Mineralisation in the Chillagoe area is concentrated within the prospective Silurian Chillagoe Formation which lies on the western margin of the Hodgkinson Province, and is bound to the west by the Palmerville Fault, which marks the contact with the Precambrian Dargalong Metamorphics. Locally, the formation is separated from the Palmerville Fault by a thin fault wedge of Ordovician-age Mulgrave Formation sediments. To the east, younger Devonian-age Hodgkinson Formation overlies the Chillagoe Formation.
The Chillagoe Formation occupies a five to ten kilometre wide north-westerly trending belt that extends for over 150km from Mt Garnet in the south-east to 70km north-west of Chillagoe where the belt, and bounding Palmerville Fault, changes to a northerly trend and extends for a further 120km. The formation comprises units of limestone, sandstone, siltstone, chert, basalt and conglomerate with a cumulative thickness of approximately one kilometre, however extensive thrust faulting during the Late Devonian to Mid Carboniferous resulted in significant structural thickening of the formation. In the Mungana to Red Cap area, at least 12 thrust-induced stratigraphic repetitions have been identified. The steeply-dipping thrust faults trend north-westerly, sub-parallel to the stratigraphy and the Palmerville Fault.
Igneous activity in the Late Carboniferous to Early Permian resulted in the widespread intrusion of granitic rocks and extrusion of felsic volcanic rocks and the localised emplacement of high-level rhyolitic porphyry stocks in the Chillagoe region. Mineralisation in the Chillagoe region is related to this Late Carboniferous to Early Permian intrusive activity. Age dating and whole rock geochemistry have identified three overlapping supersuites of igneous rocks, emplaced over the period of 326-292Myr, variously associated with gold, copper, molybdenum, zinc, lead, tin, tungsten and bismuth mineralisation. In particular, the localised high-level emplacement of Late Carboniferous porphyry stocks is intimately associated with gold-copper-molybdenum, bismuth mineralisation, exemplified by the Red Dome and Mungana porphyry- and skarn-hosted gold-copper-molybdenum ore bodies.
In the region, there are ranges of diverse mineralisation styles including:
The combination of favourable host rocks, favourable structural history, and long-lived and extensive magmatic intrusive activity, particularly in the Late Carboniferous period, has greatly enhanced the metals endowment of the Chillagoe Formation.
Exploration in the Chillagoe area is currently focussed in the King Vol and Red Cap-Victoria areas, with drilling expected to commence in late September on a number of regional base metal targets, including King Vol North, Rusty File, Wild Horse Creek, Prices Dam, Ivors, Tartana South and Ootan. All of these targets comprise strong zinc and/or copper soil anomalies and most are expected to be related to skarn alteration similar in nature to that developed at Mungana, King Vol and Red Cap/Victoria.
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