info:eu-repo/semantics/article
GOLD IN SERICITE-QUARTZ HYDROTHERMALITES CONTROLED BY BRASILIANO CONJUGATE SHEAR ZONES IN THE CAVALCANTE (GQ) REGION, CENTRAL, BRAZIL
OURO EM SERICITA-QUARTZO HIDROTERMALITOS CONTROLADOS POR CISALHAMENTOS CONJUGADOS BRASILIANOS, NA REGIÃO DE CAVALCANTE (GO) .BRASIL CENTRAL
Autor
SILVA, LUIZ JOSÉ HOMEM D'EL-REY
FILHO, VIRDÁLIO SENNA
Institución
Resumen
In the Cavalcante area, north-northeastern part of the Goiás State, Central Brazil (coordinates 47° 30 - 47° 20 W and 13° 40 -13° 50 S), about eighty lens-shaped bodies of sericite-quartz S-C mylonites have been mapped and most of them are along dextral, ENE- and sinistrai WNW-trending, sub-vertical, ductile-brittle shear zones that intercept each other and cross-cut both the Archean-Paleoproterozoic basement and the Mesoproterozoic Araí Group. The shear zones stretch for 1-5 km whereas the Au-bearing bodies are much shorter and have an average width about 20-30 m. Seventy of these bodies have been sampled and contain gold in variable amounts, whereas the remaining ten bodies have not been prospected yet. The Cavalcante shear zone (dextral) is one of such structures and encloses the Cavalcante Mine, which has been producing gold (and platinum) since 1750, from underground operations in a 60 m-long segment of the Cavalcante sericite-quartz mylonite body, which is about 500 m-long, 20-25 m-wide and displays a sub-vertical, N60°-70°E trending C foliation, and a N10°-30°E trending S foliation dipping around 75° -80° to ESE. Abundant geology and chemistry data from drill holes and underground galleries have allowed to state that the Cavalcante orebody is an amalgamation of several lenses displaying a map-view sigmoidal geometry with 10-20 m-long axis parallel to the S foliation and a 3-5 m-long short axis in the perpendicular direction. They plunge about 80° to ENE and are continuous at depth for several tens of meters, as demonstrated by the mining operations. Gold occurs as generally sub-mm flattened grains controlled along the foliation planes and the higher grades are associated with ore displaying a hydrothermal alteration characterized at least by pyrite, tourmaline, magnetite and carbonate minerals. Detailed structural relationships clearly demonstrate that the mineralisation is syn-tectonic and the deformation was progressive, as Au-bearing syn-tectonic siliceous veins emplaced sub-parallel to the S-C planes or along synthetic R planes (possibly R' planes as well) were also sheared and washed by Bo-bearing fluids. An absolute age determination of the mineralisation is still missing, but the conjugate pair of shear zones fits well with a nearly E-W trending maximum horizontal stress that is entirely compatible with the Brasiliano event already documented in the surroundings of Cavalcante. The tens of Au-bearing bodies of hydrothermalite along the shear zones places the Cavalcante area in the rank of those with a very high potential for gold exploration. In the Cavalcante area, north-northeastern part of the Goiás State, Central Brazil (coordinates 47° 30 - 47° 20 W and 13° 40 -13° 50 S), about eighty lens-shaped bodies of sericite-quartz S-C mylonites have been mapped and most of them are along dextral, ENE- and sinistrai WNW-trending, sub-vertical, ductile-brittle shear zones that intercept each other and cross-cut both the Archean-Paleoproterozoic basement and the Mesoproterozoic Araí Group. The shear zones stretch for 1-5 km whereas the Au-bearing bodies are much shorter and have an average width about 20-30 m. Seventy of these bodies have been sampled and contain gold in variable amounts, whereas the remaining ten bodies have not been prospected yet. The Cavalcante shear zone (dextral) is one of such structures and encloses the Cavalcante Mine, which has been producing gold (and platinum) since 1750, from underground operations in a 60 m-long segment of the Cavalcante sericite-quartz mylonite body, which is about 500 m-long, 20-25 m-wide and displays a sub-vertical, N60°-70°E trending C foliation, and a N10°-30°E trending S foliation dipping around 75° -80° to ESE. Abundant geology and chemistry data from drill holes and underground galleries have allowed to state that the Cavalcante orebody is an amalgamation of several lenses displaying a map-view sigmoidal geometry with 10-20 m-long axis parallel to the S foliation and a 3-5 m-long short axis in the perpendicular direction. They plunge about 80° to ENE and are continuous at depth for several tens of meters, as demonstrated by the mining operations. Gold occurs as generally sub-mm flattened grains controlled along the foliation planes and the higher grades are associated with ore displaying a hydrothermal alteration characterized at least by pyrite, tourmaline, magnetite and carbonate minerals. Detailed structural relationships clearly demonstrate that the mineralisation is syn-tectonic and the deformation was progressive, as Au-bearing syn-tectonic siliceous veins emplaced sub-parallel to the S-C planes or along synthetic R planes (possibly R' planes as well) were also sheared and washed by Bo-bearing fluids. An absolute age determination of the mineralisation is still missing, but the conjugate pair of shear zones fits well with a nearly E-W trending maximum horizontal stress that is entirely compatible with the Brasiliano event already documented in the surroundings of Cavalcante. The tens of Au-bearing bodies of hydrothermalite along the shear zones places the Cavalcante area in the rank of those with a very high potential for gold exploration.