Gites de graphite de la region de la Gatineau, Quebec

The metasedimentary rocks of the Grenville Supergroup host 90% of the lump-graphite (vein-graphite) and flake-graphite deposits of the Hull - Lachute - Mont-Laurier sector of the Gatineau area, Quebec.;Because of the geological diversity and the disputed origin of the graphite deposits, a descriptive classification was established. This classification is useful to mineral exploration and provides a consistent and objective base for genetic studies.;For economic reasons, the disseminated flake-graphite deposits represent the best exploration targets. The aluminosilicate-bearing paragneisses and porphyroblastic marbles are the most favourable rock types to host these deposits.;Granoblastic marbles and quartzites generally contain lower grade deposits with lesser economic potential. However, blue-colored quartzites may be used as metallotects in the exploration for high-grade graphite deposits.;Graphite concentrations of economic interest were reported in iron formations, however no published information is available concerning the continuity and size of these occurrences.;The size of the disseminated graphite-bearing pegmatites is too small to be of interest as a source of graphite.;Graphite veins are not recommended as primary exploration targets in Quebec. Graphite veins cutting wollastonite-bearing rocks could be of interest if both graphite and wollastonite were selectively mined and processed.;Field work, petrographic, geochemical, isotopic, fluid inclusion studies, and thermodynamic calculations of the mineral's field of stability were done to elucidate the origin of the various types of graphite deposits. These studies indicate that the disseminated flake-graphite in quartzites, paragneisses, and marbles formed by graphitation of organic material.;Higher grade graphite concentration ;Graphite contained in iron formations was probably produced by metamorphism of organic materials or by precipitation from carbon-bearing fluids derived by the destabilization of siderite.;Graphite veins probably formed by mixing of carbon-bearing fluids derived by decarbonation of marbles and by devolatilization of paragneisses or from fluids associated with igneous intrusive rocks.;Graphite disseminated in pegmatites and in contact zones of mafic intrusions probably precipitated due to the mixing of the fluids derived from marble decarbonation and fluids from associated intrusive rocks.