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TO THE ESTIMATE OF
GRANITOID ORE-FORMING POTENTIAL IN THE
ANGARA-VITIM BATHOLITH
Khrustaljov V.K.
Geological
Institute SB RAS, Ulan-Ude, Russia, smetanina@gin.bscnet.ru
In
West Transbaikalia, the Angara-Vitim batholith is one of the most
surprising objects. It exceeds all the largest granite plutons in
the world by area of occurrence (130 thous. km2)
(Salop 1958; Litvinovsky et al. 1993). During the fifty year period
of studying the batholith granitoids, big set of geological
information was collected. However, the most principal problems of
their geological and structural position, matter composition, age,
genesis, volume and mechanism of formation remain sharply discussed
by present. As for estimating the ore-forming potential of the
granitoid massives that compose batholith, where the deposits of Sn,
W, Mo, Be, U, Pb, Zn, Au and Ag have been prospected, however, the
available data on this most important problem are rather limited
(Komarov et al. 1978; Khrustaljov 1990).
Based
on generalization of numerous data and due to our geological surveys
and research work (Khrustaljov 2000), it is reasonable to define the
two dominating varieties of the Barguzin granite complex within the
total area of batholith, i.e. allochthonous and autochthonous ones.
The autochthonous granitoids (main phase, including 60-80% volume of
batholith) actively interact with more ancient host rocks
(crystalloschists, basites, gneisso-granites) and are therefore
characterized by mixed composition with transitions from normal
biotite granites through adamellites, plagiogranites to
granosyenites and monzonites. Contacts of granites are diffuse with
formation of hybrid rock zone in thickness from the first hundreds
meters to first kilometers. The allochthonous granitoids have the
sharply cutting contacts with host rocks and are represented by
porphyry-like and middle-grained biotite granites, more rarely
leucogranites and granite-porphyries.
We
carried out the geological and geochemical studies of granitoids in
13 autochthonous and 12 allochthonous massives in the central and
south-eastern parts of the batholith:
1. Ina river basin –
allochthonous massives (Aliferovskiy, Sholokikan, Polyakovskiy,
Gakshinskiy, Akul'skiy, Devil's bald peak, Ushmanskiy (central
part); autochthonous massives (Upper Akulskiy, Olenij, Ushmanskiy
(marginal part).
2. Turka and Kydzhimit river
basin – Borodinskiy (autochthonous) and Solonetz
(allochthonous) ones.
3. Zaza river basin –
Upper Zaza (allochthonous)
4. Right bank of the Vitim
river – Koloushinskiy (allochthonous)
5.
Kurba and Ona river basins – allochthonous massives:
Usty-Khokhyartinskiy, Usty-Khuzhir, Zolkhunskiy, Upper Kurba
(central part), Shara-Gorkhon, Right Abaginskiy; autochthonous:
Upper Kurba (marginal zone), Bogunskiy, Upper Ona, Feodorov,
Ambarchik.
The
analyzed elements were determined by the main types of endogenic
mineralization in the region. In addition, granitoids of batholith
could participate in their formation. These elements are Sn, W, Mo,
Br, Pb, Zn, U and Au. Except them, a group of alkali metals (K, Na,
Rb, Li), volatiles (B, F) and also Sr and Ba are included, their
character of distribution having important genetic information.
The
results of geochemical studying the masssives of granitoids and
their phase-facial structure with use of triangle geochemical
diagram of ore-bearing, calculations of elemental formulae and
indices of concentration (INC) by V.D. Kozlov's methods (1985)
permitted to give a general estimate of efficiency rate and possible
scales of endogenic mineralization that is related to the studied
massives. Since the main necessary and interindependent features of
highly productive ore-bearing granite massives are their
leucogranite subalkaline composition and contrasting rare
metal-bearing of granitoids, these two main genetic features for
granitoids of batholith can be considered the determining factors in
formation of regional hydrothermal-metasomatic mineralization. In
this respect, the Koloushinskiy and Upper Kurba massives are
distinguished on the background of the studied granitoids being
completely ore barren. They could realize their ore potential for
gold and rare metals in favourable geodynamical conditions (frontal
paleostructures of ensimatic island arcs and others).
References
Khrustaljov V.K. (1990)
Geochemistry and ore-bearing of the Vitim Plateau Paleozoic
granitoids. Novosibirsk, Nauka, P.132.
Khrustaljov V.K. (2000)
Rb-Sr age of Barguzin complex granitoids. Izd-vo of Buryat Research
Centre SB RAS, Ulan-Ude, P.41-54.
Komarov Yu.V. et al.
(1978) Tin mineralization of the Turka-Vitim deep fault in West
Transbaikalia. IZK of SB, USSR Acad. of Sci., Novosibirsk, Nauka,
P.92.
Kozlov V.D. (1985) Geochemistry and ore-bearing of
granitoids in rare metal provinces. M., Nauka, 303p.
Litvinovsky B.A., Zanvilevich A.N.,Alakshin
A.M.,Podladchikov Yu.Yu. (1993) The Abgara-Vitim batholith is the
largest granitoid pluton. Novosibirsk, izd-vo UIGGM, SB RAS, 141p.
Salop L.I. (1958)
Pre-Cambrian magmatism of Baikal mountain area. Geological structure
of the USSR. M., Gosgeolizdat. v.2, P.47-57.
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