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.

Deep basement cores from petroleum and stratigraphic drill holes through central and southwest Queensland show that the subsurface Thomson Orogen is dominated by monotonous metasedimentary units but also includes scattered felsic volcanic rocks and more abundant (locally batholithic-scale) intrusions. These igneous rocks and small granitoid exposures along the Eulo Ridge provide means of probing the deeper crustal composition and the geological evolution of this vast area that is mostly covered by deep sedimentary basins.

Analysis of the distribution patterns of Pb isotope data from mineralised samples using the plumbotectonic model of Carr et al. (1995) indicates systematic patterns that reflect major metallogenic and tectonic boundaries in the Lachlan and Delamerian orogens in New South Wales and Victoria. This distribution pattern accurately maps the boundary between the Central and Eastern Lachlan. The Central Lachlan is characterised by Pb isotope characteristics with a strong crustal signature, whereas the Eastern Lachlan is characterised by a variable signature. The Macquarie Arc is dominated by Pb with a mantle signature: known porphyry Cu-Au and epithermal Au-Cu deposits in the arc are associated with a zone characterised by the strongest mantle signatures. In contrast, granite-related Sn deposits in the Central Lachlan are characterised by the strongest crustal signatures. The Pb isotope patterns are broadly similar to Nd isotope model age patterns derived from felsic magmatic rocks, although a lower density of Nd isotope analyses makes direct comparison problematic. Comparison of Pb isotope data from the Girilambone district (e.g., Tritton, Murrawombie and Avoca Tank deposits) with that from the Cobar district in north central New South Wales indicates a less radiogenic signature, and probably older age, for deposits in the Girilambone district. Hence, a syngenetic volcanic-hosted massive sulphide origin for these deposits is preferred over a syn-tectonic origin. The data are also consistent with formation of the Girilambone district in a back-arc basin inboard from the earliest phase of the Macquarie Arc. From the AIG Bulletin

Integration of potential field derived architectural maps and mineral deposits in the Tasmanides

Magnetotelluric techniques have been used to investigate structural trends in the McArthur Basin . Observations were made at 34 sites, extending 450 km across the Wearyan Shelf, the Batten Fault Zone, and the Bauhinia Shelf. For sites on the Wearyan Shelf, the orthogonal components of resistivity are generally similar, suggesting continuous horizontal strata and uniform basement depths. However, lateral changes in resistivity, evident on the Bauhinia Shelf, become extreme in the Batten Trough. For sites near the Emu Fault, the two components diverge at long periods, indicating a major change in structure with a pronounced vertical contact. Resistivities associated with the Tawallah Group appear distinct enough to show that no appreciable thickness of McArthur Group can be present east of the Emu Fault. The data are consistent with geological models based on the assumption that the Batten Trough formed as a syndepositional graben with rapid changes in depositional thickness at the boundary faults.

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.

The middle Miocene macropodoids of the Riversleigh, Bullock Creek, and Kangaroo Well local faunas are the oldest recorded assemblages of kangaroos. Five new species are described here. One, Bulungamaya delicata n. gen. and sp., is placed with Wabularoo naughtoni Archer, 1979 in the new potoroid subfamily Bulungamayinae. Gumardee pascua Ii n. gen. and sp. is placed within the Potoroinae. Balbaroo camfieldensis n. gen. and sp. and Balbaroo gregoriensis n. sp. are placed in a new macropodid subfamily, the Balbarinae. Galanarla tessel/ala n. gen. and sp. is placed in the Macropodidae , but cannot as yet be assigned to a particular subfamily. All the new species are from the Riversleigh local fauna, except B. camfieldensis from the Bullock Creek local fauna. The previously known Kangaroo Well macropodid appears to be referable to the genus Balbaroo. The Bulungamayinae is represented by forms which, although related to potoroines, have bulbous premolars and lophodont molars. The Balbarinae includes generally plesiomorphic forms that may have been ancestral to other macropodids. None of the macropodoid genera described here are known from more recent deposits. This suggests that a radical transition in the dominant kinds of macropodoids took place between middle and late Miocene times.

The Proterozoic I-type Kalkadoon and Ewen Batholiths and their comagmatic extrusive equivalents, the Leichhardt suite, form an association covering at least 5000 km2 in the central part of the Mount Isa Inlier. U-Pb zircon data and some Rb-Sr total rock data show that these rocks crystallised from melts emplaced between 1840 and 1870 m.y. ago and are the oldest dated igneous rocks in the Inlier. Chemically and isotopically, these granites are relatively uniform and, compared with most other Mount Isa granites , they have higher Sr and Al2O3 contents, and lower TiO2 , Zr, Nb, and Th contents . These chemical characteristics appear to be restricted to felsic igneous rocks known to be older than 1800 m .y. and may be useful in identifying the older felsic melts of the Mount Isa Inlier. The source for the rocks of the Kalkadoon- Ewen- Leichhardt association is estimated to have had an SiO2 content of 55-60 per cent. Relative to other large Palaeozoic and Mesozoic I-type batholiths elsewhere, this Mount Isa association is enriched in K20, Rb, Th, U, La, Ce, Zr, and Nb, and depleted in CaO, MgO, Ni, and Cr. The least isotopically disturbed granites of the association have relatively low initial 87Sr/86Sr ratios (about 0.704), which implies that the age of the source for these melts was not much older than the age of their emplacement. As chemically and isotopically similar granites occur in most Proterozoic areas of Northern Australia, it is inferred that during the period 1900-2100 m.y. a significant mantle differentiation event took place, during which large volumes of material were accreted to the base of the crust in these areas. Post-emplacement metamorphism and deformation , which have a maximum age of 1640 m.y. , caused significant textural and mineralogical changes in the Kalkadoon Batholith, but had a lesser effect on the Ewen Batholith . Igneous textures are commonly preserved in the Ewen Batholith, but the Kalkadoon Batholith, which has been metamorphosed from lower greenschist to upper amphibolite grade, shows significant isotopic disturbances.

Discussion is around the renaming of the Corella Formation (introduction of the name Doherty Formation), and potential down-grade of its status to beds.

The Poodyea Formation, comprising boulder conglomerate, cross-stratified sandy conglomerate and pebbly sandstone, crops out as narrow linear and sinuous belts of small outliers within and to the south of the Toko Range, in the Georgina Basin, western Queensland and Northern Territory. The outliers are confined to present-day narrow valleys in the Carlo Sandstone, corresponding closely to either the Toko Syncline axis or cross-cutting structures, and form low linear ridges over plains of Mithaka Formation. The Poodyea Formation is considered to be of probable Tertiary age, and represents a river-channel deposit derived from reworking of parts of the Mesozoic, Palaeozoic, and Proterozoic sequences. In the past, outcrops of the formation have been included in Palaeozoic units. The formation is discussed and defined.