CONTRIBUTION TO THE ORIGIN OF THE SYNGENETIC URANIUM ENRICHMENT IN THE EARLY MIOCENE CARBONATES OF THE EUPHRATES FORMATION, IRAQ

S. Al-Bassam, Khaldoun; A. Mahdi, Mohammad; R. Al-Delaimi, Muhal

	CONTRIBUTION TO THE ORIGIN OF THE SYNGENETIC URANIUM ENRICHMENT IN THE EARLY MIOCENE CARBONATES OF THE EUPHRATES FORMATION, IRAQ
Iraqi Bulletin of Geology and Mining
Article 1, Volume 2, Issue 2, 2006, Pages 1-21
Authors
Khaldoun S. Al-Bassam; Mohammad A. Mahdi; Muhal R. Al-Delaimi
Abstract
A model is presented in this paper to account for various genetic aspects related to the origin and mode of formation of the so-called ''syngenetic'' uranium mineralization in the upper parts of the Euphrates Formation (Early Miocene).The proposed model considers the thick uraniferous Paleozoic clastic rocks as source rocks, lying several kilometers underneath. The late Early Miocene tectonic unrest triggered fracturing and faulting that allowed for uraniumrich groundwater, trapped in the Paleozoic aquifers, to ascend to surface in the shallow parts of the late Early Miocene Sea, together with bitumen and H2S seepages. Uranium was precipitated in the interstitial pore environment, below sedimentwater interface, where carbonate ion concentration was low, (following the precipitation of lime mud), uranium concentration was high and strong reductants were available (bitumen and H2S). Shortlived tectonicallyinduced regressive phases led to episodes of emergence in the pertidal environment, which caused significant increase in the uranium concentration in the pore water environment leading to thin horizons of anomalous uranium concentration superimposed on a generally higher than background uraniferous carbonates. Early diagenetic dolomitization trapped the uranium, as uranoorganic phases or cryptocrystalline pitchblend, inside the minute dolomite crystals, which generally kept them from oxidation and remobilization.

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