Legacy product - no abstract available

Legacy product - no abstract available

Beach sand deposits along the Australian east coast (Gardner, 1951 a, b) have yielded a large part of the world supply of zircon and rutile since the year 1936. During 1953 the returns from the export of these minerals amounted to more than £2,000,000. In addition the black sands contain a small proportion of monazite, which is a source of cerium and of thorium, a fissionable element that may be used for the generation of atomic power. From a comparatively small beginning the mid-1930's the beach-sand industry grew rapidly during the war and early post-war years. Little was known of the distribution and reserves of the deposits; hence the Bureau of :Mineral Resources undertook a detailed investigation of the coastal area between Southport, Queensland, and Woody Head a little north of the mouth of the Clarence River, New South Wales. The primary object of the survey was to determine the reserves of monazite and therefore of thorium; the reserves of zircon, rutile, and ilmenite were also determined. In this report the source rocks of the sand and heavy minerals are considered in a brief outline of the physiography and general geology of the country between the coast and the main divide. The deposits are described and their origin and distribution discussed in connexion with late Pleistocene and recent changes, in sea level. The reserves and distribution of the heavy minerals arc broadly summarised, and more details of reserves and dimensions of deposits and overburden are given in descriptions of the individual areas.

At the request of the Geological Survey of Western Australia, the Bureau of Mineral Resources, Geology and Geophysics provided geophysical staff and equipment to assist in the search for underground water supplies in certain areas of Western Australia where additional supplies are required for further development of the farming 'industry. The main objects of the survey were to test several -types of resistivity equipment and to determine their limitations and optimum working conditions, to estimate the accuracy of depth determinations to formation discontinuities, to determine, the nature of the discontinuities, and to estimate the degree of salinity of the ground water. Results show that in 75 per cent of the measurements made, errors in depth determinations were within ± 20 per cent. Although limited control data were available, it was often possible to recognize limestones, cementation zones in limestone, sands and ground-water levels, and in granite areas, the transition from weathered to fresh granite was readily recognized. Where conditions were favourable, a satisfactory correlation was obtained between resistivity values and the salt content of solutions in a formation, provided the porosity of the formation was known. Although the main object of the survey was not, the finding of new underground water supplies, this WJ.S one of the aims in the Cue area, and a location was found where conditions for a large supply of good-quality water appeared to be favourable. The resistivity meter which was used in the tests was developed by the Bureau of Mineral Resources, and operated very satisfactorily. The Megger earth tester was reliable up to electrode spacings of 100 feet. The value of future test surveys for underground water would be greatly enhanced if more comprehensive bore information were available for correlation and combination with geophysical and geological observations. Such information should include the porosity and permeability of formations, screen analyses of samples, and salt content and resistivity of bore water.

The Cape Range Structure, which occupies the North-West Cape peninsula, is a closed anticline in Tertiary limestones. The structure is at least eighty miles long and twenty miles wide, and has a vertical closure of 1200 feet and a closed area of 1200 square miles. The physiography is a reflection of the structure-a young fold mountain with mainly consequent, closely-spaced, drainage. The Tertiary sediments were laid down in a shelf area of the southwestern arm of the Indo-Pacific geosyncline. Because of the stability of the adjoining Western Australian shield, they did not attain the thickness of the sediments laid down elsewhere in the Indonesian geosyncline, nor were they affected to the same extent by subsequent tectonic disturbance. Five Tertiary formations are exposed on the Cape Range-the lower Miocene (e-stage) Mandu Calcarenite (265 feet of chalky limestone), the lower Miocene (f1-stage) Tulki Limestone (225 to 420 feet of hard crystalline limestone) and the possibly lower Miocene (f1 to , ?f2stage). Trealla Limestone (18'0 feet of white crystalline limestone), constituting the Cape Range Group; and the possibly lower Miocene Pilgramunna Formation and possibly Pliocene Vlaming Formation, forming the Yardie Group (calcareous sandstone and fine conglomerate up to 300 feet thick). Beneath the Miocene limestones are probably at least 3,000 feet of Cretaceous and Eocene marine sediments and possibly up to 18,000 feet of Permian, Carboniferous, and Devonian marine sediments. In vertical closure and closed area the Cape Range Structure is' the largest in the Carnarvon (North-West) Basin. Potential drainage of oil is unrestricted on the west flank and on the northern two-thirds of the east flank. Further geophysical (gravity and seismic) investigations should be carried out so as to try to determine the thickness of sediments and the shape of the structure in depth.

At the request of West Australian Petroleum Pty. Ltd. and the Department of Mines, Western Australia, the Bureau carried out a seismic velocity survey in Rough Range No.1 Well, with the object of obtaining velocity distribution data for use in the interpretation of results of seismic refraction surveys in the area. Twenty-two shots were fired from a shot point about 1,000 feet from the well. Geophone depths in the welI ranged from 2,000 feet to 14,000 feet, usually at intervals of 500 feet, but the intervals were varied at points where there was a significant change in the stratigraphy. Recordings from 16 of the shots were used in the calculations. Results indicated that, as would be expected, the hard crystalline limestone which comprises the top 700 feet of section has a much higher velocity than the clastic limestones which underlie it. An abrupt velocity change from 7,100 ft/sec. to 12,600 ft/sec. at 3,250 feet corresponds approximately with the change from Windalia Radiolarite to Muderong shale, and also with a density change from 2.1 to 2.4. A second major velocity change from 12,600 ft/sec. to 16,500 ft/sec. at 6,800 feet also corresponds approximately with a density change from 2.5 to 2.7. An abnormal increase in velocity recorded at about 9,000 feet must be considered as very doubtful and velocities at this depth have been averaged.

The preliminary investigation was made when the Bureaut s seismic party was held up by flooded rivers, while on its way t o Christmas Creek in May, 1954. Results show that the seismic aethod is applicable to the Broome area, and that a sedimentary section of the order of 12,500 feet exists. They further show that a syncline and anticline not known from the surface geology may possibly exist at depth.

These documents have been scanned by the GA Library. Please refer to the document for contents.

These documents have been scanned by the GA Library. Please refer to the document for contents.

These documents have been scanned by the GA Library. Please refer to the document for contents.