The Cairn Hill Gold Project is located along a regionally significant mineralised trend in the highly prospective Ashburton region of Western Australia approximately 40 kilometres west-northwest of Paraburdoo. The project lies between and along strike from the Northern Star Limited’s Paulsen’s Gold Mine and the Mt Olympus Mining district.
The project was identified in regional surface geochemical surveys undertaken by BHP in the late 1980’s although little work was done until the late 1990’s when Newcrest / SIPA were active on the region following the discovery of the nearby Mt Olympus and Paulsen’s deposits. Drilling undertaken by Newcrest identified some high grade mineralisation amongst a broader area of low grade gold mineralisation although the work was not exhaustive. The most significant intersection of 20m @ 29g/t Au from 30m (CHR007) and 6m @ 12g/t Au from 142m (CHR010) are 130 metres apart and remain open and untested along strike and down dip. The high grade gold results are located within a 3,000 metre by 500 metre arsenic anomaly on a regional northwest structure.
The geological setting of the Cairn Hill Gold Project is analogous to the Paulsen’s Gold Mine.
The Cairn Hill Gold Project (E08/2248) straddles the contact between the Hamersley (Mount Bruce Supergroup) and Ashburton (Wyloo Group) basins. The Palaeoproterozoic Wyloo Group rocks recognised on the tenement belong to the Mount McGrath Formation that are composed of ferruginous sediments, with a small carbonate rich rock component, and the Duck Creek Dolomite composed of dolomites, dolomitic sediments and various siliceous weathered variants.
Regional location of the Cairn Hill Gold Project
These units unconformably overly Archaean Fortescue Group basalts and dolerites of the Mount Bruce Supergroup. Regional strike is northwest–southeast with the rocks folded, faulted and occasionally cut by northeast trending dolerite dykes. Approximately 50% of the tenement is covered by regolith obscuring bedrock and is unsuited to direct surface geochemical exploration methods.
Cairn Hill Gold Project tenement on regional geology
The Cairn Hill Gold Project occupies a structurally complex part of the Ashburton north margin, the contact between the Fortescue Group mafic volcanics and the Mount McGrath Formation is tectonic and is believed to be a thrust block rather than simply a strike-slip structure and has resulted in the deletion of a significant part of the Hamersely Group. This structural complexity complicating earlier attempts at modelling.
1982 – 1998 Exploration
In 1982 Esso Australia carried out base metal exploration over an area that included much of the current area of E08/2248. Ironstone and rockchip sampling identified a number of anomalous ironstones that were subsequently percussion drilled. One hole, was located 300 metres northeast of the Central Cairn Hill Prospect. The hole targeted a ferruginous quartzite (Mount McGrath Formation) and intersected weathered ferruginous quartzite.
During 1986 and 1987 Billiton Australia (as manager of the larger Mt McGrath Joint Venture between Billiton Australia and Austamax Resources Ltd) conducted gold exploration over an area that included the vast bulk of the area underlain by Wyloo Group rocks. Their program included aerial photography, geological mapping, regional and follow-up BLEG and -80# stream sampling, BLEG and -80# soil sampling, ground magnetics, trenching, RAB, percussion and RC drilling.
This work generated a gold-in-soil map. Clearly evident are three main anomalies, one of which is on the Cairn Hill Prospect. Billiton costeans over that anomaly obtained generally low-order gold anomalism.
Late 1980’s Billiton bleg soils results identifying Cairn Hill Prospect (blues background, yellow/green increasing anomalism red/pinks strong anomalism – max 73ppb Au)
Percussion holes tested beneath that costean and other Billiton holes tested to the west and northwest of the core of the soil anomaly. The assays also demonstrate that the gold anomalous domains are accompanied by elevated As and antimony (Sb), a metal combination now well established as important in defining gold mineralisation along the north Ashburton margin. Billiton also noted that the central geochemical anomaly (west of the Cairn Hill Gold Project) coincided with ground magnetic trends and ‘a magnetic BIF’ (possibly jasperoid).
Examination of the BLEG soil patterns shows that the main anomalies correlate with areas of residual regolith whilst more subdued results correlate with more transported regoliths. Berkut believes it is likely that the actual gold (plus As–Sb) anomalous corridor is more continuous than suggested by surface sampling alone and hence that the Billiton efforts were only a partial test of the target.
Newcrest 1999 – 2007
Newcrest undertook work in the years 1999 to 2005 and included stream sampling, soil sampling, rock sampling, detailed ground magnetics, RAB/Aircore drilling (202 holes for 8524 metres) and RC drilling, (34 holes for 6965 metres) and one RC/core hole for 465.5 metres. The regional RAB drilling was undertaken at 500m x 500m centres with subsequent infill to 100m x 100m and the RC program was designed to test anomalous RAB results ans was not systematic.
Newcrest Historic Drill locations
In 2000 the first RC hole, CHR007, was drilled at the Cairn Hill Prospect area targeting earlier Billiton gold targets. The remainder of the Newcrest drilling (both RAB/AC and RC/core) concentrated on a broad area targeting a large sediment hosted gold model with no further testing of the extensive alluvium-covered areas. Significant intercepts are included in the following table and are shown as weighted averages based on the sum of length*assay divided by total length.
Newcrest Historic Drill locations at Cairn Hill Prospect
Table of Significant intercepts Cairn Hill Gold Project – Newcrest historic drill results returning greater than 1m @ 1g/t Au
Coccinella Pty Ltd 2013-2015
In 2013 Coccinella undertook field mapping and rock chip sampling aimed at improving the geological understanding of the Cairn Hill Prospect area. In 2016 Cocinella joint ventured the project to the then private company Berkut Minerals.
Previous exploration has concentrated mainly on an area originally shown to be anomalous in Au, As, Sb in soils by Billiton Australia. In 1986 Newcrest determined potential for epithermal gold mineralisation. This drilling confirmed the existence of widespread though erratic and bedrock Au (plus As-Sb) mineralisation, hosted by altered sandstones and dolomites including its weathering products, but failed to target any major structural controls for that mineralisation. Exploration of potential extensions to that mineralisation under cover in areas not amenable to simple surface geochemical techniques has been cursory. It is considered that very good potential remains within the Cairn Hill Gold Project for the discovery of significant structurally controlled and sediment-hosted gold mineralisation, both oxide and primary.
The structural trend hosting the Cairn Hill Prospect and geochemical and alteration extensions have been lightly explored and warrant more detailed exploration. In particular the area of colluvial and alluvial cover immediately east and southeast of Cairn Hill, approximately 3 kilometres across, requires additional testing with geophysics, deeper geochemical sampling and follow up drilling.
Arsenic Anomaly at the Cairn Hill Prospect
Historic Newcrest drilling results on schematic long-section showing possible high-grade plunge
The more immediate high grade structural gold target requires further drilling of the strike extension, and possible up dip extensions of CHR010 and CHR007, both which intersected significant gold grades as shown in the preceding table. CHR017 drilled 92 metres north of CHR010, which intersected elevated Au and anomalously high As values at a vertical depth of 140 metres. Other results in the drill program were generally of lower order as listed in the table above. It is not known if the two intersections are directly linked but this area requires drilling along strike to the east of the intersection in CHR010, and infill drilling between CHR010 and CHR007. The south-east strike extension of the current mineralised horizon remains open and requires further examination, as does the further, soil covered, south-east potential.