GEOLOGY AND RESOURCE POTENTIAL OF THE SOUTHERN GEORGINA...

GEOLOGY AND RESOURCE POTENTIAL OF THE SOUTHERN GEORGINA BASIN

"Known base metal prospects and occurrences have been documented and additional studies undertaken. All available mineralised intercepts have been reassayed using a standardised technique. The best Cu occurrences are in Neoproterozoic siliciclastic rocks. Known Pb-Zn prospects and occurrences are widespread and throughout the succession from Neoproterozoic siliciclastic rocks to Lower Ordovician carbonate and mixed carbonate-siliciclastic rocks. There is a wide range of mineralisation styles. At the Box Hole Mine, galena and barite occur along 6.5 km of strike in the Late Cambrian Arrinthrunga Formation. About 15 t of ore, averaging 65-70% Pb and 60 g/t Ag, has been handpicked. Mineralisation is stratabound epigenetic replacement and vug-fill in a stromatolitic dolostone, possibly localised by proximity to a feeder fault. Similar surface galena and minor pyrite occur at the Trackrider Prospect. Host rocks are vuggy siliceous and manganiferous
dolostone of the Late Cambrian Arrinthrunga Formation, just below the contact with the overlying Tomahawk Formation. Mineralisation at both Box Hole and Trackrider is similar to Mississippi Valley-type (MVT) orebodies. Visible Zn-Pb mineralisation (up to 1.2% Zn) occurs in association with hydrocarbons in and just below a shale cap at the contact of the Arthur Creek Formation and Thorntonia Limestone in Baldwin 1 and may have affinities to Century-type, stratiform, shalehosted
base metal mineralisation. A fault breccia at the Boat Hill Prospect contains two intervals with percent levels of Zn. NTGS drilling also intersected percent levels of Zn and visible galena in the Thorntonia Limestone in this area, which considerably extends the area of known mineralisation. Previously undocumented visible galena has also been recognised in the Neoproterozoic Elyuah Formation at the Mount Skinner Prospect in ALCOOTA. This core contains 2.44 m assayed at
0.3 m intervals, all of which are >2000 ppm Pb. Lead isotope data have been acquired for galena in host rocks ranging from Neoproterozoic to Late Cambrian–Early Ordovician. These, together with previously published data from Queensland, show a close correlation to a single isochron indicating a single mineralising event with an initial ratio close to crustal Pb (no mixing). This is interpreted as a 1840- 1780 Ma Pb source and a 420-280 Ma mineralisation age, corresponding to the Alice Springs Orogeny. Bureau of Mineral Resources (BMR, now Geoscience Australia) and exploration company surface geochemical data have been compiled into an Explorer 3 database. These data are log normalised and are presented as colour-contour maps. However scavenging by the regolith complicates their interpretation. Contouring of rock chip Pb highlights Box Hole and Zn anomalies are centred on Box Hole and Boat Hill. Cu in soils was considered unreliable by previous explorers, but there are clearly anomalies within the Neoproterozoic Central Mount Stuart Formation."

This project could be good!