The region of Caçapava do Sul, in the State of Rio Grande do Sul, is characterized by the occurrence of a granite batolite (Granite Caçapava) with outcrops of 25 x 10 km, oriented in the N - S direction. The Caçapava Granite is surrounded by a belt of metamorphites of the Porongos Group, and attributed to the Upper Precambrian by RIBEIRO et alii (1966). Including in these metamorphics is a body of carbonate rocks of lenticular aspects, with clear contacts, interpenetrated by granitic apophyses and with an outcrop of approximately 17 km 2 Samples of this rock body were studied by means of microscopy, diffractometry and x - ray spectrometry, electron microprobe and wet chemical analysis, in order to identify and characterize the carbonate and silica minerals.
By means of staining techniques, it was possible to distinguish dolomite (Do), calcite (Cc) and ferric calcite (Ccf).
The modal and chemical analyzes indicated the predominance of carbonates on silicates, the latter being more related to the rock bands.
The silica minerals detected were: talc, tremolite, diopside, forsterite, chlorite and phlogopite. In smaller quantities appear titanite, apatida and quartz, being also, common, serpentine originating from forsterite alteration.
The results of the study of these rocks allowed them to be classified as unclean dolomite marbles of contact.
