COMPOSIÇÃO E GEOTERMOMETRIA DOS FLUIDOS MINERALIZANTES EM DEPÓSITOS DE Zn-Pb DAS COBERTURAS NEOPROTEROZÓICAS DO CRÁTON DO SÃO FRANCISCO: IMPLICAÇÕES METALOGENÉTICAS

Abstract

Fluid inclusion studies in primary and pseudo-secondary inclusions in sphalerite from sediment-hosted Pb-Zn deposits of the Sao Francisco Craton Neoproterozoic basins were performed to obtain minimum formation temperatures, and fluid composition. These data could be used to interpret the physico-chemical environment of the ore deposition and for exploration programs. In the Morro Agudo deposit, fluid inclusions in sphalerite indicate moderate saline solutions, around 14%wt eq. NaCl. The wide range of salinity within the orebodies is apparently related to a zonal distribution in relation to the main fault zone that controls the mineralization. Total homogenization temperatures (T H ) indicate also a zoned pattern closely related to the main fault zone. They are relatively higher in the ‘A’ Block, closer to the fault zone, varying from 122° to 283°C with a mean of 170°C in the JKL orebody. Away from the main fault , to the west, paleotemperatures are gradually lower, ranging from 80° to 168°C with a mean at 155°C, in the ‘C’ block. The stratiform ‘N’ orebody, in the upper part of the section exhibits the lowest temperature interval, varying between 120° and 144°C with a mean of 138°C. In the Nova Redencao deposit, fluid inclusions show moderate to high salinity aqueous solutions, with 24.3 wt%. NaCl eq., probably containing Ca, K and Mg salts. The homogenization temperatures range from 140° to 190°C with a mean of 185°C. In the Irece deposits, limited determinations in primary inclusions of sphalerite show homogenization temperatures (T H ) between 140 and 200°C and salinity between 3 and 10% NaCl equivalent. When compared with T H and salinities from typical MVT, SEDEX and Irish deposits, the obtained data fall in the field of Irish type.