Summary:
The Pilar District, containing the Pilar UG Mine, includes two additional projects containing mineral resources and reserves which include R75 and Suçuarana.
The Pilar Mine is located in the southern part of the Caraíba Operations within the Curaçá Valley. The geology of the mine consists of a high-grade metamorphic terrain, composed of gneiss and migmatite of the Caraíba Complex that were intruded by mafic, ultramafic and late granitic rocks. The mafic and ultramafic intrusions are mainly composed of pyroxenite, norite, and gabbro. The melanorite is a term used for logging purpose to describe a host rock, either a gneiss, a gabbro or a norite, that is intruded by several mafic-ultramafic dykes that are too small individually to be logged separately.
The gneissic country rocks have gone through 3 phases of deformation and show fold-interference patterns. The ultramafic units as well as the late granitic and pegmatite intrusions were emplaced after the 3 phases of deformation in the gneiss and generally dip steeply to the west and strike northerly. Underground mapping indicates that some of the pegmatite dykes were emplaced along faults (Ero Brasil, 2020). The NW-striking diabase dykes and quartz veins crosscut the metamorphic and intrusive units. A series of shear zones, oriented NNE and NNW with moderate westerly dip, represent a late deformation event but their relative displacement is not well documented (D’El Rey Silva, 1984, Frugis, 2017). Finally, a series of late faults, oriented NE to ENE and NW, are also reported by D’El Rey Silva (1984) but with unclear sense and amount of displacement.
The gneiss and migmatites, together with some intrusive bodies are affected by various alteration assemblages including potassic (phlogopite and K-feldspar), sodic (albite), calcsilicate (diopside), carbonate, as well as epidote and lesser garnet. The alteration variably overprints the original texture of the rock units and it obliterates the gneissic foliation where the alteration is more intense. The phlogopite was generally developed later than the k-feldspar and the diopside alteration and is frequently associated with the copper mineralization.
Mineralization at the Pilar UG Mine is composed of copper sulphides in the form of chalcopyrite, bornite and rarely chalcocite that occur in four different styles: disseminated, veins, massive, and brecciated. Other sulphide minerals include millerite, pyrite and pyrrhotite. Magnetite is the dominant oxide mineral and occurs intergranular together with chalcopyrite and bornite (Tappert, 2020). The sulphides are heterogeneously distributed in the pyroxenite units in the form of lenses that trend N-S, dip steeply to the west and range from less than 1 meter to 20 meters thick. The known copper mineralization at Pilar extends for 1.2 km N-S, up to 170 m E-W, and has been drilled to a depth of more than 1.6 km along its steep northerly plunge. The mineralized bodies occur in sharp contact with migmatites and at variable angle to the main foliation of the host-rock. In the P1P2 sector of the mine, located in the upper levels of the Pilar UG Mine, mineralization is distributed around an interpreted steeply west dipping tight syncline plunging shallowly to the south. The fold hinge is interpreted as a structural trap for high-grade copper mineralization. Strongly foliated sub-vertical anastomosing shears as well as brittle faults crosscut and locally displace the mineralization.
The Suçuarana copper deposit is located in the southern part of the Curaçá Valley and 14 km to the SSW of the Pilar Mine. The copper mineralization is associated with a regionally interpreted steep westerly dipping, northerly trending, 100-meter-wide amphibole-rich unit that extends for over 1.35 kilometers in a N-S direction.
This unit represents most probably a series of sub-parallel mafic and ultramafic dykes that are strongly altered. The amphibolite unit is hosted in gneiss and migmatites that are intruded by late granite and pegmatite dykes. A series of phlogopite-rich units, that possibly represent altered mafic- ultramafic units, trend northerly and cross-cut the folded gneiss. At the local scale, the phlogopite- rich units are injected in an anastomosed pattern with dominant vertical and horizontal contacts.
Alteration consists of green hornblende and intense brown phlogopite flakes that are generally randomly oriented.
The known copper mineralization extends over 2.0 km, including mineralization of the historical Suçuarana pit. Mineralization is dominated by chalcopyrite with minor bornite that is mostly associated with the phlogopite-rich units. The copper mineralization is irregularly distributed over approximately 100 m E-W and has been drill-tested to a depth of 250 meters and remains open at depth.