Pegmatite Veins Research Articles

The effect of pegmatite veins on fracture behaviors of granite in a deep large underground cavern

The effect of pegmatite veins on fracture behaviors of granite in a deep large underground cavern

Controls on Corundum Formation: Metasomatism of Ultramafic Rock, Nattavit, South-East Greenland

Abstract The geotectonic setting for plumasite-type corundum occurrences is understudied, even though it is of importance for the understanding of trace-element patterns used for fingerprinting of ruby and sapphire. Mineral reactions related to metasomatism caused by pegmatite intrusion into ultramafic rock result in a characteristic trace element signature in corundum and thereby control its colour. The Nattivit area, Isertoq Terrane, South-East Greenland, provides a natural laboratory to investigate these mineral reactions and corundum trace element patterns given the excellent exposure of a typical plumasite-type occurrence where pegmatites intruded ultramafic rocks of different composition, namely lherzolite and dunite. The pegmatite dykes are 10 to 50 cm wide in the ultramafic rocks, whereas the adjacent alteration zone in the ultramafic rock reaches widths between 10 and 30 cm. Metasomatism resulted in desilication of the pegmatites and a decrease in Ca, Mg, K, Mn, Al and Fe away from the centre of the pegmatite dyke. Chromium, Ni, Mg, Fe, Sc, Co, V, Zn, Ti and Mn in the metasomatic reaction zones are predominantly derived from the ultramafic rock. We identify three zones with different mineral assemblages. In the lherzolite, tschermakite and biotite are formed in the centre of the reaction zone, which is followed by anorthite-rich plagioclase, hercynite, dolomite and ultimately pink corundum that occurs in the most heavily reacted part of the metasomatic reaction zone. The metasomatic reaction zones in the ultramafic rock include an intense reactionzone at direct contact to the pegmatite dyke with biotite and actinolite, and two alteration zones further away from the pegmatite dyke with enstatite, actinolite, anthophyllite, phlogopite, dolomite, sulphide, apatite and chrome-spinel. In the dunite, no biotite formed and hence, corundum contains more Fe, Mg and Ti. The plumasite-type corundum from Nattivit contains more Fe than Cr, which is typical of pink corundum hosted in mafic-ultramafic rocks. The corundum-forming reaction is dated from the pegmatite vein to 1843±4 Ma (U-Pb zircon age), which is coinciding with convergence of the Rae and North Atlantic cratons resulting in the Nagssugtoqidian Orogen. Only syn-tectonic, corundum-normative, peraluminous, calc-alkaline pegmatites of granitic to granodioritic composition that intrude into ultramafic rocks in the upper plate formed corundum in this area. The pegmatites are classified as muscovite class granitic pegmatites and intruded at upper amphibolite facies conditions. These pegmatites possible originated from partial melting of mafic granulite or a subducted oceanic plate. The formation of granitic pegmatites and related corundum mineralization in the upper plate of a collisional orogen described here is comparable to other corundum occurrences, e.g. Polar Urals, and thus is regarded as a typical geotectonic setting for plumasite-type corundum.

Petrography and geochemistry of pegmatite and leucogranite of Ntega-Marangara area, Burundi, in relation to rare metal mineralisation

Abstract The Ntega-Marangara area, part of the Kanyaru supergroup, Western Domain of Karagwe Ankole Belt, hosts numerous pegmatite veins related to the leucogranite. This investigation aims to characterise the granitoids, their alteration products, and rare metal mineralisation potentials. Quartz, plagioclase, microcline, albite, and muscovite are the essential minerals in both the pegmatite and leucogranite. The ΣREE of the pegmatite and leucogranite are 147 and 102 ppm, respectively. The greisen with Rb, Cs, Ta, Li, Nb, and Sn of 5,940, 1,015, >2,500, 130, 1,595, and 671 ppm, respectively, is higher than the corresponding values of 636, 62, 32, 74, 58, and 110 ppm of the kaolinised pegmatites. This enrichment classifies them as lithium–caesium–tantalum pegmatite. The mean K/Rb, K/Cs, and Nb/Ta in the leucogranites are 106.86, 2819.24, and 4.30, pegmatite is 35.33, 469.47, and 3.1, and greisen is 14.05, 82.2, and 0.64, respectively, which suggest that greisenisation due to metasomatic reactions of late hydrothermal activity could have increased the potential for rare metal mineralisation of the altered pegmatite. Pegmatite of Ntega-Marangara area is enriched in LREE relative to HREE with K/Rb ratio <100, indicating a high level of fractionation and mineralisation in Ta–Nb, Sn, and Li in contrast to the leucogranite that is less fractionated and barren.

The structural elements controlling the subsurface mineralization as deduced from the integration of magnetic and self-potential methods, Wadi Khosh El-Daba area, southern Sinai, Egypt

Significant copper mineralization are observed to be associated, in most cases, with some radioactive anomalies related to increased uranium and thorium contents in Southern Sinai, Egypt. These mineralizations are related to intense post-magmatic, structurally controlled hydrothermal activities in many localities. Wadi Khosh El-Daba area is one of these locations which is mainly composed of monzogranites dissected by andesite dyke and pegmatite vein. This work deals with the application of ground magnetic and self-potential methods to establish the magnetic sources governing the mineralization, to interpret the significant trends that affected the study area, and to delineate the mineralized zones. The magnetic data were processed, enhanced and interpreted using advanced techniques, such as the first-order vertical derivative (FVD), the tilt derivative (TD), Euler deconvolution (ED), and source parameter image (SPI). The main structural lineaments/contacts that control the distribution of hydrothermal alterations and mineral distributions are oriented to the NW–SE, NE–SW, and NNW–SSE directions. The self-potential (SP) data show that there are numerous mineralized zones; most of them are distributed mainly along the structural lineaments deduced from the magnetic study. The quantitative interpretation revealed that the mineralized bodies are at shallow depths ranging from 5.6 m to 12.7 m, with half-width from 5 m to 13 m. These bodies are shallow to moderate dipping towards the south and north directions. Based on this study an anomaly map is originated to locate the preferred structural elements that may be controlling the mineralization in the area for further future exploration.

Petrography and Geochemistry of the Farchana-Hadjerhadid Granitoids (Ouaddaï Massif, Eastern Chad)

Work in the Farchana-Hadjerhadid sector is focused on petrography, with the main aim of mapping the geological formations of the eastern Ouaddaï Massif in order to identify petrographic types and gain an understanding of the geodynamic history of this area. The fieldwork showed that the Farchana-Hadjerhadid granitoids consist mainly of granites and diorites and are intersected by numerous pegmatite veins. Microscopic observation shows that the diorite is made up of plagioclase, amphibole, biotite, and quartz. The granite is composed of alkali feldspar, quartz, amphibole, plagioclase, and biotite. The granitoids in the study area are moderately differentiated (SiO2 = 55.62% to 71.67%) and belong to the medium to highly potassic calc-alkaline series. They are ferriferous type I metaluminous granitoids (A/CNK < 1.1). The parent magma was derived from the partial melting of the metabasalts, and the petrographic types evolved by assimilation and fractional crystallization.

Zircon and cassiterite geochronology of Sn-polymetallic pegmatite from the Xianghualing ore field, South China: Implications for multi-stage magmatic-hydrothermal events

The Nanling metallogenic belt (South China) is one of the largest W-Sn polymetallic provinces in the world. The ore bodies are mainly hosted in Triassic-Jurassic granitoids which formed during a complex history of magmatic evolution. Among them, the Laiziling pluton, which forms the northern part of the Xianghualing district, is an example of Sn-polymetallic deposits that underwent multiple Mesozoic episodes. In this study, the first in-situ U-Pb age dating of zircon and cassiterite minerals, trace element, and Lu-Hf isotopic data are reported for Laiziling NYF-type pegmatites. Four types of pegmatites are identified: stock-like pegmatite, vein-type pegmatite, peripheral vein-type pegmatite, and cap/sill-like pegmatite. Zircon LA-ICP-MS U-Pb geochronology of pegmatites yields an age of ~150 Ma, which is consistent with the age of the associated mineralized granitic pluton. Results of cassiterite age dating indicate that the W-Sn mineralization took place at ca. 150 Ma coeval with pegmatite emplacement. Combined with structure and trace element composition, two young ages (i.e., ~130 and 90 Ma) can be identified from pegmatite veins, suggesting that the studied zircon crystals experienced two distinct periods of magmatic-hydrothermal evolution during the Cretaceous (related to Late Yanshanian magmatism). In addition, some zircon grains are obviously enriched in LREE, which is associated with hydrothermal metasomatism. Compared to the narrow range of magmatic zircons, a wide range of inherited zircons (Proterozoic to Paleozoic) are observed in the studied Late Jurassic pegmatite (Pg1 and Pg2b), suggesting that they were incorporated from pre-existing basement rocks during magma ascent and/or emplacement. Furthermore, U-Pb data for 14 disseminated cassiterite grains yield a 206Pb/238U age of 221.5 ± 4.2 Ma, documenting evidence of cassiterite inheritance during melt ascension from country rocks or representing the initial stage of Sn enrichment. The εHf values of magmatic zircons show negative εHf values from −4.4 to −16.6 and their crustal model ages (TDM2) vary between 1328 Ma to 2200 Ma, suggesting the parent magma of the Laiziling pegmatites were derived from partial melting of older crustal components (Proterozoic basement in the Cathaysian Block of South China) and the mixing of mantle materials. This study proposes that multi-stage magmatic-hydrothermal events may have occurred not only in the Xianghualing area but also in the whole Nanling Range, and provides fresh insights into the formation processes of rare metal-bearing pegmatites in South China.

Response characteristics and detectability of pegmatitic rare-metal deposits using different grounded-wire configurations

The differential electrical dipole (DED) and differentially normalized electromagnetic method (DNME) have a stronger transverse magnetic field than the horizontal electric dipole (HED) and, thus, have been successfully used for resource exploration in conductive ocean environments. However, which of these two is more suitable for the exploration of resistive targets on land, such as pegmatite veins and ore-related mafic and ultramafic intrusions in mineral deposits, remains unknown. Thus, we conduct a comparative study of the DED, DNME, and HED based on forward modeling and application to a field survey. The signal amplitude of the horizontal electric field measured using the DED and DNME is substantially weaker than that obtained via the HED with the same source length and transmitting current. The lateral variation in the horizontal electric field response observed via the DNME reflects the change in the shallow electrical structure, indicating the spatial distribution of pegmatite veins, as verified by the 3D simulation results and data obtained in a field survey of pegmatitic rare-metal deposits in Lushi County, China. The DED and DNME exhibit similar abilities for detecting resistive targets. Both methods show higher detectability than HED based on 3D synthetic modeling. Our results indicate that the DNME, with its higher responses and better lateral resolution, is a better choice in field surveys on land than the DED.

A New Insight into the Genesis of Graphite Deposits in Madagascar Using U–Pb Zircon Dating and Electron Microprobe Analysis

Madagascar is globally recognized as an important producer of high-quality flaky graphite. However, current research on graphite deposits in Madagascar remains insufficient. Previous studies have linked the genesis of Madagascan graphite deposits to the metamorphism of sedimentary organic matter. Here, we provide a case study of graphite deposits in Madagascar, combining new data from the Ambahita graphite deposit (AMG) in southern Madagascar with data from the Antanisoa graphite deposit (ANG) in central Madagascar and the Vohitasara graphite deposit (VOG) on the east coast of Madagascar. We note that the mineral assemblages of graphite-bearing rocks in the AMG, ANG, and VOG are not typical of metamorphic mineral assemblages but rather the results of filling and metasomatism by mantle-derived fluids that occurred after peak metamorphism. Electron microprobe analysis indicates that the graphite of the AMG, VOG, and ANG is usually associated with phlogopite or Mg-biotite; the phlogopite shares a common genesis with other widespread phlogopite deposits across Madagascar. We reveal that the distribution of graphite deposits in Madagascar is primarily controlled by ductile shear zones between blocks. Ductile shear zones that extend deep into the mantle can provide an ideal migration channel and architecture for the emplacement of mantle-derived fluids. The graphite mineralization formed no earlier than the peak metamorphism (490 Ma) and no later than the intrusion of pegmatite veins (389 ± 5 Ma). The distribution of graphite deposits, graphite orebody morphologies, mineral associations, and geochemical data suggest that the genesis of graphite deposits in Madagascar is linked to mantle-derived fluid filling rather than the metamorphism of sediments, as previously suggested. These findings have important implications for similar deposits in Madagascar and potentially globally.

The Geology and Mineral Chemistry of Beryl Mineralization, South Eastern Desert, Egypt: A Deeper Insight into Genesis and Distribution

Beryl mineralization in the Nugrus-Sikait domain in the South Eastern Desert (SED) of Egypt occurs as disseminated crystals in granitic pegmatite and quartz, as well as pegmatite veins crosscutting mélange schist and ophiolitic rocks. When granitic pegmatite comes into contact with the ophiolitic rocks, phlogopite and amphibole schists are formed due to K metasomatism. The ophiolitic mélange is intruded by leucogranite and related pegmatite along the NNW to NW Nugrus shear zone. Beryl samples have been collected from Um Sleimat, Madinat Nugrus, Wadi Abu Rusheid, and Wadi Sikait. Major oxides and in situ trace and rare earth elements (REEs) of beryl and associated minerals were analyzed through EPMA and LA-ICP-MS, respectively. The investigated beryl, based on its color and chemical compositions, can be classified into the two following types: pegmatitic beryl (type I) and schist-related beryl (type II). The former is colorless to pale green, and is mainly restricted in pegmatite veins; it is poor in Cr2O3 (up to 0.03 wt%) and MgO (Nil). The latter, deep green in color, is rich in Cr2O3 (up to 0.27 wt%) and MgO (up to 2.71 wt%), and occurs within quartz veins, phlogopite schists, and tremolite schists. The abundant beryl mineralization in phlogopite schists and their related quartz veins suggests that granite and associated pegmatite are the source rocks for the Be-bearing fluids that migrate along the NW-SE trending deep-seated tectonic zone, such as the Nugrus shear zone. Therefore, the formation of beryl in schists is attributed to the interaction of granitic/pegmatitic-derived Be-bearing fluids with serpentinite and gabbro interlayered with mélange schists. Variations in the trace and REE contents of both beryl types (I and II) indicate their two-stage formation from different compositions of Be-rich fluids, where light REEs, Zr, Nb, Ba, and Th decrease from type I beryl to type II. These two phases of beryl could be attributed to the magmatic/hydrothermal fluids associated with the pegmatite emplacement. The early phase of the late-stage magmatic-derived fluids was closely related to magma evolution and pegmatite formation, forming euhedral type I beryl. The late phase of pegmatite-derived fluids was mixed with serpentinite/schist-derived fluids that cause high V and Cr content in type II beryl. The composition of parent magmas of felsic rocks, the high degree of magma fractionation or the late stage melts, fluid compositions (rich in Be, Li, Cs, Rb, K), and alkali metasomatism, as well as the linear NW-SE trending deep-seated shear zone, are all factors possibly influencing beryl mineralization in the SED of Egypt.

Metallogenetic epoch and material source of Be-pegmatite differentiated from biotite granite in Mufushan complex

The Mufushan Complex (MFSC) is a significant rare metal mineralized in the central China district and is renowned for its marked economic value of rare metal deposits. While the main rare metal mineralization (RMM) stage in the MFSC relates to the magmatic event of two-mica monzogranite, the mineralization event related to biotite monzogranite remains unknown. To fill this gap, this study focuses on porphyritic biotite monzogranite and adjacent Be-rich pegmatite samples obtained from Changqing Pegmatite No. 1, which is situated in the southeastern part of the MFSC. We subjected these samples to zircon U–Pb dating and Hf isotope analysis using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) and utilized an electron probe X-ray microanalyzer (EPMA) and LA–ICP–MS to examine the major and trace elements present in the muscovite samples. Our findings revealed precise chronological data for the geological history of Changqing, pinpointing the intrusion age of biotite monzogranite to 145.8 ± 1.1 Ma and the crystallization age of Be-rich pegmatite to 144.9 ± 1.1 Ma, firmly situating these events within the Late Jurassic to Early Cretaceous epoch. Regarding isotopic composition, zircon εHf (t) for granite ranged from −9.29 to −5.09, and their corresponding TDM2 ranged from 1788 to 1520 Ma. Similarly, zircon εHf (t) for pegmatite ranged from −7.89 to −5.47, and their corresponding TDM2 ranged from 1699 to 1544 Ma. These isotopic signatures strongly indicate a shared origin for the initial magma of granite and pegmatite. The partial melting of the thick Lengjiaxi Group tasedimentary strata serves as a material source for RMM. The transition from granite to pegmatite exhibits remarkable constancy in the primary components of muscovite. By examining its geochemical attributes, we observed synchronous decreases in FeO, MgO, SiO2, MnO, Be, Rb, and Cs, coupled with synchronous increases in Nb and Ta contents, along with Ta/Nb values. These findings strongly imply that the Changqing biotite monzogranite and Be-rich pegmatite originate from the continuous differentiation and evolution of a common magmatic source, establishing a clear genetic relationship between them. The MFSC has its origins in three distinct stages of magmatic activity and RMM spanning from 160 Ma to 120 Ma. Considering the distribution patterns of similar pegmatite veins, the metallogenic potential observed during the biotite granite stage may serve as an external indicator of marked mineralization within large batholiths.

Shear zone-hosted hypogene high-grade iron deposit: The Cuité case study

The Cuité iron ore deposit consists of high-grade schistose lenses (>60 wt% Fe) hosted in a tectonic sliver of iron formation associated to mica schist (Serra da Serpentina Group). It is located at the southeastern border of the São Francisco Craton, enclosed by sheared Sthaterian granitoids (Borrachudos Suite), Neoarchean ortogneiss (Guanhães Complex), quartz and pegmatite veins. The iron formation encloses schistose to massive high-grade ore lenses, with a pervasively, continuous to anastomosed schistosity defined by millimetric elongated hematite plates and quartz grains enclosing hematite granoblastic domains. Kenomagnetite/maghemite and martite pseudomorphs (after magnetite) overgrow the foliation and intergrow with granoblastic hematite. Three high-grade iron ore types are identified, according to the fabric and mineralogy of the main iron oxides: lamellar-granular hematitic (LGO), magnetitic (MO), and granular hematitic ore (GO). Intrusive pegmatite bodies related to the swarms of the Eastern Brazilian Province (late Ediacaran to early Cambrian) and to post-collisional Cambrian vents of the Brasiliano Orogeny caused extensive hydrothermal alteration in the country rocks, encompassing recrystallization of the detrital zircon grains from the associated psammopelitic units, which yielded Cambrian ages, formation of kaolinite-rich lenses, and generation of granoblastic ore bodies. The association of intense stretching along foliation and circulation of hydrothermal fluids from pegmatite intrusion is responsible for the ore formation.

The Geology and Geochemistry of Kakafu Pegmatites: An Investigation for Lithium Ore Bearing Minerals (Lepidolite-Spodumene), Pategi North Central Nigeria

The preliminary investigation of the Kakafu pegmatites was conducted, with the aim of carrying out detail geological mapping and geochemical analysis to reveal common field and geochemical features that will lead to understanding the nature of the Kakafu pegmatites, for the purposes of identifying its lithium minerals potential. Geological mapping reveals three lithological units in the area, which includes; muscovite schist, biotite granite and pegmatite veins. Mineral composition observed in the field and as hand specimen are quartz, plagioclase and orthoclase feldspars, muscovite, biotite and tourmaline. Also the two lithium minerals recognized by the investigation; lepidolite and spodumene (kunzite) grades vertically with depth and along the veins in areas where the veins swells. The main lineament features (fractures, joints and folds) observed trends in the NE-SW, NW-SE, N-S and E-W directions, these directions correspond with orientations of the pegmatites in the study area. Geochemical plots of K vs Rb; K/Rb vs Rb; Li2O vs SiO2 and Ca O vs SiO2 show linkages amongst the pegmatites of the study area. Also the plots of A/CNK vs SiO2 and TiO2 vs SiO2 show all the pegmatites samples fall in the fields of S-type and igneous protolith respectively. These linkages amongst the Kakafu pegmatites suggest they are genetically related to one another, and have same origin (igneous protolith). In terms of mineral potential assessment, the plots of A/CNK vs SiO2; Li2O vs SiO2 and REE show that the Kakafu pegmaites are strongly peraluminous and hence potential for lithium ore mineralization. Furthermore, the concentrations of Li2O of Kakafu pegmatites ranges between (0.82-2.27wt%) and averagely all are above 1wt%. This suggests the Kakafu pegmatites to be moderately potential for lithium ore mineralization.

Exploration of suspected magnetite ore minerals in Emure – Ekiti, Southwestern Nigeria using integrated geophysical methods of very low frequency electromagnetic (VLF-EM) and magnetics

Investigation on the occurrence of magnetite ore minerals in Emure – Ekiti, Southwestern Nigeria was carried out by integrating magnetic and very low frequency electromagnetic (VLF-EM) methods on the suspicion that the major part of the magnetite ore being sought lies in the subsurface. Eight traverses in total were established with five traverses occupied in the northeast–southwest direction and the other three in the northwest–southeast direction. Six traverses were established across the exposed part of the pegmatite (magnetite) veins to serve as a control. Inter-station spacing of 1 m was chosen, so as not to miss any significant ore occurrence. The VLF-EM profile is a plot of the real and filtered real components. The KH-filter geophysical software was used to invert real data into a two-dimensional subsurface map that revealed variations in conductivity. The results of the geophysical interpretation for both methods indicate anomalous signatures observed on the exposed section of the pegmatitic veins, which are indicative of magnetite ore. These anomalous signatures align with certain zones along the Tr4 and Tr8 transects. Some of the high magnetic anomalies observed on traverse 5, 6, and 7 coincide with low conductivity suggesting the concentration of minerals such as quartz, microcline, plagioclase, and biotite, which are commonly associated with magnetite. The study has not only enhanced the mapping of the subsurface characterisation of the deposit but also confirms the reliability and suitability of using magnetics and VLF-EM geophysical methods for mapping magnetite deposits.

Gold-bearing quartz veins and associated rocks in the Wawa area, western Nigeria: Insights to their nature from field investigation, petrographic study, and geochemical analysis

This study focused on the Wawa area, a southern extension of the Zuru Schist Belt (ZSB) in Northwestern Nigeria. The ZSB is one of western Nigeria's broadest and least studied schist belts. Information about its full extent, petrological, and geochemical characteristics still needs to be improved. Preliminary field investigations have shown that the Wawa study area possibly hosts orogenic gold deposits. This study carried out field investigation, petrological study, and geochemical analysis to understand and characterize the tectonic setting and possible origin of gold mineralization in the area. In total, 40 rock samples were studied under the microscope and 72 samples were subjected to geochemical analysis, including X-ray fluorescence (for major and trace elements) and X-ray diffraction analyses. The field investigation revealed that the rocks in the area are mainly gneiss, migmatite, amphibolitic rocks, phyllites, granitoids, and intrusive rocks such as quartz veins and pegmatite veins. Gold mineralization is confined to the quartz veins in amphibolitic rocks, and micro veins of pyrite and chalcopyrite are apparent in the amphibolitic rocks as well. The petrological and mineralogical studies showed that quartz is dominant in the samples from the Wawa study area, together with feldspars, mica, and other accessory minerals. The XRF data showed that the rocks underlying the Wawa study area are highly enriched in silica; meanwhile, several trace elements exist in anomalous concentrations compared to the corresponding average elemental values in the upper continental crust and based on several other reports from western Nigeria. The underlying rocks in the study area are mostly peraluminous with few plotting as peralkaline. Gneisses in the area are orthogneisses. The amphibolitic rocks in the area show both tholeiitic and calc–alkaline affinity. The K2O/Al2O3 vs Na2O/Al2O3 discrimination plot suggested that gold-bearing fluids in the area are likely from igneous and sedimentary sources. Despite the new data/information contributed by this study, further geochemical studies within the ZSB are required to fully understand the evolution and origin of gold mineralization in the area.

Mn–Fe-rich genthelvite from pegmatites associated with the Madeira Sn–Nb–Ta deposit, Pitinga, Brazil: new constraints on the magmatic-hydrothermal transition in the albite-enriched granite system

AbstractGenthelvite from pegmatite veins hosted by the albite-enriched granite (ca.1.8 Ga) corresponding to the Sn–Nb–Ta (F, REE, Li, Zr, U, Th) Madeira deposit, Amazonas, Brazil was studied. Genthelvite, the exclusive Be-bearing mineral within the deposit, occurs as massive crystals of up to 4.7 cm in size. Compositions are homogeneous within individual crystals, although there is moderate variation in the overall composition reflecting relatively limited substitutions within the helvine–genthelvite–danalite solid-solution series, with relatively high Zn contents (36.96 to 49.45 wt.% ZnO), lower Mn contents (0.61 to 3.03 wt.% MnO), and variable Fe contents (2.10 to 10.94 wt.% FeO), completing an existing compositional gap in this system. Genthelvite formed in an alkaline and subaluminous environment, under stable conditions within the late-evolved fluids, at relatively high temperature (>400°C), in a reducing environment. The extremely high concentration of fluorine in the magma and the crystallisation of magmatic galena resulted in an effective reduction of H2S fugacity. This resulted in the stabilisation of genthelvite during the transition from the late magmatic to early hydrothermal stages of the albite-enriched granite evolution. The variability in Fe content within genthelvite is associated primarily with localised variations in the mineral assemblage (e.g. the presence of riebeckite and polylithionite). Genthelvite was altered by low-temperature aqueous fluids rich in F which resulted in the incorporation of Fe, Mn, Mg, Pb, Ba, Na, K, U and REE into the Zn2+ structural site and the allocation of excess Si, Al, Ti and P in the IVSi and IVBe structural sites. The substantial content of U and REE substituting for Zn, together with Si substituting for Be, is charge balanced by the presence of vacancies at the A site.

Contrasting sources and enrichment mechanisms in lithium-rich salt lakes: A Li-H-O isotopic and geochemical study from northern Tibetan Plateau

Lithium (Li), a crucial mineral resource for modern high-tech industries, is notably abundant in the northern Tibetan Plateau, primarily within lithium-rich salt lakes. However, the exploration and development of these resources are hindered due to an incomplete understanding of their nature and origin. Here we present results from a comprehensive study on the hydrochemical parameters, whole-rock geochemistry, H-O isotopes, and Li concentrations in surface brine, river water, geothermal springs, and associated rocks from two representative lithium-enriched salt lakes, the Laguo Co (LGC) and Cangmu Co (CMC) in Tibet to understand the genetic mechanisms. Our water-salt balance calculations and H-O isotopic analysis reveal that Li in LGC and CMC primarily originates from the Suomei Zangbo (SMZB, ∼91%) and Donglong Zangbo (DLZB, ∼75%) rivers, respectively. It is estimated that the LGC and CMC took a minimum of 6.0 ka and 3.0 ka to accumulate their current lithium resources, respectively. The distinct geological characteristics reflect evolutionary differences between the two lakes, suggesting diverse lithium sources and enrichment processes. The high lithium ion concentration and light lithium isotope composition in the SMZB river waters indicate the genetic relationship with lithium-enriched geothermal springs in the Tibetan Plateau. Our results suggest that lithium in the LGC originates from lithium-enriched geothermal springs and is primarily supplied through the small-scale SMZB river. In contrast, the formation and evolution of CMC are influenced by the northern Lunggar rifts, receiving a prolonged and stable input from the DLZB, resulting in high lithium concentrations and isotopic values. The absence of lithium-enriched geothermal springs and the prevalence of silicate rocks in the CMC catchment suggest that lithium may be sourced from the weathering of silicate rocks, such as granitic pegmatite veins containing lithium-rich beryl, widely distributed in the upstream area of DLZB. The forward modeling approach, quantifying the contribution fractions of different reservoirs (atmospheric precipitation, silicate, carbonate, and evaporite), indicates that the distinct lithium concentrations in the mainstream (>1 mg/L) and tributaries (<0.1 mg/L) are positively correlated with the ratio of silicate contributions to carbonate contributions, suggesting that dissolved lithium in river waters primarily originates from the weathering and dissolution of silicate rocks. The distinct sources and enrichment mechanisms of lithium in these two salt lakes are attributed to various evolutionary processes, topographical features, hydrological factors, fundamental geological settings, and tectonic histories, despite their spatial proximity. Furthermore, our study highlights the significant role of rivers in the formation of young salt lakes, in addition to geothermal springs.

Geochemistry and Genesis of Magnesium Tourmalines in Jian Forsterite Jade Deposits from Ji’an County, Jilin Province, Northeast China

The Jian forsterite jade, so named because of its enrichment in end-member forsterite, is a new type of jade found in Ji’an County (Jilin Province, Northeast China). Tourmaline is discovered in Jian forsterite jade deposits and is characterized by magnesium enrichment. In this study, three types of magnesium tourmaline were identified from the pegmatite veins (type 1), the contact zone (type 2), and the tourmaline veins in jade (type 3). The results are shown by the main test methods, such as EPMA, Micro-XRF, and LA-ICP-MS. The substitutions of Fe2+−1Mg2+−1, (□Al3+)−1 (Na+Mg2+)−1, (□Al3+2)−1 (Ca2+R2+2)−1, etc. are inferred by the variations in the major element compositions. From type 1 to type 2 tourmaline, the content of Mg, Sr, and Sn gradually increases, the content of Fe, Zn, K, Mn, Sc, Ga, and Co gradually decreases, the content of Ca initially decreases and then increases, and the content of Na initially increases and then decreases. Type 3 tourmaline has significantly higher Si and Al than the first two types, and the content of the remaining elements lies between the above two types. We propose that tourmalines in Jian forsterite jade deposits are typically of hydrothermal origins and are mainly constrained by magnesium, which is related to the contact metasomatic metamorphism of pegmatite-related hydrothermal fluid with the Jian forsterite jade, and the chemical composition of tourmaline indicates the fluid characteristics of gradual serpentinization of Jian forsterite jade.

Appraisal of Water Resources Development Action Plan for Groundwater Recharge in Raghunathapalli Watershed, Jangaon District, Telangana State, India

Water is elixir of life which needs regular assessment for maintaining ecological balance. Micro watershed wise (a few thousand hectares of extent) water resource action plan is need of the hour especially for a hard rock terrain like Raghunathapalli watershed of Jangaon District. Geologically, the area is underlain by Quartzite and Pelitic Schist of Older Metamorphics and Leuco Granite / Grey Alkali FelpsarGranite Terrain (Peninsular Gneissic Complex) belonging to Archeans. The Archeans are intruded at several places by several Pegmatite Veins and Basic Dolerite Dykes. The average annual rainfall of the study area for the past 19 years is 946 mm and that of monsoonal rainfall is 746 mm. In order to do artificial ground water recharge, the study and analysis of parameters that control the ground water recharge is very important for effective ground water recharge. The spatio-temporal variations in rainfall, regional/local distribution in geological formations and geomorphic composition of various units have led to uneven occurrence and distribution of water resources. Different thematic layers like Geology, Geomorphology, Stream Network, Micro Watersheds, Digital Elevation Model, Contours (2m), Base Layers, Soil and Ground Water Potential maps are prepared using Geospatial technologies like Remote Sensing &amp; GIS. Existing Recharge Structures are marked using 1:25,000 scale Survey of India Toposheets and new locations are updated with high resolution satellite imagery. Micro watershed wise Water Balance studies are carried out and Water Resources Development Action Plan is prepared using Ridge to Valley concept with new artificial recharge structures like Check Dams (22), Percolation Tanks (10), Contour Trenches (68Kms), Subsurface Dyke (2), Farm Pond (268), Recharge Pit (179), Recharge Shaft (16), Desilting Tank (24 nos) etc at suitable terrain conditions. Newly proposed locations for constructions of Rainwater harvesting structures in the gap areas will improve the ground water regime and improves the sustainability of wells for agriculture in the drought prone area of Raghunathapalli watershed. Thus Geospatial technologies are cost effective tools for management and conservation of water resources.

Fluid properties and ore-forming process of the giant Jiajika pegmatite Li deposit, western China

The world class Jiajika lithium deposit in the Songpan-Ganze orogenic belt, western China is related to Late Mesozoic S-type granitic pegmatite. More than 500 pegmatite veins have been discovered in the Jiajika deposit and they show well defined zonal mineral pattern, including microcline pegmatite zone (Ⅰ), microcline-albite pegmatite zone (Ⅱ), albite pegmatite zone (III), albite-spodumene pegmatite zone (IV), and albite-lepidolite pegmatite zone (Ⅴ) from the center outward. Pegmatite Li orebodies are primarily hosted in zones III, IV and V. Barren samples of zones I and II were collected from the recent Jiajika Scientific Drilling (JSD) project performed in the years of 2020–2021 and ore samples of zones III, IV and V were collected from outcrop pegmatite veins No. 308, No. 134, and No. 528, respectively. Fluid inclusions in quartz from the Jiajika deposit include intermediate density CO2-bearing inclusions (type A), high density aqueous inclusions (type B), and low density CO2-rich inclusions (type C). Type A inclusions are predominant in zones I and II, whereas coexisting type B and C inclusions are prevailing in zones III, IV and V. Fluid inclusion microthermometry indicates that type A inclusions in zones I and II show homogenization temperatures ranging from 328 to 362 °C and salinities from 1.2 to 4.5 wt%. Type B inclusions and coexisting type C inclusions in the zones III, IV and V show homogenization temperatures of 278 to 336 °C and 301 to 358 °C, respectively. Their salinity values are 8.1 to 11.6 wt% and 0.8 to 3.6 wt%, respectively. The estimated pressures of type A inclusions are 310 to 424 Mpa, and those of immiscible type B and C inclusions are 151 to 239 Mpa. The change of fluid types with decreasing pressure indicates that extensive fluid immiscibility occurred during the formation of Li pegmatite veins in zones III, IV and V. Moreover, the LA-ICP-MS microanalysis demonstrates that chemical composition of fluid inclusions in this deposit is relatively simple, mainly containing Li, Na, K, Rb, Cs, B, and As. Such enrichment of alkaline elements (Li, Na, K, Rb and Cs) and volatile elements (B and As) is a typical geochemical index for lithium pegmatite. We suggest that the high-degree fractionated of parent magma and strong fluid immiscibility promoted the formation of the giant Jiajika Li deposit. This study highlights that immiscible fluid inclusions and strong enrichment of alkaline elements in inclusions can be an excellent tool for explorations of lithium pegmatites like Jiajika.

Mineralogy, petrology and P-T conditions of the spodumene pegmatites and surrounding meta-sediments in Lhozhag, eastern Himalaya

Several giant industrial-grade rare-metal deposits have been discovered in the Himalaya most recently. However, the mechanism of how rare-metals mineralization formed in the prototype of the collisional belt is poorly understood, mainly due to insufficient studies on mineralogy, petrology and emplacement conditions. In this study, we have reported the whole-rock and mineral compositions of spodumene pegmatites, leucogranite, skarns and P-T paths of metapelites from Lhozhag, eastern Himalaya. Four spodumene pegmatite veins were studied that are enriched in lithium, beryllium, cesium and tantalite (Li-Cs-Ta subtype), mainly hosted by minerals of spodumene, petalite, elbaite, lepidolite, zinnwaldite, and margarite. Li-Be margarite is first reported from the Himalaya, and its lithium and beryllium come from the breakdown of spodumene and beryl. The surrounding skarns are enriched in lithium, beryllium, and tin, mainly hosted by minerals of vesuvianite, scapolite and garnet. Petrography and P-T estimates from the andalusite-staurolite phyllites suggest two stages of metamorphism that earlier Barrovian metamorphism was superimposed by Buchan metamorphism at conditions of 3.1 ± 0.3 kbar and 535°C or 580°C (52–56°C/km) during leucogranite emplacement. Combined with zircon and monazite saturation temperatures and conditions of Buchan metamorphism, the leucogranites should have undergone a first-stage isothermal decompression to crystallization conditions at ∼3.1 kbar and 650–720°C and a second-stage isobaric cooling at ∼3.1 kbar. The pegmatite probably underwent a similar P-T evolution supported by the appearance of two-stage growth of spodumene (Spd-1 and Spd-2 + Qz), petalite corona around spodumene, and cymatolite. The leucogranites/pegmatites have emplaced into the surficial Tethyan Himalayan Sequence simultaneously, causing contact metamorphism, skarnization and undercooling, which may have facilitated rare-metals mineralization in the pegmatites and skarns during the emplacement stage. We suggest that the pegmatites and skarns in Lhozhag, eastern Himalaya have enormous potential for rare-metals exploration.