關鍵字： 廬山溫泉區、熱液礦物、黃鉀鐵礬、PHREEQC;The Lushan hot springs， located within the slate belt of the Central Range， represent a non-volcanic， orogenic-belt geothermal system. This study examines minerals precipitated near the fumarolic vents of the Mahaipu hot spring outcrop， using X-ray diffraction (XRD) and Raman spectroscopy—referenced against the RRUFF and ICDD databases—for mineral identification， and optical/scanning electron microscopy (SEM-EDS) to characterize mineral habit， paragenesis， and elemental composition. Spring water chemistry was also analyzed， and PHREEQC geochemical modeling was applied to evaluate mineral precipitation mechanisms. The identified hydrothermal minerals include trona， sulfur， sideronatrite， bloedite， thenardite， copiapite， magnesiocopiapite， hexahydrite， epsomite， halotrichite， tamarugite， and jarosite. Jarosite and tamarugite typically form under acidic conditions， while trona and thenardite form under alkaline conditions. However， the original hydrothermal fluid at Lushan has a near-neutral to weakly alkaline pH (6.9–8.2)， low sulfate concentration， and no active volcanic H₂S source， making the occurrence of sulfur-bearing minerals near the vents anomalous. PHREEQC simulations show that flash evaporation alone cannot produce these minerals; instead， sulfate released from oxidative dissolution of wall-rock pyrite lowers the fluid pH， enabling precipitation of alunite and jarosite. Alunite precipitates only above pH ~4， while jarosite remains supersaturated—and thus continues to precipitate—regardless of dry- or wet-season stream water mixing. These results indicate that although the Lushan hydrothermal system is fundamentally near-neutral to alkaline， localized acidification from wall-rock pyrite oxidation drives the formation of sulfur-bearing minerals， explaining their unusual occurrence near the fumarolic vents.
