Summary:
Property Geology
The north-south trending Rio Jacaré Intrusion underlying the Maracás Mine property and can be traced for the full 8 km strike length which occurs on the property to the north of Campbell Pit, and for over 25 km to the south. Recent work by Largo Inc. has resulted in a detailed subdivision of the Upper Zone of the Rio Jacaré Intrusion within the Project area into several cyclic units.
Individual Deposits
The NNE-striking, ~70° ESE-dipping Paleoproterozoic Rio Jacaré Intrusion occurs throughout the 40 km long Project exploration permits. Along the strike of the Rio Jacaré Intrusion within the property, several discrete deposits or areas containing vanadium-rich titanomagnetite bodies have been defined from north to south Novo Amparo North (NAN), Novo Amparo (NAO), São José (SJO), Gulçari A North (GAN), Gulçari A (Campbell Pit), Gulçari A South (GAS), Água Branca (ABR), Jacaré (JAC), Braga (BRG), Ilha Grande (ILG) and Rio de Contas (RIOCON). Each of these deposits are at various stratigraphic heights within the Rio Jacaré Intrusion, and thus occur within different cyclic units
Deposit Types
Mineralization Styles
The deposits which are subjects of this Report are hosted within the Rio Jacaré Intrusion, which contains the largest known vanadium resources in the Americas. The Rio Jacaré Intrusion is composed of a series of mafic-ultramafic rocks with a strike length of 70 km along the N-S direction and 1.2 km wide in the E-W direction. The Rio Jacaré Intrusion is a layered mafic to ultramafic intrusion characterized by rhythmic and cryptic layers the deposit was described in this way by the way it was generated: an initial magmatic ore type deposit formed by concentration through liquid immiscibility.
Vanadiferous titano-magnetite (VTM) mineralization at the Project shows similarities to other magmatic VTM or ilmenite deposits associated with layered mafic intrusive complexes including the Bushveld Complex (South Africa), the Lac Doré Complex (Quebec, Canada) and the Skaergaard Intrusion (Greenland). In these layered complexes, VTM and ilmenite deposits typically form in the upper portions of the magmatic stratigraphy. It suggests that magnetite crystallization is initiated when the evolving magma becomes sufficiently iron-enriched to form oxide minerals.
Mineralization
Vanadium and titanium are the elements of interest at the Maracás Mine. Vanadium is hosted within titaniferous magnetite, which is the major oxide phase found within the deposit. Ilmenite forms a second oxide phase which is commonly present, and which hosts titanium mineralization. Magnetite occurs as primary magmatic crystal grains that may be partly transformed to martite. These occur as anhedral grains, with grain sizes of between 0.3 mm and 2.0 mm, which form a polygonal mosaic together with ilmenite, which occurs as discrete anhedral magmatic crystals but may also occurs as inclusions within in the titaniferous magnetite, commonly displaying exsolution textures. Magnetite from the lower cyclic units (particularly the C3 unit at the Campbell deposit) has higher V2O5 concentrations than magnetite from the upper cyclic units – this is consistent across all deposits and is typical of layered magmatic magnetite deposits.
Massive magnetitite layers are formed by ilmenite-magnetite heterogenic cumulates that form 2 cm to 3 m thick layers containing variable amounts of clinopyroxene. They occur together with layered mafic and ultramafic cumulates, which comprise olivine-magnetite cumulates, and clinopyroxene-magnetite cumulates, and together form rhythmically micro-layered gabbro, magnetite, and magnetite-pyroxenite bands.
Besides primary magnetite, fine-grained magnetite also occurs locally as inclusions within silicate grains and results from alteration of iron-rich silicates (e.g. uralitization of pyroxene and serpentinization of olivine).
Silicate phases associated with the magnetite include augite, plagioclase, hornblende, and rare grains of clinopyroxene, olivine and spinel. Rare olivine and pyroxene grains are observed within the magnetitite, but most are altered to serpentine or chlorite. The Rio Jacaré Intrusion has been intensely metamorphosed, so the pyroxene compositions observed reflect metamorphic reequilibration rather than original magmatic compositions. In addition, Brito (2000) also documented orthopyroxene. Garnet and biotite are present in the Gulçari B and Novo Amparo deposits.
Sulfides (chalcopyrite and pentlandite with rare pyrite and pyrrhotite) are minor and only account for up to 1% of the rock within the magnetitite layer. Chalcopyrite is more abundant than the other sulfides and is most common in the rock types containing 50% magnetite or less. It commonly occurs in association with magnetite or ilmenite enclosed by amphibole and plagioclase. Pentlandite is much less abundant and occurs within in the magnetitite layer. Minor sphalerite and galena grains are found together in the silicates, associated with the other sulfides, especially in the magnetite-poor rock types. However, the dominant trace minerals are nickel and cobalt sulfides and arsenides and cobalt-rich pentlandite. Many times, the arsenides are associated with the sulfides and appear to be alteration products of the sulfides.
Besides the vanadium and titanium that form the focus of exploration and mining at the Maracás Mine, elevated platinum and palladium values have been found associated with magnetite-rich zones in the Rio Jacaré Intrusion. They are much richer in platinum-group metals than the surrounding silicate rocks, and there are significant correlations between all the PGMs and between PGM and copper.
In the magnetite zones, palladium-rich minerals, especially bismuthides and antimonides, are the most abundant PGM minerals. Most times, these occur with interstitial silicates or within silicate inclusions in magnetite and ilmenite grains, and are associated with pentlandite and, sometimes, with arsenides. Sperrylite is the most abundant platinum mineral and is associated with silicates interstitial to magnetite and ilmenite grains. At sites where the igneous mafic minerals have been altered to amphiboles, sperrylite may be altered to platinum-iron alloys.
It is suggested that copper, nickel and PGM were concentrated in the magnetite layers by the coprecipitation of a small quantity of sulfide with the magnetite. These PGM-bearing base metal sulfides subsequently exsolved the platinum minerals. The association of palladium minerals with base metal sulfides and the minor variation in the Pt/Pd ratio (4:1) suggests that the PGMs have not been extensively remobilised in the magnetite.
The association of PGM enrichment with magnetite layers in the Rio Jacaré Intrusion has similarities with the Rincón del Tigre, Skaergaard and Stella Complexes. This enrichment is rarely associated with visible sulfides but suggests a target for PGM exploration.
Oxidation
In the Maracás area, the water table lies 30 m below surface. The rocks are fresh below this water table and over it they weather and oxidize to varying degrees, with deeper oxidation near faults, which may provide a conduit for fluid ingress. In weathered zones, silicate minerals weather (to clay minerals) more rapidly than oxides weather (Figure 7-12). Oxide minerals such as magnetite and ilmenite oxidize to other minerals such as maghemite, hematite, goethite, and other iron oxides. The main effect of weathering / oxidation is a potential reduction in vanadium recovery to the magnetite concentrates – since the oxidized products of magnetite (e.g., hematite) are not magnetic, increased weathering may result in a lowering of vanadium recoveries.