Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Features of kimberlitic  magmatism in the North-East part of the Kirovograd megablock of the Ukrainian Shield.

Kalashnyk G.A. *, Palkina E. Yu. **

*-Geological prospecting expedition  37 «Kirovgeology», Kiev, Ukraine, kalashnik_anna1@mail.ru **-Crimean office of UkrGGRI, Simferopol, Ukraine, e_leyka@mail.ru

Signs of kimberlitic magmatism by three epochs tektonical-magmatic activation in the north-eastern part of Kirovograd megablock of the UkrSh was discovered. The earliest era of kimberlitic magmatism by dykes facies on the Lelekovsky fault was identified. They recorded in tectonic sites established violations of the Northwest, latitudinal and North-Eastern spread. Ages of kimberlitic dykes are 1815 and 1900 mln. years. Kimberlitic dikes exposed in 14 wells (on Lelekovsky, Shorsovsky, Ositnyaznsky sites). The bulk of the kimberlite rock of Lelekovsky fault is talc-carbonate- micaceous aggregated. Kimberlitic deeps xenolites by size of 2-8 mm to several centimeters are mainly a mixture of plate-fibrous serpentine, bastit, ore mineral. Xenolites underlying rocks according to petrographical characteristics of correspond to garnet dunite and garcburgite. On the composition of the xenolites and the cementing of two intrusive phases of implementation. Kimberlite of explosive phase, most productive on diamond, was not identify in bored wells. In the examined mineralogical samples of kimberlite was discovered by a full set of indicator minerals of kimberlite (IMK): pyropes, picroilmenites, chromspinells, chromediopsides, highmagnezial olivine. However, the chemical composition of the minerals-indicators, these kimberlite do not qualify for inclusion in the diamond-bearing facies (377 chromspinells from kimberlite of Lelekovsky site content Cr₂O₃ ranges from 10 to 47% (26 cases it exceeds 40%) and MgO contents vary within 14-20%. In chromspinells from kimberlites of the Shorsovsky site the maintenance of Cr₂O₃ makes 31–50 %, the maintenance of MgO fluctuates within 10–17 %. In chromediopsides the maintenance of Cr₂O₃ fluctuates from 0,98 to 1,29 %. The allocated grenades correspond a grossulyar-pyrope-almandine. It allows to assume about eklogitic association. In test T-96-1 by weight 280 kg in the Crimean office of UKRGGRI two crystals of diamonds octahedral gabituse in the size 0,19х0,18х0,14mm, 0,07х0,07х0,05mm were are revealed. The thickness of kimberlitic dykes on the Shorsovsky site changes from 0,5 to 18,2 m. Falling of bodies the vertical. Rock containing kimberlites are granites. The average thickness of kimberlitic dykes on the Lelekovsky site on all crossings (42 crossings) makes 3,1 m and hesitates from 0,1 m to 7,8 m. Vertical scope of bodies of kimberlites makes 91,6 m. Falling of bodies the subvertical.

A Devonian era of tectonic activization in the central part of UkrSh treats a eruptive breccia on Rovenskaya structure formed owing to eksplozive process. In explosive breccia the following IMK were found: chromebearing low-ferruterous diopsides of  lherzolite paragenesis by graphite-pyrope facies of depth typical for lherzolitic nodules from kimberlites, high-chromic spinells (Cr₂O₃=46,60-58,58%), and also grain of high-chromic magnezial ilmenite (Cr₂O₃=3,27 %, MgO=3,03 %). Considering the low maintenance of IMK in technological probe (probe 4-1 by weight 2060 kg) most likely that on the Rovno site productive pipes of explosion where the magmatizm was shown mainly by means of gas break with emission of a small amount of a kimberlitic material were created.

The most productive concerning eksplozive activity in the central part of UkrSh is low Paleocene stage of tektono-magmatic activization. Manifestations are diverse. Products belong to eksplozive to a formation of breccia and eksplozive-sedimentary educations which in the UkrSh center in a Paleocene associate with Raygorodskaya stratum. The first group of eksplozive structures is located in near contact parts of rocks of Korsun-Novoukrainsky diphasic pluton. On many sites within Raygorodskaya stratum direct signs of a kimberlitic magmatizm (sites by Gruzka, Lesnoe, Ositnyazhsky) are revealed. Manifestations of  avtolitic breccia of kimberlite are referred to them, diamonds and IMK in the rocks forming rings of emission eksplozive diatreme. As performance of eksplozive structures is characterized by presence of mantle derivatives, it testifies to powerful eksplozive activity of endogenic character during eras of their formation. It is remarkable that at the diamonds found around works including established in the tests which have been selected from xenotufobreccia of eksplozive structures, the defects connected with radiation exposure (the center of 575 nanometers and others which consider typical for diamonds from spreading of Ukraine), by results of spectral researches are absent. All established defective centers are typical for the natural kimberlitic diamonds which were not staying in spreading (Калашник and others, 2010). The second group of the eksplozive structures connected with a Paleocene era of tectonic activization is localized within Subbotsky and Zelenogaysky sites and shown already on considerable removal from a pluton in a northwest part Priingulsky syncline. One of the main observable features of a chemical composition of IMK of eksplozive structures of the Kirovograd megablock is similarity to that of mantle nodules of dunite-gartsburgite structure of diamondiferous kimberlites of Yakutia. It can testify to close physical and chemical conditions of formation of those and other IMK (tab. 1,2).

Table 1. The Chemical compound chromshpinells from kimberlites and eruptive breccia of  the Kirovograd megablock and from kimberlites of Yakutia (Афанасьев and others, 2001)

Table 2 the Chemical composition of garnets from kimberlites of the Kirovograd megablock and Yakutia (Афанасьев and others, 2001)

In the course of carrying out diamond-searching works we established a spatial and temporary associativity of kimberlitic dykes (ages are 1815 and 1900 million years) and hydrothermal fields of uranium (age of the main uranium ore of an albititic formation is 1850-1700 million years) in the Kirovograd uranium-ore area in the Subbotsko-Moshorinsky mineragenetic zone of mantle penetration. The analysis of noted associativity on UkrSh allowed to draw a conclusion that hydrothermal fields of uranium are dated for feeding fluid systems of zones of the deep faults, carrying out the CO₂ solutions enriched with mantle uranium. Such zones are diagnosed by manifestations of kimberlitic, the ultrabasic alkaline rocks, the phenomena of carbonate formation of rocks of various structure. The spatial proximity of manifestations of the ultrabasic alkaline magmatizm and uranium ore facilities means an important role of deep factors in formation of a rich uranium ore formation. Thus the faults marked by kimberlitic objects, serve as effective conductors of specialized uranium-bearing fluids of a mantle origin to what high concentration of uranium in kimberlites of the Kirovograd uranium ore area (18-20 g/t (Цымбал and others, 2003), in particular, testifies. The kimberlites considerably enriched with uranium, from our point of view, are petrological-geochemical indicators of existential activization of sites of mantle enriched with uranium – potential sources of U-ore-forming fluid streams. In such conditions spatial communication of hydrothermal fields of uranium and kimberlitic dykes is caused by a uniform structural and tectonic factor of a ore formations – an arrangement over active mantle structures, a community of a mantle source of uranium and the carbonic acid, generating kimberlitic magmas on upper mantle depths and the deep fluids which were an integral part which are carrying out its transportation on the top structural floors. As it is represented, the established feature can be considered in addition in a complex of criteria of detection of hydrothermal fields of uranium in other a little studied potentially uranium-ore areas, areas, junctions and zones. It can promote increase of efficiency and focus of look-ahead and search and search works on uranium. It can promote increase of efficiency and focus of look-ahead and search and search works on uranium. Besides carried out in a northeast part of the Kirovograd megablock of research and the revealed manifestation of a kimberlitic magmatizm, a find of  radical diamonds and the highpressure IMK similar on structure to diamondiferous kimberlites of Yakutia testify to prospects of the region on detection of diamondiferous rocks of kimberlite structure and need of continuation of researches of this direction.

Literature: 

Афанасьев В.П., Зинчук Н.Н., Похиленко Н.П. Морфология и морфогенез индикаторных минералов кимберлитов. Новосибирск. 2001. 275 с.

Калашник А.А., Палкина Е.Ю., Макивчук  О.Ф., Кирьянов Н.Н., Хренов А.Я. Результаты поисковых работ по выявлению алмазоносных объектов в северо-восточной части Кировоградского блока УЩ// Зб. наукових праць УкрДГРІ.  2010. № 3-4. С. 44-60.

Цымбал С.Н., Кривдик С.Г. Особенности вещественного состава кимберлитов Украины // Матер. наук.-техн. наради «Стан, перспективи та напрямки геологорозвідувальних робіт на алмази в України». К.: УкрДГРІ, 2003. С.22-31.