Woodgreen, Northern Territory : explanatory notes
Northern Territory Geological Survey
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Geology; Georgina Basin; Arunta Region
Northern Territory Government; Northern Territory Government
Australia 1:100 000 Geological Map Series
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
28 Orogeny (17301700 Ma). Correlations: May have affinities with the Deep Bore Metamorphics, exposed in HUCKITTA. Mollie Granite Complex (new name) Proposers: PW Haines and IR Scrimgeour. Derivation of name: Mollie Bluff (2208'S, 13424'E). Synonymy: Previously mapped (Shaw and Warren 1975) as undivided granite. Constituent units: None named. Parent unit: None. Distribution: Scattered outcrops lie in a northwest-trending belt, about 25 km long and 5 km wide, centred at about 2210'S, 13424'E, within the northeastern quadrant of Woodgreen. Geomorphic expression: Low hills of weathered granite and low domes, pavements and tors of fresh granite. Much of the complex is covered by Cenozoic deposits. Type locality: Low dome and tor outcrops, centred about 3.5 km east of New Bore, in northeastern quadrant of Woodgreen (227'44"S, 13420'42"E). Description at type locality: Dark biotite-rich granodiorite, with abundant dark enclaves, is intruded by younger leucocratic microgranite and leucocratic porphyritic granite, with a distinctive flow foliation of tabular K-feldspar phenocrysts. Later phases are intimately interlayered and appear to be comagmatic. Lithology: Fresh outcrops include biotite-rich granodiorite, leucocratic microgranite and leucocratic porphyritic granite, with a distinctive flow foliation of tabular K-feldspar phenocrysts. Deeply weathered outcrops (dominant) are tentatively identified as representing similar rock types, biotite-rich phases of which commonly show a steeply dipping foliation (possibly strongly enhanced by weathering, as fresh outcrops show no obvious foliation). Pegmatite common. Tabular bodies of fresh, layered calc-silicate rock are present within the granitoid, about 4 km east-northeast of New Bore; these are likely to represent a large raft or rafts of metasedimentary country rock. Relationships and boundary criteria: Intrudes unnamed amphibolite near Utopia tantalite prospect at the southeastern end of the complex; inferred to intrude the Utopia Quartzite in the northwest. Unconformably overlain by several Neoproterozoic units of the Georgina Basin and is faulted against such rocks along the northern margin of the complex. Age and evidence: Not dated, but assumed on regional evidence to have been intruded during the late Palaeoproterozoic. Lack of regional deformation in fresh outcrops suggests that these phases were most likely related to the Strangways Orogeny (17301700 Ma). Correlations: Tentatively related to Strangways Orogeny granitoids. Comments: Aeromagnetic interpretation indicates that the scattered outcrops of granitoid rocks mapped as Mollie Granite Complex are likely to comprise a single body. However, outcrops within the Mollie Granite Complex show a wide lithological range, even in a single outcrop, and it is uncertain whether all phases are comagmatic, or whether they comprise two or more unrelated intrusions. Interpretation is complicated by the fact that many outcrops are deeply weathered. APPENDIX 2 NTGS ELEMENTAL GEOCHEMICAL RESULTS FOR QUARTER CORE COMPOSITES. Results of NTGS multielement analyses of quarter core composites from drillholes CMS4 and Mount Skinner 3 are presented in Appendix02.xls. Samples were pulverised in a chrome-steel mill and treated using near-total-attack four-acid digest. Analysis used: ICPMS (A/MS) = Inductively Coupled Plasma Mass Spectrometry, or ICP-OES (A/OES) = Inductively Coupled Plasma Optical Emission Spectrometer. Values below detection limit are reported as negative numbers.
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