Understanding how quartz microfractures heal under hydrothermal conditions is crucial for constraining the evolution of permeability, fluid flow, and gold mineralisation in orogenic systems. Early experimental studies established that microfracture healing in quartz is a thermally activated, diffusion-controlled process governed by silica transport and influenced by temperature, fluid chemistry, and fracture geometry. Recent advances combining microstructural observations and phase-field modelling have revealed the cyclic nature of fracture-healing and its feedback on permeability. However, the quantitative relationships between temperature, fluid chemistry, and fracture geometry that control sealing rates remain poorly constrained. To address these issues, we conducted high-temperature (500–650 °C), high-pressure (1.5–3.6 kbar) hydrothermal experiments on quartz in sulphur-rich fluids, integrated with correlation analysis and reactive-transport modelling. The results show that healing time decreases markedly with increasing temperature and increases with fracture width, indicating that thermal activation accelerates silica mass transfer, while wider fractures heal more slowly. Mixed HS⁻–Cl⁻ fluids promote the fastest sealing, followed by sulphur- and chloride-rich systems, whereas CO₂-bearing fluids retard healing owing to lower silica reactivity. Numerical simulations using COMSOL Multiphysics reproduce these trends, showing that quartz precipitation under a pressure gradient causes porosity loss, permeability reduction, and localised fracture sealing. To complement these experiments, Gaussian Process Regression modelling was developed to predict gold solubility in H₂S-rich fluids as a function of temperature, pressure, and HS⁻ concentration, revealing solubility maxima above 600 °C at moderate HS⁻ levels (~0.1–0.2 mol kg⁻¹). Together, these results demonstrate that temperature and fluid composition jointly control quartz sealing and gold transport, emphasising the thermally and chemically driven nature of hydrothermal sealing and episodic mineralisation in orogenic systems.