Paper No. 6
Presentation Time: 10:15 AM


WARTMAN, Jakob, Cliffs Natural Resources, Eveleth, MN 55734, MORTON, Ronald, Geological Sciences Department, University of Minnesota Duluth, Department of Geological Sciences, 1114 Kirby Drive, HH 229, Duluth, MN 55812 and HUDAK III, George J., Precambrian Research Center, NRRI, University of Minnesota, 5013 Miller Trunk Highway, Duluth, MN 55811,

The Rainy River Gold Project is located within the Neoarchean Rainy River Greenstone Belt 75km northwest of Fort Francis, Ontario. This advanced stage exploration project has NI 43-101 compliant Proven and Probable Mineral Reserves of 4.0 million ounces gold and 10.3 million ounces of silver. Detailed field mapping, diamond drill core logging, and petrographic and lithogeochemical studies have enabled the stratigraphy, volcanic facies, and hydrothermal alteration mineral assemblages to be identified, and processes associated with precious metal mineralization to be better understood. Volcanic facies at the deposit include coherent dacitic flows and associated synvolcanic intrusions, autoclastic breccias, hyaloclastites, peperites, and syn- to post-depositional resedimented volcaniclastic deposits. Coherent dacitic flows are massive, are up to 150 meters thick and have strike lengths up to 2500 meters. Coherent dacite flows grade into a heterogeneous facies, characterized by pods and lobes of coherent dacite, enveloped by autoclastic breccia and hyaloclastite. Flows are interspersed with altered volcaniclastic sediments that are locally punctuated by peperites. Volcanic facies reconstruction indicates the presence of lobe-hyaloclastite dome/flow complex fed, and locally intruded by, synvolcanic dacite hypabyssal intrusions. An apparent feeding fissure is centered to the west of the main area of mineralization. Hydrothermal alteration is widespread and includes silicification, chloritization, sericitization, and carbonitization. Quartz, sericite and chlorite are ubiquitous in the deposit. Alteration assemblages are dominantly stratabound, and their distribution is related to original rock permeability, with flow tops, autoclastic breccias, and volcaniclastic sediments being most strongly altered. Shear zones also preserve stronger alteration intensities. Gold mineralization appears to have initially occurred within highly permeable units associated with a synvolcanic, low sulfidation epithermal system. Post-volcanic remobilization of the gold appears to have occurred, as the highest gold values in the deposit are spatially related to shear-zones and associated quartz-carbonate-epidote veins.