The Fowler Domain within the western Gawler Craton region of South Australia is finally revealing its potential for hosting magmatic (intrusion-related) nickel–copper mineral systems, nearly 30 years after the Geological Survey of South Australia (GSSA) and others recognised the region had the right geological ingredients for such systems.

Western Areas announced to the market in June 2020 the visual intersection of extensive massive to disseminated sulfide mineralisation at their Sahara prospect and followed this up with the release of a discovery intersection of 104.42 m at 0.21% Ni and 0.12% Cu from 145 m downhole, including discrete intervals of up to 1.4% Ni (Fig 1). This result is a proof-of-concept demonstrating the region’s potential to host economic nickel–copper mineralisation, and likely ranks it as one of the most significant exploration outcomes in South Australia over the last generation.

Figure 1 Examples of Sahara mineralisation in drill core. The bottom image is of massive sulfides grading 1.38% Ni. (Courtesy of Western Areas, ASX releases 23 June 2020 and 24 July 2020)

The Sahara prospect is located approximately 175 km north-northwest of Ceduna and 75 km east-northeast of the Jacinth-Ambrosia mine (Fig 2), within joint venture tenure Western Areas is exploring with Iluka Resources. The sulfide mineralisation is hosted within a thick ultramafic (metagabbro–pyroxenite) intrusive body and preliminary analysis indicates the nickel and copper are present within the minerals pentlandite and chalcopyrite, within the more dominant pyrrhotite–pyrite sulfide mineralisation which was observed to occur over a mostly continuous interval of 250 m downhole (Fig 3).

Figure 2 Location of Western Area Ltd’s Sahara prospect shown over magnetic imagery. (Courtesy of Western Areas, ASX release 23 June 2020)

Figure 3 Cross-section through Sahara prospect illustrating drillhole traces and summarised geological context. Note the ~20 m of barren post-mineralisation cover sediments which effectively mask any surface expression of the mineralisation. (Courtesy of Western Areas, ASX release 24 July 2020)

Western Areas has arguably been the most persistent and committed explorer in this region having been on the ground since 2014, culminating in a maiden diamond-drilling program which commenced in early 2020. Until this point the company has been undertaking a range of geophysical surveys and aircore drilling campaigns to methodically map the basement rocks and test a range of geological settings, identifying numerous zones of elevated (oxide) nickel–copper ± platinum group elements mineralisation in weathered basement.

An aspect of Western Areas’ approach that sets it apart from similarly targeted exploration in other districts is the differences in workflows applied. Other notable magmatic nickel–copper discoveries in Australia such as Nova-Bollinger (Fraser Range, WA) and Nebo-Babel (Musgrave province, WA) are close to surface with conventional geochemical sampling playing a key role in their respective discovery histories.

The Sahara prospect is masked by 10–20 m of Quaternary aeolian dunes and at least 10 m of completely oxidised basement which rules out the application of surface geochemical techniques for exploration targeting. Extensive dune fields make access inherently slow and challenging. In addition, the geophysical (electrical) responses from the basement rocks in this region are relatively subdued, further complicating the process of target delineation.

An overarching hindrance for the Fowler Domain has been the lack of geological context and understanding relevant to exploration for magmatic nickel–copper mineralisation. Notably, one of the contributing elements to the Sahara discovery has been the significant advances in the understanding of the region made by Western Areas in collaboration with the GSSA over the past five years.

Now the exploration model has been validated, Western Areas’ challenge will be to prove the economic potential for nickel–copper mineralisation.

– Marc Twining, October 2020

Back to news articles