Summary:
The Project is located within the Carajás Mineral Province (CMP), located in the southeastern margin of the Archean Amazonian Craton. The CMP is composed mostly of granites and greenstone belts and also hosts the largest gold deposits in the Amazon Craton. Gold deposits are concentrated in the Archean and Paleoproterozoic terranes, including the Archean Carajás Mineral Province.
Deposit Type
The principal geological unit on the mineral property is the Luanga Layered MaficUltramafic Complex (“Luanga Complex”). The Luanga Complex is a 6 km long and up to 3.5 km wide (~18 km²) mafic-ultramafic layered intrusion that belong to the Neoarchean Large Igneous Province (LIP) of the Carajás Mineral Province. The intrusion is characterized by abundant unweathered outcrops, massive blocks and boulders. The layering forms an arc-shaped structure that matches the morphology. Host rocks of the Luanga Complex consist of highly foliated gneiss and migmatite of the Xingu Complex in the south/southeast, and mafic volcanics and iron formations of the Grão Pará Group in the north/west.
The central portion of the Luanga Complex has the thickest sequence of layered rocks. To the north and northeast, the layered sequence is truncated by granitic intrusions and to the south, it becomes progressively thinner. The Luanga Complex and host rocks are crosscuted by NNW-SSE dolerite dykes. These vertical dykes are up to several metres wide and consist of fine-to medium-grained intergranular to ophitic textured rocks. They belong to a Proterozoic swarm of magnetic mafic dykes that occurs in the Serra Leste region.
Magmatic Ni-Cu-PGM sulfides form by the accumulation of immiscible sulphide liquid that scavenged chalcophile elements from a coexisting silicate magma (e.g., Naldrett, 2004, Barnes et al., 2016). Textural relationships between sulphides and their host silicates are key evidence for their origin as immiscible sulphide liquids (Barnes et al., 2017, 2018). The magmatic origin of the Luanga PGM + Au + Ni deposit is supported by textural and mineralogical features described in different styles of PGM mineralization, particularly the MSZ, Ni-Rh and SZ. In these different PGM zones, sulphide blebs consisting of po+pn±cpy are interstitial to cumulus olivine and/or pyroxene. In addition, sulphide blebs enclosed in cumulate crystals, as well as their rounded/corroded faces, provide unequivocal evidence for a magmatic origin of sulphides and PGM. Variable lithochemical features in PGM zones located in distinct stratigraphic horizons of the Luanga Complex, including different metal tenors, as well Pt/Pd and Rh/Pd ratios, indicate that several events of mineralization occurred during the magmatic evolution of the Luanga Complex. The occurrence of several mineralized horizons in the Luanga Complex, including PGM mineralization hosted in chromitites, has remarkable similarity with reef-type productive deposits.
The widespread alteration of rocks from the Luanga Complex has partially disrupted their primary magmatic features. In the Luanga Complex, magmatic silicates are partially altered and commonly occur as pseudomorphs. The magmatic sulphides have also been partially altered during the widespread alteration. The most common alteration of primary sulphides (po-pn-cpy) consists of their replacement by magnetite and Fe-hydroxides. Because this alteration is heterogeneous at different scales (from mineral crystals, up to several hundred meters thick zones) and largely preserves primary textures and compositions of cumulate rocks and PGM mineralized zones, magmatic features can be recognized throughout the layered intrusion.
The Luanga layered sequence is subdivided in three zones, based on the different type and/or proportion of cumulus minerals, Ultramafic Zone (UZ), Transition Zone (TZ) and Mafic Zone (MZ). The estimated thickness of the layered sequence is some 3,500 m, as indicated in both the stratigraphic column, which is likely to represent the axial portion of the original magma chamber.
The Ultramafic Zone (UZ) is about 9 km long, up to 1 km wide and has an estimated thickness of 800 m. It consists of wehrlite (Olivine (Ol) + Clinopyroxene (Cpx) cumulates) and lesser dunite and lenses of clinopyroxenite.
The Transition Zone (TZ) is about 5 km long and up to 1 km wide, comprises a pile of interlayered ultramafic and mafic cumulate rocks, which is up to 500 m thick. Interlayering of different rock types in different scales (from a few centimetres up to dozens of metres), is a distinctive feature of the Transition Zone. Cumulate rocks have variable textures and assemblages. The most common rock types are orthopyroxenite and lesser interlayered harzburgite and norite.
The Mafic Zone (MF), about 5 km long and up to 3.5 km wide, comprises a thick monotonous pile of noritic rocks. Norite consists of medium-grained orthopyroxene + plagioclase cumulates. Primary textures and minerals are variably altered to fine-grained aggregates consisting mainly of amphiboles (hornblende-actinolite), chlorite and epidote-group minerals. Minor interlayered ultramafic rocks in the MZ, including orthopyroxenite and minor chromitite, have petrographic features.
Mineralization
The Luanga PGM + Au + Ni mineralized envelope follows the arc-shaped structure of the Mafic-Ultramafic Complex along approximately 8.1 km. The deposit is subdivided into three separate mineralized sectors, named North, Central and Southwest.
The TZ of the Luanga Complex hosts several PGM mineralized units, including the Main Sulphide Zone (MSZ) which hosts the bulk of PGM resources of the Luanga Complex. Other mineralized layers are identified within the TZ and on the UZ.
In addition, several thin chromitites layers or lenses occur in the Luanga Complex either in the upper or in lower stratigraphic portions of the TZ, the latter occurring where they are hosted by ultramafic cumulates. The upper chromitite layers are developed on the immediate contact with the overlying MZ, where they are hosted by plagioclase-bearing norite cumulates.