Exploration Models for Mid and Late Cretaceous Intrusion-Related Gold Deposits in Alaska and the Yukon Territory, Canada

ABSTRACT
Several major plutonic-related gold deposits are among a band
of mineral occurrences extending from southwestern Alaska into the
Yukon Territory, Canada, called the Tintina Gold Province (TGP).
Current gold resources in Alaska and the Yukon Territory have
increased from approximately 1 million ounces in 1985 to over 70
million ounces in 1999, with more than half of these resources
occurring in the TGP.
Rb-Y-Nb concentrations from plutonic rock samples indicate
most of this gold mineralization is due to arc-related magmatic belts
of two separate age suites: ~88 to 110 Ma and ~65 to 70 Ma.
Because the mid Cretaceous plutons are related to a subduction
event along the Denali fault, Fort Knox, Pogo, Ryan Lode or True
North direct analogues are not likely to be found south of the Denali
fault. Conversely, the 65-70 Ma subduction-related plutons and
related deposits can be found on either side of the Denali fault due
to a more southerly subduction zone -placement of the magmatic
suites relates deposits now separated up to 450 kilometers from one
another, and shows areas of favorable gold exploration, particularly
where pluton density is high and where the mid and Late Cretaceous
regions overlap.
Extensive multi-element assay data have been compiled from
more than 10 of the TGP deposits for systematic comparison with
respect to mineralization age, depth of emplacement, and proximity
to causative pluton. Bismuth, gold and arsenic are the three most
closely linked metals of these deposits, and variations in their statistical
correlations and ratios change systematically with respect to
depth of emplacement and proximity to a causative pluton. We show
that the correlation between Bi and Au (as well as the Bi:Au ratio)
systematically increases with depth of emplacement and proximity
to a causative pluton. Average Bi:Au ratios range from 31:1 for
deeper and more proximal deposits to 0.36:1 for shallower and more
distal deposits. Bi vs. Au correlations range from r = 0.89 for deeper
and/or more proximal deposits to r = 0.12 for shallower and/or more
distal deposits. Conversely, the correlation between As and Au
increases from r = 0.23 with deeper and/or intrusion-hosted deposits
to r = 0.86 for shallower and/or more distal deposits. The change in
As:Au ratios are much less predictable than Bi:Au ratios. Such variations
in metal correlations and Bi:Au ratios may be used on a
regional scale to target areas for exploration. Further, the Bi:Au ratio
varies so systematically with respect to proximity to probable fluid
sources that it may be possible to use it on a deposit scale to model
the direction and path of fluid transport, and hence, target new areas
for drilling.