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Elemental Scientific Lasers’ NWR Systems

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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).

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 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.

Post-Linear Pottery cultural boundary and repopulation of the German Rhineland: Revisiting the Western contacts hypothesis

Year: 2019
Products: NWR193;ESI;
Authors: Denis, S;Gjesfjeld, E;Moreau, L;
Journal: Journal of Archaeological Science: Reports

The lack of consensus surrounding the macroscopic determination of high-quality black flint discovered at the Aldenhoven Plateau sites (Rhineland, North-Western Germany) from the beginning of the Middle Neolithic has far-reaching consequences for the anthropological understanding of the socio-cultural dynamics involved in the neolithization of North-Western Europe. This flint has been assigned to Western Belgian 'Obourg' flint type and is used as a key indicator of strong links between populations from West Belgium (Mons Basin) and the German Rhineland at the beginning of the 5th millennium BC. Here, we present an integrated study of this flint using geochemical and lithic technological approaches. This work rules out attribution of the analysed flint artefacts to the Upper Cretaceous flint sources of the Mons Basin; however, the exact origin of the black flint used in the Rhineland remains unanswered. Our results do not support the hypothesis of intensive contact between populations from West Belgium and the German Rhineland and highlights the urgent need for further combined petrographic and geochemical analyses in the region, particularly on geological samples, in order to build up an extensive and reliable comparative reference collection.

XRF and LA-ICP-MS studies of gold and silver artefacts from a 12–13th century CE tumulus in Senegal: Implications for the medieval African gold trade

Year: 2019
Products: NWR193;ESI;TwoVol;
Authors: Magnavita, S;Mertz-Kraus, R;
Journal: Journal of Archaeological Science: Reports

Silver and gold artefacts from a 12–13th c. CE tumulus in Senegal were recently analysed by means of XRF and LA-ICP-MS. The identification of major, minor and trace elements allowed gaining a rare insight into the composition of precious metals circulating in that part of Africa in medieval times. The results show that all objects were made of polymetallic alloys. Comparisons with analyses from other West African as well as North African and European silver and gold artefacts suggest that the metal from the studied objects most probably originate from outside West Africa. At least in the case of the gold artefacts, this is quite surprising, as we expected to come across pure West African gold. The results hint at a hitherto little known facet of the medieval African gold trade. It is concluded that, in addition to the acknowledged mass export of West African raw gold toward North Africa, there was also a thus far widely ignored traffic of alloyed gold (and silver) into West Africa.

LA-ICP-MS labels early medieval Tuscan finds from Siena and Donoratico as late natron glass

Year: 2019
Products: NWR193;
Authors: Hellemans, K;Cagno, S;Bogana, L;Janssens, K;Mendera, M;
Journal: Journal of Archaeological Science: Reports

The late antique/early medieval age in Central Italy is a well-suited context to verify the implications of the end of the natron glass supplies, and to explore the beginnings of the new plant-ash glass technology. We present the results of a LA-ICP-MS analysis campaign conducted on archaeological glass finds excavated at the Santa Maria della Scala hospital site in Siena and in Donoratico. This provided us with major, minor and trace element quantitative data for 49 glass samples belonging to drinking vessels and lamps, dated mainly between the 5th and the 8th century. On the basis of these data, we have sought to identify the working processes and possible glassware trade that are reflected in the glass composition. Major and minor element contents revealed that most samples, also at the later boundary of the explored timeframe, fit well within known late Roman glass classifications (e.g. HIMT, Levantine). Trace element analysis provided further information on the raw materials that were used in the glassmaking process, indicating the use of coastal sands as a silica source and allowing us to formulate different hypotheses on the materials used for the colouring process.

Chemical analyses and production technology of archaeological glass from Athienou-Malloura, Cyprus

Year: 2019
Products: New Wave;
Authors: Lin, Y;Liu, T;Toumazou, M;Counts, D;Kakoulli, I;
Journal: Journal of Archaeological Science: Reports

Ancient glasses (between ca. 480 BCE and 647 CE), from the archaeological site of Athienou-Malloura near the modern village of Athienou in central Cyprus, was analyzed using a multi-analytical approach, contributing to scientific scholarship of pre-Late Antique Cypriot glass composition and production technology and to ancient glass chemistry of the Mediterranean region and the broader Middle East. Glass microsamples were analyzed using scanning electron microscopy (SEM) and electron probe micro-analysis (EPMA) for the characterization of the major and minor elements, and by quadrupole-laser ablation-inductively coupled plasma-mass spectrometry (q-LA-ICP-MS) for quantification of trace elements and rare earth elements (REEs). Results indicated a soda-lime-silicate glass, characteristic of the Mediterranean natron glass used from the middle of the first millennium BC to the ninth century AD. Most glass fragments studied were de-colorized through the intentional addition of antimony and/or manganese-containing minerals, a practice commonly applied and documented during the Roman period. Trace elements analysis suggested at least two different sources of sands and minor mixing or recycling. Comparison with published chemical analyses on Cypriot Early Byzantine glass from coastal regions suggested similar sources of raw materials used in glass making from the Cypro-Classical to the Roman period, which points to a possible continuity in glass supply to Cyprus from the same primary production centers in the ancient Levantine coast.

Forensic comparison of PVC tape backings using time resolved LA-ICP-MS analysis

Year: 2019
Products: NWR193;ESI;
Authors: Kuczelinis, F;Weis, P;Bings, N;
Journal: Forensic Chemistry

Adhesive tapes are common tools for criminal acts such as the construction of improvised explosive devices. Hence, tape samples can be used as evidence to link a suspect to a scene of crime or different crime scenes to each other. A set of 87 black electrical tapes was the subject of a study evaluating a LA-ICP-MS method for the characterization of tape backings regarding their elemental composition in a forensic context. LA-ICP-MS is a powerful tool in forensic investigations due to fast, quasi nondestructive analysis of small samples and detection or determination of elements up to the ultra-trace range. In this study, the development of a semiquantitative LA-ICP-MS method for forensic tape examination using doped polymethacrylate as an “in-house” external calibration standard is presented. Semiquantitative data of Al, B, Ba, Bi, Ca, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Nb, Nd, Ni, Pb, Pr, Rb, Sb, Sr, Ti, Tl, W, Y, Zn and Zr were obtained. These data were used to assess different match criteria with respect to their performance for the discrimination of tape samples originating from different rolls and association of tape samples from the same roll. A dataset of 87 PVC electrical tape samples from different rolls and a dataset of 24 samples (3 fragments from 8 sections) from each of three different rolls were analyzed to assess the discrimination and association potential of the method. The best compromises were found to be at 99.3% (100%) correct associations and 98.5% (97.5%) discrimination for symmetrical 5 (6) sigma match criteria using fixed relative standard deviations, which considered inter-day variations.

Provenance of sediments in western Foothills and Hsuehshan Range (Taiwan): A new view based on the EMP monazite versus LA-ICPMS zircon geochronology of detrital grains

Year: 2019
Products: UP213;New Wave;New Wave Research;
Authors: Chen, C;Lee, C;Lin, J;Chu, M;
Journal: Earth-Science Reviews

The provenance of sediments in western Taiwan has been the subject of debate in recent years. Previous investigators, solely based on the U-Pb zircon geochronology for the detrital grains, all advocated the important roles, but with varying emphasis, of drainage systems in the South China Block. Influence of the Changjiang (Yangtze) River from the far-source Yangtze block versus nearby systems like Zhujiang, Minjiang and Jiulongjiang Rivers in the Cathaysia block has been the main issue. However, the fundamental question of whether the provenance is really the South China Block has never been evaluated. Here we report both the U-Pb zircon and Electron MicroProbe (EMP) monazite age data for seven sediment samples from two sides of the Taiwan Strait and synthesize the published data for all these rivers and sedimentary strata in western Taiwan to tackle this problem. The lack of, or insufficient, ~1.8 Ga monazites in the sediments of river mouths for all drainage systems in the South China Block makes them unlikely to be the source of Miocene sediments in western Taiwan where ~1.8 Ga monazite grains occupy 14.5–33.3% of the total age population. With reference to the tectonic evolution of the coastal southeast China-Taiwan region during Early Cretaceous to recent time, we propose a new explanation that invokes a now-concealed microcontinent along the Manila Trench. This microcontinent, probably related to a Paleoproterozoic orogen in Gondwana, eventually collided with the South China Block causing uplift of the easternmost structural element—the Pingtan-Dongshan Metamorphic Belt (PDMB) at ca. 130–120 Ma. It then drifted away sometime after 100 Ma and split into two parts with one becoming today's Palawan-Mindoro terrain of the Philippines. As indicated by the geophysical data near southern Taiwan, the remainder of this split microcontinent had subducted underneath the Philippine Sea plate along Manila Trench as a result of the opening of the South China Sea at ~33 Ma. Both the Peikang and Kuanyin basement highs in the offshore western Taiwan represent the unsubducted remnants of this microcontinent and also the major suppliers of Late Oligocene-Miocene sediments in western Taiwan. On the other hand, the Eocene-Early Oligocene strata of the Hsuehshan Range in central Taiwan show both zircon and monazite age patterns resembling the Eocene-Early Oligocene and recent sediments of the Zhujiang drainage system, indicating the southwestern origin of the protolith Taiwan. This scenario also matches the recent proposition that part of the Central Range belongs to the deep-level accretionary prism of a Miocene subduction system.

A new upper Paleogene to Neogene stratigraphy for Sarawak and Labuan in northwestern Borneo: Paleogeography of the eastern Sundaland margin

Year: 2019
Products: NWR193;New Wave;
Authors: Hennig-Breitfeld, J;Breitfeld, H;Hall, R;BouDagher-Fadel, M;Thirlwall, M;
Journal: Earth-Science Reviews

The Miri Zone in Sarawak contains thick Paleogene to Neogene sedimentary successions that extend offshore into the Sarawak Basin (Balingian and Central Luconia Provinces) and Sabah Basin. Exploration offshore has shown the Sarawak Basin in the South China Sea contains major hydrocarbon reservoirs. The sediments on land are age equivalents of the offshore successions and can be used to provide insights into their sedimentological and stratigraphic relations. However, because the rocks are found in mountainous regions covered by dense rainforest much of the stratigraphy in the Miri Zone is poorly known, as are timings and causes of major unconformities in the region that are essential for understanding the tectonic history, basin development, and sedimentary pathways. In this study we integrate fieldwork, UPb zircon dating, biostratigraphy, and light and heavy mineral analyses to present a revised stratigraphy for the region as well as paleogeographic maps, including major paleo-river systems for the main sedimentary basins. Rocks studied include parts of the Cretaceous to Eocene deep marine Rajang Group, fluvial to marginal marine sediments of the Oligocene to Early Miocene Tatau, Buan, Nyalau and Setap Shale Formations, and the Miocene sediments which are assigned to the Balingian, Begrih and Liang Formations in the Mukah-Balingian province, and the Belait Formation on Labuan.

Recurrent Quaternary magma generation at Baekdusan (Changbaishan) volcano: New zircon U-Th ages and Hf isotopic constraints from the Millennium Eruption

Year: 2019
Products: NWR193;ESI;
Authors: Cheong, AC;Jeong, YJ;Jo, HJ;Sohn, YK;
Journal: Gondwana Research

It is well known that Baekdusan (Changbaishan), an active 2744-m-high stratovolcano located on the border between North Korea and China, initiated trachytic/commenditic eruption in the Pleistocene but the petrogenetic and temporal evolutions of this alkaline magma system remain insufficiently constrained. The so-called “Millennium Eruption” (ME) in the mid-10th century, which resulted in the formation of the world's highest caldera lake (Cheonji, or Tianchi) atop the mountain, was one of the largest and most violently explosive volcanic eruptions to have occurred on Earth in the past 2000 years. Here, we present U–Th disequilibrium ages and Hf isotopic compositions of zircons from trachydacitic pumices ejected during the ME. Taken together with the previous U–Th isotope data, our laser ablation-multicollector ICPMS analyses of the zircons yielded multiple age components consisting of an earliest Holocene cluster (11.3 ± 1.3 ka) and Middle–Late Pleistocene populations (ca. 230 and 110 ka), which indicates that Baekdusan magma has been generated episodically at intervals of ca. 120–100 ky. If the eruption ages assigned for the samples analyzed in the previous isotopic studies are correct, the consistent age pattern of zircon may suggest the persistent existence of the same magmatic plumbing system beneath Baekdusan since the ME. The wide range of zircon εHf values (+5.8 to −3.5) reflects an interaction between the EM1-type primitive magma and pre-existing crustal materials, evidenced by the presence of a xenocrystic zircon core showing a significantly negative εHf value (=−21). A broad negative correlation observed between zircon εHf and the published δ18O values can be ascribed to the progressive assimilation of weathered supracrustal rocks, likely in the course of magma chamber expansion.

U-Pb detrital zircon geochronology and provenance of Neoproterozoic sedimentary rocks in southern Siberia: New insights into breakup of Rodinia and opening of Paleo-Asian Ocean

Year: 2019
Products: UP193-FX;ESI;
Authors: Gladkochub, D;Donskaya, T;Stanevich, A;Pisarevsky, S;Zhang, S;Motova, Z;Mazukabzov, A;Li, H;
Journal: Gondwana Research

We present the synthesis of new data on detrital zircon geochronology of the Neoproterozoic strata of the southern part of the Siberian craton as well as a comprehensive analysis of previously published stratigraphic, sedimentological and geochronological (LA-ICP-MS) data obtained for key sections in this area that allows us to trace the process of birth and early stages of development of the Paleo-Asian Ocean (PAO). Before the break-up of Rodinia and opening of PAO, Tonian – Cryogenian intracontinental sedimentary basin existed between southern Siberia and northern Laurentia. The detachment of the southern flank of the Siberian craton from northern Laurentia and opening of the PAO between these cratons took place in Cryogenian. The detrital zircon ages from lower parts of Neoproterozoic successions suggest the Siberian craton as the sole provenance area right after the opening of the PAO. The age constraints on the lower parts of the studied Neoproterozoic successions, which are based on correlation of their tillite horizons with the Marinoan glaciation, suggest the late Cryogenian age for these sedimentary rocks. A clear change in the age spectra of detrital zircons from “unimodal” (Early Precambrian only) in older sedimentary rocks to “bimodal” (Early Precambrian as well as Neoproterozoic) in younger sequences of the studied successions marks the next stage of the PAO evolution. The abundance of youngest (630–610 Ma) detrital zircons in the upper parts of the studied sequences reflects a shrinkage of the oceanic basin as a result of the convergence of the craton with the microcontinents and island arcs within the Paleo-Asian Ocean. We suggest that a passive oceanic margin along the southern margin of the Siberian craton has been transformed into a series of foreland basins at ~610 Ma.

The disastrous copper. Comparing extraction and chelation treatments to face the threat of copper-containing inks on cellulose

Year: 2019
Products: NWR193;ESI;
Authors: Zaccaron, S;Potthast, A;Henniges, U;Draxler, J;Prohaska, T;McGuiggan, P;
Journal: Carbohydr Polym

Iron gall inks are known to be detrimental to the permanence of historic documents. Among the transition metals present, copper is the greatest threat and an open challenge due to the lack of Cu-specific treatments. In this study, we address the inhibition of copper by comparing extraction (a newly proposed glucose-based treatment) vs. chelation (phytate-based) approaches in terms of performances in scavenging copper and slowing the degradation rate, and of possibly induced side effects. Results show that the glucose treatment partially extracts copper, but it causes long-term damages to paper, i.e. increased fragility and discoloration. The phytate protocol was found beneficial in inhibiting the catalytic activity of copper-rich inks. It limits both long-term oxidation and hydrolytic breakdown of samples without compromising the visual appearance.

A Paleoproterozoic mantle source modified by subducted sediments under the North China craton

Year: 2019
Products: UP213;New Wave;
Authors: Xu, C;Chakhmouradian, A;Kynický, J;Li, Y;Song, W;Chen, W;
Journal: Geochimica et Cosmochimica Acta

Subduction is an effective mechanism for deep recycling of supracrustal rocks and mantle refertilization. However, the timing of the onset of modern-style deep subduction is debated. Here we report geochronogical and geochemical data for an intrusive suite of ultramafic, syenitic and carbonatitic rocks, a carbonatite-hosted peridotite xenolith, and granulites from the Paleoproterozoic Trans-North China orogen in the North China craton (NCC). The xenolith differs in composition from typical cratonic mantle peridotites. It equilibrated at T ≈ 1100 °C and P ≈ 29 kbar, i.e. under hotter conditions than cratonic mantle xenoliths worldwide. The carbonatites and associated alkaline rocks were emplaced at 1810 ± 3 Ma and are related to the Paleoproterozoic collision between the Western and Eastern segments of the NCC. These intrusions show Sr-Nd isotope compositions consistent with an enriched mantle source [(87Sr/86Sr)i = 0.7027–0.7039; εNd(t) = −4 to −6], and contain zircon characterized by unradiogenic Hf isotope compositions [εHf(t) = −5 to −9] and high δ18Osmow values (7.9–9.5‰). In contrast, basement granulites and wall-rock granites are enriched in radiogenic Nd and Hf isotopes, but low in 18O. These differences rule out the possibility of crustal contamination. Our results thus suggest that modern-style plate tectonics dates back at least to the Paleoproterozoic Era, and the post-collisional Paleoproterozoic alkaline magmatism in the NCC tapped mantle sources modified by deep sediment recycling.

Timing and petrogenesis of metamafic-ultramafic rocks in the Southern Brasília orogen: Insights for a Rhyacian multi-system suprasubduction zone in the São Francisco paleocontinent (SE-Brazil)

Year: 2019
Products: NWR213;ESI;
Authors: Pinheiro, M;Suita, M;Lesnov, F;Tedeschi, M;Silva, L;Medvedev, N;Korolyuk, V;Pinto, C;Sergeev, S;
Journal: Precambrian Research

A systematic investigation of amphibolites and a metaultramafite granofels was carried out in the southernmost Brasília Orogen, part of the reworked margin of the São Francisco paleocontinent. These rocks occur interleaved within Neoproterozoic metasediments and the Archean-Paleoproterozoic basement. The amphibolites from the Andrelândia, Liberdade and the Carrancas nappe system show an N-MORB signature, enriched to slightly depleted in LILE (Large Ion Lithophile Elements) and LREE (Light Rare Earth Elements) and depletion in the HFSE. They define a flat sub primitive mantle (PM) normalized curve with negative anomalies of Nb and Ce. The Lima Duarte nappe amphibolite has an andesitic basalt with an E-MORB signature and magmatic arc filiation. U-Pb (SHRIMP) zircon dating on the different samples yielded similar crystallization ages of ca. 2.15 Ga. Metamorphic conditions record amphibolitic facies for all the samples and can be linked to lower intercepts aged between 560 and 590 Ma. Whole rock Nd isotopic data suggest a juvenile source with TDM ages between 1.95 and 2.22 Ga. The associated metaultramafite, from Carrancas Klippe, highlights inherited cryptic layering and fractional crystallization processes from mineral and whole rock chemistry. It is enriched in LILE and shows negative anomalies of Th and Nb and positive anomalies of Sr and Zr. The Platinum group elements present a total PGE abundance of 16.5 and 30.8 ppb. The Iridium group defines a steep positive normalized curve while the Palladium group defines a gentle positive one, as expected for differentiated liquids. U-Pb zircon dating yielded three data clusters: i) the ca. 2.5 Ga, interpreted as inheritance, ii) the ca. 2.1 Ga, considered as the crystallization age and, iii) the youngest, being ca. 600 Ma, associated with the amphibolite facies metamorphic overprint. REE analyses on Rhyacian zircons suggest plagioclase crystallization under the influence of free-REE bearing minerals. A magmatic zircon grain containing a quartz inclusion, presents a distinctive REE pattern, with a positive normalized curve and a strong negative Eu anomaly. It suggests a hybridized crystallization under influence of plagioclase-rich and silica-saturated fluids prior or during the igneous crystallization, possibly due to the influence of slab derived materials. These data unravel new insights towards mafic-ultramafic rocks formation in different settings within a Rhyacian suprasubduction system in the southernmost part of the São Francisco paleocontinent, later reworked during the Gondwana amalgamation.

The nature and significance of the Faroe-Shetland Terrane: Linking Archaean basement blocks across the North Atlantic

Year: 2019
Products: UP213;NewWave;
Authors: Holdsworth, R;Morton, A;Frei, D;Gerdes, A;Strachan, R;Dempsey, E;Warren, C;Whitham, A;
Journal: Precambrian Research

Core samples of the continental basement rocks that underlie the eastern Faroe-Shetland Basin (FSB) and its inshore margins west of Shetland reveal a suite of predominantly granodioritic to granitic orthogneisses (including TTG), together with lesser volumes of foliated granitoids and subordinate dioritic to mafic gneisses and amphibolites. A small area of lithologically similar gneisses also crops out onshore at North Roe/Uyea west of the Caledonian front in Shetland. In the core samples, coarse grained gneissose textures and mineralogies consistent with upper amphibolite facies metamorphism are overprinted by a weak, but ubiquitous, static greenschist facies retrogression. Later structures include widespread epidote-quartz veining, and local developments of mylonite, cataclasite, pseudotachylite and phyllonite. Regions associated with the Rona Ridge oil fields (e.g. Clair, Lancaster) also preserve extensive brittle fracturing and associated low temperature hydrothermal mineralization (quartz, adularia, calcite, pyrite/chalcopyrite) with significant fracture-hosted hydrocarbons. New and published U-Pb zircon analyses from the gneisses offshore give a relatively narrow range of Neoarchaean protolith ages (ca 2.7–2.8 Ga) spread over a geographic area of 60,000 km2 west of Shetland. Detrital zircon data from overlying Triassic-Cretaceous sedimentary sequences in the FSB suggest an equivalent limited range of Neoarchaean source materials. Hf isotopic data indicate involvement of Palaeo- to Mesoarchaean crustal sources. Overall, our findings suggest that a major phase of Neoarchaean crustal formation and associated high grade metamorphism dominates basement rocks in the region. They are similar in age and lithology to the protoliths of the nearest onshore Lewisian Complex of NW Scotland (Rhiconich Terrane). However, they lack geochronological or textural evidence for the widespread Proterozoic Laxfordian events (ca 1.7–1.8 Ga) which are widespread in Scotland. This suggests that the Precambrian rocks west of Shetland – the Faroe-Shetland Terrane – can be correlated with the Archaean rocks of the Central Greenland-Rae Craton and that a northern limit of Proterozoic reworking lies just offshore from the north coast of Scotland.

Conflicting zircon vs. titanite U-Pb age systematics and the deposition of the host volcanic sequence to Kiruna-type and IOCG deposits in northern Sweden, Fennoscandian shield

Year: 2019
Products: UP213;
Authors: Billström, K;Evins, P;Martinsson, O;Jeon, H;Weihed, P;
Journal: Precambrian Research

The Northern Norrbotten region, and in particular the Kiruna area, hosts a number of large apatite iron oxide deposits (e.g. the huge Kiirunavaara ore) of significant economic importance. Age data from rock lithologies hosting these ores, represented by metamorphosed rocks of the Porphyrite and Kiirunavaara Groups, are complex to interpret. This is illustrated by (LA-ICP-MS) data for titanite, and to some extent for rutile, which scatter considerably yielding ages within a span from ca. 2.1 Ga to 1.7 Ga. These analysed hydrothermal minerals, characterized by complex BSE images revealing darker and brighter zones, are located in ore zones and associated with e.g. strong scapolitisation, albitisation and actinolitisation. Previous (TIMS) zircon ages of host rocks, on the other hand, define a more narrower age interval between ca. 1900 and 1870 Ma, and this is supported by new U-Pb zircon results presented here. Furthermore, one coherent set of SIMS data for titanite from the Luossavaara ore favour that crystallization took place at ca 1.88 Ga, although laser ICP data from the same locality are much more complex. An implication arising from published pre-1.9 Ga laser ablation ages for titanites is that the emplacement of host rocks started already at around 2.1 Ga. As the depositional time of these rocks is crucial for the understanding of the overall crustal formation in northern Norrbotten, additional rocks were selected for age dating. New zircon age data (LA-ICP-MS and SIMS) give support to a scenario where host rocks to ores started to develop at around 1900 Ma and this calls for a re-evaluation of published LA-ICP-MS data of hydrothermal mineral phases.

Grenvillian orogeny in the Oulongbuluke Block, NW China: Constraints from an ∼1.1 Ga Andean-type arc magmatism and metamorphism

Year: 2019
Products: UP213;NewWave;
Authors: Yu, S;Li, S;Zhang, J;Liu, Y;Peng, Y;Sun, D;Li, Y;
Journal: Precambrian Research

A systematic petrologic, geochemical, and zircon U-Pb and Lu-Hf isotopic investigation of an ∼1.1 Ga arc magmatism and metamorphism was studied to evaluate the Grenvillian orogeny and assembly of Rodinia in the Oulongbuluke Block in NW China. The peak metamorphic P-T conditions of the paragneiss were restricted to 4.8–5.8 kbar and 652–700 °C based on P-T pseudosection and conventional geothermobarometry. Zircon U-Pb ages of 1132 ± 33 Ma, 1118 ± 9 Ma, and 1124 ± 12 Ma were determined for the metabasite, augen granitic gneiss, and paragneiss, respectively, indicating magmatic intrusion and a metamorphism event in the late Mesoproterozoic. The metabasites exhibited enrichment of light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) and depletion of heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs), resembling the geochemical characteristics of Andean arc magmatism. The whole-rock geochemistry and in-situ zircon εHf(t) values of 4.3 and 11.2 suggested that the protolithic mafic magma originated from a subduction-modified lithospheric mantle. The low zircon εHf(t) values of −5.2 and −0.5 also suggested that the calc-alkaline augen granitic gneisses were derived from the partial melting of a late Paleoproterozoic crustal source. The ∼1.1 Ga arc-related magmatism and metamorphism in the Oulongbuluke Block indicated the occurence of a tectonic-thermal event in an Andean-type active continental margin in the late Mesoproterozoic. In this regard, the Oulongbuluke Block was likely temporarily connected to the Qilian Block and Tarim Craton, forming a single continuous block with similar Grenville age during the late Mesoproterozoic to early Neoproterozoic (1.1–0.9 Ga).

Removing a mask of alteration: Geochemistry and age of the Karadag volcanic sequence in SE Crimea

Year: 2019
Products: NewWave;
Authors: Popov, DV;Brovchenko, VD;Nekrylov, NA;Plechov, PY;
Journal: Lithos

The Karadag Massif in south-eastern Crimea hosts a thick sequence of volcanic rocks, which underwent significant secondary alteration. Here we deduce the effects of alteration, remove their mask and estimate the primary chemical composition and age of these volcanic rocks using their bulk chemical analyses, as well as chemical data from plagioclase, ortho- and clinopyroxene-hosted melt inclusions, and Ar isotope analyses of plagioclase and groundmass from the freshest andesite. Our data reveal two distinct magmatic series in the Karadag Massif. The first defines a subalkaline, calcic, medium-K series with high enrichment in LILE, U, Th and LREE relative to HREE, Y, Zr, Hf, Nb and Ta, which is typical of supra-subduction volcanic rocks. According to previously published trace element data, most of the Karadag volcanic rocks belong to this series. We use Ar isotope data to argue that the age of these rocks is 172.8 ± 4.5 Ma, which is consistent with the biostratigraphy. No reliable major-element chemical data and no isotopic data were obtained from the second series, although its trace-element signature is similar to that of some Nb-enriched supra-subduction volcanic rocks. It is characterised by less pronounced enrichment in LILE, U, Th and LREE relative to HREE, Y, Zr, Hf, Nb and Ta, and relatively high contents of Nb and Ta. Typical supra-subduction series of the Karadag Massif is similar to other pre-Cretaceous magmatic rocks exposed in Crimea, and hence likely formed in a similar environment. Literature data on Middle Jurassic magmatic rocks of the Pontides Belt in northern Turkey also allow to distinguish two magmatic series, which closely correspond to the magmatic rocks in Crimea. This is consistent with palaeotectonic reconstructions which suggest that the Pontides Belt was joined to Crimea prior to the opening of the Black Sea, and they formed a single volcanic arc.

Geochronology, geochemistry, and Sr–Nd–Hf isotopic compositions of mafic–ultramafic intrusions in the Niubiziliang Ni–(Cu) sulfide deposit, North Qaidam Orogenic Belt, NW China: Implications for magmatic source, geodynamic setting, and petrogenesis

Year: 2019
Products: UP213;NewWave;
Authors: Yu, L;Sun, F;Li, L;Li, B;Peng, B;Xu, C;Li, R;Wang, F;Shen, D;
Journal: Lithos

Whole-rock geochemical and SrNd isotopic data, and zircon U–Pb–Hf isotopic data are reported for mafic–ultramafic intrusions in the Niubiziliang Ni–(Cu) sulfide deposit, located in the westernmost segment of the North Qaidam Orogenic Belt (NQOB), NW China. NiCu sulfide ores of economic interest are found within these intrusions, with the Niubiziliang III and IV intrusions hosting most of the Ni–(Cu) mineralization. The Niubiziiang mafic–ultramafic intrusions intrude biotite–plagioclase gneiss of the Paleoproterozoic Dakendaban Group. Zircons separated from the gabbro, plagioclase-bearing clinopyroxenite, and olivine websterite yield UPb ages of 389 ± 2, 373 ± 2, and 380 ± 2 Ma, respectively, indicating a genetic linkage with Middle–Late Devonian regional magmatism (390–370 Ma). Gabbro zircons have εHf(t) values of 4.2–10.9 with older TDM1 ages (0.86–0.59 Ga). The Niubiziliang intrusions contain many xenoliths of Paleoproterozoic biotite–plagioclase gneiss, and the intrusions have similar trace element patterns with strong enrichment in LILEs (e.g., K, Rb, and Th) and moderate depletion in HFSEs (e.g., Nb, Ta, P, and Ti). The major and trace element characteristics, and Sr–Nd–Hf isotopic compositions indicate the parental magmas originated from a metasomatized, asthenospheric mantle source that had previously been modified by subduction-related fluids. The magmas experienced significant crustal contamination both in the magma chamber and during ascent, triggering sulfur over-saturation that resulted in the deposition and enrichment of sulfides. Considering the tectonic evolution of this region, we infer that the Niubiziliang mafic–ultramafic intrusions formed in a post-collisional extensional setting related to delamination of the subcontinental lithosphere.

Late Eocene granites in the Central Sakhalin Island (Russian Far East) and its implication for evolution of the Sakhalin-Hokkaido orogenic belt

Year: 2019
Products: UP213;New Wave;
Authors: Zhao, P;Alexandrov, I;Jahn, B;Liao, J;Ivin, V;
Journal: Lithos

The Sakhalin-Hokkaido orogenic belt along the western margin of the Okhotsk Sea is an important early Cenozoic accretionary orogen related to subduction of the Paleo-Pacific oceanic plate. In order to study the Eocene evolution of this accretionary orogen and related magmatism, we carried out zircon UPb dating, whole-rock elemental and SrNd isotopic analyses on the Langeri and Val'za granitic plutons that intruded the East Sakhalin accretionary complex in the central Sakhalin Island. Zircon UPb dating results revealed that the Langeri and Val'za plutons were emplaced in the late Eocene at 38–36 Ma. Whole-rock elemental data indicate that granitoids are mainly peraluminous S-type with subordinate I-type granites, and all granitic samples show arc-like geochemical affinity. Whole-rock SrNd isotopic results show consistent low initial 87Sr/86Sr ratios (0.7042 to 0.7049), positive εNd(t) values (+1.7 to +3.1) and young Nd two-stage model ages (611 to 717 Ma). Elemental and isotopic data reveal that granitic rocks of the Langeri and Val'za plutons were generated from remelting of metasediments and amphibolites in the accretionary complex. From comprehensive analyses of regional tectonics, we concluded that the late Eocene granitic rocks were generated in a syn-collisional tectonic setting, marking the timing for formation of the Sakhalin-Hokkaido orogenic belt. The middle-late Eocene welding of the Okhotsk Sea Plate and the Eurasia Plate is the most plausible mechanism that caused crustal thickening beneath the Sakhalin Island, and anatexis of metasediments and oceanic crustal materials in the lower crust might be responsible for the formation of late Eocene granitic rocks. Considering the Eocene tectonic events in NE Asia, late Paleocene to early Eocene subduction of the Kula-Pacific ridge beneath the Hokkaido Island and Eocene initial rift of pull-apart basins along strike-slip fault system in the Hokkaido and Sakhalin Islands may also contribute to the emplacement of Eocene magmatism in the Sakhalin-Hokkaido orogenic belt.

Mantle melting variation and refertilization beneath the Dragon Bone amagmatic segment (53°E SWIR): Major and trace element compositions of peridotites at ridge flanks

Year: 2019
Products: New Wave;ESI;
Authors: Wang, J;Zhou, H;Salters, V;Liu, Y;Sachi-Kocher, A;Dick, H;
Journal: Lithos

The evolution of the mantle melting regime and the process of refertilization beneath cold lithosphere remain ambiguous at ultraslow spreading ridges. Few previous studies were concerned with the temporal variations of mantle melting indicated by peridotites on the flank of a single ridge segment. Here, we present in-situ major and trace element analyses of harzburgites from the Dragon Bone ridge segment both from near the spreading axis and from rift mountains up to tens of kilometers from the ridge axis. We propose that the Dragon Bone mantle had been depleted anciently at higher pressures, prior to the recent ascent under the ridge at lower pressures, and only a limited volume of melt was generated during recent melting beneath the ridge. This interpretation is consistent with the high degree of depletion of the Dragon Bone harzburgites with little trapped melt, and thin discontinuous igneous crust on the seafloor. Comparison of peridotites from near-ridge locations with those further out on the flanks indicates that the melting regime has progressively shrunk over time creating at present a nearly amagmatic segment. Peridotites from segment ends are seldom affected by late-stage refertilization, while those from the segment center are highly depleted mantle residues (resembling those from fast spreading ridges) that sustained syn-melting metasomatism.

Early Palaeozoic metamorphism of Precambrian crust in the Zheltau terrane (Southern Kazakhstan; Central Asian Orogenic belt): P-T paths, protoliths, zircon dating and tectonic implications

Year: 2019
Products: UP213;NewWave;
Authors: Pilitsyna, A;Tretyakov, A;Degtyarev, K;Salnikova, E;Kotov, A;Kovach, V;Wang, K;Batanova, V;Plotkina, Y;Tolmacheva, E;Ermolaev, B;Lee, H;
Journal: Lithos

Palaeoproterozoic amphibole-biotite orthogneisses with a protolith age of ~ 1840 Ma and Neoproterozoic muscovite-chlorite orthogneisses with an estimated protolith age of ~ 790 Ma have been identified in the structure of the Zheltau terrane (Southern Kazakhstan; west Central Asian Orogenic belt). In addition, metasedimentary complexes represented by prevailing garnet-mica schists and subordinate muscovite-chlorite schists with obtained detrital zircon ages in the range of 604 - 2819 Ma (with two peaks at ~ 991 Ma and ~ 1082 Ma) also comprise the Zheltau terrane. In accordance with the Sm-Nd whole-rock isotopic compositions, the protolith of the observed Palaeoproterozoic orthogneisses formed as a result of a mixing of the Neoarchean crustal source with a juvenile source, whereas the formation of the Neoproterozoic orthogneisses protolith may have been related to the melting of Palaeoproterozoic crustal material. In turn, Late Mesoproterozoic – Early Neoproterozoic granitoids or felsic volcanic rocks, which formed as a result of the melting of Palaeoproterozoic continental crust, are considered as possible sources for the studied detrital zircons obtained from the schists. The terrigenous protolith of the schists from the Zheltau terrane accumulated in the range of ~ 600 to ~ 490 Ma, corresponding to the Ediacaran-Cambrian. Subduction processes in the Early Palaeozoic led to the burial of different horizons of the Zheltau terrane continental crust to significant depths; some of the complexes experienced high-pressure metamorphism at P 15 – 18 kbar; T 750 – 850 °C (high-pressure granulites), whereas most of the rocks were evidently metamorphosed at maximum amphibolite facies and avoided high-pressure re-equilibration. The spatial proximity of the studied metamagmatic and metasedimentary crustal complexes and similar metamorphic changes during the latest stages of retrogression imply their possible mutual exhumation from different levels during the period between 490 and 470 Ma and their following juxtaposition as a package of tectonic slices.

A record of assimilation preserved by exotic minerals in the lowermost platinum-group element deposit of the Bushveld Complex: The Volspruit Sulphide Zone

Year: 2019
Products: UP213;New Wave;New Wave Research;
Authors: Tanner, D;McDonald, I;Harmer, R;Muir, D;Hughes, H;
Journal: Lithos

Low-gradeplatinum-group element mineralisation in the Volspruit Sulphide Zone is sulphide-poor (<5 vol. %), distributed over a ~60 m-thick horizon in the lowermost cumulates of the northern limb of the Bushveld Complex. Unlike any other platinum-group element (PGE) deposit of the Bushveld Complex, the Volspruit Sulphide Zone is hosted exclusively within harzburgitic and dunitic cumulates in the Lower Zone of the Rustenburg Layered Suite. Here, we present a petrological investigation on the distribution of PGEs and chalcophile metals in mineralised pyroxenite cumulates from the Volspruit Sulphide Zone, to determine the origin of the PGE mineralisation in ultramafic cumulates and evaluate whether Volspruit-style mineralisation could occur in the stratigraphically lowest, ultramafic portions of other layered intrusions. Electron microscopy of pyroxenite cumulates revealed (1) chromite inclusions containing dolomite, albite, monazite, Pb-chlorides, base metal sulphides and Pt-As minerals, (2) the presence of exotic microxenocrysts (<300 μm diameter) in the pyroxenite matrix such as grains of CaCO3, U-Th-oxide and Mn-ilmenite, and (3) base metal sulphide assemblages enclosing grains of primary galena, sphalerite and Pb-chlorides. Systematic mapping of high-density mineral assemblages in pyroxenite cumulates across the Volspruit Sulphide Zone identified 196 precious metal mineral grains (Pt-, Pd-, Rh-, Au- or Ag-minerals), 98 Pb-sulphide grains (± Se, Cl), 27 Pb-chloride grains (± K, Se, Te, S), as well as 1 grain of Pb-telluride, 1 monazite grain and 1 grain of U–Pb-Th oxide. Trace element analyses of base metal sulphides reveal the highest S/Se values in pyrrhotite and chalcopyrite yet recorded in the Bushveld Complex. While some base metal sulphides are enriched in PGEs, the overall low-grade of the deposit and inferred fertile ultramafic magma(s) require relatively low R-factors (mass of silicate to sulphide melt) compared to other sulphide-poor PGE deposits, with a calculated R factor of ~500–3000. We consider that the presence of exotic inclusions in chromite, exotic microxenocrysts, and Pb/Zn/Cl grains enclosed within primary base metal sulphide assemblages provide strong evidence for crustal contamination in the Volspruit Sulphide Zone. The Malmani dolomite and the Black Reef quartzite within the lower Chuniespoort Group (2.2–2.4 Ga) are the most likely source of xenocrysts, assimilated in a staging chamber beneath the main Grasvally chamber, in which the Volspruit Sulphide Zone developed. It is possible that the Malmani dolomite contained an enrichment of Pb, Zn, Cl, and S minerals prior to assimilation. The assimilation of dolomite and limestone would locally increase the fO2 of the magma, triggering chromite crystallisation. The sudden removal of Fe from the melt, coupled with the addition of external sulfur triggered saturation of an immiscible sulphide melt in the ultramafic Volspruit magma. Chromite and base metal sulphides were subsequently emplaced into the main Grasvally magma chamber as a crystal-bearing slurry. Therefore, we consider it is possible for PGE mineralisation to occur in the ultramafic portion of any layered intrusion intruding in the vicinity of carbonate units. Even if this style of mineralisation in the lowermost portions of layered intrusions is sub-economic, it may reduce the grade or opportunity for PGE mineralisation higher up in the local magmatic stratigraphy, or in later magma emplacement events sourced from the same reservoir.

Petrogenesis of Cenozoic high–Sr/Y shoshonites and associated mafic microgranular enclaves in an intracontinental setting: Implications for porphyry Cu-Au mineralization in western Yunnan, China

Year: 2019
Products: New Wave;
Authors: Zhou, Y;Xu, B;Hou, Z;Wang, R;Zheng, Y;He, W;
Journal: Lithos

Cenozoic high–Sr/Y shoshonites in western Yunnan, China, are spatially and temporally associated with porphyry deposits and mafic volcanic rocks that formed at a post–collisional setting. However, the petrogenesis of these rocks and the origins of the associated mineralization remain unclear. Here we present new geochemical data for the high–Sr/Y shoshonites and associated mafic microgranular enclaves (MMEs) in the Jinshajiang–Ailaoshan mineralization belt, which formed as a result of India–Asia collision during the Cenozoic. Both fertile and barren shoshonitic porphyries were emplaced during the Eocene–Oligocene (32–37 Ma) and are characterized by enrichment in large–ion lithophile elements (LILE), depletion in high field strength elements (HFSE), high K2O (4–6 wt%), Sr contents (674–1370 ppm), and low Y contents (7–18 ppm). The barren Zhanhe, Yongsheng, Songgui, and Jianchuan, and fertile Machangqing (Cu–Au–Mo mineralization) porphyry intrusions have variable zircon εHf(t) values of −6 to +9 and old TDM2 ages of 1433 to 900 Ma. However, the barren Shigu porphyry intrusion yields relatively positive zircon εHf(t) values (−4 to +8) and younger TDM2 ages (903–631 Ma). These features indicate that the Shigu intrusion was derived from late Permian juvenile lower crust, and the other high Sr/Y shoshonites were derived mainly from Neoproterozoic juvenile lower crust. Fertile and barren porphyries have variable whole–rock εNd(t) values (−5 to −0.7) and (87Sr/86Sr) i ratios (0.70595–0.70788) that are within the range of coeval mafic magmas in western Yunnan. The MMEs comprise mafic enclaves and andesitic enclaves that formed during the Eocene (34–35 Ma) and have spheroidal shapes, igneous textures and contain acicular apatites. This indicates that the MMEs are globules of coeval mafic magma that was injected into and mixed with the host shoshonitic magma. The enclaves show low TiO2 contents (0.7–0.8 wt%), high MgO (6–9 wt%), Cr (184–450 ppm) and Ni contents (98–157 ppm), positive LILE anomalies, marked negative HFSE anomalies, a narrow range of εNd(t) values (−1.2 to −0.6), and (87Sr/86Sr) i values of 0.70556–0.70635. The andesitic enclaves show adakitic geochemical affinities and have similar zircon εHf(t) values (−2.7 to +2.5) to the host porphyries, whereas, the mafic enclaves have relatively negative zircon εHf(t) values (−8.7 to +1.5), similar to enriched mantle. These evidences suggest the high−Sr/Y shoshonites were produced by partial melting of juvenile lower crust mixed with ultrapotassic or potassic mafic magmas as represented by the andesitic enclaves. The mafic enclave melts were derived from enriched mantle metasomatized by slab–derived fluids, which elevated the Mg#, Cr, Ni contents of the host porphyries at Machangqing, Zhanhe and Yongsheng.

LA-ICP-MS/MS improves limits of detection in elemental bioimaging of gadolinium deposition originating from MRI contrast agents in skin and brain tissues

Year: 2019
Products: NWR193;New Wave;New Wave Research;
Authors: Clases, D;Fingerhut, S;Jeibmann, A;Sperling, M;Doble, P;Karst, U;
Journal: J Trace Elem Med Biol

A novel analytical method to detect the retention of gadolinium from contrast agents for magnetic resonance imaging (MRI) in tissue samples of patients is presented. It is based on laser ablation - inductively coupled plasma - triple quadrupole - mass spectrometry (LA-ICP-MS/MS). Both Gd and P were monitored with a mass shift of +16, corresponding to mono-oxygenated species, as well as Zn, Ca, and Fe on-mass. This method resulted in a significantly reduced background and improved limits of detection not only for phosphorus, but also for gadolinium. These improvements were essential to perform elemental bioimaging with improved resolution of 5 μm x 5 μm, allowing the detection of small Gd deposits in fibrotic skin and brain tumour tissue with diameters of approximately 50 μm. Detailed analyses of these regions revealed that most Gd was accompanied with P and Ca, indicating co-precipitation.

Origin of the Mo-bearing Xiaoshuijing Syenogranite in the Tengchong Terrane, SW China

Year: 2019
Products: NewWave;
Authors: Zou, H;Cao, H;Bagas, L;Zhang, Y;Zhang, S;Zhang, Q;Liu, H;Li, Y;
Journal: Ore Geology Reviews

The Xiaoshuijing Syenogranite is the host of Mo mineralisation recently discovered in the Tengchong Terrane of southwestern China. Here, we present new zircon U-Pb ages and molybdenite Re-Os ages, whole-rock geochemical data, and zircon Hf isotopic data for the Xiaoshuijing Syenogranite hosting disseminated Mo mineralisation. The syenogranite’s mineralogical and geochemical characteristics indicate it is a high-K, alkaline, and peraluminous granite. LA-ICP-MS analysis of zircon yields an age of 65 ± 1 Ma (n = 14, MSWD = 2.1), and yields negative zircon εHf(t) values ranging from −18.23 to −12.92, interpreted to have a crustal source. The Re-Os Mo age of 64 ± 2 Ma (n = 4, MSWD = 2.2) for the mineralisation is the same as the syenogranite’s age, within error. The geochemistry also indicates that the syenogranite is related to a thickened crust resulting from the eastward subduction of the Neo-Tethyan oceanic lithosphere shortly before the collision of the Indian and Eurasian continental crusts.

Formation of the Baiyun gold deposit, Liaodong gold province, NE China: Constraints from zircon U–Pb age, fluid inclusion, and C–H–O–Pb–He isotopes

Year: 2019
Products: NewWave;
Authors: Liu, J;Liu, F;Li, S;Lai, C;
Journal: Ore Geology Reviews

The Baiyun gold deposit is located in the Liaodong peninsula in NE China. The gold orebodies are hosted in the Paleoproterozoic Liaohe Group metamorphic rocks. The alteration/mineralization can be divided into three stages: (I) quartz ± pyrite ± K-feldspar veins, (II) quartz-polymetallic sulfide veins, (III) quartz-carbonate veins. New LA–ICP–MS zircon U–Pb dating suggests all the ore-related porphyries, including monzonite porphyry (224.2 ± 1.3 Ma), quartz porphyry (221.4 ± 1.2 Ma) and diorite porphyry (221.8 ± 1.2 Ma), were emplaced in the Late Triassic. Four types of fluid inclusions (FIs) are identified in the ore-related quartz, i.e., liquid-rich two-phase, vapor-rich two-phase, CO2-bearing and pure CO2 FIs. The ore-forming fluids were likely characterized by medium temperature, low salinity, low density, CO2-rich, and belong to the H2O–NaCl–CO2 ± N2 ± C4H6 system. We propose that fluid phase separation likely caused rapid precipitation of the ore minerals. The C–H–O–Pb isotope data indicate that the ore-forming fluids may have had multiple sources, including magmatic, metamorphic and meteoric fluids. The ore-forming materials may have mainly derived from metamorphic rocks of the Proterozoic Gaixian Formation, and minor from the Triassic intermediate-felsic rocks. The He–Ar isotope data indicate that the ore-forming fluids were mainly crust-derived. We conclude that the Baiyun gold deposit is an orogenic-type system formed during the Late Triassic North China-Yangtze continent-continent collision.

In situ oxygen isotope, trace element, and fluid inclusion evidence for a primary magmatic fluid origin for the shell-shaped pegmatoid zone within the giant Dahutang tungsten deposit, Jiangxi Province, South China

Year: 2019
Products: UP213;
Authors: Zhang, Z;Hou, Z;Peng, H;Fan, X;Wu, X;Dai, J;
Journal: Ore Geology Reviews

The world-class Dahutang tungsten deposit is located within the Jiuling mining district of the central Jiangnan orogenic belt, Jiangxi Province, China. The deposit consists of a massive and gently dipping scheelite orebody that contains disseminated and veinlet-hosted mineralization located within a medium- to coarse-grained biotite granodiorite. The No. 1 ore block of the deposit also contains a 1.50–1.75 m thick shell-shaped pegmatoid zone that defines an inner contact zone between the mineralization-related porphyritic-like biotite granite and strongly mineralized biotite granodiorite that hosts the tungsten deposit. This pegmatoid zone contains very low concentrations of tungsten, but records the processes involved in the migration and enrichment of this element within the deposit. The pegmatoid contrasts with typical hydrothermal pegmatite-type ore in that it often contains megacrystic to giant alkali feldspar, quartz, and muscovite, and is spatially zoned in terms of unique texture and composition. The pegmatoid is zoned from a felsic aplite zone with a layered texture proximal to the intrusion through quartz–feldspar pegmatoid and feldspar–quartz pegmatoid zones to a final distal quartz-dominated zone. The quartz–feldspar pegmatoid is striped and contains megacrystic feldspars that have grown nearly perpendicular to the edge of the pegmatoid, indicating the direction of movement of early exsolved magmatic fluids. Cathodoluminescence imaging indicates that there are five types of quartz within the feldspar–quartz pegmatoid: megacrystic, large phenocrystic, small phenocrystic, matrix, and vein-hosted quartz. Each of these generations of quartz crystallized early, with the disseminated metasomatic quartz that crystallized during the middle stages of pegmatoid generation being followed by the uniform crystallization of late-stage, space-filling quartz. In situ oxygen isotopic and trace element analysis indicates that all of the quartz within the pegmatoid records accelerated growth, with the middle-stage disseminated metasomatic quartz associated with an increase in δ18Oquartz values, and the late-stage space-filling quartz associated with a decrease in δ18Oquartz values. All of this quartz contains elevated concentrations of alkali metals and has low Li/Al ratios (generally <0.35), indicating the majority of this quartz has an igneous origin, although some quartz formed from magmatic–hydrothermal or hydrothermal fluids. All the quartz formed under medium–high temperatures (≥483 °C) and elevated δ18O (11.05‰ ≤ δ18Oquartz ≤ 15.07‰) conditions. The majority of δ18Oquartz–water values are >10‰, reflecting the fact that the fluids that formed these minerals were of the peraluminous granite water (PGW). The trace element compositions of the samples analyzed during this study also indicate a drop in the pH of the pegmatoid-forming fluids over time. The quartz within the feldspar–quartz pegmatoid also contains melt and gas–liquid fluid inclusions, with the latter containing significant amounts of gas-phase CH4, indicating that the pegmatoid formed from low oxygen fugacity fluids. Our data indicate that the shell-shaped pegmatoid zone within the Dahutang No. 1 ore block formed from primary PGW exsolved from the hosting intrusion, with the pegmatoid recording the transition from magmatic to hydrothermal processes during the continuous but multi-stage evolution of the Dahutang deposit. The late-stage, high-temperature, water-rich, high δ18O, alkali-metal-rich, low oxygen fugacity, and acidic nature of the hydrothermal fluids that formed the deposit promoted the transportation and further deposition of tungsten.

The Yinachang Fe-Cu-Au-U-REE deposit and its relationship with intermediate to mafic intrusions, SW China: Implications for ore genesis and geodynamic setting

Year: 2019
Products: New Wave;
Authors: Zhu, L;Liu, J;Bagas, L;Carranza, E;Zhai, D;Meng, G;Wang, J;Wang, Y;Zhang, F;Liu, Z;
Journal: Ore Geology Reviews

The Yinachang Fe-Cu-Au-U-REE deposit is located in the Kangdian region at the southwestern margin of the Yangtze Block. This contribution presents petrological, geochronological, whole rock geochemical, and Rare Earth Elements (REE) geochemistry of zircons of gabbro and diorite dykes associated with the Yinachang Fe-Cu-Au-U-REE deposit, aiming to constrain the age of the mineralisation and help refine our understanding of the tectonic setting of the region. Zircons from diorite have a Palaeoproterozoic U-Pb age of 2014 ± 30 Ma, and zircons from the gabbro could not be dated because they are metamict, having a high concentration of uranium. The ca. 2014 Ma age of the zircons in the diorite indicates that the southwestern part of the Yangtze Block is partly synchronous with the Columbia Supercontinent. Geochemically, the diorite and gabbro are enriched in large-ion lithophile elements (LILEs) such as Rb and U, and depleted in high-field-strength elements (HFSEs) such as Nb, P, Ti, Ba, and Sr. The diorite is enriched in light REEs (LREEs) and has a slight to negligible Eu anomaly, which are characteristic of ocean-island basalts containing mantle-derived high potassic calc-alkaline rocks. In contrast, the gabbro is weakly enriched in LREEs and has a slightly negative Eu anomaly similar to those of potassic calc-alkaline enriched mid-ocean-ridge basalt. The average combined REE content of zircons from the gabbro is 19401 ppm and is significantly higher than that of the zircons from the diorite averaging 1020 ppm. This indicates that the gabbro is closely related with the REE mineralisation at the deposit. The geochemistry of the diorite indicates that it formed at the continental margin of a volcanic-arc. It also indicates that the magmatic rocks in the region have a possible mantle plume origin contaminated by crustal material and located at a transitional zone between a rift and an ocean-continent tectonic setting.


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