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GEOCHRMICAL FEATURES OF THE
SOUTH-EASTERN PART OF EAST SAYAN
GOLD-BEARING GRANITES
Damdinov B.B.
Geological
Institute
SB RAS, Ulan-Ude, Russia, damdinov@gin.bscnet.ru
South-eastern
part of East Sayan granitoids are consolidated to some differently
aged granitic complexes. Among Archean and Early Paleozoic intrusions
by belsky, kitoisky and onotsky migmatite-plagiogneisogranitic
complexes are distinguished. Middle and Late Proterozoic intrusions
are presented by uriksky, sumsunursky, sayansky and holbinsky
granitoid complexes. Paleozoic granitic intrusions are divided to
tannuolsky, sarchoisky, and ognitsky complexes. However, using
A.B.Kuz’michev data (2004) occurrences of granitic magmatism
attached to tectonic events. Different Early Paleozoic granitoids of
Tuva-Mongolian massif, which early were divided to sarchoisky,
ognitsky and sumsunursky complexes, are combined to the postcollision
granitic magmatism related to the Tuva-Mongolian microcontinent with
craton and island-arc terranes collision. Whereas sumsunursky and
holbisky complex tonalities and trondiemites have a Late Riphean age
and relate to the active continental margin magmatism of the
Tuva-Mongolian microcontinent.
Last
investigations allow revealing some gold deposits in the Riphean and
Early Paleozoic granitoids of the south-eastern part of East Sayan.
However, as a result of granitoid bad study, the granite typification
problem appeared. Distinguished granitoid complexes are differently
interpreted by different researchers, especially it refers to the Oka
structure-formation zone granitoides. Furthermore grantoid massifs
age is not reliable determined. Existent dating is carried for single
massifs and has a fragmentary character.
Granite-related
gold mineralization represented by two geochemical types:
gold-telluric and gold-bismuth. Gold-telluric type deposits confined
to the Last-Riphean tonalite-plagiogranites (Tissa-Sarchoy ore zone),
whereas gold-bismuth type deposit is related to Early-Middle
Paleozoic two-feldspar leukogranites (Pogranichnoe deposit). These
leukogranites are referred to the sarchoisky complex by some
features. The tonalite-plagiogranite attribute to some granitic
complex is still unclear. In sixteen ages of twenties century these
granites were considered as the horingolsky volcano-plutonic complex.
Later, they were referred to the tannuolsky granitic complex. Mainly
it is connected with the absence of the studied granite massifs
reliable dating.
We carried out investigations of
the absolute age using Rb-Sr method on the gross granite composition
(analysist V.F.Posokhov, GIN SB RAS). Tissa-Sarchoi ore zone
granitoids have a 633±140 Ma age, with a 0.70448 primary
Sr-ratio. Pogranichnoe deposit granites age has a 440-525 Ma values,
with a 0.7050 primary Sr-ratio. Studied granites are distinctly
divided to the island-arc (Tissa-Sarchoi ore zone) and postcollision
(Pogranichnoe deposit) granites by geochemical features.
The post collision magmatism,
presented by tannuolsky granitic complex in this region, aged as
451±5.7 Ma determined by U-Pb-method (Kozakov et al., 1998).
Most probably, studied sarchoisky complex granites have a similar age
taking into consideration its dating and granite geochemical
features.
Gold-telluric
mineralization bearing plagiogranites are older and comparable with
Last Riphean island arc plagiogranites of the Kuznets Alatau, which
have age value about 800 Ma, taking high dispersion of Rb-Sr dating
age (Rudnev et al. 2006). Using Yb-Eu and Yb-Sr correlation diagrams,
we determined that plagiogranite formation was a result of
plagioclase-hornblende (gabbroidic) paragenesis melting in 1000ºC
temperature and 8 kbar pressure conditions (Turkina, 2000). These
conditions are corresponding to oceanic plate melting in subduction
zone.
Thus, Last
Riphean island-arc and Middle Paleozoic postcollision granites have a
different metallogenic specialilazation. Island-arc plagiogranites
contain gold-telluric mineralization, whereas postcollision
leukogranites contain gold-bismuth mineralization. Formation of both
types of gold deposits is genetically related to granites, that were
established by our and N.A.Goryachev, G.N.Gamyanin et al.
investigations (Gamyanin et al., 1998; Gryachev, Gamyanin, 2006;
Damdinov et al., 2007 et al.).
Investigations was supported by
RFBR grant (¹06-05-64993).
References
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