Series of information sheets designed to provide landholders and local community with information regarding the activities being underatken as part of the Southern Thomson pre-competitive geoscience project, run in collaboration with the Queensland and New South Wales State Geological Surveys.

In January 1974 aerial observations were made of the very severe flooding which occurred in the low-gradient plains country adjacent to the southern Gulf of Carpentaria. Floodwaters were derived from two sources, the extensive river channel network throughout the plains mostly carried silty water which originated from hinterland regions, while the plains surfaces were flooded with clear water derived from local rainstorms. Runoff of clear storm water caused active erosion around peripheries of planar interfluves on the clay plains. There was generally no flood- water erosion or deposition in the sandy plains. Flooding was extensive on tidal mudflat areas, particularly behind beach ridge remnants which inhibited runoff. Despite the severity of flooding, the overall lack of erosion and overbank flooding suggests that landforms of the fluviatile plains were developed under conditions of greater runoff than prevail during normal wet-season flooding. The major landform features were probably developed In the Late Pleistocene and have not been substantially modified since then.

The reefs of the Capricorn-Bunker Group in the southern Great Barrier Reef were the focus of a Bureau of Mineral Resources survey in September-October 1976. Subaerial and submarine exploration of seven reefs was conducted (Figure 1). The objectives of the expedition were: 1. To define the depth, shape and origin of the surface on which the present reefs rest. 2. To determine the effects of the present-day hydrologic regime on the growth of the reefs. 3. To define the time framework of modern growth. 4. To study the physical and chemical changes involved in the reef lithification processes. 5. To estimate the potential for metal accumulation of reef sediments and to determine the time of removal and deposition of metals in the carbonate sequence. The M. V. Escape was chartered from Gladstone to provide the platform for field studies. Shallow seismic refraction, echo profiling, underwater investigations using SCUBA, underwater coring, current, wave and water monitoring studies, and sediment sampling of lagoons were the principal field operations. Eighty-eight shallow seismic refraction traverses, each 120 m in length, were conducted using a Huntec FS-3 facsimile seismograph with a hammer or detonator sound source, and two subminiature land geophones or one pressure-sensitive hydrophone. The profiles cover windward and leeward algal ridges, cays, and in one case a lagoon and a lagoonal patch reef (One Tree Reef). This paper records field data and observations with the major emphasis placed on data relating to the morphologic growth of reefs. No attempt is made at this stage to present evidence relating to lithification or to processes and products of metal accumulation.

The tectonic evolution of the fault-bounded volcanic-sedimentary Leichhardt River fault trough is reinterpreted in the light of detailed mapping of a part of this structure. Two major unconformities are indicated, the first above the Kalkadoon-Leichhardt acid igneous complex, and the second at the base of the ore-bearing Mount Isa Group and its equivalents - the Mingera and Surprise Creek Beds. A complex succession of movements is indicated, involving (1) early faulting of the Kalkadoon-Leichhardt acid igneous complex; (2) long-acting penecontemporaneous faulting; (3) folding and uplift accompanying or post-dating emplacement of Sybella Granite, and (4) a younger major faulting phase. During phase (2) syndepositional block movements resulted in differential accumulation of volcanic flows and of sediments, reflected by abrupt thickness changes across faults. In other instances the observed thickness variations can be explained by strike faulting of lenticular sedimentary units. Basic dyke swarms which intrude the volcanic- sedimentary sequence of the Leichhardt River fault trough have postdated the folding and predated the major faulting event defined as phase (4). The Sybella Granite, thought by some workers to be younger than the Mount Isa Group on the basis of structure and lead isotope ratios, is considered by us to be older than this unit. The ore lead in the Mount Isa deposit could be related to erosion or leaching of lead from older rocks such as the Kalkadoon-Leichhardt basement complex and the Eastern Creek Volcanics. An age of between I500-1600 m.y. is indicated for the syngenetic lead deposit at Mount Isa. The Eastern Creek Volcanics show very high Pb relative to average basalt, and high Cu, Zn and Pb levels relative to other basic volcanic rocks in this region, and may have a genetic relation to the Mount Isa Cu and Ag-Pb-Zn ore deposits. Geochemical features of basalts of the Eastern Creek Volcanics are consistent with those of continental flood tholeiites, showing high FeO, FeO/ MgO ratios, TiO2, K2O, P2O5, Ba and Rb and low Al2O3. Structural, sedimentological and geochemical changes between the Mount Isa area and the CIoncurry area to the east - where ocean floor type tholeiites occur - can be interpreted in terms of a transition into a continental margin environment in this direction.

Orientation geochemical studies indicate that stream-sediment sampling is a potentially powerful exploration technique in the Westmoreland region of Northern Australia. Uranium, copper, tin, and lead mineralization can all be detected by the use of a combination of sieved samples and heavy-mineral concentrates. Vein-type uranium deposits occur in a variety of rock units in the area. The secondary dispersion of uranium from these deposits appears to be dominantly chemical, and sieved samples are very effective in prospecting; heavy-mineral concentrates rarely contain detrital uranium minerals and consequently are less efficient. Arsenic is a useful pathfinder element for uranium mineralization in some instances. Copper deposits are encountered in both the granites and the basic igneous rocks of the area. Heavy-mineral concentrates are particularly sensitive in tracing copper mineralization. At several localities no anomalous copper was detected chemically in sieved samples, whereas malachite was conspicuous among the heavy minerals. Tin deposits occur in pneumatolytically altered zones within high-level granites and acid volcanic rocks. The chemical analysis of sieved samples and the optical examination of heavy-mineral concentrates for cassiterite are equally effective in prospecting for tin. If sieved samples are preferred, lithium and tungsten are useful pathfinder elements. Lead mineralization of syngenetic origin is associated with the dolomitic rocks of the region. The analysis of heavy-mineral concentrates appears to have great potential in exploration for this type of deposit, but the technique has yet to be fully evaluated. Near mineralization sieved samples contain anomalous lead and zinc; minor enrichment of copper also occurs. Scavenging by secondary manganese compounds leads in places to false zinc anomalies, so great care is required in the interpretation of anomalous zinc values.

Q-mode factor analysis classified the estuarine samples from Broad Sound into two main geologically distinct groups representing intertidal and supratidal deposition. This classification was supported statistically by stepwise discriminant analysis, and mathematically by Q-technique canonical correlation analysis. Analysis of variance was useful in identifying significant error with some of the measured variables, and proving the stability of the pH and Eh readings over time. Using R-mode factor analysis, with the associated correlation coefficients, and stepwise regression analysis, the various processes controlling the concentration of P2O5, Cu, Pb and Zn, in the supratidal and intertidal sediments are identified. Although Cu, Pb, and Zn are mainly deposited in both supratidal and intertidal zones adsorbed onto iron hydroxide colloids, the three trace elements (but especially Pb) are released with decreasing pH and Eh in the intertidal zone and form metal sulphides or metallo-organic complexes. The reduced iron is also redeposited as iron sulphide. Under supratidal oxidizing conditions the Cu and Zn remain attached to the iron colloids but Pb is released with increasing acidity. The absorption of P2O5 on clay particles increases with acidity in the intertidal zone, but P2O5 is mainly associated with organic carbon in the supratidal sediments.

Two sets of beach ridges are known from the western side of Cape York Peninsula. The older set are thought to be late Pleistocene. They rest on a basement of older fan deposits and are regarded as a regressive sequence of barrier islands. The younger ridges represent a progradational sequence post-dating the Holocene transgression. The earliest formed ridge, which is poorly developed, formed as a chenier. It was followed by a barrier island complex whose development lasted until about 3000 years B.P. Subsequently, there was rapid progradation and the development of two sets of chenier-type beach ridges, the younger of which is locally discordant to the ridges of the barrier island complex. These ridges rest on a marine sand and mud unit which appears continuous with a similar unit mapped offshore. The Pleistocene ridges consist of quartzose sand, with negligible carbonate, while the Holocene ridges consist of quartzose sand, shell sand and shells. They show a progressive leaching with age.

On the western side of Cape York Peninsula, north Queensland (Fig. 1), in the Weipa-Aurukum area, surface water supplies are seasonal, and mining and pastoral development relies on the availability of groundwater. Artesian water is obtainable from the Mesozoic sandstone units of the Carpentaria Basin throughout the area, but the water is slightly saline (1000 ppm total dissolved salts) and unacceptably high in fluorine (around 15 ppm). Domestic and stock water is taken almost entirely from shallow aquifers within the late Cretaceous or early Tertiary Bulimba Formation, which underlies most of the area and supplies all the domestic and some of the processing water at Weipa and the domestic and irrigation water at Aurukun Mission. Because of the variable permeability of the Bulimba Formation pattern drilling is expensive for groundwater investigations on a large scale; in the area studied drilling alone had a 1 in 35 success rate. There is a need for a cheap reconnaissance geophysical method to locate favourable areas for drilling. The purpose of this note is to describe a resistivity traversing technique, supported by drilling, which was developed in a detailed geophysical and geological study (Pettifer et al., 1976) of a test area between Weipa and Aurukum, and to outline some interesting aspects of the use of resistivity methods in this type of environment.

One Tree Reef is one of fourteen reefs in the Capricorn Group, southern Great Barrier Reef. The reef has an asymmetrical triangular shape, 5.5 km long and 3 km wide, with a small coral shingle cay on the southeastern corner. One Tree Reef evolved from a karst carbonate platform, now 10 to 25m below sea level, but emergent during the last sea-level low before 9600-9000 years B.P. With rising sea level, vertical organic accretion was dominant, although there was some lateral accretion on the higher southeastern corner. By 4400 years B.P. the reef grew up into the influence of the present wind-induced southeasterly wave regime. Present reef shape approximates a bow of a ship facing into wind, with the resultant wave refraction and diffraction producing a symmetrical energy pattern which has influenced the present sediment pattern. This pattern is symmetrical about a lagoonal axis of interaction of wave fronts. Present lagoonal sedimentation is controlled by flood tide and swash or wave surge transport, swash sorting and slack water periods when sediment in suspension is deposited.

The Mary Kathleen uranium deposit in northwest Queensland is contained in west-dipping middle Proterozoic calcareous, dolomitic and alkali-rich metasediments of the Corella Formation, which are metamorphosed to hornblende hornfels grade by the Burstall Granite, and are also intruded by a swarm of rhyolite and microgranite dykes associated with this granite. An early, higher temperature metasomatic event has formed K feldspar-rich and scapolite-pyroxene bands from the original metasediments; a later lower temperature metasomatic event has resulted in extensive garnetization and skarn replacement of earlier formed rocks, and uraninite-allanite mineralization. Fluids associated with this second event appear to be enriched in Na, Cl, H2O, O, U and rare earths, and are spatially and probably genetically related to the rhyolite dyke swarm. This is supported by the high uranium content of the dykes (12 ppm average) compared to that in Burstall Granite (7 ppm), metasediments (3.5 ppm), quartzite (1 ppm) and basic rocks (0.7 ppm). Uranium-rich fluids moved westwards from the dykes, following decreasing temperature gradients. They were impeded in most places by a chemically inert layer of quartzite, but breached this barrier in at least two places and intersected a sequence containing permeable lenses of conglomerate, within which the broadly stratabound orebody was deposited. Similar orebodies could be expected in the vicinity of other permeable zones stratigraphically above quartzite and adjacent to fractures and acid dykes, but such sites appear to have been removed by faulting and erosion. However, fractured areas of the quartzite hanging wall (i.e. the eastern side of the quartzite), in the vicinity of rhyolite dykes, could also be sites of economic uranium mineralization at depth.