Spatial Geostatistical Analysis Applied To The Barroso-Alvao Rare-Elements Pegmatite Field (Northern Portugal)

The geological science has been in recent years an excellent playground for GIS applied studies, especially regarding the mineral deposits prospectivity. Other fields of study in the geological science (e.g. soil risk management, mining exploitation, geothermal resources…) also took advantages of this geocomputing methodology to extract spatial information. The geoscientist community fairly agrees that interrelations between mineral deposits and certain geological features are observed in the terrain, presenting also a non-random spatial regional distribution pattern in a vast majority of cases. This is where the spatial analysis using geocomputational techniques, in this particular case for rare-elements pegmatites, can be used as a great analytical tool to produce a mapping of mineral potential, or unveil the regional zonation patterns for this type of mineralization. In this study, statistical spatial analyses were performed for the pegmatites to highlight any possible relationship, or lack of it, between them and the surrounding granitic plutons, shear zones or schistose foliations. To accomplish our proposed objectives, the geocomputational method of Distance to Nearest Neighbours (DNN), Ripley’s L’- function and pegmatites orientations families were employed to study the spatial distribution pattern of the pegmatites, whereas Euclidean distance and Kernel density distributions aimed the spatial association between these same pegmatites to the various geological features within the study area. The obtained results show: i) Pegmatites spatial distribution following a clustering pattern, presenting the Lienriched pegmatites a higher rate and extent compared to the total pegmatites, as well as a spatial association with moderate to high pegmatites density; ii) Three distinct families of pegmatites orientation; iii) No statistically significant spatial relationship for the total pegmatites or Li-enriched relatively to the granitic pluton; iv) A regime of deformation within the study area, suggesting the presence of corridors of deformation with NW to NNW orientations; and v) Pegmatites spatial emplacement suggesting shear-zones control.

Keywords: DNN, GIS, Geostatistics, Interpolated foliation, Kernel density, Pegmatites, Ripley’s L’-function, Shear-Zones, Spatial analysis, Variogram.