繁昌地区矽卡岩型铁矿成矿流体与成矿年代学研究  

Study of ore-forming fluid and ore-forming age of skarn-type iron ore in the Fanchang area

作　　者：张嵩松 杨晓勇[1] 李伟[2] 王克友[2] 韩长生 阳运楼 ZHANG Songsong;YANG Xiaoyong;LI Wei;WANG Keyou;HAN Changsheng;YANG Yunlou(School of Earth and Space Sciences,University of Science and Technology of China,Hefei,Anhui 230001,China;Geological Survey of Anhui Province,Hefei,Anhui 230001,Chinas;No.812 Geological Team of East-China Metallurgical Bureau of Geology Exploration,Tongling,Anhui 244000,China)

机构地区：[1]中国科学技术大学地球和空间科学学院,安徽合肥230001 [2]安徽省地质调查院,安徽合肥230001 [3]华东冶金地质勘查局812地质队,安徽铜陵244000

出　　处：《地质学报》2022年第4期1297-1320,共24页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42030801,42011540384,41673040);安徽省公益性地质项目“南陵-繁昌地区铜金多金属矿远景调查项目”联合资助成果。

摘　　要：繁昌地区位于长江中下游成矿带,与邻区宁芜盆地不同,其以矽卡岩型铁矿与锌矿为主要成矿类型,已发现的矿床规模较小,对该区矽卡岩型矿床的深入研究和总结对深入认识长江中下游地区中生代成岩成矿作用有重要意义。本文对小阳冲矽卡岩型锌铁矿和松园矽卡岩型硫铁矿进行了成矿流体和成矿年代学研究,在此基础上探讨繁昌地区矽卡岩型矿床成矿流体特征与来源,并与宁芜盆地玢岩型铁矿进行了对比,结论如下:(1)流体包裹体测试表明,两个矿床矿石中的石英、方解石等透明矿物中主要发育气液两相的包裹体。石英-硫化物阶段,两个矿床流体包裹体均一温度变化范围为150~380℃,盐度介于3.6%~22.0%NaCleq,密度为0.70~1.00 g/cm^(3),成矿深度变化范围为0.50~2.00 km。(2)电子探针分析测试结果显示,两个矿床中石榴子石的组分特征(钙铁榴石为主,钙铝榴石次之)以及微量元素在环带上的变化趋势指示其形成于偏氧化及偏碱性的环境。(3)通过对H、O、S同位素的综合分析和讨论,结合磁铁矿的多成因类型,认为矽卡岩阶段流体向石英-硫化物阶段流体的演变过程中,除了岩浆水和地表水的混合之外,还有膏盐层卤水参与成矿过程。(4)与宁芜盆地玢岩型铁矿相比,繁昌地区矽卡岩中的磁铁矿的形成温度的范围较窄且偏低。通过普通Os校正后获得的小阳冲锌铁矿主要成矿阶段的黄铁矿Re-Os年龄为125.7 Ma,稍晚于宁芜地区玢岩型铁矿的成矿年龄。The Fanchang area is located in the Middle-Lower Yangtze metallogenic belt, where the skarn type iron ore and zinc ore are the main metallogenic types. These deposits are relatively small in scale and different from the neighboring Ningwu basin.It is therefore important to obtain insights into the Mesozoic diagenesis and mineralization in the Middle-Lower Yangtze metallogenic belt. In this study, ore-forming fluid and ore-forming age of the Xiaoyangchong skarn-type zinc-iron deposit and the Songyuan skarn-type pyrite deposit have been investigated. The source of ore-forming fluid of the skarn type deposit in the Fanchang area has been discussed, then the comparison with the porphyrite-type iron ore in the Ningwu basin has been illustrated. First of all, results of fluid inclusion experiments show that the transparent minerals, such as quartz and calcite in the two deposits, comprise mainly gas-liquid two-phase inclusions. In the quartz-sulfide stage, the homogenization temperature of fluid inclusions varies from 150~380℃, and the salinity is 3.6%~22.0%NaCleq, density from 0.70~1.00 g/cm^(3)leading to the mineralization depth of 0.50~2.00 km, reflecting the characteristics of epithermal mineralization. Secondly, results of electron probe analysis show that andradite is dominant while grossularite is secondary in both the deposits. Combining with the variation trend of trace elements in the garnet composition belt, it indicates that the garnet has formed in an oxidizing and alkaline environment. Thirdly, based on the comprehensive analysis and discussion of H, O, S isotopes, as well as the multi-genetic types of magnetite, it is concluded that not only the mixing of magmatic water and surface water, but also deep brine would also have been involved in the mineralization process during the evolution process from skarn stage to quartz-sulfide stage. Finally, compared with porphyrite type iron ore in the Ningwu basin, the formation temperature range of magnetite in skarn in the Fanchang area is narrower and lower. A

关 键 词：长江中下游成矿带 矽卡岩型铁矿 流体包裹体 H、O、S同位素 RE-OS年龄 

分 类 号：P618.31[天文地球—矿床学] P597.3[天文地球—地质学]