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Geochemistry, petrology
and ore-bearing ability of the Proterozoic apogranitoid metasomatites in
Azov domain of the Ukrainian shield
Donskoy A.N.,
Donskoy N.A., Legkaya L.I., Kompanets N.N.
M.P. Semenenko Institute
of geochemistry, mineralogy and ore formation of NAS of Ukraine, Kiev,
Ukraine
donick_gg@mail.ru
Prevalence of alkaline
granites associates to lineament zones and coincides with granosyenite
and alkaline massifs, such as Kalchikskiy, Kalmiusskiy, Elanchikskiy,
Oktyabrskiy.
Alkaline granites usually
frame alkaline syenite massifs, composing edge zone of the massifs.
There is no clear intrusive contact. Rock-forming minerals are
represented by feldspar, plagioclase, quartz, orthopyroxene,
clinopyroxene, amphibole and biotite. Accessory minerals are apatite,
zircon, magnetite, ilmenite, molybdenite, garnet, thorite, rutile,
orthite and chevkinite.
According to dark-coloured
minerals’ content the granosyenites and the quarz syenites are
subdivided into quartz-containing pyroxene and pyroxene-amphibole
syenites. The quartz syenites are gradually replaced by alkaline
syenites by means of reducing of quartz content in the rock. For the
rocks studied metasomatic processes of the last stages are
characteristic. These processes are similar to fenitization ones. If it
studies the rock alteration from non altered host rocks (normal
granites) then following metasomatic zoning is observed (from edge to
center): normal (hornblende-biotite) granites → potassium-sodium (biotite)
granites → potassium granites → alaskites (microcline-albite apogranite)
→ granosyenite → quartz syenites → alkaline syenites.
Table 1. Average chemical
composition of alkaline rocks formed during syenite stage, wt. % (Donskoy,
1982; Eliseev et al., 1965; Lyashkevich, 1971;
Pyatenko et al., 1966)
|
Rock name |
SiO2 |
TiO2 |
Al2O3 |
Fe2O3 |
FeO |
MnO |
MgO |
CaO |
Na2O |
K2O |
P2O5 |
F |
|
Hornblende-biotite
granite |
74.51 |
0.29 |
12.01 |
1.85 |
1.55 |
0.03 |
0.27 |
1.05 |
2.7 |
5.4 |
0.07 |
0.26 |
|
Biotite granite |
74.5 |
0.06 |
12.8 |
0.6 |
1.28 |
0.015 |
0.2 |
0.82 |
3.7 |
4.8 |
0.03 |
0.53 |
|
Biotite-albite-microcline granite |
72.54 |
0.11 |
13.57 |
0.88 |
1.3 |
0.01 |
0.19 |
0.95 |
3.06 |
6.38 |
0.05 |
0.5 |
|
Muscovite-albitite
apogranite |
72.2 |
0.03 |
15.45 |
0.49 |
0.93 |
0.02 |
0.16 |
0.94 |
5.97 |
2.62 |
0.026 |
— |
|
Quartz albitite
|
74.6 |
0.04 |
14.32 |
0.45 |
1.03 |
0.02 |
0.12 |
0.32 |
4.5 |
3.57 |
0.07 |
— |
|
Apogranite |
64.34 |
0.22 |
17.09 |
3.44 |
0.94 |
0.18 |
0.57 |
0.57 |
7.6 |
4 |
0.08 |
— |
|
Granosyenite |
69.52 |
0.6 |
12.84 |
3.23 |
2.23 |
0.01 |
0.73 |
1.78 |
2.54 |
6.08 |
- |
0.1 |
|
Quartz syenite |
62.45 |
0.55 |
16.31 |
3 |
3.8 |
0.1 |
0.71 |
2.47 |
4.39 |
5.42 |
0.05 |
0.14 |
|
Alkaline syenite |
57.09 |
1.55 |
18.22 |
2.21 |
4.04 |
0.27 |
1.46 |
3.04 |
6.55 |
4.66 |
0.31 |
0.05 |
Notice.
«—» means content is lower than a detection threshold.
In the table 1 it shows a
change of rock composition during alkalinization process. At the
beginning of the process silica is relatively inert. Then silica content
goes down due to quartz content decreasing. Behavior of Al2O3
is opposite: it rises at the final stage. At the beginning stage Fe+3
is decreased in the granosyenites and the quartz syenites. During
alkalization Fe+2 is increasing. In the host granites Fe+2/Fe+3
≈ 1, at the final stage Fe+2 is enlarged twice. Relative Fe+2
content is increased in three times. Na and K contents
vary in wide range when total alkalinity rises.
Lithium accumulation is
observed at the beginning stage of granites’ alkalanization (table 2).
Table
2. Average contents
of trace elements in alkalinized rocks according to spectral and
chemical analyses, wt. %
|
Rock name
(sample
location) |
Li |
Rb |
Та |
Nb |
Ве |
Zr |
∑TR |
Sample size (n) |
|
Hornblende-biotite
granite (Kamennyie Mogily) |
0.006 |
0.03 |
0.0003 |
0.007 |
0.0007 |
0.07 |
0.08 |
6 |
|
Biotite granite |
0.011 |
0.06 |
0.0007 |
0.006 |
0.0006 |
0.01 |
0.06 |
22 |
|
Biotite-albite-microcline granite |
0.016 |
0.07 |
0.0005 |
0.007 |
0.0007 |
0.02 |
0.06 |
10 |
|
Apogranite (Dmitrievskiy
open pit) |
0.003 |
0.013 |
|
0.04 |
0.002 |
1.000 |
0.05 |
17 |
|
Quartz albitite
(Kamennyie Mogily) |
0.022 |
0.07 |
0.004 |
0.007 |
0.0005 |
0.002 |
0.02 |
6 |
|
Granosyenite (Oktyabrskiy
massif) |
— |
— |
— |
|
0.0001 |
0.084 |
0.02 |
7 |
|
Quartz syenite
(Oktyabrskiy massif) |
— |
— |
— |
0.04 |
0.0003 |
0.057 |
0.03 |
4 |
|
Alkaline
syenite (Oktyabrskiy massif) |
— |
— |
— |
0.04 |
<0.0003 |
0.075 |
0.05 |
26 |
Notice.
«—» means content is lower than a detection threshold.
Rubidium behavior
correlates lithium one. In the host rocks Ta and Nb contents are close
to clarke but during alkalanization process they are shortly increasing.
If at the beginning stages (hornblende granites) Ta and Nb are probably
in dark-coloured minerals as isomorphic impurities than at the last
stages their peculiar Ta- and Nb-minerals appear, such as fersmite,
columbite, pyrochlore, ilmenorutile.
Zr is a characteristic
element of alkaline complexes. Zirconium increased content usually
associates niobium one. Major mineral which accumulates Zr is a zircon.
In alkalinezed granites
increased TR elements’ content is determined (0.02-0.08%). Minerals
accumulating Zr are zircon, rinkite, britholite and TR-apatite.
Granitoids altered during
alkaline metasomatic process form wide fenitization zones which can be
considered as indirect characteristic of a presence of alkaline massifs
with rare-metal mineralization.
References:
Donskoy A.N.
Nepheline complex of Oktyabrskiy alkaline massif. Kiev: Naukova dumka.
1982. 150
p.
(in Russian).
Eliseev N.F., Kushev
V.G., Vinogradov D.P.
Protherozoic intrusive complex of Eastern Azov region. Moscow-Leningrad:
Nauka, 1965. 204 p. (in Russian).
Lyashkevish Z.M.
Metasomatites of Eastern Azov region. Kiev: Naukova dumka, 1971. 203 p.
(in Russian).
Pyatenko I.K. Sitnin
A.A., Lavrinenko A.F.
Geochemical features of metasomatic altered granitoids of Azov region //
Soviet geology. 1966. No 12. P. 81-98. (in Russian). |