Gneiss Research Articles

Assessment of Micronutrient Status in Soils Derived from Three Parent Materials on the Jos Plateau, Nigeria

Parent materials play significant roles in determining the resultant characteristics of various soils. However, not much information is available on their micronutrient status of soil of the Jos Plateau. Hence, the objective of this study was to assess plant available Cu, Zn, Mn and B in soils derived from migmatite, granite gneiss and biotite granite parent materials on the Jos Plateau. Seven profile pits were dug in each geologic unit and soil samples obtained using guidelines in the soil survey manual. Available Cu, Zn, and Mn in soil samples were determined using the 0.1 M HCl extraction method and data collected was subjected to one-way analysis of variance. The results indicated that there were significantly higher contents of available Cu in the A horizon for soil derived from migmatite than in those over biotite granite or granite gneiss. Mean available Cu contents in the A horizon were 1.61 (± 0.35), 1.7125 (± 0.96), and 3.33 mg/kg (± 0.16) for granite gneiss, biotite granite and migmatite respectively; whereas for the B horizon mean contents were 2.06 (± 0.40), 2.98 (± 1.31), and 4.13 mg/kg (± 1.93) for granite gneiss, biotite granite and migmatite respectively. Generally, there were no significant differences in distribution of Mn, Zn and B among the geologic units. Implying that soils derived from migmatite, granite gneiss and biotite granite seems to behave similarly in contents of available Cu, Mn, Zn and B. Also, soil particle size had a significant moderate relationship with Cu and may influence its distribution in these soils.

Field Observations and Geophysical Research Applied to the Detection of Manganese (Mn) Deposits in the Eastern Part of Oban Massif, South-Eastern Nigeria: An Integrated Approach

The growing need for an industrialized world, especially in Africa, cannot be feasible without adequate mineral resources. Thus, the search for more mineral deposits will continue to be necessary. An integrated approach involving geological mapping and a high-resolution geophysical (aeromagnetic) investigation was conducted to assess the manganese mineralization in parts of the Oban Massif, southeast Nigeria. The aeromagnetic data were processed using regional-residual anomaly separation techniques, first vertical derivative (1VD), analytical signals, source parameters imaging (SPI), and Euler deconvolution to better understand magnetic source distributions and their depths of occurrence. The geological investigation revealed a dominant variety of metamorphic rock types, including migmatitic (banded) gneisses hornblende granite gneisses, amphibolites, charnockites, and some quartzite ridges. Also present are some indications of pockets of dolerites. The study area also observed epithermal Mn+Fe+Qtz vein type mineralization associated with hydrothermal alteration zones whose orientation coincides with dominant structural orientation from aeromagnetic interpretation. Analysis of aeromagnetic data shows that the study area is dominated by ENE, NNE, and E-W structural directions (near-surface basement structures), with the ENE trends related to mineralization in the area. The manganese mineralization within Oban Massif is structurally controlled. The depths of the magnetic anomalies in the study area were estimated using SPI and Euler decomposition algorithms. SPI delineated the shallow, intermediate, and deep magnetic anomalies at 84–142 m, 152–200 m, and 215–656 m, respectively. Euler decomposition, however, revealed that shallow, intermediate, and deep depths occurrence of the magnetic anomalies are at 200–377 m, 393–472 m, and 499–793 m, respectively.

About the building stones of the Eneolithic cromlech, sanctuary, and burial constructions near Shakhtar village (Dnipropetrovsk region, Ukraine)


 
 
 The article presents the results of petrographic research of building stone that was used for the construction of a cromlech, sanctuary, and the ceiling of the Eneolithic burials No. 20 – 22 from the kurgan No. 29 near Shakhtar village, Nikopol rayon, Dnipropetrovsk oblast. The purpose of this work was to establish a probable place for mining the stone blocks and rubble used in the construction. As a result of petrographic and X-ray fluorescence analysis, it was determined that the studied rocks can be divided into two groups, namely granitoids and limestones. The group of granitoids included tonalites, plagiogran- ites (trondhjemites), altered granite gneiss, and feldspar crystal from pegmatite. All the limestones were represented by spherical lay- ered aggregates, which most likely belong to oncoids – carbonate structures that form as a result of cyanobacteria growth. The studied samples from the materials of the cromlech and the sanctuary of burial No. 22 were represented by plagiogranitoids, pegmatoid granite, and limestones. The first of them served as the main material for the construction of the cromlech. Carbonate aggregates together with the granites were also used as a backfilling when installing wooden pillars of the cult complex associated with the burial. The plates covering the burials No. 20 and 21 were made of tonalites. All the studied granitoids are typical rocks for the area where the excavations took place. In the Middle Dnipro Area, plagiogranitoids are represented by the rocks of the Dnipropetrovskyi, Surskyi, Saksahanskyi, and Inhuletskyi complexes of the Archaean. Plagiogranitoids of the Dnipropetrovskyi complex are the most common in the studied area. They occur here in the middle and upper reaches of the Solona River and along the rivers of Bazavluk and Bazavluchok upstream the Sholokhove Reservoir. The closest to the excavation site are the occurrences of plagiogranitoids, which are exposed on the right bank of the Solona River, opposite the village of Shakhtar. In this area, pegmatoid granites are found in the form of veins that intersect plagiogranitoids. In the area of excavations, carbonate oncoids are found in the Sarmatian limestones of the Neogene. Most often they are found as the uncemented specimens that spilled out of the limestones. Today, such structures occur on both banks of the Kakhovske Reservoir, located south of the village Shakhtar. However, in ancient times there may have been closer outcrops of these rocks, as the Sarmatian limestone occurrences are common in the immediate vicinity of the excavation site, namely between the rivers Bazavluk and Solona, near their confluence, and the middle and upper reaches of the Chortomlyk River. As a result of the research, it is proved that in the valley of the river Solona during the Eneolithic, there began the active extraction of stone raw materials for mound construction, which was continued in later epochs, particularly, in the Scythian time.
 
 

Lithostratigraphy, Origin, and Geodynamic Setting of Iron Formations and Host Rocks of the Anyouzok Region, Congo Craton, Southwestern Cameroon

In Cameroon, most of the iron formation occurrences reported are found within the Nyong and Ntem Complexes. The Anyouzok iron deposit is located in the Nyong Complex greenstone belts, which represent the NW margin of this Congo craton. The main lithological units comprise the iron formations (IFs) unit, consisting of banded IFs (BIFs) and sheared BIFs (SBIFs), and the associated metavolcanic rocks unit consisting of mafic granulite, garnet amphibolite, and biotite gneiss. Within the Anyouzok area, BIFs are rare, while SBIFs are ubiquitous. This study reports the petrography, mineralogy, and whole rock geochemistry of IFs and interbedded metavolcanic rocks of the Anyouzok iron deposit. The abundance of cavities, higher Fe contents (49.60–55.20 wt%), and strong Eu anomalies (Eu/Eu* = 2.14–3.17) within the SBIFs compared to the BIFs suggest that SBIFs were upgraded through post-depositional hydrothermal alteration activities. REE signatures indicate the contribution of both seawater and hydrothermal fluids during BIFs precipitation. Mafic granulite and garnet amphibolite protoliths were derived from the partial melting of a metasomatized spinel lherzolite depleted mantle source. The overall compositional variations of the Anyouzok IFs and interbedded metavolcanic rocks endorse an Algoma-type formation deposited in the back-arc basin under suboxic to anoxic conditions.

Tectonic switch of the north Yangtze Craton at ca. 2.0 Ga: Implications for its position in Columbia supercontinent

Two episodes of magmatism with zircon U-Pb ages of 2.46 Ga and 2.0 Ga were studied in the Jinpan Complex in the north Yangtze Craton of South China. The ca. 2.46 Ga gneissic granites with various chemical compositions were formed by remelting of different crustal materials in a collisional event. The occurrence of both negative and positive whole-rock εNd(t) and εHf(t) values in these rocks indicates the growth of juvenile crust and reworking of Archean crust during early Paleoproterozoic. The ca. 2.0 Ga trondhjemites have high (La/Yb)N and Sr/Y ratios as well as negative whole-rock εNd(t), εHf(t) and zircon εHf(t) values, suggesting that they were formed by remelting of thickened lower crust in a collisional orogen. The ca. 2.0 Ga A-type granites have high Zr, Nb, Y contents and Ga/Al, Y/Nb ratios, belonging to A2 type granite. Their negative whole-rock εNd(t), εHf(t) and zircon εHf(t) values are similar to those of the ca. 2.0 Ga trondhjemites. These evidences suggest that they were produced by remelting of the residue after extraction of earlier granitic magma in an extensional tectonic setting. The 2.0 Ga mafic dykes show significant enrichment in LILEs but weak negative Nb, Ta anomalies and various Nb/U ratios. This is consistent with a parent magma similar to continental flood basalts and experienced different degrees of crust contamination. The co-occurrence of 2.0 Ga trondhjemites, A-type granites and mafic dykes implies a tectonic switch from convergence to extension at ca. 2.0 Ga in the north Yangtze Craton. Based on the similarities of the ca. 2.0 Ga magmatic rock association and metamorphic records in the north Yangtze Craton and south Siberia, the position of the Yangtze Craton in Columbia supercontinent is proposed to be close to south Siberia.

Ultrahigh-pressure metamorphism and P-T-t path of the Yangkou eclogites and granitic gneisses from the central Sulu orogenic belt, eastern China, based on phase equilibria modelling

ABSTRACT Coesite-bearing eclogites and garnet-bearing granitic gneisses from the Yangkou area in the middle portion of Sulu ultrahigh pressure (UHP) metamorphic belt records three stages of metamorphism: I) Prograde to peak stage, II) Early retrograde stage, and III) Late retrograde stage. The prograde stage is recorded in the core to mantle in garnet and Si (3.38–3.43) in phengite in eclogite that has the assemblage of Grt-Omp-Amp-Phg-Lws (+ Qtz + Rt + H2O), and the P-T conditions are constrained at 25–27 kbar and 585–595°C. Stage II is constrained by Xgr (0.48–0.55) in garnet from mantle to rim, XAn (0.009–0.011) from mantle to rim in plagioclase of granitic gneiss, and the P–T conditions are estimated to be 29–35 kbar and 865–990°C with the mineral assemblage of Grt-Bt-Pl-Phg-Liq (+ Qtz/Coe). Stage III is constrained by two P-T ranges: mineral assemblage of Grt-Ep-Bt-Pl-Phg-Liq (+ Qtz) and Xgr (0.45–0.72) from mantle to rim in garnet in granitic gneiss constrained an earlier P-T range of 22–23 kbar and 800–820°C, while Xgr (0.34–0.39) and Xpy (0.16–0.18) from mantle to rim in garnet in eclogite in the assemblage of Grt-Omp-Amp-Phg-LL (+ Qtz + Rt + H2O) constrained a later P-T range of 17–18 kbar and 675–690°C. The formation and evolution of these assemblages have important implications for the generation and differentiation of continental crust through the operation of plate tectonics. The data suggest that both mafic and granitic rocks in the Yangkou area subducted to a depth of more than 115 km and underwent UHP metamorphism. The three stages of metamorphism in the study area are consistent with the regional well-established metamorphic evolution history, from UHP eclogite facies, through HP/HT eclogite facies, to amphibole eclogite facies with the timing of 230, 225, and 195 Ma, respectively.

Geochemistry and U–Pb zircon geochronology of the Jutogh Thrust sheet, Himachal Pradesh, NW‐Himalaya: Implications to the petrogenesis and regional tectonic setting

We present datasets of the whole‐rock geochemistry and U–Pb zircon geochronology from the Jutogh Thrust (JT) sheet of eastern Himachal Pradesh, NW Himalaya, in order to explain the tectono‐magmatic environment in which they formed. The metapelite and granitoids of the JT sheet have moderate to high SiO2, Al2O3, Na2O, K2O, and rare earth elements (REE). The A/CNK (Al2O3/CaO + Na2O + K2O) ratio with magnitudes ≥1, indicates the peraluminous nature, calc‐alkaline series, and S‐type granitoids. The high values of Rb and Th as compared to Nb and the negative Ba anomaly also suggest the dominance of crustal source material. The distinct enrichment of large‐ion lithophile elements of Rb, Th, K, Ba and Pb and strong depletion in high‐field‐strength elements (HFSE) of Zr, Nb and Ti results in high incompatible elements/HFSE ratios, which suggest that the source is derived from many intra‐crustal tectonic environments. All samples are well‐fractionated REE patterns [(La/Yb)N = 6.06–17.37] and characterized by moderately flat enriched [(La/Sm)N = 2.31–4.71] of light rare earth elements. The negative Eu anomalies (Eu/Eu* = 0.18–0.71), suggest the plagioclase fractionation from the sourced magma and the origin of granitic gneiss through the high temperature (~800°C). The zircon U–Pb ages of granite range between 883.0 ± 15.0 Ma and 1260.0 ± 10.0 Ma, with a consistent peak of ~925.0 Ma. It confirms that the northern edge of the Indian Plate collided with an unnamed microcontinent. Also, in a contemporaneous process, the upper crust underwent partial melting, and the generated magma intruded in an extensional tectonic set‐up of the northern edge (i.e., presently known as the Jutogh and Vaikrita thrust sheets) of the Indian Plate during the Neoproterozoic. The available zircon U–Pb ages of the JT sheet range between 550–2750 Ma. The magmatic nature of zircons, with two peaks of ~825 Ma and ~910 Ma, suggests that episodic magmatic processes have taken place during the Neoproterozoic. This study revealed that the Higher Himalayan Crystalline Sequence was a meta‐sedimentary sequence and was deposited in an active margin set‐up of the northern edge of the Indian Plate.

Tracing remnants of Ediacaran S-type granitoids from beach placers in SE Madagascar

Southeast Madagascar hosts several major deposits of beach placers, the provenance of which is little understood. To redress this imbalance, we present new laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) U-Pb ages, and trace elements of zircons and monazites, as well as Hf isotopes of zircons from heavy mineral beach sands at Taolagnaro (Fort Dauphin) in SE Madagascar. The ages of detrital zircon grains range from 650 Ma to 450 Ma and from 1900 Ma to 1700 Ma (one grain has an age of 2633 Ma), and detrital monazite ages range from 574 Ma to 484 Ma. The Ediacaran−Cambrian zircons (650−450 Ma) and monazites (574−484 Ma) record a major Pan-African orogenic event in SE Madagascar. Geologically, the 650−450 Ma ages correlate well with coeval granitic gneisses in southern Madagascar, and a few 1900−1700 Ma ages can be linked to putative Paleoproterozoic protoliths of metasedimentary rocks from the Anosyen Domain and from the Itremo Group of central Madagascar. The zircon mineral chemistry indicates that some of the grains (P>25 μmol g−1) were sourced from S-type granitic rocks. The monazite chemistry points toward a metamorphic provenance from garnet-bearing amphibolite facies rocks, such as migmatitic gneisses in southern Madagascar. The Hf isotopic compositions of detrital zircons indicate reworking of their probable Paleoproterozoic−Archean source rocks. We conclude that the beach sand zircons and monazites were largely sourced from the uplifted and eroded Anosyen and Androyan Domains in SE Madagascar, and with minor contributions from central Madagascar, which were all transported by rivers to the ambient ocean to the southeast.

Nature and origin of anorthosite enclaves within Proterozoic granite of Chotanagpur Granite Gneiss Complex of Eastern India

The Central Indian Tectonic Zone (CITZ) is a Proterozoic suture along which the Northern and Southern Indian Blocks are inferred to have amalgamated, forming the Greater Indian Landmass. The Chotanagpur Granite Gneiss Complex (CGGC) represents the eastern extension of the CITZ and exposes several granite plutons. Enclaves of diverse origin are present as minor constituents within these granitic bodies. This study reports new major and trace element data for anorthosite enclaves hosted within granites in the Pattharkatti and Rajgir area from the northern margin of CGGC to get modern insights into the petrogenesis of anorthosites. Anorthosite enclaves show sharp contact with the host granite. They contain cumulus plagioclase (An87–94), intercumulus amphibole (magnesiohornblende and ferrotschermakite), and biotite (Mg-biotite and phlogopite) along with minor iron oxides. Amphibole crystallization pressure and temperature are constrained between 0.5 and 6.4 kbar and 653–780°C for the anorthosites. The studied anorthosites display a very gradual and steady increase in whole-rock rare earth element (REE) contents from Lu to La [(La/Yb)N = 1.22–13.08]. They also show a sharp decline in Fe2O3(t) and MgO, whereas Al2O3 increases with increasing silica contents from 45.69 to 51.16 wt%. In the chondrite normalized REE diagram, plagioclase exhibits LREE enriched patterns with strong positive Eu anomaly. The composition of parental liquid for anorthosite from the study area was estimated by adopting the equilibrium distribution method. Parental melt curves from Sm to La are near parallel and constrained broadly between trapped melt fractions (TMF) = ∼5%–15%. Anorthosites of the study area may have formed from the plagioclase-saturated basaltic melt.

Geochemistry and U–Pb zircon geochronology of granitic gneisses in the Mewengo iron deposits: evidence of Archean fingerprints within the Paleoproterozoic Nyong Group, Cameroon

Geochemistry and U–Pb zircon geochronology of granitic gneisses in the Mewengo iron deposits: evidence of Archean fingerprints within the Paleoproterozoic Nyong Group, Cameroon

Distribution of Radionuclides and Radiological Health Assessment in Seih-Sidri Area, Southwestern Sinai.

The current contribution goal is to measure the distribution of the radionuclide within the exposed rock units of southwestern Sinai, Seih-Sidri area, and assess the radiological risk. Gneisses, older granites, younger gabbro, younger granites, and post granitic dikes (pegmatites) are the main rock units copout in the target area. Radioactivity, as well as radiological implications, were investigated for forty-three samples from gneisses (seven hornblende biotite gneiss and seven biotite gneiss), older granites (fourteen samples), and younger granites (fifteen samples of syenogranites) using NaI (Tl) scintillation detector. External and internal hazard index (Hex, Hin), internal and external level indices (Iα, Iγ), absorbed dose rates in the air (D), the annual effective dose equivalent (AED), radium equivalent activity (Raeq), annual gonadal dose (AGDE), excess lifetime cancer risk (ELCR), and the value of Upper Continental Core 232Th/238U mass fractions were determined from the obtained values of 238U, 232Th and 40K for the examined rocks of Seih-Sidri area. The average 238U mg/kg in hornblende biotite gneiss and biotite gneiss, older granites, and syenogranites is 2.3, 2.1, 2.7, and 8.4 mg/kg, respectively, reflecting a relatively higher concentration of uranium content in syenogranites. The results suggest that using these materials may pose risks to one’s radiological health.

Geology of the Neoarchean-Rhyacian Supracrustals of the Northern Intracontinental Sector of the Araçuaí Orogen: Evidence for Overlapping Basins

The northern region of the intracontinental sector of the Araçuaí Orogen preserves geological records related to overlapping basins and tectonic reactivations between the Mesoarchean to the Cryogenian. The representatives are the metavolcanosedimentary sequences (i) Leandrinho (LMVS), here defined, that intercalates aluminous schists (metapelite), metagreywackes, acid metatuffs, and metalapillites, with a crystallization age of 2550 ± 2 Ma and; (ii) Rio São João (RSJMVS), with metagreywackes and metarkoses, metapelites, metarhytmites, itabirites, hematite-schists, and schistified mafic-ultramafic metavolcanics, presenting maximum depositional ages of 2280 ± 46 and 1971 ± 50 Ma for the Ibiassucê and Água Branca units, respectively. The metavolcanics of the LMVS are mainly subalkaline, sodic, magnesian, metaluminous to peraluminous, and of continental arc setting, with chemistry similar to TTG correlates. One sample has a chemical composition similar to that of sanukitoids. The model age (TDM) varies between 3003 and 3074 Ma and ƐNd between −5,06 and −5,84. In the SMRSJ, schistified metamafics, metagreywackes and metarkoses, and metapelites present chemical signature and geological context associated with a continental arc setting. These siliciclastic rocks have a model age (TDM) between 2618 and 3069 Ma, with ƐNd between −2,70 and −9,21. The entire sequence of the Araçuaí-West Congo intracontinental sector was deformed and metamorphosed during the Ediacaran, generating a prominent gneissic banding that embeds the sequences. The main point of the paper is the description of the previously unrecognized Leandrinho metavolcanosedimentary sequence (LMVS). Subordinately, to demonstrate the superposition of two basin-forming events, at the end of the Neoarchaean and during the Rhycian/Orosirian.

Geothermal potential of Manuguru geothermal field of Godavari valley, India

The Godavari geothermal field in India is one of the potential areas manifested by several geothermal waters and groundwaters. The geothermal waters of the area are near neutral (pH: 6.5–7.3) with surface temperature ranging from 30 to 55 °C while groundwaters are also near neutral (pH: 6.6–7.5) with surface temperature ranging from 24 to 28 °C. The hydrogeochemistry of the geothermal waters suggests that the geothermal waters show a Na-Ca-SO4-HCO3 to a Ca-HCO3 type and groundwaters are of the Ca-HCO3 to Na-Ca-HCO3 type while groundwaters and river waters are of the Ca-Na-SO4 types. The geothermal waters of the study area are enriched in SO42– and Cl–, due to the interaction with the pyrite-bearing Gondwana sediments and granitic gneiss basement rocks. Furthermore, enrichment of Ca2+, Mg2+ and an increased HCO3/Cl ratio in geothermal water is caused by the exchange and/or mixing process that takes place during water-rock interaction at an elevated temperature while ascending to the surface. This type of behavior of water is also observed during the water-rock interaction experiment at 100 °C.Studies on geothermal gas geochemistry suggest the deeper circulation of geothermal waters in the crust and high helium concentration as a thermal gas that can be utilized for commercial purposes. Estimated reservoir temperatures from quartz and Na-K-Ca geothermometry are in the range 110–195 °C. Therefore, the geothermal water of the study area is categorized as a moderate enthalpy geothermal system. Thermal logging in the borewell and depth range from 50 to 1000 m suggest that the geothermal gradient in the Manuguru area ranges from 22.5 to 105.5 °C/km and heat flow ranges from 83 to 388 mW/m2, which is higher than the regional condition. Therefore, 3584 MWe power can be produced by using the Organic Rankine Cycle (ORC) from the Manuguru geothermal area of Godavari valley.

Influences of EDZ and Cross-Section Shapes on Spalling Failure Depth of Non-circular Tunnels in Gneissic Granite

Influences of EDZ and Cross-Section Shapes on Spalling Failure Depth of Non-circular Tunnels in Gneissic Granite

Tectonic affinity of the Zhusileng–Hangwula Belt in the northern Alxa area: Evidence from the zircon U–Pb ages and Hf isotopic compositions of the Mesoproterozoic (~1.4 Ga) igneous rocks

Precambrian rocks are necessary to understand the tectonic and crustal evolution of the Central Asian Orogenic Belt, especially the tectonic affinities of embedded microcontinents. We conducted a combined analysis of whole‐rock geochemistry, zircon U–Pb geochronology, and Hf isotope on the Mesoproterozoic igneous rocks from the Zhusileng–Hangwula Belt of the northern Alxa area to investigate its tectonic affinity. The zircon ages show that the gneissic granites, metagabbro, and amphibolite formed at 1,433–1,424 Ma, 1,383, and 1,373 Ma, respectively. Furthermore, zircon xenocrysts from the rhyolite in the Zhusileng area exhibit a206Pb/238U ages cluster at about 1.4 Ga. Geochemically, the gneissic granites are high‐potassium calc‐alkaline granitoids and exhibit light rare earth element‐enriched pattern, pronounced significant negative Eu anomalies, negative Nb–Ta anomalies, positiveεHf(t) values (3.2–11.3), and young two‐stage model ages (2.21–1.46 Ga), indicating that they were derived from a magma source of rapid reworking of juvenile mantle‐derived materials with a limited ancient crustal contamination. The FeOT, CaOm and MgO contents of mategabbros and amphibolite are high, but their total rare earth elements are relatively low (TREE = 31.45–32.74). They are characterized by relatively positive zirconεHf(t) values (5.3–11.0), and very young two‐stage model ages (1.98–1.49 Ga), indicating that they were generated from the depleted mantle. Our geochemical data suggest that these Mesoproterozoic rocks in the Zhusileng–Hangwula Belt are consistent with the formation period and tectonic environment of juvenile basement rocks from the Central Tianshan Arc and southern Beishan Orogenic Belt, whereas a Mesoproterozoic correlation with the Tarim Craton is highly unlikely. Thus, we believe that the Zhusileng–Hangwula Belt has an analogous tectonic evolution and a close affinity with the Central Tianshan Arc and southern Beishan Orogenic Belt during the Mesoproterozoic.

Granite series assessment, nature and crystallization condition of Paleoproterozoic granite gneisses from Askot and Chiplakot klippe, Kumaun Lesser Himalaya, India

Granite series assessment, nature and crystallization condition of Paleoproterozoic granite gneisses from Askot and Chiplakot klippe, Kumaun Lesser Himalaya, India

Source-to-sink analysis of Mesozoic–Cenozoic sandstone-type uranium deposits in the Qaidam Basin

Accurate evaluation of uranium sources and identification of their spatiotemporal correlations with uranium deposits (or sinks) in sedimentary basins are important for exploring sandstone-type uranium deposits. This study examines the source-to-sink system of Mesozoic–Cenozoic sandstone-type uranium deposits in the Qaidam Basin (QB) through a literature review in conjunction with logging and seismic data and yields the following findings. (1) The uranium-supplying capacity of a source rock in the uranium source area depends on primarily its type and to a lesser extent, the tectonic zone where it is located and the episode during which it formed. (2) The initial uranium content, U0, is the core parameter for classifying and evaluating the uranium-supplying capacity of a source rock. At U0 > 1.5 ppm, uranium begins to migrate from a source rock. The uranium variation coefficient, ΔU, and the amount of uranium migration, ΔUt, decrease continuously to –55 % and –5 ppm respectively as U0 increases up to 9.5 ppm, which suggests that at most 5 ppm of uranium in the source rocks can migrate away. As U0 increases beyond 9.5 ppm, ΔU and ΔUt fluctuate around –55 % and –7 ppm respectively, which suggests that approximately 7 ppm of the uranium in the source rocks can migrate away. (3) Of the different types of rocks, silicic igneous rocks (including both intrusive and volcanic igneous rocks) and granitic gneisses have the highest uranium-supplying capacity; intermediate igneous rocks and gneisses come second; mafic–ultramafic igneous rocks and the other metamorphic rocks (except granitic gneiss and gneiss) come third. Of the sub-source areas (tectonic zones), the western segment of the Eastern Kunlun and the Qiman Tagh have the highest uranium-supplying capacity; the Central and Southern Altyn Tagh come second; the others come third. (4) Uranium sources are the fundamental prerequisite for the formation of uranium sinks. Other geological factors control the specific formation process of uranium sinks as well as their spatiotemporal distribution patterns. For QB, the most economic and prospective uranium sink, Neogene formations of Gy anticline, was fed by the source areas which had the highest uranium-supplying capacity. This suggests that the Neogene of WEK anticline belt, Quaternary of Kumukol Basin and Qarqan River Basin are the most noteworthy metallogenic prospective areas. The uranium-source evaluation scheme and “source-to-sink” ore exploration approach introduced in this study have practical value for advancing the exploration of uranium deposits in sedimentary basins in northern China and other parts of the world.

On the origin of shear-band network patterns in ductile shear zones

Ductile yielding of rocks and similar solids localize shear zones, which often show complex internal structures due to the networking of their secondary shear bands. Combining observations from naturally deformed rocks and numerical modelling, this study addresses the following crucial question: What dictates the internal shear bands to network during the evolution of an initially homogeneous ductile shear zone? Natural shear zones, observed in the Chotonagpur Granite Gneiss Complex of the Precambrian craton of Eastern India, show characteristic patterns of their internal shear band structures, classified broadly into three categories: type I (network of antithetic low-angle Riedel (R) and synthetic P-bands), type II (network of shear-parallel C and P/R bands) and type III (distributed shear domains containing isolated undeformed masses). Considering strain-softening rheology, our two-dimensional viscoplastic models reproduce these three types, allowing us to predict the condition of shear band growth with a specific network pattern as a function of the following parameters: normalized shear zone thickness, bulk shear rate and bulk viscosity. This study suggests that complex anastomosing shear-band structures can evolve under simple shear kinematics in the absence of any pure shear component.

Reappraisal of 75 Years of Exploration for Atomic Minerals in India and the Way Forward

Abstract In India, Atomic Minerals Directorate for Exploration and Research (AMD), the oldest unit under the Department of Atomic Energy (DAE) is mandated with the exploration and augmentation of atomic mineral(s) resources of the country to support the Nuclear Power Programme (NPP) of India. AMD, till date have established four (04) generations of uranium metallogeny in India, distributed in 46 deposits and several other occurrences, major share of which are contributed by the globally unique, stratabound carbonate hosted, syn-diagenetic Tummalapalle Group of deposit (~59%), metamorphite type deposits along the Singhbhum Shear Zone (~21%), unconformity related deposits in northern part of Cuddapah Basin (~5%) and sandstone type deposits in Cretaceous Mahadek Basin (~6%). Besides these, metasomatite type deposits along the North Delhi Fold Belt (4%) and granite related-structurally controlled, high grade deposits in Bhima Basin (2%) along with some small hydrothermal/metamorphite/migmatite type deposits in Aravalli, Kotri-Dongargarh, Higher Himalaya belts and Chhotanagpur Granite Gneiss Complex contribute to the national inventory which stands at 3,76,000 tonne uranium oxide. AMD have stockpiled substantial quantities of Nb-Ta, Be and Li minerals needed for the NPP of India from prospective pegmatite belts in the country. AMD have established immense potential for REE mineralization in carbonatite complexes of Ambadungar in Gujarat and per-alkaline granite-rhyolite of Siwana Ring Complex, Barmer district, Rajasthan. Exploration along the coastal and riverine placers of the country has established 130 heavy mineral placer deposits with substantial thorium and REE resources. The progressive advancements by AMD through adaptation of integrated multidisciplinary exploration techniques coupled with major thrust in airborne/ground geophysics and expansion of state-of-the-art analytical facilities have facilitated systematic planning for future augmentation of atomic mineral(s) resources. Exploration inputs are envisaged to be intensified in the brownfield target areas for resource augmentation while R&D and phase-wise exploration inputs will be focused for developing the identified greenfield areas following a planned roadmap to ensure selfsufficiency in atomic mineral resources for sustained growth of the NPP to reach the target of net zero carbon emissions by 2070.

The Application and Analysis of Slug Test on Determining the Permeability Parameters of Fractured Rock Mass

Based on the proposed calculation method for determining the different dip angle fracture permeability coefficients derived from the well flow vibration equation and the self-developed slug test system, research on the slug test in a field in fractured rock mass was carried out based on the underground water sealed cavern project of the National Huangdao Petroleum Reserve. The formation lithology of the test site was granite gneiss, and the fractures were not developed, which is conducive to the research of slug tests on fracture permeability. On the basis of obtaining the geological information of boreholes by using the self-developed slug test system, comparative research on the segmented slug test and conventional water pressure test was carried out. The test results show that the proposed slug test method and self-developed test system has good accuracy and applicability for determining the fracture permeability coefficient, equivalent permeability coefficient and rock mass permeability coefficient tensor, which is more convenient and efficient than other test methods.