Molybdenum isotope fractionation mechanism of metal sulfides in magmatic hydrothermal systems: Constraints from the Pulang porphyry Cu deposit, Yunnan, Southwest China

Exploration of the application of Mo isotope in the field of mineralogy with precise knowledge of the geochemical behaviors of Mo in the PCDs is of considerable concerns. This study puts critical constraints on the Mo isotope geochemistry in magmatic-hydrothermal systems based on analysis of Mo isotope of the metal sulfides from different mineralization stages (i.e., epidote-chlorite, chlorite-illite, and quartz-illite stages) in Pulang porphyry Cu deposit, Yunnan, Southwest China. We observed that pyrites, chalcopyrites and pyrrhotites with highly variableMo abundances and heavier δ98Mo (-0.34 ± 0.04‰ to 3.01 ± 0.03‰) in comparison to molybdenites (δ98Mo: -0.90 ± 0.04‰ to 0.08 ± 0.04‰), whole-rock ore-forming porphyries (δ98Mo: -0.18 ± 0.03‰ to -0.08 ± 0.03‰) and surrounding rocks (-0.41± 0.05‰ to -0.14± 0.03‰).The variability of δ98Mo signatures of these metal sulfides is independent of lithology of originally magma sources, which instead constrained by the evolutions of ore-forming fluids, changes of ore-forming temperature or metallogenic settings, as well as differential geochemical behaviors of Mo species. In the magmatic hydrothermal metallogenic system, there is a progressive partitioning of Mo into exsolved metallic minerals, with molybdenites preferentially partitioning lighter δ98Mo while pyrites, chalcopyrites and pyrrhotites are enriched in heavier δ98Mo. Additionally, these metallic sulfides have a preference for relatively heavier δ98Mo enrichment in the early metallogenic stage, thereby leaving residual metallogenic fluids with progressively homogenized lighter δ98Mo, and consequently relatively homogeneous but lighter isotopes of the metallic minerals in the later stages. The extensively maintained Mo isotope fractionation in PCDs is indicative of a maldistribution of ore-forming components in the sulfides, of which it is this disequilibrium effect that points to the enrichment of metal elements as well as the significant process of magmatic hydrothermal metallogenesis. Mo isotope systematics provide a robust geochemical proxy to interrogate PCDs genetic mechanisms and metal precipitation stages, allowing to consider it as a subservience indicator for the complex metal enrichment that can be extrapolated to other porphyry-type deposits.

精准认知斑岩铜矿床（porphyry copper deposits, PCDs）中钼的地球化学行为，并探索钼同位素（Mo isotope）在矿物学领域的应用，具有重要的研究意义。本研究以中国西南云南普朗斑岩型铜矿床不同成矿阶段（即绿帘石-绿泥石、绿泥石-伊利石及石英-伊利石阶段）的金属硫化物为样品开展钼同位素分析，为岩浆热液系统中的钼同位素地球化学特征提供关键约束。研究发现，黄铁矿、黄铜矿与磁黄铁矿的钼含量差异显著，其δ⁹⁸Mo值（-0.34 ± 0.04‰ 至 3.01 ± 0.03‰）偏重；与之相比，辉钼矿（δ⁹⁸Mo：-0.90 ± 0.04‰ 至 0.08 ± 0.04‰）、成矿斑岩全岩（δ⁹⁸Mo：-0.18 ± 0.03‰ 至 -0.08 ± 0.03‰）及围岩（-0.41± 0.05‰ 至 -0.14± 0.03‰）的δ⁹⁸Mo值相对偏低。上述金属硫化物的δ⁹⁸Mo同位素组成变化与原始岩浆源区的岩性无关，而是受成矿流体演化、成矿温度变化或成矿背景，以及钼物种的差异化地球化学行为所制约。在岩浆热液成矿系统中，钼会逐步分配至析出的金属矿物中：辉钼矿优先富集轻δ⁹⁸Mo，而黄铁矿、黄铜矿与磁黄铁矿则富集重δ⁹⁸Mo。此外，在成矿早期阶段，这些金属硫化物更倾向于富集相对偏重的δ⁹⁸Mo，从而使残余成矿流体的δ⁹⁸Mo值逐步均一化并趋于偏轻，进而导致后期形成的金属矿物具有相对均一但偏轻的同位素组成。斑岩铜矿床中广泛存在的钼同位素分馏现象，表明硫化物中成矿组分的分布并不均衡；而这种非平衡效应正是金属元素富集与岩浆热液成矿作用显著的标志。钼同位素体系可为揭示斑岩铜矿床的成矿机制与金属沉淀阶段提供可靠的地球化学代用指标，可作为复杂金属富集过程的辅助指示指标，且该结论可推广至其他斑岩型矿床。

搜集汇总

背景与挑战

背景概述

该数据集聚焦于岩浆热液系统中金属硫化物的钼同位素分馏机制，以中国云南普朗斑岩铜矿为案例进行研究。通过分析不同成矿阶段硫化物（如黄铁矿、黄铜矿）的δ98Mo同位素组成，发现其变异性主要受成矿流体演化、温度变化等因素控制，揭示了钼在矿物中的分馏模式（辉钼矿富集轻同位素，其他硫化物富集重同位素）以及早期阶段富集较重同位素的特征。研究强调了钼同位素系统作为地球化学指标的重要性，可用于理解斑岩铜矿的成因机制和金属沉淀过程，为类似矿床研究提供参考。