Lead isotope variations across terrane boundaries of the Tien Shan and Chinese Altay

The Altaid orogen was formed by aggregation of Paleozoic subduction-accretion complexes and Precambrian basement blocks between the Late Proterozoic and the Early Mesozoic. Because the Altaids are the site of abundant granitic plutonism and host some of the largest gold deposits in the world, understanding their formation has important implications on the comprehension of Phanerozoic crustal growth and metallogeny. In this study, we present the first extensive lead isotope data on magmatic and metasedimentary rocks as well as ore deposits of the southern part of the Altaids, including the Tien Shan (Tianshan) and southern Altay (Altai) orogenic belts. Our results show that each terrane investigated within the Tien Shan and southern Altay is characterized by a distinct Pb isotope signature and that there is a SW-NE Pb isotope gradient suggesting a progressive transition from a continental crust environment in the West (the Kyzylkum and Kokshaal segments of the Southern Tien Shan) to an almost 100% juvenile (MORB-type mantle-derived) crust environment in the East (Altay). The Pb isotope signatures of the studied ore deposits follow closely those of magmatic and metasedimentary rocks of the host terranes, thus supporting the validity of lead isotopes to discriminate terranes. Whereas this apparently suggests that no unique reservoir has been responsible for the huge gold concentration in this region, masking of a preferential Pb-poor Au-bearing reservoir by mixing with Pb-rich crustal reservoirs during the mineralizing events cannot be exclude

Mineral Chemistry and U-Pb Garnet Geochronology of Strongly Reduced Tungsten Skarns at the Pampa de Olaen Mining district, Córdoba, Argentina

Los Guindos scheelite (±Zn, Bi, Sn, Ag) skarn presents mineral assemblages and a mineral chemistry similar to other worldwide strongly reduced W skarn deposits. Its reduced nature is defined based on the predominance of subcalcic garnets, Mo-free scheelite and absence of magnetite. Both the prograde and retrograde stages are evident at Los Guindos scheelite skarn. The prograde skarn is characterized by three zones: A zone I of garnet + helvine (Gr57Sps24Ad19Alm8 - Sps50Alm24Gr22Ad3; Grt + Hlv); a zone II of clinopyroxene + garnet (Di67Hd24Jo9 + Gr66Sps19Ad12Alm3; Cpx + Grt) and a zone III of garnet + vesuvianite (Gr73Ad22Sps3Alm2 - Gr58Sps22Ad10Alm9; Grt + Ves). Retrograde skarn is mainly represented by epidote - actinolite and minor F-rich actinolite (0.663 apfu of F) – potassium feldspar - chlorite (chamosite/clinochlore: ∼ 50/50) – muscovite – calcite - quartz. A hydrothermal stage developed in temporal continuity with retrograde skarn formed variable infilling associations of the following species: epidote – actinolite – scheelite – fluorite – calcite – quartz – sphalerite and chlorite. Scheelite mineralization process was triggered by an increase of Ca released during retrograde skarn replacements and was deposited during the following hydrothermal infilling stage. Other than sphalerite, minor bismuthinite and tetradymite, andorite, lillianite, gustavite, matildite and kësterite occur as hydrothermal associations after scheelite deposition. Scheelite-free reaction skarn preceding scheelite skarns was observed. Geobarometric calculations in this reaction skarn suggests an initial confining pressure of 2.5 kbar for the Los Guindos scheelite skarns. This pressure matches the estimated emplacement pressure of the Devonian-Carboniferous Achala batholith reported by previous authors. Geochemical correlation analyses suggest that this magmatism may have contributed mineralizing fluids channeled through regional structures and lithological contacts, causing infiltration metasomatism that originated scheelite (±Zn, Bi, Sn, Ag) mineralization in Cambrian and Ordovician country rocks. U-Pb analyses (LA-ICP-MS) of garnet in the Los Guindos scheelite skarn gave an age of 361 ± 11 Ma representing the age of the prograde stage of scheelite skarns and it should be framed within the Devonian-Carboniferous Metallogenic Epoch.Fil: Espeche, María José. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Museo de Mineralogía y Geología "Dr. A. Stelzner"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Wan, Bo. Chinese Academy of Sciences; República de ChinaFil: Lira, Raul. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Museo de Mineralogía y Geología "Dr. A. Stelzner"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Seltmann, Reimar. Natural History Museum; Reino Unid

Alkali-rich replacement zones in evolved NYF pegmatites: metasomatic fluids or immiscible melts?

IMA2018 Abstract submission Pegmatite mineralogy, geochemistry, classification and origins IMA2018-1337 Alkali-rich replacement zones in evolved NYF pegmatites: metasomatic fluids or immiscible melts? Axel Muller* 1, John Spratt2, Rainer Thomas3, Ben J. Williamson4, Reimar Seltmann2 1Natural History Museum, University of Oslo, Oslo, Norway, 2Department of Earth Sciences, Natural History Museum, London, United Kingdom, 3Chemistry and Physics of Earth Materials, German Research Centre for Geoscience GFZ, Potsdam, Germany, 4Camborne School of Mines, University of Exeter, Penryn, United Kingdom What is your preferred presentation method?: Oral or poster presentation : Replacement zones (RZ), which are a common feature of evolved granitic pegmatites, are irregular, commonly alkali-rich zones superimposing, cross-cutting and replacing the primary zonation in almost all consolidated pegmatite bodies. RZ are widely considered to result from late-stage metasomatism even though little is known about the melts and/or fluids involved in their formation. However, the observed textures and mineral paragenesis of RZ cannot be explained by metasomatism in a strict sense. In this study, the nature of the late stage silicate melt forming “cleavelandite” RZ is assessed from textural, mineralogical, chemical and melt inclusion studies of evolved, Proterozoic Niobium-Yttrium-Fluorine (NYF) rare metal pegmatites from Evje–Iveland, southern Norway. These were studied as they are mineralogically simple, compared with RZ in evolved Lithium-Caesium-Tantalum (LCT) pegmatites. Silicate melt inclusions in RZ-forming topaz and “cleavelandite” document high H2O contents of up to18 wt.% of the F-rich silicate melt from which the RZ crystallized. In addition, from mineral compositions (“cleavelandite”, “amazonite”, white mica, garnet, columbite group minerals, topaz, fluorite, and beryl), they must have also been strongly alkaline (Na-dominated) with enrichments in F (at least 4 wt.%), Cs, Rb, Ta, Nb, Mn, Ge, Bi, As, and in some cases also Li compared with host pegmatites. These elements are concentrated in a few RZ-forming minerals resulting in very distinctive mineral-trace element signatures. “Amazonite” is strongly enriched in Cs and Rb and often white mica and beryl in Li and Cs. To acquire these mineral compositions, the overall Li-Cs-Ta-poor Evje-Iveland original pegmatite melt must have undergone extreme internal chemical differentiation resulting in melt/melt immiscibility aiding rheology contrasts and resulting in RZ formation. The resulting RZ-forming H2O-F-rich silicate melt would have shown large differences in viscosity and density, and therefore physical flow/transport properties, to the host pegmatite melt resulting in discordant contacts. The mineralogy and melt inclusion data from the Evje-Iveland pegmatites document a gradient of crystallization temperatures within the investigated pegmatite bodies with highest temperatures at the pegmatite margin (during initial emplacement, ~680°C) and lowest temperatures within the RZ (<500°C). Considering the temperature and pressure conditions of the host rocks gneisses and amphibolites (~650°C, up to 5 kbar) at the time of pegmatite emplacement and the crystallization conditions of the RZ, the Evje- Iveland pegmatites and RZ likely formed over a period of 2.2 million years, assuming an exhumation rate of 1.5 mm per million years and a geothermal gradient of 45°C km-1. Such a long crystallization time contradicts the classical view that pegmatites represent strongly undercooled melts which crystallize relatively fast.The attached document is the authors’ submitted version of the oral presentation. You are advised to consult the publisher’s version if you wish to cite from it

Porphyry Cu(Mo) deposits of the Urals: insights from molybdenite trace element geochemistry

The first data on EMPA and LA-ICPMS study of molybdenite from four porphyry deposits of the South and Middle Urals (Tomino, Mikheevskoe and Benkala porphyry Cu and Talitsa porphyry Mo deposits) are presented. It is shown that most trace elements form mineral inclusions within molybdenite in all the deposits studied; only Re and W are most likely to be incorporated into the molybdenite lattice. Porphyry Cu deposits (Tomino and Mikheevskoe) formed within oceanic arc settings are featured by high contents of Re (mostly over 400 ppm) and low contents of W (<10 ppm) in molybdenite; porphyry Cu deposits from Andean-type geotectonic environment (Benkala) are featured by lower Re content (hundreds ppm) and high contents of W (tens ppm) in molybdenite. Molybdenite from porphyry deposits from collisional setting (Talitsa) has low content of Re and elevated W contents (tens ppm). It is demonstrated that trace element geochemistry of molybdenite is a useful tool to define the source of metal components and the geotectonic environment for porphyry Cu(Mo) deposits.The attached document is the authors’ submitted version of these conference proceedings. You are advised to consult the publisher’s version if you wish to cite from it

Adakite-like granitoids of Songkultau: A relic of juvenile Cambrian arc in Kyrgyz Tien Shan

The early Paleozoic Terskey Suture zone, located in the southern part of the Northern Tien Shan domain in Kyrgyzstan, comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deep-marine sediments. In the Lake Songkul area, early-middle Cambrian pillow basalts are crosscut by the Songkultau intrusion of coarse-grained gneissose quartz diorites and tonalites with geochemical characteristics typical for high-SiO2 adakites (SiO2 ​> ​56 ​wt.%, Al2O3 ​> ​15 ​wt.%, Na2O ​> ​3.5 ​wt.% and high Sr/Y and La/Yb ratios). The Songkultau granitoids have positive initial εNd (+3.8 to +6.4) and εHf (+12.3 to +13.5) values indicating derivation from sources with MORB-like isotopic signature. Volcanic formations, surrounding the Songkultau intrusion, have geochemical affinities varying from ocean floor to island arc series. This rock assemblage is interpreted as a relic of an early-middle Cambrian primitive arc where the adakite-like granitoids were derived from partial melting of young and hot subducted oceanic crust. An age of 505 ​Ma, obtained for the Songkultau intrusion, shows that hot subduction under the Northern Tien Shan continued until middle Cambrian. The primitive arc complexes were obducted onto the Northern Tien Shan domain, where the Andean type continental magmatic arc developed in Cambrian and Ordovician. Formation of the Andean type arc was accompanied by uplift, erosion and deposition of coarse clastic sediments. A depositional age of ca. 470 Ma, obtained for the gravellites in the Lake Songkul area, is in agreement with the timing of deposition for lower Ordovician conglomerates elsewhere in the Northern Tien Shan, and corresponds to the main phase of the Andean type magmatism. The Songkultau adakites in association with surrounding ocean floor and island arc formations constitute a relic of a primitive Cambrian arc and represent a juvenile domain of substantial size identified so far within the predominantly crustal-derived terranes of Tien Shan. On a regional scale this primitive arc can be compared with juvenile Cambrian arcs of Kazakhstan, Gorny Altai and Mongolia.©2020 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

The influence of fractionation of REE-enriched minerals on the zircon partition coefficients

Zircon is widely used to simulate melt generation, migration and evolution within the crust and mantle. The achievable performance of melt modelling generally depends on the availability of reliable trace element partition coefficients (D). However, a large range of DREE values for zircon from natural samples and experimental studies has been reported, with values spanning up to 3 orders of magnitude. Unfortunately, a gap of knowledge on this variability is evident. In this study we model the crystallization processes of common REE-bearing minerals from granitic melts and show that the measured zircon DREE would be elevated if there is crystallization of REE-enriched minerals subsequent to zircon. Nevertheless, compared to zircon DREE values measured from experimental studies, this mechanism appears to have a less significant influence on those from natural granite samples since the quantity of crystallized REE-enriched minerals is very low in natural magmatic systems and/or most of them crystallize prior to zircon. Combined with recently published studies, this work supports that analysis of natural zircon/host groundmass pairs provides more robust DREE values applicable to natural systems than those measured from experimental studies, which can be used to constrain the provenance of detrital zircons.This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. It is available as an open access article under a Creative Commons Licence https://creativecommons.org/licenses/by-nc-nd/4.0/

Mineralogical study of the Gonçalo Li-pegmatite deposit, Portugal

Beside the Scandinavian countries and Serbia, Portugal is among the European countries with the most significant lithium resources. The Li-rich occurrences in Portugal are mainly associated with aplite-pegmatite dykes and sills intruded in granitic and metasedimentary rocks of the Central Iberian and Galicia – Trás-os-Montes geotectonic zones (Carvalho & Farinha, 2004). The Gonçalo Li-pegmatites in the Guarda district (currently only used as decorative stone) have significant economic importance. Among other deposits, Gonçalo is a reference site in the focus of the EU FAME project (www.fame-project.eu) that aims to unlock the development potential of the most promising European Sn-W-Li ore types. Results of optical microscopy, QEMSCAN©, Raman and electron-probe microanalysis of the Gonçalo Li-pegmatite deposit have been employed to determine the mineralogical variability of the pegmatites with the aim to determine the deportment of lithium and potential rare-metal by-products and to guide enhanced mineral processing technologies.Available to download freely and reproduced here with permission of the publisher. The attached file is the published pdf

Cooling and exhumation of the Late Paleozoic Tulasu epithermal gold system, Western Tianshan, NW China: implications for preservation of Pre-Mesozoic epithermal deposits

Epithermal gold deposits are rarely well preserved in pre-Mesozoic terranes because their low-temperature mineralization in shallow crust levels, and easily destroyed by subsequent erosion or depleted by tectonic events. However, several significant late Paleozoic epithermal gold deposits have been found in the Tulasu volcanic basin in NW China, forming one of the largest gold districts in the western Tianshan orogen. Here, we report new 40Ar/39Ar age from a monzonite porphyry enclave hosted in andesite and apatite fission track (AFT) data for 10 volcanic rocks from the Tulasu basin. These data, combined with the previous dataset, are used to perform inverse thermal modelling to quantify the district's cooling and exhumation history. Our modelling indicates a phase of burial reheating during late Paleozoic sedimentation following the mineralization, and subsequent a rapid exhumation in the Jurassic to Early Cretaceous (∼196–128 Ma), and a slow exhumation until to present. The Mesozoic exhumation is likely related to the far-field effects of the Cimmerian orogeny along the southern Eurasian margin. Therefore, we suggest that the quick burial by thick sediments and the slow protracted exhumation after mineralization were crucial for the preservation of the Paleozoic epithermal gold system at Tulasu.© 2020 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics The attached file is the final accepted manuscript

Orogen architecture and crustal growth from accretion to collision (IGCP#662): Scientific Activities 2018-2019

The scientific board of the International Geoscience Programme (IGCP), jointly sponsored by IUGS and UNESCO, approved for funding in March 2018 the IGCP-662 project (2018-2023) entitled “Orogenic architecture and crustal growth from accretion to collision”. Four meetings and field excursion, as well as training courses, have been successfully held respectively in 2018 and 2019. The first workshop was held during 21th - 22nd September 2018 in Beijing, China, with a 5-day (15th - 19th September) preworkshop field trip and one-day (23 September 2018) post-conference training course on “Using isotopes in zircon and sulfides to understanding crust-mantle evolution”. The second workshop and field trip of the IGCP-662 project were held in Mongolia from July 4th - 10th, 2019. Besides, the IGCP-662 project joined as co-sponsor the organization of an international symposium “The Geology of Eurasia” held at the Helmholtz-Centre Potsdam - German Research Centre for Geosciences (GFZ) during 26th June - 1st July 2019.This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited

Plagioclase-mantled K-feldspar in the Carboniferous porphyritic microgranite of Altenberg-Frauenstein, Eastern Erzgebirge/Krusné Hory

The Upper Carboniferous porphyritic microgranite of Altenberg-Frauenstein, formerly known as Granitporphyr (Dalmer 1896) and here abbreviated as GP, forms a 36 km long and up to 18 km wide complex of ring dykes related to the Teplice-Altenberg caldera in the German–Czech border region of the Eastern Erzgebirge/Krusné Hory. The microgranites are characterized by the occurrence of plagioclase-mantled K-feldspar phenocrysts. The microgranite varieties representtwo main stages of intrusion evolved from acid (GP I) to intermediaterocks (GP II) within the intrusion. The most acid rock (GP Icum) occurs as enclaves in GP I and GP II and is interpreted as a cumulate of K-feldspar and quartz phenocrysts. The porphyritic microgranites show field, textural and geochemical evidence suggesting that some of them have formed as a result of interaction between felsic and mafic magmas. Mixing features are abundant in the porphyriticquartz-feldspar-hornblende microgranite (GP II) interpreted as a hybrid rock. They are less discrete in the early phase (GP I) and not obvious in the acid enclaves (GP Icum). This trend seems to reflect a continuous deflation of the magma chamber from the top to the bottom. According to the definition of rapakivi granites after Haapala and Rämö (1992), the porphyritic microgranite of Altenberg-Frauenstein may be considered as rapakivi granite although ovoid alkali feldspar megacrysts typical of classical rapakivi granites are not recorded.However, due to its Carboniferous age and being the only known granitewith rapakivi texture in the German–Czech part of the Variscan belt, the microgranite of Altenberg-Frauenstein is exceptional