The Palaeozoic Scott Lode gold-silver deposit, situated at Pajingo, northeast Queensland, is one of the oldest reported low sulphidation epithermal veins. It contains resource of 12 tons of gold and 47 tons of silver. The epithermal veins at the Scott Lode are hosted by feldspathic/volcanolithic sandstones, quartzose sandstones, ignimbrites, andesitic volcanic with interbedded block-and ash-deposits, lapelli tuffs and andesitic to dioritic intrusives.

The principal ore and sulphide minerals include pyrite, sphalerite, galena, chalcopyrite, hessite, tennantite- tetrahedrite, argentite, petzite, electrum and native gold. Vein gangue minerals consist of quartz, illite, adularia, and calcite. The main stage quartz is zoned with respect to mineralogy, mineralization styles, metal distribution patterns and vein textures. Three vertical mineralizatlon zones can be recognized: l) upper precious metal zone (PMZ): quartz-pyrite- electrum-gold- argentite/chalcopyrite, ii) intermediate precious + base metal zone (PBMZ): quartz-pyrite-sphalerite galena-chalcopyrite- hessite-tennantite tetrahedrite-electrum, and iii) sparse base metal zone (SBMZ): quartz -pyrite-sphalerite-galena-chalcopyrite. The ore interval occurs in the PMZ and PBMZ with the transition to SBMZ effectively defining the limit of mineralizatlon.

Fluid inclusion studies indicate that precious and base metal mineralization at the Scott Lode occurred as the hydrothermal fluidsds cooled. The homogenization temperatures decrease with increasing elevation. Cooling of the hydrothermal fluids via boiling is considered to be the principal mechanism in precipitating the vein gangue and ore minerals. Indicators of hydrothermal boiling Include the presence of coexisting liquid- and gas-rich fluid inclusions in mineralized quartz, extensive vein brecciation, vein adularia, bladed calcite and pronounced crustiform-culloform banding In quartz veins.

The effects of adiabatic boiling on a homogeneous aqueous phase employing the determined and adopted composition of the hydrothermal fluids responsible for the Scott Lode deposit have been shown through an adiabatic modeling study. The fluid composition used also approximates that of the ore-bearing hydrothermal fluids responsible for other low sulphidation epithermal deposits. In low sulphidation epithermal conditions, gold is primarily transported as Au(HS)₂, silver as AgCl₂, lead as PbCI₃ and PbCl and zinc as ZnCl and Zn(HS)₂. As the fluids undergo adiabatic boiling, the concentration of H₂S continuously drops and the fluid pH become slightly more alkaline. These factors, principally the loss of H₂S would cause the precipitation of precious and base metals from sulphide and chloride complexes. Adiabatic boiling of a fluid with initial concentration of 2-5 ppb gold at 300°C can deposit ores containing an average of 10 ppm Au and 260 ppm Ag. The precipitation of precious and base metals is accompanied by the deposition of adularia, carbonates, quartz and pyrite. The Au/Ag ratio of the ores increases with continuous boiling which may represent the trend commonly observed in many epithermal deposits.