2011

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Geologic-geophysical criteria for mineral exploration in Precambrian of Ukrainian Shield from the standpoint of plate tectonics

Sheremet E.M., Antsiferov V.А.

UkrNIMI, National Academy of Sciences of Ukraine

EvgSheremet@yandex.ru

Based on the analysis of geologic and geophysical features of suture zones ‑ Orekhovo-Pavlogradskaya (OPSZ), Western Inguletskaya ‑ Krivorozhsko-Kremenchugskaya (WIKKSZ), Golovanevskaya (GSZ), Nemirovsko-Kocherovskaya (NKSZ) we propose the following criteria for mineral exploration at Ukrainian Shield.

Geological criteria that include:

i). Paleogeodynamic position of the region under investigation.

It is understood as position of the region relative to collision junction (suture). For example, OPSZ divides the Middle Pridneprovsky megablock, which is a typical Archaean granite-greenstone region practically not affected by Proterosoic granitization, and Priazovsky megablock, which is Archaean granite-greenstone region heavily reworked in Proterosoic, with large area of development of granitoids of the eastern Priazovsky sub-alkaline Proterozoic complrex [1].

The same is typical for WIKKSZ and GSZ [2, 3].

ii). Characteristic structural and metallogenic tectonotype elements.

The eastern part of Ukrainian Shield (US) has the following structural-tectonic elements: OPSZ and adjoining to it from the east highly faulted during collision areas of adjacent Priazovsky megablock – Western Azov Sea Region; areas of stretching of the Priazovsky megablock and respectively zones of its crust increased permeability – Central Azov Sea Region; the back part of the eastern part of US – the Eastern Azov Sea Region which was heavily reworked in Proterosoic, with the area of development of sub-alkaline and alkaline magmatism.

Metallogenic and magmatic zoning in the Eastern part of US is specified by extent of movement of ocean plate under the Priazovsky megablock [1]. In OPSZ, in the adjacent to it part of the Middle Pridneprovsky megablock and in the Western Azov Sea Region (onset of the movement) widely spread are numerous deposits of sedimentary genesis (jaspilites) ‑ group I of metallogenic zoning according to [4]; groups II and III of metallogenic zoning according to [4] (Western Azov Sea Region and part of the Central Azov Sea Region) which are characterized by strong manifestations of calc-alkali magmatism and contain highly promising gold mineralization probably of Archaean age in greenstone belts (Gaichurskoe, Gulyaipolskoe, Surozhskoe and others) with their accompanying sulfidization; graphite deposits (of sedimentogene and epigenetic genesis) of lithium in pegmatites (Balka Krutaya, Shevchenkovskoe) deposits of high-grade iron ore of saksagansky type (Severo- and Yuzhnobelozerskoe, Pereverzevskoe) and carbonatite-type apatite (Novopoltavskoe) formed in collision environment; group IV of metallogenic zoning according to [4] is Central and Eastern Azov Sea Regions – the regions of development of alkaline and sub-alkaline magmatism to which zirconium-rare-earth deposits and iron deposits (Mariupolskaya group) are confined; to manifestations of gold in the Central-Priazovskaya and Maloyaninskaya fault zones some more graphite deposits are added – at the flanks of Mangushsky synclinorium.

Structural and metallogenic zonings exist also for WIKKSZ but they are more complex in connection with multiple manifestations of collision environment at different times.

iii). Geological position relative to deep faults.

Deep faults are feed channels for mantle fluids and within them endogeneous mineralization often manifests itself. Examples of this are deep faults confining the Golovanevskaya and Nemirovsko-Kocherovskaya suture zones.

iv). Regional and local metasomatosis manifestations.

Examples of these are Maiskoe and Klintsovskoe gold deposits confined to the regional metasomatosis zones; regional metasomatosis zones along the faults confining GSZ and NKSZ: with alkaline-sodium metasomatosis uranium and gold mineralizations are connected, confined to metasomatic albitites near the north closure of the Novoukrainsky massif parallel to the contact of the latter with Korsun-Novomirgorodsky pluton.

v). Definite magmatic complexes’ potential ore content in regions, territories and areas under study.

The most representative are large batholith-like intrusions of Korostensky complex (NKSZ) and Korsun-Novomirgorodsky complex (Inguletsky megablock near GSZ) and the area of sub-alkaline and alkaline intrusions of East-Priazovsky complex in the Eastern Azov Sea Region. All of them are potentially ore-bearing for rare-metal-rare earth minerals. Kimberlite dikes have been found in the vicinity of their location.

Analysis of geophysical survey of US suture zones in connection with mineral exploration gives a possibility to consider as geophysical exploration criteria the following.

1. Existence of integrated geophysical (geoelectric, gravimetric, seismic, magnetic) regional anomalies.

2. Existence of low-resistivity geoelectric anomalies, both regional and local.

OPSZ is delineated as a regional deep low-resistivity anomaly down to the depth of 50 km. WIKKSZ is within the area of advance of the known Kirovogradskaya electrical conductance anomaly. Within the limits of WIKKSZ down to the depth of 17-35 km extensional low-resistivity anomaly is detected. GSZ is characterized by clearly expressed electrical conductance anisotropy in the near-surface section, by the existence of sharp high electrical conductance inhomogeneities directly from the surface and also by the presence of conductive layer in the middle and low parts of the crust. NKSZ is within the limits of Chernovitsko-Korostenskaya electrical conductance anomaly in the zone of the contact of the areas with high and low resistivity.

3. Deep (down to 50 km) low-resistivity geoelectric anomalies, characterizing extended tectonic structures (suture zones), can serve as indicators of prediction areas for mineral exploration by projecting low-resistivity anomalies on the surface as reflection of paths of movement of mantle fluids.

A perfect example of such anomalies is OPSZ and the whole eastern part of Ukrainian Shield – the Central zone of deep faults and eastern restriction of the Priazovsky megablock – the Gruzsko-Yelanchikskaya zone of deep faults.

4. Low-resistivity deep geoelectric anomalies along extended zones of faults.

Within NKSZ and GSZ clearly delineated are their confining faults as axes of low-resistivity electromagnetic anomalies.

5. Low-resistivity geoelectric anomalies confined to zones of metasomatosis.

These anomalies are strongly exemplified in deep faults of NKSZ.

6. Contingency of low-resistivity geoelectric anomalies with metallogenic ore clusters and geochemical anomalies.

Within the limits of the Eastern Azov Sea Region contingency of a large number of geochemical anomalies with low-resistivity geoelectric anomalies is determined by special work. In GSZ contingency of low-resistivity geoelectric anomalies with metallogenic ore clusters is recorded.

References:

1. Antsiferov A.V., Sheremet E.M., Yesipchuk K.Ye. et al. Geologic-geophysical model of the Nemirovsko-Kocherovskaya suture zone of Ukrainian Shield. Donetsk, Veber, 2009, 253 p. (In Russian).

2. Azarov N.Ya., Antsiferov A.V., Sheremet E.M. et al. Geologic-geophysical model of the Krivorozhsko-Kremenchugskaya suture zone of Ukrainian Shield. Kiev, Naukova dumka, 2006, 196 p. (In Russian).

3. Azarov N.Ya., Antsiferov A.V., Sheremet E.M. et al. Geologic-geophysical model of the Orekhovo-Pavlogradskaya suture zone of Ukrainian Shield. Kiev, Naukova dumka, 2005, 190 p. (In Russian).

4. Zonenshain L.P., Kuzmin M.I., Moralev V.M. Global tectonics, magmatism and metallogeny. Moscow, Nedra, 1976, 231 p. (in Russian).