The Kwyjibo Polymetallic Iron Oxide Deposit, Northeastern Grenville Province, Quebec

2003

Isabelle Roy, Alain Cayer, Michel Gauthier,

The Kwyjibo deposit is a Mesoproterozoic Cu-REE-Mo-F-U-Au iron-oxide mineralisation occurring along the SE margin of a granitic complex of within-plate affinity in the Grenville Province. The deposit, located approximately 120 km NE of Sept-Îles, comprises a number of polymetallic showings that are related to different textural facies of magnetite and hematite. The Kwyjibo deposit was found in 1993 following field investigation of a multi-element lake sediment anomaly by SOQUEM Inc. and the Iron Ore Company of Canada. The iron-oxide host-rocks of the mineralisation were the first exploration targets, and seven polymetallic showings were subsequently found over a strike length of more than 5 km. Between 1994 and 1996, nearly 5000 m of drilling were completed in 42 holes. In 1998, SOQUEM Inc. and new partner Matamec Exploration Inc. drilled an additional 1,582 m in 6 holes. Porphyroidal leucogranite and volcanic equivalents of the Canatiche Complex are the main hosts of the mineralisation. Calc-silicate rock and hornblende-biotite gneiss, possibly belonging to the supracrustal Manitou Complex, flank the deposit to the SE and S. Magnetite is omnipresent in the Canatiche granitoids, and generally occurs as disseminations and fine agglomerations. Near the deposit, magnetite progressively increases to form veinlets, veins, stockworks and pseudo-breccias, culminating with the formation of locally-brecciated massive magnetite, the dominant type of iron-oxide concentration. Specular hematite is less common, and locally occurs as disseminations and veinlets. Mineralisation at Kwyjibo is complex and multi-stage, and is divided into Early Granitophile, Magnetite, Main Polymetallic and Specular Hematite stages. Main Polymetallic mineralisation, comprising chalcopyrite, pyrite, molybdenite, fluorite and REE-bearing minerals, is superimposed on pre-existing magnetite-rich rocks, and shows little evidence of deformation. The Kwyjibo deposit shares many similarities with other polymetallic iron oxide deposits around the world, including (1) granitic host-rocks of within-plate affinity, (2) various facies of iron oxide, and (3) sodic and potassic alteration zones. A close-spatial association with a major deep-seated structure is also postulated to exist. The Kwyjibo mineralisation is one of the most significant examples of this important class of ore deposit to have been found in the Grenville to-date.

Keywords: Polymetallic, Grenville, Hematite, granite-hosted, Kwyjibo, Copper, iron-oxide, REE, Magnetite, Mesoproterozoic