Territory Stories

Woodgreen, Northern Territory : explanatory notes



Woodgreen, Northern Territory : explanatory notes

Issued by

Northern Territory Geological Survey


E-Publications; E-Books; PublicationNT; Australia 1:100 000 Geological Map Series




Australia 1:100 000 Geological Map Wood 5458; Australia 1:250 000 Geological MapAlcoota SF5310; Australia 1:250 000 Geological MapAlcoota SF5310

Map scale

1:100 000


Made available via the Publications (Legal Deposit) Act 2004 (NT); Available from GEMIS - Geoscience Exploration and Mining Information System




Geology; Georgina Basin; Arunta Region

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Northern Territory Government; Northern Territory Government

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1st ed.


Australia 1:100 000 Geological Map Series

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Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government



Related links

https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/81885 [GEMIS]

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24 reputedly averaged 6700 ppm Pb including 2% Pb for the sample from 432433 depth (ca 131.8 m, but see the NTGS reassay below); the other had up to 950 ppm Zn over 0.3 m at 10271028 (ca 313 m) depth (Grainger 1968b, Shaw and Warren 1975). During 19691970, Utah Development Company (1970) targeted the area for Zambianstyle stratiform Cu mineralisation. Work was focused near Mollie Bluff and on the reduced host rocks at the Mount Skinner prospect, where three areas were sampled on a 15 x 61 m grid, using soil, rock chip and auger samples. A total of 8865 assays for Cu, Pb, Zn, Co and Ni were undertaken. Rock chips of the target horizon rarely yielded in excess of 300 ppm and even the best assays were less than percent level. Exploration did not advance to drilling. Centamin became operators of the Mount Skinner area in 1970. They contracted Compagnie Gnrale de Gophysique (1971) to undertake 195 km of refraction seismic, 158 line km of resistivity and 3 x 300 mspaced electrical readings. Four targets identified by the geophysical survey were tested by cored drillholes (CMS1 to 4), totalling 1780 m. The last three terminated in crystalline basement. Only selected intervals were analysed and no economic mineralisation was discovered (Cotton 1972, Chuck 1982). Alcoa targeted syngeneticexhalative sedimenthosted base metal mineralisation below the Central Mount Stuart Formation. They flew a 500 mspaced magnetic survey (Ashley in Chuck 1982) and reanalysed selected intervals of the Centamin cores by edge grind, atomic absorption spectroscopy (AAS) and Inductively Coupled Plasma Mass Spectrometry (ICPMS). Generally these returned less encouraging Cu results than the Centamin assays. In particular, CMS1 was significantly downgraded. However, thin intervals of anomalous Zn do occur in all holes and the interval 251.4254.5 m depth in CMS4 averages 0.4% Pb. Alcoa defined a drilling target, but the company withdrew from base metals exploration before it could be tested (Chuck 1983). During the early to mid1990s, CRA explored for stratabound Cu in the Central Mount Stuart Formation in BARROW CREEK and ALCOOTA. They inspected the Mount Skinner prospect and assayed the open file core for 25 elements (Menzies and Louwrens 1995). The results were not released, but generally confirmed that the reduced host rocks contain 23 times background Cu and locally elevated Ag, As, Co, Mo, Ni, Pb and Zn (Menzies and Louwrens 1995). Soil and stream sediment sampling were unable to accurately locate outcropping mineralisation, because of low Cu tenor and flatlying strata. Spectral analysis of Landsat TM data failed to unambiguously map the host reduced lithofacies of the Central Mount Stuart Formation (Menzies and Louwrens 1995). Recent work by NTGS (Dunster etal 2007) recognised previously unreported visible epigenetic galena from 251256 m depth in the Elyuah Formation in CMS4. To provide more meaningful assays than previous company edge grinds, multielement analyses of ca 30 cm quartercore composites were undertaken (Appendix2). All composites from 251.76254.20 m depth returned >2000 pm Pb, including 0.92 m at >0.5%. A lower interval at 255.42255.73 m, containing previously unreported visible galena, pyrite, chalcopyrite and fluorite, assayed 339 ppm Cu, 2555 ppm Pb and 240 ppm Zn. Percent levels of Pb, previously reported from Mount Skinner 3, could not be duplicated by quartercore sampling. Three composite samples over 131.67132.13 m depth returned a maximum of only 2 ppm Pb (Appendix2). Tantalum, niobium, tin, bismuth Tantalite and cassiterite occur at three small prospects, collectively known as Utopia, 0 km west of Utopia community (Powell 1981, Frater 2005). Shaw (1968) described the host rock as a tourmalinemuscovitefeldsparquartz pegmatite, intruded parallel to the foliation of the muscovitebiotite gneiss country rock. Some of the mineralisation contains bismuth and is weakly radioactive (Daly and Dyson 1963). Old workings occur in two areas approximately 1.8 km apart, referred to as Utopia and Utopia 3. An additional prospect, Utopia 2, occurs in the vicinity of Utopia and is not described further here. Utopia is the southernmost and smaller of the two workings, and contains minor tantalite and quartz with rare native bismuth and bismuthinite, with no evidence of radioactivity (Daly and Dyson 1963). The workings consist of a single shallow pit, 2 x 5 m in plan, gouged out of a steeply dipping, massive quartz blow, 4 m wide and trending 070. The quartz vein locally contains large salmoncoloured Kfeldspar up to 0 cm in size. A feldsparquartz (tourmaline) pegmatite abuts the vein quartz on the northern side and to the east, where the quartz vein splits and narrows into two limbs. There is no greisen developed, and only a trace of white mica in the pegmatite. Utopia 3, located 1.8 km northwest of Utopia 1, is the main prospect in the area. Shallow workings occur in an area containing several pegmatites at the northern end of a pegmatite belt that extends to Utopia in the south (Shaw 1968). Although there is no record of production, several pits and costeans in eluvial deposits and two open cuts in the outcrop indicate smallscale mining prior to 1949 (Daly and Dyson 1963). Utopia 3 consists of numerous pegmatite outcrops, ranging from veins to dykes of considerable size, with two small open cuts in a northwesttrending pegmatite dyke. Tantalite, biotite, tourmaline, magnetite, beryl and bismuth minerals have been recorded from this prospect (Daly and Dyson 1963, Shaw 1968). Shaw (1968) commented that tantalite was more prevalent in eluvium than in the pegmatite itself. A 3 mdeep pit has been cut into a complex pegmatitegreisenquartz vein. Work in the shaft appears to have been concentrated at the vein quartzpegmatite contact. No systematic internal pegmatite zoning was apparent from the observed exposure. Small pits and excavated rubble trace the pegmatite over an area of 5 x 00 m. A prominent quartz vein in the shaft trends 05 and dips vertically, but the overall trend of the pegmatite is 50. A quartzbiotitemuscovite psammite occurs at the country rock contact. The workings terminate where the pegmatite passes under sand cover to the north. However, a pegmatite with associated greisen and vein quartz reappears 400 m to the north (444300mE 7542800mN; Utopia North), where it is exposed over a 200 m strike length and a width of 40 m. Recent geochemical analysis suggests that Utopia 3 contains elevated Ta (eg 300 ppm and 390 ppm) and Nb