Two Metallogenic Models of Sedimentary-Hosted Uranium Deposit: Jingchuan and Tale Types

The existing ore-forming models related to sedimentary-hosted uranium deposits have been primarily established focusing on different ore-controlling factors such as tectonics, sedimentation, and fluids. These models are diverse and complex. Over the past decades, with the comprehensive development of secondary exploration for uranium in drilling data from coalfields and oilfields, the close spatial coexistence pattern of "coal-oil-uranium" has been rapidly revealed. This paper analyzes the reducing media that constrain the enrichment of sedimentary-hosted uranium deposits from different perspectives. By systematically comparing and analyzing the ore-forming conditions, mineral characteristics, and geochemical features of the super large uranium deposits in the Jingchuan oil and gas field and the Tale coalfield in the Ordos Basin, two uranium ore-forming models, namely the Jingchuan type and the Tale type, are established. The Jingchuan type reducing media are primarily hydrocarbon fluids (such as CH₄, H₂, CO, as well as secondary H₂S, pyrite, etc.), which are mainly derived from the expulsion and migration of deep-seated hydrocarbon source rocks after the sedimentary diagenesis period to the Lower Cretaceous Luohe Formation, coupled with the ore-forming process of surface oxygenated and uranium-bearing fluids. The ore bodies in this model are notably controlled by factors such as reservoir permeability, late-stage fault structures, and hydrological distribution, often characterized by the presence of multiple mineralized layers, typically dozens or even scores of layers. Constrained by the migration range of oil and gas, they exhibit significant lateral variations and phenomena of ore bodies cutting across bedding planes. The uranium minerals are primarily asphaltic uranium ores, appearing as emulsion texture, angular texture, vein-like texture, with relatively small grains ranging from a few to tens of micrometers, occasionally reaching several tens of micrometers, and distributed relatively evenly, accompanied by minerals such as pyrite, quartz, calcite, and rutile. In contrast, the Tale type reducing media are mainly coal debris, deposited contemporaneously during the sedimentary diagenesis period, and are produced parallel to the bedding, serving as chemical barriers for the enrichment and precipitation of uranium in surface oxidizing and uranium-bearing fluids. The ore bodies in this model are subject to dual constraints from the occurrence of coal-bearing rock layers and hydrology, generally exhibiting relatively stable lateral distribution. The mineralized layers usually consist of 2 to 3 layers, with the ore layers being essentially consistent with the coal-bearing rock layers, and phenomena of cutting across bedding planes are not evident. The uranium minerals mainly include uraninite and coffinite, showing irregularly granular texture, blocky texture, vein-like texture, feather-like texture, with significant variations in particle size ranging from a few micrometers to several hundred micrometers, unevenly distributed, and accompanied by minerals such as pyrite, mica, rutile, coal debris, quartz, and calcite. These two uranium ore-forming models exhibit significant differences in ore-forming conditions and characteristics, providing not only theoretical basis for uranium exploration, but also new directions for the response of multi-energy mineralization in basins and the study of the mechanisms of the sedimentary-hosted uranium.