USGS Professional Paper 1697 - Alaska Resources Library

50 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
deposits, many of which are stratiform or transposed and some
of which are replacement deposits, which occur along four
regional trends. The deposits consist of varying amounts of
pyrite, chalcopyrite, galena, sphalerite, and lesser malachite
and bornite. The gangue minerals are mainly quartz, carbonate,
and white mica. Hydrothermal alteration consists of chlorite,
quartz, sericite, pyrite, and Zn-Ag-Au sulfide minerals.
The massive sulfides and adjacent disseminated sulfide layers
occur in zones that average 500 m long, 200 m wide, and 15
m thick. The deposits are hosted in metamorphosed Devonian
I
W. Fork Robertson River
Mt. Kimball
7 6
Denali Fault
Strike-slip fault with
sense of displacement
Contact
VMS trends
VMS deposit or occurrence
YUKON-TANANA TERRANE
Macomb subterrane
Jarvis Creek Glacier subterrane
Tok River metasedimentary rocks
Delta metavolcanic rocks
Rumble Creek cataclastite
Tushtena Pass schist
Robertson River gneiss
Tushtena Pass schist and
Robertson River gneiss
Hayes Glacier subterrane
II
9
8
7
IV
II
8
7 6 5
I
5
4
Devonian
4 3 2 1
spilite, andesite, and keratophyre suite, which initially formed
in flows, tuff, and breccia, and in metamorphosed shallow- to
deep-marine sedimentary rocks; now mainly quartz schist,
quartz-chlorite-feldspar schist, calc-schist, and marble. The
host rocks are part of the extensive Devonian and Mississippian
Yukon-Tanana terrane. Intruding the deposits are numerous
tholeiitic greenstone sills that are interpreted as Triassic(?)
to Cretaceous(?). The largest deposit contains an estimated 18
million tonnes grading 0.3 to 0.7 percent Cu, 1 to 3 percent
Pb, 3 to 6 percent Zn, 34 to 100 g/t Ag, 1 to 3.4 g/t Au.
3
2
1
III
IV
IV
Dry Tok River Fault
0 16 km
Figure 23. Delta district of kuroko (volcanic) massive
sulfide deposits, Alaska Range and Yukon-Tanana
Upland metallogenic belt, east-central Alaska.
Schematic geologic map. Roman numerals denote
mineralization trends; arabic numerals denote volcanic
massive sulfide (VMS) deposits within a trend. Deposits:
PP-LZ Trend (I), 1-LBB, 2-PPD, 3-UPP, 4-LZ East,
5-LZ, 6-RC East, 7-RC; DD-Rum Trend (II), 1-LBB, 2-Rum
South, 3-Rum North, 4-Lower Rum, 5-DDS, 6-DDX,
7-DDY, 8-DDN; PG-Trio-HD Trend (IV), 7-PGX, 8-PG,
9-PGW. Modified from Lange and others (1993). See
figure 17 and table 4 for location.