Correlations within the Proterozoic succession are complicated by repetitions of similar rock types at different stratigraphic levels, especially acid and basic volcanics, quartz sandstones, and calcareous rocks, and also by disconformities, igneous intrusions of various ages, tight to isoclinal folding, intense faulting, regional metamorphic effects, and scarcity of reliable isotopic age data. Consequently, there is plenty of scope for alternative interpretations. The interpretation proposed is that instead of equivalent sequences of cover rocks, known as the western and eastern successions, being separated by a narrow basement belt, as suggested previously for the Proterozoic Mount Isa Inlier, the oldest cover rocks in the west, those of the Haslingden Group, pre-date the eastern succession, and basic lavas (Eastern Creek Volcanics) within this group have no correlatives to the east. It is also suggested that volcanics previously regarded as part of the basement (Magna Lynn Metabasalt and Argylla Formation) are younger than most of the Haslingden Group, and that the extensive calcareous Corella Formation represents at least two quite separate units, one being younger than the Haslingden Group, and one being part of the underlying basement. These suggestions are consistent with U-Pb zircon dating carried out to date, as well as with the field evidence.

Thelodont scales recovered from the basal (calcareous) unit of the Cravens Peak Beds in the Georgina Basin, are referable to Turinia australiensis Gross, 1971, T. cf. pagei (Powrie, 1870), and Gampsolepis ? sp. undet. The thelodonts probably lived in a marginal marine environment (as evidenced from the associated ostracods and eridostracans) at about the same time as the placoderm Wuttagoonaspis sp. lived in the freshwater bodies, now represented by the sandstone and conglomerate facies of the Cravens Peak Beds. Scales of Turinia australiensis Gross, 1971, associated with Wuttagoonaspis plates, from the lower part of the Mulga Downs Group in the Cobar/Wilcannia area of New South Wales, are at least as young as late Early Devonian (Emsian), because they post-date the Pragian age of the underlying Amphitheatre Group. By correlation, those parts of the Cravens Peak Beds (Georgina Basin) and the Tandalgoo Red Beds (Canning Basin) that also contain Turinia australiensis are approximately coeval. After reaching Australia in Early Devonian time, the Turinia fauna began an adaptive radiation to give apparently younger (Middle Devonian) stocks that have survived longer in the Australian region than elsewhere, as the youngest known scales come from the Gneudna Formation (Iatest Givetian-earliest Frasnian) in the Carnarvon Basin, Western Australia.

The Phyllis May prospect is about 29 km west of Georgetown, north Queensland (Fig. 1). It was discovered in 1970 during geological prospecting by Central Coast Exploration NL, and it was soon established that the deposit was of the porphyry-copper type (ORourke, 1971). In 1975 evidence of similar mineralisation was recognised at Mount Turner, 11 km west-northwest of Georgetown (Fig. 1), by officers of the Bureau of Mineral Resources and the Geological Survey of Queensland. Stream-sediment sampling was carried out in the two areas during 1976 to test the applicability of this technique for detecting similar deposits in other parts of the region.

In this discussion of Blake (1980) we focus on three major points: (1) Relations between the Tewinga Group, Bottletree Formation, and Haslingden Group; (2) Incorporation of some Corella Formation carbonates in 1860 m.y. old basement rocks of the Tewinga Group; (3) Unconformities.

Grimes and Doutch (1978) have identified five predominantly alluvial stages in the depositional landforms of the Carpentaria Plains. In the light of the factors which they consider to be the most likely controls on the evolution of the plains, they suggest a correlation between these stages, sea-level, climatic changes, and other depositional sequences in Queensland.

Wasson (1979) discusses our interpretation and correlation of the fluvial sequence in the Carpentaria Plains (Grimes and Doutch, 1978). His main criticisms are: (1) he considers that we have insufficient stratigraphic data to substantiate our division of the fans sequence into five stages and to support our correlation of these stages with the sequence in the southern plains; (2) he criticises the brevity of our discussion of climatic and sea levels controls on the evolution of the fans and our apparent exclusion of tectonic effects, and would seem to consider that the shifts in the depositional areas of the fans are not related to environmental changes; (3) in view of his doubts concerning the above points, he considers that the regional correlations which we suggested are suspect and that the fans provide a poor basis for attempting such correlations. We will discuss these points in sequence.

The major gravity anomalies in central and western Australia occur as elongate dipoles, either in isolation or in a series. Each dipole is thought to be caused by an abrupt change in mean crustal density at the junction of two crustal blocks and by the associated isostatically compensating masses. Typically one block has along its margin a strip with anomalously high mean crustal density, and the other block has normal density crust covered by several kilometres of low density sediment. The observed anomalies are consistent with the anomalous masses being isostatically compensated by variations in the thickness of the crust, the crustal thickness variations being gradual and extending to about 100 km from the boundaries of the anomalous bodies. The crustal block boundaries inferred from dipole anomalies correspond in position with the crustal block boundaries inferred from geology, and approximately with the position of block boundaries inferred from changes in the gravity trend pattern. Usually the block with younger basement has high density material along its margin, and the other, older block is covered with sediment; both these features are likely to be caused by the process that created or emplaced the younger block. The presence of relatively dense material high in the crust along the margins of the younger blocks suggests that younger blocks are not superficial features on a uniform old crust. The dipole anomalies on the Australian Precambrian crust are similar in magnitude and tectonic position to those recognised at Precambrian province boundaries in Canada.

Accurate modelling, using seismic and gravity data, has shown that the Donnybrook Gravity High in central Queensland is the result of a complex situation involving three discordant basins. The most significant is an old basin buried deep beneath the Drummond Basin and apparently deposited in a valley carved out of a thick sequence of Silver Hills Volcanics and related acid volcanics. The Drummond Basin wedges out westwards under the Galilee Basin and is bounded to the east by the same acid volcanics that subcrop near the Anakie Metamorphics. The illusion that the Donnybrook Gravity High is associated with the Donnybrook Anticline is the result of an intrabasement granite which introduces a large negative component, cancelling the western flank of a much broader gravity high. After the cancellation, the granite is represented by a low of only 30 ~m.s-2 The already complex situation is further complicated by a topographic feature that introduces ambiguity in the most crucial area of the interpretation . This factor demonstrates the need to combine density profiling with forward modelling.

Over the past five years, scientists of the Bureau of Mineral Resources and James Cook University of North Queensland have drilled 61 holes into 24 reefs throughout the Great Barrier Reef Province between 15°30S and 25°50S. Eleven holes penetrated to the Pleistocene and nearly 250 radiocarbon dates have been recorded. Analysis of drill-hole core has delineated five major biosedimentologic facies - coralline algal facies. coral-head framework facies, branching-coral framework facies, detrital carbonate facies, and detrital siliciclastic facies. Latitudinal uniformity in framework facies contrasts markedly with major regional variations in detrital facies, the reefs of the mid-shelf of the central region being dominated by clastic carbonates. Depositional rates of detrital carbonate facies vary between 1-4 m/1000 yr for sand flat progradation , 7-9 m/1000 yr for trade wind storm sedimentation, and 13-18 m/1000 yr for high-energy low-frequency events. Framework growth rates varv from 1- 16 m/1000yr with low rates (2 m/I000 yr) for coralline algae. intermediate rates (up to 7 ml 1000 yr) for coral head facies, and high rates (up to 16 m/lOOO yr) for branching frameworks. Rates of 8-12 m/1000 yr occur in all environments: modes of 7-8 m/1000 yr typify patch reefs , 4-6 m/1000 yr typify windward margins. and 3-9 m/1000 yr typify leeward margins. Fringing reefs usually grow at rates of 1-4 m/1000 yr and are dominated by coral-head facies. Depth to the Pleistocene is generally greater in the central region compared to the northern and southern reefs: reef initiation, however, began at the same time throughout the province (8-9000 yr B. P.). Initial reef growth lagged significantly behind sea-level rise, such that water depths of up to 12 m developed over reef surfaces prior to sea-level stabilisation. However, some reefs in the southern region exhibit no growth lag - initial colonisation and growth maintaining pace with sea-level rise. The growth rate of most reefs decreased markedly as reef surfaces approached stabilised sea level.

New chemical analyses of relatively low-grade metabasalt from the Eastern Creek Volcanics, 120-150 km north of Mount Isa, Queensland, show them to be continental tholeiites. A 2-stage model of fractional crystallisation is proposed to explain the major and trace element variation in the suite. The uncommonly high Cu content of the metabasalt (about 200 ppm) is attributed to concentration of an immiscible sulphide phase during fractionation. Examination of all available chemical data has led to the recognition of 5 types of alteration. The Cu content is depleted in metabasalts that are anomalously enriched in K2O, MgO, or CO2, but is not affected in metabasalt enriched in CaO or Na2O. This Cu depletion supports earlier models that attribute Cu mineralisation at Mount Isa to leaching of Cu from the Eastern Creek Volcanics and its redeposition in favourable pyritic, dolomitic sediments of the Mount Isa Group. The ore localisation has been associated with brecciation and appears to depend on the juxtaposition of the Mount Isa Group and the Eastern Creek Volcanics largely by faulting.