ISOTOPIC COMPOSITION OF Pb
AND SOURCE OF ORE MATTER OF BASE MATAL
DEPOSITS,
SOUTH-EAST TRANSBAIKALIA
Tatarnikov S.A., Dril S.I., Vladimirova T.A., Sasim S.A.
Institute of Geochemistry SB
RAS, Irkutsk, Russia, stat@igc.irk.ru
Forming
of numerous base metal Pb-Zn deposits
in
East
Transbaikalia
is associated with episodes of intraplate magmatic activity which
was the most intensive in the Jurassic-Cretaceous. To
reveal sources of ore matter for these deposits, we studied Pb
isotopic composition of sulfide minerals of some typical and well
studied deposits of this type.
Isotopic
composition of ore Pb was
investigated
for Mylnikovsko-Khorkirinskoe and Pochekuevskoe deposits. Both
deposits are found in the zone of Kir-Kirinskiy massif of rare-metal
morion granites of the Kukulbey complex. The first deposit is
located in the zone of dolomites and limestones of the Nortuysk
suite among Paleozoic granites. The age of suite is Riphean (Sanin,
Zorina, 1978, Geological structure…, 1997). The second
deposit is found in the zone tectonic dislocations and confined to
limestones and schist of Birkinskaya suite (Arkhangelskaya, 1963,
Geologic structure…, 1997).
The
Akatuy deposit
is found on north part of Aleksandorv-Zavodskaya rift depression
close to the Akatuy massif of monzonites and Akatuy intrusive
complex. All ore bodes are located in the Riphean limestone rocks of
the Nortuysk suite.
Fig. 1.
Points of isotopic
composition of Pb of ores: 1
–
Mylnikovsko-Khorkirinskoe; 2- Pochekuevskoe; 3- Akatuy; 4 –
area of trachybasalt compositions of Late Jurassic - Early
Cretaceous rift depression, East Transbaikalia; 5 – area of
granites compositions of Kir-Kirinskiy massif of the Kukulbei
complex East Transbaikalia; 6 – area of monzonites
compositions of the Akatuy massif, East Transbaikalia. Incut shows
lines of mixing of ore Pb of Pochekuevskoe (I),
Mylnikovsko-Khorkirinskoe (II) and Akatuy (III) deposit. Areas of
evolution of Pb isotopic composition of rocks of passive continental
margins (PCM) and island arcs (IA) calculated from data (6,8), lines
of evolution for upper continental crust and N-MORB – from
data (9); SK – lines of Pb isotopic evolution from model by
Stacey-Kramers.
Results
obtained from studies of
isotopic composition of Pb in galena, blendes and pyrites are shown
on figure 1 for three deposits. All isotopic compositions of ore Pb
are anomalous and can be interpreted as lines of mixing of Pb of
different geochemical reservoirs: earth's crust and mantle. Lines of
mixing of Pb for Milnikovsko-Khorkirinskoe and Pochekuevskoe
deposits (trend I and II) determine the evolution of ore Pb for
these deposits. The matter of upper crust with μ=10,55 and higher
can be regarded as the crust
source
of lead. Composition of terrigenous sediments of passive continental
margins
satisfy
this condition (Fig.1). The metaterrigenous rocks of the
Birkinskaya suite of the Argunsky superterrane composing the major
part of host rocks of deposits in the Klichka ore district can be
regarded as terrigenous sediments of the passive continental margin
(Parfenov, Popeko, Tomurtogoo, 1999). Lines of mixing of ore Pb
of Akatuy deposit
(trend III on incut) indicate other nature of crustal Pb source. The
Neoproterozoic
carbonate
rocks of
the
Nortuysk
suite can be regarded as such source. They host the mineralization.
Nature of mantle source of matter can be confidently determined for
ore Pb of the Akatuy
deposit,
as the trend evolution in its less radiogenic part adjoins the field
of composition of gabbro- monzonite- monzonitic rock series of
Akatuy massif. Granites of the Kir-Kirinskiy massif can be
considered as the endogenous source for Milnikovsko-Khorkirinskoe
and Pochekuevskoe deposits.
Investigations
are supported by grant RFBR
05-05-64332, 06-05-64754, 08-05-00660.
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