Lithology and petrology of drillhole TDD001, Bluebush area, Warramunga Province

Abstract

This Record presents the results of detailed logging and petrographic studies of mineralised drillhole TDD01 from the Bluebush area located between the Rover field and the Tennant Creek mineral field in the Warramunga Province, central Northern Territory. The work is part of a Northern Territory Geological Survey-Geoscience Australia collaboration project to improve understanding of the regional geological framework and resource potential of the Rover field and more broadly, the Warramunga Province. Drillhole TDD01 intersected high-magnesium, porphyritic actinolite basalt with minor schistose metagreywacke and quartz-sericite (-muscovite) phyllite. Alteration of the basalt is characterised by sulfide-bearing carbonate veins and breccias, magnesium-chlorite and talc. The sulfide-bearing carbonate veins are common between 342.5- 701.7 m, and more frequent between 342-400 m downhole depth.

Nickel mineralisation was reported for this drillhole by Page (2010): 1 m at 2100 ppm Ni from 369 m and 7 m at 2185 ppm Ni, including 1 m at 3200 ppm Ni from 376 m. Our studies of samples from TDD01 revealed that pentlandite (nickel-iron sulfide) is strongly associated with pyrrhotite (iron sulfide), typically with flame-like exsolution texture within pyrrhotite. Pentlandite is also found as disseminated grains or aggregates with chalcopyrite and pyrite. Sphalerite (zinc-iron sulfide) and galena (lead sulfide) are also observed in contact with pyrrhotite. The association of nickel-copper-iron sulfides with the lead-zinc sulfides is not clear. Although the sphalerite is in contact with pyrrhotite (and pentlandite), there are multiple examples of galena-sphalerite-bearing carbonate veinlets overprinting the dominant foliation in the basalt; this suggests a post-deformation base metal mineralising event. The mineralisation in TDD01 could represent a hybrid between an early orthomagmatic nickel-copper sulfide mineralisation overprinted by an epigenetic base metal mineralisation.