CALISTA CORPORATION

ECONOMIC GEOLOGY

In the Kuskokwim Mountains and lower Yukon River areas, placer and lode gold resources, as well as mercury deposits, are associated with Late Cretaceous-Early Tertiary plutonic rocks of two general types. Polymetallic occurrences that contain high-grade veins of gold, silver, rare and base metals are associated with ~70 million-year-old composite volcano-plutonic complexes, including the Russian, Horn and Chuilnuk Mountains; Marvel Dome; the Cripple Mountains; Mount Oratia; the Taylor Mountains; Shotgun Hills; and others in the Calista and adjacent Bristol Bay Regions. These granitic igneous complexes underlie many of the higher peaks throughout the Kuskokwim Mineral Belt, around which gold placer deposits were formed.

Other placer and lode gold resources with arsenic-antimony+mercury geochemical signatures are associated with ~70 million-year-old shallow, subvolcanic dike, sill and shallow intrusive complexes predominantly composed of rhyodacite and rhyodacite porphyry with minor amounts of lamprophyre and basaltic rocks. Donlin Creek is the best-known example of this type of deposit.

Metallic mineral resources in the Region are concentrated around historic gold placer districts. The placer districts, and associated lode resources, comprise much of the Kuskokwim Mineral Belt that extends across the Doyon Region, north and east of the Calista Region. The Kuskokwim Mineral Belt is bounded on the north and west by splays of the Kaltag fault and on the south and east by the Denali-Farewell fault zone. In the Calista Region, the Iditarod-Nixon Fork fault is central to the most conspicuously mineralized areas. The Cretaceous Kuskokwim Group comprises a thick sandstone and shale basin-fill sequence underlying the bulk of the Region. The Kuskokwim Group is the same age as Cretaceous sediments of the Yukon-Koyukuk Basin, on the lower Yukon River.

Calista Regional Geology Map (Click for larger version)