USGS Professional Paper 1697 - Alaska Resources Library

phase has a Rb-Sr isotopic age of 143 Ma with an initial Sr
ratio of 0.0761 (Nenashev and others, 1985). The ore bodies
dip steeply, range from 0.01 to 6 m thick. and are about
100 m long. The veins are most dense at a distance of 500 to
1,000 m from the intrusive contact. The major minerals are
quartz, tourmaline, cassiterite, stannite, wolframite (ferberite),
pyrrhotite, pyrite, arsenopyrite, and chalcopyrite. Also
occurring are Bi and Te minerals. The deposit is major with
an average grade of 0.7 to 2.5 percent Sn; 0.3 to 1.0 percent
W0 3, and as much as 10 g/t Au.
Origin of and Tectonic Controls for Yana-Polousnen
Metallogenic Belt
The lode deposits of the Yana-Polousnen metallogenic
belt are related mainly to the Early Cretaceous collisional
(anatectic) granitoid rocks of the northern part of the Verkhoyansk
granite belt (unit vk) (Nokleberg and others, 1994c,
1997c; Goryachev, 1995, 1998, 2003). The northern part of
this granite belt, which extends for about 600 km along northwestern
margin of the Kolyma-Omolon superterrane, consists
of inclined sheet-like plutons, as much as 200 km long, which
are generally conformable with major folds. Major lithologies
are granodiorite, granite, and, less commonly, leucogranite.
These granitoid rocks are interpreted as forming immediately
after the final, Early Cretaceous stage of accretion of
the Kolyma-Omolon superterrane to the North Asian Craton
(Nokleberg and others, 2000).
Darpir Metallogenic Belt of Sn and Associated
Felsic-Magmatism Deposits (Belt DP), Western
Part of Russian Northeast
The Darpir metallogenic belt of Sn and associated felsicmagmatism-related
deposits (fig. 61; tables 3, 4) occurs in the
western part of the Russian Northeast. The belt is hosted in a
zone of Early Cretaceous granitic intrusions that trends northwest
along the southwest boundary of the Omulevka passivecontinental-margin
terrane of the Kolyma-Omolon superterrane
(Nokleberg and others, 1994c, 1997c). The belt extends
for more than 1,000 km (fig. 61). The metallogenic belt and
zone of granitic intrusions is transverse, or nearly orthogonal
to the trend of the younger Okhotsk-Chukotka volcanic-plutonic
belt to the southeast. A diverse group of granitic-intrusive-related
mineral deposit types occur in the Darpir metallogenic
belt (table 4). The significant deposits in the belt are
the Bolshoy Kanyon Sn skarn deposit (fig. 67), the Bastion Sn
greisen deposit, the Titovskoe Sn (B) magnesian skarn deposit,
the Chibagalakh Sn-B skarn deposit, the Darpir and Lazo Sn
silicate-sulfide deposit, the Verkhne-Seimchan Co-arsenide
polymetallic vein deposit, and the Chepak granitoid-related Au
deposit (Nokleberg and others 1997a,b, 1998). The belt also
contains a few Pb-Zn skarn deposits.
The significant felsic-magma-associated deposits of the
Darpir metallogenic belt occur in diverse geologic settings.
Early Cretaceous Metallogenic Belts (144 to 120 Ma; figs. 61, 62) 149
The Sn skarn deposits at Titovskoe and Bolshoy Kanyon occur
in Paleozoic carbonate rocks near Early Cretaceous granitoid
plutons. The Sn greisen deposit at Bastion occurs in leucocratic
granite. Sn polymetallic vein and Sn silicate-sulfide
deposits, such as the Darpir and Lazo deposits, commonly
occur in or near Early Cretaceous granite plutons that intrude
contact-metamorphosed, Early and Middle Jurassic siltstone.
Bi-, Co-, and As-vein deposits, as at Verkhny Seimchan, and
granitoid-related Au deposits, as the Chepak deposit, occur in
a similar setting.
Titovskoe Sn (B) Magnesium Skarn Deposit
The Titovskoe Sn (B) magnesium skarn deposit (Dorofeev,
1979) consists of 40 ore bodies that occur along the
contact between the quartz monzonite phase of an Early
Cretaceous granitoid intrusion and Silurian and Devonian
dolomite and limestone. The ore bodies range from 5 cm to 20
m thick and from 50 to 1,000 m long. The main ore mineral
is ludwigite, which is as much as 70 to 80 percent of some
1,450 m
1,400
1,350
1,320
Map
ÀA
BÁ
Cross section
A B
Adit Drillhole
0 160 m
Alluvium
(Quaternary)
Hornfels
Granite
Ore
body
Late
Jurassic
Marble (Permian)
Contact
Fault
Figure 67. Bolshoy Kanyon Sn skarn deposit, Darpir metallogenic
belt, Russian Northeast. Schematic geologic map and cross section.
Adapted from Politov (1983). See figure 61 and table 4 for location.