MINERAIS INDICADORES KIMBERLÍTICOS E PROSPECTIVIDADE DIAMANTÍFERA DA INTRUSÃO ALFEU-01 (CANGUÇU, RS).
The Alfeu-01 kimberlite intrusion
was discovered in 1994, and is hosted by granitoid rocks of the Pinheiro
Machado Complex, of Neoproterozoic age, in the Sul-Riograndense shield.
This kimberlite is melanocratic, and has an afanitic matrix where
xenoliths of the host rocks as well as macrocrysts of phlogopite, rutil,
garnet and, possibly diopside can be observed. The petrographic
descriptions (basically phlogopite + olivine + talc + serpentine)
indicate that it is an explosive breccia, probably of diatreme facies.
In geochemical terms, the high contents of TiO2, MnO and K2O
are characteristics, in contrast with diamondiferous intrusions of
Minas Gerais. The garnets were divided into three different colors, a
strong association of colors with the Fe2O3, MgO and Cr2O3
contents having been observed. All garnets, identified as the pyrope
type, are located in the mineral fields known as G4, G5 and G9,
generally not associated to fertile intrusions. In the same way, the
high oxidation grade in the Mg-ilmenite is not favorable for diamond
preservation. Chromite data indicates that the mineral is out of the
diamond inclusion field. Diopside of the intrusion is Cr-poor, and
recognized as associated to an alkaline basalt suite. All mineralogical
parameters characteristically diverge from the observed in fertile
kimberlites of Minas Gerais; in this way, they strongly not encourage
another prospecting works on the intrusion.
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