Geology and mineral deposits of the Cullen mineral field, Northern Territory.
Authors / CoAuthors
The Cullen Mineral Field, lying in the southern central part of the Pine Creek Geosyncline, contains early Proterozoic metasediments of the Namoona, Mount Partridge, South Alligator, and Finniss River Groups. The metasediments, originally shale, siltstone, quartz sandstone, conglomerate, greywacke, dolomite, dolarenite, dololutite and tuff, were intruded by pre-orogenic sills of Zamu Dolerite before being deformed and metamorphosed to greenschist facies between 1870 and 1780 Ma. These rocks, together with unconformably overlying felsic volcanics (El Sherana and Edith River Groups), were extensively metamorphosed by syn- to post-orogenic granitoids of the Cullen Batholith emplaced between 1830 and 1780 Ma. The Batholith contains granodiorite, several varieties of granite and leucogranite, bodies of monzonite, and younger syenite dykes. Largely undeformed Middle Proterozoic, Palaeozoic, and Mesowic strata rest on earlyProterozoic rocks with marked regional unconformity and form tablelands and plains bordering the mineral field to the southwest and southeast. The main forms of metal occurrence are: hydrothermal veins and stockworks (Sn, W, Au, Ag, Pb, Zn, Cd, Cu, Bi, As, D, and Mo); volcanogenic stratabound massive sulphide deposits (Au, Ag, Cu, Pb, and Zn); alluvial deposits (Au and Sn); and residual massive oxide deposits (Fe and Mn).The vast majority of mines have worked hydrothermal deposits which are mostly located in north to northwest-trending faults, shear zones, and associated structures within early Proterozoic metasediments and granitoids. Pyritic, dolomitic and carbonaceous strata are preferentially mineralised, especially within the Koolpin and Mount Bonnie Formations. The distribution of deposits within the contact aureole defines a zonation of uranium closest to granite, through tungsten, copper, tin, silver-lead, to gold with increasing distance from the granitoid contact. This nation probably reflects decreasing temperatures within the contact aureole at the time of generation of a variety of metal-bearing fluids, either during granitoid emplacement or later. A magmatic source for some of the metals is indicated, particularly in late-stage, highly fractionated leucogranites which form cusps peripheral to the main body of the Cullen Batholith. The Cullen Mineral Field has been a major centre of metal production, mainly for gold, silver, lead, copper, tin, tungsten and iron. Minor zinc, cadmium. bismuth, arsenic, molybdenum, uranium and limestone have also been won.