The contiguous Talgai, Thanes Creek and Leyburn Goldfields together form a large area (500 km2) which covers the north-eastern Texas Beds, in south-east Queensland. This large area was mapped in order to study the regional sedimentological and tectonic history. Detailed mapping of the Talgai Mining Reserve reveals the lithological and structural setting for the major gold mines.
Both a detailed and generalized review of the history, workings and production record (25000 oz estimated total lode gold produced) for the mines is provided. Style of mineralization, wall-rock alteration, and the geophysical and geochemical responses of the veins are discussed.
The host rocks for the auriferous quartz veins are couunonly quartz-poor volcanolithic greywackes, black slates and cherts. Siltstones, spilitic volcanics and sheared andesitic? pyroclastic rocks are also present in the very thick sequence.
It is determined that an intermediate to deep water marine turbidite fan was operative during the Devonian Carboniferous. The proposed sediment provenance area is the Silverwood Volcanic Arc, which lies to the east of the three goldfields. Field associations indicate that following a deformation period (late Carboniferous) in which the Texas Beds were tightly folded and faulted, the Permo-Triassic Greymare trondhjemite and Allandale Dyke Swarm were emplaced along the southern and eastern margins of the studied area.
Using oxygen isotope, fluid inclusion and thermochemical data, together with observed geological associations and vein distribution patterns, a genetic mechanism is proposed for the auriferous lodes. This involves the release of gold into a hot (>3SOOC) brine during the synchronous regional metamorphism and deformation of the thick volcaniclastic sedimentary pile. Gold, quartz and sulphides are subsequently deposited in cooler near-surface fractures.