The Archean-Paleoproterozoic structural evolution of the Caraíba Cu-Deposit, northern São Francisco Craton, Brazil: A historical review of its understanding coevally with the development of a high-risk mining project

Abstract

The belt of basic-ultrabasic rocks within the Curaçá River Valley Province of the Bahia State, northeastern Brazil, has been known for enclosing several Cu-orebodies that helped sustain the industrial development of Brazil in the last five decades. Caraíba, Vermelhos, Surubim, Terra do Sal, Angicos, Sussuarana are the most prominent of these deposits. The Caraíba Cu-Orebody, so far the most important of all, is part of a body of Archean hypersthenites and norites that underwent poly-deformation and granulitization  in the roots of the Paleoproterozoic Itabuna-Salvador-Curaçá orogen, which records the continental collisions responsible for building the São Francisco-Congo paleocontinent in Rhyacian times, ca 2.0 Ga ago. The Caraíba Mine setup happened during the 1970 decade, together with the rush to free the country's economy from the costs of importations, exactly when the first international oil crisis (1974-1978) was suffocating the economy in many countries. Although that time coincided with the boom of geological knowledge associated with the worldwide acceptance of plate tectonics, the study of high-grade metamorphic terrains was still embryonic. In particular, the meaning of the poly-phased tectonic structures in areas recording a high degree of plasticity during deformation remained unraveled. Due to the international economic crisis, everything necessary for running the Caraíba Mine was done under pressure. Nonetheless, the coeval geological studies required for deciphering the area's structural evolution and the mineralization controls, vital for the booming mining planning and profitable exploitation of the Cu ore, had to keep the academic standards for surviving the hurry.

Part of this text is a historical novel as it describes in detail how the convenient geological knowledge of the Caraíba-Cu Orebody could be achieved progressively in the years 1980-1990, well in the middle of the rush affecting everything and everybody working in the Caraíba Mine Project.We emphasize thedetailed structural geology studies as the primary tool for guaranteeing timely technical accuracy during the ore's exploitation and profitability in the mine project.As such, it means a historical but profoundly scientific document necessary for those interested in academic and technical purposes related to large-scale mine projects everywhere. Moreover, it highlights the human drama lived by many fortunate professionals in that forgotten semi-desertic area of northeastern Brazil. The experience gained when studying several generations of tectonic structures and metamorphism at Caraíba transformed for the better and forever the lives of several geologists and other professionals equally in charge of operating the Caraíba Mine during those pioneer years.