ALLIANCE RESOURCES
During 2021 Alliance completed a systematic review of its' exploration targets at the
1,150 samples were collected during the drilling program (consisting of 1m split and 3m composite samples) and analysed for an iron ore suite of elements using the XRF fusion technique, with assay results returning broad zones of low-grade iron mineralisation. Alliance has located 888 (77%) of the historic drill sample pulps, representing 2,578 metres of drilling (76%), and re-analysed the samples at ALS commercial laboratory for Au using the fire assay technique and As, Ca, Cr, Cu, Fe, Mn, Ni, Pb, S, Sn, U, Zn using a portable XRF (pXRF) scanner.
The pXRF scanner is a semi-quantitative technique with precision and accuracy in the order of 20%, depending on sample type, that is suitable as a cost effectively early-stage exploration tool to analyse for a variety of elements.
The majority of the rocks that host this nickel mineralisation also contain elevated chromium (> 0.1 % Cr), magnesium oxide (> 18 % MgO) and low silica (< 45 % Si) common characteristics of ultramafic rocks. This geochemistry is distinct from skarn altered dolomite that occurs elsewhere in the Wilcherry project area, which alters to forsterite (olivine) and serpentine and contains low Cr values. Preliminary geological logging of RC drill chips shows that the area is overlain by between 5 and 20 metres of transported cover.
Weathering extends to greater that 100 metres depth on the western side of the prospect and nickel anomalism appears to be associated with steep-dipping ultramafic rocks that are bounded to the west by metasedimentary and granitic lithologies. The ultramafic rocks grade into mafic lithologies to the east and are the likely source of the high-magnetic anomaly as serpentine alteration of ultramafic rocks creates magnetite.
All drill holes that intersected > 0.1 % Ni are coincident with the high-magnetic anomaly.
The interpreted ultramafic rocks occur coincident with a 3km long gravity high anomaly that is displaced slightly to the east, suggesting a thickening in the ultramafic-mafic stratigraphy, with mafic rocks to the east (as observed in drilling). A 1,500m x 500m late time helicopter-borne electromagnetic (EM) conductive anomaly is also located within with the target area.
This conductive anomaly may be associated with massive nickel sulphide mineralisation, deep weathering, or conductive metasediments. A ground moving loop EM survey is required to better define the geometry and intensity of this anomaly for targeted bedrock drill testing.
Discussion
Even though the Gawler Craton is known to host volcanic and intrusive ultramafic rocks no economic concentrations of magmatic nickel sulphide mineralisation have been discovered to-date. The identification of ultramafic rocks at the Bonza Prospect was not expected and analysis of Alliance's extensive regional drilling database for the
The presence of thick zones of nickel anomalism hosted within a broad ultramafic to mafic sequence that extends over 8 kilometres strike length presents a priority nickel sulphide target area that warrants further assessment. Historic bedrock drill testing within the target zone is limited to four wide spaced traverses that were not designed to test across the ultramafic footwall contact, which is where massive nickel sulphides often accumulate, and yet drilling has intersected up to 3m @ 1.12% Ni. This intersection of nickel mineralisation also contains 0.13% Cu (pXRF analysis) and 1.3% S (XRF analysis) suggesting the presence of pentlandite (nickel sulphide), chalcopyrite (copper sulphide) and either pyrrhotite or pyrite (iron sulphide) that are common in magmatic nickel sulphide deposits.
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