Spatial simulation of the W-Sn ore grades of São Pedro das Águias skarn mineral deposit (Tabuaço, northern Portugal)

Abstract

The purpose of this study is the W-Sn grades simulation of São Pedro das Águias skarn ore deposit (Tabuaço, northern Portugal). This skarn deposit hosts a mineralization of scheelite and cassiterite. The grades modelling constrained by lens-shaped skarns is challenging, because they are numerous, thin, constrained to the structure shape and orientation, and recognized only in the drill-holes without indication of interconnections. Despite of the complexity, the proposed methodology constructs a geological model of the lens-shaped skarns, and generates a conditional model of the grades. The geological model construction begins with the automatic simulation of scenarios of the interconnections between the lens-shaped intersected by the drill-holes, conditioned to the orientation of the structure. For the simulated geometry scenarios represented by polylines in several cross-sections thicknesses are added according to the drill-cores, and the skarn relative proportion of each block is evaluated. Finally, the grid blocks between the cross-sections are filled using direct the DSS algorithm with local means from the skarn proportion variable (continuous variable). So long as the skarn thicknesses are much smaller than the blocks size, the morphological model reports the skarn proportion variable. The W-Sn grades model encompasses the local histograms estimation conditional to the geological model, and uses the PFS algorithm to generate the final images. The local histograms estimation results of a grades mixture according to the calculated skarn proportion between each block, and of a simple W-Sn simulated images conditional to the skarn and no-skarn lithological groups. The simulated grades are finally compared with the equivalent resources obtained by ordinary kriging. The simulated images enable the evaluation of the local uncertainty, and may be used for mine planning and optimizations.