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The origin of low-ca olivine from ultramafic xenoliths and host basaltic lavas in a back-arc setting, James Ross Island, Antarctic Peninsula

Year: 2019
Products: UP213;New Wave;
Authors: Altunkaynak, ;Ünal, A;Howarth, G;Aldanmaz, E;Nývlt, D;
Journal: Lithos

The James Ross Island Volcanic Group (JRIVG) at the northern tip of the Antarctic Peninsula is composed of various types of volcanic rocks erupted during the Late Miocene to Late Pleistocene. The sub-aerial lavas are the most abundant erupted products within the suite and are represented by alkali olivine basalts that contain significant amounts of ultramafic xenoliths. Precise determination of chemical compositions of olivine by electron microprobe and LA-ICP-MS reveals more than one compositionally distinct olivine population in the xenoliths and the host lavas. The majority of the olivine grains from the xenolith suite are remarkable for their high Mg/Fe ratios (>Fo88) and low-Ca contents (<500 ppm) and are similar in composition to the mantle olivine, while some others, despite their similarly low-Ca abundances, are characterized by significantly lower Mg/Fe (Fo88) from the basaltic lavas also have low Ca contents compared to MORB olivine at similar Fo, indicating an arc-melt like volatile content of the primary magma. Evaluation of minor and trace element relative abundances in olivine further indicate that the alkaline basalts in the JRIVG are the products of peridotite-dominated partial melting of a volatile-rich mantle source with signatures of mantle hydration most probably promoted by preceding subduction events. The results from olivine chemistry, when combined with the evaluation of primary melt compositions, appear to be consistent with the view that the primary magmas from which the JRIVG basalts were derived are the results of partial melting of a mantle domain that has experienced hydrous silicate melt metasomatism through interaction of peridotitic upper mantle rocks with melts of a slab-derived component, most probably generated by dehydration melting of subducted oceanic crust.

Arc related dioritic-granodioritic magmatism from southeastern Peninsular Malaysia and its tectonic implication

Year: 2019
Products: UP213;New Wave;
Authors: Hazad, F;Ghani, A;Lo, C;
Journal: Cretaceous Research

In Peninsular Malaysia, Late Cretaceous (95-76 Ma) plutons are found within the Eastern Belt. Their compositions are diverse, ranging from biotite granite, hornblende granodiorite, diorite, and gabbro. The Aur Pluton is the easternmost body and is exposed in the Johore Archipelago, southeast of Peninsular Malaysia. The rock types vary from diorite, quartzmonzodiorite and granodiorite. Ar-Ar stepheating age of the diorite and zircon U/Pb age of the granodiorite yielded ages of 77.9 ± 2 Ma and 79 ± 0.7 Ma, respectively. The overall major and trace element trends are consistent with two magmatic pulses, i.e., diorite-quartz monzodiorite and granodiorite. The diorite-quartz monzodiorites are characterized by high Fe2O3 (6.7–8.3 wt.%), CaO (5.5–7.6 wt.%), MgO (2.9–4.1 wt.%) and high but variable Sr concentrations (570–1300 ppm). The granodiorites have significantly higher total alkalicontent (8.49–8.91%), with high K2O concentrations (3.8–4.6%) and low Fe2O3 (4.7–6.5%), CaO (2.7–3.9%) and MgO (1.4–2.0%) concentrations. Low Nb/U and distinct Pb anomalies suggest that both rock types are likely derived from the crust. Furthermore, elevated LREE and trace element contents for the granodiorites, e.g., FTh (10–20 ppm), Pb (10–30 ppm), and U (2–5 ppm), also indicate that upper crustal components are involved in the magma generation. The dioritic rocks are chemically classified as calc-alkaline volcanic arc (VAG) rocks, but they also have field relationships and mineralogies typically associated with an active continental margin (ACM).

Granulite-facies gneisses and meta-igneous xenoliths from the Campo de Calatrava volcanic field (Spain): Implications for the tectonics of the Variscan lower crust

Year: 2019
Products: UP213;NewWave;
Authors: Puelles, P;Gil Ibarguchi, J;García de Madinabeitia, S;Sarrionandia, F;Carracedo-Sánchez, M;Fernández-Armas, S;
Journal: Lithos

The microstructural, petrofabric and geochronological study of deep-seated xenoliths from the La Encomienda volcano (Neogene Campo de Calatrava Volcanic Field) has helped to characterize the nature and dynamics of processes operative in the lower crust and subcontinental mantle domains of the Central Iberian Zone in the Iberian Massif (Spain). We present the finding of three new xenolith types: noritic andesine meta-anorthosites, aluminous granulites and felsic granulites. Plagioclase (andesine), hypersthene, ilmenite, apatite and zircon make up the mineral assemblage in equilibrium in the anorthosite xenoliths, whereas K-feldspar (sanidine), antiperthitic plagioclase (oligoclase-andesine), quartz, sillimanite, garnet, rutile and biotite conform the mineral assemblage in the aluminous granulites. Felsic granulites differ from the aluminous type in the smaller amount of garnet, the occurrence of perthitic microcline and the lack of sillimanite and biotite. The presence of significant fabrics in the constituent minerals indicates that they underwent high-temperature deformations representative of low crustal domains.

Origin and tectonic significance of the Hoboksar ophiolitic mélange in northern West Junggar (NW China)

Year: 2019
Products: UP213;New Wave;
Authors: Du, H;Chen, J;Ma, X;Han, B;Liu, B;Simon, A;Liu, J;Ren, R;Li, C;Zhou, L;Lei, Z;
Journal: Lithos

Although the Early Paleozoic tectonic framework of northern West Junggar is essential for understanding accretionary processes in the southwestern Central Asian Orogenic Belt, this setting is still not well understood. In order to address this issue, we employed detailed geochronological, geochemical and Sr-Nd-Hf-Os isotope analyses on the Hoboksar ophiolitic mélange in northern West Junggar. The Hoboksar ophiolitic mélange mainly consists of serpentinized peridotites, pyroxenites, gabbros, diabase, cherts, marbles, volcanic and pyroclastic rocks. It is characterized by a “block-in-matrix” structure with serpentinized peridotites as the matrix which is crosscut by later diorite porphyry and rhyolitic porphyry. Olivines and spinels in these serpentinized peridotites show high Fo# and Cr#, respectively. The clinopyroxenes in the pyroxenites exhibit high Mg#, low Al2O3 and Cr2O3. The serpentinized peridotites have extremely low rare-earth element (REE) abundances, U-shaped to flat REE patterns and positive Eu anomalies. Their particularly low Re/Os, initial 187Os/188Os and γOs(t) imply that they could represent residual phases after partial melting of upper mantle. The gabbros and diabases display slight fractionation between light REE and heavy REE, negligible Eu anomalies, depletion in Rb, Nb and Ta, enrichment in Th and U, low initial 87Sr/86Sr and positive εNd(t). The mineral and whole-rock geochemical and isotopic compositions of these ultramafic-mafic rocks demonstrate that the Hoboksar ophiolitic mélange originated from a depleted mantle in a fore-arc supra-subduction zone (SSZ) setting.

Adakites without a slab: Remelting of hydrous basalt in the crust and shallow mantle of Borneo to produce the Miocene Sintang Suite and Bau Suite magmatism of West Sarawak

Year: 2019
Products: NWR213;New Wave;
Authors: Breitfeld, H;Macpherson, C;Hall, R;Thirlwall, M;Ottley, C;Hennig-Breitfeld, J;
Journal: Lithos

We present new geochronological and geochemical data for Neogene magmatism from West Sarawak. Zircon U-Pb geochronology divides Neogene magmatic rocks of West Sarawak into a Lower Miocene West Sarawak Sintang Suite with ages of c. 19 to 21 Ma, and a Middle Miocene Bau Suite with ages of c. 12 to 14 Ma. Magmatism occurred in multiple short-lived pulses from approximately 24 Ma and was coeval with magmatic activity in NW Kalimantan and East Kalimantan. The majority of, but not all, Bau Suite samples display adakitic chemistry, while the West Sarawak Sintang Suite is predominantly non-adakitic. There was no active subduction zone or subducted slab associated with this adakitic magmatism. Instead, the geochemical diversity is consistent with the Bau and West Sarawak Sintang suites representing mixtures of mafic, mantle-derived magma with felsic magma derived from remelting of hydrous, mafic rock that had been emplaced into the lithosphere of Borneo as arc basalt tens or hundreds of millions of years previously. This origin is most evident in the main Sintang Suite of central Borneo (Kalimantan) which has preserved less contaminated examples of the mafic endmember. This endmember resembles basaltic rocks from several locations across Borneo suggesting that intraplate, mantle-derived magmatism was responsible for remelting older, hydrated basaltic rocks in the crust.

Zircon U-Pb age and Nd isotope geochemistry of latest Neoproterozoic to early Paleozoic Oeyama ophiolite: Evidence for oldest MORB-type oceanic crust in Japanese accretionary system and its tectonic implications

Year: 2019
Products: UP213;New Wave;New Wave Research;
Authors: Kimura, K;Hayasaka, Y;
Journal: Lithos

The Oeyama ophiolite is considered as one of the major ophiolites in the Japanese Islands that forms a part of the “circum-Pacific Phanerozoic multiple ophiolite Belts”. In this study, zircon U-Pb age and their REE geochemistry, and Nd-Sr isotope geochemistry are presented for the gabbroic rocks of the Oeyama ophiolite to determine the precise crystallization age and characterize the proper tectonic setting of this ancient oceanic crust. The zircon grains of the two studied gabbroic samples yield 206Pb/238U ages of 545.4 ± 2.6 Ma and 532.4 ± 3.1 Ma. From five gabbroic rocks, a comparable 566 ± 95 Ma Sm-Nd whole rock isochron age is obtained. The time-corrected εtNd values (t = 545 Ma) for each sample are ranging from +7.2 to +7.7 that suggest their normal mid-oceanic basalt (N-MORB) affinity. Discrimination diagrams using zircon U/Yb versus Hf and Y also indicate their oceanic crustal origin. This is so far known the oldest date of ophiolite in the Japanese accretionary system. On the basis of the present dataset, we have offered a scenario of the potential tectonic development highlighting the journey of this group of oceanic crustal rocks from the mid-oceanic region till their final accretion to the Japanese Islands. The present tectonic model envisages an initial oceanward subduction at ca. 530 Ma switched over to the present continentward subduction at ca. 400 Ma. Moreover, the three different units of the Oeyama ophiolite have been re-classified based on the present age dataset, and the formation and evolution of these units constituting the typical lower part of the ocean plate are explained.

Late Neoarchean slab rollback in the Jiaoliao microblock, North China Craton: Constraints from zircon U-Pb geochronology and geochemistry of the Yishui Complex, Western Shandong Province

Year: 2019
Products: NewWave;
Authors: Yu, Y;Li, D;Chen, Y;Song, L;Kang, H;Geng, J;
Journal: Lithos

Earth's plate tectonic system was initiated between 3.0 and 2.5 Ga and became the dominant regime for crustal growth and differentiation. However, it is unclear whether subduction–accretion processes, including slab rollback, occurred regionally in the area of the western Shandong Province Granite–Greenstone Terrane of the North China Craton (NCC) during the early development of plate tectonics. We quantified petrology, whole-rock geochemistry, and zircon U–Pb–Hf isotopes for felsic, mafic, and ultramafic rocks from the Yishui Complex (YC) in the NCC to constrain the origin of these rocks and the associated tectonic setting(s). The granites yield 207Pb/206Pb ages of 2509 ± 20 to 2484 ± 26 Ma, and magmatic zircon grains from these rocks have εHf(t) values of 0.6–6.4. The coeval mafic–dioritic rocks represent the fractional crystallization products of a primary magma that was derived from low-degree (<7%) partial melting of a metasomatized mantle source. The granodiorites were derived from the partial melting of oceanic slab material, with slab melts being contaminated by mantle wedge material during their ascent. The high-K granites represent the crustal reworking products of regional tonalite–trondhjemite–granodiorite and sedimentary rocks. Late Neoarchean magmatism in the YC was related to slab subduction, and slab rollback at ~2.50 Ga led to the generation of potassic rocks, coeval mafic–ultramafic xenoliths, and granulite metamorphism with a counterclockwise P–T–t path in the Yishui area.

Quantitative analysis of plant leaf elements using the LA-ICP-MS technique

Year: 2019
Products: UP213;New Wave;
Authors: Pedrosa Diniz, A;Rodrigues Kozovits, A;de Carvalho Lana, C;Trópia de Abreu, A;Garcia Praça Leite, M;
Journal: International Journal of Mass Spectrometry

The use of Laser Ablation coupled to Mass Spectrometry is a promising technique for analysis of plant tissue elements because it has advantages over conventional digestion techniques such as reduced levels of contamination and sample preparation time, possibility of spatial distribution analysis of elements, high number of repetitions, among others. This technique still has some limitations, especially with regard to calibration, which may result in inaccurate chemical analyses. The present study aims to compare two types of analyzers (quadrupole and magnetic sector field) regarding precision and accuracy. Certified material was examined, and also plant material analyzed by both solution in inductively coupled plasma optical emission spectrometry (ICP OES) and by laser ablation methods. It was observed that the magnetic sector field analyzer gave better results in relation to precision (relative standard deviation - RSD) and accuracy (recovery). An elemental composition pattern similar to that of the sample to be analyzed is relevant to validate the methodology for the analysis of leaves collected under different environmental conditions. Thus, pulverized Eremanthus erytropappus leaves were suggested as a second type of validation standard to be used in analyzes of plants belonging to the Atlantic and Cerrado Forest biomes.

Petrogenesis of A-type granites associated with Sn–Nb–Zn mineralization in Ririwai complex, north-Central Nigeria: Constraints from whole-rock Sm Nd and zircon Lu Hf isotope systematics

Year: 2019
Products: NWR193;ESI;
Authors: Girei, M;Li, H;Algeo, T;Bonin, B;Ogunleye, P;Bute, S;Ahmed, H;
Journal: Lithos

We report a combined study of whole-rock major- and trace-element geochemistry, Sm Nd isotope composition, zircon U/Pb dating, and Lu Hf systematics of peralkaline and aluminous A-type granites from the Ririwai Ring Complex in north-central Nigeria. The Ririwai peralkaline and aluminous A-type granites are strongly ferroan, alkalic to alkali-calcic, and enriched in Hf, Zr, Ga, Rb, Y and REEs. They were emplaced between 176 ± 2.3 Ma and 169.6 ± 0.75 Ma. The peralkaline granites yield relatively higher ɛNd(t) (−2.3 to −1.2) and zircon ɛHf(t) values (−5.8 to −1.7) than the aluminous granites (ɛNd(t) = −3.6 to −3.3; zircon ɛHf(t) = −7.8 to −2.4). In addition, inherited zircons in the aluminous granites yield Pan-African (~590 Ma) ages and low ɛHf(t) values (−14.0). Taken together, these data suggest that the granites formed from extensive fractional crystallization of a transitional basaltic melt derived from an enriched OIB mantle source. The depletions of MgO, CaO, Ti2O, Sr and Ba in the granites indicate that Mg-rich olivine, calcic pyroxene, calcic amphibole, feldspars and Fe Ti oxides were the major fractionated phases during magma evolution. In addition, several types of evidence, e.g., moderately negative ɛNd(t) and ɛHf(t) values, and the presence of inherited zircons, imply that the parental melt was modified by assimilation of Pan-African upper crust into which the granites were emplaced. A transtensional regime generated prior to late Jurassic breakup of Gondwana, which led to reactivation of shear zones and opening of associated transcurrent faults, paved the way for emplacement of the A-type suite. The Sn–Nb–Zn mineralization of the Ririwai A-type suite was probably linked to complex magmatic evolutionary processes involving extensive fractional crystallization coupled with crustal assimilation and late-stage hydrothermal fluid activity.

Insights on the origin of the Graciosa A-type granites and syenites (Southern Brazil) from zircon U-Pb geochronology, chemistry, and Hf and O isotope compositions

Year: 2019
Products: New Wave;New Wave Research;
Authors: Vilalva, F;Simonetti, A;Vlach, S;
Journal: Lithos

The Neoproterozoic, post-collisional, Graciosa Province (southern Brazil) comprises several A-type intrusions and related volcanics of alkaline and subalkaline (or aluminous) petrographic associations. U-Pb age determinations, trace element, and Hf and O isotopic compositions were obtained for zircons from six distinct A-type granitic and syenitic plutons from both alkaline and subalkaline associations from the province. Geochronological results indicate that their emplacement, petrogenetic evolution and crystallization spanned over a ~9 million years interval, with peak magmatism at ~580 Ma. Plutons were emplaced in a post-collisional extensional regime related to the geodynamic evolution of the south-southeastern part of the Gondwana supercontinent. Hf isotopic compositions are highly variable, with εHf(t) values between +1.4 to −31, whereas δ18O signatures are mainly between +4.7 and +6.0‰. These features, along with trace element signatures, especially for Hf, U, Nb, and rare-earth elements, suggest that generation of the Graciosa rocks occurred via partial melting of a lithospheric mantle previously metasomatized by slab-derived fluids, followed by variable degrees of crustal contamination at depth.

Origin and duration of late orogenic magmatism in the foreland of the Variscan belt (Lesponne — Chiroulet — Neouvielle area, French Pyrenees)

Year: 2019
Products: NWR193UC;ESI;
Authors: Lemirre, B;Cochelin, B;Duchene, S;de Saint Blanquat, M;Poujol, M;
Journal: Lithos

During the late stage of the Variscan orogeny, the pyrenean segment underwent intense magmatism and regional high temperature – low pressure metamorphism. In the Lesponne – Chiroulet – Neouvielle area, a granodioritic pluton was emplaced in the upper crust while dioritic to granitic magmas were emplaced in metamorphic domes. Magmatism was contemporaneous with the regional crustal partial melting recorded in the core of the domes. The area is therefore a key target in the Pyrenees to discuss potential magmatic sources as well as the age and duration of the late Variscan magmatism. Geochemical data on representative magmatic rocks highlight two distinct sources of magma: a mantle source and a metasedimentary crustal source that produced respectively metaluminous and peraluminous magmas. Geochronological results show that magmatism took place over a period of about 10 My from ca. 303 to ca. 290 Ma. During this period, the middle to lower crust was composed of partially molten metasediments intruded by mantle and crustal magmas that crystallized in a final pulse at ca. 290 Ma. Late Variscan metamorphism and magmatism recorded in the Pyrenees have to be related to a significant and rapid heating from the underlying mantle rather than to crustal processes such as the maturation of a thickened continental crust. We propose that the initiation of metamorphism and bimodal magmatism at ca. 305 Ma in the Pyrenees is the expression of the delamination of the Gondwanan lithospheric mantle at a global scale in the Variscan belt.

Two‐stage Variscan metamorphism in the Canigou massif: evidence for crustal thickening in the Pyrenees

Year: 2019
Products: NWR193UC;ESI;
Authors: Hoÿm de Marien, L;Le Bayon, B;Pitra, P;Van Den Driessche, J;Poujol, M;Cagnard, F;
Journal: J Metamorph Geol

The Variscan metamorphism in the Pyrenees is dominantly of the low-pressure-high-temperature (LP-HT) type. The relics of an earlier, Barrovian-type, metamorphism that could be related to orogenic crustal thickening are unclear and insufficiently constrained. A microstructural and petrological study of micaschists underlying an Ordovician augen orthogneiss in the core of the Canigou massif (Eastern Pyrenees, France) reveal the presence of two syntectonic metamorphic stages characterized by the crystallization of staurolite (M1) and andalusite (M2), respectively. Garnet is stable during the two metamorphic stages with a period of resorption between M1 and M2. The metamorphic assemblages M1 and M2 record similar peak temperatures of 580 °C at different pressure conditions of 5.5 kbar and 3 kbar, respectively. Using chemical zoning of garnet and calculated P–T pseudosections, a prograde P–T path is constrained with a peak pressure at ~6.5 kbar and 550 °C. This P–T path, syntectonic with respect to the first foliation S1, corresponds to a cold gradient (of ~9 °C/km), suggestive of crustal thickening. Resorption of garnet between M1 and M2 can be interpreted either in terms of a simple clockwise P–T path or a polymetamorphic two stage evolution. We argue in favour of the latter, where the medium‐pressure (Barrovian) metamorphism is followed by a period of significant erosion and crustal thinning leading to decompression and cooling. Subsequent advection of heat, probably from the mantle, lead to a new increase in temperature, coeval with the development of the main regional fabric S2. LA‐ICP‐MS U‐Th‐Pb dating of monazite yields a well‐defined date at c. 300 Ma. Petrological evidence indicates that monazite crystallization took place close to the M1 peak‐pressure conditions. However, the similarity between this age and that of the extensive magmatic event well documented in the eastern Pyrenees suggests that it probably corresponds to the age of monazite recrystallization during the M2 LP–HT event.

Fluid–rock interactions in the shallow Mariana forearc: carbon cycling and redox conditions

Year: 2019
Products: New Wave;
Authors: Albers, E;Bach, W;Klein, F;Menzies, C;Lucassen, F;Teagle, D;
Journal: Solid Earth

Few data exist that provide insight into processes affecting the long-term carbon cycle at shallow forearc depths. To better understand the mobilization of C in sediments and crust of the subducting slab, we investigated carbonate materials that originate from the subduction channel at the Mariana forearc (< 20 km) and were recovered during International Ocean Discovery Program Expedition 366. Calcium carbonates occur as vein precipitates within metavolcanic and metasedimentary clasts. The clasts represent portions of the subducting lithosphere, including ocean island basalt, that were altered at lower blueschist facies conditions and were subsequently transported to the forearc seafloor by serpentinite mud volcanism. Euhedral aragonite and calcite and the lack of deformation within the veins suggest carbonate formation in a stress-free environment after peak metamorphism affected their hosts. Intergrowth with barite and marked negative Ce anomalies in carbonate attest the precipitation within a generally oxic environment, that is an environment not controlled by serpentinization. Strontium and O isotopic compositions in carbonate (87Sr∕86Sr = 0.7052 to 0.7054, δ18OVSMOW = 20 to 24 ‰) imply precipitation from slab-derived fluids at temperatures between ∼130 and 300 ∘C. These temperature estimates are consistent with the presence of blueschist facies phases such as lawsonite coexisting with the carbonates in some veins. Incorporated C is inorganic (δ13CVPDB = −1 ‰ to +4 ‰) and likely derived from the decarbonation of calcareous sediment and/or oceanic crust. These findings provide evidence for the mobilization of C in the downgoing slab at depths of < 20 km. Our study shows for the first time in detail that a portion of this C forms carbonate precipitates in the subduction channel of an active convergent margin. This process may be an important asset in understanding the deep carbon cycle since it highlights that some C is lost from the subducting lithosphere before reaching greater depths.

Tailored and deep porosification of LTCC substrates with phosphoric acid

Year: 2019
Products: NWR213;ESI;
Authors: Hajian, A;Smetaczek, S;Zellner, C;Stöger-Pollach, M;Konegger, T;Limbeck, A;Schmid, U;
Journal: Journal of the European Ceramic Society

Low temperature co-fired ceramics (LTCC) as an advanced technology for robust assembly of electronic components, has attracted significant attention in a wide application range such as in wireless communication or automotive radar systems. However, accurate designs of micromachined devices operated at high frequencies require substrates with regions of tailored permittivities. Introduction of controlled porosity into the substrate via wet-chemical etching procedure, is a promising approach for permittivity reduction which can be applied to commercially available LTCC without necessitating to alter their composition or sintering process. In the present study, by selective dissolution of celsian phase a very deep porosification (highest reported so far) could be realized while preserving the surface quality. Also, by a careful selection of the etching parameters, the depth of porosification and hence the permittivity reduction can be delicately tailored. Laser ablation inductively coupled plasma mass spectrometry was used for the investigation of chemical compositions of substrates.

Metal fluxes during magmatic degassing in the oceanic crust: sulfide mineralisation at ODP site 786B, Izu-Bonin forearc

Year: 2019
Products: NWR213;
Authors: Patten, C;Pitcairn, I;Alt, J;Zack, T;Lahaye, Y;Teagle, D;Markdahl, K;
Journal: Miner Deposita

Volcanogenic massive sulfide deposits are enriched in metals that are either derived from hydrothermal alteration of the basement rocks or supplied by exsolution of metal-rich volatiles during magmatic differentiation. The extent to which each process contributes to metal enrichment in these deposits varies between different tectonic settings. Ocean Drilling Program Hole 786B recovered > 800 m of upper oceanic crust from a supra-subduction zone setting and includes a 30-m-thick mineralised zone. In situ S isotopic compositions of pyrite decrease from 5.9 ± 2.9‰ in the upper mineralised zone down to − 3.3 ± 2.1‰ in the extensively altered central mineralisation zone, potentially indicating strong magmatic fluid input in this area. Whole rock data and in situ trace element analyses in sulfide minerals show enrichment of Ag, As, Au, Bi, Mo, S, Se, Sb and Te in the mineralised zone. Evaluation of metal behaviour during magmatic differentiation and primary metal fertility of basement rocks suggests that degassing melt is the main source for the high Au, Se and S enrichment observed in the mineralised zone. Magmatic volatile exsolution occurred late during the magmatic differentiation (~ 2 wt.% MgO), concomitant with oxide crystallisation and metal depletion in the melt. Comparison of Ocean Drilling Program Hole 786B with volcanogenic massive sulfide deposits hosted by boninitic volcanic successions, such as in the Semail ophiolite, the Newfoundland Appalachians and the Flin Flon Belt, suggests that magmatic fluid exsolution could be a common mechanism for Au enrichment in bimodal mafic volcanogenic massive sulfide deposits.

A new freeware tool for image processing and its application to high speed LA-ICP-MS imaging

Year: 2019
Products: NWRimage;Dual Concentric Injector;
Authors: Managh, A;Reid, P;
Journal: J. Anal. At. Spectrom.

A new standalone, non-commercial software application has been developed to enable rapid generation of images from laser ablation-inductively coupled plasma-mass spectrometry data. The software locates peaks within raw data files and uses the peak locations to segment the data at appropriate intervals, enabling conversion of the data into a matrix of colour coded pixels. The app was developed in order to process baseline separated peaks produced by the latest generation of low-dispersion laser ablation systems, but it is equally applicable to rastered imaging using alternative laser ablation platforms. The peak recognition feature also has applicability to single cell and single particle ICP-MS applications. The app was demonstrated for the imaging of zinc in a stained section of rat retina tissue at lateral resolutions down to 1 μm. Less than two minutes was required for conversion of the raw data into a 60 000 pixel image.

Accurate analysis of Li isotopes in tourmalines by LA-MC-ICP-MS under “wet” conditions with non-matrix-matched calibration

Year: 2019
Products: NWRfemtoUC;
Authors: Lin, J;Liu, Y;Hu, Z;Chen, W;Zhang, C;Zhao, K;Jin, X;
Journal: J. Anal. At. Spectrom.

The Li isotopic compositions of tourmalines can be used as a powerful geochemical tracer and provide valuable information regarding magma–volatile relationships and the magmatic-hydrothermal evolution of pegmatites. Laser ablation-multiple collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) is the method of choice for in situ Li isotopic analysis. In this study, we investigated the feasibility of Li isotopic analysis in tourmalines by both ns- and fs-LA-MC-ICP-MS with (tourmalines as calibration standards) and without (NIST 610 glass as the calibration standard) matrix-matched calibration. The Li isotopes of tourmalines can be accurately analyzed with matrix-matched calibration by ns- or fs-LA-MC-ICP-MS. However, inaccurate δ7Li values were obtained when tourmalines were measured against a non-matrix-matched standard by ns- (∼10.0‰ deviation) and fs-LA-MC-ICP-MS (∼1.5‰ deviation). Wet plasma conditions can significantly reduce the matrix effect in isotopic analysis. Furthermore, the deviation in fs-LA-MC-ICP-MS can be suppressed by water addition after the ablation cell. However, a relatively large deviation (∼4‰) still existed, even though the matrix effect during ns-LA can be largely suppressed by water addition after the ablation cell (∼6‰ deviation was reduced). Fortunately, with the water addition before the ablation cell, an accurate and precise Li isotopic analysis by ns-LA-MC-ICP-MS can be achieved with non-matrix-matched calibration. This study indicated that there was a serious matrix effect in the Li isotopic analysis of tourmalines by ns- and fs-LA-MC-ICP-MS, and water-assisted ns- and fs-LA-MC-ICP-MS were an appealing option for the in situ Li isotope analysis of tourmaline with non-matrix-matched calibration.

Petrogenesis of Zeiatit gabbroic rocks in the Southern Eastern Desert of Egypt: Discrimination of arc-related Neoproterozoic gabbros

Year: 2019
Products: UP213;New Wave;
Authors: Mogahed, M;
Journal: Journal of African Earth Sciences

The area of Gabal Zeiatit, South Eastern Desert, Egypt represents one of a series of ophiolitic-island arc complexes found within the Arabian–Nubian Shield (ANS). The present study introduces new major, trace, and rare earth element analyses and mineral composition data of gabbroic rocks encountered in this area with the goal of constraining their geotectonic setting. The investigated area consists of two types of gabbroic rocks. The Zeiatit ophiolitic metagabbros (ZMG) are always associated with serpentinites of ophiolitic affinity and were subjected to metamorphism of greenschist to lower amphibolite facies and exhibit tholeiitic affinity and MORB-like characters. Serpentinites and metagabbros are tectonically thrusted over a thick pile of metavolcanic rocks. The Zeiatit intrusive gabbros (ZIG) are related to Egyptian Alaskan-type mafic-ultramafic complexes and intrude the studied ophiolitic rocks and island arc rocks. Geochemical data reveal that both studied gabbroic types originated in sub-arc setting. Mineral chemistry data for the two types of the studied gabbroic rocks indicate that they possess different characteristics.

Chemical and boron isotope compositions of tourmaline in the Hadamiao porphyry gold deposit, Inner Mongolia, China

Year: 2019
Products: New Wave;
Authors: Qiao, X;Li, W;Zhang, L;White, N;Zhang, F;Yao, Z;
Journal: Chemical Geology

The Hadamiao porphyry gold deposit in Inner Mongolia, China, is located in the northern margin of the North China Craton (NCC). Tourmaline is a common mineral in hydrothermal veins and granitic rocks contemporaneous with the mineralized granite porphyry in this deposit. The tourmaline can be divided into six types, including magmatic tourmaline (Tur-M1) in granite porphyry dikes, magmatic-hydrothermal transitional tourmaline (Tur-M2) in nodular granitic rocks, and hydrothermal tourmalines in early tourmaline veins (Tur-V1), gold-bearing quartz-tourmaline-chalcopyrite veins (Tur-V2), breccia cements (Tur-V3) and late carbonate-quartz veins (Tur-V4). The gold mineralization is closely related to the occurrence of Tur-V2. Almost all the tourmalines from the Hadamiao deposit belong to the alkali group and show a schorlitic–dravitic composition, except for some Tur-M1 belonging to uvite. The concentrations of most elements in different tourmaline types overlap. Tur-M1 has higher Ca, W, Th, U, Pb, Mn, and Zr contents than other types, and the hydrothermal tourmalines (V1–V4) show slightly higher Ba, Cu and Y contents than Tur-M1 and Tur-M2. The concentration of Au in Tur-M1 and Tur-M2 can reach up to 80 ppb and is higher than that in Tur-V1; the Au content in Tur-V2 is an order of magnitude higher than that in other stages of tourmaline. Systematic contrasts in major and trace element compositions between magmatic and hydrothermal tourmalines are attributed to the assimilation of the country rock by the magmatic-hydrothermal system.

The alkaline lamprophyres of the Dolomitic Area (Southern Alps, Italy): markers of the Late Triassic change from orogenic-like to anorogenic magmatism

Year: 2019
Products: New Wave;
Authors: Casetta, F;Ickert, R;Mark, D;Bonadiman, C;Giacomoni, P;Ntaflos, T;Coltorti, M;
Journal: Journal of Petrology

We present the first complete petrological, geochemical and geochronological characterization of the oldest lamprophyric rocks in Italy which crop out around Predazzo (Dolomitic Area), with the aim of deciphering their relationship with Triassic magmatic events across the whole of the Southern Alps. Their Mg# of between 37 and 70, together with their trace element contents, suggest that fractional crystallization was the main process responsible for their differentiation, together with small-scale mixing, as evidenced by some complex amphibole textures. Moreover, the occurrence of primary carbonate ocelli suggests an intimate association between the alkaline lamprophyric magmas and a carbonatitic melt. 40Ar/39Ar data show that the lamprophyres were emplaced at 219.22 ± 0.73 Ma (2σ; full systematic uncertainties), around 20 Myr after the high K calc-alkaline to shoshonitic, short-lived, Ladinian (237-238 Ma) magmatic event of the Dolomitic Area. Their trace element and Sr-Nd isotopic signatures (87Sr/86Sri = 0.7033-0.7040; 143Nd/144Ndi = 0.51260-0.51265) are likely related to a garnet-amphibole-bearing lithosphere interacting with an asthenospheric component, significantly more depleted than the mantle source of the high K calc-alkaline to shoshonitic magmas. These features suggest that the Predazzo lamprophyres belong to the same alkaline-carbonatitic magmatic event that intruded the mantle beneath the Southern Alps (e.g., Finero peridotite) between 190 and 225 Ma. In this scenario, the Predazzo lamprophyres cannot be considered as a late-stage pulse of the orogenicDownloaded from https://academic.oup.com/petrology/advance-article-abstract/doi/10.1093/petrology/egz031/5511843 by Springfield College user on 06 June 2019 like Ladinian magmatism of the Dolomitic Area, but most likely represent a petrological bridge to the opening of the Alpine Tethys.

The efficiency of Governmental and WFP UN Programs for improvement of nutritional status in Tajik schoolchildren as assessed by dietary intake and hair trace element content

Year: 2019
Products: NWR213;ESI;
Authors: Kirichuk, A;Skalny, A;Dodkhoyev, J;Skalnaya, M;Grabeklis, A;Ajsuvakova, O;Tinkov, A;Notova, S;Bjørklund, G;Tinkova, M;Chizhov, A;Bobrovnitskiy, I;Bolotnikova, E;Chernigov, V;Skalny, A;
Journal: Journal of Trace Elements in Medicine and Biology

Background: The objective of the study was to assess hair trace element and mineral content in children undergoing WFP UN and the governmental programs of school nutrition in Tajikistan. Methods: WFP program included provision or wheat flour fortified with micronutrients including Fe and Zn, and iodized salt, whereas within the governmental program hot meals were provided. A total of 202 children studying in schools that were not (Type 1, n = 100) or were involved in dietary intervention programs (Type 2, n = 102). Food and hair trace element content was assessed using ICP-MS. Results: Daily intake of Fe, I, Zn, B, Co, Mg, Si, and Sr in Type 2 schools was more than 2.5, 12, 4, 2.9, 2.6, 2, 3, and 2-fold higher than that in Type 1 schools. Correspondingly, anthropometric parameters in children from Type 2 schools exceeded the control values. Surprisingly, no significant difference in hair iodine levels was detected. Hair analysis demonstrated a significant increase in hair Ca, Mg, Na, Co, Cr, Cu, Fe, Li, Mn, Se, V, Zn content. Certain toxic elements including Al, As, and Be were also characterized by an increase in Type 2 schools. At the same time, nutritional intervention was associated with a significant decrease in hair B, Hg, and Sn levels. Conclusions: Nutritional intervention within WFP and the governmental program was effective in increasing essential trace element supply in Tajik schoolchildren. However, further studies including a detailed assessment of nutritional and health status with a special focus on iodine and thyroid functioning are required.

High‐Resolution Mg/Ca Measurements of Foraminifer Shells Using Femtosecond LA‐ICP‐MS for Paleoclimate Proxy Development

Year: 2019
Products: NWRfemto;ESI;
Authors: Jochum, K;Jentzen, A;Schiebel, R;Stoll, B;Weis, U;Leitner, J;Repschläger, J;Nürnberg, D;Haug, G;
Journal: Geochem. Geophys. Geosyst.

Determination of Mg/Ca in foraminifer shells as a proxy of seawater temperature is of particular interest in paleoclimate reconstruction. Here we show that femtosecond–200 nm–laser ablation–inductively coupled plasma–mass spectrometry is a suitable technique to precisely and accurately determine Mg/Ca in the micrometer‐sized calcareous chambers of foraminifers. At low fluence (0.3–0.6 J/cm2) the double‐charged 44Ca++ and the single‐charged 25Mg+ ions are measured nearly simultaneously. Integrated single‐shot measurements using a pulse repetition rate of 1 Hz enable precise analyses at a depth resolution of about 50–100 nm/pulse corresponding to an ablated material of 0.3–0.6 ng calcite/pulse for a spot size of 55 μm. High‐resolution analyses can be performed until a depth of 10–20 μm and thus particularly suitable for thin‐shelled foraminifers. Reproducibility (relative standard deviation) is about 5% as approved by homogeneous reference materials. Calibration is performed with the microanalytical synthetic reference material MACS‐3. Magnesium and Ca data of different carbonate and silicate reference materials agree within uncertainties with reference values. The procedure has been successfully applied for detailed analyses of single chambers and shell‐depth profiles of live individuals and empty planktic and benthic foraminifer tests from different ocean basins.

Low-temperature properties of BaWO4 based on experimental heat capacity in the range 5.7–304 K

Year: 2019
Products: NWR213;ESI;
Authors: Musikhin, A;Bespyatov, M;Shlegel, V;Safonova, O;
Journal: Journal of Alloys and Compounds

The heat capacity of barium tungstate single crystal was measured by the adiabatic method in the range of 5.7–304 K. No anomalies in the heat capacity associated with the phase transition were found. The analysis of the functional behavior of heat capacity near zero revealed a low-frequency peak in the phonon density of states of BaWO4. An approach was proposed to allow quantitative description of the acoustic wing of the phonon density of states. The approximation of experimental data by an analytical expression was done, including the temperature region near 0 K. The Debye temperature at absolute zero has been obtained. The thermodynamic functions were calculated: entropy, enthalpy increment and Gibbs free energy.

Evolution of the Igarapé Bahia Cu-Au deposit, Carajás Province (Brazil): Early syngenetic chalcopyrite overprinted by IOCG mineralization

Year: 2019
Products: UP213;New Wave;
Authors: Melo, G;Monteiro, L;Xavier, R;Moreto, C;Arquaz, R;Silva, M;
Journal: Ore Geology Reviews

The Igarapé Bahia IOCG Cu–Au deposit, located in the Carajás Domain, the northern part of the Carajás Province in the Amazon Craton, is one of the most economically important deposits in the province. The deposit is hosted in the metavolcanosedimentary Igarapé Bahia Group and the metasedimentary Águas Claras Formation. The Igarapé Bahia Group encompasses a lower unit with metavolcanic rocks and metagabbros, and metasedimentary rocks (metarhythmites, epiclastic rocks, and banded iron formation) of the upper unit. Epiclastic rocks are predominant in the Águas Claras Formation. Basement xenoliths within the lower unit yielded an U–Pb zircon age of 2935 ± 36 Ma, suggesting that a sialic crust was present prior to basin installation likely due to rifting. The U–Pb dating of detrital zircons yielded maximum deposition age at 2784 ± 27 Ma for the upper unit, and 2763 ± 32 Ma and 2774 ± 19 Ma for the Águas Claras Formation. Chalcopyrite nodules and layers are found within metarhythmites, concordant to primary structures, but without hydrothermal alteration halos and iron oxide. This chalcopyrite generation seems to have precipitated synchronously to the deposition of the Igarapé Bahia Group. Chalcopyrite nodules and layers show δ34SVCDT values ranging from +0.29 to +1.56‰. These data indicate that most of its sulfur is likely derived from the metavolcanic rocks of the lower unit. Host rocks and chalcopyrite nodules and layers were overprinted by the IOCG mineralization. The latter formed extensive halos of hydrothermal alteration and was accompanied by ductile deformation and hydrothermal brecciation. These processes resulted in (tourmaline)–carbonate–magnetite, (tourmaline)–carbonate–chlorite and (tourmaline)–(biotite)–chlorite mylonites and breccias. Chalcopyrite from magnetite-rich zones (i.e. IOCG mineralization) displays δ34SVCDT values from +1.36 to +5.35‰. In addition to magmatic sulfur, seawater-derived sulfate may have been incorporated in sulfides via thermochemical sulfate-reduction reactions. Trace element geochemistry in distinct copper ores (i.e. nodules and layers versus magnetite-rich) also point to different origins of both styles of mineralization. The timing of the IOCG mineralization was constrained at 2559 ± 34 Ma in the Alemão orebody. These data suggest that an IOCG-type metallogenetic event at ca. 2.5 Ga overprinted an older syngenetic-exhalative type copper mineralization. They also indicate that precipitation of early sulfide minerals within the Itacaiúnas Supergroup may have created Cu-rich sequences that could have been remobilized, generating the broad group of the IOCG deposits at Carajás.

Geochronology and geochemistry of the intrusive suite associated with the Khatsavch porphyry Cu-Au (Mo) deposit, South Mongolia

Year: 2019
Products: UP213;New Wave;New Wave Research;
Authors: Boldbaatar, E;Nanzad, B;Sereenen, J;Locmelis, M;Osanai, Y;Batsaikhan, N;Dashtseren, K;Zorigtbaatar, A;
Journal: Ore Geology Reviews

The Khatsavch porphyry Cu-Au (Mo) deposit is located in the Gurvansayhan island arc terrane of South Mongolia, approximately 45 km southwest of the Oyu Tolgoi Cu-Au district, one of the largest porphyry-type Cu-Au deposits in the world. The mineralization of the Khatsavch deposit is spatially and temporally associated with the second stage of the Baga Khachig intrusive complex, which intruded the Early Devonian Ekhiin Gol formation and is overlain by Quaternary sediments. Based on geological relationships, the age of the intrusive complex has been determined as Carboniferous; however, the precise age remains to be constrained. Here we present new geochronological, mineralogical, and geochemical data for the intrusive event that facilitated the formation of the Khatsavch deposit. Laser ablation ICP-MS analysis of U-Pb isotopes in zircons yields an age of 366 ± 6.4 Ma, which is within the uncertainty of ages of the granitoids that host the Oyu Tolgoi deposits (∼372 Ma and ∼366 Ma). Mineralogically, the granitoids of the Khatsavch and Oyu Tolgoi porphyry deposits are quartz monzonites, quartz monzodiorites, and granodiorites. Disseminated Cu-Au (Mo) mineralization occurs in quartz veins as well as in the granitoids of the Khatsavch deposit and is dominated by chalcopyrite, pyrite, molybdenite, and rare gold. Geochemically, rocks from the Khatsavch deposit are I-type granitoids with high K calc-alkaline affinity emplaced in a volcanogenic arc setting. Chondrite-normalized bulk rock rare earth element data show listric patterns similar to that of the Oyu Tolgoi, which is interpreted to reflect amphibole fractionation in arc settings. Granitoids from both deposits display smoothly decreasing Y, Yb, and Sr concentrations with differentiation, and increasing Sr/Y and La/Yb ratios with decreasing Y and Yb, which are consistent with hornblende, titanite, and plagioclase fractionation. Moreover, these granitoids are enriched in LILE, Pb, and U and depleted in Ta, Nb, and Ti. Based on the mineralogical and geochemical similarities of the Khatsavch and Oyu Tolgoi deposits, and their spatial and temporal proximity, it is argued that both ore systems are associated with the same magma source and that undiscovered deposits derived from this source may exist. Therefore, we suggest that the Gurvansayhan island arc terrane is an excellent exploration target well beyond the existing deposits.

Multiphase magma intrusion, ore-enhancement and hydrothermal carbonatisation in the Siah-Kamar porphyry Mo deposit, Urumieh-Dokhtar magmatic zone, NW Iran

Year: 2019
Products: NWR213;Electro Scientific Industries;
Authors: Rabiee, A;Rossetti, F;Tecce, F;Asahara, Y;Azizi, H;Glodny, J;Lucci, F;Nozaem, R;Opitz, J;Selby, D;
Journal: Ore Geology Reviews

The Siah-Kamar Mo deposit (SKMD) is located at the northwestern termination of the Urumieh-Dokhtar magmatic zone and it is the only porphyry Mo ore reserve in Iran. The exploration program documented 39.2 Mt proved reserves @ 539 ppm Mo and 66.4 Mt probable reserves @ 266 ppm Mo. In this study, field and petrographic investigations, integrated with geochemical (fluid inclusion and quartz chemistry) and geochronological (U-Pb zircon, Re-Os molybdenite, and Rb-Sr multimineral isochron) studies are used to propose a metallogenic model for the Mo mineralisation in the SKMD. The geology of the SKMD is characterized by the emplacement of a multiphase Oligocene basic/intermediate (at ca. 33–30 Ma) to acidic (29–28 Ma) magmatic suite, which intruded the Eocene volcanic country rocks. The alteration zone, about 4 × 3 km in size and with a general NW-SE trend, is centered within the main basic porphyry stock, grading from an inner potassic-sodic zone to peripheral phyllic/propylitic halos. The late acidic magmatic products (stocks and dykes) intruded and post-dated the main alteration zone. Two-stage Mo mineralisation is recognised, including: (i) stage-1, disseminated molybdenite, coeval with the formation of potassic-sodic alteration and minor, microscale Fsp, Bt, Qz + Po veinlets; and (ii) stage-2, high-grade molybdenite + carbonate (±sericite), structurally-controlled stockwork veining. Fluid inclusion systematics combined with TitaniQ thermometry documents a mineralising fluid system compatible with a transition from high-temperature (up to ca. 600 °C) magmatic to epithermal (250 °C) conditions during progressive cooling, exhumation and mixing with meteoric sources at shallow crustal conditions (ca. 7–3 km). The Re-Os molybdenite dating constrains the high-grade Mo ore formation at ca. 29–28 Ma, attesting for the intimate linkage between the main Mo mineralisation and the acidic magmatic phase in the area. The Rb-Sr geochronology of the potassic-sodic alteration zones confirms the two-stage magmatic/mineralisation scenarios, overlapping within errors with the results obtained from the U-Pb zircon geochronology and constraining the formation of the potassic-sodic and phyllic alteration at ca. 33 and 28 Ma, respectively. Our results document an uncommon scenario of two-stage porphyry Mo mineralisation associated with intensive late stage carbonate precipitation and achieved during a long-lasting and multiphase magmatic pulses of Oligocene age. We highlight the dominant role of acidic fluid neutralisation for further ore enrichment during polyphase magma intrusion as the dominant factor controlling the Mo mineralisation in the SKMD. Comparison at a regional-scale indicates that parameters such as longevity of magma supply, progressive magma crystallization/differentiation, and the presence of a possible pre-enriched crustal material should be considered responsible for the Mo endowment in the UDMZ.

Characteristics of REEs and trace elements in scheelite from the Zhuxi W deposit, South China: Implications for the ore-forming conditions and processes

Year: 2019
Products: New Wave;
Authors: Yuan, L;Chi, G;Wang, M;Li, Z;Xu, D;Deng, T;Geng, J;Hu, M;Zhang, L;
Journal: Ore Geology Reviews

The Zhuxi W deposit in Jiangxi, South China, with a resource of 2.86 Mt W and an average grade of 0.54% WO3, is the largest W deposit in the world. The deposit occurs at the contact between a late Mesozoic granitic intrusion and Carboniferous – Permian carbonate rocks and Neoproterozoic metamorphic rocks. The ores are divided into three types: skarn ore (dominant), sulfide ore and greisen ore. Based on occurrences and petrographic relationships, scheelite (the dominant ore mineral) is classified into three types, i.e. type I (greisen), type II (skarn, specifically in the retrograde stage), and type III (hydrothermal sulfides). Type I and type II are time equivalent but spatially separated, whereas type III is later. The different types of scheelite have distinctly different REE and trace element compositions. Type I scheelite is characterized by an average ΣREE of 67.9 ppm, LREE/HREE ratio of 24.4, δEu of 8.5, Mo of 0.1 ppm and Sr of 1058 ppm, whereas type II scheelite features an average ΣREE of 48.1 ppm, LREE/HREE ratio of 10.6, δEu of 0.67, Mo of 1892 ppm and Sr of 90.1 ppm. Type III scheelite has an average ΣREE of 53.9 ppm, LREE/HREE ratio of 4.8, δEu of 17.5, Mo of 92.9 ppm and Sr of 37.1 ppm. The extremely high concentrations of Sr and highly positive Eu anomalies in type I scheelite are likely related to release of these elements from plagioclase in the granite during greisenization, whereas the extremely low concentrations of Mo may be related to the reducing and high-temperature nature of the magmatic fluid – Mo probably was mainly in the Mo4+ state and could not replace W6+ in the scheelite lattice. In contrast, the negative Eu anomalies and high Mo concentrations in type II scheelite suggest that the mineralizing environment in the retrograde alteration stage was relatively oxidizing, causing Eu to exist mainly as Eu3+, which is difficult to replace Ca2+ in scheelite, and Mo mainly as Mo6+, which is easy to replace W6+ in scheelite. In the sulfide mineralization stage, the fluid became relatively reducing again, and Eu2+ could easily replace Ca2+ in scheelite causing positive Eu anomalies, whereas Mo mainly exists as Mo4+ and precipitated as molybdenite, and so has limited substitution for W6+ in scheelite. The REE and trace element compositions of the dominant W mineral (type II scheelite), characterized by high concentrations of Mo, high LREE/HREE ratios and negative Eu anomalies, indicate that the ore-forming materials were mainly derived from the granitic intrusions. The variation of REE and trace elements in scheelite in time and space reflects a complex magmatic-hydrothermal mineralization process involving various fluid-rock reactions within the intrusion and in the country rocks. The formation of the Zhuxi W deposit is linked with a large fertile granitic intrusion, which delivered a large amount of W to the site of mineralization through convection within the magma chamber, and W precipitation in the skarn was largely caused by an abrupt drop in temperature and increase in pH of the ore-forming fluid.

Comparative geochemical study of scheelite from the Shizhuyuan and Xianglushan tungsten skarn deposits, South China: Implications for scheelite mineralization

Year: 2019
Products: New Wave;
Authors: Wu, S;Mao, J;Ireland, T;Zhao, Z;Yao, F;Yang, Y;Sun, W;
Journal: Ore Geology Reviews

Scheelite has been analyzed from the Shizhuyuan and the Xianglushan world-class W deposits from the Nanling W–Sn region and Jiangnan W belt, respectively. The Shizhuyuan deposit consists of proximal skarn and greisen W–Sn–Mo–Bi and distal Pb–Zn–Ag veins. The Xianglushan deposit, contains layer-like sulfide–scheelite and skarn W orebodies on granite cupolas overprinted by W greisen veins. Scheelite in skarn ores from the Shizhuyuan contains higher concentrations of Mo than those in the sulfide–scheelite and skarn ores from the Xianglushan deposit, reflecting differences between oxidizing and reducing magmatic-hydrothermal fluids. Under oxidizing conditions, W is accompanied by Mo partitions into exsolved fluids to form W–Mo garnet skarns, whereas under reducing conditions, little Mo is carried by exsolved fluids to form W pyroxene skarns. Trace element patterns of scheelite from both deposits show negative Ba, Sr, Zr, and Ti, and positive Ta anomalies. Rare earth element (REE) patterns of scheelite within skarns from the Shizhuyuan deposit have negatively inclined and flat M-type tetrad patterns, and scheelite from the greisens displays flat and positively inclined M-type tetrad patterns. We infer that the fluids formed scheelite within the W skarns and greisens inherited parental magma trace element and REE characteristics (depleted Ba, Sr, Zr, and Ti, enriched Ta, negative Eu anomalies, and tetrad effects). Whereas, scheelite from sulfide–scheelite veins and skarns of the Xianglushan deposit also has W- and MW-type tetrad REE patterns. The W-type tetrad REE patterns are complementary to REE patterns from the Renjiashan granite, and the MW-type tetrad REE patterns occur during a single evolutionary stage within a complex hydrothermal environment.

Formation of the Wulong gold deposit, Liaodong gold Province, NE China: Constraints from zircon U–Pb age, sericite Ar–Ar age, and H–O–S–He isotopes

Year: 2019
Products: NewWave;
Authors: Liu, J;Zhang, L;Wang, S;Li, T;Yang, Y;Liu, F;Li, S;Duan, C;
Journal: Ore Geology Reviews

The Wulong deposit is the largest quartz vein-type gold deposit in the eastern Liaoning Province of China. The gold ore bodies are hosted by Mesozoic biotite-granites. The mineralization occurs as veins with lenticular shapes. Laser-ablation-ICP–MS zircon U–Pb dating was used to date the biotite-granite, granite porphyry, and fine-grained diorites at the Wulong deposit, yielding ages of 155.4 ± 0.9 Ma, 154.2 ± 1.2 Ma, and 123.1 ± 0.9 Ma, respectively. A sericite sample from the gold ore yields a 40Ar–39Ar plateau age of 122.8 ± 0.8 Ma (MSWD = 0.09). The calculated δ18Ow values for the quartz range from 4.8% to 8.6% and the δDW values of fluid inclusion waters in quartz vary from −98% to −77%. The H–O isotope data indicates that ore-forming fluids could be of a magmatic origin. The δ34S values of metallic sulfides range from +1.1% to +2.4%, with an average of +1.8%, suggesting that the sulfur is derived from a magmatic source. The 3He/4He ratios of fluid inclusions in pyrite range from 0.36 to 0.65 Ra with an average of 0.50 Ra. The mantle helium involved in the ore-forming fluid ranges from 3.9% to 7.2%, indicating a crustal fluid source. The Wulong gold deposit was formed at ca. 120 Ma and it has a genetic association with contemporaneous fine-grained diorite. The Wulong deposit was formed during lithospheric thinning of the eastern North China Craton during the early Cretaceous.

Major and trace elements and sulfur isotopes in two stages of sphalerite from the world-class Angouran Zn–Pb deposit, Iran: Implications for mineralization conditions and type

Year: 2019
Products: NWR193;ESI;
Authors: Zhuang, L;Song, Y;Liu, Y;Fard, M;Hou, Z;
Journal: Ore Geology Reviews

The Angouran deposit is the second-largest Zn–Pb deposit in Iran with 4.7 Mt sulfide ore (27.7% Zn, 2.4% Pb, and 110 g/t Ag) and 14.6 Mt nonsulfide ore (28.1% Zn, 4.4% Pb). Various models have been proposed to explain the genesis of sulfide ore in this deposit. Moreover, the mineralization type of its primary sulfide ores remains controversial. The major and trace element concentrations and sulfur isotopic composition of the two stages of sphalerite have been analyzed to constrain mineralization conditions and the genesis. The Angouran deposit, which contains discordant orebodies, is hosted in a Neoproterozoic/Cambrian schist-marble sequence. Two stages of sphalerite have been distinguished: early-stage (S1) red-brown sphalerite and late-stage (S2) honey-yellow sphalerite. Our result shows that, relative to the S2 sphalerite, the S1 sphalerite has higher contents of Fe, Mn, Co, Cu, Ag, Sn, Ga, Sb and In, but lower contents of As and Tl. Time-resolved depth profiles in these sphalerites determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses indicate that Fe, Cd, Co, Hg, Mn, Ge, and In are mainly present in solid solution and that Ag, Cu, Pb, As, Ni, Ga, Tl, Sb, and Sn are present in both solid solution and mineral inclusions. Correlation analyses reveal the occurrence of direct substitution mechanisms, such as Zn2+ ↔ (Fe2+, Cd2+) and 2Zn2+ ↔ Ge4++□ (vacancy) as well as coupled substitutions, such as 2Zn2+ ↔ Cu+ + Ga3+, 2Zn2+ ↔ (Cu+, Ag+) + Sb3+, 3Zn2+ ↔ Pb2+ + Tl+ + As3+, 4Zn2+ ↔ Pb2+ + 2As3++□(vacancy) or (Zn2+, Pb2+) ↔ Tl+ + As3+, and 4Zn2+ ↔ Cu+ + (Ga3+, In3+) + Sn4++□(vacancy). Geothermometer studies suggest that sphalerite in the Angouran deposit precipitated from a low-temperature (<200 °C) hydrothermal system. Trace element concentrations also reveal that the estimated average temperature of ore-forming fluid decreases gradually and becomes relatively oxidized from early stage to late stage. The low contents of Mn, and In and Zn/Cd ratios and high contents of Cd and Ge in sphalerite are consistent with those of MVT deposits but are different than that of magmatism-related deposits (e.g., epithermal, skarn, carbonate-replacement, and volcanogenic massive sulfide deposits). Meanwhile, the δ34SV-CDT values of the S1 and S2 sphalerites, which range from 5.1‰ to 10.9‰, are atypical of magma-derived sulfur isotopic compositions. Therefore, the Angouran deposit was formed in a low-temperature (<200 °C) fluid system and can be classified as a Mississippi Valley-type (MVT) deposit.

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