Channel iron deposits, a major new district around the Caliwingina Creek, central Hamersley Ranges, Western Australia

Abstract

After six year intensive exploration for high-grade hematite deposits, the channel iron deposits (CIDs) were included as a specific iron ore target in the Hamersley Province iron ore exploration programme in 2000. The exploration model was simple and was based on the then current understanding of CID genesis. Fundamental to the model was an interpretation that CIDs could be entirely concealed in their channels after their final accumulation stage. Inversion to mesas and therefore exposure of the CID profile would only occur in areas where the modern drainages follow the ancient drainages, and have significantly incised their current bedrock. After a number of partially successful attempts, exploratory drilling in 2002 in the Caliwingina valley in the northern Hamersley Range identified significant CID mineralisation. Subsequent drilling programmes from 2003 onwards revealed the presence of a large CID system which stretches from the middle reaches of the Caliwingina Creek to deep under the sediments of the Fortescue Valley, a channel length of more than 30 km. Geological resource estimation suggests that Caliwingina is presently the third largest CID system of the Pilbara (after Yandicoogina and Bungaroo) and is of comparable size to the pre-mining Robe River system (1·6 Bt), with comparable Fe-grades to the Yandicoogina global resource grade (57·7%Fe). Large detrital iron and canga deposits overlie the Caliwingina CID, or interfinger with it, and although the economics of these are presently unfavourable, they could ultimately present a low-grade iron resource of slightly smaller size to the CID mineralisation at Caliwingina. Together with the recently discovered Serenity and Solomon deposits and other smaller occurrences, the Caliwingina deposit is part of a major new CID district in the central Hamersley Ranges, approximately halfway between Yandicoogina and Robe River. Although exploration in this new district is still underway, the preliminary indications are that this area will provide a total CID resource well over 3 billion tonnes and a detrital iron resource of similar size and is on a par with the major known CID systems in the Hamersley Province.