The Sao Francisco deposit is a shear hosted and structurally controlled lode gold deposit, which appears to be epigenetic and composed of one centimetre to five centimetre wide, sericitic quartz veins containing free gold. It occurs in a hydrothermal alteration zone within the basal Fortuna Formation of the 1,200 metre-thick sequence of clastic sediments known as the Aguapei Group. The gold occurs as free gold and frequently as coarse nuggets measuring several millimetres in diameter with the quartz, as laminations along the fracture planes, and within limonite boxwork after pyrite and arsenopyrite. The ore is categorized as either gravity leach ore or dump leach ore, depending on gold content and processing method.
Modern day exploration at the Sao Francisco Mine has occurred periodically from 1990 through 2008. Exploration activities conducted during this period included diamond drilling, reverse circulation drilling, metallurgical testing and bulk sampling, with a total of 90,580 metres drilled. Currently, US$10 million has been budgeted by Aura Minerals to complete exploration and definition drilling at the Sao Francisco and Sao Vicente gold mines in 2010, to upgrade and expand the resource base.