Ana səhifə

By Sergey M. Rodionov1, Alexander A. Obolenskiy2


Yüklə 2.21 Mb.
səhifə5/149
tarix24.06.2016
ölçüsü2.21 Mb.
1   2   3   4   5   6   7   8   9   ...   149

ARCHEAN METALLOGENIC BELTS

(> 2500 MA)


West Aldan Metallogenic Belt of

Banded Iron Formation (BIF), and

Au in Shear Zone and Quartz Vein Deposits

(Belt WA) (Russia, Southern Yakutia)

This Archean to Paleoproterozoic metallogenic belt is hosted in the West Aldan granite-greenstone composite terrane (unit WA). The West Aldan belt contains large BIF deposits (banded magnetite quartzite), Au and Pt occurrences in greenstone belts, apatite-magnetite, magnetite-skarn, and zircon-ilmenite deposits. The age of BIF deposits is 3.0 to 2.7 Ga. The age of the Au occurrences is Late Archean and Paleoproterozoic. The main deposits are at Tarynnakh, Nelyuki, and Dagda (BIF) and at Lemochi and Olondo (Au in shear zone and quartz vein).

The West Aldan granite-greenstone composite terrane consists of linear greenstone belts composed of Archean metavolcanic and metasedimentary rock dated at 2.7 to 3.2 Ga that are intruded and surrounded by tonalite, trondhjemite gneiss, granite, and crystalline rocks. Units are metamorphosed under a wide range of temperatures and pressures, including granulite facies. Orthogneiss is composed mainly of tonalite, and trondhjemite and occurs in the Olekma complex that contains several large linear blocks separated by four longitudinal belts. The complex is about 300 km long and 30 km wide. The complex also contain greenstone slabs in the Subgan complex and the Kurulta granulite complex. Bounding the greenstone belts is blastomylonite. These various complexes and slabs form separate terranes and thereby the West Aldan terrane is a composite terrane.

Tarynnakh Banded Iron Formation Deposit

This deposit (Akhmetov, 1983; Gorelov and others, 1984; Bilanenko and others, 1986; Biryul’kin and others, 1990) consists of three deposits separated by gneissose granite, gneiss, and schist of varying composition. The deposits are dominated by fine-grained hornblende-actinolite-magnetite ferruginous quartzite. Cummingtonite-magnetite, chlorite-magnetite, and magnetite varieties also occur. Fe quartzite is interlayered with biotite-quartz and muscovite-sericite-quartz schist (sometimes with garnet, staurolite, kyanite, sillimanite, and andalusite) and quartzite in units ranging up to 1.4 to 3.3 km thick, as well as with amphibole-plagioclase schist and amphibolite that is 0.5 to 7 m wide and granitoid as thick as 0.2 to 8 m. Units are metamorphosed to epidote-amphibolite facies at moderate pressures. The deposits extend for 22.5 km and have a thickness of 330 m. The deposits dip predominantly west at high angles (60 to 90°). The structure of the bodies is mainly controlled by sublongitudinal faults. The deposit is large with estimated reserves of about 2 billion tonnes averaging 28.1% total Fe.


Charskoye Group of Banded Iron Formation (BIF, Superior Fe) Deposits

This group of deposits (Petrov, 1976; Myznikov, 1995; M.N. Devi and others, 1979, written commun.) occurs in the northern Chita Oblast on the left bank of the Chara River in the Kodar Ridge in the western Aldan Fe distict and comprises part of the western flank of Chara-Tokka Fe district. It extends along a submeridional trend for 185 km and is 50 km wide The main ferruginous quartzite deposits occur at Sulumatskoye, Severnoye, and Yuzhnoye, Nizhne Sakukan, Sakukannyrskoye, and Oleng-Turritakhskoye. The age of deposits is 2.6 to 2.5 Ga (Аrkhangelskaya, 1998). The deposits form a cluster near a fault basin filled with highly metamorphosed Archean volcanogenic and clastic rocks that exhibit multiple granitization and ferruginous-siliceous metasomatism events (Myznikov, 1995). Ferruginous quartzite and other ferruginous-siliceous rocks in the Chara group occur along three submeridional-striking bands. The deposits consist of steeply dipping layers of magnetite. There are ten mineral types Fe deposits. The most characteristic are banded magnetite quartzite, biotite-hornblende-magnetite quartzite, massive magnetite, and hypersthene-magnetite schist. The deposit is large with an average grade of 28% Fe.


Olondo Au in Shear Zone and Quartz Vein Deposit

This deposit (Popov and others, 1990; Popov and others, 1997; Zhizhin and others, 2000; Smelov and Nikitin, in press) consists of quartz veins and massive carbonate and amphibole-quartz-sulfide metasomatite zones cutting metabasalt and meta-ultramafic rock of the Olondo greenstone belt. Au content of the metavolcanic host rocks increases with intensity of metasomatism to a maximum grade of 0.2 to 0.5 g/t. The deposits vary from a few centimeters to 10 to 15 m wide and dip steeply. The average grade is 3-5 g/t Au, up to 2.5 g/t Pt.


Origin and Tectonic Controls for West Aldan Metallogenic Belt

The belt is hosted in the West Aldan granite-greenstone composite terrane composed of linear greenstone belts composed of metavolcanogenic and sedimentary rock with isotopic ages of 2.8-3.2 Ga. These units are surrounded by tonalite-trondhjemite gneiss, granite, and highly metamorphosed (up to the granulite facies) crystalline rock. The BIF deposits (magnetite quartzite) occur in stratiform layers and lenses in metabasalt and amphibolite, and less frequently in siliceous metavolcanic rock and schist. The BIF deposits are interpreted as forming in a back-arc basin and (or) island arc. The Au occurrences are mainly in shear zones that cut metabasalt, amphibolite, and ultramafic rock, and are interpreted as forming during amalgamation of terranes at about 2.6-2.5 Ga or during later Paleoproterozoic tectonic events.



REFERENCES: Arkhipov, 1979; Bilanenko and others, 1986; Gorelov and others, 1984; Popov and others, 1997; Parfenov and others, 2001.

Sutam Metallogenic Belt of Banded

Iron Formation (BIF) Deposits

(Belt ST) (Russia, Aldan-Stanovoy Shield)

This Archean metallogenic belt occurs in the southern part of the Central Aldan granulite-orthogneiss superterrane in the Sutam high-temperature and high-pressure granulite-paragneiss terrane. The age of the belt is interpreted as Archean (>2500 Ma). Gneiss in the Sutam terrane is dated at 2.5 to 3.0 Ga. The main BIF deposit is at Olimpiyskoe. Most of the terrane (60%) consists of paragneiss in the Seim Group and the rest (40%) is granite-and enderbite-gneiss. The Seim Group consists mainly (80%) of garnet-biotite gneiss and plagiogneiss, sometimes with sillimanite and cordierite, and lesser hypersthene-biotite, two-pyroxene, and diopside-amphibole plagiogneiss. Also occurring are quartzite, calc-silicate rock, and coarse-grained marble. The rest of the group (20%) consist of two-pyroxene, two-pyroxene-amphibole, and rarely olivine-two-pyroxene schist and magnetite quartzite. Sm-Nd isotopic ages for paragneiss parental rock range from 2.5 to 2.9 Ga whereas for orthogneiss range up to 3.0 Ga. Coeval metamorphism occurred after 2.5 Ga. The upper age limit of the early granulite metamorphism of the Seim Group rocks is constrained by the time of formation of garnet-biotite roddingite gneiss along the Seim thrust with Rb-Sr isotopic ages of 2.280.06 Ga (Gorokhov and others, 1981). The belt contains BIF composed of magnetite quartzite related to mafic and ultramafic rock. Most extensively studied is the Olimpiyskoe deposit (Kadensky, 1960; Nikitin, 1990).


Olimpiyskoe Banded Iron Formation (BIF, Superior Fe) Deposit

This deposit (Nikitin, 1990) consists of eleven lenticular deposits of medium-and coarse-grained banded hypersthene-magnetite quartzite. The deposits occur in an area that is 11 km long and ranges from 3 to 4 km wide and contains two rock groups. The first and main group consists of magnetite-hypersthene and magnetite-two mica gneiss interbedded with amphibole-two mica and magnetite-two mica-plagioclase schist in the core of an aniform. The Fe ore horizon with magnetite and hypersthene-magnetite quartzite occurs in the outer part of the antiform. The second-group occurs in the core of a synform and consists of feldspar quartzite interlayered with garnet-and sillimanite quartzite. Beds of diopside-bearing rocks and coarse-grained marble also occur. Occurring in the second-group rocks is a Fe horizon of magnetite hypersthene and spessartine-magnetite hypersthene. The deposits vary from 0.5 to 4 km thick and 20 to 200 m long. The deposit is large with resources of 500 million tonnes of Fe to a depth of 300 m, and 900 million tonnes to a depth of 500 m.


Origin and Tectonic Controls for Sutam Metallogenic Belt

Two rock groups containing BIF occur in the Sutam belt. The first is magnetite-hypersthene and magnetite-two pyroxene gneiss interbedded with amphibole-two pyroxene and magnetite-two pyroxene-plagioclase schist. The Fe deposit horizon consisting of magnetite and hypersthene-magnetite quartzite occurs in the outer part of the antiform. The second rock group consists of feldspar quartzite interlayered with garnet-and sillimanite-bearing varieties. Beds of diopside-bearing rocks and coarse-grained marble also occur. Related to the second rock group is another Fe ore horizon containing magnetite hypersthene and garnet-magnetite hypersthene. Two rock groups together form a highly metamorphosed greenstone sequence.



REFERENCES: Parfenov and others, 1999; Kadensky, 1960; Nikitin, 1990; Gorokhov and others, 1981; Dook and others, 1986; Khil’tova and others, 1988; Parfenov and others, 2001.
1   2   3   4   5   6   7   8   9   ...   149


Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©atelim.com 2016
rəhbərliyinə müraciət