Estimación no paramétrica de variables geoquímicas. Aplicación al As como trazador del Au en mineralizaciones auríferas ligadas a zonas de cizalla

Abstract

A nonparametric geostatistical method has been used to treat geochemical data. This method is the indicator kriging and is based on the topoprobabilistic behavior of geochemical variables. The indicator kriging has the great advantage of working with indicator variables. This kind of treatment does not trim the information and allows to separate raw variables in the way that the more interesting part of the information is only considered. Moreover, this methodology produces very clear graphic presentations. Therefore, this technique has the disadvantage that it is not able to distinguish between anomalous high values and high values belonging to background.
In this work, the results of the application of indicator kriging to a set of mineral exploration data carried out in NW Spain are presented. This area is characterized by presence of gold mineralizations. The specific application has been done over As, considered as a pathfinder of Au in this area, since this one allows no numerical treatment. Gold presents a great number of values equal to detection Iimit, and a series of extreme values. These characteristics bring out indicator variograms with no structure. The results of the application of indicator kriging over As allow locate a series of high values place along a N-S shear zone, considered as a structure related to presence of gold. Specifically, these points are located in relation to a kind of cataclastic rocks, where gold mineralizations appear, due to fluid circulation through these rocks.