The stratigraphy and structure of an area in the Carnarvon sedimentary basin covered by the Williambury and Moogooree one mile sheets, is described. Resting unconformably on a Pre-Cambrian basement of schists gneisses and granites, are Devonian marine sediments 4750 feet thick, followed conformably by Carboniferous approximately 2150 feet thick; these are separated from the overlying Permian more than 8000 feet thick, by a possible hiatus. The Cretaceous System is represented by about 40 feet of siltstone lying unconformably on the Palaeozoic rocks. Marine Tertiary arenaceous deposits are widespread and have a maximum thickness of 80 feet; they are not seen in contact with the Cretaceous rocks. The whole area has been subjected, in Tertiary time, to lateritisation, the most prominent feature of which is the presence of a silicified cap ranging in thickness from a few feet to 30 feet. In one place a post-laterite deposit of 12 feet of probably fresh-water limestone has been observed. An account is given of the structural geology, geological history, and physiography of the region.

The Crater Prospect is situated about 4 miles south-south-east of White's workings and 1 mile north-east of the junction of Batchelor Road and the Darwin-Birdum railway line. It is the name assigned to a type area of an extensive radioactive bed of conglomerate. Low grade but wide-spread radioactivity was discovered by R.S. Matheson and D.F. Dyson (geophysicists) in June 1951, while prospecting along the sedimentary beds out-cropping immediately south of the Rum Jungle granite on the south-side of Giant's Reef fault, and on the south side of another major parallel fault. Geiger-Muller traverses along the strike of a grit-conglomerate horizon away from the Crater prospect revealed that the radioactivity extends westwards for 1.5 miles and for half a mile to the east. The radioactivity, which was confined to the conglomerate, was low-grade and discontinuous over this distance of 2 miles. The Crater Prospect, which can be regarded as a type locality, was geologically mapped by the writer on a scale of 200 feet to one inch after the area had been radiometrically contoured, and the plan accompanies this report (Plate 1). [The geology and structure of the prospect, nature of the radioactivity, and prospecting recommendations are discussed].

An area of approximately 32 square miles in the vicinity of Rye Park has been mapped in greater detail than that of previous regional surveys. Three possible tungsten-bearing areas have been delineated as warranting magnetometric and plane-table surveys. An extension of each of these three areas is indicated. Attention is drawn to copper, tin, silver, lead, and zinc mineralisation of the area, and it is considered that there are possibilities of finding payable orebodies containing these metals.

Widespread use of radio-active tracer elements in medicine, and the increased interest in the search for radio-active minerals, have led to the development of a variety of instruments for the detection of ionising radiations, and their general use by scientists who may have had no training in physics or electronics. While these instruments present a great diversity in appearance, the functioning depends on general principles which apply to all such equipment. The aim of these notes is to present these general principles in a simple form. For details of design, which are often highly complex, and require great skill and experience, reference should be made to the works listed in the bibliography.

During 1951 three separate sets of La Cour pattern Quartz Horizontal Magnetometers were received from the Danish Meteorological Institute. These instruments which are only semi-absolute, were calibrated at the Rude Skov Magnetic Observatory against the standard adopted by that observatory. As the Australian observatories are based on the International Magnetic Standard housed at Cheltenham near Washington, U.S.A. (hereinafter referred to as I.M.S.) it was decided to compare them against the Toolangi magnetometer as soon as possible after their arrival in Australia. Moreover, as the stability of these instruments depends on the torsion properties of a quartz fibre and on the magnetic moment of a magnet, regular comparisons should be made with an absolute magnetometer and the results used to control drift that might occur. The comparisons made immediately after the arrival of the instruments in Australia would thus constitute a starting point in the future control of the Q.H.Ms. [An account is given of work done between 1951 and 1952. Results are appended.]

White's South prospect is situated on the southern bank of the Finniss River (East branch) about 400 feet south southwest of White's Deposit (Ward 1953). Rocks do not outcrop in the area, but low radioactive anomalies were located in this area by the Geophysical Section 1951 suggesting that the western continuation of White's Deposit after faulting might be beneath the soil cover. Low grade ore intersections were obtained in five diamond drill holes put down in the area in 1952. A plan of the area on a scale of 40 feet to 1 inch accompanies this report (Plate 1).

The air-borne scintillometer survey near Katherine during October, 1953, failed to cover a triangular area in the south-east corner of the Katherine sheet, as it was beyond the range of the Shoran beacons. The area is part of a Bureau of Mineral Resources reservation taken out to protect the ABC Prospect. Several trial flights were made over the area, however, in an attempt to detect the presence of any significant radiometric anomalies. During these flights, Geologist A.B. Clark acted as an observer to spot on photo-mosaics the positions at which anomalies might occur. A third order anomaly was recorded during a flight along Maude Creek at a point thought to be within 1 mile of the junction of Dorothy Creek and Maude Creek. A search was made later by D.E. Gardner with the object of finding the source of the anomaly and the results of this work are given below.

Brown's Deposit is the westernmost known area of mineralization in the Rum Jungle area. It is situated approximately two miles northeast of Rum Jungle Railway Siding and one mile southwest of White's Deposit in an area known as Brown's Workings, which was worked for copper in the early part of the century. In June 1950, preliminary geophysical investigations revealed that a radiometric anomaly was present at the eastern end of the old copper workings, and in October 1940, a self-potential survey (Allen 1950) indicated the presence of two distinct bodies of sulphide mineralization. During 1950 a geological map of the area on a scale of 100 feet to an inch was prepared, and in 1951 mapping of the area on a scale of 40 feet and 20 feet to an inch was commenced. This work at present remains unfinished due to other commitments. Three diamond drill holes, part of an extensive programme of diamond drilling planned for the area were drilled towards the end of 1951.

The Brodribb anomaly was first detected by the Bureau of Mineral Resources' aerial scintillometer survey over the Rum Jungle area in 1952. The prospect lies six miles due west of the 40 mile peg on the Stuart Highway and can be reached easily in the dry season by means of the Brodribb track. However, for several months during the wet season the track is quite impassable to heavy vehicles necessary to maintain drilling operations. Ground parties made a preliminary inspection of the area in September, 1952 and by the end of October a combined preliminary detailed geological and geophysical survey was completed (Frankovich, 1952). The results of the surveys and the consequent costeaning indicated that drilling should be carried out for a complete investigation.

The prospect is an existing cooper lease (M.L.69B) held by Messrs. J.W. Watson and K. Cooper who carried out some mining in the area in 1950. The area was first visited in 1953 by I.A. Mumme whose interest was aroused by the pre-existing copper prospects and the close proximity of the Shoobridge granite. Further examination was carried out by Mumme and the writer early in November, and detailed mapping was done on a scale of 100 feet to the inch by the writer and D.N. Smith. Radioactive rocks and the secondary uranium mineral torbernite were discovered at this prospect, which is a copper mine, on October 25th 1953 by I.A. Mumme. A survey plan of the mine shafts, pits and costeans and lines of mineralization was prepared by I.A. Mumme on the 5th and 6th of November so that a suitable base line could be chosen for magnetic and self-potential test traversing. Three magnetometer traverses were completed. P. Rosenhain visited the area on the 5th November and inspected the shafts, stopes and costeans and carried out geological mapping from the 16th November to the 19th November. Further magnetic and self-potential traversing and some reconnaissance radiometric field work was carried out during the two periods 16th November to 20th November, and 24th November to 28th November.