Document Type : Original Research Paper
Authors
1 M.Sc., Department of Geology, Golestan University, Gorgan, Iran
2 Assistant Professor, Department of Geology, Golestan University, Gorgan, Iran
3 Ph.D., Geological Survey of Iran, Tehran, Iran
4 Senior Experts, Exploration Division, Atomic Energy Organization of Iran, Tehran, Iran
Abstract
The occurrence of uranium anomalies associated with secondary Cu mineralization (malachite) at some parts of the Razgah metaluminous -peralkaline stock situated at the northeast of Sarab caused it to be a priority of Atomic Energy Organization of Iran (AEOI) to inspect the intrusion for likely uranium mineralization. Hence the current study, which is supervised by AEOI, was carried out to investigate the U mineralization potential of the stock by applying the mineralogical, petrological and geochemical studies. A fractionation trend is inferred from variations in rock compositions stretching from nepheline-bearing monzodiorite to nepheline monzosyenite, pseudoleucite monzosyenite and nepheline syenite. Consideration of geochemical features of fresh rocks of the stock and its associated dikes with emphasis on geochemical behavior of U and REEs during magmatic fractionation revealed that apatite has played a prominent role in controlling concentrations of REEs, U, and Th, in addition to zircon, which played a considerable role in accommodating HREEs, U, Th and HFSEs (Ti, Ta, Nb, Hf, Zr) in more differentiated rocks.Nepheline syenite rocks of peralkaline composition,s which are considered to be the most differentiated have low contents of HFSEs, U (up to 21 ppm), Th (up to 56 ppm) and REEs compared to average nepheline syenites but are relatively more enriched in these elements than less differentiated rocks of the stock. Most of the rocks possess negative Eu anomalies (Eu/Eu*≤1) and differentiated nepheline syenites have strong negative Eu anomalies. Abundance of ilmenite and magnetite and lack of amphibole in rocks suggests the parental magma had a reducing nature and meagre contents of volatile components, which along with metaluminous character and prepondarence of apatite in rocks have rendered the magma incapable of enriching U. Minor amounts of hydrothermal fluids released from some parts of the stock led to leaching of U from hosting minerals (apatite and zircon) and resulted in weak hypogene mineralization of U and Cu. Later supergene leaching process affected the weak primary mineralization and upgraded U tenors concurrent with formation of secondary Cu carbonate minerals. Due to thin and limited extention of these enrichment sites, they are not economically viable for uranium extraction; consequently, this area does not suggest for semi-detailed and detailed exploration program for uranium by AEOI.
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