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Round Top Mountain rhyolite(Texas, USA), a massive, unique Y-bearing-fluorite-hosted heavy rare earth element(HREE) deposit

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Journal of Rare Earths 2014年第1期32卷 90-96页

作者： PINGITORE Nicholas CLAGUE Juan GORSKI Daniel Department of Geological Sciences The University of Texas at El Paso Texas Rare Earth Resources

Round Top Mountain in Hudspeth County, west Texas, USA is a surface-exposed rhyolite intrusion enriched in Y and heavy rare earth elements （HREEs）, as well as Nb, Ta, Be, Li, F, Sn, Rb, Th, and U. The massive tonnage, estimated at well over 1 billion tons, of the deposit makes it a target for recovery of valuable yttrium and HREEs （YHREEs）, and possibly other scarce ele-ments. Because of the extremely fine grain size of the mineralized rhyolite matrix, it has not been clear which minerals host the YHREEs and in what proportions. REE-bearing minerals reported in the deposit included bastn？site-Ce, Y-bearing fluorite, xeno-time-Y, zircon, aeschynite-Ce, a Ca-Th-Pb fluoride, and possibly ancylite-La and cerianite-Ce. Extended X-ray absorption fine struc-ture （EXAFS） indicated that virtually all of the yttrium, a proxy for the HREEs, resided in a coordination in the fluorite-type crystal structure, rather than those in the structures of bastn？site-Ce and xenotime-Y. The YREE grade of the Round Top deposit was just over 0.05%, with 72%of this consisting of YHREEs. This grade was in the range of the South China ionic clay deposits that supply essentially all of the world’s YHREEs. Because the host Y-bearing fluorite is soluble in dilute sulfuric acid at room temperature, a heap leaching of the deposit appeared feasible, aided by the fact that 90%-95%of the rock consists of unreactive and insoluble feld-spars and quartz. The absence of overburden, remarkable consistency of mineralization grade throughout the massive rhyolite, prox-imity （a few km） to a US interstate highway, major rail systems and gas and electricity, temperate climate, and stable political location in the world’s largest economy all enhanced the potential economic appeal of Round Top.

关键词： heavy rare earth elements yttrium-beating fluorite yttrofluorite heap leaching rhyolite Round Top deposit

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The Late Carboniferous–Early Permian Ocean-Continent Transition in the West Junggar,Central Asian Orogenic Belt: Constraints from Columnar Jointed rhyolite

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Acta Geologica Sinica(English Edition) 2019年第2期93卷 265-282页

作者： XU Shenglin CHEN Xuanhua LI Tingdong SHI Jianjie DING Weicui LI Bing HUANG Penghui ZHANG Yiping ZHANG Yaoyao MA Feizhou School of Earth Sciences and Resources China University of Geosciences Chinese Academy of Geological Sciences Beijing Research Institute of Geological Engineering Design

The West Junggar of the western Central Asian Orogenic Belt is one of the typical regions in the term of ocean subduction, contraction and continental growth in the Late Paleozoic. However, it is still controversial on the exact time of ocean-continent transition so far. This study investigates rhyolites with columnar joint in the West Junggar for the first time.Based on zircon U-Pb dating, we determined that the ages of the newly-discovered rhyolites are between 303.6 and 294.5 Ma, belonging to Late Carboniferous–Early Permian, which is the oldest rhyolite with columnar joint preserved in the world at present. Geochemical results show that the characteristics of the major element compositions include a high content of SiO_2(75.78–79.20 wt%) and a moderate content of Al_2O_3(12.21–13.19 wt%). The total alkali content(K_2O +Na_2O) is 6.14–8.05 wt%, among which K_2O is 2.09–4.72 wt% and the rate of K_2O/Na_2O is 0.38–3.05. Over-based minerals such as Ne, Lc, and Ac do not appear. The contents of TiO_2(0.09–0.24 wt%), CaO(0.15–0.99 wt%) and MgO(0.06–0.18 wt%) are low. A/CNK=0.91–1.68, A/NK=1.06–1.76, and as such, these are associated with the quasi-aluminum-weak peraluminous high potassium calc-alkaline and some calc-alkaline magma series. These rhyolites show a significant negative Eu anomaly with relative enrichment of LREE and LILE(Rb, Ba, Th, U, K) and depletion of Sr, HREE and HFSE(Nb, Ta, Ti, P). These rhyolites also have the characteristics of an A2-type granite, similar to the Miaoergou batholith,which indicates they both were affected by post-orogenic extension. Combining petrological, zircon U-Pb dating and geochemical characteristics of the rhyolites, we conclude that the specific time of ocean-continent transition of the West Junggar is the Late Carboniferous–Early Permian.

关键词： rhyolite columnar joint zircon U-Pb dating geochemistry ocean-continent transition West Junggar

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New insights into the origin of the bimodal volcanism in the middle Okinawa Trough： not a basalt-rhyolite differentiation process

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Frontiers of Earth Science 2018年第2期12卷 325-338页

作者： Yuxiang ZHANG Zhigang ZENG Shuai CHEN Xiaoyuan WANG Xuebo YIN Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment Institute of Oceanology Chinese Academy of Sciences Qingdao 266071 China Laboratory for Marine Mineral Resources Qingdao National Laboratory for Marine Science and Technology Qingdao 266071 China University of Chinese Academy of Sciences Beijing 100049 China

In the middle Okinawa Trough （MOT）,rhyolites have been typically considered as products ofcrystallization differentiation of basaltic magma as afeature of bimodal volcanism. However, the evidence isinsufficient. This paper compared chemical trends ofvolcanic rocks from the MOT with fractional crystal-lization simulation models and experimental results andutilized trace element modeling combined with Rayleighfractionation calculations to re-examine fractional crystal-lization processes in generating rhyolites. Both qualitativeand quantitative studies indicate that andesites, rather thanrhyolites, originate by fractional crystallization frombasalts in the MOT. Furthermore, we established twobatch-melting models for the MOT rhyolites and proposedthat type 1 rhyolites are produced by remelting of andesiteswith amphiboles in the residue, while type 2 rhyolites arederived from remelting of andesites without residualamphiboles. It is difficult to produce melts with a SiO2content ranging from 62% to 68% either by magmaticdifferentiation from basalts or by remelting of andesites,and this difficulty might help account for the compositionalgap （Daly gap） for bimodal volcanism in the OkinawaTrough.

关键词： Okinawa Trough rhyolite andesite remelting fractional crystallization

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Mineral Chemistry Indicates the Petrogenesis of rhyolite From The Southwestern Okinawa Trough

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Journal of Ocean University of China 2017年第6期16卷 1097-1108页

作者： CHEN Zuxing ZENG Zhigang WANG Xiaoyuan ZHANG Yuxiang YIN Xuebo CHEN Shuai MA Yao LI Xiaohui QI Hanyan Key Laboratory of Marine Geology and Environment Institute of Oceanology Chinese Academy of SciencesQingdao 266071 P. R. China Laboratory for Marine Mineral Resources Qingdao National Laboratory for Marine Science and TechnologyQingdao 266071 P. R. China University of Chinese Academy of Sciences Beijing 100049 P. R. China

To reveal the petrogenesis of rhyolite from the southwestern Okinawa Trough, the mineral chemistry of plagioclase, orthopyroxene, amphibole, quartz and Fe-Ti oxide phenocrysts were analyzed using an electron microprobe, and in suit Sr and Ba contents of plagioclase analysed by LA-ICPMS were chosen for fingerprinting plagioclases of different provenances. Results indicate an overall homogeneous composition for each of the mineral phases except for plagioclase phenocrysts which have a wide range of composition(An=39~88). Plagioclase crystals characterized by An contents of >70 are not in equilibrium with their whole-rock compositions, and coarse-sieved plagioclase phenocryst interiors record high An contents(>70) and Sr/Ba ratios(>7), which are similar to the those of plagioclase crystals in basalt. Therefore, these crystals must have been introduced to the rhyolitic magma from a more mafic source. Equilibrium temperatures estimated using orthopyroxene-liquid, iron–titanium oxide, titanium-in-quartz and amphibole geothermometers show consistent values ranging from 792 to 869℃. The equilibrium pressure calculated using amphibole compositions is close to 121 MPa which corresponds to an approximate depth of 4 km. The fO_2 conditions estimated from Fe-Ti oxides and amphiboles plot slightly above the NNO buffer, which indicates that the rock formed under more oxidized conditions. Our results suggests that petrogenesis of the rhyolite due to basaltic magma ascend with the high An and Sr/Ba plaigoclases from deep magma chamber into the shallow chamber where the fractional crystallization and crustal assimilation happened. It also indicates that a two-layer magma chamber structure may occur under the southwestern Okinawa Trough.

关键词： geothermobarometry oxygen fugacity xenocrysts magma evolution rhyolite Okinawa Trough

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rhyolites in continental mafic Large Igneous Provinces: Petrology,geochemistry and petrogenesis

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Geoscience Frontiers 2021年第1期12卷 53-80页

作者： Mahesh Halder Debajyoti Paul Sarajit Sensarma Department of Earth Sciences Indian Institute of Technology KanpurKanpur 208016India Centre of Advanced Study in Geology University of LucknowLucknow 226007India

We present a detailed review of the petrological and geochemical aspects of rhyolite and associated silicic volcanic rocks(up to 20 vol%of all rocks)reported to date from twelve well known Phanerozoic continental mafic Large Igneous Provinces(LIPs).These typically spread overrhyolites and associated silicic volcanic rocks(60-81 wt.%of SiO2)are mostly metaluminous to peraluminous and are formed via(ⅰ)fractional crystallization of parental mafic magma with negligible crustal contamination,and(ⅱ)melting of continental crust or assimilation and fractional crystallization(AFC)of mafic magma with significant crustal contribution.rhyolites formed by extensive fractional crystallization are characterized by the presence of clinopyroxene phenocrysts,exhibit steep negative slopes in bivariate major oxides plots and weak to no Nb-Ta anomaly;these typically have temperature>900℃.rhyolites formed by significant crustal contribution are characterized by strong negative Nb-Ta anomalies,absence of clinopyroxene phenocrysts,and are likely to have a magma temperaturerhyolite melt generation in the plagioclase stability field with a minor fraction originating from lower crustal depths.A large part of the compositional variability in rhyolites,particularly the SrNd-Pb-O isotope ratios,suggests a significant role of continental crust(upper crustal melting or AFC)in the evolution of these silicic rocks in the continental mafic LIPs.

关键词： Large Igneous Province Silicic rock rhyolite Geochemistry Petrogenesis AFC

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Geochronology and Geochemistry of the Granites from the Longtoushan Hydrothermal Gold Deposit in the Dayaoshan Area,Guangxi:Implication for Petrogenesis and Mineralization

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Journal of Earth Science 2019年第2期30卷 309-322页

作者： Lihua Qian Jianqing Lai Lifang Hu Rong Cao Shilong Tao Bei You Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring Ministry of EducationSchool of Geosciences and Info-physicsCentral South University

The gold mineralization in the Longtoushan hydrothermal gold deposit is concentrated within the contact zone of the granitic complex. Whole rock geochemistry and in-situ U-Pb and Hf isotopic data were used to constrain the genesis and age of the granites and related Cu-Au mineralization in the Longtoushan Deposit. The granites mainly consist of the granite porphyry, rhyolite porphyry, porphyritic granite and quartz porphyry. LA-ICP-MS U-Pb dating of zircons from the granite porphyry, rhyolite porphyry and quartz porphyry indicates that they intruded from ca. 94 to 97 Ma. These intrusions exhibit similar trace element characteristics, i.e., right-dipping REE patterns, depletion of Ba, Sr, P and Ti, and enrichment of Th, U, Nd, Zr and Hf. The εHf(t) values of zircons from the granite porphyry, rhyolite porphyry and quartz porphyry range from-26.81 to-8.19,-8.12 to-5.33, and-8.99 to-5.83, respectively, suggesting that they were mainly derived from the partial melting of the Proterozoic crust. The Cu-Au mineralization is mainly related to the rhyolite porphyry and porphyritic granite, respectively. The Longtoushan granites were most likely formed in a post-collisional extensional environment, and the deposit is a part of the Late Yanshanian magmatism related mineralization in the Dayaoshan area and its adjacent areas.

关键词： Longtoushan gold deposit rhyolite porphyry zircon U-Pb dating Hf isotopes petrogenesis Cu-Au mineralization

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The age and tectonic environment of the rhyolitic rocks on the western side of Wuyi Mountain,South China

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Science China Earth Sciences 2008年第8期51卷 1053-1063页

作者： SHU LiangShu DENG Ping YU JinHai WANG YanBin JIANG ShaoYong State Key Laboratory for Mineral Deposits Research Department of Earth SciencesNanjing UniversityNanjing 210093China Institute of Geology Chinese Academy of Geological SciencesBeijing 100037China Center of Iron-Probe in Beijing Beijing 100037China

During the geological survey of the metamorphic rocks in Xingning-Wuhua region on the western side of Wuyi Mountain, South China, we discovered the Neoproterozoic rhyolite and rhyolitic greywacke for the first time that outcrop in the Proterozoic metamorphic rocks near Jingnan Town of Xingning County, eastern Guangdong Province. A systematic research on petrology, geochemistry and geochronology of rhyolitic rocks was conducted to understand their tectonic setting and formation age. The Jingnan rhyolite is interbedded with a coeval greywacke, with a total thickness of 60 m; both rhyolite and greywacke display a similar folding and metamorphic pattern. Meta-rhyolite consists of groundmass and phenocrystals including sanidine, orthoclase, and quartz with distinct undulose extinction; the groundmass has been recrystallized into fine-grain feldspar, quartz and sericite aggregation. Meta-greywacke is composed of crystallinoclastic grains (sanidine, orthoclase, quartz and oligoclase) and clay groundmass. Zircon grains used for the SHRIMP U-Pb analysis are light brown-colored and euhedral or subeuhedral. Dating data suggest two age groups; eight grains of magmatype zircon with an idiomorphic form yield an age of 972±8 Ma, and the other seven weakly corroded grains of zircon with euhedral to subeuhedral shape construct an average age of 1097±11 Ma, which were captured from older rocks by an uplifting magma, implying that a late Mesoproterozoic basement exists in the Nanling region. In addition, one Paleoproterozoic age, 2035±11 Ma, is obtained from a rounded detrital zircon, indicating that a Paleoproterozoic thermal event took place in the South China. Geochemically, the Jingnan rhyolitic rocks are characterized by high K2O content, intermediate Al2O3 content, with the ACNK value 0.98―1.11, and belonging to high-K alkaline series. They are rich in ΣREE, Rb, Th and Ce, depleted in Ba, Sr, Eu, Ti, P and Nb-Ta, and with moderate negative Eu and Sr anomalies. These features indicate that the Jingnan volcanic rocks have an af

关键词： rhyolite calc-alkaline series early stage of Neoproterozoic western Wuyi Mountain South China

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Mantle derived crystal-poor rhyolitic ignimbrites:Eruptive mechanism from geochemical and geochronological data of the Piedra Parada caldera,Southern Argentina

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Geoscience Frontiers 2018年第5期9卷 1529-1553页

作者： Eugenio Aragon Antonio Castro Juan Diaz-Alvarado Lucio Pinotti Fernando D'eramo Manuel Demartis Jorge Coniglio Irene Hernando Carmen Rodriguez Centro de Investigaciones Geológicas(UNLP-CONICET) 1 N^o 644(1900)La PlataBuenos AiresArgentina Departamento de Geología Universidad de Huelva21071 HuelvaSpain Departamento de Geología Universidad de AtacamaCopayapu 485CopiapóChile Departamento de Geología Universidad Nacional de Río Cuarto(UNRC-CONICET)Ruta 36 km 601Río CuartoCórdobaArgentina

Trace elements, isotopic modeling and U-Th-Pb SHRIMP zircon age constraints are used to reconstruct the eruption history and magmatic processes of the Piedra Parada Caldera. In the early Eocene, the crystal-poor Barda Colorada ignimbrite(BCI), having >>15% micro-porphyritic crystals with respect to magmatic components, erupted a volume estimated in more than 300 km^3. The Piedra Parada caldera is located in the Patagonian Andes foreland, at the southern end of the calderas field of the Pilcaniyeu Volcanic Belt(PVB). This belt is related to an extensional tectonic setting as a result of the collision of the Farallon-Aluk ridge with South America, which enabled the development of a transform ocean/continental plate margin followed by the detachment of the Aluk plate and the opening of a slab window. The BCI extra-caldera Plateau is a >100 m thick deposit, having a lower unit with high silica(Si O_2> 76 wt.%),potassium poor rhyolitic composition(trondhjemitic like magma), and an upper unit with normal to high potassium rhyolitic composition(granitic like magma). A trace elements modeling of the BCI units shows that the BCI lower and upper units did not evolve from fractionation or immiscibility in the shallow magma reservoir. The BCI also have a primitive isotopic signature(initial87 Sr/86 Sr =0.7031-0.7049 and ε_(Nd)= +3.4 to +3.65). Thus, tectonic, compositional and isotopic constraints suggest the fast ascent of high silica magmas to a shallow reservoir, and point to an upper mantle origin for these rhyolitic magmas in a transitional(Orogenic-Anorogenic) tectono-magmatic setting. U-Th-Pb SHRIMP zircon crystallization ages of the Syn-caldera stage BCI units(56 -51.5 Ma) show a protracted life of 5 Ma for this caldera reservoir. The age of 52.9 ± 0.3 Ma is considered the best fit for the possible maximum age for the caldera collapse. The Late-caldera magmatism has trachyandesitic and rhyolitic compositions.The trace element modeling suggests that these rhyolites evolve from the trachyandesites and do not evolve fro

关键词： Mantle derived rhyolite Crystal-poor ignimbrite Bimodal volcanism Slab window volcanism K poor-rhyolite

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Lajishan Ayishan Formation rhyolites: Implications for the Closure Time of the Proto-Tethys Ocean

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Acta Geologica Sinica(English Edition) 2020年第S1期94卷 55-56页

作者： SUN Yi NIU Manlan LI Xiucai Hefei University of Technology HefeiAnhui230009China

The Qilian orogenic belt,as an important component of the central orogenic system,can be divided into three tectonic units from north to south:the North Qilian tectonic belt,the Central Qilian tectonic belt and the South Qilian tectonic belt.The Lajishan ophiolitic mélange zone is an important part of the South Qilian tectonic belt.The study of the formation age and tectonic attributes of the different rock units in the Lajishan is of great significance for reconstructing the tectonic evolution of the south Qilian tectonics belt and the Proto-Tethys Ocean.The Ayishan formation is an important unit of the Lajishan mélange belt,but its stratigraphic age and formation environment are still not constrained,which limits the reconstruction of the early Palaeozoic tectonic evolution of the South Qilian tectonic belt and the closure time of the Proto-Tethys Ocean.In recent years,a set of rock assemblages consisting of andesite,rhyolite,sandstone and pebbly sandstone have been identified in the Ayishan formation exposed in the Lajishan through detailed geological mapping in the field.They are in fault contact with the underlying ophiolite mélange.Regionally,a volcano-sedimentary succession consisting of andesite,rhyolite,volcanic breccia,and volcaniclastic sandstone nonconformably overlies the Cambrian arc-accretionarycomplex system in the Ayishan area.These rocks were originally assigned to the Ayishan formation and attributed an Early Ordovician age(BGMRQP,1964,1991).Our rhyolite samples from the Ayishan formation yielded a weighted mean 206Pb/238U age of 447 Ma using zircon U-Pb dating,which can be interpreted as the eruption age of the volcanic rocks.These volcanic rock assemblages are distributed in sandstone,pebbled sandstone and conglomerate in the form of interlayers.Therefore,the zircon UPb age of the volcanic rocks can constrain the age of Ayishan formation that it should belong to the late Ordovician rather than early Ordovician.Additionally,we propose that the Ayishan rhyolites were formed in collision-related

关键词： Lajishan rhyolite Proto-Tethys Ocean South Qilian

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Geochemistry and geochronology of acidic rocks in the Beishan region,NW China:Petrogenesis and tectonic implications

Geochemistry and geochronology of acidic rocks in the Beisha...

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中国科学院地质与地球物理研究所第11届（2011年度）...

作者： Patrick Asamoah Sakyi Sanjeewa P.K.Malaviarachchi Department ofEarth Science University of GhanaP.O.Box LG 58Legon-AccraGhana Research School of Earth Sciences The Australian National UniversityBuilding 61Mills Road ActonCanberraAct 0200Australia

The dacites and granites from the Beishan region are characterized by highly-fractionated REE,enrichments in LILE,and depletion in Nb,Ta and Sr.The dacites contain zircons with ages ranging from 265 to 748 Ma.These features suggest that they were probably derived from the older lower continental crust and were later on subjected to significant crustal assimilation.The rhyolites,diorites and diabases,all of which share similar geochemical features such as trace element patterns,zircon U-Pb ages of～280 Ma, positiveε(f) andε(f),high initial(Sr/Sr)i andδO‰values,were most likely derived from the juvenile crustal sources and subsequently experienced fractional crystallization and crustal contamination. These acidic igneous rocks(except dacites and granites) and coeval mafic-ultramafic intrusions form a bimodal igneous series.This implies that the Beishan region was a Late Paleozoic rift probably developed in association with the early Permian mantle plume activity in the Tarim Basin.

关键词： Beishan Central Asian Orogenic Belt Dacite Magmatism rhyolite Zircon U-Pb-Hf-O isotopes

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