Along the southern margin of the Mesoproterozoic (~1590 Ma) Gawler Range Volcanics lava flows, on northern Eyre Peninsula, numerous occurrences of silver, lead, zinc and copper mineralisation have been recorded at or near the base of the volcanic rocks and within older metamorphosed rocks altered by hydrothermal fluids associated with the ~1590 Ma igneous event. In this investigation, exposed rocks showing evidence of hydrothermal crystallisation or alteration, previously recognised at sites near Lake Gilles and Roopena Homestead, were selectively sampled and examined to assess the style of hydrothermal activity and associated mineralisation. The work contributes data on the extent and characteristics of hydrothermal activity that can be used to refine models, currently proposed, of an extensive Proterozoic subvolcanic epithermal mineral-forming system which was active across the region. The results will assist with ongoing assessment of the potential for formation and preservation of large or high-grade mineral deposits in the district. Trace element geochemistry was determined for twenty samples that included hydrothermal granite breccia, fluid-brecciated metasediment with calcite/tourmaline/apatite or haematite/chlorite alteration, and epithermal vein quartz. Textural features of breccias and veins were described and interpreted. Alteration mineralogy was assessed using visible-shortwave infrared and thermal infra spectral analysis, and scanning electron microscopy. Accessory minerals containing copper, lead, bismuth, silver or zinc were identified with the aid of scanning electron microscopy and energy dispersive x-ray analysis. An alteration mineral assemblage of tourmaline, calcite, apatite, sericite, chlorite and haematite seen in the fluid-brecciated metasediments in the Roopena area is interpreted to be the result of mesothermal fluid activity developed around igneous intrusions and along major fractures. Quartz veins from the Lake Gilles area were crystallised along with fluorite, barite, muscovite, feldspar, kaolinite, halloysite and smectite. Minor base metal sulphides and silver minerals are contained in the quartz, but pyrite, alunite and dickite were not detected. Anomalous trace elements include Ag, Sb, Te, Bi Cu, Pb and Zn. The latter mineral assemblage and anomalous chemistry are consistent with low-sulfidation, epithermal vein systems formed within the argillic alteration zone of an intrusion-related hydrothermal system. The presence of silver and copper chlorides, copper sulfate, lead oxide, jarosite and gypsum, along with some of the goethite, haematite and opaline silica, is interpreted as being due to later oxidation by near-surface weathering under probable arid conditions. Textures in vein quartz from the Lake Gilles area show lattice bladed calcite replaced by quartz, colloform banding, and feathery and plumose quartz, all of which are indicative of boiling in hydrothermal systems. This equates to shallow crustal levels and environmental conditions favourable for the precipitation of precious metals. The preservation of the boiling zone rocks that were altered within this ancient epithermal system, along with the presence of lead, zinc and copper minerals in epithermal quartz, provide encouragement that in addition to further precious metal deposits, base metal deposits are possible within the subepithermal portion of the system.