海南石碌铁多金属矿床中钴铜矿成矿物质来源及年代学研究

The Shilu iron polymetallic ore deposit, in Hainan Province, is a famous hematite-rich ore deposit, with associated Co and Cu resources under the iron ore body. Previous researches mainly focused on the genesis of iron ore, little on Co-Cu ore. Therefore, so far the deep research on the process of mineralization such as the ore-forming material source, metallogenic epoch and the genetic relationship between Cu-Co and iron ore is scarce, which seriously constrains the understanding on the metallogenic system of Shilu iron polymetallic ore deposit. Based on field geological investigation and microscopic observation, two aspects of researches will be carried out in this project: ① the in-situ trace element analysis on pyrite, pyrrhotite and chalcopyrite by EPMA and LA-ICP-MS technique, combined with the trace element analysis on gangue mineral-dolomite, tracing ore-forming material source and the genesis of Co-Cu ore; and ② to study on metallogenic ages of Shilu Co-Cu ore by Re-Os and Ar-Ar isotopic system. According to above research, based on the contrast with domestic and foreign iron polymetallic ore deposits with similar geological characteristics, this project is aimed at discussing metallogenic process, metallogenic mechanism and ore genesis of Co-Cu ore, and further analyzing the genetic relationships between iron and cobalt-copper by integrating the previous research achievement of iron ore deposit. Moreover, The project not only will contribute to correctly understanding the metallogenic system of Shilu iron polymetallic ore deposit, also provide a scientific basis for next prospecting predicton and mineral exploration on the depth and margin of minning area.

海南石碌铁多金属矿床是我国最大的富赤铁矿矿床，铁矿的下部还伴有钴铜矿。以往研究多侧重于铁矿，而对钴铜矿的关注较少，特别是关于钴铜矿的成矿物质来源、成矿作用时代及其与铁矿的成因联系，一直缺乏深入或系统研究。本项目拟在矿区地质调查和岩（矿）相学观察基础上，着重开展两方面的工作：一是运用EPMA和LA-ICP-MS相结合的技术手段，开展矿石矿物黄铁矿、磁黄铁矿、黄铜矿的原位微区微量元素分析，结合脉石矿物白云石的微量元素分析，以期示踪成矿物质的来源；二是应用Re-Os和Ar-Ar同位素地质年代学方法，探索钴铜矿的成矿时代。结合石碌矿床以往研究进展，通过与国内外具相似地质特征的矿床对比，探讨钴铜矿的成矿过程和成矿机制与矿床成因，进一步剖析石碌铁、钴、铜多金属矿的成因联系。此项研究，不仅将有助于正确认识石碌铁钴铜多金属成矿系统，也将为指导找矿预测和矿产勘查提供科学依据。

海南石碌铁钴铜多金属矿床以“上部铁矿、下部钴铜矿”为特点，然而以往对下部钴铜矿的研究非常薄弱。本项目重点开展了钴铜矿成矿物质来源和成矿时代研究。通过详细野外地质调查，在石碌地区首次识别了三种类型的钴铜矿石：①呈层状或似层状产出，块状构造，具强烈的韧脆性变形特征；②沿构造线理发育或呈层内剪切褶皱，具条带状、浸染状和角砾状构造；③呈脉状/网脉状沿构造面理或裂隙产出，切穿早期铁、钴铜矿石。微量元素分析结果表明细粒、半自形-自形PyI具有中等的Co、As和高的Ni含量以及低的Co/Ni比值（~2-5），为沉积-变质成因；具有内部韵律生长环带的PyⅡ含有最高的Co含量（高达91913 ppm）和Co/Ni比值（av. 1241），其共生的PoI具最高的Ni含量（高达8245 ppm），CcpI具最高的Ag（266 ppm）含量，结合这一阶段大量富Co-(Ni)-(As）硫化物产出，暗示了一个富Co-Cu-Ni-Ag的热液来源；PyⅢ中等的Co/Ni比值（av. 46）暗示来源于贫Co的热液流体。不同世代金属硫化物的δ34S值具有从早到晚从17.3-18.2‰（av. 17.8‰）、13.0-18.1‰（av. 15.6‰）到9.6-14.8‰（av. 13.3‰）降低的趋势，暗示了从海水硫酸盐的热还原成因到岩浆硫混入的硫同位素演化特征。钴铜矿石3He/4He值为0.06-0.36 Ra，具壳源氦组成特征，这与石碌矿区外围花岗岩的壳源属性特征一致。基于上述研究，提出成矿物质/流体以壳源为特征，可能源区包括石碌群地层和矿区周围的印支-燕山期花岗岩。采用锆石U-Pb定年、独居石CHIME化学定年以及透闪石Ar-Ar定年相结合的年代学研究方法，获得了三期成矿事件年龄，即ca. 1070-970 Ma、ca. 560-450 Ma和ca. 255 Ma。综合以往研究结果，总结了石碌钴铜矿成矿作用过程：新元古代矿源层沉积期（ca. 1075-880 Ma）；与华南加里东运动有关的同构造变形变质成矿期（ca. 560-450 Ma）、与印支期岩浆侵位有关的第一热液成矿期（ca. 260-210 Ma）、与燕山晚期岩浆作用有关的第二热液成矿期（ca. 130-90 Ma），进而将其归为受构造和热液叠加改造的BIF型矿床。其中，第一热液成矿期是石碌钴铜矿的重要成矿阶段。