中酸性岩浆体系Sn-Nb-Ta在矿物与熔体之间分配行为的实验研究

The scientific questions of this project are about the enrichment and migration of ore-forming elements during the evolution of rare metal granite magma and the mechanism of individual ore-forming and composite ore-forming, especially for the lack of mineral/melt Sn distribution coefficient and mineral/melt Sn/Nb, Sn/Ta partition exchange coefficient. By setting different physical and chemical parameters (such as temperature, pressure, oxygen fugacity, and volatiles) according to experimental petrology and experimental geochemistry methods, the new technology of Sn-bearing precious metal sample tube is used in our high temperature (HT) and high pressure (HP) experiments. The HTHP experiments of geochemical behavior simulation and tracing of tin (Sn) -niobium (Nb) -tantalum (Ta) during magma crystallization are carried out to accurately determine the distribution coefficients of Sn, Nb, Ta between iron-titanium oxide (magnetite, Ilmenite), iron-magnesium minerals (hornblende, biotite), titanite and the melt in the intermedium-felsic magma system. This project focus on investigating the effects of physical and chemical parameters such as temperature, pressure, oxygen fugacity, and volatile content on the distribution coefficients so that to explore the metallogenic mechanism and metallogenic process of Sn-Nb-Ta metal elements, and to provide an important experimental geochemical basis for accurately revealing the enrichment and mineralization of ore-forming elements in the melt during the crystallization and evolution of intermedium-felsic magma.

本项目针对稀有金属花岗岩岩浆演化过程中成矿元素富集和迁移规律以及单独成矿和复合成矿机制等科学问题，特别是矿物/熔体Sn分配系数和矿物/熔体Sn/Nb、Sn/Ta分配交换系数的缺乏，拟使用实验岩石学和实验地球化学的研究方法，通过设定不同物理化学参数（如温度、压力、氧逸度、挥发份），采用含Sn贵金属样品管的新技术，系统地开展中酸性岩浆体系锡（Sn）-铌（Nb）-钽（Ta）在岩浆结晶过程中的地球化学行为模拟和示踪的高温高压实验研究。本项目旨在准确测定Sn-Nb-Ta在铁钛氧化物（磁铁矿、钛铁矿）、铁镁矿物（角闪石、黑云母）以及榍石等矿物与熔体间分配系数，重点调查温度、压力、氧逸度、挥发份等物理化学参数对分配系数的影响，进而探索Sn-Nb-Ta金属元素成矿机制和成矿过程，为准确揭示中酸性岩浆结晶和演化过程中这些成矿元素在熔体中的富集和成矿关键控制因素提供实验地球化学约束。

为了研究Sn-Nb-Ta等关键金属超常富集与成矿，了解Sn-Nb-Ta金属元素的地球化学行为，本项目开展了花岗质岩浆体系中温度、压力、氧逸度和熔体组成等物理化学因素对榍石、钛铁矿、铁镁矿物（角闪石和黑云母等）与花岗质熔体之间Sn，Nb，Ta分配系数影响的高温高压实验研究。在以下方面取得重要进展：.本次研究采用铼金属材料作为实验样品管，克服了传统贵金属如Pt、Au等与Sn发生合金效应的难题。在0.5-1GPa，850-1000℃，>FMQ-4 ~ FMQ+8条件下，准确地测定了Sn-Nb-Ta在榍石、钛铁矿、角闪石与中酸性熔体之间的分配系数。结果表明，榍石/熔体间Sn-Nb-Ta分配系数范围：DSn榍石/熔体=0.5-185， DNb榍石/熔体=11-122，DTa榍石/熔体=27-183；钛铁矿：DSn钛铁矿/熔体=0.04-69，DNb钛铁矿/熔体=2.5-13，DTa钛铁矿/熔体=2.4-19；角闪石/熔体间Sn分配：DSn角闪石/熔体=0.08-12.7。氧逸度、熔体组成和温度对矿物/熔体Sn分配有明显的影响：DSn随氧逸度的降低而减小，随温度降低而增加，随熔体聚合度的增加而增加。DNb和DTa也随温度降低而增加，随熔体聚合度的增加而增加。本次研究获得了Sn在榍石、钛铁矿、角闪石与熔体间的分配系数，尤其是通过榍石副矿物评估了岩浆作用过程中Sn的成矿潜力，并且对Sn，Nb，Ta富集的岩浆过程的机理以及各元素富集的关键控制因素有了进一步的理解。