Technical Report for the Fort Knox Mine - Kinross Gold

Fort Knox Mine Technical Report7.0 GEOLOGICAL SETTINGThe Fort Knox property is located in the Fairbanks mining district, a southwest–northeasttrending belt of lode and placer gold deposits that comprise one of the largest goldproducing areas in the state of Alaska. The Fairbanks district is situated in thenorthwestern part of the Yukon–Tanana - Uplands. The Yukon – Tanana terraneconsists of a thick sequence of poly-metamorphic rocks that range from Precambrian toupper Paleozoic. The polymetamorphic protoliths were primarily sedimentary, volcanic,and volcanoclastic units, with only minor plutonic rocks. The region has undergone atleast two periods of dynamo - thermal metamorphism, which included an early progradeamphibolite event, followed by a retrograde, greenschist facies event (Bundtzen, 1981).A more complex deformational history identifying four phases of penetrative tectonismhas been suggested by Hall, 1985.The Fairbanks Schist, which is Proterozoic to lower Paleozoic, is the dominant lithologyin the district. It is composed of quartz-muscovite schist, muscovite-feldspar-quartzschist, micaceous quartzites, metaconglomerate, garnet - hornblende amphibolite, andmarble, indicative of an emergent shelf environment. The Cleary Sequence consistingof bimodal meta-rhyolite and meta-basalt with actinolite schist, chlorite schist, graphiteschist, and impure marbles is intercalated with the Fairbanks Schist, indicating immaturerift basins in the shelf environment. Geological work performed in 1996 has led toreassigning the meta-rhyolite in the Cleary Sequence to the Devonian MuskoxSequence and placing it in fault contact with the Fairbanks Schist. In the northern part ofthe district, metamorphosed rocks of the Chatanika terrane have been identified. Thesequence includes type C eclogites, impure marbles, amphibolites, calc-muscoviteschist, garnet-muscovite schist, and muscovite schist, containing garnet, biotite, chloriteand graphite. The Chatanika unit in fault contact with the Fairbanks Schist is thought tobe middle Paleozoic to Ordovician and may represent a telescoped, mature rift basinwithin the shelf environment. Amphibole from the Chatanika unit yielded an OrdovicianK-Ar date (Robinson, 1990). Figure 7-1 illustrates the location of the Kinross projectswithin this geologic setting.25