Aplicação do software Datamine no modelamento geológico e cálculo de reservas das jazidas de bentonita, Boa Vista-PB.

Abstract

In the Boa Vista region of the state of Paraiba there occurs one of the biggest deposits of bentonite in Brazil. The deposit is spread out along a distance of 10 km occurring with in small basins with an average of 200-300 m radius and a depth of 8-10 m. The thickness of the bentonite beds vary highly due to irregular surface of the Precambrian rocks over which the clay originated. Clay beds are intercalated with sand, silt, chalcedony and basaltic flows. Open pit mining of the clay is carried out in the area and mining methods tend to be very simple due to smaller dimensions of the deposits. The purpose of this research is to develop model of the occurrence of some of the deposits of the bentonite in the Lages and Jua areas using the software Datamine and geostatistics and estimate the reserves using the models. The Datamine program is generally used in the mining to identify the behavior of the variables of metallic ore bodies such as assays, thickness, lithology and geometry. In this work the variable used for modeling is the thickness of the bentonita deposits, which was determined through drilling. The drilling was done with grid sampling pattern with regular intervals between the drill holes. In each drill hole, from top to bottom, variables obtained were thickness of soil cover and followed by the bentonite bed thickness. During modeling the topographic variations of the surface where drilling was done is considered. The multidimensional modeling was carried out considering the thickness of soil and the bentonite beds. In the Lages deposit spatial variation of the thickness was determined through variographic analysis. The validation of the available data was made and these new estimated values were again used to make another model. These developed models of the bentonite deposits depict the high variation in the thickness of the bentonite beds and the inaccuracy that may arise in calculating the reserves. Thickness of the bentonite deposits shows spatial correlation as shown in the variogram structure and the structure is independent of the direction. Bentonite reserve of the Lages deposit was calculated for the model developed with existing drill holes and also with a model elaborated with existing and estimated drill holes data. In the Jua deposit the bentonite reserve was calculated using the model developed with existing holes. These reserves were compared with the reserves obtained by the mining companies of these two deposits. The modeling with Datamine and the geostatistics would considerably reduce the errors made during estimation of reserves and mining of bentonite in the region.