The geology of the Balcooma massive sulphide deposit, north-east Queensland

The Balcooma massive sulphide deposit is located at 18°46'S, 144°43'E and 230 km west-north-west of Townsville in north Queensland. The deposit, which has reserves of 3.5 million tonnes of 3.0% copper, was discovered by the author late in 1978 during a search for volcanogenic massive sulphide deposits in the lower Palaeozoic sequences surrounding Charters Towers. The deposit is hosted by a sequence of metamorphosed sediments and acid volcanics were referred to in this report as the "Balcooma Metamorphics". These rocks, prior to discovery of the deposit, were included in the Greenvale Subprovince and were believed to be of Precambrian age. These rocks are now interpreted to be of lower Palaeozoic age and the Greenvale Subprovince is considered to form part of the Ravenswood Lolworth Province. The geology of the area is exceedingly complex due to at least two strong deformation events. The immediate hosts to the mineralization are a sequence of quartz muscovite biotite staurolite schists and quartz muscovite biotite schists which are interpreted to be metamorphosed fine-grained and coarse-grained sediments respectively. Quartz feldspar porphyry bodies intruded these rocks prior to deformation and metamorphism. Both copper and lead-zinc-copper mineralization occur. Copper mineralization occurs within two south-south-west plunging shoots as chalcopyrite in massive pyrite, as massive chalcopyrite with pyrrhotite, and as chalcopyrite in chlorite schist. Chlorite alteration accompanies the copper mineralization. Lead-zinc-copper mineralization occurs within folded tabular bodies of massive pyrite which are associated with gahnite bearing quartzite and quartz schists which are interpreted to be metamorphosed siliceous exhalites. The depositis considered to be a metamorphosed volcanogenic massive sulphide deposit