O DIAMANTE NA BACIA DO RIO SANTA ROSA TIBAGI PR

Abstract (English)

Several diamond occurences exist in the northern, northwestern and southeastern flanks of the Paraná Basin. In the southeast, the Tibagi river valley has yielded important gem quality diamonds which had been investigated by means of mineralogical characterization, detailed mapping and sedimentological studies in the Tibagi basin in general and in the Santa Rosa river in particular. Diamond surface textures and the lack of kimberlitic indicator minerais in the digging areas investigated indicate that the diamonds are unlikely to have been derived from a local primary source. Diamond morphology and mosphoscopic surface textures are not fully consistent with the nature of the recent sediments from which the diamonds have been recovered and part of the mineralogical assemblage in the digging areas have been inherited from one or more pre-existing secondary sources. Selected facies in the Itararé Group is inferred to have been one of such pre-existing secondary source, based on of texture and mineralogy and depositional process. Notwithstanding the poor concentration capacity of glacial environments, it is suggested that fluvial rework during the deposition of the lower Itararé Group led to the formation of reverse graded channels and re-sedimentation processes which had the diamonds incorporated in such glaciogenic deposits could have been derived from the Kaapvaal craton in South África and transported by the Kaokoveld glacial plume.