DOCSLIB.ORG

Uranium-Lead Isotopic Variations in Zircons: a Case Study1

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Uranium-Lead Isotopic Variations in Zircons: a Case Study1 URANIUM-LEAD ISOTOPIC VARIATIONS IN ZIRCONS: A CASE STUDY1 LEON T. SILVER2 AND SARAH DEUTSCH3 ABSTRACT Zircons in a single 250-pound block of Precambrian Johnny Lyon granodiorite from the Dragoon Quad­ rangle in Cochise County, Arizona, have been concentrated with special attention to yield and nature of impurities. Morphology, zoning, color, inclusions, size distribution, radioactivity, refractive indexes, cell dimensions, and other properties have been compared with the isotopic properties in the U-Pb system (and to a less precise degree in the Th-Pb system). It has been observed: (1) Uranothorite impurities, while less than 1 per cent in abundance, contribute much more than 50 per cent of the activity in conventionally pre­ pared concentrates. The presence of uranothorite drastically affects the apparent ages in the zirons. (2) The uranothorite can be satisfactorily removed by an appropriate acid-washing procedure. (3) The uranothorite­ free zircon concentrates are not homogeneous and show systematic variations in radioactivity and various isotopic properties as a function of average crystal size. (4) Individual zircons show internal variation in radioactivity and may differ in specific activity from other individuals by as much as an order of magnitude. (5) It is possible to strip outer layers experimentally from an aggregate of zircons to determine variations in composite internal isotopic properties. (6) The family of uranium-lead systems distinguished in the in­ homogeneous zircon suite may be utilized to establish patterns of isotopic ratio variations that yield much more useful geochronological information than any single system. (7) All systems in this rock appear to have formed 1,655 million years ago and to have been profoundly disturbed by an event 90 million years ago. There is no evidence of any type of disturbance other than this simple episodic pattern. (8) While the mechanism of disturbance is not directly established, it is evident that radioactivity and radiation damage strongly influ­ ence susceptibility of the systems to disturbance. (9) It is possible to offer reasonable explanations for some of the puzzling discrepancies between uranium-lead and thorium-lead ages determined on a single mineral concentrate. (10) Recognition of the existence of families of uranium-lead systems among the variable mem­ bers of a single mineral species, or in associated mineral species, in a single typical granitic rock provides a powerful tool for investigation of the processes and conditions that have influenced the age-dating systems. (11) The systematic variations in U and Th provide interesting information on the role of some trace elements and accessory minerals in the crystallization history of the rock. (12) The Johnny Lyon granodiorite is the oldest igneous rock dated in Arizona thus far and places a minimum age of 1,655 ± 20 million years on the orogeny called Mazatzal Revolution. INTRODUCTION geological setting and history of the ana­ In geochronological investigations of rock lyzed minerals bear directly on the age inter­ systems, methods involving isotope chemis­ pretations made from the carefully meas­ try and mass spectrometry have evolved as ured isotopic relationships. Apparent ages precise and useful techniques for analysis of calculated from several minerals in the same a number of natural radioactivity relation­ host rock commonly have been in significant ships. A vast body of data on parent-daugh­ disagreement. It is to be hoped that some of ter ratios in the systems K 40/ Ar 40, Rb87/Srs7, these contradictory "ages" may be recon­ u2as/pb200, u2as;pb201 and Th2a2/pb2os has ciled, in part, by combining careful minera­ been carefully determined by these tech­ logical and petrological studies of the ana­ niques yielding geochronological informa­ lyzed phases with the isotopic measurements tion of far-reaching importance to studies of to achieve a better understanding of the geo­ the earth. At the same time, it has become logical factors. Few such attempts have been apparent also that numerous factors in the made. Among the several naturally radioactive 1 Contribution No. 1070, Division of Geological isotopes used in geochronology, the constant Sciences, California Institute of Technology, Pasa­ chemical coupling of U238 and U235 with their dena, California. Manuscript received February 21, 206 1962; revised May 25, 1962. chemically similar decay products Pb and 207 2 Division of Geological Sciences, California In­ Pb introduces the fewest assumptions re­ stitute of Technology, Pasadena, California. quired for a comparison of apparent ages. It 232 3 Present address: University of Brussels, Bel­ is fortunate too that Th , a similar actinide gium. element commonly associated with uranium, 721 722 LEON T. SILVER AND SARAH DEUTSCH 208 also decays to a stable lead nuclide, Pb • activity, size, zoning, and other characteris­ Thus it is often possible to compare ages de­ tics. A number of important regularities rived from three systems in the same have been observed. These lead to the con­ analyses. clusion that within these 1! cubic feet of Larsen et al. (1952) suggested that one of granite, there exist a large number of urani­ the most attractive phases in common rock um-thorium-lead systems which, when systems for studying these three isotopic studied as a family, can elucidate some types decay relations was zircon. They proposed of apparent age contradictions and, indeed, the so-called lead-a method, or Larsen meth­ provide some significant additional informa­ od, a non-isotopic method of age determina­ tion on the history of the rock. They also tion. Tilton, Patterson, et al. (1955) and, in raise some questions about accepted as­ particular, Tilton et al. (1957, and numerous sumptions in age interpretations. GEOLOGIC SETTING OF THE ROCK The rock sample was obtained from a large Precambrian granodiorite pluton in the Johnny Lyon Hills in the Dragoon Quadrangle, Cochise County, in southeast­ ern Arizona (figs. 1, 2). Detailed geologic studies have been made of the pluton and its setting by the United States Geological Sur­ vey. Preliminary accounts are available (Silver, 1955; Cooper, 1959), and a full re­ port will be published soon (Cooper and Silver, forthcoming). The regional setting is shown on the geologic map of Cochise Coun­ ty (Arizona Bureau of Mines, 1959). The pluton is a post-tectonic intrusive in its Pre­ cambrian setting but it has been strongly modified locally by younger deformational, intrusive, and alteration processes, many of which are clearly Mesozoic or Cenozoic. This FIG. 1.-Index map of Arizona showing location particular sample (L-312) was selected to be of Johnny Lyon Hills area in Cochise County. as free as possible from detectable metamor­ phic effects, as well as from the extensive other publications) demonstrated that pre­ weathering effects characteristic of this arid cise and significant isotopic measurements region. could be made on the zircons of many differ­ The rock is a medium - to coarse-grained, ent rocks. Tilton's work more than any somewhat porphyritic, hornblende-biotite other to date has defined the applicability granodiorite. In hand specimen, coarse white and problems of U-Th-Pb systems in zircons plagioclase is set in gray quartz, scattered in age-determination studies. The present pink potash feldspar, dark green platy bio­ report is an exploration of some of these tite, greenish-black prismatic hornblende problems. and, more rarely, euhedral brown sphene. The uranium-lead systems and, with less A few very thin epidote-quartz veinlets, a precision, the thorium-lead systems have fraction of a millimeter in thickness, tran­ been examined in zircon concentrates from sect the block. a single block of granitic rock. Variations in In thin section, the rock is hypidiomor­ isotopic properties have been compared with phic-inequigranular with a slightly seriate concentrate purity and homogeneity, radio- porphyritic texture. Tabular and zoned GENERALIZED MAP OF THE LYON HILLS filiii!!ll Tertiary and Quaternary alluvium m Paleozoic or younger rocks .,, ...: u 0... c 0 ~ t?~rt.~ E 0 Zones of 0 Rhyolite porphyry I intrusive sheets ~ lp£pso I Pinal schist (Slates and oraywackes) SCALE IN MILES 0 2 3 FIG. 2.-Generalized geologic map of the Johnny Lyon Hills, showing the stratigraphic and structural relationships of Johnny Lyon granodiorite to both older and younger rocks. Samples L-312 and L-609 were collected to be as free as possible of effects of the three major shear zones and other alteration features in ~he intrusive, 724 LEON T. SILVER AND SARAH DEUTSCH plagioclase crystals vary in composition MINERAL SEPARATIONS from An35 at the cores to An2o at the rims. The original reservoir of samples collected Microcline-microperthite is anhedral, tex­ in the field weighed approximately 250 turally late, and bordered by myrmekite pounds. Almost all of the zircons used in this fringes on the plagioclase. Quartz is scat­ study came from a representative 60-pound tered in anhedral aggregates. The biotite aliquot of the original sample. It was neces­ and hornblende are subhedral to euhedral. sary, however, to process some additional Accessary minerals include magnetite, apa­ TABLE 1B tite, sphene, zircon, allanite, and urano­ thorite in sequence of decreasing abundance. JOHNNY LYON GRANODIORITE Chemical, normative, and modal analyses MODAL ANALYSIS are given in table 1. As in every other speci- (Point Count) TABLE 1A L-312* JOHNNY LYON GRANODIORITE* (Weight Per Cent) CHEMICAL ANALYSIS Quartz ........ 25.84 Plagioclase .... 45.38 Myrmekite .... 1. 93 Average of 80 L-312t Microcline- Granodioritest (Weight perthite ..... 14.20 (Weight Per Cent) Biotite ........ 6.44 Per Cent) Hornblende ... 4.06 Magnetite ..... 1.34 Si02............... 68.89 66.13 Sphene ....... 0.56 Ti02.............. 0.45 0.51 Other accessories 0.25 AbOa. .. 15.02 15.50 Fe20a.............. 1.40 1.62 Total. ...... 100.00 FeO............... 1.89 2.70 MnO.............. 0.08 0.07 Normative Analysis MgO.............. 1.43 1. 73 Salic: Cao.............. 3.44 3.70 Quartz ........ 25.02 Na20.
Load more

Recommended publications
  • Natural Analogues to the Conditions
    ~E~EI3 ~IULWLiL EP~fl3TD4-1D Natural analogues to the conditions around a final repository for high-level radioactive waste Proceedings of the natural analogue workshop held at Lake Geneva, Wisconsin, U.S.A. (october 1-3,1984) John A.T. Smellie (Editor) Swedish Geological Company Uppsala, Sweden December 1984 SVENSK KARNBRANSLEFORSORJNING AB/AVDELNING KBS Swedish Nuclear Fuel Supply Co/Division KBS MAILING ADDRESS: SKBF/KBS, Box 5864, S-102 48 Stockholm, Sweden Telephone: 08-67 95 40 NATURAL ANALOGUES TO THE CONDITIONS AROUND A FINAL REPOSITORY FOR HIGH-LEVEL RADIOACTIVE WASTE PROCEEDINGS OF THE NATURAL ANALOGUE WORKSHOP HELD AT LAKE GENEVA, WISCONSIN, U.S.A. (OCTOBER 1-3, 1984) John A.T. Smellie (Editor) Swedish Geological Company Uppsala, Sweden This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the author(s) and do not necessarily coincide with those of the client. A list of other reports published in this series during 1985 is attached at the end of this report. Information on KBS technical re.?rts ffom 1977-1978 (TR 121), 1979 (TR 79-28), 1980 (TR 80-26),. 1981 (TR 81-17), 1982 (TR 82-28), 1983 (TR 83-77) and 1984 (TR 85-01) is available through SKB. NATURAL ANALOGUES TO THE CONDITIONS AROUND A FINAL REPOSITORY FOR HIGH-LEVEL RADIOACTIVE WASTE PROCEEDINGS OF THE NATURAL ANALOGUE WORKSHOP HELD AT LAKE GENEVA, WISCONSIN, U.S.A. (OCTOBER 1-3, 1984) John A.T. Smellie (Editor) Swedish Geological Company, Box 1424, 751 44 Uppsala The Workshop was co-sponsored by the Swedish Nuclear Fuel and Warte Management Company (SKB) and the U.S.
    [Show full text]
  • Pleochroic Haloes
    V PLEOCHROIC HALOES HE pleochroic halo has been for many years a mystery. TOccurring in enormous numbers in certain rocks, more especially in the micas of granites, and exhibiting a strange regularity of structure, it seemed more difficult of explana- tion the more it was studied. Petrographers put forward many theories to account for its origin. These we have not space to enumerate. Suffice it to say that an explanation was impossible before certain facts in radioactive science became available. We shall briefly refer, first to the appearance pre- sented by haloes, and secondly to the facts which afford the required explanation of their genesis. Finally we shall draw certain deductions not without importance. The halo is most often to be found in the iron-bearing micas-e.g., in biotite. It presents the appearance of a disk- shaped or ringshaped mark of such minute dimensions as to be entirely invisible without the aid of the microscope. When carefully measured it is found to possess a maximum radial dimension of 0.040 mm. ; but a very large number- the greater number-will be found to possess a radial dimen- sion of 0.033 mm., the larger haloes being, indeed, compara- tively scarce. There is always a minute and apparently crystalline particle occupying the centre of the full-sized halo. Figure I shows the appearance of a halo of the smaller size in mica (biotite). The light is being transmitted through a thin section of the rock. It is polarised and the intense absorption of it by the halo is clearly shown.
    [Show full text]
  • Mystery in the Rocks-Printout
    A physicist’s discovery begins an extraordinary odyssey through pride and prejudice in the scientific world. MYSTERY IN THE ROCKS By Dennis Crews he early 1960s was a time of unclouded is possible to measure both the amount of a given promise for many American college students. radioactive element and the amount of lead resulting T Industry was booming, the infamous war in from that element in a rock. Scientists correlate the Indochina had not yet ground itself into public ratio of these two amounts with the known decay rate consciousness and civil rights uprisings were the of that element, to find the period of time that has concern of only a principled few. Young elapsed since the rock was formed. (Decay rates are professionals ascended by thousands into the calculated by the half-life—the time it takes for half American dream, while visions of a home in the atoms in a given element to decay.) Many suburbia, a new car in the driveway and the promise scientists rest their proof of the earth’s age upon of a comfortable retirement beckoned still more radioactive dating of rocks that are thought to be thousands of new graduates into the mainstream. associated with the formation of the earth itself. In this setting, quests for truth and justice After acquiring his master’s degree in physics seemed the stuff of history and Hollywood hype; the Gentry staked out a promising career in the defense melodrama of moral odyssey paled beside the lure of industry, working first for Convair (later to become financial success and professional recognition.
    [Show full text]
  • Extinct Isotopes and the Age of the Earth
    The Proceedings of the International Conference on Creationism Volume 6 Print Reference: Pages 335-338 Article 29 2008 Extinct Isotopes and the Age of the Earth Don B. DeYoung Grace College Follow this and additional works at: https://digitalcommons.cedarville.edu/icc_proceedings DigitalCommons@Cedarville provides a publication platform for fully open access journals, which means that all articles are available on the Internet to all users immediately upon publication. However, the opinions and sentiments expressed by the authors of articles published in our journals do not necessarily indicate the endorsement or reflect the views of DigitalCommons@Cedarville, the Centennial Library, or Cedarville University and its employees. The authors are solely responsible for the content of their work. Please address questions to [email protected]. Browse the contents of this volume of The Proceedings of the International Conference on Creationism. Recommended Citation DeYoung, Don B. (2008) "Extinct Isotopes and the Age of the Earth," The Proceedings of the International Conference on Creationism: Vol. 6 , Article 29. Available at: https://digitalcommons.cedarville.edu/icc_proceedings/vol6/iss1/29 In A. A. Snelling (Ed.) (2008). Proceedings of the Sixth International Conference on Creationism (pp. 335–338). Pittsburgh, PA: Creation Science Fellowship and Dallas, TX: Institute for Creation Research. Extinct Isotopes and the Age of the Earth Don B. DeYoung, Ph.D., Grace College, 200 Seminary Drive, Winona Lake, IN 46590 Abstract Twenty-four extinct isotopes are presented for consideration from the recent creation worldview. These are radioactive isotopes which have decayed to abundances below the threshold of detection, leaving measurable daughter products in the process.
    [Show full text]
  • Letters to the Editor
    Letters to the editor (Figures 9-11) or at the termini of interesting and important, but it is Radiohalos in those strange tubes (Figures 12 also important to test the radio- diamonds and 14); activity of the rock in which the (b) earlier investigators claimed diamond was enclosed and not just Mark Armitage's contribution on that all the Irish7 and German8 the diamond. radiohalos in diamonds1 is a valuable halos were found only along 4. As Brown13 and Dutch14,15 have contribution to radiohalo study, but conduits within the minerals; asked, why is it that only isotopes unfortunately he omitted some very (c) Armitage's Figures 4-6 and all of polonium in the decay series of important information about radio- Gentry's figures showing Po uranium, thorium and plutonium halos necessary in their evaluation (all radiohalos unassociated with have been found to produce of which is included in an earlier cracks or conduits are found in the radiohalos? Of the 26 known paper).2 These items are as follows: mineral biotite. Biotite is isotopes of polonium there are 15 1. Armitage did acknowledge (for composed of crystals in the form not in the decay series of these example, on pages 93 and 100) of sheets. The sheets are only one elements which could be dis- that difficulties exist in explaining molecule thick. Thus in biotite tinguished if they were once the relationship between Po halo- one is never more than one-half a created within minerals and then containing rocks and sediments of molecule thickness away from a allowed to decay.
    [Show full text]
  • Perspectives on the Age of the Earth and Why They Matter
    Perspectives on the Age of the Earth and Why They Matter Perspectives on the Age of the Earth and Why They Matter By Francis Ö. Dudás Perspectives on the Age of the Earth and Why They Matter By Francis Ö. Dudás This book first published 2020 Cambridge Scholars Publishing Lady Stephenson Library, Newcastle upon Tyne, NE6 2PA, UK British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Copyright © 2020 by Francis Ö. Dudás All rights for this book reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner. ISBN (10): 1-5275-4385-4 ISBN (13): 978-1-5275-4385-0 Table of Contents Table of Contents ........................................................................................v Preface ..................................................................................................... vii Section I: We Didn’t Mean to Go to Sea ...................................................1 Chapter 1: Jennifer’s Story .........................................................................3 Chapter 2: Fast Forward ...........................................................................14 Chapter 3: Fast Forward Redux ................................................................20 Section II: The Symphony .......................................................................23 Chapter 4: Symphony Hall
    [Show full text]
  • It Is Not Truisms Which Science Unveils. Rather It Is Part of the Greatness
    "It is not truisms which science unveils. Rather it is part of the greatness and beauty of science that we can learn through our own critical investigations that the world is utterly different from what we ever imagined - until our imagination was fired by the refutation of our earlier theories." "The wrong view of science betrays itself in the craving to be right." ...... only through criticism can knowledge advance." "the growth of our knowledge proceeds from problems (scientific inconsistencies with establishd "truth") and our attempts to solve them." Karl Popper, The Logic of Scientific Discovery. "The erroneous belief that science eventually leads to the certainty of a definitive explanation carries with it the implication that it is a grave scientific misdemeanor to have published some hypothesis that eventually is falsified. As a consequence scientists have often been loath to admit the.falsification of such an hypothesis and their lives may be wasted in defending the no longer defensible. Whereas according to Popper, falsification in whole or in part is the anticipated fate of all hypotheses, and we should even rejoice in the falsification of an hypothesis that we have cherished as our brain child. One is thereby relieved from fears and remorse and science becomes an exhilirating adventure where imagination and ·vision lead to conceptual developments transcending in generality and range the experimental evidence. The precise formation of these imaginative insights into hypotheses opens the way to the most rigorous testing by experiment, it being always anticipated that the hypothesis may be fa~sified and that it will be replaced in whole or in part by another hypothesis of greater explanatory power." J.
    [Show full text]
  • Occurrence of Uranium in Rocks of the Ekiek Creek Complex, Western Alaska
    UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Occurrence of Uranium in Rocks of the Ekiek Creek Complex, Western Alaska by Alan R. Wallace Open-File Report 79-1653 1979 This report is preliminary and has not been edited or reviewed for conformity with U.S. Geological Survey standards. CONTENTS Page Abstract................................................................. 1 Introduction.............................................................2 Acknowledgments.......................................................... 2 Regional and geologic setting............................................2 Methods of study.........................................................4 Geology..................................................................5 Petrography......................................................... 7 Orthoclase-nepheli ne syenite....................................7 Mica pyroxenite.................................................9 Contact zone rocks..............................................9 Monzonite......................................................12 Uranium occurrence and distribution................................12 Di scussion..............................................................16 References.............................................................. 19 Figures Page Figure 1. Location and general geology of the Kobuk-Selawik Lowlands, including the Ekiek Creek Complex................3 2. Diagrammatic illustration of field relations, Ekiek Creek Complex...............................................6
    [Show full text]
  • The Development of Pleochroic Haloes and the Alpha Radioactivity of the Nucleus Minerals*
    MINERALOGICAL JOURNAL , VOL. 1, No. 4, PP. 213-223, JUNE, 1955 THE DEVELOPMENT OF PLEOCHROIC HALOES AND THE ALPHA RADIOACTIVITY OF THE NUCLEUS MINERALS* ICHIKAZU HAYASE Geological and Mineralogical Institute , Faculty of Science, University of Kyoto ABSTRACT The pleochroic halo has been regarded as the index of the geologic age of rocks, especially of granite. The autoradiographic studies now enable us to measure the alpha radioactivity even of a single grain of minute mineral and to determine more perfectly the evolution of the halo produced around it . Thus the geologic age of a rock can be determined more easily . In this paper are treated the development of haloes and the radioactive homogeneity of the minute minerals in their nuclei. Introduction The varieties of minute radioactive minerals contained in thin sections of granite were examined by an autoradiographic method , with the nuclear emulsion ET-2E (Fuji Photo Film Co. Ltd.). From this test the author was informed that the varieties of minute radioactive minerals were included in granite and that two grain belonging to the same variety were often quite different in their radioactive order2). To be measured by this method are the alpha tracks expelled from each grain of such minute minerals. If such a grain has been in cluded in biotite, there is always to be seen a pleochroic halo, whose blackness depends upon the alpha radioactivity of the grain as well as upon the geologic age of the grain and accordingly of * Read at the meeting of the Kansai Branch of the Geological Society of Japan, on September 25, 1954.
    [Show full text]
  • V21N3 the Regression of Modern Science Part 5
    Vol. 21, No. 3 Page 1 FOUNDATIONS OF SCIENCE AUGUST 2018 The Journal of Common Sense Science FOUNDATIONS August 2018 Volume 21 OF SCIENCE Number 3 The Regression of Modern Science Part 5 The Age of the Earth Charles William (Bill) Lucas, Jr. 29045 Livingston Drive Mechanicsville, MD 20659 [email protected] Abstract. The reduction of the role of logic in modern (CMB), the large scale structure of the universe science has led to the false or incomplete theories of and Hubble's law. If the known laws of physics are electrodynamics, gravitation, strong interaction, weak used to extrapolate backwards in time to the highest interaction, special and general relativity, quantum density regime, the result is a singularity which is mechanics, the chemical atom, the atomic nucleus, the associated with the Big Bang. Measurements of the standard model of elementary particles, the Big Bang current expansion rate of the universe based on the Theory of the origin of the universe, the abiogenesis observed Hubble redshifts being interpreted as origin of life, and an age of the earth of 4.5 billion Doppler red shifts place the Big Bang at around years. This is known as the regression of modern 13.8 billion years ago, which is thus considered to be science. The solution to the problem is to properly the age of the universe. After the initial expansion, the combine the axiomatic (logical) and empirical universe cooled sufficiently to allow the formation (experimental) scientific methods in such a manner of subatomic particles, and later simple atoms like that the full potential of logic, experiment and hydrogen and helium.
    [Show full text]
  • Uraninite from the Guangshigou Pegmatite-Type Uranium Deposit in the North Qinling Orogen, Central China
    minerals Article Uraninite from the Guangshigou Pegmatite-Type Uranium Deposit in the North Qinling Orogen, Central China: Its Occurrence, Alteration and Implications for Post-Caledonian Uranium Circulation Bin Wu 1,*, Christophe Bonnetti 1, Yue Liu 2, Zhan-Shi Zhang 1,*, Guo-Lin Guo 1 , Guang-Lai Li 1, Yin-Qiu Hu 1 and Zhao-Yan Yan 1 1 State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, China; [email protected] (C.B.); [email protected] (G.-L.G.); [email protected] (G.-L.L.); [email protected] (Y.-Q.H.); [email protected] (Z.-Y.Y.) 2 Information Engineering School, Jiangxi College of Applied Technology, Ganzhou 341000, China; [email protected] * Correspondence: [email protected] (B.W.); [email protected] (Z.-S.Z.); Tel.: +86-791-83897801 (B.W.); +86-791-83897617 (Z.-S.Z.) Abstract: The Guangshigou deposit is the largest pegmatite-type uranium deposit in the Shangdan domain of the North Qinling Orogenic Belt, which is characterized by the enrichment of uraninite hosted in biotite granitic pegmatites. At Guangshigou, uraninite commonly occurs as mineral inclu- sions in quartz, K-feldspar and biotite or in interstices of these rock-forming minerals with magmatic Citation: Wu, B.; Bonnetti, C.; Liu, Y.; characteristics (e.g., U/Th < 100, high ThO ,Y O and REE O contents and low concentrations Zhang, Z.-S.; Guo, G.-L.; Li, G.-L.; Hu, 2 2 3 2 3 Y.-Q.; Yan, Z.-Y. Uraninite from the of CaO, FeO and SiO2). It crystallized at 407.6 ± 2.9 Ma from fractionated calc-alkaline high-K ◦ Guangshigou Pegmatite-Type pegmatitic melts under conditions of 470–700 C and 2.4–3.4 kbar as deduced by the compositions of Uranium Deposit in the North coexisting peritectic biotite.
    [Show full text]
  • Chsr&Itristics and Significance of Uranium Bearing Fan African Younger Granite in the Eastern Desert
    EG0000327 Tlu?'l--'ri'!i C'unfciTncc on the Peaceful Uses ofAtonm. t^nmsy, uurnascus y - u uec. IVVb AAEA Chsr&itristics and Significance of Uranium Bearing Fan African Younger Granite in the Eastern Desert, Egypt M. A, Hassan, G.A. Dabbour and T.F. Mohammden Nuclear .vlntonals Authority, P.O. Box 530, Maadi, ;\;)i!;innya. Cairo. Egypt. J.". ; . ; . -c> •-, --S, •'. ~ )__•; j • ~''i-J I t I • "<• • --*> I I i p •• v_a V I f j J-LJ *LJL_J I *\ l I 4_J_J y -^ I I tj a, , ^i I ( .-j—^UJi _wi ^' > ". > '•• i j. ^ H J " ^ 1 I 6JJ& o 'I ^." 4 • 11 -y II \ MjljjJI .JI.J (] l^| :.-• ;!—•—•-=-• ;.-{' d—~:L'_i La—i—G_2W L^_i I ,i_a. j Ji.)...L.-k <—LJI—i ft \ S j) \ -^ 1 I j < ' a J ^JJ "' * ; _ •—-o—j K~i j t J_J X-2i_j jk_j j_i j . 4—J j I -»j—I_J I jj-i • .' ' •''J _) yj .'J ' ^••* J- ~Q CJV I ft "i -^ I ..--.Vwj _ftJU ^..^J i j jj I ^J -^ A :_^_< L'.'i .vj I j..^..l ' ^-* fr J *^. i J **> ^'. M • . • •• I j j 1 I r- •_.• • _c—> . .i -1. yjj i 1__^ij ( • J a 4 i a I y^i. 6 •, " ' I I ^' ,,,.| I ) jJ I • f • -y ^ •. c JJ I — " ' ' *' * *' I i •? t I I • L -• ! _^ja_J ui yJt-IiJ 1 J i O_ul Jfcij I a JJ& CjjLJft J_JS a _ -::• t ''I v -^ J ( i T V -^ _i djj " Abstract Surficial uranium mineralization was discoverd in lour Pan African younger granite plutons in the Eastern Desert of Egypt.
    [Show full text]