Two samples of diatomite were recently received from Broken Hill Pty. Co. Limited for microscopic examination. They were from Nettle Creek, 9 miles north-east of Mt. Garnet and near Innot Hot Springs. The results of the microscopic examination are given in this report.

Increases in atmospheric CO¬2 cause the oceanic surface water to continuously acidify, which has multiple and profound impacts on coastal and continental shelf environments. Here we present the carbonate mineral composition in surface sediments from a range of continental shelf seabed environments and their current and predicted stability under ocean acidifying conditions. Samples come from the following four tropical Australian regions. 1. Capricorn Reef (southern end of the Great Barrier Reef). 2. The Great Barrier Reef Lagoon. 3. Torres Strait. 4. The eastern Joseph Bonaparte Gulf. Outside of the near-shore zone, these regions typically have a carbonate content in surface sediments of 80 wt% or more. The abundance of high magnesium-calcites (HMC) dominates over aragonite (Arag) and low magnesium-calcite (LMC) and makes up between 36 and 50% of all carbonate. HMC is significantly more soluble than Arag and LMC and the solubility of HMC positively correlates with its magnesium concentration. Using the solubility data by Plummer and Mackenzie (1974) (1), 96% of HMC in the four regions is presently in thermodynamic equilibrium or slightly supersaturated relative to global mean tropical sea surface water. When the modelled saturation state for aragonite in equatorial areas for this century (2) is converted into HMC saturation state curves, HMC is predicted to become undersaturated in the four regions between 2040 to 2080 AD with typical HMC decline rates between 2 and 5% per year. The range of respective estimated carbonate dissolution rates is expected to exceed current continental shelf carbonate accumulation rates leading to net dissolution of carbonate during the period of HMC decline. In a geological context, the decline in HMC is a global event in tropical continental shelf environments triggered by reaching below-equilibrium conditions. The characteristic change in carbonate mineral composition in continental shelf sediments will serve as a geological marker for the proposed Anthropocene Epoch.

Specimens of radioactive ferruginous sandstone from Madigan's Prospect, Bynoe Harbour, N.T., have been examined by autoradiographic, mineragraphic, mineralogical, and petrographic methods, and tested treated, and analysed chemically; radiation measurements have been made at appropriate stages in the investigation to ascertain the behaviour and distribution of the radioactive material.

These notes are compiled as a result of conversations with Government officials and mining engineers in Noumea on 4-6th July, 1951. Figures are given for the production, reserves, and exports of Nickel, Chromite, Manganese, Cobalt, Iron, and other miscellaneous minerals. Most of the figures quoted herein have been compiled from records collected by the Australian Consul.

The following report concerns the geology and mineralization of two uranium prospects in the Gimbat - Snake Creek Area of the Northern Territory. One of these prospects, referred to as Sleisbeck, can be recognised as one of the most favourable yet discovered in the Northern Territory. The radioactivity occurs in a quartzite breccia outcropping over a length of 1.5 miles and with a width of as much as several hundred feet. Geiger counter readings of 2 - 100 times background, occur frequently along the entire length of the outcrop, visible mineralization being present at three separate localities. The state of this mineralization, its associations and the geological settings are favourable to the possible occurrence of uranium mineralization at depth. Recommendations are made for further work, and problems in regional geology are discussed. The writer considers the sections of this report designated "Mineralization" and "Conclusions" to be the most important for a knowledge of the actual uranium occurrences. The remaining information is mainly geological, and, while highly pertinent, may not be of urgent interest to readers with a limited amount of time.

The occurrence of radioactive minerals with cobaltiferous deposits in the Carcoar area has been known since 1894, but until recently they have not received much attention. The present geological survey has been carried out following the discovery of three rather significant radioactive anomalies in the north-eastern part of the mined area, during radiometric surveys in 1950 and 1951. The geological survey has shown that the cobaltiferous-uranium deposits occur in strong north-south shears in an area of Silurian slates and volcanic rocks intruded by diorite sills and dykes, close to the south-eastern boundary of a large mass of hornblende diorite. Opportunities occur for the discovery of other uranium deposits in parallel shears outside the area, in which radioactive anomalies have already been found. This report gives a detailed account of the geological survey. Geology, geological structure, the workings, deposits, and mineralization are discussed, and recommendations are made for future testing and surveying of the area.

In October, 1951, the Geological Section of the Bureau of Mineral Resources recommended a geophysical survey at the newly-developed Rye Park tungsten deposit. The purpose of the survey was the delineation of the main mineralised areas around a granite cupola. The geology of the area, survey methods, and field operations are described in this report. The result of the survey and of diamond drill hole testing are discussed.

Report on the method and findings of the beach sands investigation in the area between ML180 and DC22, Broadbeach to North Burleigh. Estimates of the quantities and grades of heavy mineral concentrates, the quantities of overburden, and the quantities of each of the heavy minerals are tabulated.

Boring commenced in the Broadbeach area on an East-West line 500 feet south of the northern boundary of DC22. Subsequent boring was carried out along lines 1300 feet, 2100 feet, 2900 feet, 4500 feet, 6125 feet, 7740 feet, 9300 feet, and 10900 feet south of the northern boundary of DC22. The results of the beach sands investigation are presented here. Estimates of the tonnages of heavy-mineral concentrates, the average grades of the heavy-mineral bearing sands and the average thickness of overburden, are tabulated. The complete set of data, from which these figures have been calculated, is attached as an appendix to the report.

A report on the testing of bauxite deposits in the Tasmanian districts of Ouse, Launceston, Rosevale and Myalla. This report is supplementary to Mr. Owen's report (1946/2).