Alvo 118 Cu-Au deposit, Canaã dos Carajás, Pará, Brazili

Regional Level Types
Alvo 118 Cu-Au deposit	Deposit
Canaã dos Carajás	Municipality
Pará	State
Brazil	Country

The Alvo 118 deposit consists of Cu-Au mineralization, typical of the denuded areas of the CMP. It comprises three ore types formed during distinct evolutionary stages: (1) hydrothermal massive and disseminated copper sulfide orebodies, (2) immature gossan, and (3) saprolite. The hypogene reserves reach 170 Mt at 1% Cu and 0.3 ppm Au, while those of supergene ores are approximately 55 Mt, of which 30% correspond to the gossan orebody and 70% to the saprolite, with 0.92% Cu and 0.03 ppm Au.
The Alvo 118 is a Cu and Au deposit related to shear zone hydrothermal alteration. The hypogene IOCG mineralization comprises NW-SE subvertical tabular orebodies aligned with the neighboring Sossego and Cristalino deposits. The first mineralization type includes hydrothermal breccias comprising chalcopyrite and bornite matrix (with minor magnetite and pyrite), surrounding granite, gabbro, and schist clasts. Stockwork veins formed of quartz, calcite, and chalcopyrite represent the second mineralization type. Hydrothermal xenotime has been dated to 1869 ± 9 Ma in the breccia zone matrix and to 1868 ± 7 Ma in the stockwork veins.
The deposit area houses mafic to intermediate volcanic sequences, with mylonitic foliation and intense chloritic alteration correlated with the Grão Pará Group. Then, these rocks are intruded by granodioritic, tonalitic, and gabbroic bodies, and finally, crosscut by dacitic-rhyolitic and diabasic dykes. Toward the sulfide ore, the host rocks have been progressively subjected to sodic (albite and scapolite), potassic (biotite and alkali feldspar), chloritic, and quartz-sericitic hydrothermal alterations.
The gossan overlying the sulfide mineralization presents a mineralogical zonation, with progressive replacement of primary sulfides by secondary sulfides, and then by carbonates, phosphates, and copper oxides. In the overlying saprolite, copper is supposed to be carried by the alteration products of the primary silicates, that is, clay minerals and iron oxyhydroxides, such as in Salobo and Furnas deposits.

The deposit comprises massive and disseminated copper sulfide orebodies that have undergone two distinct supergene alteration stages. In the first stage, dominated by oxidoreduction processes, primary mineralization was partially transformed into an immature gossan profile at depth. During the second stage, near-surface weathering of the host rocks led to the formation of a thick saprolite cover, preserving high copper content. The primary sulfide reserves are estimated at approximately 170 Mt with 1% Cu and 3 ppm Au, while the supergene mineralization totals 55 Mt at 0.92% Cu and 0.3 ppm Au, comprising 30% gossan and 70% saprolite.

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