A RE-APPRAISAL OF THE GEOLOGY AND ORE DEPOSITS OF THE HORNE MINE COMPLEX AT ROUYN-NORANDA, QUEBEC

Special Volume, Vol. SV 43, No. 1990, 1990

From 1927 to 1989, the Horne mine produced 53.7 Mt of ore grading 6.1 glt Au and 2.2% Cufrom two large volcanogenic massive sulphide deposits composed primarily of pyrrhotite, pyrite and chalcopyrite. The orebodies were hosted by a package of chlorite-sericite altered epiclastic rhyolite tuffs which were deposited in a narrow palaeo-graben located on the flank of a major felsic volcanic centre. Mineralizingfluids percolated upward through the permeable footwall rocks and were further focussed along syn-volcanic, graben-bounding faults. Sulphides were deposited by a process of sub-seafloor replacement of the rhyolite tuffs. Gold-copper-( zinc) mineralization, including ore zones mined between 1985 and 1989 as the REMNOR ore zones, is present throughout the 900 m of felsic volcanic stratigraphy at the Horne. All the deposits were formed by syn-volcanic hydrothermal processes active during felsic volcanism. There is no evidence to indicate that any economic gold mineralization was introduced by a post-volcanic hydrothermal episode. De 1927 a1989, la mine Horne a produit 53.7 Mt de minerai avec une teneur de 6.1 glt Au et 2.2% Cu provenant de deux grands a mas de sulfures massifs volcanogeniques comprenant esentiellement de la pyrrhotite, de la pyrite et de la chalcopyrite. Ces gites font partie d' une sequence de tufs rhyolitiques epiclastiques chloritises et sericitises qui ont ete deposes dans un paleo-graben etroit situe sur le flanc d'un important centre volcanique felsique. Les fluides mineralises ont circule de bas en haut a travers les roches permeables sous-jacentes; ils ont ete egalement canalises par les failles syn-volcaniques en bordure du graben. Les sulfures se sont deposes par remplacement des tufs rhyolitiques immediatement et sous le plancher oceanique. Les zones mineralisees en or et cuivre (±zinc) - y compris celles qui ont ere exploitees au cours de l'operation Remnor ( 1985-1989) - se retrouvent, sans discontinuite, a travers les roches volcaniques felsiques dont l' epaisseur atteint 900 m. Ces gites se sont formes par le biais d' un processus hydrothermal qui ag issait pendant le volcanisme felsique. II n'y a aucune evidence de mineralisation aurifere d'importance economique qui soit posterieure a l'activite hydrothermal syn-volcanique.

Mots Clés: Horne Mine, Mineralization, Ore deposits,Rouyn-Noranda, Mine Horne