云南富乐铅锌矿床碳酸盐矿物化学特征及其对成矿作用的指示

Mineralogical and geochemical characteristics of carbonate and implications for ore-forming mechanism of the Fule Pb-Zn deposit,Yunnan Province,China

富乐铅锌矿床位于川滇黔铅锌矿集区东南部,该区域是我国重要的铅锌银及分散元素成矿带。该矿床的形成分为早成矿期、主成矿期和晚成矿期。应用电子探针和LA-ICPMS原位分析技术,测定了不同期次白云石和方解石的主-微量元素组成。研究表明,白云石和方解石具有不显著的Eu异常向正Eu异常和强负Ce异常向弱负Ce异常演化的趋势,表明硫化物和白云石的沉淀是由于流体氧逸度和温度降低,成矿时流体环境从碱性变为中性再到弱酸性导致的。从成矿早期到成矿晚期,Fe和Mn呈下降趋势,碱性环境下Fe和Mn进入到碳酸盐矿物中,而在酸性环境下Fe和Mn会被释放到流体中,说明由于交代作用的由强变弱,其成矿环境是从碱性为主向以酸性为主演变的;从早到晚Sr呈上升趋势,可能表示热液-围岩不断的反应使得围岩中的Sr不断的被释放到流体中。Fe-Sr图解和Mn-Sr图解表明,成矿过程存在两种流体的混合。综合以上研究,本文认为富乐铅锌矿床可能是由氧化、酸性的富含金属的流体与还原、碱性的亏损金属的流体混合导致矿质沉淀形成的。

The Fule Pb-Zn deposit is located in the southeastern part of the Sichuan-Yunnan-Guizhou （SYG） Pb-Zn mineralization district, which hosts significant Pb-Zn-Ag-dispersed elements deposits in China. Applying detailed mineralogy and elements analysis to the gangne minerals of the Fule Pb-Zn deposit, this paper reveals the characteristics and sources of ore-forming fluid, to help us understand the mechanism of mineralization. Based on the paragenesis sequence of the Fule deposit, the major elements and trace elements of gangne minerals were analyzed via Electron Probe Microanalyze （EPMA） and Laser Abrasion （LA）-ICPMS. Trace elements of carbonate in the Fule deposit reveal that there is a trend from various Eu anomaly to positive Eu anomaly and from a strong negative Ce anomaly to weak negative Ce anomaly, indicating precipitation of sulfide and dolomite are due to decreases of fo2, temperature and pH. There is a trend of decrease of Fe and Mn from early to late mineralization, indicating Fe and Mn were released in a low pH environment and incorporated into dolomite. The Sr concentration of carbonate show an increasing trend, indicating the fluid continued to react with the wall rock, incorporating more Sr. Dolomite and calcite Fe-Sr and Mn-Sr illustrate that there are mixing of two fluids. We propose that mineralization is a result of mixing of metal-rich, oxidized acidic fluid and reduced alkaline fluid.