Summary:
The Project covers the most prospective parts of the Gum Creek Greenstone Belt, located within the Southern Cross Province of the Youanmi Terrane, which forms part of the mineral rich Archaean Yilgarn Craton in Western Australia. The Gum Creek Greenstone Belt is an elongate, broadly sinusoidal formation about 110km long and 24km wide, dominated by mafic volcanic and sedimentary sequences, intruded by granitoids of various ages and compositions. The margins of the belt are typically dominated by contact-metamorphosed basalts and banded iron formations (BIF).
The greenstone sequence is relatively simple, with three broadly continuous major geological units occupying a large north-south synclinorium. The lowest unit consists of a sequence of interbedded banded iron formation and mafic and ultramafic volcanics overlain by ferruginous shales, shales and thin cherts. On the western margin of the belt this lower sequence has been partly intruded out by granites, and remains as thinner, discontinuous remnants.
The central unit consists of a sequence of basalts and felsic volcanics, contemporaneous dolerites, and lesser ultramafic volcanics and interflow sediments. The felsics contain quartz-sericite schists, quartzbiotite schists, and rhyolitic to andesitic fragmental volcanics, and sulphidic black shales. The unit has been intruded by differentiated gabbroic sills which range in composition from ultrabasic through pyroxenite to gabbro. The largest volume of gabbroic rock occurs in the central-eastern part of the belt, and the sills thin to the north and south.
The uppermost unit consists of shales, black shales, siltstones and minor cherts, with rare conglomerates and dolostones. The unit seldom outcrops and has not been explored to the same extent as the lower units, so details of its lithologies and structure are not as well known.
Later granites are intruded along north-south zones for the length of the belt. They are generally massive medium grained monzonitic bodies, and probably have a range of intrusion ages. They are not affected by ductile deformation but have been variously affected by later faulting. Intense silicification and epidotisation has occurred adjacent to all the internal granites. Two small stocks, one 5 kilometres SSW of Swan/Swift and the other 30 kilometres NNW of Swan/Swift, display very distinct magnetic signatures, and these may represent volcanic plugs rather than granitoids.
The northern third of the belt is intruded by numerous WNW – ENE Proterozoic dolerite dykes. These do not outcrop but are clearly identified on aeromagnetic imagery. Several early phases of tight to isoclinal folding have affected the banded iron formations of the lowest unit, and at least the latest of these phases has affected the upper units. Most fold axes have now been refolded into ~N-S parallelism.
The whole sequence has been refolded about tight NNE-trending fold axes, and this has produced two main synclines containing the upper sedimentary unit separated by a narrow anticline of the central unit basalts. This anticline contains at least 20 kilometres of gold mineralisation stretching from Wedge to the Wyooda Group. The western syncline appears to be doubly plunging, suggesting later open folding about E-W fold axes.
Faulting is complex throughout the Gum Creek Belt, and it is probable that the margins of the belt and many of the contacts between lithological units are fault controlled. The most prominent faulting occurs as regional-scale, NNW ductile shear zones, which appear to control the gross distribution of gold mineralisation in the region.
Sinistral NE to NNE faulting and dextral and sinistral NW faulting are common throughout the belt, and empirically the main mineralised area (i.e. Swan/Swift to Wyooda) are in zones where this faulting is more intense. Metamorphic grade in the supracrustal rocks is generally greenschist facies, with slightly higher grades (containing garnet-staurolite assemblages) in the northern areas. The margins of the belt have been contact-metamorphosed to amphibolite facies by the intrusion of granites, with mafic amphibolites, and garnet-muscovite and quartz-biotite assemblages being recorded.
Historically, gold at Gum Creek has been mined from structurally controlled Archean lode-gold deposits and associated near surface supergene gold enrichment zones. Deposits are hosted in a variety of rock types including mafic volcanics, BIF and fine-grained sediments. The Project contains numerous gold and lesser base metal prospects and deposits along its entire 80km strike length.
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