Summary:
The Tennant Creek Mineral Field (TCMF) is considered an iron-oxide copper gold deposit (IOCG) province and is host to high-grade deposits. The mineral deposits of the TCMF are hosted in rocks of the Warramunga province. The geology of the region comprises Paleoproterozoic sediments and intrusive suites that have been folded and faulted during several deformation events. An initial deposition of magnetite-hematite-quartz bodies (ironstones) formed hydrothermally into folds, cleavage planes and fault planes during early deformation. The zones are well defined within the TCMF.
The TCMF is considered an IOCG province and is host to high-grade deposits such as Nobles, Juno, Warrego and Peko.
The Project area is located within the Tennant Creek Geological Region, in the Warramunga Geological Province. This is within the Proterozoic Tennant Creek Inlier, which comprises a turbiditic flysch sedimentary sequence of volcaniclastic sediments, volcanic lavas, and volcanic rocks. In the Tennant Creek region, these rocks are typified by the Warramunga Group, which commonly strikes east-west with variable dip. These rocks have been intruded by various granites and deformed by the Tennant Event of 1850 Ma.
The hematite bodies are favourably situated in second order anticlinal folds, especially in domal positions or within faults or shear zones. The mineralisation is ‘poddy’ in nature and is typically located within steep dipping hinge zones of regionally minor folds with localised shearing and accompanying chlorite and silica with or without dolomite alteration. These dilation zones of rich gold mineralisation are also typified by strong magnetite alteration below the base of oxidation. Above the base of oxidation, the magnetite is chemically weathered to haematite.
The distribution of the metals is variable, with no direct correlation between bismuth, gold, and copper though some of the better-known deposits display zonation. For example, it is common to find an outer magnetite/dolomite altered copper zone, a mixed magnetite-silica bismuth zone and magnetite plus gold zone in the core. The mineralisation style at Tennant Creek is generally small tonnage but high-grade pods of iron rich mineralisation. Gold is also generally very fine grained in fresh deposits, but very coarse and nuggety in the oxidised deposits, such as Nobles Nob.
The mineral deposits of the TCMF are hosted in rocks of the Warramunga province in the Northern Territory of Australia. The geology of the region comprises Paleoproterozoic sediments and intrusive suites that have been folded and faulted during several deformation events. An initial deposition of magnetite-hematite-quartz bodies (ironstones) formed hydrothermally into folds, cleavage planes and fault planes during early deformation. The ironstones were then hosts to the main episode of copper, gold and bismuth mineralisation that occurred ~1,845Ma ago during later deformation, followed by a later phase of copper-rich mineralisation.
Nobles Gold Mine comprises several satellite deposits from surface stockpiles, open pit mines and underground operations such as the Black Snake, Chariot, Crown Pillar Stockpile, Eldorado, Golden Forty, Juno, Malbec, Mauretania, Nobles, Nobles North tailings, Rising Sun, Shaft 12, Weaber’s Find and White Devil deposits and other targets not reported as part of the Mineral Resources.
Mineralisation
Mineralisation is typically continuous in the short to medium range on strike, with long-range geological and grade continuity being experienced down-dip. Gold, copper and bismuth occur in the ironstones and gradually decrease in the surrounding chlorite alteration haloes. The mineralisation occurs as free-milling gold associated with fine-grained sulphides, mainly pyrite and chalcopyrite.
The TCMF mineralisation is contained within the iron oxide lode with a gradual decrease in economic mineralisation into the chloritised hanging wall and footwall lithologies. Gold, bismuth and copper mineralisation form a late-stage overprint on the hematite-magnetite lodes. Gold is typically concentrated towards the footwall of the ironstone or where the ironstone is in contact with chlorite and muscovite. Economic enrichments of gold and copper are less evenly distributed compared to the ironstone, suggesting factors other than structure and stratigraphy are involved.
Gold-copper-bismuth mineralisation has been found to be hosted by fine grained haematitic mudstones and shaley siltstones. The mineralisation occurs within lenticular bodies rich in hematite. These are replacement bodies which cut across sedimentary structures and have been referred to as ‘ironstones’ by previous workers. Tennant Creek-type ironstone bodies grade upwards from chloritic alteration into stringer zones of chloritemagnetite, coalescing higher into massive ore bearing magnetite +/- hematite, topped with talc-dolomite.
Nobles
The mineralisation at Nobles is in magnetite-hematite-chlorite (ironstone) rock, with gold as the dominant economic commodity and subordinate copper and bismuth. Gold mineralisation occurs as lenses, typically (but not entirely) hosted by the east-west striking magnetite-hematite ironstone units. There is a clear zonation, with the core of massive magnetite-hematite-chlorite, surrounded by talc-magnetite, then dolomite.
Warrego
Rising Sun, Nobles, Eldorado, Mauretania, Chariot, Juno, Golden Forty and Black Snake are all broadly similar. All are iron-oxide gold deposits with high-grade gold mineralisation preferentially hosted within magnetite-hematite-chlorite ironstones. The ironstones are hosted within greywackes and siltstones of the Proterozoic Warramunga Formation. The ironstone orebodies form a cigar shape in section and are essentially lenticular in plan view. The orebodies average 10m to 50m wide with strike lengths of approximately 90m to 400m. The bodies tend to be aligned roughly east-west, lining up with the regional foliation. Locally, the ironstones can be elevated in copper and bismuth. An exception is Warrego, which has significant copper mineralisation associated with the gold. In the fresh rock, the mineral hosting copper is chalcopyrite, but this becomes oxidised to malachite and bornite in the upper weathered zones of the deposit.