Geology and origin of epigenetic lode gold deposits, Tintina Gold Province, Alaska and Yukon

More than 50 million ounces of lode gold resources have
been defined in the previous 15 years throughout accreted
terranes of interior Alaska and in adjacent continental margin
rocks of Yukon. The major deposits in this so-called Tintina
Gold Province formed around 105 to 90 million years ago in
east-central Alaska and Yukon, and around 70 million years
ago in southwestern Alaska, late in the deformational history
of their host rocks. All gold deposits studied to date formed
from CO₂
-rich and ¹⁸O-rich crustal fluids, most commonly of
low salinity. The older group of ores includes the low-grade
intrusion-related gold systems at Fort Knox near Fairbanks
and those in Yukon, with fluids exsolved from fractionating
melts at depths of 3 to 9 kilometers and forming a zoned
sequence of auriferous mineralization styles extending
outward to the surrounding metasedimentary country rocks.
The causative plutons are products of potassic mafic magmas generated in the subcontinental lithospheric mantle that
interacted with overlying lower to middle crust to generate
the more felsic ore-related intrusions. In addition, the older
ores include spatially associated, high-grade, shear-zonerelated orogenic gold deposits formed at the same depths from
upward-migrating metamorphic fluids; the Pogo deposit is
a relatively deep-seated example of such. The younger gold
ores, restricted to southwestern Alaska, formed in unmetamorphosed sedimentary rocks of the Kuskokwim basin
within 1 to 2 kilometers of the surface. Most of these deposits
formed via fluid exsolution from shallowly emplaced, highly
evolved igneous complexes generated mainly as mantle melts.
However, the giant Donlin Creek orogenic gold deposit is a
product of either metamorphic devolatilization deep in the
basin or of a gold-bearing fluid released from a flysch-melt
igneous body.