USGS Professional Paper 1697 - Alaska Resources Library

Origin of and Tectonic Controls for Lantarsky-Dzhugdzhur
Metallogenic Belt
The Lantasky-Dzhugdzhur metallogenic belt is interpreted
as forming during Mesoproterozoic rifting along the
edge of the North Asian Craton. During rifting, coeval, large
anorthosite plutons intruded the Stanovoy suture and adjacent
area for a distance of more than 1,000 km, and adjacent region
to the south.
Ulkan Metallogenic Belt of Felsic Plutonic REE
Deposits (Belt UL), Northwestern Part of Russian
Southeast
The Ulkan metallogenic belt of felsic plutonic REE
deposits occurs in the northwestern part of the Russian Southeast
(fig. 2; tables 3, 4) (Nokleberg and others, 1997b, 1998).
The belt occurs mainly in the Paleoproterozoic Ulkan volcanotectonic
basin that has isotopic ages of 1.9 to 1.5 Ga and that
overlies folded Archean basement rocks of the North Asian
Craton (unit NSC). The REE, Be, U-Mo, Nb-Ta and related
deposits are interpreted as forming in two periods.
An older group of Be, Ce, La, Y, Nb, and Ta deposits is
related to Rapakivi-type granites with isotopic ages of 1.65
to 1.7 Ga. The granites intrude subalkalic siliceous volcanic
rocks. The Be deposits, as at Burgundiy and Nygvagan, occur
in albite-genthevite-bearing zones within granite intrusions.
The Ce, La, Y, Nb, and Ta deposits, as at Albititovoe and Gurjanouskoe,
occur within zones of quartz, microcline, albite,
riebeckite, aegirine along a linear zone of altered volcanic
rocks. For both types of deposits, the main ore minerals are
zircon, monazite, gagarinite, cassiterite, bastnasite, columbite,
xenotime, and pyrochlore.
A younger group of Y, Ce, U, Mo, Nb, and Ta deposits
exhibit isotopic ages of 1.1 to 1.3 Ga,but show no clear connection
with igneous rocks. Coeval dikes of alkalic basalt,
with as much as 12 percent K 2O, occur in the area. The large
Y-Ce deposit at Uzhnoe consists of metasomatic albite and
apatite, which occur in a fault zone. The apatite contains Ce
and as much as 1 percent Y. Other ore minerals are zircon,
synchysite, monozite, xenotime, thorite, and brannerite. The
U-Mo deposits, as at Mezhdurechnoe and Zapadnoe, are
associated with altered beresite formed of muscovite, sericite,
hydromica, pyrite, and Ca-Fe-Mg carbonate minerals. The
chief ore minerals are mainly molybdenite, native gold and
Cu-, Zn-, and Pb-sulfides. The Nb-Ta deposits, as at Krasnogorskoe,
occur in zones of argillaceous-altered volcanic
rocks now mainly quartz, hydromica, and clay. The chief ore
minerals are Nb-bearing gematite (as much as 1 percent Nb),
euxenite, and molybdenite. The deposits of the Ulkan metallogenic
belt are similar to those in the Pikes Peak, Colorado,
region in the United States. The metallogenic belt is isolated,
distant from roads, and has only recently been studied
(Kirillov, 1991, 1993). Insufficient data preclude determining
the origin of the Ulkan metallogenic belt. The Ulkan belt is
Proterozoic Metallogenic Belts (2500 to 570 Ma; figures 2, 3) 15
coeval anorthosite to the south that is interpreted as forming in
a Mesoproterozoic rift-related volcanic-plutonic center.
Bilyakchan Metallogenic Belt of Sediment-
Hosted Cu and Basaltic Cu Deposits (Belt BI),
Southwestern Part of Russian Northeast
The Bilyakchan metallogenic belt of sediment-hosted
Cu and basalt Cu deposits (fig. 2; tables 3, 4) occurs in the
southwestern part of the Russian Northeast in Proterozoic
rocks of the Verkhoyansk fold belt (unit NSV) that constitutes
the North Asian Craton Margin (Nokleberg and others,
1994c, 1997b, c, 1998; Shpikerman, 1998). The belt strikes
north-northeast for 350 km along the western folded margin
of the Okhotsk cratonal terrane and is about 50 km wide. The
deposits occur in metamorphosed sandstone and basalt of
the Riphean and Vendian Bilyakchan sequence with a thickness
of 3,100 m (Kutyrev and others, 1986). The Bilyakchan
metallogenic belt is correlated with the tectonically-displaced
Oroek metallogenic belt of ironstone and sediment-hosted Cu
deposits, which is described above.
Dzhagdag Basaltic Cu and Severny Uy Occurrences
Basaltic Cu occurrences, as at Dzhagdag, occur in the
lower part of the sequence. The Dzhagdag deposit consists
of two layers of late Riphean (Vendian) amygdaloidal basalt,
intercalated with tuff and sandstone, which contain Cu-bearing
horizons that are 0.4 to 5 m thick and contain finely disseminated
to small masses of chalcocite, bornite, native copper,
cuprite, covellite, and malachite (Kutyrev and others, 1988).
The basaltic Cu deposits and the hosting basalts are interpreted
as forming during rifting on a shallow-submerged scarp of
the western Okhotsk cratonal terrane. The sediment-hosted
(sandstone) Cu occurrences, as at Severny Uy and Borong,
occur at higher stratigraphic levels. The Severny Uy deposit
consists of Cu-bearing horizons from 1 to 3 m thick and occur
in Late Riphean (Vendian) quartz and polymictic sandstone
and siltstone (Kutyrev and others, 1986). The deposit contains
fine disseminations and pockets of massive pyrite, chalcopyrite,
bornite, chalcocite, and hematite. The sediment-hosted
Cu deposits and the host sandstones are interpreted as forming
during erosion of volcanic rocks with basaltic Cu deposits.
Origin of and Tectonic Controls for Bilyakchan
Metallogenic Belt
The southwestern part of the North Asia Craton Margin
(Verkhoyansk fold belt, unit NSV), which hosts the Bilyakchan
metallogenic belt, consists of the following major units
(1) Middle to Late Riphean shelf limestone, sandstone, and
shale with a combined thickness of more than 3 km; and (2)
Late Riphean to Late Vendian clastic and volcanic rocks,
including variegated conglomerate, sandstone, siltstone,
basalt, and rare rhyolite. The late Riphean (Vendian) sedimentary
and volcanic rock that host the Cu deposits are interpreted