贵州拉峨汞矿床方解石REE、C、O同位素地球化学特征及意义

Geochemical Characteristics and Implications of REE,Carbon and Oxygen Isotopes of Calcite from La'e Mercury Deposit

三丹汞矿带是我国重要的汞矿富集区,也是西南大面积低温成矿域的重要组成部分.为了阐明区内汞矿的成矿物质和成矿流体来源,作者对三丹汞矿带中段交犁-拉峨汞矿床中的方解石样品进行了REE和C-O同位素测试分析.结果显示方解石稀土总量(∑REE+Y=28×10^(-6)~70×10^(-6))相对较高,稀土配分模式为轻稀土(LREE)富集的右倾型(LREE/HREE=8.1~17),(La/Yb)_N为9.6~47,Y/Ho-La/Ho图解指示方解石为同源成矿流体的产物.Eu异常(δEu=0.75~3.6)变化较大,Ce异常不明显(δCe=0.86~0.98),整体呈弱正Eu异常和微弱负Ce异常,表明矿质发生沉淀时为弱氧化环境.通过与区内Au、Sb、Hg等低温矿床的C、H、Pb、S等同位素组成对比研究,认为拉峨汞矿床成矿物质来源于围岩,可能有沉积有机物质参与成矿.成矿流体以大气降水淋滤海相碳酸盐岩地层产生的壳源流体为主,不排除地幔流体参与成矿的可能性.

The Sandan mercury ore belt is an important mercury resource cluster region, and also a significant part of the large - scale low - temperature metallogenic domain in southwestern China. The La＇e mercury deposit is lo- cated in Sandan mercury ore belt. Calcite is one of the major gangne minerals in this deposit. Based on the study of the REE concentrations of gangue calcites, host rocks and Carbon and Oxygen isotopic characteristics are deter- mined to discuss the source of ore - forming fluid and ore - forming materials. The results show that the REE com- positions of gangne calcites with different occurrences are relatively high, the total REE concentrations of calcites ranging from 28 ×10^-6 to 70 × 10^-6 （ including Y）. The mode of REE with enriched LREE is right - dip curve. LREE/HREE ratios range from 8.1 to 17, while （La/Yb）N ratios are from 9.6 to 47. The REE distribution pat- terns are similar to host rocks, indicating that ore - forming materials are derived from the wall rocks. Furthermore, calcites are characterized by weak positive Eu anomaly and weak negative Ce anomaly, which indicate that the minerals are precipitated in weak oxidative environment. Through comparison with the C, H, Pb, S isotopes of low -temperature Au, Sb, Hg deposits in this region, it is summarized that the ore -forming materials in La＇e mer- cury deposit are derived from the wall rocks and the sedimentary organic substances may be involved in mineraliza- tion. The source of ore - forming fluid mainly is the leachate of carbonate and sedimentary rocks, a variety of evi- dences demonstrating that the ore -forming fluids are of the crustal type, which may be linked with mantle fluids.