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CHARACTERISTICS OF
RARE-METAL MINERALISATION IN ALBITITES AND
ALBITIZATION
GRANITES IN THE AREA OF ANGARO-VITIMSKI BATHOLITH
Rampilov M.O., Ripp G.S.,
Doroshkevich A.G.
Geological
Institute SB RAS, Ulan-Ude, Russia,
ripp@gin.bscnet.ru
There
are albitites and albitization granites massifs (Saivoninski, Irbo,
Myiski, Bezimanski, Oimyrski, Amnyninski) in the area of
Angaro-Vitimski batholit. These massifs contain minerals of niobium,
tantalum, yttrium and rare earth elements. They are also accompanied
by potassic metasomatism (amazonitezation, muscovitezation) and look
like apogranites. Most of these manifestations don’t have
geochronological bases and only Bezimanski (Kovalenko et all, 1999)
and Amnyninski (Posohov, 2001) have Rb-Sr isochronous dating, which
show 265 and 279 Ma accordingly. Similar manifistations, which also
have Late Paleozoic age, common in the south part of batholit in
Hamar-Daban mountain range (Bity-Dzhidinski, Salbartyiski, Utylik,
Haragyl, Urygydei). Some of them are promising rare earth elements,
and within some of them prospect works was lead.
These
are small bodies and dikes, located in metamorphic strata at the
periphery granite plutons, representative to a variable degree
albitization apical part of granitic projections. One might they are
result of deep differentiation magmatic melt, appeared accumulation
volatiles, rare elements and most of all niobium and tantalum. These
granites have more content silicium, alkali (9 - 10 wt. % Na2O
+ K2O)
and low content - Mg, Ca and ferric oxide than in calc-alkali
granites. Content of natrium in albitization granites is equal or
some more than potassium. Agpaitic coefficient is varying 0.85 to
1.0. Rocks characterized by high concentration of Rb, Li, Nb, Zr, F
and low – Sr, Ba.
We
studied three bodies of albitization rocks. They are present
leucogranites and alkaline granites. Leucogranites (Antipin et all,
1997) similar to rare-metal lithium-fluoric type (Bezimanski,
Amnyninski bodies). Alkaline granites (river basin Kelyana) have
essentially microclinic composition and contain alkaline pyroxene
and amphibole. These types distinctly differ in characteristics of
rare-metal and rare earth mineralization. It presents scattered
impregnation elements grains of metallic minerals and theirs
accretions in albitization parts of rocks.
Niobium
generally associates with columbite and sometimes with fergusonite
and samarskite in albitization granites of Bezimanski massif.
Fergusonite and samarskite characterized by high content of yttrium,
uranium, thorium and
heavy
lanthanides. Apart from this niobium (to 5 – 7 wt. % Nb2O5)
is in rutile and some in ilmenite and ilmenrutile. Thorium and light
lanthanides accumulated in allanite and monazite.
Many
minerals enriched by manganese. In biotite and allanite MnO is
present to 4 wt. %, in columbite it presents more than 0.6 f. c. and
in garnet to 45 % is a spessartine minal. There are some minerals
contain high manganese (to jacobsite) in magnetite. The
characteristic of micas is higher concentration of lithium, and
ferruginosity to siderophyllite.
As
in Bezimanski massif niobium generally associated with columbite in
albitization granites of Amnyninski massif. Albitization granites of
Amnyninski massif have muscovite, lepidomelane, polilithionit,
fluorite. Nb2O5
is present to 1.5 wt. % in titanite and thorite.
REE contain in allanite, monazite,
fluocerite, yttrofluorite. REE present by light lanthanides in first
three minerals and in last mineral by heavy. In fluocerite, thorite,
allanite and monazite yttrium is present to the first
percent.Amnyninski massif has minerals with high manganese too, such
as Bezimanski has. There are to 4 wt. % MnO in biotite, to 2.16 % in
allanite, to 3.6 % in arfvedsonite, 13.0 – 14.5 wt. % in
columbite.
Alkaline
granites of rivers basins Kelyana and Irbo (Vodorazdelni, Sredni,
Ozerni I, II areas) are present bodies of potash feldspar
albitization rocks with aegirine, riebeckite, biotite and some
magnetite, fluorite. Manganese
is not typical of these rocks in contrast to areas described above.
Mica is a biotite, it contains TiO2
from
1.5 to 2.35 wt. %.
Adjoining
schists, gabbro, granitic pegmatites are albitization too. Dykes
consisting of fine-grained albite are found often. A lot of minerals
appearances with niobium, tantalum, yttrium, REE are typical for
these manifestations. Niobium mainly situated in pyrochlore,
fersmite, fergusonite, Nb-tscheffkinite, titanite, (to 3.67 wt. %),
allanite (to 0.8 – 1.8 wt. %). Pyrochlor is remarkable for
higher tantalum (usually more than 5 wt. % Ta2O5)
and titanium (to 10 wt. % TiO2),
it approximates to betafite. Content of uranium (uranpyrochlor,
fergusonite, thorite) is high in some minerals and in other thorium
(thorite, tscheffkinite, fergusonite, thalenite, yttrialite) is
higher. One of the specific features in these manifestations is
prevalence of minerals with yttrium and selectively fortified (15 –
17 wt. %) heavy and medium lanthanides (yttrialite, thalenite,
fergusonite, xenotime, Y- britholite). But for that time
concentration of heavy lanthanide especially lutetia often exceed 1
% (to 2.7 %) and ytterbium 4 % (to 8 – 9 %). Yttrium is
typical for titanite, pyrochlor, thorite either.
Light lanthanides concentrate
in tscheffkinite and allanite, sometimes in Ce-fergusonite.
Zircon
is usual mineral of albitites. It contains 1 – 6 wt. % HfO2.
Emulsive impregnation of thalenite, yttrialite, xenotime, thorite
with uranium and thorium is present in some zircon grains. These
elements are determining metamictization of minerals.
Apogranites
and albitization granites which contain Nb, Òa,
REE and Y are most inviting among other mineralization in the area
of Angaro-Vitimski batholit. Searching of these massifs should be
concentrate in bearing strata of periphery massifs and among roof
pedants.
References
Antipin V.S., Goreglad
A.V., Savina E.A.,
Mitichkin M.A. Evolution of Li-F granites with rare-metal micas
schlieren formation // Geology and geophysics, 1997, v.38, ¹7.
Kovalenko V.I.,
Kostitsin Y.A., Yarmolyk V.V., Budnikov S.V., Kovach V.P., Kotov A.B., Salnikova E.B., Antipin
V.S. Magmas sources and isotope (Sr, Nd) evolution of rare-metal
Li-F granitoids // Petrology, 1999, v.7 ¹4, P.401-429.
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