Summary:
The Surubim District, containing the Surubim OP Mine (including planned production from underground), located at 9°34’12” S and 39°51’52” W, also includes the C-12 OP/UG Mine, located at 9°34’44” S and 39°52’27” W, the Lagoa da Mina project, located at 9°30’13” S and 39°47’48” W adjacent to the past producing Angicos Mine, the Cercado Velho project, located at 9°30’36” S and 39°47’52” W and the Terra do Sal project, located at 9°38’1” S and 39°49’6” W.
The Surubim District is located in the central part of the Curaçá Valley. The C12 deposit is located 1.2 km to the SW of the Surubim Mine. The Cercado Velho and Lagoa da Mina deposits are approximately 10 km to the NE of the Surubim Mine whereas the Terra do Sal deposit is situated 8 km to the SE of Surubim Mine. The Surubim Mine and C12 Deposits are hosted in the Surubim gneiss (alternating tonalitic and granorioditic bands with gabbro and diorite bands) whereas the other three deposits of the Surubim District are hosted in the Caraíba gneissic complex (biotite orthogneiss with local migmatite). The geology of the Surubim Mine and C12 deposit consists of large gabbro-dominant units with minor pyroxenite units and remnants of gneiss that are at least 400m wide. In both deposits, the mafic-ultramafic units are intruded by late north-striking granite and pegmatite dykes. The geology of the Cercado Velho, Lagoa da Mina and Terra do Sal consist of orthogneiss and migmatites intruded by ultramafic units measuring a few centimeters up to 15m thick.
In all the deposits of the Surubim District, the mafic-ultramafic lithological units are generally northerly oriented, and they dip steeply to moderately the west (Figure 7-28, A, B). Two main systems of easterly dipping anastomosing faults occur at the Surubim mine and are oriented NNE-SSW and NNW-SSE respectively. The movements along those faults, and their importance to the copper mineralization, are not well documented.
The mafic-ultramafic intrusive rocks and the gneiss were subjected to variable alteration, including phlogopite, silica, chlorite, K-feldspar, epidote, serpentine, and carbonate. Moderate to intense phlogopite alteration is characteristic of the Surubim deposit whereas k-feldspar, diopside and silica alteration zones are dominant in the Cercado Velho and Lagoa da Mina deposits.
The copper mineralization of the Surubim Mine and C12 deposit occurs as lenses that are hosted by phlogopite-altered gabbro injected by pyroxenite dykes to form what is designated as the ultramafic complex. Sulphide minerals are chiefly chalcopyrite and bornite in a ratio of 4:1 that mainly occur as disseminations and veins. Chalcocite, covellite and cubanite also occur as minor sulphides associated with the mineralization surrounding the Surubim Mine. Magnetite and minor pyrite and pyrrhotite are also associated with the mineralization with pyrrhotite being an important sulphide at the Lagoa da Mina and Cercado Velho deposits. The Terra do Sal deposit is characterized by disseminated and veinlets of pyrrhotite, chalcopyrite with minor bornite, pyrite and pentlandite. Specifically:
- At Surubim, the Cu mineralization is hosted in a series of moderately NW-dipping, NNW-SSE striking lenses measuring a few meters up to 45 m thick. Mineralization is known over 300 m in the N-S direction and 100 m E-W and extends to 400 m below surface. The mineralization remains open at depth and to the NNE extension.
- At C12, the Cu mineralization occurs as several interpreted N-S striking lenses measuring a few meters and up to 75 m thick. However, the general trend of the higher-grade Cu mineralization extends for over 170 m to the NW, approximately 50 m in the NE-SW direction, and is known to a depth of 300 m below surface. The mineralization remains open along the NW and NE extensions and at depth.
- The Cu mineralization at Lagoa da Mina corresponds to a series of steep westerly-dipping, northerly-striking lenses associated with melanorite and pyroxenite and measuring from 10 to 50 m thick and up to 110 m long. The deposit covers an area of 200 m N-S by 80 m E-W and is know to a depth of 430 m. The Cu mineralization remains open in its NW-SE strike extensions and at depth.
- At Cercado Velho, the Cu mineralization is hosted in a series of northerly-trending lenses associated with gabbro and norite and measuring from 5 to 30 m thick by up to 110 m long. The deposit covers an area of 455 m N-S by 200 m wide and is known to a depth of 220 m. The Cu mineralization remains open to the north, the south, and at depth.
- The Cu mineralization at Terra do Sal is hosted in several northerly-trending lenses associated with pyroxenite and gabbro and varying between 10 and 50 m thick and reaching up to 120 m in length. The deposit covers an area of 180 m N-S by 130 m in its E-W extension and is known to a depth of 380 m. The
Cu mineralization remains open in all directions except to the west.