Geology and genesis of the Red Dog deposit, western Brooks Range, Alaska

CIM Bulletin, Vol. 82, No. 929, 1989

L.E. Young, Cominco Alaska Exploration, Anchorage, Alaska

The Red Dog deposit of the western Brooks Range, Alaska was discovered in the 1970s. Two mineralized areas are present, the Main and Hilltop deposits. With indicated and inferred reserves of 77 million tonnes of 17.1 % zinc, 5.0% lead and 82 g/tonne silver, the Main deposit of Red Dog represents one of the world's largest zinc-lead deposits. Since serious evaluation by Cominco commenced in 1980, a better understanding of deposit geology has been gained through 10 715 m of diamond drilling and concurrent geologic, geophysical and geotechnical studies. The Red Dog deposit is of Mississippian to Pennsylva-nian or Early Permian age, and straddles a redox transition in fine-grained and chemical sediments of the Red Dog structural sequence. The Main deposit has been modified by regional Mesozoic thrust faulting and isoclinal folding, resulting in complex interrelationships between silica rock, sulphide rock and barite. Multiple lines of evidence suggest the Main deposit contains both a syngenetic stratiform and a replacement component. Ore fluids were probably derived by regional lateral movement of brines through a coarse clastic footwall aquifer, then upwards along block faults to the site of the Red Dog deposit.

Keywords: Geology, Red Dog deposit, Western Brooks Range, Ore reserves