Buxton has identified a series of high amplitude density anomalies from a recently released Falcon helicopter gravity gradiometer survey flown by GSWA in 2017. These anomalies cover an aggregate area of 33.5 km2.
MIM’s work within the Shogun Project area included soil geochemistry, heavy mineral concentrate (HMC) sampling, and shallow (maximum 24 m depth) percussion drilling. MIM’s HMC sampling identified an unusual emerald-green spinel (the precise mineralogy was not confirmed), red spinel and enstatite (orthopyroxene) close to one of the new gravity gradiometry anomalies. MIM’s soil sampling included assays for nickel, and the highest nickel assay (183 ppm) correlates with the highest amplitude gravity gradiometry anomaly despite the surficial dune systems that blanket the Project area. Elsewhere in the district, MIM’s HMC sample analysis identified tremolite, platinoids and chromite. Of the five drillholes in the Project area, only one (TP 170) penetrated the cover sequence at 10 m depth to intersect a doleritic lithology which was not sampled for geochemistry or petrology. These data from MIM’s work indicate that substantial volumes of magic-ultramafic intrusive rocks are located within the Project area.
One of the gravity gradiometry anomalies is also a prominent magnetic feature. This was baptised the “Blaine Plug” by Marengo Mining who were also targeting diamonds. Marengo drilled hole BLC001 in 2004 and this RC hole intersected serpentinised peridotite below 33 m of unconsolidated cover sediments.
Marengo’s assays suggest that this peridotite is tholeiitic and highly depleted in nickel and PGE.
The two least weathered samples (solid squares on the graphs below) average ~0.2% sulphur, and petrological analysis of drill chips from this interval report traces of chalcopyrite and violarite (copper and nickel bearing sulphide minerals). This geochemical signature is highly encouraging for Ni-Cu-PGE exploration as it suggests that a sulphur saturation event may have occurred close to the present erosional level and is presently within reach of modern high powered electrical geophysical tools.
Serpentinisation is a post-magmatic alteration process that commonly affects ultramafic rocks and typically results in the formation of magnetite. This explains the Blain Plug magnetic anomaly. However, these alteration zones may be structurally controlled and localised. Any unaltered zones within the mafic-ultramafic intrusions would therefore not form prominent airborne magnetic anomalies although they will likely be evident as prominent gravity anomalies.
Given the recent availability of high-resolution gravity in the area, such intrusions may now be readily apparent for the first time as depicted below.
In summary, the Shogun Project presents several excellent regional and prospect-scale prospectivity indicators for magmatic nickel-copper-PGE mineralisation related to the Proterozoic-Cambrian Large Igneous Provinces in the region.
Buxton will continue to progress these applications toward grant during the coming Quarters. Field reconnaissance will be conducted when access to the Canning Stock Route Track becomes possible.