个旧超大型锡矿床锡石矿物学、矿物化学和U-Pb年代学研究

Gejiu super-large tin deposit, located in the combination area between the circum-pacific tectonic domain and Tethyan tectonic domain, is one of the most well-known tin product bases in the world. Seven metallic deposit types have been occurred in Gejiu ore district. But there are no research data of cassiterite mineralogy, cassiterite chemistry and cassiterite chronology from these different ore deposits, so we can not discuss the ore genesis of Gejiu tin deposit thoroughly. And the practical metallogenic mode can not be built. Lacking of the data is also one of the reasons that different researchers hold different viewpoints on the ore genesis. This is no helpful to study the extensive tin metallogenesis in the southeast of Yunnan province. Taking the cassiterites from different metallic deposit types as research objects, we will study the cassiterite mineralogy, cassiterite chemistry and cassiterite U-Pb chronology systematically.Based on the compared analysis of the research data, the genesis and temporal relationships among different metallic deposit types can be analyzed specifically. Through compared analysis of the ore-forming time between Gejiu tin deposit and the other key tin deposits such as Dulong and Bainiuchang tin deposit in the southeast of Yunnan province, the extensive tin mineralization of southeast Yunnan provice can be researched deeply.. In a word, the expected research outputs may have the scientific and academic significances to discuss the ore genesis and build the practical metallogenic mode. In addition, the precious scientific credible data of cassiterite mineralogy, cassiterite chemistry and cassiterite chronology have been obtained. These data can be used to disscuss the extensive tin mineration in southeast of Yunnan province and the inherent relationships among the seven metallic deposit types in Gejiu tin deposit.

地处环太平洋构造域与特提斯构造域复合部位的个旧超大型锡矿床是举世闻名的锡生产基地之一。矿集区目前已发现7种矿床类型，但由于缺乏可用于各类型矿床之间对比的准确可信的锡石矿物学、矿物化学和成矿年代学资料，无法深入探讨矿床的成因和建立切入实际的矿床成矿模式，这也是不同学者对个旧锡矿矿床成因的认识难以统一的原因之一，不利于深入研究滇东南大规模的锡成矿作用。我们拟利用形成个旧锡矿不同矿床类型的直接矿物锡石研究锡石矿物学、矿物化学和锡石U-Pb成矿时代，对比分析各类型矿床的时间域关系和成因联系，将所得结果与滇东南的其它矿床如都龙、白牛厂等锡矿的成矿时代作对比分析，探讨滇东南的大规模锡成矿作用。研究成果对深入探讨个旧锡矿的矿床成因，建立切合实际的矿床成矿模式具有重要的理论意义，同时可为深入研究滇东南的大规模锡成矿作用及探讨滇东南锡矿带各类型矿床的内在联系提供可靠的锡石矿物学、矿物化学和年代学证据。

本项目为了解决个旧锡多金属矿床的成因争议，4年来针对个旧矿区6种类型矿床进行了锡石矿物学、矿物化学与锡石U-Pb年代学进行深入系统的研究，按计划完成了研究任务，达到了预期目标。（1）锡石矿物学研究表明，锡石的晶形特征、内部结构特征及晶胞大小与锡石的形成温度与压力呈正相关性，温度与压力越高，晶形及内部结构越复杂，晶胞越小；（2）锡石矿物化学研究发现，锡石中（Fe+Mn）/（Nb+Ta）比值指示个旧锡矿中锡石具热液锡石的特征，Zr2O3、Hf2O3含量及Zr/Hf指示成矿热液可能来自于高分异的花岗质岩浆，In2O3指示成矿压力及成矿温度从块状硫化物型、矽卡岩型、电气石细脉带型、含锡白云岩型到层间氧化矿型依次降低。此外，锡石中“锯齿状”环带结构中成分暗示流体的多期多阶段性。锡石包裹体测温显示，成矿流体温度从云英岩型、块状硫化物型、矽卡岩型、电气石细脉带型、含锡白云岩型及层间氧化矿型依次降低。包裹体的气相成分以CO2和H2O为主，云英岩型矿床中流体包裹体气相成分含有少量CH4，块状硫化物矿床中流体包裹体气相成分含有少量CH4、N2；包裹体中阳离子为K+、Na+、Ca2+、Mg2+，富Na+贫K+，阴离子为F-、Cl-、NO3-、SO42-，富Cl-贫F-，H、O同位素显示，个旧锡矿成矿流体主要来自于岩浆水，在成矿过程中可能有大气降水的混入；C、O同位素显示，流体中的C主要来自于岩浆系统，层间氧化矿型矿床中的碳部分来自于沉积物中有机质的氧化；（3）运用LA-ICP-MS微区原位U-Pb同位素测年技术，对个旧矿区的锡石颗粒进行了研究，获得了云英岩型锡矿化的谐和年龄为 (85.6± 1.0 Ma), 矽卡岩型锡矿化的谐和年龄为(86.3±5.4 Ma), 电气石细脉带型锡矿化的谐和年龄为 (85.9±1.8 Ma)， 块状硫化物型锡矿化的谐和年龄为 (86.2±1.7 Ma), 和层间氧化物型锡矿化的谐和年龄为 (86.7±2.8 Ma) 。