Abstract

The formation of ore minerals in hydrothermal deposits is the result of a complex interplay between physical and chemical processes that are conditioned by the geologic environment in which they occur. In the last decades, research has increasingly indicated that many of these processes display different forms of scale invariance, i.e., they show fractal geometry. This suggests that behind the apparent disorder and irregularity of the geometry of mineral deposits at different scales, an underlying regular pattern is present. If properly understood, this regular geometrical pattern could be useful in a variety of theoretical and applied fields. A great portion of this scale invariance is given by the structural framework during mineralization because structures are a dominant factor controlling fluid flow. Here, we assess the geometry of iron oxide copper-gold (IOCG) mineralization in the world-renowned Carajás mineral province, focusing on one of the largest and most economically important orebodies, the Sossego deposit. The geometry of mineralization is evaluated at the microscale (ore minerals in thin sections), local scale (orebodies in mine maps), and regional scale (deposit distribution on regional maps). We show that the spatial distribution and shape of ore minerals at the microscale is largely nonrandom, presents fractal geometry, and displays defined trends in spatial distribution and anisotropy. Additionally, the geometric trends observed at the microscale mimic those of the local-scale geometry of orebodies, as well as the regional-scale distribution of mineralization. The main property controlling the observed scale invariance is permeability, which is intrinsically associated with structures at multiple scales. These results contribute to further understanding the fractal nature of processes controlling mineral deposit formation and revealing new multiscale approaches to investigate structural controls on ore deposition.

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