GEOLOGIA, GEOQUÍMICA E MINERALOGIA COMPARATIVA ENTRE AS INTRUSÕES DIAMANTÍFERAS CANASTRA-

GEOLOGIA, GEOQUÍMICA E MINERALOGIA COMPARATIVA ENTRE AS INTRUSÕES DIAMANTÍFERAS CANASTRA-1 E ABEL RÉGIS (MINAS GERAIS).
Hundreds of alkaline-ultrabasic intrusions occur in the south-southwestern region of Minas Gerais state. Two of these intrusions, both diamondiferous, were studied in detail evolving their geological, geochemical and mineralogical aspects. The second was still a subject of LA-MC-ICP-MS dating in zircon. In the geologic aspect, such intrusions present significant morphological differences: the Canastra-1 surface is distorted and of little dimension (150 m in length), while the Abel Régis has large circular diameter (1.4 km); the first presenting root facies, and the other crater facies. The rock chemistry of these intrusions shows peculiar characteristics, mainly related to the alkaline elements: the Canastra-1 pipe is depleted in Na₂O and K₂O, oxides that have significant contents in the Abel Régis pipe. This pipe has been dated in 86.1 ±4.5My. Mineralogical aspects of the diamond indicator phases also were distinct: abundance of Cr-spinel, besides the presence of sanidine, and the mineral chemistry of ilmenite and diopside, indicate a possible lamproitic “tendency” to the Abel Régis pipe, while the Canastra-1 has geochemical and mineralogical features of a typical kimberlite.