Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The Cabacal Deposit is located in the southern part of the Amazonian Craton (Brazil). It is hosted within the felsic volcanic and volcanoclastic rocks of the Proterozoic Alto Jauru Greenstone Belt.;The processes leading to the deposit are under debate. Some consider the Cabacal Deposit to be of shear-related origin, whereas some interpreted it to be a syngenetic deposit. The present study concludes that the Cabacal Deposit is a deformed volcanogenic massive sulphide deposit. The age of the volcanic system is around 1.7Ga, and of deformation is around 1.6Ga.;Host rocks are commonly sheared parallel to lithological boundaries. Intensive alteration affected the host rocks in the vicinity of the ore bodies. This alteration zone consists of an inner chloritized core, surrounded by a sericitic zone similar to those that occur in VMS deposits. The felsic volcanic host rocks have chemical characteristics pointing to their generation in an island arc environment.;Of the intrusive bodies of the area, the Cabacal Tonalites have some chemical similarities with the felsic volcanic rocks from the Manuel Leme Formation. They also show characteristics of an island arc environment. Possibly, the intrusion took place simultaneously with the shear that affected that area.;Ore in Cabacal is distributed in three zones (South, Central and East Copper Zones) composed of a portion rich in copper and a stringer zone of quartz and sulphide veins. The Central Copper Zone shows a massive sulphide body. Mineralization occurs as landed, veined, breccia and massive ore.;The first mineralizing event in Cabacal is syngenetic with the Manuel Leme formation deposition and it generated a VMS deposit. The second mineralizing event is deformation-related, and redistributed gold into structural features, creating zones with high gold grades. Different fluids were involved in the first mineralization event. Geochemical and thermometric studies suggest fluids with low salinities and of a wide range in temperature (240 to 340{dollar}\sp\circ{dollar}C). Gold transport occurred as Au(HS){dollar}\sp-\sb2{dollar} or AuCl{dollar}\sp-\sb2,{dollar} depending on the associated paragenesis. Results of oxygen isotope studies indicate a fluid with low {dollar}\delta\sp{lcub}18{rcub}{dollar}O ({dollar}-{dollar}2.85 to +2.3), similar to those from the Kuroko mines.



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