Geoinformática e Geoestatística: Uma Visão Geral

Filtration of Components of Sieroszowice Mine Copper Ore Deposit Variogram Models by Means of Estimation Ordinary Kriging Technique

Barbara Namysłowska-Wilczyńska

This paper presents the results of investigations into the spatial variation of the basic geological parameters of strategic mineral resources, i.e. the copper ore deposits in the Foresudetic Monocline in the Lubin-Sieroszowice area (SW part of Poland).
The studies were based on data obtained by sampling the deposit with groove samples distributed mostly uniformly (at a spacing of 15÷20 m) over the area of Sieroszowice mine post-mining block S-1. The studies concerned the Cu grade in and the thickness of the (recoverable) deposit concentrated in Weissliegend sandstones, Zechstein copper-bearing shales, calcareous-dolomitic formations and moreover the accumulation (quantity) of the deposit.
An evaluation of the basic statistics, an analysis of the distribution histograms and an examination of the correlation r between the values of the deposit parameters are presented against the geological structure of the copper ore deposit in block S-1. Isotropic and relative semivariograms of the deposit parameters were  calculated. The shapes of the isotropic semivariograms were approximated using composite theoretical (geostatistical) models consisting of a cubic model and a spherical model, combined with the nugget effect.
Estimated averages Z* and estimation standard deviation σk for the investigated deposit parameters in the centres of the elementary grid blocks were estimated taking into account the determined parameter values of the theoretical isotropic semivariogram models. 
An attempt was undertaken to successively filter off the individual components, making up the composite semivariogram models of the copper ore deposit parameters, using the ordinary (block) kriging technique. Nugget effect C0 and the cubic model, the spherical model and the sum of the cubic model and the spherical model were filtered off.
As a result of the estimations a very detailed picture of the variation in the values of the basic deposit parameters within block S-1 was obtained, which was then presented on various raster maps of the surface distributions of averages Z* (together with the corresponding values of estimation standard deviation σk). The maps show the mineralization of the deposit rocks with copper compounds, broken down into the particular components corresponding to the adopted models and to nugget effect C0.
Thanks to the filtering the mutual shares of the different model components in overall variation C of the considered parameters were identified and the scale and extent of both short- and longterm variation were assessed. 
Zones of elevated or reduced copper concentrations and subareas varying in the width of the mineralized lithological profile of the deposit series, i.e. in the thickness of the mineralized deposit rocks, and also of various accumulations (quantity) were identified within block S-1.