为主。总体而言,成矿流体属于中低温、中低盐度、中低密度的NaCl-H_(2)O体系,但成矿早阶段存在高温、相对高盐度的流体端元(温度大于300℃,盐度为2.0%~2.7%NaCleq),推断永丰复式岩体晚阶段岩浆热液参与早阶段萤石成矿作用,提供F的来源和热源。隆坪萤石矿床流体包裹体中的δD_(V-SMOW)和δ^(18)O_(V-SMOW)值均较低,分别为-66.8‰~-53.1‰(平均值为-59.5‰)和-5.9‰~-3.3‰(平均值为-4.6‰),成矿流体主要来源于大气降水和地热水。成矿早阶段萤石沉淀机制主要为岩浆热液和大气降水混合与水-岩反应,而流体冷却作用是成矿主阶段和晚阶段萤石沉淀的主要机制。隆坪萤石矿床属断裂控矿、中低温热液裂隙充填型萤石矿床。

The Longping large-scale fluorite deposit in Xingguo county, southern Jiangxi Province, is located in the Xingguo-Ningdu fluorite metallogenic belt on the west side of Dayu-Nancheng deep fault. Fluorite ore bodie are primarily in the silicified fracture zone of the outer contact zone of the Yongfeng complex in the form of plate, stratoid and vein. This paper divides the ore-forming stages of the deposit, and discusses the nature, source, evolution and ore-forming model of the ore-forming fluid of the deposit through the study of fluid inclusions and H-O isotopes. According to the interpenetrating relationship of minerals and the characteristics of mineralogy, the Longping fluorite deposit is divided into early ore-forming stage(fluorite-quartz stage), main ore-forming stage(quartz-fluorite stage) and late ore-forming stage(fluorite-calcite stage). The types of inclusions are mainly liquid rich two-phase inclusions. Fluid inclusions in the fluorite and quartz show homogenization temperatures(111~374℃), salinities(0.53%~3.55% NaCleq), and densities(0.58~1.02 g/cm^(3)). Raman spectroscopy showed that the fluid phase is dominated by wate. Generally, the ore-forming fluid belongs to NaCl-H_(2)O fluid system, which is characterized by medium-low temperature, medium-low salinity and medium-low density. However, there exists fluid end-elements with high temperature and relatively high salinity in the early stage of mineralization(temperature higher than 300℃, salinity 2.0%~2.7%NaCleq). It is inferred that the magmatic hydrothermal fluids in the late stage of the Yongfeng complex participate in the early ore-forming stage and provides the heat and the source of F. The δD_(V-SMOW)values of the fluid inclusions in the Longping fluorite ranged between-66.8‰ and-53.1‰(average value is-59.5‰), while the δ^(18)O_(V-SMOW)values ranged from 5.9‰ to-3.3‰(average value is-4.6‰). Collectively, the ore-forming fluid is dominated by meteoric water and geothermal water. Both the mixing magmatic hydrothermal fluid with meteoric water and water-rock reaction are the likely mechanisms of fluorite precipitation in early ore-forming stage, while fluid cooling is the main mechanism of fluorite precipitation in the main and late ore-forming stage. Therefore, it can be inferred that the Longping fluorite deposit is a fault-controlled, medium-low-temperature hydrothermal, fracture-filling type deposit.