USGS Professional Paper 1697 - Alaska Resources Library

g/t Au or 368.2 Au gold. The deposit may be the largest currently
known in Alaska (Bundtzen and others, 2000).
Vinasale Granitoid-Related (Porphyry) Au Deposit
The Vinasale Mountain granitoid-related Au (porphyry
Au) deposit (fig. 111) (DiMarchi, 1993; Nokleberg and others,
1995a), which lies about 25 km south of McGrath, consists
of Au-Ag-Sb-Pb-As sulfide minerals that occur as disseminations,
in breccia, and in dolomite veins and segregations.
Mafic minerals exhibit silica, sericite, and propylitic replacements.
The highest Au concentrations occur in the central zone
of the deposit in areas of intense sericite and silica alteration.
Creek
Donlin
Approximate Location
Donlin Bench
Queen
Queen Gulch
placer deposit
Lewis Gulch
placer deposit
Lewis Gulch
Late Cretaceous and Early Tertiary Metallogenic Belts (84 to 52 Ma) (figs. 102, 103) 233
Inset map below
Gulch
Donlin
Fault
Snow
area
0 2 km
More than ninety percent of the gold occurs in As and Sb
sulfides and sulfosalts. Correlation coefficients are highest
between Au and As (0.81). The deposit is hosted in various
phases of the Vinasale pluton, which consists of a multiphase,
6 km 2 intrusion composed of monzonite, quartz monzonite,
and granite porphyry. The pluton intrudes the Late Cretaceous
Kuskokwim Group. A K-Ar biotite isotopic age of 69.0 Ma is
obtained for a quartz monzonite phase of the Vinasale Mountain
pluton (Bundtzen, 1986). On the basis of about 11,260
m of drilling, a central zone of the Vinasale Deposit contains
reserves of about 10.3 million tonnes grading 2.40 g/t Au
(24,540 kg of gold resource) and with minor Ag and Sb (Bundt-
Snow Gulch
placer deposit
Upper
Lewis
area
50
Snow
40
Gulch
Queen
area
45
35
Snow Area
84BT259a
1 m channel,
pyrite rich,
700 ppm As
50
84BT259b
9 cm stibnite,
3 g/t Au,
2500 ppm As
Placer and dozer
tailings
Alluvial terrace
deposit
Granite porphyry
dikes and sills
(Late Cretaceous)
Hornfels
Kuskokwim Group
(Late Cretaceous)
High angle fault;
dotted where
inferred or
concealed
Anticline
Contact
Strike and dip of
bedding
Channel sample
Prospect trench
Creek
84BT259g
1 m channel,
stibnite, 110 g/t Ag
84BT259d
10 cm channel
stibnite, 11 g/t Au,
2000 ppm As
84BT259c
20 cm stibnite,
12.3 g/t Au,
7000 ppm As
Figure 110. Donlin Creek porphyry Au deposit, southwestern Kuskokwim Mountains metallogenic belt,
southwestern Alaska. Schematic geologic map of Donlin Creek dike swarm and adjacent units. Adapted
from Retherford and McAtee (1994) and Bundtzen and Miller (1997). See figure 103 and table 4 for location.