2011

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Petrological-geochemical parameters and ores of granitoids of the Kryvbas frame.

Velikanov Y.F., Velikanova O.Y.

M.P. Semenenko Institute of geochemistry, mineralogy and ore formation of NASU, Kyiv, Ukraine.

Both from east and west the mainly metamorphic formations of Kryvbas abut on granitoids of Saxagan, Demurinka, Bokovyano-Lozovatsky, Ingulets and Kirovograd complexes.

Each of the above-noted granitoids complexes is characterized by specific mineral composition, textural-structural appearances, petro- and geochemical parameters, age and structural position, having important information interpretation of conditions and regularities of formation of ore showings and deposits of different mineral products.

Saxagan plagiogranites are situated eastward of the Kryvbas, are exposed along scarps of Saxagan River and were penetrated by numerous drillholes. The plagiogranites are mid-granular, light-gray, have massive textures. Their composition (%): plagioclases (60-70), quartz (15-20), biotite (10-15); accessories: zircon, apatite, epidote; ore minerals: magnetite and sulfides.

Demurinka granite form Demurinka massif. Local outcrops of these granites can be observed on the large area eastward of the Kryvy Rig – Kremenchug syncline zone. These rocks are grey with rose feldspar, have porphyric massive textures. They consist of (%): microcline (30-60), plagioclases (30-40), quartz (25-30), biotite (10-15). Accessories: zircon, allanite, apatite, titanite; ore minerals: magnetite and sulfides.

Bokovyano-Lozovatsky granites were penetrated by drillholes in the eastern frame of the Annivka belt. The rocks are red colored, porphyric, Composition (%): microcline (40-50), plagioclase (15-20), quartz (20-25), biotite (15-20). Accessories: zircon, monazite, allanite, titanite and apatite; ore minerals: magnetite and sulfides.

Ingulets plagiogranites are spatially located in the meridionally extended area between Kryvy Rig-Kremenchug syncline structure from the east and Western-Ingulets fault from the west. The rocks are light-grey colored, mid-granular, composed by (%): plagioclases (40-50), quartz (25-30), biotite (10-15) and K-feldspar (5-7); accessories: zircon, apatite; ore minerals: magnetite and sulfides.

Kirovograd granites were developed along western border of the Kryvy Rig – Kremenchug structure where they compose the Kirovograd massif but in the Saxagan belt were found by borehole 19929 southward from the V.I. Lenin mine. The granites are mid-granular, gray or rose-gray. Textures are massive locally porphyric. They comprise (%): microcline (50-60), plagioclases (10-20), quartz (25-30) and biotite (10-15); accessories: zircon, apatite, titanite, allanite, monazite, garnet; ore minerals: magnetite and sulfides. They serve as the host rocks of a range of gold and uranium ore deposits and showings in the Ingul megablock.

Annivka granites form middle-positioned massif among the rocks of the Kryvy Rig series in the north part of the Annivka belt. This massif was explored by two profiling ranges of boreholes. Mineral composition and textures of granites are irregular. The rocks were intensively deformed under fragile deformation regime with extended development of catalases textures, but also were altered by superimposed metasomatic processes: albitization, carbonatization, quartzification, sericitization and chloritization. Some literature sources suggest subconcordant position of the Annivka granites relatively to the host metasedimentary beds of the Kryvy Rig series. However, a few boreholes demonstrated that the Annivka granites shear the host beds. The granites are rose-grey colored, mostly having porphyric microcline-plagioclase and plagioclase-microcline composition. They consist of (%): microcline (40-60), acidic plagioclases (30-40), quartz (25-30), biotite (10-15). Accessories: zircon, apatite, titanite, allanite; ore minerals: magnetite and sulfides. Mineral composition of the Annivka granites is similar with mineral composition of the Demurinka granites. However, structural position and geochemical characteristics of these granites are different. Absolute age of the Annivka granites was not determined.

The major petrogenetic components which were used to determine petrochemical characteristics of the rocks are silica, alumina, iron, magnesia and alkalinity.

From averages of chemical analyses sets, the highest silica concentrations were established in Annivka and Bokovyano-Lozovatsky granites. High alumina was established in Saxagan plagiogranites. The highest iron contents was found in the Kirovograd granites whereas the lowest in the Annivka granites. Relatively higher magnesia concentrations were manifested by Saxagan, Ingulets and Demurinka granites, but the lower magnesia contents were detected in Kirovograd, Annivka and Bokovyano-Lozovatsky granites. The highest concentrations of K₂O are related to Kirovograd granites at the lowest concentrations of Na₂O and the highest concentrations of Na₂O were detected in Saxagan plagiogranites at the correspondingly lowest concentration of K₂O.

A set and distribution of trace elements in the different granitoids studied mostly show contrasting behavior. However, the differences between the rocks are well displayed only in fresh rocks whereas in metasomatically altered granitoids element ratios were greatly changed due to different element mobility and contrasting redistribution.

The most prominent sets of trace elements in increased content, characterizing different granites are as follows: Kirovograd granites – U, Th, La, Ce, Cu, Zn, Sr, Ba, Mo, Pb, Li, Zr and Nb; Saxagan plagiogranites – V, Zr, Rb, Sr and Ba; Demurinka granites – Ce, V, Rb and Nb; Ingulets granites – Sm, Eu, Lu, Ga, Li, Rb, Zr; Bokovyano-Lozovatsky granites – Cu, Mo, Zn, V, Rb, Sr, Zr, Nb and Y; Annivka granites are contrastingly depleted in Be, Sb, V, Pb, Zn and As in comparison with younger microcline granitoids developed in the western frame of the Kryvbas. However, Annivka granitoids regularly contain high concentrations of TR, Sn, Cu, W and Mo, typically for granitoids of the eastern frame and metasomatically altered rocks.

Ores in granitoids were developed either due to primary accumulation of ore elements during their crystallization or as a result of their redistribution during later metamorphic and hydrothermal-metasomatic alterations.

Multiplicative and diverse migration of the ore elements by postmagmatic solutions has led to significant redistribution of the ore components, often with complete changing of geochemical patterns characterizing fresh rocks.

Along with intrusions of different age granitoid magma in the sedimentary-volcanogenic rocks of the Kryvbas, which stimulated hydrothermal activity, the granitoids were altered to different type metasomatites: quartzites, greisens, sericitolites, albitites etc., which contain diverse ore mineralization of Au, Cu, Mo, Zr, U, Th, Sc, V, Sn, W, As and TR.

In metabasites of the Eastern-Annivka zone there are intense ore showings of Cu, Mo, W, Sn, Bi, As, Au and other elements. Spatially, this mineralization is controlled by contact of the Bokovyano-Lozovatsky granites dated at 2600 Ma [1] with the host mid-granular hornblende amphibolites of the New Kryvy Rig suite which contain zones of quartzification and greisenization. In metabasites, in the contact zone, the sedimentary-volcanogenic rocks were microclinized, quartzifized and sulfidized due to active influence of granitic magma on the host volcanogenic-sedimentary strata. With increasing distance from the contact zone, the contact metasomatic alterations gradually disappear. The relation of metasomatic processes to postgranitic fluids is also confirmed by a range of geochemical positive anomalies of Mo, W, Sn, Bi, As, Be, Nb, TR etc., the set of elements which are considered as a typochemical characteristics of granitic magmatic systems.

With serpentinization which obviously was derived from hydrothermal influence on the rocks of the Eastern-Annivka zone, ore mineralization of Au, Cu, Zn, Pb, Mo, W, Sn etc. is connected. This hydrothermal activity is connected with intrusions of the Bokovyano-Lozovatsky or Kirovograd granites, the latter dated at around 2.0 Ga [2].

U-TR and V-Sc ore deposit is known in the zones of sodium metasomatism in the Zhovta Richka iron-uranium deposit [3].

Along Ingulets River, granitoids contain alkali, calcareous and quartz-sulfide metasomatism resulted in accumulation of ores of Cu, Pb, Zn, Au, Zr and TR.

In the Pervomayske and Zhovta Richka deposit, and along the Eastern-Annivka zone, the volcanogenic-sedimentary strata of the Kryvy Rig series was injected by shear TR-pegamtoid dikes, which in contrast to uniform pegmatites contain anomalously high contents of Li, Rb, Cs, Sr, Nb, Ta, Be, F, B etc. Their age is still undetermined.

Reference

1. Semenenko N.P., Yaroschuk E.A., Yaroschuk E.A., Kurlov N.S. et al. Isotopic age of Saxagan metabasite series and Bokovyano-Lozovatsky complex of the Ukrainian Shield // Theses of XXI session of Komission on determination of absolute age of geological formations. – Ufa, 1979. – P. 148-149.

2. Kononov Y.V. Kirovograd granites and migmatites of the Kirovograd-Bobrynets and Dolinsky massifs. In: Stratigraphy of UkrSSR. Precambrian, Kyiv, “Naukova Dumka” Press, 1972, 348 p.

3. Tarhanov A.V., Kudlayev A.R., Petrin A.V. et al. The Zhovta Richka vanadium-scandium deposit // Geology of ore deposits. – 1991, No 6. – P. 50-56.