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Paper No. 9
Presentation Time: 4:00 PM


DAY, Warren C., US Geological Survey, MS 911, Denver, CO 80225, O'NEILL, J. Michael, USGS, Denver Federal Center, MS 964, Denver, CO 80225, DUSEL-BACON, Cynthia, USGS, 345 Middlefield Rd., MS 901, Menlo Park, CA 94025, ALEINIKOFF, John N., U.S. Geol. Survey, Denver, CO 80225 and SALTUS, Richard W., MS 964, US Geological Survey, Federal Center, Box 25046, Denver, CO 80225-0046,

The mineral resource potential of the Yukon-Tanana Upland in east-central Alaska, a vast region concealed beneath Quaternary surficial deposits, is poorly known. The Upland is part of the Tintina Gold Province, an arc-shaped, 1,200 km (750 mile)-long metallogenic province extending from northern British Columbia, through Yukon, and into southwestern Alaska. In Alaska, the Province is bounded by the Tintina-Kaltag fault to the north and the Denali fault to the south, both of which are major right-lateral strike-slip fault systems. Thus bound in a dextral wrench zone, the Province is transected by northeast-trending systems of faults across the Upland that create structural blocks 10’s of kms wide and 100’s of kms long, which glide past each other along left-lateral high-angle faults. Our new geologic mapping and geochronologic research in the Goodpaster and Fortymile mining districts is illuminating how that these fault systems, active at least since the Late Cretaceous up through the Quaternary, influence emplacement of plutonism, volcanism, and ore formation.

In the Goodpaster district, dikes, volcanic centers, and lode gold deposits lie within, adjacent to, and are cut by recurrent movement of high-angle northeast-trending fault systems. 109 Ma subvolcanic diorite dikes and 105 Ma (Newberry et al., 1998) gold-bearing veins intrude, a 57 Ma rhyolite flow-dome complex erupted, and Quaternary deposits are offset along the NE-trending Black Mountain tectonic zone. In the Fortymile district, 100-98 Ma and 70 Ma granitoid dikes intruded along the northeast-trending, left-lateral dip-slip Kechumstuk and kinematically related faults, recording recurrent intervals of regional magmatism and deformation. Several carbonate replacement Zn-Pb-Ag prospects occur within 200 m of these faults. One hypothesis is the faults acted as conduits for ore-forming hydrothermal fluids that then replaced the carbonate units in the Paleozoic country rock. Careful geologic mapping coupled geochronologic, metallogenic, and geophysical research is yielding tools that are helping to evaluate the mineral resource endowment of concealed regions of interior Alaska.

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