Geological mapping of the aurifeous Rancho Novo area, Minas Gerais state, Brazil

The 1:10.000-scale geological mapping was undertaken near the towns of Conselheiro Lafaiete and Ouro Branco, Minas Gerais state, Brazil. The area is a segment of the southwestern portion of the Quadrilatero Ferrifero region, known for its mineral wealth especially gold and iron. The area belongs to the 40-km-long Congonhas Lineament, a shear-dominated structural regional trend. Eight lithological units are recognized, and encompass rocks of the Metaultramafic, Mafic Metavolcanic, Lower and Upper Metasedimentary units, which are the main host to gold, and the units Metagranodiorite, Alto Maranhao tonalite, Metadolerite Intrusions, and Recent Alluvial Cover. The two mapped structural domains are the Lineament domain, which occurs in the N-NE and is the most affected by the Congonhas Lineament shear zone, and the Sinclinorium domain dominating the central and southern portions. Two metamorphic events affected the area, with the regional metamorphism of greenschist facies conditions being best recognized in the supracrustal rocks. Biotite and amphibole reflect a contact metamorphic event on mafic rocks. Gold occurs in shear-related hydrothermal alteration zones, mainly in the NE portion, in close association with sulfide-quartz-rich veins and veinlets. Alteration is represented by the presence of sericite/chlorite, and quartz-carbonate veins and sulfides. Gold occurrences are characterized as orogenic.