Compositional and geometrical features in ore deposits: A comparison between karst bauxite deposits

The interest for the study of karst bauxite deposits has dramatically increased recently since these deposits are frequently enriched in valuable elements of major economic importance (Abedini and Calagari, 2015; Herrington, 2013; Mongelli et al., 2017) and furthermore they provide useful information regarding the paleo-conditions during their formation (Boni et al., 2012; Mindszenty et al., 1995; Mondillo et al., 2011; Mongelli et al., 2016). The texture of karst bauxites may be “ooidic” when composed of sub circular concretions (ooids), dispersed in a fine matrix (Bardossy, 1982). These sub-spherical concretions show a concentric structure with different composition that testifies an alternation of different climatic conditions during their formation (Mongelli et al., 2015). Fractal geometry represents a valuable approach for analyze several range of structures ranging from molecules and atoms to the coastlines of continents (Meakin and Fowler, 1995). Meakin (1991) observed the aggregation of small particles to form larger structures are important in several natural processes. Buccione et al. (2016) stated that the formation of minerals can be described in terms of fractal geometry performing image analysis on textural components of Southern Italy bauxite samples, which provide geometric parameters of the ooids (circularity, aspect ratio and fractal dimension). In particular, fractal dimension is quite interesting since the growth of sub-spherical concretions, such as ooids within karst bauxites, can be considered as the growth of fractal aggregates. Fractal dimension (D) for the Salento autochthonous bauxite pebbles, for instance, is very close to D values related with diffusion-limited aggregation models while Campania bauxites exhibited higher Fractal Dimension values which are close to the fractal dimension associated to the diffusion-limited cluster aggregation processes where small particles join together to form further clusters that continue to keep on join to form larger and larger clusters (Meakin, 1991; Mongelli et al., 2016). The shape, the number and composition of these aggregates is strongly dependent on climatic conditions and so the study of these parameters in bauxite deposits of different localities can provide information regarding the climatic and environmental conditions at the time of their formation. In this work, image analysis results carried out on some Mediterranean type karst bauxite deposits on which, image analysis, has never been performed.