Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available Never published, see Record 1965/048 instead

Wauchope wolfram field* is situated 260 miles by road north of Alice Springs, Northern Territory. Wolfram occurs in a series of quartz reefs the series is traceable over a strike-length of 3,000ft and the reefs are 6in. to i8in. thick. The main production has come from three reefs 12in. to 18in. thick. The field was discovered in 1917 and, from then until 1941, the deposits were worked at such times as tungsten prices were favourable (Fig. 2). Most of the mining was done on tributing basis, and the exploitation of the field was rather unsystematic. Production during that time was approximately 1,000 tons} of concentrate, obtained from an estimated 10,000 tons of quartz mined. Mining had ceased when the Commonwealth Government took over the field in April, 1942, and there were no accessible working faces. Employing Chinese labour, the Government drove 2,800ft. of exploratory and developmental adits, drives, and rises and stoped a small amount of ore. Five drill holes aggregating 1,108ft. tested the reefs ahead of the workings. The results of the testings were disappointing. It was found that payable Ore was largely confined to one shoot (Shoot A) with a maximum strike-length of 300ft and extending down-dip for 120ft. to 200ft. from which most of the ore had been extracted. The shoot occurs near the outcrop of the vein system, and the long axis is roughly parallel to the outcrop. Vein-contouring shows that it is situated in a structural basin in the beds and reefs (which are mainly parallel to the bedding) of 151 samples taken from the quartz remaining within the structurally favourable ground, the weighted mean content was 0.96 per cent WO, Ore from within the shootlimits yielded 1.2 per cent W0 3. On the basis of these figures it was estimated that, when the Government ceased mining at the end of 1943, 5,000 tons of quartz averaging 1.2 per cent recoverable W03 remained in Shoot A (Plates 4 and 5).

This Bulletin presents an account of the general geology, stratigraphy, structure, and mineral resources of the Brock's Creek district, Northern Territory. The general geological mapping of the district was carried out by the Aerial, Geological, and Geophysical Survey of Northern Australia in 1939, and a brief account of the results then obtained has been published (A.G.G.S.N.A., 1939). Some further mapping was carried out in 1950. The most important sedimentary rocks of the district are believed to be of Lower Proterozoic age and have been called the Brocks Creek Group (Noakes, 1949). They are dominantly argillaceous in type, but contain sandy formations as well as thin beds of conglomerate and limestone. Numerous sills of amphibolite, which are of igneous origin, are found within the sedimentary sequence. The sediments and interrelated amphibolites probably attain a thickness of 18,000 feet. Unconformably overlying the Brock's Creek Group is a comparatively thin formation of quartzite which is probably late Proterozoic, in age and is known as the Ruldiva Quartzite. Horizontally bedded Lower Cretaceous sandstone and shale up to 200 feet, thick is found capping mesas ill the district. In the north-eastern section of the area mapped is a concordant body of granite (Brock's Creek Granite), roughly circular in shape at the surface, and haying an average diameter of approximately six miles. A smaller area of concordant granite occurs near Mt. Shoobridge in the south-western portion of the area mapped. A discordant cross-cutting granite (Margaret Granite) cuts through the Brock's Creek sediments in the south-eastern portion of the district and exends for many miles to the south. The Buldiva Quartzite is only gently folded and is not intruded by igneous rocks, but the Brocks Creek Group has been subjected to considerable folding and faulting. The fold axes trend north-westerly or northerly, and marked cleavage has been produced parallel to the fold axes. The fine-grained sediments have been converted into schist in many places. Comparatively broad domal and basin-shape1 folds dominate the general structure of the district, but some anticlinal folds have been comparatively tightly compressed---e.g., the Howley Anticline. Within the 300 square miles of country mapped, it was found that deposits of gold and copper occur within, or close to, one formation, which may be repeated from place to place by folding and faulting. The favourable formation is a graphitic slate but is closely associated with a thin band of conglomerate and is normally associated also with sills of amphibolite. A limestone commonly occurs above or below the graphitic slate, but is lenticular in habit. Ore is commonly found in domal and anticlinal structures within these beds, especially near the more crenulated portions of the structure.

The Oaklands-Coorabin Coalfield in the Riverina Division of New South Wales has been known for many years. Coal is produced from a small colliery near Coorabin and a minor amount of exploratory drilling in the general vicinity of this mine has been carried out by New South Wales and Commonwealth Government authorities. This exploration has shown that coal seams extend over an area of a few square miles near Coorabin. The coal occurs in Permian rocks which do not crop out but are covered by Tertiary and younger sediments with a minimum thickness of 100 feet. Examination of the regional geology led to the conclusion that the coalfield is far more extensive than the limited area proved by drilling. Because of the Tertiary cover, normal geological methods cannot be used to map the boundaries of the Coal Measures and for this reason geophysical survey's, which have been used successfully on similar problems elsewhere, were undertaken to map the sedimentary basin. A gravity survey was carried out first and as the work proceeded it became obvious that a pronounced regional anomaly is present. Consequently, seismic methods were employed to try to obtain the thickness of the sediments at a number of critical places and to provide a control for separating the effect of the sediments from the regional effect. A residual gravity contour plan was obtained and indicates the general shape of the sedimentary basin. This plan provides a satisfactory basis for recommending drilling to test the potentialities of the basin. An area of approximately 1,450 square miles was covered by the geophysical surveys and, after correcting for regional effect, the residual gravity pattern suggests the presence of a Permian basin approximately 600 square miles in area, with a possible extension in a north-westerly direction. Recommendations are made for testing the geophysical results by drilling at five widely-spaced sites in the supposed basin. Five additional drilling sites are recommended and are designed to prove reserves near the known coal occurrences.

The lead-silver-zinc ore deposit of Broken Hill, New South Wales, is among the great ore deposits of the world because of its size, richness, and continuity. To the end of 194.6, approximately £50,000,000 in dividends had been won from recoverable metals worth £210,500,000 gross contained in 63,800,000 tons of ore. The deposit is a hypothermal deposit of Pre-Cambrian age resulting from the selective replacement of two closely adjacent, tightly and complexly folded stratigraphic rock layers. The original sedimentary rocks of the area now consist of tightly folded sillimanite-garnet gneisses with subordinate thin quartzite beds. These contain numerous folded sills of augen gneiss (granite), amphibolite (gabbro), and pegmatite. Post-folding peridotite, granite and pegmatite occur. Probably after considerable uplift and erosion, thin dykes of diabase (dolerite) were intruded, then pegmatite dykes and silicifying solutions, and finally ore-bearing solutions. The folds of the region are tight; steeply inclined, and extremely complex structures resulting from plastic deformation. Individual minor folds were studied in great detail by a method of axial-plane and axial-line analysis. An angular relationship exists between minor and major folds due to strain under torsional stresses. The regional pitch is flatly south. However, sudden reversals of pitch and divergences of pitch in adjacent folds are common. Second-order folds or folded folds exist. Cutting and offsetting the folds are buckles with vertical axes and crush zones of schisted rocks resulting from post-folding but pre-ore faulting movements. The lode occurs in a belt of attenuation between a wide arch on the west and a wide basin on the east. It consists of ma3sive lead-zinc-sulphide replacement orebodies forming (before erosion) a long continuous, irregular, flat, curving pencil of ore, 2,000 to 3,000 feet high and 300 feet thick. In longitudinal section it describes a flat arc pitching downward at each end. The lead lodes resulted from the selective replacement of two closely adjacent, highly folded, favourable beds. Each lode is distinguishable by its gangue mineralogy and metal ratios. No.3 Lens (the lower) has fluoritic rhodonitic gangue and comparatively high Zn:Pb and Ag:Pb ratios. No. 2 Lens, the upper, has calcitic gangue and comparatively low Zn :Pb and Ag :Pb ratios. At least three zinc lodes, with similar mineralogy, occur at higher stratigraphic horizons at the south end of the field. There is little observable zoning. Ore solutions are believed to have migrated up the regional pitch from the south. Intra-mineralization fracturing helped to localize ore shoots within favourable formations.

The area tested by drilling comprises approximately 30 acres of the Parish of Cullen Bullen in the County of Roxburgh, and is immediately to the east of the Portland-Mudgee railway line about 1.5 miles northward from Cullen Bullen Station. The purpose of drilling was to test the Irondale and Lithgow seams of the Upper Coal-Measures for thickness and quality, and thus determine whether or not the more detailed investigation of proving is warranted. Seven holes, with an average depth of 116 feet, were drilled by Goldfields Diamond Drilling Co. under contract to the bureau of near sites chosen by the Geological Survey of N.S.W. The total footage drilled was 810 feet and coal-core recovery averaged 89%. Core drilling in the Tyldesley Area has indicated the presence of 41,000 tons of banded high-ash coal in the lower split of the Lithgow Seam. The coal is considered unsuitable for exploitation by open cut methods and a proving campaign is not recommended.

This statement sets out the results of drilling by the Bureau within Swansea Sub-area N.S.W. (J.B.C. plan BG-4). The area investigated comprises approximately 115 acres, about 2 miles south of the township of Swansea in the parish of Wallarah, Country Northumberland. In the Swansea area 'test and define' core drilling by the Bureau has indicated coal reserves of approximately 302,000 tons within the physical limits required for open cut exploitation. This total is made up of more than 87,000 tons in the "Open Cut Block" and 215,000 tons in the "West Block". Proving is recommended for the open cut Block and for the West Block, except that in the latter area the obstruction which will be offered to open cutting by the presence of the P.M.G. cable should be considered before proving is undertaken.