Total REE Contents Research Articles

Ultramafic–mafic and granitoids supra‐subduction magmatism in the southern Ashanti volcanic belt, Ghana: Evidence from geochemistry and Nd isotopes

Geochemical and Nd isotope data are presented for Palaeoproterozoic ultramafic to mafic rocks and granitoids which are associated with volcanic rocks in the southern part of the Ashanti greenstone belts of Ghana. The Prince's Town granitoids display subduction‐zone geochemical features, with some showing signatures similar to high‐SiO2 adakites (HSA). Their initial εNd (2.1 Ga) values range from −1.01 to +2.92, and they have TDM2 of 2.17–2.51 Ga. The gabbros show slightly LREE‐depleted and ‐enriched patterns, Th–U troughs, negative Nb, Zr–Hf and Ti anomalies, spikes in Sr and Pb, have εNd (2.1 Ga) values ranging from −1.23 to +5.23, and TDM2 values from 2.08 to 2.57 Ga. The Ahama ultramafic body is characterized by two groups of pyroxenites. Both groups show LREE enrichment patterns, display Th–U and Nb–Ta troughs, minor or pronounced negative Zr–Hf and Ti anomalies. However, the Group I pyroxenites exhibit minor Ce anomalies and lower total REE contents (28.1–32.8 ppm) whereas Group II pyroxenites show significant negative Ce anomalies and relatively higher total REE contents of 57.1–124 ppm. The pyroxenites show negative initial εNd (2.1 Ga) values (−0.58 to −5.68) and have TDM2 values of 2.52 to 2.75 Ga. The pyroxenitic and gabbroic rocks were most likely originated from a subduction‐related lithospheric mantle. The Aketakyi ultramafic–mafic complex is made up of mainly cumulate dunite, harzburgite, pyroxenites, and gabbro. The rocks display LREE‐depleted to flat patterns with low total REE contents (1.71 to 22.3 ppm) and demonstrate a supra‐subduction affinity. They show high positive initial εNd (2.1 Ga) values (+3.69 to +4.93), and TDM2 values of 1.99 to 2.04 Ga, which suggest that they were derived from depleted mantle magmas and were juvenile at their time of formation. The Nd isotopic data provides evidence for a possible contamination of the juvenile Birimian crust of the southern Ashanti belt by some amount of a pre‐Birimian (or Archaean?) crustal material. The trace element and isotopic signatures as well as the field relations of the studied granitoids and mafic–ultramafic rocks show they were derived through supra‐subduction‐related magmatism during the Palaeoproterozoic.

Petrogenesis and metallogenic significance of multistage granites in Shimensi tungsten polymetallic deposit, Dahutang giant ore field, South China

The Shimensi tungsten polymetallic deposit, situated in the Dahutang ore field, South China, is one of the largest tungsten deposits in the world, with an estimated WO3 reserve of 0.74 million tons. Coarse-grained porphyritic biotite granite (CPBG), fine-grained porphyritic biotite granite (FPBG), fine-grained biotite granite (FBG) and biotite granite porphyry (BGP) are all ore-related, but their diagenetic relationships and contributions to W-Cu-Mo mineralization are still in dispute. LA-ICP-MS monazite U-Pb dating of the CPBG, FPBG, FBG and BGP yield emplacement ages of 147.9 ± 1.1 Ma, 146.4 ± 1.1 Ma, 138.6 ± 0.98 Ma and 142.8 ± 1.7 Ma, respectively. Whole-rock geochemical results indicate that the four granites should be classified as S-type granites, but BGP has distinct features transitional between S- and I-type granites. They were possibly generated by partial melting of upper crustal pelites and basic volcanic rocks with different proportion from the Neoproterozoic Shuangqiaoshan Group in the source. Proportional variation in the magmatic source (clay and basic basalts) induces the change of geochemical compositions of the Shimensi granites. Geochemical characteristics suggest that they were derived from two magma chambers (the CPBG, FPBG and FBG vs. the BGP) and experienced different evolutionary processes and different degree of magmatic differentiation during magmatic evolution. Chondrite-normalized REE patterns for the four granites display low total REE contents, variable and strongly enriched LREE relative to HREE and medium-strong negative Eu anomalies. They are enriched in Rb, Th, U, Ta and depleted in Ba, Nb, Sr, P, Ti. Biotites are iron-rich and aluminum-poor, and can be classified as ferro-biotite (CPBG, FPBG and FBG) and siderophyllite (BGP). The partial melting of tungsten-rich metasediments of the Shuangqiaoshan Group and high degree of fractional crystallization led to enrichment in tungsten in the magma suites. Oxygen fugacities of the CPBG and FPBG declined from early (most above the NNO buffers) to late stages of fractional crystallization (between the NNO and QFM buffers) because of the higher degree of magmatic differentiation in the late stages. In the early stages of fractionation, tungsten accumulated in the residual melts rather than partitioning into accessory minerals. In the late stages, lower oxygen fugacities and high fluorine contents promoted the removal of tungsten from the residual magma into reduced hydrothermal fluids. On the other hand, the FBG and BGP remained constant (above the NNO buffers) over the entire process of crystallization owning to the stable degree of magmatic differentiation, promoting retention of tungsten in the melt and resulting in low grade tungsten mineralization. Tungsten mineralization in the Shimensi deposit is greatly controlled by the redox states of the associated magma. The two porphyritic granites (the CPBG and FPBG) are most likely the main contributors of tungsten, while the FBG and BGP are mainly responsible for copper and molybdenum in the Shimensi deposit. Prolonged multiphase magmatism and prolonged W-Cu-Mo mineralization play important roles in the formation of Shimensi large tungsten polymetallic deposit.

Crustal versus mantle origin of carbonate xenoliths from Kimberley region kimberlites using C-O-Sr-Nd-Pb isotopes and trace element abundances

Carbonate-bearing assemblages in the mantle have been interpreted to be the source for Si-undersaturated, CO2-rich magmas, including kimberlites. However, direct evidence for carbonate in the mantle is rare in the contemporary literature. Here we present petrography, trace element, and C-O-Sr-Nd-Pb isotope composition for a suite of carbonate xenoliths from the Kimberley region kimberlites to ascertain their mantle or crustal origin and gain insight to the potential for the occurrence of carbonate in the mantle. Carbonate xenoliths were found in large kimberlite blocks from the Bultfontein kimberlite and Big Hole region. The xenoliths are characterised by pale green alteration margins made of fine-grained microlites of an unknown mineral as well as spherules surrounded by glassy material. They are generally 1–4 cm in size, coarse-grained (1–2 mm), and comprised entirely of calcite.Carbonate xenoliths from the Bultfontein kimberlite have low total REE concentrations (0.2–4.9 ppm), constant 87Sr/86Sri (0.7047–0.7049) combined with variable ƐNdi (−0.1 to −26.2) and 206Pb/204Pbi, 207Pb/204Pbi, and 208Pb/204Pbi of 16.7–18.8, 15.3–15.6, 36.5–38.4, respectively. Xenoliths from the Big Hole sample have higher 87Sr/86Sri (0.7088–0.7095), lower ƐNdi (−24.5 to −3.8), and 206Pb/204Pbi, 207Pb/204Pbi, and 208Pb/204Pbi of 18.9–19.9, 15.7–15.8, 38.4–38.8, respectively. The δ13C values for both Bultfontein (−5.7 to −6.6‰) and Big Hole (−4.7 to −5.4‰) carbonates are within the typical range expected for mantle-derived carbonate. The δ18O values (15.5–17.5‰) are higher than those of mantle silicate rocks, indicative of late-stage low-temperature interaction with fluids; a common feature of groundmass calcite in the Kimberley kimberlites.The Sr- and C- isotope composition of the Bultfontein xenoliths indicates a mantle origin whereas the Big Hole xenolith Sr- and C-isotopes are more ambiguous. Isotope mixing models are inconsistent with interaction between the host kimberlite and carbonate xenoliths. Correlation between ƐNdi and δ18O values for the Bultfontein xenoliths indicates late-stage interaction with low-temperature fluids, which may also be responsible for the large range in ƐNdi. This in turn indicates that the highest ƐNdi of −0.1 represents the primary carbonate xenolith signature, and this value overlaps typical Group I kimberlites.We discuss two possible origins for the carbonate xenoliths. (1) Carbonate xenoliths from the sub-continental lithospheric mantle (SCLM), where quenched margins and the large range of ƐNdi are related to formation in the mantle. (2) Carbonate xenoliths from an earlier phase of carbonatite magmatism. The similarity of isotope signatures of the Bultfontein carbonates to Group I kimberlite may further suggest a link between kimberlite and carbonatite volcanism such as observed elsewhere in the world.

Tholeiitic basalts of Deccan large igneous province, India: An overview

The Deccan large igneous province (DLIP) of Peninsular India is predominantly composed of tholeiitic basalts with a minor amount of alkaline, carbonatite, and silicic rocks. The tholeiitic basalts of DLIP are enriched in incompatible trace elements and divisible into low‐Ti basalts (TiO2 < 2.5; Ti/Y < 500) and high‐Ti basalts (TiO2 > 2.5; Ti/Y > 500). Despite variable total REE content, both low‐Ti and high‐Ti basalts exhibit almost similar geochemical patterns in the chondrite‐ and primitive‐ mantle‐normalized diagrams. The mantle potential temperature (Tp) of high‐Ti tholeiites estimated at Ca.1368°C, which is consistent with an ambient mantle temperature (1300–1400°C) whereas the Tp of low‐Ti tholeiites is around 1553°C, which indicates its derivation from the mantle plume axis. Extensive assimilation of the crustal components into the ascending plume have masked the nature and compositional characteristics of both high‐ and low‐Ti basalts. The low‐Ti basalts indicate significant contamination with crustal components than the high‐Ti basalts. The geochemical and isotopic compositions indicate the involvement of multiple mantle components. In general, the differentiated tholeiites of DLIP are the products of plume and depleted sections of the mantle with or without contributions from the continental crust. The main phase of Deccan magmatism intensely affected the atmosphere and hydrosphere, which was a possible trigger for the mass extinction event at the K–Pg boundary.

Metacarbonatite rocks from Amesmessa area (In Ouzzal Terrane), Hoggar shield, Algeria

The Hoggar Shield (South Algeria) belongs to the 3,000 km-long Pan-African Trans-Saharan Belt which formed in the Neoproterozoic and Cambrian, between 750 and 545 Ma. At the western part of this shield, carbonate rocks crop out to the north and south of Amesmessa gold deposit. They occur as lensoid bodies and dikes cross-cutting Archean granulitic rocks, and are consistently associated with mafic rocks and syenite. The petrogenesis of the Amesmessa metacarbonate rocks, which have previously been interpreted as marbles of Archean age, are reconsidered in the present study. Within the Amesmessa area, a small volume of carbonate rocks consisting of calcite, biotite, clinopyroxene, hornblende, olivine and apatite, and are spatially associated with ultramafic rocks, are surrounded by granosyenite, pyroxenite and rhyolite. The cross-cutting relationship and other outcrop features of the area indicate that the carbonate rocks are an intrusive phase and younger than the other surrounding Archean rocks. The average total REE concentration in the metacarbonate is up to 5,700 ppm. However the associated rocks; syenite and pyroxenite contain only 60 and 12 ppm, respectively. Sr concentration is also high (>1,390 ppm) which is normally high in carbonatitic rocks and low in limestones. On the basis of available chemical analyses and outcrop evidence, it becomes clear that the Amesmessa carbonate rocks consist of metamorphosed carbonatite.

New U-Pb and Sm-Nd Data and REE Distribution in Sulphides of Paleoproterozoic PGE Layered Intrusions in the Arctic Part of the Fennoscandian Shield

The U-Pb (on zircon) and Sm-Nd analysis is a popular isotope-geochronological tool for estimating the age of rocks from PGE mafic-ultramafic intrusions. Sulphides can be used to study the geochronology of ore processes as well, since they should indicate the time of ore mineralization. Gabbronorite has been sampled from the Passivaara reef at the Penikat layered intrusion (Finland) for U-Pb and Sm-Nd isotope single zircon analyses in order to separate sulphide minerals. The Sm-Nd isotope age of gabbronorite has been dated at 2426 ± 36 Ma; eNd(T) = −1.4 ± 0.4. The Sm-Nd isotope age on sulphides and rock-forming minerals reflects the crystallization time of the ore-bearing gabbronorite from the Passivaara reef of the Penikat layered intrusion. The mass-spectrometer analytical environment and modes of operation have been adjusted to detect REE in sulphide minerals on example of pyrite from the PGE Penikat layered intrusion (Finland) and chalcopyrite from the Talnakh deposit (Norilsk area, Russia) has been estimated. The total REE content in pyrite is ca. 3.5 ppm, which is enough to define the Sm-Nd age of pyrite. The study shows how to use the mineral/chondrite spectra to evaluate the accuracy of the REE analytical results on example of State Standard Sample 2463 (Russia).

Primorskoe Epithermal Ag-Au Deposit (Northeastern Russia): Geological Setting, Mineralogy, Geochemistry, and Ore Formation Conditions

The potentially large Primorskoe epithermal Au-Ag deposit is represented by three areas: the Kholodnyi, Spiridonych, and Teplyi. It is located in the Omsukchan district of Magadan oblast, where mining is carried out at the largely similar Dukat, Lunnoe, Gol’tsovoe, Arylakh, Tidit, Pereval’noe, and other deposits. The deposit under review is located in the Kalalaga volcano-tectonic depression, where ore has been emplaced in a gently dipping sequence of Late Cretaceous ignimbrites and rhyolites more than 700 m in thickness crosscut by numerous intermediate and mafic dykes. According to drilling data, there is a leucocratic granite massif 400–500 m beneath the deposit, which is exposed on the surface in the northeastern part of the ore field. The presence of Bi-bearing galena and matildite, as well as medium- to high-temperature metasomatic facies (epidote and actinolite) and the specific physicochemical conditions of epithermal Ag-Au ore emplacement, attests to the above-intrusion position and the role of granitoids as high-temperature magmatic fluid generators responsible for supplying Bi and heating the host rock. The ore chemistry is quite consistent with its mineral composition. High Mn and Ag; elevated Au; low Cu, Pb, Zn, Sb, As, Bi, and Te; and low total REE concentrations were established, along with negative Eu and positive Ce anomalies. The high Te/Se, Sr/Ba, Y/Ho, and U/Th ratios in the ores are due to their location in the area influenced by the granitoid pluton. The physicochemical parameters of ore emplacement in the Teplyi area are unusual: high temperatures, low salt concentrations, and fluid densities typical of a “dry vapor” environment. The obtained data allow the Primorskoe to be classified as an intermediate sulfidation epithermal deposit. The data discussed below are of practical use for regional metallogenic forecasting, exploration, and economic assessment of epithermal Ag-Au deposits.

Mineralogical and geochemical features of karst bauxites from Poci (western Henan, China), implications for parental affinity and bauxitization

The Poci bauxite deposits in western Henan, China, are hosted in the lower member of Upper Carboniferous Benxi Formation, unconformably overlying upon the paleokarst surface of the Ordovician Majiagou Formation. The orebodies comprise a high-grade bauxite horizon (characterized by the association of diaspore-illite-anatase) and a basal iron-rich horizon (diaspore-goethite-hematite-illite-anatase), sandwiched between the overlying clayey layer (illite-diaspore-goethite-anatase) and the underlying clayey layer (illite-diaspore-microcline-goethite). Geochemical investigations reveal that Rb, Cs, Ba, Cu, Zn are depleted, while B, Ga, Bi, V, Sc, Zr, Hf, Nb, Ta, W, U and Th are enriched in bauxite horizons. B is highly enriched in bauxite ores and clays (contents 176–1061 ppm) and positively associated with SiO2, indicating B is mainly hosted in clay components, e.g. dominantly illite, which are considered a mixture of authigenic minerals transformed from kaolinites during diagenesis and unaltered detrital minerals. Mass change calculations reveal that Hf, Zr, Nb, Ta, U, Th, Sc, Cr, and Ga are stable relative to TiO2 during the bauxitization process, indicating these elements are mainly associated with anatase and diaspore. The bauxite horizons and the underlying clays are more enriched in total REE contents (ΣREEs) and display more intense LREE/HREE fractionation than the overlying clays. Provenance analysis shows that parental materials of Poci bauxites were mainly derived from felsic-dominated igneous rocks along the southern margins of the North China Craton, with minor contribution from siliciclastic sedimentary rocks and argillaceous components of underlying carbonates. A conceptual model is proposed for the formation and evolution of Poci bauxites. Uplift caused by the North Qinling orogenesis along the southwestern margin of NCC led to the formation of karstic topography, allowing aluminum-rich source materials to be transported to the low karst plain and transformed into incipient bauxites under hot and humid tropical conditions. When the platform was submerged, Fe2+ ions were released from Fe/Al oxides/hydroxides under the reducing conditions associated with bacteria activity in an organic-rich environment, and redeposited as pyrites and siderites, generating a high-grade bauxite horizon and an iron-rich bauxite horizon. This marine modification resulted in further aluminum enrichment of bauxite ores.

Landscape evolution and geochemical dispersion of the DeGrussa Cu-Au deposit, Western Australia

Sedimentary systems associated with ore deposits may act as mechanical dispersion agents of pathfinder elements at local and regional scales. The DeGrussa Cu-Au Volcanogenic Massive Sulfide (VMS) deposit (12.4 Mt @ 4.7% Cu and 1.8 g/t Au) was discovered in a deeply weathered landscape in Western Australia. The DeGrussa deposit is geochemically characterized as being enriched in Cu, Zn, Au and Ag, as well as significant enrichments in In, Mo, Se, Te, Bi, As, Cd and Co, and depletions in Nb, Hf, Th, REE, Cr, Ni, V, Sc and Ba. The Cenozoic palaeochannel sedimentary package that overlies the DeGrussa deposit displays elevated Cu, Zn, Au, and Ag concentrations, as well as significant enrichments in Cr, Ni, V, Sc, In, Mo, Se, Te, Bi, As, Cd and Co, and a remarkable depletion in REE.The palaeochannel sedimentary package shows similarities in its chemical signature to the DeGrussa deposit and associated basement rocks. However, due to the complexity of the landscape evolution and weathering impacts, there is uncertainty regarding the source(s) of this anomalous signature. It may represent (1) the geochemical signature of the immediately underlying basement rocks and/or the DeGrussa deposit; (2) concentration related to the weathering intensity experienced by the sediments, (3) concentration related to the cannibalistic nature of the sedimentary system, resulting in the reworking of previous deposits, or (4) a combination of the above. The Cenozoic channel clay deposits display strikingly depleted values of total REE (TREE) content, which has been interpreted to indicate that the palaeochannel clay units were mostly derived from weathering of proximal dolerite, with no mixing with other weathering products. This, in combination with high Mo, In and Se, and elevated Cu, Zn, Au, and Ag concentrations, may represent the relics of the DeGrussa footprint. Chromium Ni, V, and Sc are interpreted as being sourced mainly from the mafic basement units.Despite the geochemical signatures reported, this study has discovered that the metal geochemical footprint observed in the palaeochannel sedimentary package represents the footprint of the DeGrussa deposit. Hence the geochemistry of the transported cover can be used as an efficient tool for mineral exploration in specific landscape contexts, since the cover can preserve key elemental vectors of the mineral deposit and the geochemical signature of the basement rocks.

In-situ elemental and boron isotopic variations of tourmaline from the Sanfang granite, South China: Insights into magmatic-hydrothermal evolution

Tourmaline often occurs in boron-rich granites and its genesis is still in dispute either formed from residual boron-rich silicate melt or from magmatic hydrothermal fluids with or without external fluid involvement. Here, we present a systematic investigation of in-situ major, trace elemental and boron isotopic variations of tourmaline from the Sanfang granite in Guangxi Province of South China, which demonstrate both the magmatic and hydrothermal origin for the formation of the tourmalines. The tourmaline occurs mainly in quartz-tourmaline nodules and tourmaline pegmatitic segregations within the Sanfang granite. Four types of tourmaline are identified: (1) isolated and disseminated tourmaline (Tur-D type) distributed in granite; (2) euhedral and subhedral tourmaline in quartz-tourmaline nodules (Tur-N type); (3) the earlier stage tourmaline (Tur-PE type) in pegmatitic segregations and (4) the later stage tourmaline (Tur-PL type) which replaced the Tur-PE type tourmaline in pegmatitic segregations. All the tourmalines belong to the alkali group representing dravite-schorl solid solution series with the former three types being schorl and the Tur-PL type being dravite. Petrography, chemical discrimination diagrams and Al occupations in the Y-site suggest that the Tur-D, Tur-N and Tur-PE type tourmalines are of magmatic origin and the Tur-PL type tourmalines are of hydrothermal fluid origin. Elemental and boron isotopic composition variations of tourmalines reflect the compositional and environmental evolution from late boron-rich magma to exsolved hydrothermal fluids. Chemical variations from the Tur-D to the Tur-N tourmalines are controlled by magma differentiation. The increase of Mg/(Mg + Fe) and Ca/(Ca + Na) ratios from the Tur-N to the Tur-PE tourmalines suggests the contamination of surrounding strata (e.g. the Sibao Group). Hydrothermal tourmalines have higher Mg/(Mg + Fe) and lower Na/(Na + Ca) ratios than the magmatic tourmalines. There is clear correlation at least in some trace elements (e.g. Sr, Pb) with major elements for all tourmalines, indicating the potential crystal chemical effects on their incorporation. Other trace element incorporation in tourmaline is largely controlled by melt and fluid composition. Hydrothermal tourmalines have high and stable V, Co and Ni contents, indicating relatively constant partition coefficient between hydrothermal tourmalines and the fluid. Hydrothermal tourmalines exhibit lower total REE contents but more pronounced positive Eu anomalies than the magmatic tourmalines. The δ11B values of all tourmalines from the Sanfang granite vary from −14.4‰ to −9.3‰, which indicate the boron in the Sanfang granite was mainly derived from partial melting of the metasedimentary source rocks. Boron isotopic variations of tourmaline are controlled by fractionation between melt-fluid and Rayleigh fractionation.

Mineralogy and geochemistry of recent alluvial sediments from the Ngaye River watershed, northern Cameroon: Implications for the surface processes and Au-PGE distribution

In this work, six vertical sequences were selected to understand the petrological features of recent alluvial sediments as well as Au-PGE distribution in heavy mineral concentrates from two terraces of Ngaye River watershed in Northern Cameroon, using mineralogical (XRD) and geochemical (XRF and ICP-MS) instruments. The Ngaye River watershed is located in the tropical region with contrasted seasons. The lithotypes are mainly made up of gneisses, granites, and amphibolites with different textures. Granites contain high average contents (n = 7) in SiO2 (69.54 wt.%), Al2O3 (15.21 wt.%), Na2O (4.39 wt.%) and K2O (2.00 wt.%) contrary to gneisses with moderate average contents (n = 7) in SiO2 (64.32 wt.%), Al2O3 (15.75 wt.%), Fe2O3 (5.03 wt.%), CaO (4.45 wt.%), and MgO (2.79 wt.%). Several major element contents are higher in gneisses than amphibolites except for Fe2O3 (11.38 wt.%), CaO (8.63 wt.%), and MgO (6.41 wt.%). Amphibolites (n = 7) are more enriched in Cr, V, Ni, Zn, and Co whereas granites exceed in Ba, Sr, and Rb. Ngaye rocks have moderate REE content (75–122 ppm) with variable LREE/HREE values (5.88–18.83). The alluvial sediments are mainly clayey sandy and are made up of abundant quartz associated to smectite, kaolinite, feldspars, illite, and accessory rutile, amphibole, olivine, pyroxene, ilmenite, and goethite. The occurrence of olivine in one the sequences approves the occurrence of basalts in the watershed. The SiO2 contents range from 55 to 83.41 wt.%, the contents of this oxide show an increasing tendency while those of Al2O3, Fe2O3, MgO, TiO2, and LOI decrease. Several oxides are negatively correlated with SiO2; this confirms the high proportion of silicate minerals and different weathering of source rocks (ICV ∼0.77–0.96; CIA ∼59–80%; PIA ∼64–83%). These sediments are also highlighted by high contents in Ba, Zn, and Sr, and moderate contents in transition trace metals (Cr, V, Ni, and Zr) which confirm the felsic nature of the source rocks. Meanwhile, selected trace elements correlate negatively with SiO2 and explain the low contents in trace elements. The total REE content is twofold high compared to the lithotypes but the LREE/HREE values show similar trend like those of the rocks. The spider diagrams display (i) homogeneity of patterns; (ii) negative anomalies in U, Nb, and P; (iii) and slight positive Zr anomalies. Chondrite-normalized REE patterns exhibit negative Eu anomalies (Eu/Eu∗ = 0.56–0.89) contrary to the PAAS normalization (Eu/Eu∗ = 1.25–1.37). The total Au-PGE contents are very low (1.49–3.94 ppb) in the heavy mineral concentrates contrary to slightly higher contents in Ngaye amphibolites (8.43 ppb). Despite the low contents, the heavy mineral concentrates are richer in PPGE, particularly in Pd and Pt. This geochemical survey has revealed that further alluvial Au-PGE exploration may not be necessary.

Early Paleoproterozoic (ca. 2.36 Ga) post-collisional granitoids in Yunnan, SW China: Implications for linkage between Yangtze and Laurentia in the Columbia supercontinent

The early Paleoproterozoic is an essential period for understanding the early tectonic evolution of the Yangtze Block and its reconstruction in the Columbia supercontinent, whereas these issues are largely unknown due to the scarce preservation of early Paleoproterozoic geological records. This study presents rarely reported early Paleoproterozoic granitoids from the southwestern Yangtze Block, with integrated studies of zircon U-Pb ages, Lu-Hf isotopic compositions and whole-rock geochemistry. Magmatic zircon U-Pb dating for two monzogranite samples yields weighted mean 207Pb/206Pb ages of 2359 ± 16 Ma and 2363 ± 16 Ma, providing unambiguous evidence for the presence of early Paleoproterozoic magmatism in the Yangtze Block. All the samples have high A/CNK values of 1.30–1.61, typical of S-type granite. These rocks have low total REE contents of 72.5–139.0 ppm with marked enrichment in LREEs ((La/Yb)N = 10.73–23.83) and conspicuously negative Eu anomalies (Eu/Eu* = 0.46–0.55). The rocks exhibit uniform primitive mantle-normalized trace element patterns with enrichment in Rb, Th, U and Pb and depletion in Sr, Nb, Hf and Ti. These dated zircon grains have consistent negative εHf(t) values of −6.2 to −2.8 and TDM2 ages of ca. 2.97–3.16 Ga, indicative of Mesoarchean crustal materials as their magma source. Considering the existence of the ca. 2.36 Ga regional high-grade tectono-metamorphic event, we propose that the ca. 2.36 Ga monzogranites were most likely generated in the early stage of post-collisional extension. Therefore, the southwestern Yangtze Block likely experienced a collision event during ca. 2.40–2.36 Ga, indicative of the involvement of the Yangtze Block in the ca. 2.5–2.3 Ga Arrowsmith orogeny of Laurentia. In addition, a series of accretionary events might also have occurred in the western Yangtze Block before the final assembly of the Columbia supercontinent, implying a tight spatial connection between the Yangtze Block and northwestern Laurentia within this global-scale supercontinent.

Geochemical evidence for K-metasomatism related to uranium enrichment in Daejeon granitic rocks near the central Ogcheon Metamorphic Belt, Korea

A new type of uranium occurrence in Korea was identified in pegmatitic and hydrothermally altered granite in the Daejeon area. The U-bearing parts typically include muscovite, pink-feldspar and sericite as alteration minerals. In this study, the geochemical characteristics and alteration age of the granitic rocks were examined to provide evidence for hydrothermally-enriched uranium. The K-Ar ages of muscovite coexisting with U-bearing minerals were determined as 123 and 128 Ma. The U-bearing rocks have relatively low (CaO + Na2O), high K2O contents, and high alteration index values by major element geochemistry. The trace element geochemistry shows that the uraniferous rocks have significantly low Th/U ratios and strongly differentiated features. The rare earth element patterns indicate that the uraniferous rocks have a low total REE and LREE contents with depletion of Eu. Considering the geochemical variation of the granitic rock major, trace and rare earth elements, it can be concluded that uranium enrichment in pegmatites and altered granite should be genetically related to post-magmatic hydrothermal alteration of K-metasomatism after emplacement of the two-mica granite. This is the first report for geochemical characteristics of Mesozoic granite-related U-occurrences in South Korea. This study will help further research for uranium deposits with similarities in geological setting, mineralogy and age data between South China and Korea, and can also be expected to help solve the source problems related to high uranium concentrations in some groundwater occurring in the granitic terrane.

Composition and U—Pb ages of apatite in the Amba Dongar carbonatite–alkaline complex, India

AbstractThe Amba Dongar carbonatite‐alkaline complex is regarded as a late phase intrusion (ca. 65 Ma) associated with Deccan volcanism. Existing age constraints on the Amba Dongar carbonatite are based on phlogopite 40Ar–39Ar plateau ages derived from carbonatite and associated alkaline rocks within the complex. We explore the utility of apatite, a common accessory mineral in Amba Dongar carbonatites, as a petrogenetic and geochronological tool to constrain further the evolution of the carbonatites. Apatite exhibits different crystal forms—from hexagonal stubby prisms to ovoid and elongate grains. Apatite occurs as cumulate and disseminated grains that are either primary, fractured, or recrystallized. SrO content is high in primary apatite (3.17 wt%) but less in recrystallized (1.90 wt%) and disseminated grains (0.47 wt%). MnO and Cl are negligible while FeO is typically low in all samples. SiO2 content is low except for a few primary grains which measure up to 1.35 wt%, correlating with high REE content. LREEs dominate the total REE budget of Amba Dongar apatite, with HREEs below EPMA detection limit in most samples. Total REE content is generally low, though some primary apatite contains up to 3.19 wt% REEs. We also report UPb apatite ages from the carbonatites analysed in situ by LA‐ICP‐MS. The data from all samples combined on a UPb Tera–Wasserburg concordia yield a lower intercept age of 65.4 ± 2.5 Ma (MSWD = 2.8, 207Pb/206Pbi = 0.8272 ± 0.0028), and the Amba Dongar carbonatites are thus interpreted to represent a phase of coeval magmatic activity with Deccan volcanism.

Petrogenesis of Triassic granite from the Jintan pluton in Central Jiangxi Province, South China: implication for uranium enrichment

Numerous Triassic biotite granites and two-mica granites crop out in the interior of South China, and some of them possess high U contents, which have been regarded as the sources for later hydrothermal mineralization. Their petrogenesis is therefore crucial for constraining the possible origins of the U enrichment. Here we report new LA-ICPMS zircon UPb ages, mineral geochemistry of biotite and muscovite, whole rock geochemical results and SrNd and zircon Hf isotope data from the Jintan pluton in Central Jiangxi Province, South China. LA-ICPMS zircon UPb dating indicates that both biotite granite (BG) and two-mica granite (TMG) in the Jintan pluton crystallized at ~220 Ma. The TMG have higher U contents (7.85 to 48.90 ppm, average18.44 ppm) than theBG (4.99 to 17.72 ppm, average 8.64 ppm). Both BG and TMG show negative whole-rock εNd(t)and zircon εHf(t)values and contain some inherited zircons. The TMG are strongly peraluminous (A/CNK = 1.13–1.33), contain abundant primary muscovite, and display S-type affinity on plots of Yvs Rb and Th vs Rb, suggesting that they are S-type granites. The BG also display S-type granite affinities on plots of Yvs Rb and Th vs Rb. The suites display similar SrNd isotope compositions (BG initial 87Sr/86Sr values = 0.711389 to 0.714225 and εNd(t) = −9.91 to −9.16, TMG initial 87Sr/86Sr values = 0.711832 and εNd(t) = −10.02) and are spatially associated, suggesting that the BG should also be classified as S-type granites. The TMG have higher zircon εHf(t)values (−6.4 to −1.1) than the BG (−8.7 to −3.7), indicating the TMG and BG might be derived from similar sediments but possibly with some distinct characteristics in their sources. The BG exhibit linear covariations in chemical compositions with relatively high total REE and light REE contents and MgO contents, while the TMG displays broader compositional variations but with relatively low total REE, light REE and MgO contents. Biotite geochemistry indicates the TMG formed in a more reduced magmatic system than the BG. The temperatures estimated by zircon saturation thermometry indicate the BG had distinctly higher magmatic temperatures than the TMG. The TMG display relatively high Al2O3/TiO2 ratios and low CaO/Na2O ratios than the BG but have higher Sr/Y and La/Yb ratios. The geochemical and petrological data suggest the BG were derived from clay-poor psammite sources at deeper levels with higher temperatures and higher oxygen fugacity, and underwent an extensive fractional crystallization, while the TMG was derived from clay-rich pelitic sources at higher levels and lower temperatures and oxygen fugacity with only limited fractional crystallization. We conclude that the combination of U-rich sources, physical-chemical conditions such as low partial melting temperature or low degrees of partial melting, a reduced environment and low REE and LREE contents of magmas controlled the U enrichment in TMG.

Geochemical features of the Menteşe Formation dolostones (Rhaetian) in the Karacahisar-Kasımlar area (Isparta-Turkey)

The purpose of this study is to determine the geochemical characteristics of the Mentese dolostones (Rhaetian) in the west Taurus Mountains, Turkey. The isotope characteristics of the Mentese dolostones show a variation in the δ18O values of the dolomites between + 1.35 and − 2.72‰ (VPDB) and a variation in the δ13C values of the dolomites between + 1.6 and + 3.33‰ (VPDB). Most of the Mentese dolostone samples have positive oxygen isotope values; others have weak negative isotope values, which indicate early diagenetic development. In addition, oxygen, carbon, and strontium isotopes and trace element analyses suggest that these dolostones were probably resulted from insignificant recrystallizaion process than chemically similar fluids. Furthermore, Mn/Sr values of the Mentese dolostones indicate that there is no significant diagenetic alteration. The total REE contents of the Mentese Formation dolostones display a strong positive correlation with Si, Al, Fe, K, Ti, Ba, Rb and negative correlation with Mg, hence REE content is associated with in the first degree titanium-bearing minerals (probably sphene, rutile, anatase), second degree phosphate (apatite), and barium and rubidium-bearing minerals (probably barite). Ce anomalies versus Nd concentrations of the Mentese dolostone samples indicate that these dolostones are formed in an anoxic environment. In addition, the K/Rb ratios of the Mentese dolostones are not exposed to any metamorphism and indicate some diagenetic alteration. Calculated temperature values using δ18O values of the Mentese dolostones yield precipitation temperatures of 17 to 42 °C, and suggest burial depths of 67 to 900 m. Sources of magnesium for dolomitization of the Mentese Formation carbonates were most likely fluids from seawater and/or diagenetic brines (slightly modified seawater). The Mentese dolostones formed as early diagenetic (Rhaetian to Cenomanian) in shallow burial areas at lower temperatures than seawater and/or diagenetic brines (slightly modified seawater).

Genesis of Permian sedimentary manganese deposits in Zunyi, Guizhou Province, SW China: Constraints from geology and elemental geochemistry

The Permian was a key period of manganese deposition in Southern China, as evidenced by a series of large-to medium-scale manganese deposits along the margin of the Yangtze Block. This study characterizes representative examples that occur in late Middle Permian silicon–mud–limestones in Zunyi and adjacent areas and examines their implications for manganese deposit genesis and sedimentary environment. The manganese deposits are typical carbonates deposits, with the main manganese-bearing mineral being rhodochrosite, followed by calcimangite, capillitite, manganocalcite, and kutnohorite in decreasing abundance. The ore bodies, hosted in the black shale series of the Late Permian Maokou Formation, are mainly stratiform or stratoid in shape, usually have lamellar, massive, banded, fragmental, or pisolitic structures, and contain paragenetic gangue minerals including rutile, barite, pyrite, and chalcopyrite, etc. These features are characteristic of hydrothermal exhalative sedimentary deposits, implying that this was their mode of genesis. The Mn-ores have higher Co, V, Ni, Cu, Sr and total REE content, lower Y/Ho ratios, and characterized by the Fe–Mn–(Cu + Co + Ni) × 10, lgTh vs. lgU, P2O5vs. Y and Fe/Ti vs. Al/(Al + Fe + Mn) diagrams strongly suggest hydrothermal activity during manganese mineralization. The Th/U, V/Cr and V/(V + Ni) ratios of samples from the Zunyi manganese deposits are 0.38–3.27, 3.11–24.00 and 0.38–0.99, respectively, indicating the sedimentary environment was weakly oxidizing to reducing condition.

Origin of the Muguayuan veinlet-disseminated tungsten deposit, South China: Constraints from in-situ trace element analyses of scheelite

The Late Triassic Muguayuan W deposit is located in the middle of the Jiangnan Orogen, South China. This deposit is characterized by veinlet-disseminated W mineralization that developed in the Sanxianba granitic porphyry stock. The ore minerals are mainly scheelite with minor molybdenite and wolframite. Scheelite mineralization was closely related to greisenization and phyllic alteration, and took place in two stages. Stage I involved scheelite ± wolframite ± molybdenite + quartz veinlet and disseminated mineralization, whereas Stage II resulted in scheelite + quartz + sericite veinlet mineralization. Sulfide and quartz + calcite ± pyrite veinlets formed during the post-ore stage. Scheelites from the two mineralization stages have different textures and compositions. Cathodoluminescence (CL) images of Stage I scheelites reveal two generations of growth (I-a and I-b). Stage I-a scheelite is dark under CL with oscillatory zoning, and has light rare earth element (LREE)-enriched chondrite-normalized patterns, negative Eu anomalies, and high total REE contents. Stage I-b scheelite forms rim overgrowths on Stage I-a scheelite, is bright under CL, and shows positive Eu anomalies and relatively low REE contents. Although Stage II scheelites are nearly uniform under CL, they can be subdivided into two generations according to their REE systematics. Stage II-a scheelite yields middle REE (MREE)-enriched chondrite-normalized patterns, with negative Eu anomalies, whereas Stage II-b scheelite has MREE-depleted patterns with positive Eu anomalies. Minor amounts of apatite formed in both stages of mineralization. Stage I apatite contains 1370–1930 ppm Mn and 97.7–127 ppm Sr, whereas Stage II apatite has lower Mn (111–158 ppm) and higher Sr (2170–4690 ppm) concentrations. The distinct trace elements compositions of the scheelite and apatite from the two stages identify two ore-forming fluids that had different origins and compositions. The ore-forming fluids in Stage I-a were relatively reduced magma-derived fluids with high Mo, Mn, Nb, and Ta, and low Sr. Fluid modeling shows that the initial fluids of Stage I-a were LREE-enriched with negative Eu anomalies, similar to the Sanxianba granitic porphyry. Precipitation of early apatite and scheelite, as well as plagioclase decomposition, altered the fluid composition and led to relative depletions in REE, Nb, and Ta, and increases of Eu and Sr in the Stage I-b fluids. Cooling of these fluids and the addition of recycled meteoric water led the fluids to become relatively oxidized and Sr-rich; Stage II scheelite precipitated from these fluids. Precipitation of Stage II-a scheelite resulted in the Stage II-b fluids becoming progressively MREE-depleted. Extensive alteration, especially greisenization and phyllic alteration, led to plagioclase decomposition, which provided the Ca necessary for scheelite mineralization. This process was important in generating the W mineralization in the Muguayuan deposit, and perhaps for other granite-hosted, veinlet-disseminated scheelite deposits in the Jiangnan Orogen.

The effect of the 2013 flood on the rare earth elements content in alluvial soils of the Amur River floodplain

Disastrous flood effect on the content of the total and mobile form of rare earth elements has been studied in the alluvial soil in the middle reach of Amur River. Relationships between rare earth and major element concentrations and soil properties before and after the flood have been revealed. Elements concentration was measured by using ICP–MS.Correlation test used for revealing the interactions between soil properties and REE concentrations. Contents of REE in soils increasing with the distance from the riverbed and heaving of granulometric soil composition. Total contents of REE prior the flood varied from 70 to 170 mg/kg–1 while mobile forms of REE varied from 1 to 11 mg/kg–1. Flood results in REE accumulation in the alluvial soils, accumulation mainly occurred on the surfaces of clay minerals and mobility of REE is affected by soil pH. Flood increase adsorption of REE by organic matter and phosphates. In average total REE contents increased by 10%, mobile forms — by 70%. Correlation coefficients with organic matter and phosphorus oxides after flooding are improved.

Differentiation of ironstone types by using rare earth elements and yttrium geochemistry – A case study from the Bahariya region, Egypt

This paper deals with the geological and geochemical characterization of ironstone deposits encountered in two different sedimentary successions (upper Cretaceous and lower Cenozoic) in northern Bahariya, Egypt. The ironstones occur as uneconomic thin bands, lenses and concretionary beds in Cenomanian clastic rocks of the Bahariya Formation and as economic iron ore associated with Eocene carbonate depositional units. The ironstones contain similar iron-bearing minerals, mainly goethite and hematite, which display a variety of fabrics, i.e. concretionary, massive, stromatolitic-like, oolitic, pisolitic, reniform aggregates, boxwork, liesegang, geode-like and brecciated. The iron-rich minerals preferentially replaced and/or cemented the primary and diagenetic (mainly dolomite) carbonates. Preservation of fabrics, sedimentary structures and thickness of the precursor carbonates is conspicuous.Whole-rock composition of the Cretaceous ironstones shows lower Fe2O3 and MnO contents and relative enrichment in detrital-derived elements, namely Al, Zr and Nb, when compared with the Eocene ironstones, the latter showing enrichment in Fe, Mn, Si, and Ba oxides as well as Cu, Zn, Ni and Sr trace elements. Total REE content in the Cretaceous ironstones ranges widely from 70 to 348 ppm whilst the Eocene ironstones show quite low content, mostly from 1.96 to 31 ppm. Post Archean Australian Shale (PAAS)-normalized patterns of the upper Cretaceous ironstones display flat REE patterns, with small positive Eu and Pr, slightly negative Y and Ce anomalies which are close to unity and intermediate Nd concentrations (between 10 and 100 ppm). In contrast, PAAS-normalized REE + Y patterns of the Eocene ironstones display LREE positive slope with enriched flat HREE trend as well as negative Ce anomaly, positive Y and Eu anomalies, and low Nd concentration (in general less than 10 ppm).Geochemical data along with sedimentary features of the upper Cretaceous and Eocene ironstones in Bahariya point to different origins in the two ironstone types, the former having been originated diagenetically whereas the latter were constrained by hydrothermal fluids. A syngenetic marine origin is ruled out for any of the studied ironstones. Higher amount of detrital derived elements as well as higher REE concentration in the upper Cretaceous ironstones than in the Eocene ironstones suggest some contribution from the associated clastic sediments. The negative Ce anomaly determined in both types indicates anoxic iron-rich solution that passed to oxidized surface. The presence of positive Y and Eu anomalies in the Eocene ironstones suggests that iron precipitation was favoured by hydrothermal reducing conditions, when slightly acidic fluids reached oxidizing alkaline waters.