Summary:
The Mt Carrington deposits are hosted by the Drake Volcanics; a NW-trending 60km x 10km Permian bimodal volcano-sedimentary sequence within the Wandsworth Volcanic Group near the north-eastern margins of the southern New England Fold Belt.
The Drake Volcanics overlie or is structurally bounded by the Carboniferous to Early Permian sedimentary Emu Creek Formation to the east and bounded by the Demon Fault and Early Triassic Stanthorpe Monzogranite pluton to the west. The sequence is largely dominated by andesite and equivalent volcaniclastics, however basaltic through to rhyolitic facies stratigraphic sequences are present, with numerous contemporaneous andesite to rhyolite sub-volcanic units intruding the sequence. The Razorback Creek Mudstone underlies the Drake Volcanics to the east, and Gilgurry Mudstone conformably overlies the Drake Volcanic sequence. In addition, Permian and Triassic granitoid plutons and associated igneous bodies intrude the area, several associated with small scale intrusion-related mineralisation. The Drake Volcanic sequence and associated intrusive rocks are host and interpreted source to the volcanogenic epithermal Au-Ag-Cu-Pb-Zn mineralisation developed at Mt Carrington. The majority of the Drake Volcanics and associated mineralisation are centred within a large scale circular caldera with a low magnetic signature and 20km diameter.
The Mt Carrington Project contains several epithermal gold and silver deposits with distinct metal zonation, including silver-rich deposits in the northeast that gradually transition to gold-zinc and goldcopper deposits to the west. Key gold-rich deposits include Strauss, Kylo, Carrington, and Guy Bell, which are typically structurally complex with steeply dipping veins, and locally show stratabound controls, particularly at Strauss. These deposits are notable for their high zinc content, averaging 1-2% Zn at Strauss. Silver-rich mineralisation is concentrated along the Cheviot Hills Fault Trend, with notable deposits at Lady Hampden and Silver King, hosted in volcaniclastics and lapilli tuffs.
The Strauss and Kylo deposits are low sulphidation epithermal vein type mineralisation that manifests as a zone of stockwork fissure veins and vein breccia associated with extensive phyllic to silicic alteration. Veining is localised along the margins of an andesite dome/plug and lava flow within a sequence of andesitic volcaniclastics (tuffaceous sandstone and lapilli tuff). Economically mineralisation is Au-dominant with minor Ag and significant levels of Zn, Cu & Pb.
Mineralisation at Strauss occurs as a broad zone of stockwork veining that narrows with depth. Within the stockwork zone there are two dominant vein orientations: near vertical north trending veins and bedding parallel veins striking north-east and dipping approximately 20° towards the southeast. Recent drilling intersected the vertical veining at 20° to 40° and the bedding parallel veining at 70° to 90°. The mineralisation at Strauss strikes NNE to SSW and extends approximately 360 m in this direction, with a vertical extent in excess of 130 m. The across strike extents of the mineralisation is approximately 200 m. The individual mineralisation lenses generally range in thickness from 2 m to up to 15 – 20 m true thickness.
The mineralisation at Kylo can be divided into two zones, Kylo West and Kylo North.
Mineralisation at Kylo North occurs as a broad zone of stockwork veining that is dominated by near vertical north trending veins focused on the near vertical north trending andesite-volcaniclastic contact. Most drilling typically intersected mineralisation at approximately 20° to 40°. The mineralisation wraps around the eastern edge of the porphyry with a change in strike to NNE-SSE and a steep dip to the west. The mineralisation extends up to 140m along strike with a similar dip extent (140m). Widths range from 2 – 5 m true thickness at the down dip extensions of the mineralisation to more than 90 m in the upper parts of the deposit.
Mineralisation at Kylo West occurs as two parallel zones of stockwork veining that strike east-west and dip 70° towards the south. Most drilling typically intersected mineralisation at approximately 30° to 70°. At Kylo West, the mineralisation is comprised of two subparallel zones striking E-W with a steep southerly dip, related to a porphyry intrusive contact. The main mineralised zone has a strike length in excess of 300m, with a dip extent of up to 150m. The mineralised zone varies from 2m to more than 40m true width, with much of the mineralisation being between 10 – 20m wide.
The White Rock deposit is located in the altered rhyolitic to andesitic rocks of the Permian Drake Volcanics and features low to intermediate sulphidation epithermal mineralisation. The deposit includes a broad alteration zone with silica veining, breccia fill, and silicified zones associated with a polyphasal felsic intrusion and hydrothermal brecciation events. Silver-rich mineralisation is primarily hosted in tetrahedrite and pearceite-polybasite sulphosalts, with minor Zn, Pb, Cu, Au, and Sb. High-grade silver is found in reactivated colloform silica and sphalerite veins, and the system shows a weak geochemical zonation towards Au-Cu in the W/SW, suggesting increasing temperatures and depth. The magmatic source for the sulphides remains unidentified.
Mineralisation at the Red Rock deposit is primarily hosted in silica-rich veinlets and hydrothermal breccia, with sulphides found in banded, crustiform, and colloform textures. The veins range from small, fine cracks to larger, more complex breccias and show increased complexity near the surface. The sulphide minerals include pyrite, sphalerite, galena, chalcopyrite, and minor sulphosalts like tetrahedrite and pearceite. Gold is primarily hosted in electrum or pyrite and is enriched near the rhyolite cryptodome, with higher grades found in more complex veins at shallow depths. The mineralisation shows good geochemical zonation, with gold near the surface, silver at the extremities, zinc throughout, and copper and lead increasing at depth. The deposit's mineralisation is interpreted as a continuous process following the emplacement of the cryptodome and is driven by ongoing hydrothermal activity.