No abstract available

[en] The Litchfield province is herein defined as the westernmost outcropping unit of the Pine Creek Geosyncline extending from the Giant's Reef Fault at about longitude 130⁰50'E westerly to the edge of the Bonaparte Gulf basin. The northern half of the province has been remapped using company drillhole data and a Bureau of Mineral Resources air magnetic-radiometric survey. Five areas have been found to be entirely granitoid, garnetiferous and gneissic in part, with composition in the range adamellite to granodiorite. A single Rb/Sr age of about 1800 m.y. has been published. The granitoid margins are migmatised and transitional into large areas of metasediments, varying in metamorphic grade from greenschist (fine grained chloritic graphitic schist) to upper amphibolite/granulite grade (course grained quartz - feldspar gneiss). The regional strike is northerly to northwesterly, and these metasediments are thought to merge into the Burrell Creek Formation beyond the border of the province. Two periods of metamorphism affected the Litchfield province metasediments, but only one phase can be detected in the granitoids, thus these are assumed to be younger, probably formed during the 1800 m.y. orogenesis known elsewhere in the Geosyncline. Minor areas of unmetamorphosed gabbro, dolerite and quartz-diorite occur, probably of Middle Proterozoic age. Cover rocks include quartz sandstones of the Middle Proterozoic Moyle River Formation and Depot Creek Sandstone, and Cambro-Ordovician sandstones of the Daly River Basin. The formation boundaries in the Litchfield province are not particularly confused or complicated, nor are the igneous lithologies particularly diverse. There is no evidence for an Archaean age for the part of the Litchfield province north of the Daly River, and it is thus proposed that the term 'Litchfield Complex' should be abandoned. (author)

[en] The Mount Fitch copper and uranium deposits are contained in chloritic, sericitic and graphitic schists of the Namoona Group and magnesite of the Batchelor Group. The main uranium deposit is confined to a major breccia zone in the magnesite. Total ore reserves are approximately 1500 tonnes U₃O₈. Secondary copper mineralization is contained in residual clays overlying the magnesite and reserves are estimated at 290,000 tonnes of ore with an average grade of 0.65 Cu. An interpretation of the structure suggests that the metasediments were initially folded during the orogenesis of the Pine Creek Geosyncline. Later faulting and cross folding, complimentary to Giants Reef Fault intensively brecciated the metasediments. It is suggested that the mineralization is syngenetic or introduced during the orogenesis of the Pine Creek Geosyncline and upgraded by later weathering which was most effective in the breccia zone, facilitated by the high permeability. The copper mineralization represents a major enrichment by removal of magnesite during weathering. (author)