TOPOLOGICAL AND STATISTICAL INVESTIGATION OF A AU-BEARING STOCKWORK REVEALS ITS REMOBILIZATION DURING PROGRADE AMPHIBOLITE FACIES METAMORPHISM, CHEECHOO DEPOSIT, NORTHERN QUEBEC

Precambrian vein-hosted Au deposits are commonly emplaced under greenschist facies conditions, and in some cases superimposed by amphibolite facies metamorphism and deformation that may lead to Au redistribution. The structural characterization of vein networks and the prediction of the metal grade distribution in such contexts are key challenges for mineral exploration and production. In this contribution, we use a topological and statistical approach to compare Au distribution with vein connectivity and density in the Archean Cheechoo Au deposit in Northern Quebec, Canada. The deposit is hosted by a deformed granodioritic to tonalitic intrusion emplaced into wacke and that underwent several stages of deformation, hydrothermal alteration and formation of Au-bearing veins recrystallized during prograde amphibolite facies metamorphism. Au-bearing quartz-feldspar-diopside (Qtz-Fsp-Di) veins and Qtz veins exert a strong control on the mineralization, as shown by the close relationship between Au grade, showing a lognormal distribution, and the density and connectivity of the vein networks. Strongly albitized zones are also present and are characterized by a similar statistical and topological vein distribution. However, these zones have a multimodal Au grade distribution, typical of nugget effects. Syn-kinematic Au-bearing pegmatites injected after peak metamorphism crosscut the previous vein networks and alteration zones. The Au grade distribution in pegmatites is also multimodal with local high-grade values up to several g/t, and is interpreted to result from Au remobilization during pegmatite emplacement. Accordingly, the combination of (i) a structural analysis, (ii) topological characterization of successive vein networks and (iii) statistical Au grade distribution allow to decipher mineralizing events and predict metal grade distribution in such metamorphosed polyphased vein-hosted deposits.