The Canastra Range Diamondiferous Province and the Canastra-1 kimberlite: first primary

The Canastra Range Diamondiferous Province and the Canastra-1 kimberlite: first primary economic source of diamonds in the country.
The Serra da Canastra Province integrates one of the four great diamondiferous provinces of Minas Gerais State, and can be divided into two districts, named as Alto São Francisco and Médio Rio Grande districts. Kimberlitic and parental rocks mainly cut mesoproterozoic(?) metasedimentary rocks of the Canastra Group, in the Alto São Francisco District. In the case of the Canastra-1 diamond-bearing intrusion, the ages are around 120 Ma. In the Médio Rio Grande district, the main (secondary) source of the diamonds is the Lower Cretaceous conglomeratic rock occurring in the north side of the Paraná basin (Bauru Group). The sedimentary source area for these sediments included the Canastra Range zone. The Canastra-1 body is part of a cluster with approximately 40 pipes outcropping on the south side of the Canastra Range, near the sources of the São Francisco River. The intrusion is made up of two blows aligned along NE-SE, which is the region's structural trend defined on the metasedimentary rocks of the Canastra Group. The smaller blow has only negligible diamond content, while the SE blow is mineralized with an average content of 12 to 18 ct/100 tonnes of rock. There are also significant differences in the petrographic facies of the two bodies, which is homogeneous in the NW blow while the SE blow is heterogeneous, with the occurrence of a mixture of several facies. The mineral chemistry of the pyrope, ilmenite and diopside showed some resemblance with some diamondiferous African kimberlites, mainly those of the West African Craton. Data from experimental mining activities of SAMSUL Mining Company indicated an excellent quality for this kimberlite's diamonds, with US$180-200/ct estimated average value; certainly, this is one of the highest values worldwide.