Abstract
In adjustment to fulfill the requirements of the investigation regarding the lower Cretaceous sandstone uranium deposit in the Naogaodai area within the northwest of Ordos Basin, twenty-seven sandstone samples obtained from the Lower Cretaceous Huanhe Formation were analyzed for major, trace and rare earth elements (REE). The source of clastic and tectonic background was additionally analyzed. The results show that Huanhe sandstone is feldspar rich sandstone, and also the mineral composition is principally quartz, albite and plagioclase; the ratio of light to heavy rare earth elements (LREE/HREE) is 9.25–10.83, with an average value of 10.00; (La/Yb)CN is 10.20–12.53, with an average value of 11.24, demonstrating that LREE is enriched and fractionated compared with HREE. REE distribution patterns are similar, which additionally reveals that Huanhe sandstone has a homogenous source; the Index of Compositional Variability (ICV) value is 1.17–1.73, with an average value of 1.35, both greater than 1, showing an immature property, which may be first-order cycle deposition. The average value of the Chemical Index of Alteration (CIA) is 50.29, suggesting that the source rock has encountered weak chemical weathering; sandstones are near-source first-cycle provenance, which is not significantly influenced by sedimentary sorting and recycling. The geochemical qualities further indicate that Huanhe sandstone was deposited in a passive margin and experienced moderate weathering.
Highlights
In recent years, various exceptional remarkable achievements have been made in recognising the geotectonic background throughout the formation of rocks, the provenance of the basin and the tectonic background of the provenance area, providing a new perspective for understanding the evolution of the basin and its source area [1,2,3,4,5,6,7,8]
Bulk rock geochemistry of sandstones has been used in the determination of their provenance, tectonic setting and paleoweathering of the source area [8,15,16,17,18]
An integrated approach employing mineralogy, petrography together with bulk-rock geochemistry in order to reveal the provenance, tectonic setting, paleoweathering and paleoclimate has been widely documented by many researchers [13,19,20]
Summary
Various exceptional remarkable achievements have been made in recognising the geotectonic background throughout the formation of rocks, the provenance of the basin and the tectonic background of the provenance area, providing a new perspective for understanding the evolution of the basin and its source area [1,2,3,4,5,6,7,8]. Detrital mineralogy and geochemical characteristics of siliciclastic sediments will effectively reveal the provenance area, tectonic settings, transportation, paleoweathering conditions of the source area, and establish a basis for understanding paleoclimate and diagenesis [9,10,11,12]. An integrated approach employing mineralogy, petrography together with bulk-rock geochemistry in order to reveal the provenance, tectonic setting, paleoweathering and paleoclimate has been widely documented by many researchers [13,19,20]. Several studies have documented the stratigraphy, sedimentology and structural framework of the Lower Cretaceous Huanhe Formation in the Ordos Basin, but there are no data regarding its provenance, tectonic setting, paleoweathering and paleoclimate. This study aims to determine provenance, tectonic setting, source area paleoweathering, and paleoclimatic conditions of the Huanhe sandstones through a combination of mineralogical composition, petrographical analysis and bulk-rock geochemical data. By studying the provenance of the detrital sediments of the Huanhe Formation, we can have a deeper understanding of the mineralization process of sandstone-type uranium deposits
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