70 research outputs found
Mineral Chemistry and U-Pb Garnet Geochronology of Strongly Reduced Tungsten Skarns at the Pampa de Olaen Mining district, Córdoba, Argentina
No full textLos 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?
No full textIMA2018 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.NHM Repositor
Trace elements and cathodoluminescence of quartz in stockwork veins of Mongolian porphyry-style deposits
No full textThe combination of scanning electron microscope–cathodoluminescence (CL), fluid inclusion analysis and high-resolution electron probe microanalysis of Al, Ti, K and Fe in vein quartz has yielded results permitting a greater understanding of the complex mineralisation of the Central Oyu Tolgoi and Zesen Uul porphyry-style deposits, southern Mongolia. These data demonstrate the relationship between quartz precipitation, dissolution and ore deposition as the mineralising fluid chemistry changed through time. Four major quartz generations are identified in the A-type veins from the stockworks of both the Central Oyu Tolgoi (OTi to OTiv) and Zesen Uul deposits (ZUi to ZUiv). Despite differences in the associated alteration and mineralisation style, the observed CL textures and trace element signatures of the quartz generations are comparable between deposits. The OTi and ZUi stage formed both the primary network of A-type veins and pervasive silicification of the host rock. Using the Ti-in-quartz geothermometer, crystallisation temperatures for OTi and ZUi of between 598°C and 880°C are indicated. The main stage of sulphide mineralisation was accompanied by the dissolution of pre-existing quartz (OTi and ZUi) and precipitation of a weakly luminescent generation of quartz (OTii and ZUii) with a low Ti content, reflected in a calculated temperature drop from approximately 700°C to 340°C in Central Oyu Tolgoi and 445°C in Zesen Uul. OTii and ZUii stage quartzes show high and variable Al concentrations. The next stage of quartz in both deposits (OTiii and ZUiii) forms a fine network of veins in cracks formed in pre-existing quartz. OTiii and ZUiii quartz contain measurable fluid inclusions of moderate salinity (3–17.1 wt.% NaCl eq.), entrapped in the temperature range 256°C to 385°C. OTiii and ZUiii are not related to any sulphide mineralisation. The final OTiv and ZUiv stages are characterised by quartz–calcite micro-breccias that penetrate the A-type veins. Based on the calculated entrapment temperatures, the OTiv/ZUiv stage crystallised between 212°C and 335°C, and the quartz is characterised by elevated but variable Al and Fe contents. The CL and trace element signatures of the OTi to OTiii and ZUi to ZUiii stages of the two Mongolian porphyries show similar features to those observed in porphyry-style deposits from other regions. This suggests that a common sequence of quartz crystallisation occurs during the formation of early veins in many porphyry copper systems
A review of mineral systems and associated tectonic settings of northern Xinjiang, NW China
No full textAbstractIn this paper we present a review of mineral systems in northern Xinjiang, NW China, focussing on the Tianshan, West and East Junggar and Altay orogenic belts, all of which are part of the greater Central Asian Orogenic Belt (CAOB). The CAOB is a complex collage of ancient microcontinents, island arcs, oceanic plateaux and oceanic plates, which were amalgamated and accreted in Early Palaeozoic to Early Permian times. The establishment of the CAOB collage was followed by strike-slip movements and affected by intraplate magmatism, linked to mantle plume activity, best exemplified by the 250 Ma Siberian Traps and the 280 Ma Tarim event. In northern Xinjiang, there are numerous and economically important mineral systems. In this contribution we describe a selection of representative mineral deposits, including subduction-related porphyry and epithermal deposits, volcanogenic massive sulphides and skarn systems. Shear zone-hosted Au lodes may have first formed as intrusion-related and subsequently re-worked during strike-slip deformation. Intraplate magmatism led to the emplacement of concentrically zoned (Alaskan-style) mafic–ultramafic intrusions, many of which host orthomagmatic sulphide deposits. A huge belt of pegmatites in the Altay orogen, locally hosts world-class rare metal deposits. Roll-front, sandstone-hosted U mineralisation completes the rich mineral endowment of the northern Xinjiang terranes
15th Quadrennial International Association on the Genesis of Ore Deposits Symposium - Symposium Proceedings
No full textFil: Servicio Geológico Minero Argentino; Argentina.Fil: International Asociation on the Genesis of Ore Deposits (IAGOD)Fil: Asociación Geológica Argentina; Argentina.El simpósio "15th Quadrennial International Association on the Genesis of Ore Deposits Symposium" se llevó a cabo en Salta, Argentina, entre el 28-31 de agosto del 2018.CONTENT
SESSIONS
CHAPTER 1: EPITHERMAL GOLD DEPOSIT /
Convenor: Diego Guido ;
CHAPTER 2: ORE DEPOSITS IN EXTENSIONAL TECTONIC SETTINGS /
Convenor: Silvia Lagorio ;
CHAPTER 3: ORE DEPOSITS RELATED TO GRANITES: FROM ORE FORMING PROCESSES
TO METALLOGENY /
Conveners: Jingwen Mao, Shao-Yong Jiang, Xiaoming Sun ;
CHAPTER 4: METALLOGENY OF THE ANDES /
Convenor: Nora Rubinstein ;
CHAPTER 5: METALLOGENY OF CRATONIC AREAS /
Convenor: Martín Gozalvez ;
CHAPTER 6: GLOBAL TECTONICS AND METALLOGENY: ORE DEPOSIT SETTINGS AND PREDICTIVE
MODELLING APPLIED TO MINERAL RESOURCES /
Convenor: Martín Gozalvez ;
CHAPTER 7: GEOCHEMISTRY OF ORE FORMING FLUIDS /
Convenor: Daniel Moncada ;
CHAPTER 8: PRECISION GEOCHRONOLOGY AND ISOTOPE GEOLOGY OF ORE-FORMING PROCESSES:
ITS IMPORTANCE IN EXPLORATION AND METALLOGENIC MODELLING /
Convenor: Carlos Herrmann ;
CHAPTER 9: ORE MINERALOGY /
Convenor: Nigel Cook ;
CHAPTER 10: NEW DISCOVERIES AND NEW RESEARCH ON SKARN DEPOSITS /
Conveners: Zhaoshan Chang, Larry Meinert ;
CHAPTER 11: NEW DEVELOPMENTS IN MAGMATIC SULFIDE AND OXIDE DEPOSITS IN SOUTH
AMERICA AND WORLDWIDE /
Conveners: María Emilia Schutesky Della Giustina, David Holwell ;
CHAPTER 12: MAGMATIC-HYDROTHERMAL SYSTEMS AND THE FORMATION OF ORE DEPOSITS /
Conveners: Fernando Tornos, David Lentz ;
CHAPTER 13: HIGH-TECH CRITICAL METALS: EVALUATION AND DEPOSIT MODELS. MEETING THE
RESOURCE DEMANDS OF THE LOW /
Conveners: Kenzo Sanematsu, Yasushi Watanabe, Jens C. Andersen, Reimar Seltmann ;
CHAPTER 14: TECHNICAL DEVELOPMENTS AND GEOLOGICAL APPLICATIONS IN REMOTE SENSING:
FROM SATELLITES TO UNMANNED AERIAL VEHICLES (UAV) /
Conveners: Valery Bondur, Sergey Cherkasov ;
CHAPTER 15: URANIUM DEPOSITS AND RESOURCES /
Conveners: Luis López, Michel Cuney, Mostafa Fajek ;
CHAPTER 16: BASE METALS IN SEDIMENTARY SEQUENCES /
Conveners: Thierry Bineli-Betsi, Josefina Pons, Joseph Zulu ;
PLENARY LECTURES
METALLOGENIC POTENTIAL OF ARGENTINA /
Eduardo Zappettini ;
SINGULARITY OF LITHOSPHERE PHASE TRANSITION AND ORIGINATION OF PORPHYRY MINERALIZATION /
Qiuming Cheng ;
NATIONAL MINERAL EXPLORATION STRATEGIC ACTION PLAN-APPLICATION OF METALLOGENIC
THEORY AND EXPLORATION IN CHINA /
Li Jinfa ;
MINERAL EXPLORATION MODELS FROM SIMPLE FICTION TO COMPLEX REALITY /
Reimar Seltmann ;
COPPER DEPOSITS IN BRAZIL: GEOLOGICAL SETTING, PROCESS AND EVOLUTION OF MINERAL SYSTEMS /
Lena Monteiro ;
CHARACTERISTIC FEATURES OF THE EPITHERMAL ENVIRONMENT THAT HAVE IMPLICATIONS
FOR EXPLORATION /
Jeffrey Hedenquist ;
PALEOZOIC PORPHYRY CU (MO, MU) SYSTEMS FROM THE URALS /
Olga Plotinskaya ;
WHY DETAILED MINERALOGY IS IMPORTANT: UNDERSTANDING EVOLUTION OF THE
OLYMPIC DAM IRON-OXIDE COPPER-GOLD SYSTEM, SOUTH AUSTRALIA /
Nigel Cook ;
IRON OXIDE COPPER-GOLD (IOCG) SYSTEMS: EXAMINATION OF END-MEMBER MODELS, PHYSICOCHEMICAL PROCESSES, AND POSSIBLE MODERN ANALOGUES / David Lentz ;
MICROBIOLOGY AND THE FORMATION OF ORE DEPOSITS / Fernando Tornos ;
RARE EARTH MINERAL SYSTEMS ASSOCIATED WITH ALKALINE INTRUSIONS AND CARBONATITES / Franco Pirajn
Geodynamics and metallogeny of the central Eurasian porphyry and related epithermal mineral systems: A review
No full textTwo different types of granitoids in the Suyunhe large porphyry Mo deposit, NW China and their genetic relationships with molybdenum mineralization
No full textCassiterite U-Pb geochronology constrains magmatic-hydrothermal evolution in complex evolved granite systems: The classic Erzgebirge tin province (Saxony and Bohemia)
No full textThe influence of fractionation of REE-enriched minerals on the zircon partition coefficients
No full textZircon 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/.NHM Repositor
Geological and mineralogical characteristics of REE mineralisation of the Verkhnee Espe and Iysor granitoid massifs (East Kazakhstan)
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