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 .
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).
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)