大厂矿田铜坑-长坡锡石硫化物矿床铅 同位素特征及其地质意义

[摘 要] 铜坑 - 长坡锡石硫化物矿床是大厂矿田中规模最大、最具有代表性的矿床,本文通过该矿床大量铅同位素资料的系统分析,运用全方位对比法和△β- △ч示踪法对矿床成矿物质来源进行了研究,不管是层状矿体、细脉带矿体还是大脉带矿体,其成矿物质主体具有统一来源,主要来自岩浆岩、泥盆系及基底物质,但也有少量的幔源物质参与。铜坑-长坡矿床的形成可能经历了两个阶段,即:早期的基性岩脉阶段和晚期的燕山期岩体阶段。     

大厂锡多金属矿田铜坑-长坡92号矿体Rb-Sr测年及其地质意义

铜坑-长坡锡石硫化物矿床是广西大厂锡多金属矿田中一个规模最大、特征最为典型的超大型锡矿床,矿体呈脉状、层状两种形式产出,其中的92号层状矿体是该矿床中规模最大的一个矿体.本文应用Rb-S等时线法获得92号矿体成矿年龄为93.4±7.9 Ma(1σ),这一年龄值不仅与矿田中部龙箱盖黑云母花岗岩的SHRIMP锆石U-Pb年龄93±1 Ma吻合,而且在测试误差范围内与前人所获得的龙头山100号矿体、铜坑-长坡91号矿体以及亢马矿床的成矿年龄基本一致,表明区内锡多金属成矿作用发生在燕山晚期.92号矿体成矿流体的87Sr/86Sr初始值为0.71351±0.00100,与龙箱盖黑云母花岗岩87Sr/86Sr的初始值0.7110接近.成矿年龄与成矿流体的87Sr/86Sr初始值均表明铜坑-长坡92号矿体的成矿作用与龙箱盖岩体具有一定的成生联系.     

大厂锡多金属矿田铜坑-长坡矿床流体包裹体研究

铜坑-长坡锡石硫化物矿床是桂西北大厂矿田中的一个超大型矿床,由浅部的脉状矿体和中-深部的层状矿体组成。文章应用显微测温和激光拉曼光谱分析对铜坑-长坡矿床进行了系统的流体包裹体参数和成分的测试。结果显示,铜坑-长坡矿床脉状和层状矿体的流体包裹体具有相同特征,包裹体的类型主要有CO2型和NaCl-H2O型。3个成矿阶段的均—温度分别为：270～365℃,210～240℃和140～190℃。早阶段(Ⅰ、Ⅱ阶段)成矿流体成分主要为CO2和H2O,含少量CH4和H2S,密度为0．324～1．093g／cm^3,盐度w(NaCleq)主要集中于1％～7％;晚阶段(Ⅲ阶段)成矿流体成分主要为H2O,且Ca^2 和Mg^2 含量增加,密度为0．893～0．972g／Cm^3,盐度w(NaCleq)主要集中于3％～10％。流体包裹体特征和He、Ar、S同位素组成共同表明,铜坑-长坡矿床脉状及层状矿体具有相同的成矿物质来源和相同的成因,成矿作用与燕山期构造、岩浆热事件有关。基于^3He／^4He比值高和富CO2流体的存在,认为在铜坑-长坡矿床成矿过程中有深部地幔流体的参与。     

The origin of the Tongkeng-Changpo tin deposit,Dachang metal district,Guangxi, China: clues from fluid inclusions and He isotope systematics

Tongkeng-Changpo is the largest tin deposit within the giant Dachang polymetallic tin ore field in Guangxi, southern China, which is part of a large skarn system associated with Cretaceous granitoids. The Tongkeng-Changpo mineralization consists of veins and stockworks in the upper levels and replacement stratiform orebodies (mantos) at lower levels. Based on textural relationships, three major mineralizing stages can be recognized: stage I with cassiterite, sulphides, stannite, tourmaline, and quartz; stage II with cassiterite, sulphides, sulphosalts, quartz, and calcite; and stage III with calcite as the main phase. The study of fluid inclusions has shown that there are two main fluid types: CO₂ and NaCl-H₂O. Homogenization temperatures are 270 to 365°C, 210 to 240°C, and 140 to 190°C for stages I, II, and III, respectively. Salinities range from 1 to 7 wt.% NaCl equiv. in the early ore stage and 3 to 10 wt.% NaCl equiv. in the late stages. Laser Raman Spectroscopy indicates that the inclusion fluids in stages I and II were of carbono-aqueous composition, with minor amounts of CH₄ and H₂S, whereas those in stage III were aqueous. Helium isotopic analyses of inclusion fluids indicate that the ³He/⁴He ratios in the ore veins are in between 1.2 to 2.9 Ra (Ra = 1.4 × 10⁻⁶, modern atmospheric ratio), and range from 1.6 to 2.5 Ra in the stratiform orebodies. This range of ³He/⁴He ratios is significantly higher than that of crustal fluids (0.01–0.05 Ra). The similar characteristics of fluid inclusions and their He isotopic composition, as well as age constraints, indicate that the ore veins and stratiform orebodies of the Tongkeng-Changpo deposit formed from the same hydrothermal system, likely related to granite intrusions of the Mesozoic Yanshanian tectono-thermal event. In addition, the high R/Ra ratios indicate a mantle contribution in the ore fluids.