Huang, Zhijie2025-11-122025-11-12https://hdl.handle.net/1885/733794103The highly Siderophile Elements (HSE) comprise Re and Au, along with the six platinum-group elements Os, Ir, Ru, Pt, Rh and Pd. Importantly, for geologists and metallurgists, the HSEs are valued for their distinctive geochemical properties as both siderophile and chalcophile elements, i.e. having a strong affinity for both metal and sulphur phases. Micro-sized metal particles (nuggets) in quenched silicate melts have been a major obstacle in the experimental study of HSE geochemistry. The persistence of even a small fraction of nuggets can have a significant influence on the measurement of the very low HSE concentrations in quenched silicate melts (glasses). Consequently, experimentally reported partition coefficients between metals, sulfide liquids, and silicate melts can be severely compromised, leading to erroneous and misleading inferences. Furthermore, the influence of sulfur on the solubility of the HSE requires further evaluation, despite sulfur being one of the most abundant volatiles in terrestrial magmas. Published HSE partition coefficients between metals, sulfide liquids, and silicate melts can vary by orders of magnitude, and these differences can be due to failing to eliminate the nugget effect or to underestimating the influence of S on the solubility of the HSE in silicate melts. The primary objectives of this study were to: (i) develop and evaluate strategies to minimize the nugget effect, (ii) improve analytical methods for quantifying trace HSE analyses using silicate melt-based standards (e.g., GM-01), (iii) quantitatively assess the effect of sulfur on HSE solubility in silicate melts, and (iv) identify the dissolution mechanisms of HSEs in silicate melts. The experiments were conducted at ambient pressure using synthetic silicate melts. Both sulfur-free (S-free) and sulfur-bearing (S-bearing) conditions were studied, at controlled oxygen fugacity (fO2) and sulfur fugacity (fS2). Strategies to suppress nuggets included oxidation state management to prevent initial oversaturation and extended duration experiments to eliminate or manage nuggets through Ostwald ripening. Samples with low Pt were analysed by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS), which has an order-of-magnitude lower detection limit for Pt than conventional ICP-MS analyses. Nugget formation was eliminated or reduced to a manageable level through a combination of redox control and extended experiments (Ostwald ripening), facilitating high-quality data acquisition. Under S-free conditions, Au and Pd solubility increased with fO2 with Au1+ and Pd1+ identified as dominant species alongside neutral valences. Sulphur significantly enhanced Au solubility in S-bearing systems confirming dissolution via a previously unrecognised AuS2 complex. Pd solubility, however, was independent of sulfur, indicating no ligand preference. Pt exhibited increased solubility with fS2, with Pt0 and Pt2+ species in silicate melt together with PtS under S-bearing conditions. Rhodium solubility is also dependent on fO2 and fS2, but the effect of S is less constrained due to limited data. The effect of S on the solubility of the HSE in silicate melts is established as Au > Pt > Rh > Pd, reflecting sulfur's variable influence. These results provide refined metal-silicate melt partition coefficients (D(Metal/SM)) for the HSEs, which have applications in geodynamic modelling of planetary differentiation and Pt-Pd-rich horizons in layered intrusions (e.g., Skaergaard, Stillwater and Bushveld complexes). The solubility models will help metallurgists optimize HSE extraction during smelting. Future work should expand data on D(Sulfide liquid/Metal)and integrate thermodynamic parameters for the sulfur content of silicate melts at sulfide saturation (SCSS) to advance predictive frameworks for HSE behavior in natural and industrial systems.en-AU202610.25911/8925-9E25