Tsymbal S.N.*, Kryvdik S.G.*, Tsymbal Yr.S.*, Geiko
Ju.V.**, Baran A.N.**
* N.P. Semenenko Institute of Geochemistry, Mineralogy and Ore formation, NAS of Ukraine, Kyiv, Ukraine; ** "Pivnichgeologia" regional geological enterprise of Ukrainian geological survey, Kyiv, Ukraine
It is known four alkaline
ultrabasic intrusions in North-Western part of the Ukrainian Shield
(Novograd-Volynsk block): Gorodnitsa, Glumcha, Pokoshevo, Bolyarka.
Three of these intrusions have been discovered and studied earlier [1, 2, 3]. The Bolyarka intrusion was discovered in 2005. Its
studying is continuing. In papers [4, 5] the data on this intrusion has been
first concerned.
According the geological and the
geophysical data the intrusion is up to 10 m width, its hade is steep (more
than 80о), hade's direction is
South-Western. This body intrudes biotite-microcline-plagioclase granitoides
contained a small quantity of garnet (spessartine-almandine) and zircon. The
granitoids are intensively altered by fenitization. The fenitization zone is
5-7 m.
The intrusion is composed
predominantly by melteigites and subordinately by ijolites and jacupirangites
which have been amphibolized to different degree. The rock texture is
medium-grained; close to granitoid's contact one is fine-grained. The main
rock-forming minerals are clinopyroxenes, magnesian amphiboles, olivines and
nepheline. Cancrinite, zeolite; apatite and phlogopite occur seldom. Zircon,
chrome-spinelides, chrome-magnetite, sphene, rutile, ilmenite, sulphides and
also xenogenic minerals such as garnet, biotite, crome-diopside, orthopyroxene,
chrome-spinelides, high-magnesium olivine are detected
in crashed samples.
The clinopyroxenes are usually
zonal. Their composition corresponds chrome-diopside
with different amount of jadeite and aegirine minals: the central grain zone is
enriched in jadeite minal, margin zone in aegirine one. At the same time
aegirine minal and accordingly Fe2O3 increasing occur in
accordance with TiO2 increasing and MgO decreasing.
Judging from Ca/(Ca+Mg) ratio the chrome-diopside enriched in jadeite minal
is more high-temperatured in comparison with the aegerine-bearing one. As a
rule the latter grew on the previous and includes amphibole, nepheline,
chrome-magnetite and chrome-spinelides enriched in manganese. The most enriched
in iron (FeO - 6,0-8,5 %) diopsides are enriched
in Na2O (1,9-2,3 %), MnO (0,15-0,20 %) and are depleted in
Al2O3 (0,4-0,7 %), Cr2O3, TiO2.
They had been crystallized in a final stage of the intrusion formation by
increased potential of natrium and oxygen.The olivine is usually intensively
altered. This notice concerns the nepheline too. It is altered to zeolites and
cancrinite.
The amphiboles are posterior
magmatic and autometasomatic. They are represented by calcium and
calcium-natrium amphibole types. The Na2O contents vary from 3,3 to 7,8 %, K2O - from 0,1 to 0,7 %. A
composition of the most of the amphiboles varies from hastingsite to edenite,
from edenite to kathophorite, from edenite to richterite. On AlIV -
(Na+K) diagram they have distinct hastingsite-richterite trend. Some of their
compositions correspond kathophorite and winchite one,
or close to arfvedsonite one. They are high-magnesium (70-80 %),
low-titanian (TiO2 - 0,1-1,0 %, up to 1,5-1,7 % seldom),
low chromian (Cr2O3 - 0,0-0,8 %, sometimes 1,0-1,6 %)
and high-alumina (Al2O3 - до 13,5 %). The high-TiO2
amphiboles occur seldom. As a rule they are enriched in Al2O3
and K2O, in comparison with less titanian amphiboles
(low-temperature) they are depleted in Na2O.
The phlogopite is rare mineral.
It is low-titanian (TiO2 is up to 0,6 %)
and with increased chrome (Cr2O3 up to 0,5 %).
The ilmenite often forms
aggregates with alkaline amphibole and sphene. It is represented by
high-manganic type (MnO - 12,1-13,2 %) with low
MgO (< 0,5 %), Cr2O3 (< 0,15 %) and Nb2O5
(0,05-0,15 %). Earlier manganic ilmenites of the similar composition have
been discovered in jacupirangites in Gorodnitsa intrusion [1].
Among sulfides pyrrhotite and
pyrite predominate, the pentlandite and the
chalcopyrite relatively often occur too. Mostly they form inclusions in
amphiboles; their origin is autometasomatic.
The apatite belongs to fluorine
type (F - 1,7-3,0 %) with low MnO (<0,1 %),
Cl and rare-earth elements of cerium groupe. It often forms inclusions in
amphibole and nepheline.
The zircon crystals occur as
fine-grained prismatic ones and as light-brownish aggregates. In crystal's margin
the zoning has noted. A xenogenic core is absent. On crystal's surface occurs a
dilution sculpture.
The xenogenic minerals have been
discovered in meltiegites and jakupirangates of the Bolyarka intrusion. They
originate from crust and upper mantle.
The spessartine-almandine (Mn -
8.6 %), the spessartine-grossular-almandine garnets (Mn - 2,1-2,5 %, CaO - 7,3-12,0 %) and the biotite have a crust
origin. Sometimes they have inclusions of quartz, ilmenite and magnetite. The
upper mantle minerals are represented by pyrope, pyrope-almandine,
chrome-spinelides, orthopyroxene, magnesian clinopyroxene and olivine.
Pyrope contains 2,1 % Cr2O3 and 4,3 % CaO. By
its composition it belongs to paragenesis of granular Iherzolites from
graphite-pyrope facies of the upper mantle. Pyrope-almandine (MgO - 5,8 %, Cr2O3 - 0,03 %) belongs
toeclogitic upper mantle paragenesis.
Orthopyroxene forms grains of
irregular shapes to 0,6 mm size which has reaction
contacts with amphiboles. By chemical composition they corresponds
alumina enstatite and bronzite (Al2O3 - 2,3-4,1 %,
Mg# - 86-90) with increased contents CaO (0,3-1,0 %) and Cr2O3
(0,19-0,27 %). It may be as a result of disintegration of upper mantle
chrome-spinel peridotites.
Among rock-forming pyroxenes of the
Bolyarka intrusion the chromian (Cr2O3 - 0,4-1,1 %) diopside with increased amount of aluminium
Al2O3 (2,5-4,5 %), FeO (3,0-4,5 %) and Na2O
(0,6-1,0 %) and low - TiO2 (less 0,12 %) are discovered. These
pyroxenes have reaction contacts with nepheline and alkaline amphiboles. Their
relation with other clinopyroxenes is not finally clear. On diagram Al2O3
- Na2O, Cr2O3 - Na2O and FeO - TiO2
they separates from diopside enriched in aegierine minal.
Chrome-spinelides have no
perfect crystals. They are usually represented by oval grains with reaction
keliphytic rims that consist of chrome-magnetite with increased contents of
MnO. Presence of these keliphytic rims evidence on long being in nonequilibrium
relationship with alkaline-ultrabasic melts, so they are products of
desintagration of upper mantle chrome-spinel peridotites. The composition of
non-altered chrome-spinelides vary in wide range: amount of Cr2O3
varies from 33 to 60 , MgO - 10-18 , TiO2
-0,1-0,6 %. On the diagram MgO - Cr2O3 they lies in
field of chrome-spinelides from mantle peridotites in kimberlites. They contain
inclusions of diopside with increased Cr2O3 (0,7-1,8 %) and Na2O (1,3-1,8 %).
Among the studied
chrome-spinelids the chromite crystal (Cr2O3 - 60,3 %) that close to chromites of diamond-bearing
association in kimberlites and lamproites has been found. In this chromite the
inclusions of high-magnesian forsterite with 0,4 %
NiO was discovered. It is identical to olivine (inclusions) in diamond. That
mineral paragenesis may consider them as a product of desintagration of dunites
from diamond facies. It is possible to guess that initial alkaline-ultrabasic
magma for the Bolyarka intrusion has been generated in upper mantle in field of
diamond stability. The rocks of studied intrusion can be diamond-bearing and
are worthy of detail investigation.
The age of amphiboles from early
generation is 2000 ╠ 25 Ma, later one - 1885 ╠ 40 Ma (K-Ar method),
and zircon age is about 2100 Ma (thermoemission method).
References:
Tsymbal S.N., Scherbakov I.B.,
Kryvdik S.G., Labusniy V.F. Alkaline-ultrabasic rocks of the Gorodnitsa
intrusion (North-Western of the Ukrainian Shield) // Mineral. Journ. (Ukraine). 1997. Vol. 19, ╧ 3. P. 61-80. (in Russian)
Kryvdik S.G., Tsymbal S.N.,
Geiko Yu. V. Proterozoic Ultrabasic Magmatism of the North-Western of the
Ukrainian Shield as an Indicator of Kimberlite Formation // Mineral. Journ. (Ukraine). 2003. Vol. 25, ╧ 5/6. P. 57-69. (in Russian)
Tsymbal S.N., Shumlyanskyy L.V.,
Bogdanova S.V., Bisllstrom K. Alkaline-ultrabasic rocks in North-Western of the
Ukrainian Shield: Age, Isotope, Geochemistry // Proc. of seminar "Alkaline
magmatism of the Earth and their ore-bearing ability". Donetsk (10-16
Sept. 2007). P. 248-250. (in Russian)
Tsymbal S.N., Geiko Yu.V., Kryvdik S.G., Baran A.N., Tsymbal Yr.S. The Bolyarka
intrusion of alkaline-ultrabasic rocks (North-Western of the Ukrainian Shield)
// Proc. of seminar "Actual problems of geology of Belarus and neighbor
territories". Minsk (8-9 Dec. 2008). P. 35-40. (in
Russian)
Geiko Yu. V., Prychodko V. L.,
Tsymbal S.N., Baran A.N. Alkaline-ultrabasic rocks of Novograd-Volyn region and
possible their relationship with kimberlitic magmatism // Abst. of seminar "Parental and placer deposits of diamond and
main metals". Simpheropol (15-21 Sept. 2008). P. 13-15. (in Ukrainian)