Terramin’s South Gawler Project (SGP) is located along the southern margin of the Gawler Ranges, northern Eyre Peninsula, South Australia. The project comprises a group of 17 Exploration Licences totalling 8321 km2 and one Exploration Licence Application (ELA 2017/174 covering 637 km2 (Figure 1), all held by Menninnie Metals Pty Ltd (MMPL), a wholly-owned subsidiary of Terramin.
Since June 2017 the project is being explored under an earn-in joint venture agreement with Evolution Mining Limited (Evolution) whereby:
- Evolution can earn 70% equity in the project for A$4 million exploration spend over four years
- Terramin may then elect to contribute, otherwise Evolution can earn an additional 10% (total 80%) by spending a further A$2 million over two years, after which a pro-rata period will operate
- Evolution can withdraw from the project after a minimum spend of A$500,000 within the first year
The SGP partners are primarily targeting shallow Iron Oxide-Copper-Gold (IOCG) deposits in the region and, to this end, since June 2017 have more than doubled the project area under licence.
The SGP covers extensive exposures of the Gawler Range Volcanics (GRV) formed by large-scale eruptions of felsic magmas associated with the widespread emplacement of high-level granitic intrusions and associated mineralising systems (Figure 2) approximately 1.59 billion years ago. The GRV and underlying metamorphic rocks are prospective for a range of mineral 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 of several significant deposits (Figure 2). The latter include the 42Moz Paris silver deposit located just 6km to the south of EL 5430 and the 7.7Mt Menninnie Dam lead-zinc-silver deposit located on the SGP’s EL 5949 (Figures 1, 2).
The Menninnie Dam deposit – the largest undeveloped lead-zinc deposit in South Australia – 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 SGP is flanked by several significant gold prospects that are yet to be fully evaluated. These include Barnes-Baggy Green, Weednanna, and Parkinson Dam along the southern margin of the GRV (Figure 2) and the Nankivel prospect, located 2km east of the Paris deposit, where recent drilling is showing evidence for the presence of a large porphyry copper-gold system. The Glenloth and Tarcoola goldfields and the Tunkillia gold 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 metamorphic 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 The upper GRV contain widespread epithermal quartz ± hematite vein systems and multi-stage hematite-rich breccias. These show many characteristics consistent with them having formed near the palaeosurface above hydrothermal IOCG breccia complexes comparable in many ways to the Olympic Dam, Prominent Hill and Carrapateena deposits. The SGP is testing the likelihood that these breccia systems developed along major fault systems active in the lower GRV at the time they were buried by eruption of the upper GRV. This faulting and associated hydrothermal activity then pierced the upper GRV, establishing near-surface, fault-associated vein and breccia bodies. Based on typical IOCG metal zonations, gold and copper is expected to be concentrated in and near sulphide-bearing breccias beneath the more oxidised silica-hematite zones that formed in more oxidised near-surfaced conditions in the upper GRV.
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. The SGP covers much of the highly prospective ground between the two principal locations where the Mineral Systems Drilling Program (MSDP) was recently carried out (August 2015 to April 2016). The MSDP was a major world-first collaboration of mineral explorers, drillers, government agencies and research institutes. The Government of South Australia contributed $2.5m and this investment was leveraged overall into an $8m program through partner contributions and in-kind support. The MSDP, which included field mapping programs, recorded new occurrences of:
- epithermal veining and alteration in the upper GRV,
- skarn-related Pb-Zn±Ag mineralisation,
- altered GRV volcaniclastic rocks locally hosting Pb-Zn±Ag mineralisation,
- volcaniclastic rocks within the GRV – locally altered and hosting anomalous Pb-Zn±Ag,
- greisen associated with Hiltaba granites.
All these occurrences are close to the western margin of the SGP and they show some similarities to hydrothermal vein/breccia systems and volcaniclastic rocks (likely fluid/metal “sponges”) identified within the SGP area. The MSDP has contributed to the rapid growth of evidence showing that hydrothermal systems related to Hiltaba-GRV magmatism are widespread within and adjacent to the GRV. Although some areas near MSDP drilling are prospective for IOCG systems, the program did not target this deposit type. The SGP is being expanded to include some of these areas (eg EL 6093 and ELA 2017/174).
Exploration activities to date have included:
- Due diligence on ground assessments and applications
- Aboriginal heritage and liaison and positive land access discussions
- Field investigations and collection and processing of samples as part of a regional geochemical survey
- A gravity survey that focused on several iron-rich vein and breccia systems in the central part project area. Results indicate a low probability for a large subsurface iron-rich deposit in the survey area.
Further analysis of the gravity data and an integrated magnetic/gravity inversion model is currently being completed. This will be combined with results from the regional geochemical program to improve understanding of the geological setting of the veins and breccias and plan the next phase of IOCG targeting.
Preliminary results from reprocessing of aeromagnetic and gravity data by Archimedes Consulting Pty Ltd suggest that the top of the lower GRV is generally less than several hundred metres below surface in the central part of the project area. This places the target breccia zones well within reasonable drilling/mining depths (<500m). Some steep zones of discrete magnetic anomalism have been identified extending from the interpreted metamorphic basement into the GRV. These zones likely represent structural breaks that provided pathways for hydrothermal fluids that formed the IOCG-style epithermal features seen in outcrop in the upper GRV. They will be studied in detail early in 2018 to rank their potential as targets and plan a drilling program to test the best.