岩浆-热液系统中铟的成矿作用

铟作为支撑新兴高科技产业发展的关键金属,主要应用于电子工业、半导体、焊料合金及航空航天等领域,对国家安全和经济发展至关重要.当前铟的重要来源是与花岗质岩浆有关的锡多金属矿床,其中铟的富集程度远超其他类型矿床.文章在简要概括铟矿床类型的基础上,探讨了铟在岩浆-热液系统各演化阶段的富集过程以及锡、铟同步富集的原因.在岩浆演化过程中,如果有黑云母、角闪石等铟的主要载体矿物发生分离结晶,铟的成矿潜力便会被大大削弱.当铟进入成矿流体后,铟的氯化物、氟化物和氢氧化物对铟的搬运有重要作用,流体的温度、pH值以及金属配体的种类和浓度是控制铟迁移和沉淀的重要因素.而当铟从流体中沉淀时,因四次配位的In3+与贱金属硫化物(闪锌矿、黄铜矿、黝铜矿等矿物)中四次配位的金属离子更相似,造成大量的铟以类质同象替换的方式进入硫化物而与锡发生分离;沉淀后的含铟矿物在后期地质过程中可能经历铟的重新活化、迁移和扩散等过程,导致铟再次富集.铟的富集过程与锡有关,这可能是由于铟和锡具有相似的地球化学性质,二者在表生环境中活动性弱,会滞留在经历化学风化的富黏土的沉积岩中,这样的沉积岩经变质作用会形成大量的云母类矿物,而黑云母作为铟和锡的共同载体,其在高温条件下发生分解可能是导致铟和锡在矿床中同步富集的根本原因.此外,新近在一些贫锡岩浆热液矿床中发现铟也能够超常富集,其机理尚不清楚.加强表生环境中锡与铟预富集过程的研究以及贫锡矿床中铟富集机制的研究,对查明铟-锡共生、分离机制和完善铟成矿理论至关重要.

Metallogenesis of indium in magmatic hydrothermal system

Indium, as one of critical elements, is widely used in such high-tech industries as electronic industry, semiconductors, solder alloys and aerospace industries, thus playing a significant role in national security and economy. Since the indium concentration in granite-related tin polymetallic deposits are much higher than that in other types of deposits, the In-Sn polymetallic deposits are ideal for studying indium mineralization. Indium-rich deposits are known to be genetically associated with granitic magmatism. During magmatic evolution, the potentiality of indium ore formation decreases greatly if the main host minerals of indium, such as biotite and hornblende, crystallize and separate from the melt. In hydrothermal fluid, indium, which is closely associated with tin, can be transported in the form of chlorides, fluorides and hydroxides of indium. Such a process is controlled by temperature, pH as well as types and concentrations of ligands in ore-forming fluids. When indium precipitates, it mainly enters sulfides (e.g. sphalerite, chalcopyrite and tetrahedrite) due to similar ionic radius of In³⁺ to metal elements in Zn-Cu-bearing sulfides and decouples with tin. After precipitation, these indium-bearing minerals might undergo subsequent geological processes, resulting in reactivation, migration and diffusion of indium and contributing to further indium enrichment. The close association of tin and indium might result from similar geochemical behaviors. They are immobile in surficial environments and tend to remain in clay-rich sediments during chemical weathering, which would form biotite and muscovite during metamorphism. Then the breakdown of biotite at high temperature would result in synchronous enrichment of indium and tin in magma source. Recently, significant indium enrichments have been found in tin-poor polymetallic deposits associated with granitic magmatic hydrothermal systems, but the enrichment mechanism of indium in such a system remains unclear. Consequently, future studies should focus on the pre-enrichment processes of indium and tin as well as the enrichment mechanisms of indium in tin-poor polymetallic deposits so as to obtain a better understanding of the coupling and decoupling of tin-indium enrichment and the metallogenesis of indium.