No abstract available

As a result of the field activities of the Bureau during 1953 regional geological maps have been prepared for the Rum Jungle district, the Katherine-Edith River district and the Coronation Hill-Goodparla district, which cover the Katherine, Lewin Springs and Mt. Todd 1 mile military sheets and portions of the Marrakai, Mt. Tolmer, Batchelor, Tumbling Waters, Goodparla North, Goodparla South and Mt. Evelyn sheets. Detailed geological and geophysical reports and plans have also been prepared for all known radioactive mineral prospects, costeaning and diamond drilling has been undertaken to test some of the prospects and inspectional reports have been made on practically all airborne scintillometer anomalies located during surveys in 1952, and on some of those found during 1953. Prospecting operations have also been undertaken. A summary of the activities of the Bureau during 1953 and the results achieved is given in the following pages, and further details can be obtained from reports mentioned in the list of references.

Legacy product - no abstract available

The principal deposits of bauxite occur on Bintan and adjacent islands which lie about 50 to 100 miles south-east from Singapore. This report is comprised of three extracts which have been drawn from papers made available to the writer by the Australian Government Commissioner for Malaya. The production figures, composition, and nature of the bauxite deposits are described in these extracts.

Two million alluvial macrodiamonds recovered from Tertiary deep leads in the Copeton/Bingara (C/B) area of New England (NSW) formed by ultrahigh pressure metamorphism during Phanerozoic subduction - based on unique isotopic composition (?13C>0), unique inclusions and high pressures on inclusions. The techniques used were either destructive or only succeeded on 3% of 200 stones tested with inclusions. Some researchers have suggested that UHP microdiamond (e.g. from Kochetav) lacks the 2nd order Raman spectral pattern (2200-2700cm-1) that is prominent in cratonic diamond. Our work on African cratonic macrodiamond shows this peak is suppressed if the stone is UV fluorescent, but is strong at 15-75× (signal to noise ratio S/N) for a low background (?1100 counts per second). For NSW macrodiamond with a low background, this peak is greatly reduced at 2-14× S/N for C/B (45 stones), Mt Airly (4), Walcha (2), Frenchmans (1 ) and Wenona Diatreme (1), calibrating the test. This new combined technique (UV lamp, 2nd order Raman) is much faster and works on a larger fraction of stones (including those without inclusions; 13% of C/B stones are low background). Strong brittle/plastic deformation during growth of C/B diamond is confirmed by growth textures and Laue Xray photography, indicating growth during subduction - promoting strong nitrogen aggregation, and suppressing the 2nd order Raman spectral signal. This Raman test should apply to all subduction diamond, including superdeep diamond.

Raman spectroscopy has been used for the identification of both common and uncommon minerals in melt inclusions in Group-I kimberlites from Siberia, Canada, SW Greenland and South Africa. The melt inclusions all contained high abundances of alkali-Ca carbonates, with varying proportions of cations, and Na-Ca-Ba sulphates. However, no hydrated carbonates or sulphates were detected in melt inclusions from the Udachnaya-East kimberlite which is in agreement with its dry matrix mineralogy. In contrast, the melt inclusions in kimberlites from Canada, South Africa and SW Greenland were found to contain bassanite, pirssonite, and hydromagnesite suggesting that greater amounts of water were present in their residual magmas. This suggests that enrichment in alkali carbonates and sulphates is widespread across a range of Group-I kimberlites and implies that they commonly have an alkali-, and sulphur-rich residual kimberlite melt.

Bauxite was found on Manus Island in 1952 by J.E. Thompson, Senior Resident Geologist, Territory of Papua and New Guinea, at three separate localities. At Lepatuan a dacite flow overlies bedded tuffs and both have been bauxitized. The former parent rock yields a porous granular bauxite containing about 1 percent silica, 55 percent alumina, 10-13 percent ferric oxide and 1 percent titania. Bauxite developed on the tuffs is nodular in character, and consists of gibbsite nodules embedded in soft clay-like bauxite. The composition of one sample of this bauxite is 11.7 percent silica, 51.0 percent alumina, 10.8 percent ferric oxide and 1.0 percent titania. The bauxite is forming at the present day by direct alteration of the dacite without an intervening clay zone, but the tuffs are kaolinized in the first stage of alteration. It is of high significance that bauxite can develop on small flat elevated areas (50 acres at Lepatuan) during the present weathering cycle. Essential conditions for bauxitic alteration to take place appear to be - (a) high mean temperature, high rainfall and dense vegetation, (b) relatively flat terrain, and (c) elevation above immediate surroundings to ensure adequate ground-water movement. Total resources of bauxite at Lepatuan are about 600,000 tons, and possible reserves are negligible at the other localities. Difficulties of access and distance from markets militate against commercial exploitation of the deposit, but prospects of finding more bauxite in the islands of the volcanic arcs of Bismark Archipelago cannot be lightly dismissed.

Legacy product - no abstract available

It has been fairly firmly established that the fineness of the gold in any ore deposit varies with the depth from the surface at which the deposit was formed and as a corollary to this, that it is dependent upon the temperature and pressure at the time of deposition. This relationship is such that, under certain conditions, the gold fineness, taken into consideration with other recognised criteria, furnishes a very sensitive and reliable guide to the relative temperature of ore formation, at least within the epithermal and the upper part of the mesothermal range. The definition, determination, relation to deposits, and application of gold fineness are discussed in this report.

The presence of laterite described as high-silica bauxite at Mt. Roe on Cobourg Peninsula had been reported early in this century by H.Y.L. Brown, who submitted a specimen for analysis. In the absence of information about the mineralogical composition of the rock the chemical analysis alone affords a very incomplete description of the material. It was considered that the rock might be somewhat similar to the commercially valuable high-silica bauxite which occurs in the Netherlands East Indies and Malaya. At the request of the Australian Aluminium Production Commission the writer was instructed to examine the area in the vicinity of Mounts Roe and Bedwell, and to sample and report on any accessible bodies of apparently aluminous laterite. The locality, topography, and general geology of the area are briefly described. Accounts of the laterite occurrence at Mounts Roe, Bedwell, Kura, and Victoria are given. The mineralogical character of the laterite is described.