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Wednesday 15th May, 2019
5.30pm Drinks, 6.00pm Presentation
Irish Club
21 Townshend Rd, Subiaco
The advent of routine, low detection level multi-element geochemistry has the potential to delineate new “near ore” signatures.
In the example discussed, integration of geology with the multi-element geochemistry and an understanding of regolith processes has enabled the recognition of new near surface targets in a supposed mature terrain where previous work has focused on detecting deep targets.
A program of deep (600-1000+m) drillholes had been conducted primarily to be used as a platform for downhole geophysical exploration. Most of these holes were neither logged nor assayed in the weathered zone. Although the stratigraphy of the project area is well defined, the weathered rocks were considered too difficult to accurately place in the defined stratigraphy. Multi-element analysis of these weathered intervals has not only assisted stratigraphic classification but also detected previous unrecognised near ore signatures.
Recent aircore drilling at this project, which has been profile sampled from surface, coupled with low level multi-element analysis has enabled target delineation in an area that was previously considered adequately explored. This has led to an immediate re-evaluation of the prospectivity of the near surface environment (defined as 0-150m below surface by the author) of this area.
In many regions of Australia, it is considered that the near surface environment has been effectively explored and the potential for new discoveries in this zone is negligible. Much of this near surface work may have been conducted +30 years ago & although may appear on a surface location map of drilling to have been an adequate “test” of a target, could in fact be misleading information.
Point sampling, particularly bottom of hole RAB, may not provide an adequate test of an area’s potential. Even low level multi-element analysis of this point sample may be inadequate if it is geologically “inappropriate”. Samples may have been taken too far up the weathering profile (depleted) or in a “bedrock” which is not representative of the prospective sequence (e.g. intrusive dyke).
“Deep” exploration appears to be the current flavour of government and industry – the Australian Government has funded 25% of the $215M MinEx Cooperative Research Centre. This appears to be testament to the belief in the lack of prospectivity of the “shallow”. Is this the real fallacy?
