33
Kaive belt (Kola peninsula), and also granulites of Stanovskoy zone (Aldan
shield).
Ores of argentums are connected with Archean formation of metabasics
and kyanitekeeps schists of the Baltic shield; among them there are nickel-
cobalt formation «fahlband», composing workable deposits Konsberg,
Snarum and others. The very large titanemagnetite-ilmenite and hematite –
ilmenite deposits, bound with anorthosite formation, which are found in
Canada, Norway and Russia. In the East - Antarctic shield there is
stratified
pluton of anorthosites (massif Volta), where rich ilmenite- titanemagnetite
ores have been detected.
Most ancient pegmatites with absolute age 3,500- 2,800 Ma are found in
the Canadian and Baltic shields, in Southern Africa, Hindustan, Western
Australia and East Antarctic shields. The fields of ceramic and muscovite
pegmatites are concentrated among high-aluminum and kyanites gneisses on
the Baltic shield. The pegmatites with cassiterite and tantalito-niobite,
raremetalic pegmatites with beryl-lithium mineralization are found in the
craton Caapvaal of Southern Africa. The fields of muscovite and beryl, the
largest in the world, are connected with granite pegmatites of the Bengalian
belt in India. The rich seashore places of monazite, ilmenite and zircon were
generated on the South India and Sri Lanka at the extensive denudation of
the early Archean pegmatite. Micaceous, lithium - beryl and rare metal
pegmatites are detected on the land Queens Mod, and in Prince-Charles
mountains of East Antarctic shields. The quartz – crystal veins are known
among quartzites and andalusite gneisses of Aldan and Ukrainian shields.
Мetamorphic ledges of iron, represented by jaspilites and ferrous
quartzites of early Archean age, constituted the largest deposits among the
grey-gneissis complex of Imataky (3,400 Ma), on the Guyana shield and in
the state Minas Gerais (3,100 Ma), as well as on Brazilian shield, and in
Africa (Transvaal), India, Western Australia and other shields. The rich
metamorphic deposits of manganese (gondite) are found in the same
regions, where two thirds of the world mining of manganese is produced.
II. 2. A r c h e a n g r a n i t e – g r e e n s t o n e a r e a s are
represented by the paragenesises of subgeosynclinal greenstone belts and
granite intrusions, by way of framing them. They occupy not less than two
thirds of the area of the shields. Granulite-grenstones belts occupy the
remaining part. Just opposite the Katarchean oval structures, the Archean
greenstone belts perform the prolated structures with their length ranging
from several hundreds up to thousand kilometers and with their width of
tens to several hundreds kilometers. They are alternated with extended areas
folded by granitoids, paragneisses and less of metamorphic sedimentary
rocks. Among granite - greenstone areas, some age generations are being
selected (3,800-3,500; 3,400-3,300; 3,200-3,100; 3,000-2,800; 2,700-2,600
Ma), that testifies to the particular cyclic of tectono-magmatic processes in
Archean (Condy, 1983).
In the constitution of the greenstons belt dominate volcanic rocks from
ultra basic - basic up to acidic and even of alkaline composition under
34
considerable prevalence of mafic rocks. Sedimentary and chemical deposits
are present in fewer amounts. It has been found, that the ejection of magma
took place predominantly in the water environment. The lavas, widespread
in greenstons belts, have obtained the title comatiite compound the
particular feature of Archean. The comatiites are represented by ultra-basic
and basic effusive rocks with the speenifex structure, adduced by sceletal
laminar crystal of olivine and / or pyroxene. As for their
composition, the comatiites are forming the following petrographic rank of
rocks: peridotites, pyroxenites and basaltic comatiites. Peridotite’s
comatiites, apparently, represent the outcome of considerable (up to 50 %)
melting of mantle rocks at rather high temperature (about 1,850
o
С) at the
depths of 150-200 km. The mating in sections of the greenstones belts
peridotite’s comatiites with tholeiite’s basalts testifies to irregular allocation
of temperatures in Archean mantle and different depth of melting the rocks
(Green, 1975; Vrevskiy, 1989)
The nickel ores, directly bound with comatiites lavas and sills, are
characteristic only for Archean greenstons belts. They are rarely combined
with intrusions of ultrabasic rocks. The nickel ores were crystallized from
sulphides melts separated from ultrabasic magmas. All large workable
deposits of nickel ores are coupled with comatiites complexes of late
Archean age (2,900-2,700 Ma). The major deposits of nickel of this type are
installed in greenstons belts of Western Australia (cratons Pilbara and
Yelgarn), Canada (belt Abitiby, Thompson), Southern Africa (belt
Barberton, Merchison, Limpopo). The impurity of platinum elements
together with sulphide-nickel ores, as well as cobalt and gold are noticed in
volcanites of Western Australia (deposits Kambalda, Root-Well, Mann-
Sholl). The platinum-gold ores in scarn are known among acidic vulcanites
of vent phases in the field Coronation-Hill (Western Australia). The
deposits of chrysotile-asbestos, talc and magnesite are connected with
magnesium rocks of the greenstons belts. Low-sulphide quartzy veins and
stockworks, dated to the greenstone volcanic rocks or to peripherals of
granite plutons, breaching volcanites of the greenstone belts, represent
Аrchean hydrothermal deposits of gold. There are such gold deposits in the
belt Yellowknife on the Canadian shield, ore district Calgurly of Western
Australia, field Кolar in India.
For the first time in the history of the Earth in the late Archean
greenstons belts, widespread occurrence have received sulphide ore deposits
of copper, zinc, gold, silver and cadmium. Most ancient among them is the
copper-zinc deposit Khuntoushan (3,100 Ma) on the north of China. With
acidic volcanic rocks of greenstone belt Abitiby are coupled massive and
streak-ingrained pyrrotite-pyrite-chalcopyrite ores with impurity of gold and
silver (fields Noranda, Malarty). They resemble younger Cenozoic ores of
type Kuroko in Japan.
The ferriferous ledges (sometimes with impurity of gold) are widespread
in the greenstone belts, where they associate predominantly with acidic and
midlle volcanites (deposits Kostomuksha and Olenegorskoe on Kola