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Petrology and ore-bearing ability of Vysokopolie structure in the Krivoy
Rog Iron Ore Basin
Velikanov Ju.F.,
Velikanova O.Ju., Donskoy N.A.
Semenenko N.P. Institute of Geochemistry, Mineralogy and Ore Formation
NAS of Ukraine, Kiev, Ukraine
olgavelikanoval@rambler.ru
Vysokopolie structure is represented by a fragment of synclinal fold of
north western direction which is located among granites and migmatites
of dnepropetrovskiy complex and is composed of sedimentary and
volcanogenic formations. Metabasic-ultrabasic rock assosiation on a plan
looks like a stripe 35 km long roughly and 1.5-2.5 km width. Ultrabasite
rocks compose tiny bodies from 100 m to 2.5 km long and from some meters
to up to 300 m high. Host rocks are amphibolites, amphibole schists,
gneisses, plagiogranites and migmatites.
Ultrabasite body detected by drill hole #20572 is intensively altered by
secondary processes, such as serpentinization, silicification,
amphibolization, carbonatization, talcization, chloritization. It
consists of antigorite serpentinite in central part of the body and
serpentine-carbonate-talc schist in edge parts.
Mineral composition of antigorite serpentinite: antigorite 40-50%;
carbonates: magnesite dominated, dolomite and calcite are from
individual grains to up to 10%; amphiboles: actinolite and tremolite
15-20%; chlorite 5-7%; relict olivine 10-20%; magnetite 3-10%.
Serpentine-carbonite schists are represented by antigorite and
chrizotile (5-10%), carbonates (15-50%), talc (5-70%), chlorite (1-3%),
magnetite (up to 7%), relict olivine grains occur.
Actinolite-tremolite schists are almost monomineralic rocks. There are
merely small quantities of chlorite, carbonates, and magnetite.
Chlorite schists actually consist of chlorite. There are small
impurities of actinolite, carbonates, magnetite.
Petrochemical characteristic of the massif is based on 10 chemical
analyses calculated.
Average value of F/M coefficient is 4.3. It varies from to 3.4 to 5.2.
Average value of femic component, b, is 47.78%.
2c coefficient varies in a range 7.2-14.3%; average value is 11.09%. The
rocks of the massif are serpentinised. Serpentenization coefficient, h,
varies from 20.7 to 44.2%; average value is 29.5%.
According to virtual mineral components ratios of the massif ultrabasic
rocks’ compositions the orthorhombic pyroxenes slightly prevail: virtual
component y varies from 29.8% to 62.2%
Magnesium coefficient, KM, is 75.44%; ferruginosity one, KF,
is 21.16%; alkalinity one, KA, is 0.40%.
Thus, the petrochemical coefficients of ultrabasic rocks studied allow
attributing these rocks to basic magma derivates or ultraferbasites
according to N.D. Sobolev classification (Sobolev, 1959).
The petrochemical components’ values for the rocks of Vysokopolie massif
are comparable to petrochemical characteristics of ultraferbasites of
Buh region (Fomin, 1984).
In ultrabasites of the massif TiO2 content varies in
sufficiently wide range from 0.21 to 0.73%. Alumina content is
5.83-10.85%. It confirms about high alumina of generous magma, not high
pressure and temperature conditions during magma’s establishing period (Vaganov,
Sokolov, 1988). Total iron abundance varies in 7-12% range. Generally,
Fe2O3 predominates over FeO. MgO content is
20.37-24.42%, CaO 4.43-10.3%, K2O 0.12-0.73%, NaO 0.15-0.72%
According to petrochemical coefficients by N.P. Semenenko (Semenenko,
1963) ferromagneousity of ultrabasites is comparably high (FМ
is up to 74.09 %). Alumina content and calcium one
are 20 and 18% respectively.
In accordance with petrochemical coefficients and discriminatory
diagrams the rocks studied are on peridotite’s and gabbro-peridotite’s
fields.
Main ore elements of ultrabasites which are prospective for exploration
are Ni, Co, Cr and Cu. Most of them are concentrated in impurity form in
magnesium-ferrous silicates, general rock-forming minerals. As well they
are in sulfides and magnetite. Sulfide minerals are represented by
pyrite, pyrrhotine, chalcopyrite, pentlandite, cobaltite, cobalt-pyrite,
which form fine dissemination of different intensity or intersecting
veinlets.
Ni-mineral is pentlandite. Minerals containing nickel are pyrrotine (up
to 0.8%), serpentine (0.1-0.6%), talc (0.06-0.4%), magnetite
(0.08-0.3%), actinolite (0.003%).
Nickel raised content associates with zones of serpentinization,
talcization and carbonatization where ore elements concentration is
observed, as well as sulfide mineralization.
In talc-containing rocks the Ni content is a bit less than in the
serpentinites. It is 0.0n%. It maybe caused of nickel containing
sulfides and magnetites in these rocks are less than in serpentinite.
According chemical analysis in serpentinite the cobalt content is
0.003-0.3%, in actilnolite-tremolite schist is 0.001-0.006%.
Considerable amount of Co is scattered in ferrous-magnesium silicates.
Co content in serpentine is 0.01-0.023%, in talc is 0.005-0.012% and in
amphibole is 0.001-0.06%. In magnetite the Co content goes as far as
0.015%, in pentlandite is 1.5% and in pyrite
is 0.1-0.2%.
In some locations chrome content exceeds its abundance ratio for
ultrabasic rocks in 2-3 times but is not a prospective one as for
exploration purpose. According chemical analysis the chrome content in
serpentinite on some intervals is 0.51-0.8%, in actinolite-tremilite
schists is 0.18-0.31%. There is only chromite of peculiar Cr-minerals.
It composes a fine dissemination of rounded grains. Chrome is also
concentrated in olivine (0.18%), antigorite (0.04-0.1%), talc
(0.1-0.2%), magnetite (0.6%).
In ultrabasites of Vysokopolie structure copper is sufficiently
wide-spread but its distribution is not regular one. Scattered copper
mineralization is identified in serpentinites; copper content is 0.07%.
In actenolite-tremolite and chlorite schists the copper content doesn’t
exceed 0.0n%. In magnetite the copper content is 0.01-0.02%, in olivine
is 0.001-0.003%. Characteristic feature of high copper rocks is
disseminated sulfide mineralization and intersecting sulfide and
quartz-sulfide veinlets.
References:
Fomin A.B.
Geochemistry of ultrabasites of the Ukrainian Shield. Kiev, Naukova
dumka. 1984. 232 p. (in Russian)
Semenenko N.P.
Metamorphism of flexible zones. Kiev, NAS of Ukraine, 1963. 258 p. (in
Russian)
Sobolev N.D.
On petrochemistry of
ultrabasic rocks // Geochemistry. 1959. P. 979-695. (in Russian)
Vaganov V.I., Sokolov S.V.
Thermobarometry of ultrabasic paragenesises. Moscow,
Nedra,
1984, 1988. 150 p.
(in Russian) |