International Geologiical Congress - Oslo 2008

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MRD-10 Large ore provinces of Central Asia

 

Alkaline magmatism and rare metallic ore-beareness

 

Murat Bekzhanov, Academy of Mineral Resources (Kazakhstan)
Kaidar Abdrakhmanov, Institute of Geological Sciences (Kazakhstan)
 

 

There could be distinguished four types of alkaline magmatism within Kazakhstan folded area.

The first type is represented by the comendite - alkali-granite formation of folded areas which has spatial-and-temporal and petrogenetic connection with potassium-granite of the granitization cycle late stage.

Development of the comendite - alkali-granite magmatism is possible in mature continental crust under the influence of highly alkaline fluids. Same conditions could be realized at the late stage of orogenic-collision cycle of folded areas. Alkali-granites and leukogranite - alaskites synchronically formed in the different parts of continental area could be interpreted as agpaite and plumasite branches of genetically united series of potassium-granites.

Based on the depth facies of their formation alkaline-granites are distributed in volcanic, hypo- and mezobyssal facies. On the basis of alkali-granites of Kazakhstan there were developed petro-geochemical criteria of the evaluation of their formation depth.

The most ore-bearing granites are hypo abyssal ribekito-alkali-granites characterised by apogranite type of evolution, fluorine - albite -metasomatites and enriched with zirconium, niobium, heavy lanthanides, rare zonation and variety of accessories.
The second type is represented by leucite - tephrite - bazanite, alkali-gabbro-shonkinite-leucitophire, alkali syenite - nepheline syenite, trachyandesite, gabbro-monzonite-cienite sub formations of a single leucite-tephrite-shonkinite-syenite formation.

This type of alkali basaltoide magmatism of the potassium profile is known in Talas Alatau (Irisu-Daubaba complex of the late perm-early-triasse age) and Ishim strata volcano (late-Devonian Ishim).

Alkali basaltoide - gabbro - shonkinite magmatism is laid over the orogenic-granitization cycle and connected with deep zones of tectonic-magmatic activisation.

The third type of the alkali magmatism is fixed with alkali-ultra basic formation (Krasnomay complex of the mid-late Cambrian) and is typical for pre-Cambrian middle massives bedding in the form of disconnected blocks. The forth type of the alkali magmatism is represented by essexite-monzonite-cienite and monzonite-granocinite formations known in the Kastek ridge of the North Tien-Shan and Kokshetau massive.

 

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