鲁西微山稀土矿床成矿机制研究现状及展望

Present Condition of Prospect Study on Metallogenic Mechanism of Weishan Rare Earth Element Deposit in Western Shandong Province

摘要:

鲁西微山稀土矿床是一个典型的碳酸岩型内生轻稀土矿床，其成矿机制目前仍存在结晶分异作用、流体不混溶作用及热液蚀变作用等方面的分歧。该稀土矿床中发育大量的熔体、熔体—流体包裹体和富CO2流体包裹体，这些包裹体在常压测温过程中易爆裂或泄露，很难测得它们的完全均一温度等相变数据，导致该矿床岩浆→岩浆—热液→热液完整的成矿流体演化过程及其热力学性质仍不清楚。此外，稀土在成矿流体演化各阶段的流体中进行高效迁移和富集沉淀的机制，尚缺少原位的微区成分分析和高温高压实验模拟方面的约束。以上研究中存在的问题极大限制了研究人员对微山稀土矿床成矿机制的深入认知。将来，针对上述问题，可以通过对高内压的熔体包裹体、熔体-流体包裹体和富CO2流体包裹体开展热液金刚石压腔均一测温，以厘清成矿流体完整的演化过程；对单个包裹体开展原位LAICPMS微区成分分析，以定量刻画稀土在岩浆流体演化过程中的分配行为；将热液金刚石压腔与拉曼光谱仪联用，模拟稀土元素与CO2-3、SO2-4和F-等配体络合后进行有效迁移的络合物类型及氟碳铈矿的沉淀机制。最终，阐明微山稀土矿床成矿流体完整演化过程及稀土富集矿化机制，为碳酸岩型稀土矿床成矿流体演化和成矿机制研究提供新的研究思路，并解决当前碳酸岩型稀土矿床中存在的熔体包裹体、熔体-流体包裹体及富CO2流体包裹体等均一温度难以测定的“卡脖子”实验技术难题。

Abstract:

Weishan rare earth element deposit in western Shandong province is a typical endogenic light rare earth element deposit of carbonatite type. Its metallogenic mechanism is still divergent in terms of crystallization differentiation, fluids immiscibility and hydrothermal alteration process. A large number of melt inclusions, melt fluid inclusions and CO2 rich fluid inclusions are formed in rare earth element deposit. These inclusions are easy to decrepitate or leakage during the temperature measurement at atmospheric pressure. It is difficult to measure their total homogenization temperature and other phase change data, which leads to unclear understanding of the complete evolution process of ore-forming fluids from magma to magma-hydrothermal solution and its thermodynamic properties. As a result, the complete evolution process and thermodynamic properties of ore-forming fluids from magma to magma-hydrothermal and to hydrothermal fluids stage in the deposit are still unclear. In addition, the mechanism of efficient migration, enrichment and precipitation of rare earth elements in ore-forming fluids at various stages of evolution is still lack of constraints from in-situ micro-area composition analysis and high-temperature and high-pressure experimental simulation. The problems existing in the above studies have greatly limited the researchers' in-depth understanding of the metallogenic mechanism of the Weishan rare earth element deposit. In the future, in order to solve the above problems, the complete evolution process of ore-forming fluids can be clarified by homogeneous temperature measurement of melt inclusions, melt-fluid inclusions and CO2 rich fluid inclusions with high internal pressure by using the hydrothermal diamond-anvil cell (HDAC). In situ LA-ICP-MS microanalysis of individual inclusion should be carried out to quantitatively characterize the distribution behavior of rare earth elements in the evolution of magmatic fluids. HDAC together with Raman spectrometer are used to simulate the types of complexes of rare earth elements that effectively migrate after complexing with ligands, such as CO23, SO24 and F and the precipitation mechanism of bastnaesite. Finally, the complete evolution process of ore-forming fluids and rare earth element enrichment and mineralization mechanism of Weishan rare earth element deposit will clearly clarified, which provides a new research idea for the study of oreforming fluids evolutionary process and mineralization mechanism of carbonatite type rare earth element deposit. It also solves the "bottleneck" experimental technical problem that the homogenization temperatures of melt inclusions, melt-fluid inclusions and CO2 rich fluid inclusions in carbonatite rare earth element deposits are difficult to determine.