The Carrapateena iron oxide copper-gold deposit, which is located within the Olympic IOCG Province on the eastern rim of the preserved Gawler craton in northern South Australia, is ~100 km SSE of Olympic Dam and ~130 km north of Port Augusta in South Australia, immediately to the SW of the Carrapateena embayment on the central-western shore of Lake Torrens.
Carrapateena, Olympic Dam, Prominent Hill, Moonta-Wallaroo and Hillside and all of the other significant known IOCG mineralised systems of the Gawler craton are hosted within Palaeo- to Mesoproterozoic rocks and are distributed along the eastern edge of the currently preserved craton to define the Olympic IOCG Province.
The oldest rocks of the Gawler craton comprise Mesoarchaean to early Palaeoproterozoic metamorphics and igneous suites that form a core to the craton, immediately to the west of the Olympic IOCG Province. On its eastern margin, and within the Olympic IOCG Province, this older nucleus was overlain after ~2000 Ma by the Hutchison Group, a sequence of subaerial to shallow marine clastic and chemical metasedimentary rocks, with minor felsic and mafic volcanic rocks, that were deposited on a continental passive margin (Parker, 1993; Daly et al., 1998). Along the eastern margin of the craton, including the Carrapateena district, the cratonic core and the Hutchison Group were both intruded by ~1850 Ma granitoids of the Donington Suite during the Cornian orogeny (Hand et al., 2007; Reid et al., 2008). This suite is dominated by granodiorite gneiss, with subordinate metamorphosed alkali-feldspar granite, gabbronorite, tonalite and quartz monzonite intrusions with mafic dykes (Ferris et al., 2002). Between ~1770 and 1740 Ma, subsequent to the emplacement of the Donington Suite, extension along the eastern, northern and western margins of the craton, resulted in the development of a series of extensive basins, some of which contain bimodal volcanic rocks, including the Wallaroo Group, which is extensively developed within the Olympic IOCG Province and is an important host to IOCG alteration and mineralisation. During the Palaeoproterozoic, the Curnamona Province is believed to have collided with and been accreted to the Gawler craton in the east. A major linear discontinuity in magnetic and gravity data beneath the Neoproterozoic cover of the Adelaide Geosyncline intracratonic rift complex is interpreted to mark the suture zone (Hayward and Skirrow, 2010, and sources quoted therein). The interval between ~1730 and ~1630 Ma encompasses the Kimban orogeny (1730 to 1690 Ma), Ooldean Event (1660 to 1630 Ma), and the widespread emplacement of various felsic igneous rocks, and formation of several small intracontinental sedimentary basins (Hand et al., 2007).
Towards the close of the Palaeoproterozoic, from ~1630 to 1615 Ma, the Nuyts Volcanics and St Peter Suite bimodal magmas were emplaced in the southwestern part of the Gawler craton, which although poorly exposed, cover an extensive area (Fanning et al., 2007). Between ~1600 and ~1575 Ma the centre of magmatism shifted eastward with the development of the high-volume intrusive Hiltaba Suite and extensive co-magmatic bimodal Gawler Range Volcanics (GRV) to form a large felsic igneous province (covering a preserved area of >25 000 km2) over the central and eastern parts of the Gawler craton, including the Olympic IOCG Province. Between 1580 to 1550 Ma, magmatism progressed eastward to form the Benagerie volcanics and Bimbowrie Suite I- and S-types in the Curnamona Province, the easternmost development of the diachronous eastnortheast-trending corridor of continental I- and A-type magmatism that extends across the Gawler and Curnamona cratons from the St Peter Suite in the southwestern part of the craton (Hayward and Skirrow, 2010).
Known significant IOCG districts/deposits within the Olympic IOCG Province, including Carrapateena, are found where oxidised (magnetite-series), A-type granitoid plutons of the 1595 to 1575 Ma Hiltaba Suite which were emplaced into an accreted Palaeoproterozoic terrane, and where mafic volcanic rocks of the lower GRV are most abundant. These rocks were emplaced during a short-lived episode of NNW-SSE extension that approximately coincided with eruption of the GRV (~1595 to 1590 Ma), preceded and followed by more protracted NW-SE to NNW-SSE contraction (Hayward and Skirrow, 2010).
Tectonism subsequently appears to have migrated northwards and westward, with the ~1570 to 1540 Ma Kararan and 1470 to 1440 Ma Coorabie orogenies respectively. The Archaean to Mesoproterozoic crystalline basement rocks of the Gawler craton were not subjected to any substantial deformation after ~1450 Ma until the early Palaeozoic Delamerian orogeny (Parker, 1993). Much of the Olympic IOCG Province is overlain by flat lying Neoproterozoic to Lower Palaeozoic sedimentary rocks of the Stuart Shelf, equivalents of the sedimentary succession of the Adelaide Geosyncline intracratonic rift complex which separates the Gawler craton and Curnamona Province and was the result of extension preceding and during the rifting and break-up of the Rodinia supercontinent from immediately to the east of the Curnamona Province.
The Carrapateena deposit is hosted by strongly brecciated granitoids (variably foliated and/or sheared gneissic quartz-granite and quartz-diorite) which have been dated at 1857±6 Ma and are assigned to the Palaeoproterozoic Donington Suite. It occurs within the core of a north-south oriented, 30 x 100 km mass of that suite, that is overlain 10 to 15 km to the west by ~1590 Ma mafic and felsic volcanic rocks of the Gawler Range Volcanics, which are comagmatic with the Hiltaba Suite granitoids that host the Olympic Dam deposit.
The ore deposit lies beneath a ~470 m thickness of flat lying Neoproterozoic sedimentary rocks, and occupies a north-south elongated area of approximately 800 x 600 m at the unconformity surface with the underlying Palaeoproterozoic host rocks. It is reflected by a broad, weak and diffuse 200 nT magnetic peak and a slightly offset, ellipsoidal, 3.5 km diameter, 2 mGal gravity anomaly.
Mineralisation is confined to a steeply plunging, pipe-like body of hematite and hematite-granite breccia, the Carrapateena Breccia Complex (CBC), which is interpreted to be cut at its centre by an east-west- to eastnortheast-trending complex zone of faulting. To the north of this inferred zone of faulting, the mineralised mass is wedge-shaped, tapering rapidly downward into the fault zone and may conceivably follow that structure to depth.
The Carrapateena Breccia Complex (CBC) varies from heterolithic clast- to matrix-supported hematite-rich breccias. Many of the clasts are milled and rounded such that the 'breccia' may have the appearance of a 'conglomerate' when samples are viewed in isolation. The clasts are predominantly of medium grained, gneissic diorite, with granite gneiss and vein quartz, variably altered to chlorite, sericite and hematite, as well as hematite-dominated clasts of earlier breccia phases within a matrix with a variety of textures that has also been altered to an assemblage of hematite, quartz and sericite. Higher grade copper intersections are typically associated with a grey hematite matrix within strongly brecciated granite.
To the south, the CBC comprises an irregular, ~300 to 400 m diameter, ellipsoidal-cylindrical mineralised body that has been traced by drilling from the unconformity to a depth in excess of 1 km below that surface, from where it continues unclosed.
Mineralisation is zoned laterally outward, and to the north, vertically downward, from bornite to chalcopyrite-bornite to chalcopyrite to chalcopyrite-pyrite. Three kernels of bornite-rich mineralisation have been delineated, one wedge-shaped zone to the northeast that tapers southward into the inferred central zone of faulting, and two steeply plunging elongate zones, one above the other, in the upper and lower parts of the core to the main mineralised pipe-like mass of the CBC in the south.
The principal alteration minerals are hematite, chlorite and sericite, with locally abundant quartz and carbonate (siderite and/or ankerite), and secondary barite, monazite, anatase, magnetite, apatite, fluorite and zircon.
An audited inferred (OZ Minerals, 2011) resource for the main deposit, in the southern half of the deposit area, at a cut-off of 0.7% Cu, totals:
203 Mt @ 1.31% Cu, 0.56 g/t Au, 0.27 kg/t U308, 6 g/t Ag;
The northern half, has a potential to contain a further:
25 to 45 Mt @ 1.0 to 1.1% Cu, 0.4 g/t Au, 0.14 kg U308.
The estimated Mineral Resource at 31 October 2012 (Oz Minerals ASX Release, 21 January, 2013) has been upgraded to:
Indicated Resource at
0.3% Cu cut-off - 392 Mt @ 0.97% Cu, 0.39 g/t Au, 165 ppm U, 4.2 g/t Ag;
0.5% Cu cut-off - 282 Mt @ 1.20% Cu, 0.48 g/t Au, 197 ppm U, 5.2 g/t Ag;
0.7% Cu cut-off - 202 Mt @ 1.43% Cu, 0.56 g/t Au, 227 ppm U, 6.2 g/t Ag;
Inferred Resource at
0.3% Cu cut-off - 368 Mt @ 0.58% Cu, 0.21 g/t Au, 120 ppm U, 2.3 g/t Ag;
0.5% Cu cut-off - 193 Mt @ 0.76% Cu, 0.26 g/t Au, 144 ppm U, 2.8 g/t Ag;
0.7% Cu cut-off - 90 Mt @ 0.96% Cu, 0.30 g/t Au, 162 ppm U, 3.6 g/t Ag;
Total Resource at
0.3% Cu cut-off - 760 Mt @ 0.78% Cu, 0.30 g/t Au, 143 ppm U, 3.3 g/t Ag;
0.5% Cu cut-off - 475 Mt @ 1.02% Cu, 0.39 g/t Au, 175 ppm U, 4.2 g/t Ag;
0.7% Cu cut-off - 292 Mt @ 1.29% Cu, 0.48 g/t Au, 207 ppm U, 5.4 g/t Ag;
(Source: Porter GeoConsultancy Pty Ltd, www.portergeo.com.au, 2010)