The Tarcoola goldfield in central South Australia is hosted by the Paleoproterozoic Paxton Granite and Tarcoola Formation metasedimentary rocks. Both of these units are intruded by narrow dikes of the Lady Jane Diorite, which is considered to be part of the Gawler Range-Hiltaba volcano-plutonic event. Crosscutting relationships and 40Ar/39Ar dating of alteration sericite and primary hornblende have demonstrated that veining, alteration, and mineralization occurred synchronously with intrusion of the diorite dikes at ~1580 Ma. Mineralization at the Perseverance deposit in the Tarcoola goldfield is hosted by quartz veins in both granite and the lower parts of the Tarcoola Formation. Alteration intensity and mineralization are related to fracture density. Very high gold grades (up to 270 ppm) are recorded in carbonaceous siltstones of the Tarcoola Formation.
Primary fluid inclusions from mineralized quartz veins at Perseverance are dominated by two-phase aqueous inclusions and three-phase H2O-CO2 (l) - CO2 (v) ± CH4 inclusions. Both inclusion types have salinities of <10 wt percent NaCl equiv, with evidence of other salts being present. Both types homogenize between 150° and ~340°C. They occur together in single quartz grains, which suggests the coexistence of aqueous and carbonic fluids. At the Perseverance deposit the maximum depth of fluid inclusion formation is estimated as 10 km. Processes resulting from pressure fluctuations during brittle fracturing causing phase separation are suggested to be the dominant gold precipitation mechanism, although definitive fluid inclusion evidence for either phase separation or fluid mixing is lacking. Wall-rock sulfidation may have also contributed to gold deposition.
Pb isotope compositions of galena from gold-bearing mineralized veins at Perseverance are similar to K-feldspar and whole-rock samples of the Paxton Granite. This is consistent with a common source of Pb and possibly other ore components for both the granite and galena, but not all potential reservoirs were tested. Variably altered and gold mineralized samples that had Paxton Granite precursors show a loss of Nd and a trend from eNd(1580Ma) values of about −6.2 in slightly altered samples toward more positive eNd values of about −3.3 in high-grade gold samples. Of the local lithologic units, the Lady Jane Diorite has eNd(1580Ma) values of about +0.1 and is the most probable source of the more primitive Nd isotope components in mineralized samples.
Mineralization in the Tarcoola goldfield has similarities to both orogenic and intrusion-related gold styles. The demonstrated coeval timing of diorite dikes and mineralization at Tarcoola, together with the Nd isotope constraints on metal sources, and the presence of similar mafic dikes in several other known gold prospects in the central Gawler gold province, suggests that the diorite was an essential part of the gold mineralization event throughout this province.
We have functionally analyzed the orthologous SRPN6 genes from Anopheles stephensi and Anopheles gambiae using phylogenetic, molecular, reverse genetic, and cell biological tools. The results strongly implicate SRPN6 in the innate immune response against Plasmodium . This gene belongs to a mosquito-specific gene cluster including three additional Anopheles serpins. SRPN6 expression is induced by Escherichia coli and both rodent and human malaria parasites. The gene is specifically expressed in midgut cells invaded by Plasmodium ookinetes and in circulating and attached hemocytes. Knockdown of SRPN6 expression by RNA interference in susceptible An. stephensi leads to substantially increased parasite numbers, whereas depletion in susceptible An. gambiae delays progression of parasite lysis without affecting the number of developing parasites. However, the An. gambiae SRPN6 knockdown increases the number of melanized parasites in the L3-5 refractory strain and in susceptible G3 mosquitoes depleted of CTL4 . These results indicate that AsSRPN6 is involved in the parasite-killing process, whereas AgSRPN6 acts on parasite clearance by inhibiting melanization and/or promoting parasite lysis. We propose that these observed phenotypic differences are due to changed roles of the respective target serine proteases in the two mosquito species.
The Tarcoola Goldfield is one of several districts included in the recently proposed central Gawler gold province. Understanding of the genesis of the deposits in this metallogenic province is in its infancy, and dating the age of alteration, mineralisation and microdiorite dyke intrusions has been carried out at Tarcoola as a first step towards developing mineral‐systems models for the province. At Tarcoola, four samples of sericite from alteration as well as one sample of hornblende from a microdiorite dyke yield 40 Ar/ 39 Ar ages of ca 1580 Ma. Geological and petrological relationships suggest that this age represents the time of fracture‐controlled Au mineralisation. These data provide evidence for coeval Au mineralisation, microdiorite dyke intrusion and local deformation. This mineralisation age is indistinguishable from U–Pb ages for the regional Gawler Range – Hiltaba volcano‐plutonic complex, and is more than 100 million years younger than the Paxton Granite, which is part‐host to the mineralisation. Possible temporal and genetic relationships with other deposits in the central Gawler gold province remain to be tested.
A new approach for developing a 3D temperature map of the Australian continent is currently being developed that relies on combining available proxy data using high-performance computing and large continental-scale datasets. The new modelling approach brings together the current national-scale knowledge contained in datasets collected by Geoscience Australia and others, including AusMoho, OZTemp, OzSeebase, OZCHEM, surface temperature, the Surface Geology of Australia, sedimentary basins’ thermal conductivity and the National Gravity Map of Australia. Bringing together such a range of datasets provides a geoscientific basis by which to estimate temperature in regions where direct observations are not available. Furthermore, the performance of computing facilities, such as the National Computational Infrastructure, is enabling insights into the nature of Australia’s geothermal resources which had not been previously available. This should include developing an understanding of the errors involved in such a study through the quantification of uncertainties. Currently the new approach is being run as a pilot study however, initial results are encouraging. The pilot study has been able to reproduce many observed temperature trends without using direct bore-hole temperature observations as an input into the modelling process. Furthermore, a number of regional areas have now been identified which may warrant further study.
Collaborative work is under way to develop an accessible method for rapid calculation of the spatial variation of temperature directly from a 3D geology model. The need for a tool of this nature stems from Australia?s emerging geothermal energy exploration and production industry. The prohibitive cost and huge task involved in acquiring comprehensive sets of heat flow data, means that the ability to accurately model heat flow at surface, and/or predict 3D temperature distribution for a modelled part of the crust will be key to supporting this industry and possibly others. Here we explain the approach we have taken. The Mount Painter region in South Australia is used as a case study to showcase the developments.
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