Química de minerais indicadores de intrusões kimberlíticas com ênfase na província diamantífera Serra da Canastra (MG): importância na prospecção de intrusões férteis

Abstract

This work included the study and evaluation of major elements chemistry of the main sources of indicator diamond minerals. The intrusions analyzed are a set part of alkaline igneous rocks affinity grouped in the Alto Paranaíba Alkaline Province. This province located in west bank of São Francisco Craton, with its lithologies deposited on members of their own craton and Brasilia Belt, has well as rocks and carbonatites, kamafugites, a series of kimberlitic intrusions outcropping or suboutcropping. These kimberlitic intrusions by their spatial distribution and physiographic context are distributed in provinces, where the diamond content is present, then as characterizing these regions as kimberlitic/diamondiferous provinces, because diamond content is not always present and associated with intrusions that occur in the area. In the scope of work to Serra da Canastra Kimberlitic/Diamond Province is the focus of the work. In this province a series of intrusions, is known to drilling companies and researchers working in the region (Canastra-1, Canastra-3, Canastra-5, Canastra-8, and Canastra-35 pipes) had their meeting of indicator minerals analyzed (pyrope, diopside-Cr, picroilmenite and chromite) and its main prospective aspects described extensively in the literature. Since the characteristics presented reflect mainly kimberlitic affinity and favorable fertility characteristics of diamonds. For comparison, intrusions, already described in the literature, such as intrusion Vargem (Alto Paranaíba Kimberlitic/Diamond Province) and Abel Régis (West São Francisco Province) intrusions. The main distinguishing characteristics of the intrusion of these provinces, lies the presence of only a trend in pyrope compositions lherzolite-pyroxenite), while in the Serra da Canastra intrusions show two trends, one pyroxenitic to lherzolitic, and other for harzburgite to lherzolite composition, typically associated with fertility and diamond potential. For the Cr-diopside, Serra da Canastra region has two peridotite distinct sources, but kimberlitic affinity. The ilmenite essentially reflects the kimberlitic composition, in terms of reducing environment partially preserved, where part of the diamond content and was not reabsorbed by the system. The chromite data reflect a high concentration in composition corresponding with the occurrence of this mineral as inclusions in diamonds. Since this is indicative of the fact that so many diamonds as chromite are cogenetics. These data reflect the particular conditions in the provinces related to geological and geotectonic aspects of the São Francisco Craton. The kimberlitic intrusions of Serra da Canastra Kimberlitic/Diamond Province seen as intrusions residents have banded mobile chemical aspects that reflect the behavior of intrusions in cratonic areas of deep roots able to sample the mantle zones of diamond stability. This factor is supported by the significant diamond content of the intrusion Canastra-1 and by recent data that reflect the stability of mobile belts during the Cretaceous period. Thus the continental shelf would have dimensions well beyond the craton limits like is widely known.