Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

I metaUogeoic belt, now located a few hundred krn to the east in Southern Alaska. However, available paleomapetic data (table 3
inNokleberg and others (2000)), lodicate that the Wrangellia superterrane, that hosts the East~rn Alaskan Range metallogenic
bell was withia a few degrees of Be Late Triassic paleoequator. In contrast, the three subterranes (Dilhger, Nixon Fork, and
Mystio), colYfituling the Farewell tmne, are interpreted as having been located several thousand km away, near he North
American Craton Margin (fg 34) (Ndrleberg and others, 2000). Additional work is needed to determine ths tecfonic origin of the
Farewell metallogenic belt, ccmtained deposits, and host rocks. Herein, the Farewell metallogenic belt is interpreted a6 wing during incipient Late Triassic rifting ~EDiIlinger and adjacent passive continental margin terranes
i
! M ~ ~ nQeb i Formed c in
Middle Mesozoic Tm+k.etna-Bonzana
lslond Arc in Wragellla Superterrane
Kodak khad and Border Ranges
Metallogedc Belt of Podifom Cr Deposits
(blt KOD) Sohem Coastad Nwka
The Kodittk laland and Border Ranges metallogenic belt of podiform Cr deposits and om gabhie Ni-Cn depmt (fig
32; tables 3,4) occurs along the northern margin of Kodiak Island, on the Kenai Peninsula, and along the northern flu& af UIU
Chugacb Mountains in swrhem coastal Alaska (Foley, 1985; Foley and others, 1997). This belt occurs discontimusly dong a
strike dipkme ofseveral hundred kihmeters from Kodiak Island pn the southwest to the eastern CBugach Motmtaim w Ihe east.
The mttallogcuic beh is hosted in the Border Ranges ultramafic-mafic assemblage which forms the southern part o€ the Talkeem
part of the TalLeetna-Bonznna island arc in Wrangellia superterrane (Bums, 1985; Plafker and others, 1989; Nokbcrg and o h ,
1994c, t997c, 2000). The sipifitant deposits are at Halibut Bay, Claim Point, Red Mountain, and Bernard and h t Mountains; a
at Spirit Mountain (table 4) (Nokleberg and others 1997a, b, 1998).
possibly dated gabbroic Ni-Cu w i t
The Red Mountain podifonn Cr deposit (fig. 35) (Guild, 1942; Bundtzen, 1983b; Burns, 1985; Foley and Barker, 1985;
Foley and others. 1985, 1997) consists of layers and lenses of chromite in dunite tectonite; the layers and lensea w e up to
several hundred meters long and 60 m wide. The largest chrornite layer is about 190 m long and up to 1.5 m wide, md mom &an
10 smaller ore bodits exist. TRc host Late Triassic to Early Jurassic dunite tectonite is interlayered with subrhte pyweaite in
mws about 60 m thidc. Sqentinite is locally abundant along contacts of bodies. Exploration and development occurred
spora&aI.ly fiom but 1919 to the 1980's. Several hundred meters of underground workings and trenches were cmstmcted. An
eatimatdd 26,000 tonne of ore, ranging fiom 38 to 42% Cr203, was produced from 1943 to 1957. The two Largest remaining
deposits are esthatsd to contain 87,000 tonnes grading about 25 to 43% Cr20,. An additional, low-grade deposit contains im
estimated 1.13 million tomes Cr201. The nearby Windy River chromite placer deposit, which occurs downs~eam from Red
Mountah deposit, in hosted in glrtciohial sand and gravel deposits and is estimated to contain 15.6 millh m3 grading about
133% Crp,.
Origin of and Technic ConVols for
thdhk lslsnd 8nd Border Ranger Metallogenic Belt
The Kodiak lsland and Border Ranges metallogenic belt of podiform Cr and associated deposits occlrn in She La&
Triassic to Early Jurassic Border Ranges ultrarnafic and mafic assemblage (Bums, 1985; Plaker and athers, 1989; DeBari and
Cala~lan, 1989; Fdey and o h , 1997). The assemblage is a major belt of ultramafic tectonite, cumulate gabbm, d norite
which ocuws almg bbe southern, faulted margin of the Peninsular sequence of the Wrangellia island luc wpemrrme cbdy
mrlh ofthe Border R~agea fault system (unit WR, fig. 32) (MacKevett and Plaker, 1974; Burns, 1985; Plafker p ~d ohm, 1989;
Nokleberg and ohen, 19Wc, 1997~). In this region, the ultrarnafic and mafic rocks are interpreted as the decpTevd mot dthc
Late Trimk to Jurassic Peninsular sequence (Talkeetna part of the Talkeetna-Bonanza island arc) of t k WrangeHia supertarrane
(Burns, 1985; hbui ard Coleman, 1989). This sequence consists of the Late Triassic(?) and Early Jurassic marine mdesito
vokrulic rocks of tbe Talkaetna Formation and the Middle Jurassic plutonic rocks of the Alaska-Aleutian Raage balbolith. lk ep
of the Talkeetna part oftbe Talkeeba-Bonanza island arc is interpreted as about 180 to 2 17 Ma (Newbemy and other& 1986q
Rocske and others, 1989). Tbtse data hdicate that the Kodiak Island and Border Ranges melallogenic belt an a deep-levd suih of
lode deposits formed in the root of the Talkeetna-Bonanza island arc along the margin of the Wrangellia amrrane (NoWcrg
and olba 1994d, 2000).