Topological characterization of a polyphased gold-bearing vein network

Abstract It is challenging to evaluate the connectivity of metal-bearing hydrothermal vein systems, i.e. the degree to which fractures or veins are connected within a network. Moreover, many ancient ore-bearing vein networks have been deformed and metamorphosed, which hinders the reconstruction and quantification of their primary characteristics. Here, we explore the reliability and limitations of the network distribution and topologic (classification of vein terminations into I, Y and X nodes) approaches to study deformed and metamorphosed mineral deposits. We focus on the Cheechoo gold deposit located in the Eeyou Istchee James Bay area of Quebec, Canada (Archean Superior Province). This gold deposit shows a complex hydrothermal and magmatic polyphased gold-bearing vein system hosted in a granodioritic-tonalitic intrusion. The Cheechoo deposit is composed of quartz-feldspar-diopside (Qtz-Fsp-Di) and quartz (Qtz) veins that underwent ductile deformation and amphibolite facies metamorphism. The high-grade metamorphism led to the modification of vein shape, relative position and spacing, making these parameters unreliable for the characterization of the Cheechoo vein system and similar metamorphosed networks. However, the number of veins per length unit and topology are reliable tools to characterize such networks. In the gold-bearing Cheechoo system, the gold mineralization appears to be mainly controlled by (i) the number of Qtz and Qtz-Fsp-Di veins per length unit and by (ii) the connectivity of these networks as shown by the increase of both parameters with the gold grade. Furthermore, we introduce the Y/I ratio as a simple topological parameter to quantify the connectivity of two dimensional (I-Y dominated) systems. This parameter is positively correlated with the number of connections per branch (CB) used to quantify network connectivity, and ultimately represent the development of a fault or fracture zone.