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  • Legacy product - no abstract available

  • This report outlines corrections and additions to previous mapping on the Huckitta, Hay River and Tobermory Four-mile Sheets, Northern Territory, and presents all available data on water bores drilled in those areas. On the May River Sheet, Upper Cambrian and Lower Ordovician sediments on the western limb of the Toko Syncline are faulted against Upper Proterozoic sediments along a complex north-west trending fault zone named the Toomba Structure. The maximum throw of the main fault exceeds 2,000 feet, and there are smaller, parallel strike faults which affect Middle Ordovician sediments. A section of 460 feet was measured in a ? Ordovician sandstone sequence which overlies the Middle Ordovician Mithaka Beds. Samples obtained from several water bores along the Field River show the presence of a locally non-outcropping sequence, probably the Tarlton Formation, overlying the Upper Proterozoic Field River Beds. On the Tobermory Four-mile Sheet, the effects of lateritisation on the mixed lithologies of the Upper Cambrian and Lower Ordovician units were unravelled, and it was shown that the change from the Tomahawk Beds of the Huckitta area to the Ninmaroo and Kelly Creek Formations of the Toko Range is a facies variation. A. small disconformity was established between the Nora Formation and the Carlo Sandstone in the Tarlton Range. Numerous measurements in the Tarlton Range show that during the deposition of the Carlo Sandstone currents came from the south-east. Further plant fossils were collected from the Tarlton Formation; they indicate a probable Triassic or early Jurassic age. On the Huckitta Four-mile Sheet, two sections of about 750 feet were measured in the predominantly dolomitic Arthur Creek Beds, in the area west and South west of Huckitta homestead; in one section, trilobites and brachiopods were discovered 85 feet, stratigraphically, above archaeocyathids in the top of the Lower Cambrian Mount Baldwin Formation. Three new fossiliferous horizons were found in the Upper Cambrian Arrinthrunga Formation; one is near the base and contains trilobites of lower Upper Cambrian age; the other two horizons are near the top of the formation and contain trilobites and brachiopods. Revised structural mapping and measurement of new sections show that the Arrinthrunga Formation is about 3,200 feet thick. The Middle Ordovician Nora Formation which occurs only in the southern foothills of the Dulcie Range, has been mapped as a separate unit from the Tomahawk Beds which formerly included it .Additional samples of Devonian fish were collected from a new locality in the Point Spring area.

  • 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.

  • Legacy product - no abstract available

  • Legacy product - no abstract available