ABSTRACTThe Saidiwasan (also known as Siriwasan) carbonatite‐sill is located approximately 10 km to the north of the well‐known Ambadungar carbonatite–alkaline complex within the Chhota Udaipur carbonatite‐alkaline province. This complex comprises prominent sövite plugs within carbonatitic breccias, each exhibiting diverse and variable mineralogical assemblages that include pyroxene, amphibole, apatite, pyrochlore, perovskite and titanite. The enrichment of rare earth elements (REEs) in the Saidiwasan sövites is closely associated with the presence of pyrochlore, perovskite, apatite and monazite. This study employs detailed mineral chemistry to elucidate the secondary processes affecting pyrochlore and apatite grains. Primary magmatic pyrochlore in Saidiwasan sövites are characterised by elevated concentrations of calcium, niobium, fluorine and sodium, which are subsequently replaced by secondary cation‐deficient grains due to supergene weathering. These alterations primarily occur at the A site and occasionally at the B site, involving the substitution of fluorine by hydroxide (OH–) groups. During alteration, calcium and sodium are leached from the pyrochlore structure, with charge balance maintained by the substitution of REE, Th, U, Ba or Sr. In the later supergene stages, marginal and fractured zones of pyrochlore grains experience metamictization, resulting in Pb‐rich and cation‐deficient hydrated varieties. Fluoro‐apatites within the sövites display significant REE concentrations and are relatively unaltered. LREE constitute the dominant proportion of the total REE content in Saidiwasan apatite. Based on mineral chemistry and bulk rock analyses, this study aims to provide a comprehensive understanding of the Saidiwasan sövites. Despite its promising characteristics, the Saidiwasan carbonatite complex remains underexplored and largely overlooked within the Chhota Udaipur Province, although it possesses significant potential for hosting economically viable mineral deposits, thus warranting further investigation and exploration.

ABSTRACTThe global shift toward low‐carbon energy technologies has significantly increased the demand for critical minerals such as lithium, rare earth elements (REEs) and helium. This special issue “Critical minerals” brings together 19 original research articles and review papers that address recent advances in both extraction technologies and the geological understanding of critical mineral deposits. The first section focuses on innovative recovery methods for lithium and REEs from sources such as electronic waste and salt lake brines, with promising industrial applications reported in China, Algeria and India. It also includes a study on optimising carbon capture and storage through improved source‐sink matching. The second section investigates ore‐forming processes and exploration strategies for hard‐rock and brine‐type deposits, including pegmatite‐hosted lithium, carbonatite‐related REEs, sandstone‐hosted uranium, quartz‐vein tungsten and porphyry copper deposits. Several studies from the Qinghai‐Tibet Plateau offer new insights into lithium enrichment mechanisms in geothermal and saline environments, using geochemical and isotopic methods. Additionally, a new model for helium accumulation in shale gas reservoirs highlights the structural controls on gas migration and trapping. Collectively, these contributions advance our understanding of mineralizing processes in diverse geological settings and support the sustainable development of critical mineral resources essential for the global energy transition.

ABSTRACTThe Guokuidingzi is a poorly studied porphyry copper (Cu) deposit situated in the eastern Xar Moron–Changchun Cu–Mo metallogenic belt (XCMB), positioned along the northern margin of the North China Craton (NCC). The mineralization of copper is predominantly hosted within porphyritic granodiorite. The mineralisation process of the Guokuidingzi porphyry Cu deposit can be classified into three distinct stages. In hydrothermal quartz and calcite grains, four distinct types of primary fluid inclusions (FIs) have been identified across different mineralisation stages: liquid‐rich FIs (L‐type), vapour‐rich FIs (V‐type), CO2 FIs (C‐type) and daughter mineral‐bearing three‐phase or multiphase FIs (S‐type). From stages I to III, the fluid inclusion assemblages (FIAs) change from L‐, S‐, and C‐types to L‐, V‐, and S‐types, and finally to L‐types only. The corresponding homogenisation temperatures range from 371°C–418°C, 289°C–351°C, and 144°C–222°C, respectively, and the salinities equate to 4.69–49.25, 0.53–42.50, and 1.05–3.85 wt.% NaCl equiv. The δ18OH2O values vary from −6.30‰ to 5.30‰, and δ D values from −103.3‰ to −95‰, both of which indicate a magmatic origin for the fluids. The δ34 S values of sulphides are 1.9‰–2.7‰ (average 2.3‰), suggesting that the sulfur isotopes were derived from the porphyritic granodiorite. The Pb isotope compositions of the sulphides (206Pb/204Pb = 18.139–18.436, 207Pb/204Pb = 15.511–15.572, and 208Pb/204Pb = 37.856–38.249) are consistent with those of the porphyritic granodiorite. The mineral assemblages, fluid inclusions, and H–O–S–Pb isotopic data collectively suggest that the initial ore‐forming fluids were exsolved from the porphyritic granodiorite and were characterised by high temperatures and high salinities. As the temperature and pressure decreased gradually, the fluid underwent a process of immiscibility, ultimately resulting in the formation of minor metal sulphides such as arsenopyrite and pyrite during stage I in a relatively confined environment. Subsequently, complex physical–chemical changes, including fluid boiling, declining temperatures and pressures, and the influx of minor meteoric water, led to the precipitation of Cu and other metal sulphides from the ore‐forming fluids during stage II (the major stage of Cu mineralisation). Finally, the incorporation of additional meteoric water and the continued decreases in temperature and pressure caused the ore‐forming fluids to evolve into a homogeneous NaCl–H2O fluid system. The Guokuidingzi Cu deposit is an Early Triassic porphyry‐type Cu deposit and exhibits a comparable genesis to the contemporaneous porphyry‐type deposits on the western XCMB, indicating that the eastern XCMB also has significant potential for the exploration of Early Triassic porphyry‐type deposits.

ABSTRACTThe Proterozoic to Neoproterozoic Cuddapah Basin (CB) contains a thick pile (i.e., 6–12 km) of arenaceous, argillaceous and carbonate rocks with substantial igneous rocks. The evolution of the CB is mainly defined based on igneous rocks with a limited study on siliciclastic rocks. Here we report geochemical and isotopic data from shale samples of the Lower Cuddapah formations for the first time to comprehend their provenance, palaeoweathering, and tectonic setting. The shale samples were collected from Gulcheru, Vempalle and Tadpatri formations of the Lower CB. The geochemical and isotopic data divide Gulcheru Formation shales into two groups: Gulcheru shale I (GS I) and Gulcheru shale II (GS II). The CIA (chemical index of alteration), CIW (chemical index of weathering) and Al2O3–CaO + Na2O–K2O (ACNK) diagram of the shales decipher a low chemical weathering for the GS I. In contrast, GS II, Vempalle shale (VS) and Tadpatri shale (TS) exhibit a medium to high degree of chemical weathering. The major and trace element ratios, provenance diagrams, and higher sub‐chondritic εNd(t) values of GS I (−8.18 to −7.62) compared to GS II (−5.34 to −3.63), VS (−6.25 to −4.41) and TS (−5.2 to −3.78) along with fSm/Nd versus ɛNd(t) diagram suggest the decrease of sediment input from older crustal provenance, that is, Eastern Dharwar Craton (EDC) with increase of ‘more juvenile’ source. The tectonic discrimination diagrams, as well as the primitive mantle (PM) normalised multi‐element diagram, characterise a back‐arc origin of the CB. The more evolved εNd(t) values and younger detrital zircon grains in the Pulivendla Formation indicate that the basin was opened by westerly subduction along the east coast of India at ~2 Ga. The continuous collision of the Dharwar Craton with Antarctica at ~1.6 Ga suggests the last phase of the Columbia Supercontinent formation.

ABSTRACTThe present study provides the nexus between green technology, renewable energy systems and sustainable economic growth in China by assessing comprehensive time series data from 1990 to 2021. It employs quantile‐on‐quantile regression and the Augmented Dickey–Fuller test to assess how policies promoting green technology and renewable energy systems impact China's sustainable economic trajectory towards building a low‐carbon economy for climate change mitigation. The results reveal that all variables become stationary at first difference, except for green technology. There is a positive correlation between green technology, renewable energy systems and sustainable economic growth. Notably, an increase in the rate of green technology and resource management efficiency tends to increase economic growth, emphasising their transformative potential for fostering sustainability. In contrast, the increase in interest rates hinders economic growth. Furthermore, inflation and gross capital formation exhibit positive associations with sustainable economic growth. Policymakers should focus on transition to a low‐carbon economy through targeted resource allocation for low‐carbon technologies and the policies promoting energy efficiency, especially in the urban and industrial sectors. The current study also identifies limitations, like data constraints, methodological challenges and policy interaction complexity. By highlighting these limitations and further exploration can assist multi‐criteria decision making and policymakers to foster green, prospect and sustainable climate change.

ABSTRACTTectonic modifications of the Tertiary geologic succession in the North Assam Shelf (NAS) have impacted the basin's petroleum system, providing insights into the region's tectono‐stratigraphic framework. This research investigates the lithofacies variation and tectonic controls experienced by the Girujan Formation, which was deposited in the basin during the Upper Miocene. To achieve this, we integrated and interpreted outcrop and subsurface data to elucidate the litho‐tectonic controls during the Girujan interval in the basin. Specifically, outcrops from the Amguri and Tipongpani sections were analysed, and these findings were combined with petrophysical logs from drilled boreholes across the southwestern, central and southeastern parts of the NAS. Our observations reveal that while the Girujan Formation is characterised by mottled clay, significant lithological variation exists throughout the basin. In the western region, mottled clays—both sticky and non‐sticky—are interbedded with medium‐grained sand facies. In contrast, the central and eastern regions exhibit a dominance of sand lithology alongside clay facies. Notably, the thickness of the Girujan Formation increases from west to east across the basin, where lithological variations are structurally influenced by the tectonic activities of the Naga‐Margherita‐Disang Thrust sequences. Moreover, the Upper Miocene Girujan Formation exhibits significant lithological diversity, functioning variably as a cap rock in the western and central areas due to its clay content and intercalation with sand and shale/coal streaks, while in the eastern region, it is intermixed with sediments of the Barail and Tipam formations, which rendered it as a potential reservoir rock.

ABSTRACTThe geochemical signatures of trace elements in coal serve as crucial indicators of material sources and depositional environments during its formation. This study focused on 13 coal seams from the Longtan Formation in the Dahebian syncline, Guizhou, China. It involved industrial analysis, sulphur measurement, elemental profiling, coal ash composition analysis, maceral identification and trace element quantification. The research explored petrological, mineralogical, sedimentological and geochemical characteristics of coal samples to evaluate the vertical evolution of coal‐forming environments and variations in provenance within the Longtan Formation. The study investigated relationships between changes in depositional environments and material sources and developed a sedimentary filling model for the late Permian in western Guizhou. Key findings include: (1) The overall depositional environment of the Longtan Formation was predominantly humid and reducing, and the coal‐forming plants were mainly aquatic and herbaceous. However, the depositional environment in the upper segment is more stable than that in the lower segment, with a trend towards arid and oxidative conditions in the later depositional stages. (2) Instabilities in the depositional environment of the lower segment of the Longtan Formation could be attributed to magmatic dike eruptions and volcanic ash fallout from the Emeishan region. The shift towards arid and oxidative conditions during the later stages of deposition in the Longtan Formation might be linked to extensive acidic volcanic eruptions around the periphery of South China towards the end of the late Permian.

ABSTRACTThe paleogeography and kinematic evolution of the Lhasa terrane during the Cenozoic time are key aspects to understanding the tectonic evolution of the Tibetan Plateau. Previous studies have focused on the paleolatitude reconstruction of the Lhasa terrane before and during the onset of the initial India–Asia collision. However, there exists an important gap between the period immediately after the onset of the India–Asia collision and the precise time at which the Lhasa terrane reached its present‐day latitude in terms of its kinematic evolution throughout the Cenozoic time. To this end, we performed an integrated study including paleomagnetism and isotopic geochronology on the Paleogene sediments of the Niubao (NB) Formation to provide a new constraint on the late Eocene paleolatitude of the Lhasa terrane. In combination with rock magnetic and petrographic results, our obtained results show that 91 inclination‐shallowing corrected characteristic remanent magnetizations (ChRM) are of pre‐folding origin and have passed the reversal test, indicating their primary nature. Based on these inclination‐shallowing corrected 91 filtered ChRM directions from sediments, the paleopole was calculated as λp = 77.2° N, φp = 308.2° E, with dp/dm = 3.0°/5.1°. This new result indicates that the Lhasa terrane was at 21.7° ± 3.0° N for the reference site at ca. 38 Ma, suggesting that the Lhasa terrane was still underway to its northward motion before its final arrival at present‐day latitude. This further suggests that a total magnitude of ca. 1700 km crustal shortening was partitioned within Asia since 38 Ma to the present day.

ABSTRACT The Abiod carbonate reservoir of the Campanian‐Early Maastrichtian age represents a major oil reservoir In the Pelagian block of eastern Tunisia, forming complex fractured networks that are poorly understood. Given the total absence of geological outcrops of Campanian‐Maastrichtian age in the study area, 2D seismic reflection, geological modelling and well log datasets were integrated to characterise the subsurface geodynamic structures, investigate the petrophysical characteristics, the relationship between fault systems and fracturing and define their implications for petroleum exploration. Analysis of seismic profiles, lithostratigraphic logs, borehole data and geological modelling has shown the prevalence of three major fault networks: northwest–southeast (NW–SE), E–W and northeast‐southwest (NE–SW). These faults have controlled the thickness of the limestones of the Abiod reservoir, favouring highly subsiding NW–SE trending zones where the thickness has exceeded 500 m. Based on responses of the Gamma Ray (GR) and Sonic curves, this formation is made up of four different lithological units (U1–U4). The wireline log analyses concluded that the gross thickness of the Abiod reservoir includes good reservoir property intervals with average effective porosity ranging from 8.6% to 20.6% and average shale volume ranging from 2% to 17%. Furthermore, analysis of the fracturing affecting the Abiod reservoir, based on oil well FMS image logs, has shown the presence of open and partially open fractures that are key to hydrocarbon accumulations. The rose diagrams of fracture directions at the wells and the rose diagram of major fault directions of the map are in perfect agreement with the clear predominance of the NW–SE directions. Beyond the main uplift faults, the structural features that impact the studied area's stratigraphy are divided into three main categories. This study showed that the brittle tectonics play a role in the enhancement of the petrophysical characteristics of the studied limestone reservoir and controlled the charge access of the hydrocarbons into the reservoir. The majority of the fractures affecting the Abiod reservoir are parallel to the large fault and have the same direction of movement, while the others are distributed in a conjugate family close to perpendicular to the large fault and with complementary directions of movement. The combination of geological factors and logging parameters indicates that the tectonic legacy and structural inversions play an important role in the structuring of the cover and the evolution of the petroleum system, which have made this chalk one of the most important oil reservoirs in eastern Tunisia. Finally, the developed 3D structural model suggests favourable locations for high‐potential areas in the studied region and provides insights for the reservoir development.

ABSTRACTAs hydrocarbon exploration progresses in the Santanghu Basin, tight oil reservoirs in Carboniferous volcanic rocks have become a focal point for exploration and development efforts. This study aims to account for significant industrial oil flow from the tight tuff layers of the Kalagang Formation in well blocks Ma 71 to 33 in the Malang Sag within the basin. Through experiments including organic carbon analysis, rock pyrolysis, and nuclear magnetic resonance (NMR), this study systematically investigated the principal characteristics and determinants of the tight oil reservoirs, culminating in the development of hydrocarbon modes, thus providing a reference for tight oil exploration and production in the study area. The results indicate that the Kalagang Formation is composed predominantly of tuff, especially vitric tuff. The storage spaces of this formation include dissolution pores, tectonic fractures, and dissolution fractures, with devitrification pores less common. Compaction plays a crucial role in rendering the tuff reservoirs tight. Nevertheless, differentiated diagenetic alterations have improved the microscopic storage spaces and their interconnectivity. Well blocks Ma 3301 and Ma 33, having undergone significant weathering (leaching), exhibit superior reservoir physical properties and connectivity compared to well blocks Ma 71 and Ma 73. In contrast, well blocks Ma 71 and Ma 73 experienced more significant alterations due to organic acid dissolution and devitrification under the influence of source rock types and hydrocarbon generation. The comprehensive analysis indicates that tight oil reservoirs in the Malang Sag were formed due to the close superimposition of source rocks and reservoirs, along with the effective connection of source rock‐rooted faults. This results in the formation of two sets of proximal tight tuff reservoirs with the ‘lower‐source rock and upper‐reservoir’ and ‘self‐sourced reservoir’ modes.