Geological controls of copper, gold and silver in the Serra Geral Group, Realeza region, Paranل, Brazil

The Serra Geral Group has high Cu concentrations in southern Brazil, including the Realeza (Paraná) region where Au and Ag also occur. The basalts (46.7–50.8 wt.% SiO2) have breccias at the top of 10 out of 31 studied flows in the Realeza section and at the top of 5 out of 7 analyzed flows in the Capanema section. Sand injectites occur at the top of basalts in 18 out of 23 flows from the Realeza section. The average content of Cu in three samples of mineralized breccias is 3788 ppm. One sample from a silicified sandstone sill intruded at the top of a basalt flow has up to 0.66 ppm Au. K2O was not leached during basalt alteration. The hydrothermal breccias, particularly when sand is present, show enrichment in U which leads to higher values of scintillometry (rate of emission of K, U and Th). In the basalts, breccias and sandstones, Pd (17.5 ± 8.4 ppb) is higher than Pt (12.5 ± 5 ppb), suggesting a hydrothermal remobilization of the metals. The Serra Geral Group is thus shown to have high potential for precious and base metal deposits.