Terramin’s Gawler Ranges Project (GRP) is located along the southern margin of the Gawler Ranges, northern Eyre Peninsula, South Australia. The project comprises a group of ten Exploration Licences totalling 4539 km2 and one Exploration Licence Application covering 210 km2 (Figure 1).
The GRP tenements were formerly grouped into two projects: the Menninnie Project (ELs 4865, 4669, 4813 5039 5453), which was joint ventured with Musgrave Minerals Ltd, and the Mt Ive Project to the west (ELs 5458, 5518, 5266, 5276, 5430 and ELA 2015/183) managed by Menninnie Metals. The GRP was formed when termination of the Menninnie Dam Mining Farm-In and Joint Venture Agreement with Musgrave Minerals (announced on 21/07/2015) was finalised on 20 August, 2015, returning exploration management of all tenements to Menninnie Metals.
The southern Gawler Ranges region in the Gawler Craton of South Australia is increasingly becoming recognised as an under-explored province with high discovery potential. Terramin’s GRP covers much of the highly prospective ground between the two principal locations where the Mineral Systems Drilling Program (MSDP2015), a major world-first collaboration of mineral explorers, drillers, government agencies and research institutes, is currently in progress. The Government of South Australia is contributing $2m to the MSDP and this investment has been leveraged into a $7m program through partner contributions and in-kind support. Terramin’s project is well placed to adapt and apply the new understanding of the region’s mineralising systems that is likely to emerge from the MSDP.
The project area covers extensive exposures of the Gawler Range Volcanics (GRV, Figure 2) formed by extensive eruptions of felsic magmas associated with the emplacement of high-level granitic intrusions approximately 1.6 billion years ago. The GRV and underlying metamorphic rocks are prospective for a range of deposit styles that include various combinations of gold, silver , copper, molybdenum, lead, zinc, rare earth elements, graphite and tin ± tungsten. The prospectivity is evidenced by numerous mineral occurrences in the region, and the presence pf several significant deposits (Figure 2). The latter include the 33Moz Paris silver deposit located just 6km to the south of EL 5430 and Terramin’s 7.7Mt Menninnie Dam lead-zinc-silver deposit – the largest undeveloped lead-zinc deposit in South Australia. The Menninnie Dam deposit, located on EL5039, consists of two main mineralised zones: the Menninnie Central zone and the nearby Viper zone. The lodes at Menninnie Central and Viper have been combined to estimate a JORC 2004 compliant Inferred Resource totalling: 7.7Mt @ 3.1% Zn, 2.6% Pb and 27g/t Ag, at a 2.5% Pb+Zn cut-off (ASX: TZN 1st March 2011). The GRP is also flanked by several significant gold prospects that are yet to be fully evaluated, including Barnes-Baggy Green, Weednanna and Parkinson Dam along the southern margin of the GRV (Figure 2). The Glenloth and Tarcoola goldfields and the Tunkillia deposit flank the GRV to the northwest.
Two broad groupings of GRV are recognised: an upper (younger) group consisting of extensive comparatively flat-lying flow units of porphyritic dacite and rhyolite, and a lower (older) group that is more compositionally and texturally varied (rhyolitic to basaltic lavas and tuffs) and locally more steeply tilted. The lower GRV and underlying basement rocks host most of the mineral deposits and occurrences mentioned above, contributing to a general perception that mineralising fluids have been unable to penetrate the upper GRV. This perception is false.
In recent years Menninnie Metals has found extensive exposures of epithermal quartz (± hematite) vein systems (Figure 3), sericite-clay altered brittle shear zones, strongly altered tuffaceous units, probable hot spring and sinter deposits, and hematite-rich breccias comparable to those occurring near ore zones at Olympic Dam, Carrapateena, Prominent Hill, and IOCG deposits elsewhere (Figure 4). These veins and breccias occur within both upper GRV and lower GRV throughout the project area, and highlight the potential for discovery of precious metals and copper in near-surface epithermal and IOCG deposits throughout the GRP. Most of these veins, breccias and shear zones were hitherto unknown. The few occurrences noted by previous explorers received only cursory attention and their implications were not fully investigated. Menninnie Metals’ understanding of the potential of these GRP veins and breccias to host precious metals and copper comes from comparative observations at Olympic Dam and detailed modelling of the fluid evolution and metal zoning in the Olympic Dam deposit and nearby deposits (some of which has been published e.g., Haynes et al., 19951).
Menninnie Metals’ exploration work is currently focused on mapping and sampling the hydrothermal breccias, epithermal veins and shear zones to identify where geophysical work and follow-up drilling will have the best chance of defining shallow IOCG and shear-zone-hosted gold deposits.
- Haynes, D.W., Cross, K. C., Bills, R. T., Reed, M. H., 1995: Olympic Dam ore genesis; a fluid-mixing model: Economic Geology v 90, p. 281-307