Iron Oxide Cu-Au Monograph - Volume 3, Abstract

The Carrapateena iron oxide copper-gold deposit (203 Mt @ 1.31% Cu, 0.56 g/t Au, 0.27 kg/t U) is located within the Olympic IOCG Province on the eastern rim of the preserved Gawler craton in northern South Australia, approximately 100 km southsoutheast of Olympic Dam. The deposit is hosted by strongly brecciated granitoids 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. 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. The host CBC varies from heterolithic clast- to matrix-supported hematite-rich breccias. Many of the clasts are milled and rounded, and are predominantly of gneissic diorite, with granite gneiss and vein quartz. Higher grade copper intersections are typically associated with a grey hematite matrix within strongly brecciated granite.