Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The Chibougamau area, NE corner of the Abitibi subprovince, is characterized by an abundance of Cu-dominated magmato-hydrothermal mineralizing systems. Several of these systems are investigated as part of the Metal Earth project (Laurentian University), which aims at unrevealing the key differences between well metal-endowed and less endowed greenstone belts. This contribution provides an overview of the projects conducted at UQAC with the support of Metal Earth. One of these projects, which focuses on the Chibougamau pluton and its related Cu-Au mineralization, is then be presented in more details. The Chibougamau pluton is a Neoarchean (~†2715-2718 Ma) multiphase intrusion (diorite and tonalite) genetically related to Cu-Au porphyry-style deposits. In Archean greenstone belts, porphyry-style mineralisation is marginal and poorly documented. Such deposits are however important in the Chibougamau area, where the main historical mining camp (Central Camp) is interpreted as a magmato-hydrothermal system. The comprehension of such systems requires a documentation of the chemistry of the related magmas. This contribution focuses on the petrogenesis of the Chibougamau pluton and on its capacity to contribute Cu and Au to mineralising systems. Using field descriptions, whole rock analyses and petrographic observations, the mode of production, emplacement mechanism and chemical evolution of the Chibougamau pluton is addressed. The Chibougamau pluton is a TTD (tonalite-trondhjemite-diorite) suite containing more K than most plutons of similar ages. The magma was generated at ~†20 kbar from an heterogeneous source, i.e. hydrated basalt and mantle metasomatized by TTG melt. These are rare and possibly prospective characteristics for Archean intrusions. In addition, prolonged differentiation of the diorite phase may have favoured the concentration of metals and fluids in the evolved magma. These magmatic constrains are to be tested against a renewed comprehension of the Cu-dominated mineralising systems of the Chibougamau area.