Nie and 10 co-authors reported in late 2025 from China that sandstone-hosted uranium deposits represent one of the most critical global uranium resources suitable for in situ recovery, with their formation closely associated with organic matter (OM).
Diagram showing a two-fluid uranium deposition model
The authors conducted a systematic literature review to synthesize over 100 published studies sourced from authoritative databases (Elsevier, Google Scholar, Web of Science, Scopus, CNKI, etc.). This study systematically summarizes the types and geological characteristics of OM in sandstone reservoirs and thoroughly analyzes the geochemical mechanisms by which OM regulates the transport and precipitation of aqueous uranium. By integrating case studies of representative sandstone uranium deposits globally, three major OM-related metallogenic models are proposed with distinct core characteristics:
1) the humic-dominated model is driven by the complexation and direct reduction of uranium by humic substances/coal-derived OM;
2) the roll-front model relies on reactions between oxidized uranium-bearing fluids and scattered OM, as well as
3) microbially generated sulfides at the migration front; and the seepage-related model is fueled by upward-migrating deep hydrocarbon fluids (petroleum, methane) that act as both uranium carriers and reductants.
Furthermore, this review explores the spatial coupling relationships between OM distribution and uranium mineralization in typical geological settings, evaluates the guiding significance of OM for uranium exploration, and outlines key unresolved scientific issues. The findings refine the genetic theoretical framework of sandstone-hosted uranium deposits and provide important technical support and theoretical guidance for future uranium exploration deployment and resource potential evaluation.
The authors concluded that OM exerts multiple, essential controls on sandstone-hosted uranium systems: it complexes U(VI), thereby extending transport distances; it acts as a precipitating agent through both direct and microbially mediated reduction; and it drives wall-rock alteration and bitumen formation while leaving diagnostic organic–geochemical fingerprints.
Several points of consensus have emerged over the past decade:
1) Sedimentary humic substances—particularly coal-derived humic acids—are the most common and potent drivers of sandstone uranium mineralization, with their coupled complexation–reduction processes supported by extensive experimental results and numerous field examples.
2) Microbially mediated reduction is pivotal in many deposits. In roll-front systems, H2S-generated by sulfate-reducing bacteria (SRB) is widely regarded as the dominant reductant, consistent with the prevalence of biogenic pyrite in ores.
3) Liquid and gaseous hydrocarbons provide an alternative pathway in petroliferous basins, where deep hydrocarbon fluids may potentially both transport uranium and trigger its reduction and precipitation.
4) Uranium mineralization commonly coincides with pronounced transformation of OM itself, including elevated maturity, anomalous asphaltene/bitumen residues, and related textures, which indirectly attest to intense U-OM interactions.
Despite this progress, several issues remain unresolved and materially affect genetic interpretation and prediction:
1) In any given deposit, the quantitative contributions of sedimentary OM, hydrocarbon fluids, Fe2+, and other reductants, as well as their hierarchy of influence, demand quantification via multi-isotope tracing and reaction network modeling.
2) Whether OM concentrated first and subsequently trapped uranium, whether U precipitation induced OM polymerization, or whether both processes were broadly synchronous appears to vary by deposit type (humic-type systems often favor “OM first,” whereas roll-front occurrences of uraniferous bitumen imply U-driven polymerization).
3) The speciation by which hydrocarbons carry U, the geometry and permeability hierarchy of conduits, and the staging of enrichment remain poorly constrained and tightly linked to basin plumbing.
4) Regarding radiation overprints on coalification and hydrocarbon generation, emerging evidence indicates that uranium radiation can accelerate OM maturation, stimulate hydrocarbon generation, and yield diagnostic gaseous products, with implications for unconventional resources in uranium provinces.
Future advancements will likely hinge on three complementary directions:
1) Greater interdisciplinarity that integrates organic geochemistry, geomicrobiology, and isotope geoscience across molecular, pore-scale, and basin-scale observations to resolve U-OM mechanisms.
2) Greater reliance on in situ analyses and modeling. For instance, using in situ spectroscopy and spectromicroscopy and synchrotron X-ray imaging to directly observe the nanoscale co-localization of uranium and OM in ore and distinguish non-crystalline U(IV)–OM from uranium minerals (uraninite/coffinite). Alternatively, numerical modeling can quantify the role of organic complexation in uranium transport, while real-time redox kinetics can be tracked under controlled anoxic conditions with variable pH–Eh. In reactive transport modeling, a dissolved OM (DOM) speciation framework should be integrated, coupled with surface complexation and Monod-type kinetics for bacterial sulfate reduction (BSR), anaerobic oxidation of methane (AOM), and iron reduction.
3) Multi-indicator exploration models that incorporate total organic carbon (TOC), sulfur-isotope signals, microbial biosignatures, and related metrics into predictive frameworks for targeting, evaluation, and in situ recovery (ISR) design. Pursued collectively, these lines of inquiry will refine process-based genetic models and providea stronger scientific basis for more efficient exploration and production of sandstone-hosted uranium deposits around the world.
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