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  • A collection of papers on the metallogenic provinces and mineral deposits in the southwestern pacific.

  • 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.

  • Since the discovery of gold at Cape River in 1867, mining has played an important role in North Queensland by providing income, opening up new areas to settlement and providing markets for pastoralists and retailers. Mining is valued at more than $700 million per annum. Over 24 million ounces of gold have been mined or discovered in North Queensland. The Charters Towers district is a world class gold province with 15 million ounces of gold discovered in that area alone to date. Bauxite is a major commodity, contributing 10% of the world's production. The area has also been a major tin producer, and has produced, or is producing, base metals, nickel, tungsten, kaolin, antimony, silver, gemstones, limestone, dimension stone, dolomite, perlite, fluorite, molybdenum and diatomite.

  • The island of New Guinea lies in an area of complex tectonic interaction between the relatively stable Australian continental landmass and the geologically active circum-Pacific Belt. Thus the Palaeo-zoic - Mesozoichistory of the southern half of the island is closely related t o the Palaeozoic - Mesozoic development of northeastern Australia, whereas in the northern half of the island there are Cainozoic geosynclinal and volcanic belts which cross-cut the Palaeozoic - Mesozoic basement and are parallel to the circum-Pacific margin in this region. In mainland Papua New Guinea, intrusive igneous activity before Tertiary time was restricted to the southern part of the Central Highlands and, from the data available, appears to have been rather sporadic. The Upper Permian Kubor Granodiorite, dated at about 2 4 0 m.y., represents the largest and oldest-known igneous massif in New Guinea. A number of small Mesozoic granitic bodies were emplaced in the Early Jurassic (190m.y), Early to Mid-Jurassic (172m.y) , and mid-Cretaceous (90m.y). Increased tectonism in the mid-Tertiary is evidenced by several late Oligocene and early Miocene results (26 to 20 m.y. range) in four metamorphic terrains and in granitic intrusives in the south Sepik area. Volcanic and plutonic igneous activity reached a climax in the mid - Miocene , between 12 and 15 m.y. ago. K - Ar dating on some of these volcanic rocks in close stratigraphic relationship with palaeontologically controlled sedimentary rocks provided the basis for constructing a physical time scale for the East Indies letter stages. The 12-15 m.y. (mid - Miocene) pulse of plutonic activity continued to a lesser degree in the late Miocene and Pliocene. These Miocene - Pliocene bodies lie in an arcuate northwest-trending belt (New Guinea Mobile Belt) over 700km long. Porphyry copper and gold mineralization events are temporally and spatially associated with the middle Miocene and Pliocene high-level intrusives in this belt. All the volcanic and plutonic rocks have low initial Sr 87 / Sr 86 ratios, suggesting that they were derived from mantle sources with little or no contamination by crustal material. A close relation between the major tectonic processes of faulting, volcanism, and plutonism in the New Guinea Mobile Belt, over a relatively short time span of a few million years in the mid - Miocene, corresponds to the waning stages of the Papuan Geosyncline sedimentary history and the beginning of the main mountain-building processes in the New Guinea highlands. It is hypothesized that this climactic upsurge in the tectonic history of New Guinea was triggered in the early to mid - Miocene by interaction and collision between the Pacific Plate and the northward-moving Australian Plate, which has New Guinea at its leading edge.

  • The Timor Sea region discussed in this Bulletin covers the Sahul Shelf and Timor Trough between 123° and 130° East longitude. The area includes a wide, stable continental platform bordered on one side by an ancient, low-lying, deeply weathered continent, and on the other by a moderately deep, tectonically unstable geosynclinal trough. The purpose of this Bulletin is to describe and interpret the morphology of this area, to define and characterize the sedimentary facies and their distribution patterns, and to discuss the topographic, oceanographic, geological, and biological factors that control them. The study forms part of a series of investigations of modern sedimentary facies in a variety of geological settings along the continental margins. See also Bulletin 83A (GeoCat # 111).

  • Since the publication in 1967 of the monograph on the marine geology of the Timor Sea,1 the Bureau of Mineral Resources has initiated a program of systematic reconnaissance geological surveys of the continental shelf. The results of this work are being published in the BMR Bulletin series accompanied by 1:1 000 000 lithofacies maps of the shelf sediments. Three sheets (Rowley Shoals, W.A.2; Scott Reef, W.A.2 ; and Arafura Sea, N.T.8 ) have been printed by early 1974, and work on two further sheets covering part of the east Australian continental shelf is well advanced. Users of the map should refer to Bulletin 83 (GeoCat # 163) to assist in interpretation. For instance, wide areas of the shelf are non-depositional, or even subject to erosion, and therefore the variations in lithology portrayed are not exclusively the result of variations in the modern depositional regime. Also the map does not distinguish sediments which are relics of earlier regimes from modern ones; however, some information of the distribution of these older sediments can be obtained from Bulletin 83 (GeoCat # 163) and inferred from a study of the gravel content in relation to the bathymetry.

  • <p>The Murray Basin extends over 300 000 km of inland southeastern Australia, is flanked by subdued mountain ranges, and forms a low-lying saucer-shaped basin with thin flat-lying Cainozoic sediments. Over the past 100 years, the Murray Basin has become one of the most important agricultural regions in Australia. Unfortunately it is also a closed groundwater basin, which consists of a thin sequence of sediments containing a number of aquifer systems, with little capacity to absorb additional recharge. Irrigation and clearing of natural vegetation have increased recharge to these aquifer systems. Resultant rising groundwater levels and discharge of saline water into the landscapes and river systems of the basin, have created salinity problems that threaten to have an increasingly adverse impact on both the regional economy and natural environments. Many of the reasons for salinisation lie in the subsurface geology, and can be related to the development of the structural and stratigraphic framework of the basin over the past 60 Ma. Knowledge of these is a prerequisite to understanding hydrogeological systems and processes contributing to the salinity problem. This document summarises the geology of the Murray Basin. <p>Beneath the Murray Basin, geophysical and borehole evidence indicates that folded and partly metamorphosed Proterozoic and Lower Palaeozoic basement is block-faulted, and that the Cainozoic sequence is locally underlain by poorly defined infrabasins preserved in graben-like troughs. These contain thick sequences of Devonian to Lower Carboniferous sedimentary rock and discontinuous, erosional remnants of Upper Carboniferous, Permian, Triassic and Cretaceous platform-cover sediments. <p>The Cainozoic succession of the Murray Basin forms an extensive blanket of sediment, with a maximum thickness of about 600 m preserved in the deeper, central-western parts of the basin. A subsidiary depocentre with over 400 m of sediment underlies the central-west Riverine Plain, but in most northern, eastern, and southern parts of the basin the sediment succession is generally less than 200-300 m thick, and could be more accurately described as forming a thin platform-cover succession rather than a true basinal sequence. Within the Tertiary succession at least three major depositional sequences (Paleocene Eocene to Lower Oligocene, Oligocene Middle Miocene, and Upper Miocene Pliocene) have been identified. Each sequence consists of a package of genetically related formations separated by disconformities. Poorly consolidated, non-marine sand, silt, clay, and carbonaceous sedimentary rocks predominate in the east and north, but each of the depositional sequences includes weakly lithified marine sedimentary rocks in central and southwestern areas. The stratigraphy translates into a number of regional aquifer systems, confining layers and permeability barriers to groundwater flow, each with distinctive characteristics. <p>In the Mallee region of the west, the Tertiary sediments of the Murray Basin are almost entirely concealed beneath a mainly fossil' arid and semi-arid landscape of Quaternary aeolian dunefields, with minor fluvial and lacustrine morphostratigraphic units. Farther east, where the basin and adjacent highlands are drained by the Murray, Murrumbidgee and Lachlan Rivers, the Tertiary sequence underlies flat-lying fluvio-lacustrine and minor aeolian sediments of the semi-arid landscape of the Riverine Plain. Within the Mallee and Riverine Plain landscapes, active and fossiV (currently inactive) groundwater discharge lake complexes can be identified by characteristic assemblages of Upper Quaternary sediments forming stranded lake floors, gypsum flats, salinas, gypsum and clay pellet dunes and lunettes. These have developed within low-lying areas during the past 0.5 Ma. Their extent indicates the presence of widespread salinisation under 'natural9 conditions at times in the recent geologic past. <p>The main emphasis of the study is on improving our understanding of the geological context of groundwater and surface discharge in the Murray Basin, but at an early stage the scope of the study was expanded to include reference to other mineral resources. These include Cainozoic limestone, alluvial gold, kaolin, heavy minerals, gypsum and halite deposits. The Tertiary succession contains extensive deposits of currently sub-economic brown coal, underlain by Upper Permian coal in the Oaklands Infrabasin in New South Wales. The Cainozoic Murray Basin is not prospective for hydrocarbons, but several concealed pre-Cainozoic infrabasins remain poorly investigated.

  • Three zones of retrograded crystalline basement rocks have been delineated in central Australia. One, along the southwestern margin of the Amadeus Basin, was deformed about 600 m.y. ago during the Petermann Ranges Orogeny. Two one north of the Amadeus Basin, the other north of the Ngalia Basin were deformed during the Carboniferous Alice Springs Orogeny. Each retrograded zone is highly deformed and is flanked on one side by folded and thrust sedimentary rocks and on the other by granulite and amphibolite facies rocks. The high-grade rocks appear to have resulted from several metamorphic episodes in the Precambrian. A major gravity gradient is associated with each retrograded zone; the Bouguer anomaly highs generally occur over the areas of high-grade metamorphic rocks, and the lows over the sedimentary basins and retrograded rocks. In general, the deformed and retrograded zones are moderately to gently dipping. The gravity gradients are so wide and steep that to explain them the deformed zones must pass through the crust into the mantle beneath. The crust and mantle above each deformed zone have been upthrust, bringing granulite facies rocks to the surface and producing Bouguer gravity anomaly highs over the uplifted lower crust and mantle. The deformed zones are similar to the subduction zones that may develop on the margins of continents, but there is no evidence of continental collision in central Australia when they were formed, and they are regarded rather as possible examples of intracontinental plate reactions. They may have extended right across the continent or may terminate against strike-slip (transform) faults. A possible site for such a transform fault in Western Australia is discussed, but its existence is speculative.

  • Contents: 1. Some early cretaceous plant microfossils from Queensland/ by D. Burger. 2. Palynological observations in the Officer Basin, Western Australia/by E.M. Kemp.