OLIVEIRA, G. V.; http://lattes.cnpq.br/3949007978551948; OLIVEIRA, Gracílio Varjão de.
Résumé:
The vermiculite deposits of the Queimada Nova locality of the Paulistana
region of Piaui State in northeast Brazil is associated with the ultrabasic intrusives
which are enclosed by the country rocks composed of garnet schists and migmatites
of the Lower Proterozoic age. The basic rocks in which the vermiculite is explored,
tend to be highly altered and the vermiculite occur disseminated in the rock and also
as veins and veinlets. The vermiculite is mined extensively and processed
granulometrically in the region for variety of industrial uses. The deposit has an
extension of approximately 2000m x 1500 m and the mineral is explored in various
open pit mines. Due to highly irregular nature of the deposit the systematic mining is
becoming difficult and costly. In this work an attempt has been made to define the
nature of the deposit with variographic analysis. This study was carried out in two
areas Cava Nova and Cava Piloto to examine the variation of the thickness of the
deposit within a limited terrain. The thickness was determined through a total of 89
and 102 drill holes resepectively that were distributed in a grid pattern. The thickness
of vermiculite beds varies from a minimum of 0.85 m to a maximum of 19.39 m with a
mean of 10.8 m in Cava Nova. In Cava Piloto the thickness varies from 0.84 m to
10.0 m with an average of 3.91m The coefficient of variation obtained was 36,54% in
Cava Piloto and 40.42 in Cava Piloto indicating a considerable variation in thickness.
Variographic analysis of the thickness data obtained from drill holes showed an
average variogram with a reasonably good structure without anisotropy. Variation in
the sample pair distances helped improve the variogram structure. The variogram is
an undulating curve with hole effect, reflecting the apparent pinch and swell nature of
the deposit resulting from intrusives in the form of dykes and sills in the study area.
The three dimensional model shows highly irregular nature of the deposit, and
geometry of the deposit varies greatly, reflecting the apparent pinch and swell nature
of the deposit resulting from intrusive in the form of dykes and sills in the study area
and modified my structural deformation.
