Gibsonvale tin field is situated approximately three miles southeast of the village of Kikoira. This preliminary report was prepared following an examination of the tin field by the writer. Aspects of the general and economic geology of the field are discussed herein.

The Flowery Gully Limestone Deposit, twenty miles north of Launceston, was surveyed in detail to delineate the most suitable portions for supplying limestone to the Australian Aluminium Production Commission's plant at Bell Bay, five miles to the north east across the Tamar Estuary. Basic requirements for the limestone were that it lie in an area suitable for quarrying and have as low a silica and magnesium carbonate content as possible so that it could be used efficiently in the aluminium extraction process. The preliminary reconnaissance revealed a stratigraphical chemical control and it was found possible to divide the section measuring 1,700 feet in true thickness into three stratigraphical zones, the topmost of which contains the purest limestone and is most suitable for Bell Bay; the middle zone contains isolated areas of high quality stone. The more detailed survey to reveal quarryable stone in these two zones defined one major and one minor deposit in the upper zone and one minor deposit in the middle. These three deposits contain indicated and inferred reserves totalling 1,000,000 tons; of this figure 100,000 tons has an average grade of 0.4% silica and 5.7% magnesium carbonate and the remainder has a grade not exceeding 0.5% silica and 4% magnesium carbonate. The investigation of the depositional environment revealed quiet and consistent conditions of deposition, which information was used to indicate possible areas for exploration for additional reserves when necessary. Numerous bedded chert nodules are present in the high-silica-content areas of the middle zone. The origin of the silica of this zone was investigated chemically and petrologically, but the results were inconclusive. It was discovered however that practically all silica was syngenetic. It is now mainly in the form of quartz grains and in smaller amounts as a component of the small percentage of clay present; however where chert nodules are present the silica of the cherts is in the form of chalcedony. Areas of marked dolomitization were noted, particularly in the upper and middle zones; they probably represent algal reefs (stromatoporoid bioherms). One of them had a lateral extent of at least 1,600 feet. A distinct disconformity was revealed by the detailed mapping at the top of the limestone section.

This report is an account of geological and geophysical investigations of the Burrundie Radioactive Prospect, which is located three and a half miles west-south-west of Burrundie Siding on the North Australian Railway.

A reconnaissance survey of the eastern half of the Canberra 4-mile sheet was made during the period January - February 1952. The area mapped may be arbitrarily divided into two sections: the western section includes the eastern halves of the Canberra, Michelago, and Bredbo 1-mile sheets, and the eastern section comprises four 1-mile sheets - Lake Bathurst, Braidwood, Araluen and Bendethera. Belts of strongly folded Ordovician, Silurian and Devonian strata, with associated elongate masses of granite rocks, were encountered; they trend gradually northwards. Graptolites collected from Ordovician strata provide means to date these rocks accurately, and further study of the corals collected from Silurian limestones will similarly permit precise dating. Three fossil localities were found in the Devonian strata, but the brachiopods collected, although well-preserved and representative of many genera, do not permit precise stratigraphical placing without more intensive examination. Outcrops are generally very good in all parts except the Lake Bathurst area, where an extensive cover of Tertiary and later deposits obscures the Palaeozoic rocks.

A significant proportion of the mineral endowment of eastern Australia is related to Phanerozoic granites and comagmatic volcanic rocks. Accordingly, considerable scientific research and data gathering has been focussed on these magmatic systems within eastern Australia, over the last 15 years. A major outcome has been the recognition that the nature and style of this mineralisation (porphyry Cu-Au, porphyry Cu-Mo, vein-style W, Mo, Sn, Au) clearly varies with both the mineralogy and chemistry of the related magmatism (e.g., Blevin & Chappell, 1992). Further research is increasingly recognising that the development of mineralisation, is controlled by many factors other than just the chemistry and intensive parameters intrinsic to the magmatic systems. Wall rock controls, such as oxidation state, chemical reactivity, competency, porosity and structural preparation, are now considered critical as to whether mineralisation will form. The mineralogical composition of the host rocks also appears important; certainly playing an important role in metal precipitation, e.g., many deposits are hosted by rocks rich in reductants such as magnetite, graphite and/or sulphide. Interestingly, empirical data also indicate that deposit types may be host rock specific, e.g., Haynes (2003) suggests Fe-oxide Cu-Au and porphyry Cu deposits are found in settings where host rocks contain little or no reduced carbon minerals (e.g., graphite); conversely, Wyborn (2003) suggests Au-only deposits occur where host rocks are carbonaceous. The potential for host rocks to play a significant role in the mineralising environment is clear, even more so when it is considered that mineralisation may occur up to 2-3 km from the granite body (ref). Unfortunately, previous studies of magmatism and related metallogenesis in eastern Australia have largely ignored country rocks and their role, beyond simple criteria such as level of emplacement and level of exhumation.

Proterozoic Granites in Australia crop out over at least 145 000 km2 (Table 1). To assess their metallogenic potential a systematic study was undertaken of all granites as well as the composition of rocks within five kilometres of the granite boundaries (Budd et al., 2001). For the granites, data on the field characteristics (presence of alteration, miarolitic cavities, presence or absence of pegmatites etc) as well as the mineralogical, major and trace element compositions of the granites were compiled. Individual granite plutons were then aggregated into suites and Supersuites on a province basis. Data were also assembled on the mineralogical composition of the host rocks, specifically the presence of reactive minerals such as carbonate, carbon, feldspar, magnetite and hematite. A GIS was constructed of all data, and simply proximity analysis was used to intersect the granite plutons as well as 5 km buffers around each pluton with known mineral deposits and occurrences. The commodities and ore deposit types were recorded around each pluton. Each occurrence was checked to ensure its age was ? the age of the related intrusion. On the basis of similarities between Suites/Supersuites of different provinces nine granite associations were identified based on their chemical characteristics, pressure/temperature conditions in their source region and their associated metallogeny. Due to insufficient data, 8.3% of exposed Australian Proterozoic granites could not be classified (Table 1). The differences between each Association and its metallogeny is believed to be controlled by first order differences in temperature and pressure conditions in their source regions. Second order changes that also influenced metallogeny, are imposed by interaction with their host rocks.

Chemical modeling of gold mineralisation in the Lachlan Fold Belt shows that gold can be precipitated over a wide temperature range (from 320 to 200 ?C in this study) from CO2-bearing, low salinity, aqueous fluid flowing upwards through faults in turbiditic sequences. In agreement with field observations, the veins are predicted to be mostly quartz (> 93 vol.%) with minor amounts of pyrite, arsenopyrite and muscovite (sericite) precipitating above 230 ?C. The predicted alteration assemblage contains pyrite, arsenopyrite, calcite, muscovite (sericite), chlorite and feldspar. Varying some of the chemical characteristics of the initial fluid has resulted in the following changes to the model: Preventing the fluid from boiling stops gold precipitating below 310 ?C but has little effect on the vein mineralogy or the mineralogy of the surrounding alteration assemblage. Removing CO2 from the fluid also prevents gold precipitation in the veins below 300 ?C. The modeling also generates an alteration assemblage with a number of Ca-rich minerals as less calcium carbonate exists in this system. Removing sulfur species from the initial fluid decreases the amount of gold precipitated by more than a factor of ten, which is to be expected if sulfur ligands are the main species for gold transport. However, the vein assemblage and the lack of sulfide minerals in the surrounding alteration assemblage also suggest that sulfur species are important in this mineral system. Increasing the initial oxidation state (?O2) of the fluid inhibits gold precipitation in the veins above 260 ?C and leads to a high proportion of dolomite in the surrounding alteration assemblage. On the other hand, decreasing the initial oxidation state of the fluid lead to gold precipitation over a range of temperatures below 310 ?C but predicts that mainly graphite ? quartz precipitates in the veins and that the surrounding alteration assemblage is dominated by feldspar proximal to the veins. This style of mineralogy is not commonly observed in gold deposits in the Lachlan Fold Belt. Increasing the initial pH of the fluid inhibits the amount of minerals that precipitate in the veins, which are dominated by calcite at high temperatures and graphite at low temperatures and corresponding minor amounts of gold. The proximal alteration assemblage is dominated by K-feldspar with amphibole, biotite and epidote. This mineral assemblage is not commonly observed in these deposits. Decreasing the initial pH of the fluid allows gold to precipitate below 280 ?C but generates a proximal alteration assemblage dominated by pyrophyllite, which again is not commonly observed. The results are in agreement with the widely accepted premise that gold is transported as bisulfide complexes and that the ore-bearing fluid is typically a low-salinity, mixed aqueous-carbonic fluid with low-moderate CO2 contents (Ridley and Diamond, 2000). However, the modeling has shown that the absence of certain physico-chemical processes or fluid constituents, such as boiling or lack of CO2 may inhibit gold precipitation in some environments. Large fluctuations in ?O2 or pH will also significantly change the vein and alteration mineralogy and generally reduce the amount of gold that is precipitated. This suggests that these fluids remain rock buffered during their journey from the source to the trap site.

Models for the crustal evolution of the Yilgarn Craton have changed in the last 25 years from generally autochthonous greenstone development on sialic crust (Gee et al. 1981, Groves & Batt 1984) to alloch-thonous models that highlight the importance of accretionary tectonics (Myers 1995). Recent models highlight the importance of mantle plumes and long-lived convergent margins for both Au and Ni (Barley et al. 1998). The role of sialic crust in the development of the abundant mineral systems in the Yilgarn, and Archaean cratons in general, however, remains problematic. Felsic rocks from across the Yilgarn Craton are used as crustal probes, with their geochronology, zircon inheritance and Nd isotopic character used to constrain the age and extent of basement terranes. The studies reveal a collage of crustal fragments and implicate both autochthonous and allochthonous crustal development, with increasing importance of accretionary tectonics, particularly after 2.8 Ga. The crustal evolution places significant constraints on the development of metallogenic associations.

The authors were engaged in geological reconnaissance work in the Fitzroy Crossing - Halls Creek area, during the period 16th August to 23rd September, 1948. The principal object of the investigation was to examine the area covered by the Mt. Ramsay Sheet of the Army Series. Work was extended beyond the limits of this sheet however in order to obtain information with regard to the age relationship of some formations, and a visit was made to the Wolf Creek Meteorite Crater 63 miles south of Halls Creek. During the survey, work was concentrated chiefly in mapping the distribution of rocks and different geological periods, determining their relationships and economic possibilities, and recognising areas warranting more detailed investigations. Accompanying geological plans and aerial photographs are included.

The Kowan District occupies the north-eastern lobe of the A.C.T., to the north-east of Queanbeyan. The purpose of the survey was to determine the general geology and structure of the Kowen District as part of a planned mapping of the whole of the A.C.T. In addition a search was made for commercial occurrences of rock suitable for use as a building stone. Field work was extended over most of January and February, 1949. Igneous intrusions were plotted directly onto aerial photographs where possible. Strikes of beds and faults and other suitable information were measured by prismatic compass and dips and pitches were measured by Abney level or clinometer compass. Information was then plotted on a Federal Territory feature map. A full account of this survey work and its findings is given in this report. Descriptions of specimens and geological plans of the district are appended.