USGS Professional Paper 1697 - Alaska Resources Library

164 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
of 80 to 90 Ma (Ognyanov, 1986) and a Rb-Sr whole-rock isochron
age of 78 Ma (Gonevchuk and others, 1998). Common
in the belt are both Sn greisen deposits with topaz-muscovitequartz
greisen, which formed adjacent to plutons (as at Khingan,
Nizhnee, Obeshchayushchee, and Verkhnebidzhanskoe
deposits), and volcanic wood tin deposits (as at Dzhalinda),
which formed in the upper part of felsic vents or calderas. The
major Sn quartz vein deposits is at Verkhnebidzhanskoe.
Solnechnoe Sn Quartz Vein Deposit
The Solnechnoe Sn quartz vein deposit (fig. 73) (Ognyanov,
1986, Ishihara and others, 1997) consists of highly
altered quartz-tourmaline veins with numerous apophyses and
is related to a long north-south, left-lateral, strike-slip fault.
The deposit varies from 0.5 to 15 m thick, 800 m long, and
extends to the depth more than 500 m below the surface. Five
vertically zoned mineral assemblages are distinguished, from
bottom to top (1) quartz-tourmaline, (2) quartz-arsenopyritecassiterite
with wolframite, bismuthinite, and scheelite, (3)
quartz-sulfide (pyrrhotite, chalcopyrite, and marcasite), (4)
quartz-galena-sphalerite, and (5) quartz-carbonate. The deposit
is closely related to a K-rich granite phase of a gabbro-dioritegranodiorite
complex with K-Ar isotopic ages of 75 to 86 Ma.
The deposit is medium with an average grade of 0.56 percent
Sn, 0.05 percent W, and 0.1 percent Cu. The deposit has been
mined since 1960’s(?) and is mostly exhausted.
Pravourmiskoe Sn Greisen Deposit
The Pravourmiskoe Sn greisen deposit (fig. 74) (Ognyanov,
1986) consists of disseminations and veins that occur in
a linear area more than 1,500 m long and 5 to 25 m thick and
extends several hundred m down dip. An earlier ore assemblage
consists of quartz-topaz-cassiterite with fluorite, and a
later assemblage consists of quartz-arsenopyrite-chalcopyrite,
and quartz-tourmaline with cassiterite and stibnite. Found in
addition to Sn, W, and Cu, are Bi, Pb, and Sb. The gangue is
composed of quartz-siderophyllite (zwitters) with quartz-topaz
greisen. The deposit is large with an average grade of 0.1 to 5
percent Sn, 0.05 percent WO3, and 0.5 percent Cu. The deposit
occurs along an east-west-trending thrust fault with small
offset. The deposit is hosted in and genetically related to Late
Cretaceous felsic volcanic rocks that overlie the large, shallow,
granite and leucogranite complex of the Verkhneurmiisky
batholith with K-Ar isotopic ages of 75 to 85 Ma. The granite
has a long-ranging Rb-Sr age of 95 to 83 Ma with an initial Sr
ratio of 0.703 to 0.708 (Lebedev and others, 1994).
Khingan Sn Greisen Deposit
The large and well known Khingan Sn greisen deposit
(fig. 75) (Ognyanov, 1986) is of hypabyssal origin and occurs
in a pipe-shaped ore bodies of hydrothermal explosion breccia
that cut a sequence of felsic volcanic rocks. The deposit
contains more than 15 ore zones from 10 to 50 m across and
100 to 500 m wide that are concentrated down-dip in a sym-
metrical breccia zone about 250 to 300 m across. The zone
has been traced to depths of more than 1200 m. At the upper
levels of the deposit, the breccia is replaced by chlorite, and
at the depths of 700-800 m, the breccia is replaced by quartzmuscovite
(sericite)-topaz greisen. Most of the ore zone is
quartz-fluorite-cassiterite. Arsenopyrite, marcasite, loellingite,
chalcopyrite, and Bi-minerals are subordinate. The deposit
is interpreted as probably genetically related to subalkaline
potassium granite with a K-Ar age of 80-90 Ma and a Rb-Sr
whole-rock isochron age of 78 Ma with an initial Sr isotopic
ratio of 0.7123 (Gonevchuk and others, 1991). The deposit has
been mined since the 1970’s. The deposit is of large and averages
0.6 to 0.7 percent Sn.
Verkhnebidzhanskoe Sn Quartz Vein Deposit
The Verkhnebidzhanskoe Sn quartz vein deposit (Ognyanov,
1986) is hosted in Late Proterozoic dolomite adjacent to a
rhyolite porphyry stock. The deposit occurs at a tectonic contact
of the dolomite with Late Proterozoic schist. The deposit
consists of metasomatic quartz-sulfide lenses that range from
50 to 80 m along strike and extend as much as 70 m downdip
with a maximum thickness of 10 to 12 m. The deposit extends
for about 1,300 m. The dominate late-stage ore minerals are
mainly sulfosalts (boulangerite, jamesonite). The subordinate,
earlier-stage ore-minerals are quartz, cassiterite, and arsenopyrite.
Alteration minerals include talc, calcite, siderite,
and dolomite. Both the sedimentary and volcanic rocks are
extremely rich in Sn (as much as 10 clarkes). A Late Cretaceous
rhyolite porphyry stock, which contains geochemically
anomalous Sn (about 0.005 percent), is interpreted as the
source for the vein Sn that formed during hydrothermal alteration.
The deposit is small and contains an average of 0.3 to 2.0
percent Sn.
Origin of and Tectonic Controls for Badzhal-Ezop-Khingan
Metallogenic Belt
The Sn deposits of the Badzhal (northern) part of the
Badzhal-Ezop-Khingan metallogenic belt are hosted in or near
the Early and mid-Cretaceous Khingan-Okhotsk volcanicplutonic
belt (unit ko, fig. 61) (Nokleberg and others, 1994c,
1997c). The deposits occur mainly around the outcrops of
large intrusions of crustal-derived granite and leucogranite or
crustal- to mantle-derived granitoid rocks that intrude mainly
along older, elongate, east-west-striking faults that were
subduction zones in the Middle Jurassic to Early Cretaceous.
The Cretaceous Khingan-Okhotsk volcanic-plutonic belt is
divided into two main sequences—(1) Barremian to Cenomanian
andesite and minor basalt, with coeval gabbro, diorite,
and granodiorite. Andesite exhibits calc-alkalic composition,
whereas basalt exhibits tholeiitic composition, and (2) Late
Cretaceous (mainly pre-Senonian) suite of K-rich felsic volcanic
rocks, tuff, ignimbrite, and coeval subvolcanic intrusive
and granitoid rocks. These Cretaceous granitoid rocks include
granite, leucogranite, and composite gabbro-diorite-granodiorite
plutons (Ognyanov, 1986). The plutonic units are coeval