PROJECTS – cockabidnie

Cockabidnie EL 2815 covers an area of diverse geology. Beneath the thin veneer of sand, clay and calcrete, basement rocks are largely Middleback Subgroup schist, amphibolite and BIF but these are intruded by granite that has been deformed along with the metasediments to form granite gneiss. This gneiss occupies the eastern half of the tenement. In the SW quadrant of the tenement, the metasediments and granite gneiss are overlain unconformably by Mesoproterozoic sandstone and conglomerate of the Blue Range Beds. The latter are locally hematitic.

The BIFs form significant aeromagnetic anomalies and are similar to BIFs of the Koppio and Bald Hill regions. However, they are slightly lower metamorphic grade and hence slightly finer grained. They are comprised of Fe-rich gneisses and jaspilite with magnetite variably altered to hematite (martite) near the surface.

No significant exploration has been undertaken on the BIFs of the Cockabidnie area for iron ore. However, regional Government geological mapping and aeromagnetic surveys indicate potential for magnetite and possibly hematite resources similar to Bald Hill and Koppio. Based on regional aeromagnetics, there is at least 5km of strike potential along a NNE-trending open fold in the centre of the tenement with the fold closure outside the tenement to the north. Modelling by Cowan (2005a) shows both western and eastern limbs of the fold dipping to the east, with the eastern limb steeper but shallower.

On the western margin of the tenement (Section 5, Hundred of Campoona) there are two small deposits of hematite within the Blue Range Beds. SADM mapped the area (Appleby, 1960) and concluded that the hematite occurred in an E-W shear zone(s) dipping approximately 80ºN. Hematite occurs as both earthy and metallic botryoidal forms in two parallel EW trending zones:

• a 3m thick zone ca. 1100m long including 520m of outcrop;
• a thinner 0.6m thick zone ca. 180m long about 1km N of the main zone.

Costean samples assayed 37.5% acid soluble Fe but were likely contaminated by wall rocks. A 2m rock chip sample from outcrop assayed 55% Fe while pure botryoidal hematite assayed 66% Fe. Trace gold was detected in 3 assays and seen in a petrographic section. Appleby estimated that the outcropping main hematite zone contained ca. 210,000 tonnes of hematite (SG=4.5) per 30m of depth extent. No drilling has been undertaken to determine the depth extent of the hematite mineralisation. Vertical RAB drilling by Pancontinental Mining Ltd adjacent to the hematite bodies intersected variably hematitic sandstone. An outcrop of lateritised Katunga Dolomite and conglomeratic Blue Range Beds with an intensely hematised matrix has also been reported (Geoex, 1982 in Davies, 2000).