The geochemical characteristics of primary halos can effectively identify axial variations of indicator elements within ore bodies, providing guidance for exploring concealed ore bodies. The Mailong gold deposit, a newly discovered large-scale deposit in the Gouli ore district of the East Kunlun Orogenic Belt (EKOB), has significant exploration potential. To guide deep exploration targeting, a detailed primary halo geochemical study was conducted on the AuVII ore bodies along exploration line No. 60. Statistical analysis of 15 elements (Au, Ag, Cu, Pb, Zn, W, Sn, Mo, As, Sb, Hg, F, Mn, Bi, and Co) established the characteristic of element associations: near-ore halo (Au, Ag, Cu, Zn, Pb), front halo (Hg, Sb, F, As), and tail halo (Co, Mn, Sn, Bi, W, Mo). Using the Grigoryan zoning index, the axial zoning sequence from top to bottom is: Mn, Sn, Au, Ag, Zn, Mo, W, Hg, Cu, Co, Sb, As, Bi, Pb, and F. The primary halo exhibits reverse zoning with significant superposition of front, near-ore, and tail halo elements. Anomalies extend downward without pinching out, suggesting that the ore body continues to extend axially at greater depths. Geochemical parameters (F/Co, Hg/Bi, (Hg × F)/(Co × Bi), (Hg + F)/(Co + Bi)) and trilinear diagram analysis further imply a high likelihood of blind ore bodies at depth. To validate the prediction, drill hole ZK6004 was deployed in the proposed target area along exploration line No. 60. The drilling intersected a 1.67 m thick ore body with 2.37 g/t Au at a depth of 660 m, confirming the reliability of the integrated geochemical–geophysical approach. These results demonstrate substantial deep exploration potential in the Mailong deposit and provide an effective example for applying primary halo superposition methods to deep mineral exploration in similar orogenic gold deposits.
Many strata-bound Fe−Mn deposits (umbers) occur in accretionary complexes and ophiolites. Previous investigations have been limited to low-grade metamorphic umber deposits, however, and no umber counterparts have been identified in high-P/T metamorphic belts in accretionary complexes. Here, we report new geochemical data from a hematite-quartz schist in the Nagatoro area, central Japan, part of the Sanbagawa high-P/T metamorphic belt. The Nagatoro hematite-quartz schist consists mainly of an Fe- and Mn-rich component, silica, and calcium carbonate. In Fe-rich layers, Mn, Ca, P, Co, Ni, Zn, As, Sr, Pb, and rare-earth elements (REEs) except Ce are enriched relative to post-Archean average Australian shale (PAAS), and bulk concentrations of these elements are positively correlated with Fe2O3. PAAS-normalized REE patterns of the schist have clear negative Ce anomalies indicative of oxic depositional environments and similar to those of Japanese umbers and present-day mid-ocean ridge (MOR) metalliferous non‑carbonate sediments. The schist is enriched in light and middle REEs relative to present-day MOR metalliferous carbonates, implying a continuous uptake of REEs from pore water by Fe-oxyhydroxides via diagenetic reactions after burial. We conclude that the Nagatoro hematite-quartz schist was originally deposited as hydrothermal metalliferous sediments near a MOR, equivalent to umber; the sediment was subsequently subjected to accretion and metamorphism. This study provides a novel report of umber in a high-P/T metamorphic zone in an accretionary complex, demonstrating that the essential geochemical features of the umber were retained even after metamorphism.
Despite growing interest in mine tailings valorization, most previous studies on thermally induced mineral transformations have focused on monomineralic systems, leaving the behavior complex, multimineral mine residues comparatively unexplored. Thermal treatment of fine-grained mining wastes is proposed as a method to enhance their reuse within the mining industry itself or in other related industries like civil and chemical engineering. Four fine-grained mining wastes (three mine tailings and one sludge from an acid mine water treatment plant) were chemically and mineralogically characterized across a temperature range of 40 °C to 950 °C using a combined TGA, XRD and SEM-EDS approach. The three mine tailings correspond to deposits classified as IOCG-type (iron‑copper‑gold oxides), volcanogenic massive sulfides (MSS), and carbonatites. Depending on their initial mineralogy, one or more of the following mineral transformations were observed: 1) conversion of gypsum to bassanite and anhydrite within the ranges of 100–200 °C and 850–950 °C, respectively; 2) a two-steps transformation of chlorite (i.e. chamosite) into a diffraction X-ray-amorphous phase, tentatively termed “meta-chlorite” by analogy with meta-kaolinite, between 650 °C and 800 °C and a concomitant neoformation of hematite and a Si-rich matrix; 3) transformation of carbonates (i.e., calcite and dolomite) into oxides (i.e., lime and periclase) within the 800–950 °C range. These mineral transformations confer greater reactivity to the residues, showing strong potential as low-cost precursors for alkali-activated cementation processes, thereby supporting the valorization of mine residues within a circular economy framework, with direct applications in underground mine galleries backfilling, construction materials (plasters and 3D-printing pastes), and other industrial uses as alkaline reagents.
Exploration geochemistry, while extraordinarily successful for magmatic-hydrothermal deposits in mountainous terrains, has demonstrated lower discovery rates for supergene deposits that form in depositional sinks after long-distance transport. This paper argues that this ‘effectiveness paradox’ is not a failure of geochemical exploration, but a cognitive-methodological mismatch: reverse-tracing principles optimized for source-type mineralization have been persistently applied to sink-type deposits—including evaporites, placers, weathering-leached REE, and sandstone-hosted uranium—that require fundamentally different tracing strategies. To resolve this mismatch, we develop a holistic source-to-sink (S2S) exploration framework that explicitly links erosional sources, transport pathways, and depositional sinks within a unified process-based architecture. The framework is grounded in a synthesis of advances in climatology, geomorphology, regolith science, pedology, hydrology, and critical zone research—disciplines that collectively govern element release, transport, and accumulation at the Earth's surface. Four Chinese case studies—Tarim (potash), Boziguer (zircon placer), Honghe (ion-adsorption REE), and Qaidam (sandstone-hosted uranium)—validate the framework by demonstrating that source-specific proxies (total K, heavy mineral fingerprints, U₀/Th/U) and sink-specific proxies (soluble K+, heavy mineral enrichment, exchangeable REE, U6+/U4+/TOC) are systematically distinct. International examples from diverse tectonic and climatic settings—including the Lithium Triangle, Klondike, Jos Plateau, Dongqiao, Frome, Wyoming, and Esperance—further demonstrate global transferability.The framework operationalizes three principal transitions—from reverse-tracing to whole-chain tracing; from total-element-dominated proxy suites to tiered systems incorporating process-sensitive dynamic proxies; and from empirical targeting to quantitative coupling assessment—through a dual-proxy system and a four-stage workflow, with numerical terrain analysis (ksn, χ, VeSi_val, DeDi_val) serving as the initial step to enable systematic identification of erosional versus depositional domains prior to geochemical sampling. The S2S framework is offered not as a universal solution, but as a systematic approach to a specific class of problems—exploration for supergene deposits in depositional sinks—complementing rather than replacing existing exploration techniques.
Rising greenhouse gas (GHG) emissions have intensified the need for effective carbon mitigation strategies, making carbon capture, utilization and storage (CCUS) a key technology for achieving long-term decarbonization. Future deployment of CCUS projects is expected to be supported by the Paris Agreement's Article 6 mechanisms, together with India's emerging domestic carbon market and carbon-pricing frameworks. Owing to its extensive sedimentary basins, India possesses significant geological potential for long-term CO2 storage. This review provides a comprehensive assessment of the geological CO2 storage potential of major subsurface formations in India and evaluates their suitability for long-term geological CO2 storage and future CCUS development. A systematic review of the published literature from 2000 to 2025 was conducted using peer-reviewed journal articles, conference proceedings, books, government reports, and publications from internationally recognized organizations. The review critically evaluates geological storage options, storage-capacity estimation approaches, reservoir characteristics, monitoring strategies, uncertainty assessment, and recent policy developments. In addition, a bibliometric analysis based on the Scopus database was performed to identify publication trends and emerging research directions. The bibliometric analysis identified 1138 publications, demonstrating a substantial increase in geological CO2 storage research, particularly after 2020. India comprises approximately 3.4 million km2 of sedimentary basins with an estimated national geological CO2 storage potential of 400–500 Gt CO2. Deep saline aquifers constitute the largest storage resource (300–400 Gt CO2), followed by basalt formations (200–400 Gt CO2), while depleted oil and gas reservoirs (5–10 Gt CO2) and unmineable coal seams (∼5 Gt CO2) provide additional storage opportunities. The review also proposes an Integrated Geological Storage Potential Framework (IGSPF) for comparative screening and prioritization of Indian sedimentary basins based on storage capacity, reservoir quality, injectivity, caprock integrity, geological maturity, and data availability. Deep saline aquifers are identified as the most promising option for long-term geological CO2 storage in India, while basalt formations offer additional potential through mineral carbonation. Overall, the findings highlight the need for standardized storage-capacity assessment, detailed reservoir characterization, robust monitoring and risk management, and supportive policy frameworks. As the storage-capacity estimates presented in this review are derived from published literature, future CCUS deployment will require site-specific characterization, reservoir modelling, and pilot-scale validation before field-scale implementation.
