High Rb Contents Research Articles

Geochemical exploration for tantalum in coltan-rich pegmatites at Bewadze-Mankoadze area of the Kibi-Winneba Belt, southern Ghana: Constraints from exploratory data analysis

The Bewadze-Mankoadze pegmatites in the Kibi-Winneba Belt of Ghana host several columbite group minerals (WGM) and wodginite group minerals (WGM) as well as other rare and radioactive elements such as uraninite and cesium. In this study, petrographic studies of rock samples from pegmatite outcrops and statistical analysis of the major and minor elements were conducted to identify the pathfinder elements of a new tantalum deposit in the area. Ten samples were obtained from each town for whole-rock geochemistry and thin sections were prepared from some of the samples taken for petrographic analysis. The petrographic analyses showed the presence of quartz, K-feldspars, plagioclase, muscovite, spodumene, albite, tourmaline, columbite group minerals, and montebrasite, which indicate that the studied samples are granitic pegmatites. The geochemical data of the 10 samples obtained from each town showed high concentrations of Cr, Cs, Rb, Sm, and Ta. The Ta concentrations ranged from 10.5 to 773 ppm with an average value of 260 ppm. Q-Q plots showed outliers and variations from the dataset's normal distribution, which were fixed by centred log-ratio transformation and demonstrated to be normal by the Kolmogorov-Smirnov test and Shapiro-Wilk test for normality. Spearman correlation revealed that Sc, Ga, Nb, and Cs showed a moderate to strong correlation with Ta. Factor analysis indicated elemental association of Ta with Cs, Zn, Nb, MgO, Sc, Ga, and V. Three (3) multi-element relationships were discovered by hierarchical cluster analysis: (1) As, La, Hf, CaO, U, Co, Pb, Ce, Ba and Na2O, (2) V, Nb, Ta, Ga, Sc, Cr, Cu, Nb and MgO, and (3) Ni, SiO2, Cs, Zn, Sm, Rb, K2O, Y, Th, Al2O3 and Fe2O3. Hence, a comparison of the results of the multivariate statistics established Sc, Ga, Nb, and Cs as the pathfinders of tantalum in the Bewadze-Mankoadze area. Geochemical anomalies involving these elements can be observed in the south-western portion of the study area, according to single and multi-element halo mapping. It is therefore recommended that exploration activities for tantalum mineralization should focus on the south-western part of the study area, where the anomalies of the pathfinder elements are located.

Early Jurassic A-type granite and monzodiorite from the Baoji batholith: Implication for tectonic transition from post-collision to post-orogenic extension in the Qinling Orogenic Belt, China

Introduction: The early Jurassic granitoids in the Qinling Orogenic Belt (QOB) play a crucial role in understanding the tectonic implications for the geological evolution of China. To elucidate the early Jurassic tectonic setting of QOB, we performed a comprehensive analysis of zircon U-Pb ages, whole-rock geochemistry, and in situ zircon Lu-Hf isotopes from early Jurassic monzodiorite and Kfeldspar granite within the Baoji batholith in western QOB.Geochronology Method and Results: The intrusions yielded zircon U-Pb ages of 186 ± 2 Ma and 188 ± 2 Ma, respectively.Geochemistry Results: The monzodiorites are characterized by relatively high MgO, Rb, Th, U, and LREE contents, as well as low P, Ti, and HREE contents. They also exhibit high Nb/Ta ratios (20.6–23.4). The zircon εHf(t) values for the monzodiorite sample range from −4.36 to 6.47, indicating significant contributions from a fertile continental lithospheric mantle with the involvement of crustal components. The K-feldspar granites are enriched in K2O+ Na2O, Rb, Zr, Hf, and Nb, and lower Ba, Sr, Ti, and P. They exhibit high Nb/Ta and Ga/Al ratios but low Y/Nb and Yb/Ta ratios. Their geochemical characteristics reveal an A-type granite affinity with elevated zircon saturation temperatures (848°C–900 °C). Additionally, the K-feldspar granite exhibits REE and trace element patterns similar to those observed in the monzodiorite. However, a wide range of zircon εHf(t) values (−4.72 to 3.98), differing from those of the monzodiorite, indicate that the parental magma of the K-feldspar granite experienced magma mixing between a monzodioritic magma and a crustal-derived felsic magma.Discussion: These findings suggest that both A-type K-feldspar granite and monzodiorite likely formed during post-orogenic processes. Additionally, the QOB commenced its postorogenic evolution as an extensional tectonic environment during the early Jurassic period.

Li-mineralized pegmatite of anatectic origin: Constraints from Li[sbnd]Hf isotopes and geochemical modeling

Pegmatites are important reservoirs of lithium resources. There is an ongoing debate as to whether Li-mineralized pegmatites were generated from evolved granitic systems via extreme differentiation or by direct melting of metasedimentary rocks. The Chinese Altay is one of the largest pegmatite provinces in the world, and includes many rare-metal pegmatites (e.g., Koktokay, Kelumute, Kaluan and Azubai). However, they display significant differences in formation ages and isotopic compositions compared with the neighbouring or potential parental granites. In this contribution, we present a case study of the Kaluan Li ore deposit in the Chinese Altay, elucidating the origins of pegmatites and related Li mineralization. The Kaluan Li-mineralized pegmatites are characterized by high SiO2, K2O, Na2O, Li, Cs, Ta, and Rb contents; low Fe2O3T, MgO, Ba, and Sr contents; and peraluminous signatures. They have homogeneous HfLi isotopic compositions (εHf (t) = −0.6 to +2.5; δ7Li = +1.6 to +5.8‰) that are within the range of HfLi isotopic compositions of the Kulumuti Group schists (εHf (t) = −2.8 to +7.5; δ7Li = −8.6 to +10.8‰). In addition, the chemical compositions of the melt derived from the partial melting of the Kulumuti Group by phase equilibrium modeling are compatible with our analyses of the Kaluan Li-mineralized pegmatites. These similarities suggest that the Kaluan Li-mineralized pegmatites were derived from the partial melting of the Kulumuti Group schists at depths during the Triassic, in a post-orogenic and extensional setting. The generation of these pegmatites was mostly controlled by biotite dehydration melting at relatively high temperatures, rather than by the low-temperature melting of muscovite. Trace elements modeling results show that approximately 33–36% partial melting of the average Kulumuti Group schist may produce melts with maximum Li concentrations ranging from 664 to 751 ppm. Subsequently, a high degree of fractionation exceeding 85%, was required for the Li concentration of the residual melt to reach concentrations suitable for crystallization into albite-spodumene pegmatites. Based on our research, an anatectic origin model may have general applicability in explaining the genesis and mineralization of rare-metal pegmatites in the Chinese Altay.

Revisiting the fluid regime during anatexis of metasedimentary rocks: New constraints from an integrated approach on the Cenozoic Himalayan granites

Water plays a critical role in the formation of granitic magmas and continental crust, but distinguishing water-present and water-absent anatectic scenarios using the geochemistry of granites is controversial. In this study we use an integrated approach that combines whole-rock major and trace element geochemistry, Ti-in-zircon thermometry, phase equilibrium modeling and trace element modeling to study the water regime that produced the Miocene granites from the Malashan-Gyirong area in central Himalaya to solve this controversy. The Gyirong granites have relatively low CaO, Sr and Ba and high Rb and (87Sr/86Sr)i and the Malashan granites have relatively high CaO, Sr and Ba and low Rb and (87Sr/86Sr)i, and were classified as group A and group B granites, respectively. Following previous interpretation, group A and group B granites are consistent with the products of water-absent and water-present melting of metasedimentary rocks, respectively. Ti-in-zircon thermometry yielded maximum values of 761–796 °C for the Gyirong granites and 730–764 °C for the Malashan granites. Distinct variation trends in zircon trace element compositions indicate that these two groups of granites were not linked by crystallization differentiation. Using average compositions of Proterozoic pelite as starting materials, phase equilibrium modeling was carried out at a variety of P–T–H2O conditions typical of the Himalayan orogen, P = 5, 10 and 15 kbar, T = 600–800 °C, H2O = 0–10 wt%. Pelite can produce melts with coupled CaO–Na2O contents for both groups at 10 kbar. Specifically, constraints from compositions and temperatures require that the bulk H2O content is ca. 1–2 wt% for group A granites and > ca. 4 wt% for group B granites. Compared with the maximum structural water content of the pelite at 10 kbar (1.77 wt%), this study testifies that group A granites formed under water-absent conditions and group B granites under water-present melting conditions. Modeling shows that water-present melting can produce melts with high Sr–Ba and low Rb contents resembling group B granites, while water-absent melting can produce melts with low Sr–Ba and high Rb contents resembling group A granites. This study highlights that water can indeed cause differences in granite geochemistry but a comprehensive investigation is required to better determine the role of water during crustal anatexis.

Mineralogy and 40Ar-39Ar dating of the recently discovered tainiolite occurrences in the Kaerqiaer fluorite Belt, western Altyn Tagh Terrane

The Kaerqiaer Fluorite Belt (KFB) contains the Kaerqiaer, Xiaobaihegou, Kumutashi, Northern Layidan, and Gaijike fluorite deposits in the western Altyn Tagh Terrane of NW China. An occurrence of Li-bearing mica tainiolite (KLiMg2(Si4O10) F2) has been recently discovered, associated with fluorite-bearing alkali feldspar granite. The tainiolite is hosted by fluorite-calcite veins that contain assemblages of tainiolite-fluorite-calcite and apatite-bastnaesite-tainiolite-fluorite-calcite along the contact zone with alkali feldspar granite. The tainiolite occurs as euhedral crystals and has high concentrations in the veins. 40Ar-39Ar dating of the tainiolite from Xiaobaihegou yields an age of 421 ± 2 Ma, and single-crystal X-ray diffraction confirms the tainiolite has a monoclinic 1 M−type with a C2/m (#12) space group. Minor structural variations in the mica are attributed to the substitution of Li for Mg. EPMA and LA-ICP-MS analyses show that the tainiolite has high Li, Rb, Cs, Sn and Nb concentrations, and low Ta, total REE concentrations. The average Li2O content of the fluorite-tainiolite veins reaches 0.36 %, surpassing the economic cut-off grade. We suggest that the fluorite deposits formed from highly fractionated Li-F-P-rich residual melt evolved from the parental magmas of alkali feldspar granite. The tainiolite mineralisation may result from subsequent hydrothermal activities caused by the reactivation of regional faults under the extensional regime between the Middle Altyn and Eastern Kunlun terranes. The discovery of tainiolite occurrences made KFB a potential area for not only F but also Li resources.

Strontium isotope proxy of sedimentological records reveals uplift and erosion in the Southeastern Neo-Tethys ocean during the late Cretaceous

The mutual interplays between plate tectonic processes, orogenesis and continental uplift, high-flux magmatism, and high sedimentation rates can affect the geochemical signatures and composition of marine sediments. Here, we examine two major disconformities, the Cenomanian–Turonian boundary (CT-ES) and the middle Turonian (mT-ES) exposure surfaces, from the Upper Cretaceous sedimentary successions of the southeastern Neo-Tethys Ocean in the Zagros Basin (Iran). The disconformities are expressed as distinct positive peaks in rubidium (Rb) contents and 87Sr/86Sr isotopic ratios of carbonates. The 87Sr/86Sr values of samples bracketing the disconformities in seven well cores give average age ranges of 94.4–93.6 Ma for the CT-ES and 91–86 Ma for the mT-ES. These ages fall in the timespan of forearc/ophiolite formation through subduction initiation in the Neo-Tethys realm (southern margin of Eurasia), high convergence velocities between Arabia and Eurasia, and blueschist exhumation. All these processes involved buckling of the Neo-Tethyan lithosphere, initiating the Neo-Tethys closure and a high erosion rate on the Eurasian margin. The first two mechanisms exerted considerable compressional forces on the adjacent carbonate platforms, reactivated basement faults, and led to the uplift and erosion of the Arabian Plate, which provided the high contents of Rb and the high 87Sr/86Sr ratios in the carbonates.

Petrogenesis of the granitoids related to skarn-type mineralization in the Nyainqentanglha Metallogenic Belt, Tibet

The Nyainqentanglha Metallogenic Belt (NMB) is an economically important lead-zinc ore province located in the Central and Southern Lhasa subterrane, Tibet. The NMB consists mainly of skarn-type lead-zinc polymetallic deposits that form at the contact between Late Cretaceous-Eocene intrusive rocks and carbonatite/volcanic-sedimentary strata. These deposits are generally considered to be related to S-type granites formed by the Indo-Asian continental collision. However, the εHf(t) (ave. −1.6) of zircons from the mineralization-related granitoids indicates that it is crust-mantle mixing products. In addition, the volcanic rocks of the Dianzhong Formation, which have a close spatio-temporal relationship with the skarn-type deposits, typically show mantle-derived features. Therefore, the occurrence of AFC processes in mantle-derived material passing through the thick basement of the Lhasa Terrane may better explain the genesis of the mineralization-related granitoids. In this study, we present results on zircon U–Pb ages, major and trace elements of the granitoids associated with skarn-type mineralization from the Narusongduo district. LA-ICP-MS zircon U–Pb dating shows that the granite formed in the Paleocene (58.6 ± 0.5 Ma). Combined with published regional data, we propose the mineralization age of the skarn-type deposits in the NMB ranges from the Late Cretaceous to Eocene. Detailed petrology and geochemistry of mineralization-related granitoids are evaluated to constrain the magmatic evolution process. The granitoids have high contents of SiO2 (mean 72.8 %), K2O (mean 4.0 %), Rb (mean 186.9 ppm), DI (differentiation index) 84.7, A/CNK (mean 1.3), and low contents of MgO, TFe, suggesting that the granitoids have undergone strong differentiation. In addition, the continuous decrease of P2O5 with progressive differentiation and the lower average P2O5 abundance suggest that the mineralization-related granitoids belong to the I-type granite. The results suggest that the mineralization-related granitoids in the NMB originated from the mantle and is the fractionated I-type granite formed by the process of AFC (Assimilation and Fractional Crystallization). Considering that Pb and Zn often coexist in deposits, we suggest that magmatic differentiation may play an important role in the formation of the granite-related Pb and Zn mineralization.

Age, clinopyroxene geochemistry and petrogenesis of post-collisional magmatic rocks in the Jonob-e-Sechangi area, Lut block, eastern Iran

The Lut-Sistan region, eastern Iran has an extensive record of Eocene-Oligocene magmatism the origin of which is not fully understood. In this study, we analyze a set of volcanic rocks in the Jonob-e-Sechangi area of the Lut block. U-Pb zircon analyses demonstrate that magmatism can be divided into two age groups. Group 1 formed at ∼45 Ma and involved different felsic (calc-alkaline rhyolitic to dacitic) and intermediate (high-K calc-alkaline andesitic) rocks. All samples from Group 1 display nearly identical initial 87Sr/86Sr values (87Sr/86Sri = 0.7045-0.7056). However, the felsic rocks show higher ԐNdt (+2.21 to +2.73) and lower TDM (0.51-0.61 Ga). In contrast, intermediate rocks have ԐNdt values of +1.27 to +2.23 and TDM values between 0.63 and 0.74 Ga. Additional geochemical variations suggest that the felsic and intermediate rocks of Group 1 are not co-genetic. The felsic extrusive rocks in the Jonob-e-Sechangi area likely formed from the partial melting of the amphibolitic arc crust. In contrast, the high-K calc-alkaline andesitic rocks of Group 1 may have originated from low-degree partial melting of a spinel-peridotite mantle source.Group 2 formed basaltic andesite to andesitic rocks at37-40 Ma, showing high-K calc-alkaline to shoshonitic compositions, relatively high 87Sr/86Sri (0.7047- 0.7076) and relatively low ԐNdt (0.48 to-5.86). These geochemical features require magma derivation from a mantle source that is not only elementally but also isotopically enriched, followed by variable fractionation and crustal contamination. The enriched mantle source was most likely resided in the lithosphere and formed by metasomatism by continental crust-derived materials. Clinopyroxene trace elements compositions display marked variations between different magmatic rocks. Clinopyroxene in dacitic samples of Group 1 shows relatively high contents of Sr, Rb, and Ba whereas that in Group 2 rocks has relatively high contents of Sc, V, Ga, Nb, Zr, Hf, Y and rare earth elements (REE). The findings of this study show that the intricate interactions between the lithosphere and asthenosphere, stemming from post-collisional delamination processes following the closure of the Sistan Ocean and the collision of the Lut-Afghan blocks, led to differing levels of partial melting in the region's heterogeneous metasomatized mantle. This phenomenon explains the diverse range of volcanic rocks found not just in the Jonob-e-Sechangi area but also in other regions of the Lut Block.

Petrogenesis of Miocene high Ba–Sr granitoids from the Central Pamir: Implications for continental growth

High Ba–Sr granitoids differ from the I-, S- and A-type granitoids, and their petrogenesis and role in the evolution of the continental crust remain enigmatic. This paper reports a study of whole-rock geochemistry, and Sr–Nd isotopes, zircon U–Pb geochronology, and Lu–Hf isotopes of the Zankan high Ba–Sr intrusion in the Central Pamir. U–Pb dating of zircons suggests that the pluton was emplaced during the Miocene (10.2 ± 0.1 Ma). The Zankan rocks have high contents of K2O (3.83 to 12.3 wt%), Rb (212–483 ppm), Ba (701–6910 ppm), and Sr (503–3371 ppm). They have several geochemical characteristics that are consistent with A-type granitoids, such as high Na2O + K2O (8.10–14.2 wt%) and Zr + Nb + Ce + Y (336–1393 ppm) contents. All samples have enriched Sr–Nd–Hf isotope compositions, with 87Sr/86Sri = 0.7097 to 0.7126, εNd(T) = −9.3 to −8.4, and εHf(T) = −12.2 to −4.0. Their isotopic compositions differ from those of mafic lower crust in the Central Pamir. Alternatively, the Zankan rocks may have been derived from an enriched lithospheric mantle. Combining our new isotopic results with data from the literature, we propose that a shift from isotopically juvenile to more isotopically evolved compositions in mantle-derived magmas took place from the Eocene to Miocene. The isotopic shift reveals that South Pamir lower crust was underthrusted beneath the Central Pamir lithosphere during the Miocene. Although high Ba–Sr granitoids generally exhibit “crust-like” isotopic characteristics, our data indicate that they play a role in continental growth.

Magmatic-hydrothermal evolution of the aquamarine-bearing Yamrang Pegmatite, Eastern Nepal: Insights from beryl, garnet, and tourmaline mineral chemistry

The Ikhabu Pegmatite Field (IPF) in the Nepal Himalaya is a newly discovered rare-element (REL) pegmatite field that hosts the Yamrang pegmatite, the primary source of the famous Nepalese aquamarines. In this contribution, we provide a comprehensive description of the geology of both the IPF and the Yamrang pegmatite, offering insights into the evolutionary stages of the Yamrang pegmatite based on its internal texture and the mineral chemistry of beryl, garnet, and tourmaline. The Yamrang pegmatite is classified as a beryl-columbite subtype of REL pegmatite, exhibiting axial symmetric zonation and is differentiated into five mineralogical-textural zones during magmatic and hydrothermal stages. The magmatic stage involves undercooling, disequilibrium crystallization, and fractional crystallization whereas the hydrothermal stage comprises alkali-enriched fluid exsolution, the formation of miarolitic cavities, and the crystallization of aquamarine. Yamrang aquamarines are enriched in FeO, up to 1.1 wt%, with Fe2+ as the primary chromophore, resulting in their blue color. Two types of beryl have been identified: magmatic beryl in zones 3 and 4 and hydrothermal beryl in miarolitic cavities (zone 5). Magmatic beryls are characterized by their alkali-poor to sodic composition, prismatic to columnar habit, homogeneous texture, and the presence of Fe-Al octahedral substitution. In contrast, hydrothermal beryls belong to the sodic to Li-Cs beryl group, with tabular to acicular habit, weak compositional zoning, and channel-tetrahedral substitution. Yamrang garnet belongs to the almandine-spessartine series, while the tourmalines are Mg-Ca rich dravite-schorl to Fe-Mn rich schorl variety. Alkali-poor to Li-Cs beryl with low REE contents, spessartine garnet (spessartine component, Xsps ∼ 52) with high HREE, and schorl with high Ti but low Li, Pb, and REE contents suggests that the Yamrang Pegmatite is an intermediate-fractionated REL pegmatite. Potential pegmatite evolution indicators for IPF include high alkali, Fe, Mn, and Rb contents in beryl, high Xsps in garnet, and an increase in Li, Fe, Mn, Zn, Ga, and Nb, alongside depletion of Mg, Ca, Ti, and Ta in schorl. The identification of a rare metal pegmatite field in the Nepalese Himalaya reinforces the general rare metal mineralization potential of the entire Himalaya region.

An active molybdenum (polymetallic)-enriching system in foreland basins

Molybdenum (polymetallic)-rich saline brines from the Badain Jaran Desert to the north of the Tibetan Plateau reveal active enrichment of trace metals in the groundwater systems of foreland basins. Molybdenum (polymetallic)-rich brines have salinities of 224–338 g/L and high concentrations of Mo (~3.7 mg/L), Li (~5.8 mg/L), U (~0.65 mg/L), Rb (~2.0 mg/L), Sr (~6.1 mg/L), Mn (~0.62 mg/L), and Ni (~0.52 mg/L). The major ions in the brines are Na+ and Cl−, with small amounts of SO42−. The pH and Eh values are 8.50–8.82 and >200 mV, respectively, with dissolved O contents of >6 mg/L. The δD and δ18O values of these saline brines are −29.2 ‰ to −31.0 ‰ and +0.3 ‰ to +2.8 ‰, respectively, and they exhibit a similar trend to the regional evaporation line, suggesting that the Mo (polymetallic)-rich saline brines originated from evaporation of groundwater in the Badain Jaran Desert. The 3He/4He (R) and R/Ra ratios of the brines are 0.42–2.11 and 0.30–1.51, respectively, and the 38Ar/36Ar and 40Ar/36Ar ratios are 0.194–1.464 and 267.4–360.2, respectively. These results suggest that the Mo-rich saline brines interacted with detrital material in the Badain Jaran Desert and extracted both cosmogenic 3He and radiogenic 4He. We propose that the Mo (polymetallic)-rich saline brines originated from evaporation of groundwater in the Badain Jaran Desert. Regional faults are responsible for the supply of precipitation-derived groundwater to the study area.

Early to Middle Jurassic (ca. 182–164 Ma) fractionated granitoids in the Korean Peninsula: Implication for the tectonomagmatic history of East Asia

The Jurassic granitoids (200–164 Ma) are distributed in the Korean Peninsula due to the Paleo-Pacific plate subduction. Early Jurassic (200–182 Ma) granitoids are mainly distributed in the southern Korean Peninsula. By contrast, Early to Middle Jurassic (182–164 Ma) granitoids are distributed in the central Korean Peninsula. In this study, we report detailed petrology, zircon U–Pb ages, and whole-rock geochemistry from the Seoul–Uijeongbu and Pocheon–Gimhwa pluton units in the central Korean Peninsula. The Seoul–Uijeongbu unit is dominated by biotite granite, with minor porphyritic biotite and garnet-biotite granite while the Pocheon–Gimhwa unit consists of biotite granite and porphyritic biotite granite, garnet-biotite granite, and two-mica granite. Zircon U–Pb age from those granites gives 180–167 Ma. The granitoids in the Pocheon-Gimhwa unit formed through fractional crystallization from biotite granite and porphyritic biotite granite to garnet-biotite granite, and two-mica granite based on gradually decreasing their Nb/Ta, Zr/Hf, and Eu/Eu* ratios. The strongly fractionated granitoids are garnet-biotite granite and two-mica granite. The LILE enrichment, Ta–Nb, Sr–P, and Eu–Ti troughs, and Ba depletion in most granitoids are similar to those of granitoids due to the subduction in the arc environment. Thus, these Jurassic granitoids (180–167 Ma) are mainly peraluminous granites with moderate crystal fractionation corresponding to I-type granite. Alkali feldspar granite associated with ore mineralization occurs in the Gwanaksan pluton from the southwestern Seoul–Uijeongbu unit. The alkali feldspar granite displays distinct negative Eu anomaly with high contents of Rb, Hf, Cs, and Nb compared with other granites. These characteristics imply that alkali feldspar granite experienced strong hydrothermal activity leading to feldspar ore mineralization compared to the other granites. The formation of a wide range of moderately evolved peraluminous granitoids is presumed to be related to rapid flat-subduction during 182–164 Ma, and the mineralization-related alkali feldspar granite indicates the termination of Jurassic granitoid magmatism in the central Korean Peninsula.

Petrological, geochemical and geodynamic evolution of the Wadi Al-Baroud granitoids, north Arabian-Nubian shield, Egypt

The Wadi Al-Baroud area, in Egypt's Eastern Desert, exposes Neoproterozoic rocks of the Arabian-Nubian Shield (ANS), including both syntectonic granitoids (granodiorite and tonalite) and post-collisional granites. We present field work, petrographic study, mineral compositions, and whole-rock geochemistry results from these granitoids and discuss their petrogenesis, magmatic sources, evolution, and tectonic significance. The syntectonic granitoids show subduction affinity and an anomalous steep trend of K-enrichment that suggests assimilation of a granitic component during their evolution. The post-collisional granites form two plutons, on opposite sides of Wadi Al-Baroud, named here the Ras Baroud pluton (RBP) and the Abu Hawis pluton (AHP). They intruded the syntectonic granitoids with sharp intrusive contacts. The post-collisional plutons are devoid of mafic enclaves and are cut by very few dikes. They dominantly consist of biotite monzogranite that grades into muscovite monzogranite. The latter lithology hosts Nb-Ta oxide minerals (columbite, tantalite, and wodginite) displaying a variety of textural and compositional features. The cores are primary columbite-(Mn), whereas rims are overgrown or partly replaced by tantalite-(Fe) and wodginite due to late interactions with highly fractionated residual melt. The highly-evolved AHP and RBP granites are typical of the post-collisional granitoids of the ANS, including high concentrations of rare earth elements (REE), Ta, Hf, Nb, Zr, Y, and Rb; elevated ratios of Ga/Al; and low contents of Sr, CaO, and MgO. Their geochemistry suggests that the parental magma of both plutons formed from an I-type tonalitic source rock that underwent partial melting during the thermal disturbance that followed a lithospheric delamination event during the post-collisional stage of the East African Orogeny. The variations in major oxide and trace element contents among individual samples of the AHP and the RBP cannot be explained as a liquid line of descent due to fractional crystallization; rather we interpret them as sampling variable proportions of an evolved liquid and the solid crystals in equilibrium with that liquid.

Magma Composition and Formation Conditions of Alkaline-Salic Rocks of the Early Mesozoic Adaatsag Bimodal Association of the Kharkhorin Rift Zone, Central Asia: Data from the Study of Melt Inclusions in Minerals

The composition and formation conditions of magmas of comendites of the Early Mesozoic Adaatsag volcanic association are determined using electron and ion microprobe analysis of melt inclusions, and mechanisms favorable for the accumulation of trace and rare earth elements are identified. The melt and fluid inclusions are found in quartz of comendites sampled in various parts of the section of a volcanic sequence. The melt inclusions consist of glass, a gas bubble, and daughter minerals (fluorite, polylithionite, and K-feldspar). The composition of a gas phase in melt inclusions was studied using Raman spectroscopy. The dominant gas phase components include water and hydrogen. The fluid inclusions are aqueous fluids probably corresponding to KF. The thermometric studies of melt inclusions and the analysis of glasses of homogenized melt inclusions in quartz phenocrysts of comendites showed that magmas crystallized from water-saturated rare metal melts with high Li, Zr, F, Rb, Nb, Y, and Th contents at a temperature of 880–930°C and a pressure of 1000 bar at a depth of ~3.5 km accompanied by degassing. The comparison of our data of the study of melt inclusions in phenocrysts of alkaline salic rocks of the coeval Adaatsag, Dzarta-Khuduk, and Sant volcanic associations, which occur within the Kharkhorin Rift Zone, revealed common principles of magma evolution. This allowed us to propose a similar mechanism of their formation, involving the accumulation of many rare and rare-earth elements, as well as volatile components (F, H2O) in the process of crystallization differentiation. Subsequently, a salt melt rich in Li, F and water could be separated from such comendite magmas. The detection of fluoride aqueous inclusions in quartz allows us to suppose the further evolution of the salt melt leading to the appearance of a concentrated aqueous fluid and the possible participation of the latter in metasomatic processes.

Two Distinct Fractional Crystallization Mechanisms of A-Type Granites in the Nanling Range, South China: A Case Study of the Jiuyishan Complex Massif and Xianghualing Intrusive Stocks

The petrogenesis of A-type granites with different occurrences in the Nanling Range remains unclear. In this study, a case study of the Jiuyishan complex massif and Xianghualing intrusive stocks was conducted to determine this problem. The Jiuyishan complex massif is composed of four units (Jinjiling, Pangxiemu, Shaziling and Xishan). These four units have similar zircon U-Pb ages of approximately 153 Ma, with high Zr + Nb + Ce + Y contents (>350 ppm), high 10,000 Ga/Al ratios (>2.6), and a high crystallization temperature, indicating A-type affinities. They show a gradual change in lithology and geochemistry, implying a fractional crystallization process. These units also have similar εNd(t) values (−8.2 to −5.8) and zircon εHf(t) values (−7.5 to −2.2) except for the Shaziling MMEs (mafic microgranular enclaves) (−14.2 to 4.8), demonstrating their lower crustal source. However, the Shaziling unit may have contributed mantle-derived magma based on the geochemical data of its hosted MMEs. In comparison, the two Xianghualing intrusive stocks have similar geochemical features but exhibit highly evolved features (high Rb, U, Y, Ta and Nb contents and low Eu, Ba, Sr, P, Ti, Ca, Mg and Fe contents, with V-shaped REE distribution patterns). They have different zircon U-Pb ages of approximately 160 Ma and 155 Ma. The two stocks also have similar whole-rock εNd(t) values (−6.5 to −5.7) and zircon εHf(t) values (−7.6 to −2.7) and equally illustrate a lower crustal source region. Combining with their vertical zonation, they may have experienced remarkable fractional crystallization with possible assimilation processes. We propose that the Jiuyishan complex and Xianghualing stocks have two distinct fractional crystallization mechanisms during their formation. The Jiuyishan complex was formed by in situ crystal mush fractionation, while the Xianghualing stocks were formed by flowage differentiation during magma ascent or gravitational settling during magma solidification after emplacement. However, more than one mechanism affected the fractional crystallization processes of these granitic rocks.

Formation and evolution of multistage hydrothermal fluids in the Baishitouwa quartz–wolframite vein‐type deposit in the southern Great Xing'an Range tungsten belt, NE China: Constraints from individual fluid inclusion LA‐ICP‐MS analysis

Revealing hydrothermal evolution from the early oxide to late carbonate stages for quartz–wolframite vein‐type deposits is essential for understanding the ore‐forming process. In this study, we choose the Baishitouwa tungsten polymetallic deposit located in the southern Great Xing'an Range tungsten belt as a case study, and present detailed deposit geology and in situ fluid inclusion (FI) analyses including microthermometry, laser Raman spectra, and LA‐ICP‐MS microanalysis to address this issue. Four stages of hydrothermal activity were identified: (1) quartz–wolframite (I), (2) quartz–wolframite (II)–pyrite–chalcopyrite, (3) quartz–polymetallic sulphides, and (4) quartz–carbonate. Four types of FIs were recognized: CO2‐rich, CO2‐bearing, liquid‐rich, and brine inclusions. Microthermometric data showed that the homogenization temperatures and salinities from the early to late stages are 380–460°C, 7.4–17.3, and 29.3–43.2 wt% NaCl equiv., 300–390°C and 7.1–17.0 wt% NaCl equiv., 220–320°C and 2.7–8.1 wt% NaCl equiv., and 150–250°C and 0.5–4.8 wt% NaCl equiv., respectively, suggesting a decreasing trend. Geochemically, all stage fluids contained high Rb and Mn concentrations, high Rb/Na, Cs/Na, Li/Na, K/Na, Rb/Sr, low K/Rb, and consistent Cs/Rb and Cs/(Na + K) ratios, indicating that the mineralizing fluids originated from a common source—an underlying, geochemically uniform, and highly fractionated granitic magma. Fluid immiscibility and cooling are the main mechanisms for wolframite precipitation, whereas greisenization is subordinate; the incursion of meteoric water into the hydrothermal system initiated at the sulphide stage, and fluid mixing is the dominant mechanism for sulphide precipitation.

MAGMA COMPOSITION AND FORMATION CONDITIONS OF ALKALI-SALIC ROCKS OF THE EARLY MESOZOIC ADAATSAG BIMODAL ASSOCIATION OF THE KHARKHORIN RIFT ZONE OF CENTRAL ASIA (DATA FROM THE STUDY OF MELT INCLUSIONS IN MINERALS)

Based on the method of investigation of melt inclusions using electron and ion microprobe, the magma composition and formation conditions of comendites of the Early Mesozoic Adaatsag volcanic association (Mongolia) were studied. The mechanisms leading to the accumulation of rare and rare earth elements in them were determined. Melt and fluid inclusions are found in quartz from the comendites, collected from different parts of the volcanic sequence. The melt inclusions consist of glass, a gas bubble and daughter minerals represented by fluorite, polylithionite and potassium feldspar. The use of the Raman spectroscopy method made it possible to study the composition of the gas phase in melt inclusions. It is determined that the predominant components of the gas phase are water and hydrogen. Fluid inclusions are represented by aqueous solutions that correspond to KF in composition. The concentration of KF in the solution reach up to 4.0–4.1 wt. %. Thermometric experiments with melt inclusions and analysis of the composition of glasses of homogenized melt inclusions in quartz of the comendites showed that the crystallization of magmas of these rocks occurred from water-saturated rare-metal melts with high contents of Li, Zr, F, Rb, Nb, Y and Th at temperatures of 880–930°C and at a pressure of 1000 bar at a depth of ~3.5 km and was accompanied by degassing processes. Comparison of the obtained data on the study of melt inclusions in the phenocrysts of the alkali-salic rocks of the same age volcanic associations Adaatsag, Dzarta-Кhuduk and Sant, developed within the Kharkhorin rift zone, revealed general patterns of their magma evolution. This allowed us to propose a similar mechanism of their formation, involving the accumulation of many rare and rare-earth elements, as well as volatile components (F, H2O) in the process of crystallization differentiation. Subsequently, a salt melt rich in Li, F and water could be separated from such comendite magmas. The detection of fluoride aqueous inclusions in quartz allows us to suppose the further evolution of the salt melt leading to the appearance of a concentrated aqueous fluid and the possible participation of the latter in metasomatic processes.

Hydrogeochemical Characteristics and Isotopic Tools Used to Identify the Mineralization Processes of Bottled Mineral Water in Morocco

Bottled waters are among the most important products in the human diet. In Morocco, eleven bottled mineral waters were analyzed (physicochemical composition and water stable isotopes) to identify their geologic origins and hydrochemical characteristics. The study of the ionic ratios shows that the mechanisms of water–rock interaction, such as the dissolution of carbonate and silicate minerals, influence the chemistry of these mineral waters, which are controlled by lithology and tectonics, sometimes with the influence of deep flux through fractures. The water from the Oulmes plateau shows a Na-HCO3 chemical facies in relationship with alkaline granite. Moreover, the carbonated waters (EMG and EMGL) are characterized by high concentrations of Si, Li, Rb, Sr, and Cs due to deep CO2 flux origin. The waters of Saiss, Middle Atlas, and Rif are of the Ca-HCO3 type linked mainly to carbonate formation. The stable isotope contents of water range from −7.74 to −5.35‰ for δ18O and −45.4 to −30.4‰ for δD. The recharge altitude of the aquifer was estimated to be between 250 and 1200 m, following a δ18O altitudinal gradient between 0.25 and 0.27‰ per 100 m. The industrial production process and the natural presence or artificial addition of CO2 can also influence the isotopic composition of water. These results can be a relevant guide to decision makers for better exploitation and assessment of the water quality.

Genetic significance of trace elements in hydrothermal quartz from the Xiangzhong metallogenic province, South China

Despite the Xiangzhong metallogenic province being globally the most important ore-concentrated area of antimony (Sb) mineralization, the genesis of Sb-(Au-W) deposits in this region is still under debate. In this study, trace element compositions of hydrothermal quartz from four representative Sb-(Au-W) deposits (Xikuangshan, Woxi, Banxi, and Zhazixi) in the Xiangzhong metallogenic province have been investigated to constrain the origin of ore-forming fluids and physiochemical conditions of Sb mineralization. The fsLA-ICP-MS data indicate that Li, B, Na, Al, P, K, and Sb are relatively enriched in quartz, probably mainly incorporated into the quartz crystal lattice, and dominated by the coupled substitution of (Al3+, Sb3+, B3+) + (Li+, Na+, K+, H+) ↔ Si4+ and (Al3+, Sb3+, B3+) + P5+ ↔ 2Si4+. In the Xikuangshan Sb deposit, charge-neutrality conditions of cations reveal that (Al3+, Sb3+) + Li+ ↔ Si4+ is the most important substitution mechanism in quartz from early-stage Sb mineralization (quartz-stibnite veins), whereas (Al3+, Sb3+) + (Li+ + H+) ↔ Si4+ may control the trace element contents in quartz from late-stage Sb mineralization (calcite-quartz-stibnite veins). The relatively high Al content and the low variability in trace element content suggest that quartz from the Xikuangshan Sb deposit may have precipitated from a relatively acidic and stable ore-forming fluid. Combined with the high Sr and Rb contents of quartz, a plausible explanation is that acidic hydrothermal fluids promoted water–rock reaction that dissolved large amounts of Sr and Rb, resulting in the high Al, Rb, and Sr contents in crystallized quartz from the Xikuangshan Sb deposit. In contrast, the relatively low but inhomogeneous Al content indicates that quartz from the Woxi and Banxi Sb-(Au-W) deposits may have precipitated from a less acidic ore-forming fluid and supports the idea of fluid mixing. More importantly, the relatively high contents of Rb, Ge, and Ti in quartz from the Woxi and Banxi Sb-(Au-W) deposits, combined with the low Al and Sr contents, imply that magmatic-hydrothermal systems possibly contributed to the ore-forming fluids. Based on the trace element compositions of quartz, two major types of Sb deposits were identified in the Xiangzhong metallogenic province: the giant Xikuangshan epithermal deposit in which the ore-forming fluids are relatively acidic, stable and have experienced water–rock reaction, generally similar to the Qinglong Sb deposit in the Youjiang metallogenic province. The second type is the orogenic-type deposit represented by the Woxi Sb-Au-W deposit, including the Banxi Sb deposit, where the ore-forming fluids have undergone fluid mixing and relatively weak water–rock reaction, and may have been joined by a small amount of magmatic-hydrothermal fluids. Together with the recently published Sb mineralization ages (149–144 Ma) of the Woxi Sb-Au-W deposit, it supports the idea that this type of Sb deposit is related to the Mesozoic magmatism. The Zhazixi Sb-W deposit shows transitional features between these two types of Sb deposits.

Soil Contamination and Risk Assessments on Selected Dumpsites within the Basement Complex and Sedimentary Formations of Ogun State, South-western Nigeria

The concentrations of inorganic elements in soils of Saje, Ita-Oshin, Premier, and Oke-Diya dumpsites were determined using an X-Ray Fluorescence spectrometer to assess the soil quality through chronological changes with depths. A soil core sampler collects 56 samples at 20, 40, 60, and 80 cm depths. Saje showed high mean concentrations of Ca, K, Fe, Rb, and Ti at all depths, while Oke-Diya revealed high mean concentrations of Ca, K, Fe, Rb, Ti, Mn, Zn, V, Cr, and Ni at all depths. These concentrations were in a closed range suggesting a build-up of elements in the soil profiles. Oke-Diya had the highest pollution index, followed by Saje, and the contaminations were from anthropogenic and geologic sources. The mean concentrations of Fe, Zn, Ni, Mn, Ti, K, and Ca were high at all depths in Ita-Oshin, and in Premier, the mean concentrations of K and Fe were high at all depths. Premier had the lowest pollution index. Ita-Oshin and Premier enrichment factors showed geologic sources. Saje and Oke-Diya revealed unacceptable non-carcinogenic risks for adults and children, and Ita-Oshin and Premier recorded acceptable limits. Saje and Oke-Diya samples had high carcinogenic risks for adults due to Cr, Pb, and As. Elements Cr and As in Ita-Oshin, and Pb in Premier evinced unacceptable carcinogenic risks for adults. Saje, Oke-Diya, and Premier indicated unacceptable carcinogenic risks for children due to Cr. The study showed toxins build-up in the soil system, and the study areas are not suitable for growing crops and sinking water wells for agricultural and domestic uses.