塔里木盆地巴什布拉克铀矿床赋矿灰色砂体成因与铀成矿作用分析OA

The genesis of ore-bearing gray sandbodies of the Bashbulak uranium deposit is the key to understand the metallogenic mechanism of the deposit.At present,there are two viewpoints:'original deposition theory'and'epigenetic reduction theory',which need to be further determined.In order to find out the genesis of the ore-bearing gray sandbodies in the Lower Cretaceous and the uranium mineralization of the deposit,the ore-bearing gray sandbodies and hosting rock were studied in detail by means of rock and mineral identification,element geochemical analysis and isotope analysis.The results show that the ore-bearing sandbodies is a primary red formation when it was deposited.It has undergone multi-stage reductant fluid alteration,generating a large number of dark metal sulfides,chlorite and other color-causing minerals and filled with oil and gas substances,so that the primary red sandbodies'fades'into gray sandbodies.The Lower Cretaceous strata have experienced at least five stages of epigenetic fluid activities:reducing hot brine generated by volcanic eruptions in the Tuoyun basin;oxygen-containing uranium-containing water that entered the ore-bearing sandbodies along the denudation window during the tectonic uplift period;the sulfur-rich fluid discharged from thermal decomposition of stratal organic matter(TDS),the surface leaching oxidizing fluid during the tectonic uplift period and the hydrocarbon-bearing fluid discharged from Jurassic source rocks during hydrocarbon generation period.The superposition of early reducing hot brine and interlayer oxidizing fluid formed early uranium ore bodies at the redox interface.The superposition of the late sulfur-rich reducing fluid and the surface leaching oxidizing fluid made the uranium element further enrich in the ore-bearing layer to form a rich ore body.The charging of late hydrocarbon-containing fluid has little relation with uranium mineralization.The superposition of multi-stage oxidation and reductant fluids provided the material basis for the migration and enrichment of uranium elements.Clay minerals,P-containing minerals,Ti-containing minerals and asphalt provided the carrier for the enrichment of uranium elements.The sandbodies with good permeability,rich in metal sulfides,ferrous minerals,oil and gas provided a reduction barrier and ore-bearing space for the precipitation and enrichment of uranium elements.These three factors synergistically control uranium enrichment and ore-body emplacement,forming an infiltration-effusion superimposed sandstone-type uranium metallogenic model characterized by the trinity of fluid-carrier-environment.