Using multifractal modelling, singularity mapping, and geochemical indexes for targeting buried mineralization: Application to the W-Sn Panasqueira ore-system, Portugal

The Panasqueira Mine is a world-class W-Sn-Cu vein-type deposit, currently exploited by Beral Tin & Wolfram Portugal, which has promoted the sampling and analysis of a series of chip-rocks covering an approximate area of 8 × 3 km over the Mine prospect and adjacent areas, with the objective of identifying geochemical signatures related to the Panasqueira granite emplacement and thus targeting new areas with potential W-Sn mineralization of the same ore-system. The geometry of the Panasqueira granite is still unknown but some drill-cores and geophysical techniques provided indications of its extension and presence beyond the current mine exploitation permit. The opportunity of using whole-rock samples, jointly with the current knowledge of the complex mineralizing stages and related geochemical signatures, allowed the proposal of empirical elemental ratios and exploration indexes, which combined with multifractal models for anomaly characterization and singularity mapping, provided a fairly complete and coherent picture of different anomaly patterns for Sn, W, and Cu. These patterns not only target the current exploited areas over the Panasqueira Mine but, more importantly, sustain the occurrence of additional anomalies that can potentially increase the current reserve estimation and consequently extend the mine's life-span. Most elements showed a single anomaly threshold, as W at 1.8 ppm, but others showed two, including Sn at 2.3 and 13.6 ppm, the latter notably close to the empirically deduced one of 15 ppm. The evidence for the extension of the current anomalies also relies in the singularity and anomaly mapping based on the different thresholds using associated elements, such as Nb, Ta, and Ti for W, F, Li, element ratios, for Sn, and ISW and IBM indexes.