OZ Minerals operates the Carajás East hub in Brazil.
On May 2, 2023, BHP announced the completion of the OZ Minerals acquisition and implementation of the scheme of arrangement for BHP Lonsdale Investments Pty Limited, a wholly owned subsidiary of BHP Group Limited, to acquire 100% of the shares in OZ Minerals Limited (OZL) (the Scheme). BHP Group Limited is now the ultimate parent company of OZL.
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Summary:
Pedra Branca iron oxide copper gold deposit is hosted within the Carajás Mineral Province which is located in the southern part of the Amazon Craton. Locally the craton is overlain by metavolcanic–sedimentary units of the Rio Novo Group and the 2.76 Ga Itacaiúnas Supergroup. The Itacaiúnas Supergroup hosts all the known Carajás iron oxide copper gold deposits and is thought to have been deposited in a marine rift environment. The Carajás Mineral Province represents one of the best endowed mineral districts in the world and contains the world’s largest known concentration of iron oxide copper gold deposits including the, Salobo, Igarapé Bahia, Alemão, Cristalino, Gameleira, Furnas, Alvo 118, Antas, Pedra Branca, Santa Lucia and Pantera deposits.
The Pedra Branca deposit consists of two distinct bodies, Pedra Branca East (PBE) and Pedra Branca West (PBW). Both exhibit typical IOCG features such as hydrothermal alteration types (sodic, calcic-sodic, calcic-ferric and potassic-ferric) and mineralisation style characterised by chalcopyrite + pyrrhotite ± pyrite in semi-massive levels, blebs, strings and disseminations.
Simplistically the geology of the PBE deposit is characterised by a series of strongly foliated to gneissic granitic composition footwall rocks to the north and a foliated diorite to granodioritic composition series of hanging wall rocks to the south. Between these two units a felsic mylonite shear zone is located which also hosts hydrothermal lithotypes dominated by actinolite and sulphide breccia. The mineralised breccia mapped at the contact of the hanging wall rocks usually has the highest grades of copper and is clearly delineated by an intense foliation of the hanging wall lithology.
The mineralised breccia includes mostly amphibole-magnetite fragments set in a sulphide-rich matrix displaying a chaotic fabric. Fragments vary from angular to sub-rounded in shape, interpreted to possibly be due to chemical erosion by the hydrothermal fluid. The matrix is mostly dominated by chalcopyrite and pyrrhotite, but also contains magnetite, apatite, and minor chlorite and ilmenite.
The actinolite domain is a pinkish rock bearing a foliated fabric dominated by actinolite, K-feldspar, apatite, tourmaline. Lenses of sulphide and magnetite occur within this domain in portion where the shearing was more penetrative.
At PBW, mineralisation is not as clearly constrained, and has been modelled as multiple lenses dipping approximately parallel to foliation. The main mineralised zone of interest at PBW is located towards the southern edge of the broader mineralised zone, near but not concordant with the boundary between the diorite and the gneiss.
Dimensions
The estimated Mineral Resource extends 1,700 metres along strike, with a 350 metres gap between the eastern and western lodes. Plan thickness varies between 130 metres in the west where there is a series of stacked vertical lenses to 20 metres in the east where the orebody presents as a single mineralised zone. Depth below surface to the upper limit of the Mineral Resource is 10-20 metres with the mineralisation extending vertically for 560 metres in the west and 815 metres in the East.