DOCSLIB.ORG

CM17 469.Pdf

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
CM17 469.Pdf Canadian Mineralogist VoL 17, pp.469-482 (1979) THEROLE OF GOLLECTORSIN THE FORMATIONOF THE PLATINUMDEPOSITS IN THEBUSHVELD COMPLEX S.A. HIEMSTRA Natianal Institute tor Metallurgy, Prtvate Bag X3015, Ratrdburg 2125, Soutlt Alrica ABsrRAcr INTRoDUcTIoN We consider the formation of the platinum de- Most of the sulfide occu,rrences of the posits in the Merensky and UG-2 Reefs in connec- Bushveld complex are associated with enriclr- tion with the action of collectors settling under ments in platinum-group metals. However, there the influence of gravity. The sulfides in the UG-2 the Reef, too small to have settled on their own, were are only three known occurrences where carried down by larger chromite grains in pieey- concentrations of these elements reach value$ back fashion. The sulfide droplets adhered to the of economic significance. These are the Merens- chromite grains either because they could wet the ky Reef (under which, for present puryroses chromite more readily than the silica.tes, or nu- is included the Plat Reef), the Upper Chromitite cleation of sulfide liquid droplets could have taken Layer (or UG-2 Reef), and the three dunite place preferentialli otr the surfaces of chromite pipes Driekop, Onverwacht and Mooihoek in grains. An iron alloy, stable only under exceptionally the eastern Bushveld. In this paper, attention Iow oxygen fugacity, could have acted as an effi- is given to one aspect of platinum deposits: the cient collector of platinum-group metals, which processes gave to the con- could have caused exceptional enrichment of some collection that rise magma fractions. Some of the mineral intergrowths centration of the platinum-group metals. in the Merensky Reef may be relics of iron-plati- num grains that reacted with sulfur, to form intergrowths of iron-platinum alloy with base Gsot-octclr- CoNsroEnatloNs metal sulfides that are pseudomorphous after the original crystals. As shown by von Gruenewaldt (1977) the occurrencesof platinum-group metals of econo- mic significance in the Bushveld complex, the SoMMATRE Merensky Reef and the UG-2 Reef follou, each other fairly olosely.In the western Bushveld, On considdre la formation des gisements de the Merensky Reef is situated only about 150 platine des bancs Merensky et UG-2 et le r6le m a.bove the UG-2 layer (von Gruenewaldt d'agents collecteurs dans un champ gravifique. Les 1977), but in the eastern Bushveld at the Atok grains petits pour de sulfures du banc UG-2, trop mine, this distance is increased to 300 m pouvoir se d6poser d'eux-memes, auraient 6t6 trans- (Schwellnus er a/. 1976). Idealized sections port6s "i cheval" sur des cristaux de chromite" plus gros. Les gouttelettes de sulfure auraient adh6r6 through a portion of the Merensky suite of aux cristaux de chromite i cause soit d'une tendan- rocks are given in Figures I and 2. Cousins ce i mouiller Ia chromite plut6t que les silicates, & Feringa (1964) provided sections through soit de la nucl6ation pr6fdrentielle de gouttelettes the UG-2 suite of rocks. Descriptions of the de sulfure liquide sur la surface des cristaux de three dunite pipes can be found in Wagner chromite. Un alliage de fer, stable seulement sous (1973, pp. 50-92). fugacit6 d'oxygdne exceptionnellement basse" aurait Bushveld com- servi de collecteur pour les platinoides, Most workers agree that the enrichis- .form sant ainsi fortement certaines frac.tions du magma. plex was emplaced in the of a magrna Certaines intercroissances min6rales du banc Me- from which the different rock units were formed rensky semblent Ctre des reliques de cristaux d'un by fractional crystallization and sedimentation alliage fer-platine qui, par r6action avec le soufre, of the crystals into cumulates (Willemse 1969, auraient donn6 une intercroissance d'un nouvel Lombaard 7934, and many others). More than alliage fer-platine avec des sulfures de m6taux one heave of magrna is postulated, but some vils, pseudomorphe des cristaux originels. workers (Coertze 1970, Schwellnus 1956) think (Traduit par la R€daction) that most different rock units are separate in- 469 470 THE CANADIAN MINERALOGIST trusions of magmas that underwent differentia- tion at depth. Usuolthickness. The origin of the mafic magma is seen as the result of a process of differential melting of the upper mantle, but there was $ome degree of assimilation of the rocks that came into contact with the magma. In some instances, this assimilation could have played an impor- Frqn < I metre tant role in tle formation of sulfide deposits to >' 7 metres. (Coertze 1970, Liebenberg 1970, de Waal 1977, Naldrett & Cabri L976). The upper mantle also must be consideredto be the source platinum-group of the elements in mafic rocks. Fran 0 to obout 3 metres. CorvcsNTRAuoN AND Drposrrrox There are two concepts of concentration and deposition that are of interest in the present Ftc. 1. Idealized section through the Merensky paper: (1) crystal settling (Liebenberg 1970, Reef in the western Bushveld complex. Brynard et al, 1976), which suggeststhat plati- nlrm-group minerals settled out of a magma to become concentrated at the bottorn of the magma chamber, and (2) concentration in a col- from 25 meire lectot e,9., sulfide which settled out of the mag- Bose metol to O5 metre. Porphyritica ma, thus also concentrating the platinum-group sulfides Oi From0.35 metre elements. The rates of settling in both these cnd plotinum $ ryroxeniteT I to 0.5metre. instancesmust have been such that the platinum- groupminerol group minerals or sulfide droplets settled at a From030 metre rate different from that of the other crysta{s to l.52metre. that formed in the magma at the same time; no concentration would have been effected by the settling process alone. The conditions under whish particles or droplets can settle out From060 metre of a magma have been discussedby Wadsworth to 9.0 metres. (L973) among others. The grain sizes and densities measured by the author and his col- leagues, or collected from the literature, are given in Table 1, and these were used, following Wadsworth (1973), for the calculation of the settling velocities for various mineral consti- Fro. 2. Idealized section through the Merensky tuents (Table 2). Reef in the eastern Bushveld. As only relative settling speeds are of in- terest here, tfie sarne density (2.58 g.cm-s) and the same viscosity (1000 P) were used in all further factor to be taken into account is that the calculations, although the estimates for the crystails could have increased in size during these values given in the literature range from settling and after deposition. As will be shorrn lower to higher values. Stokes' for'mula then later, it is probable that many of the grains of simplifies to V : I7169.4D (p" - 2.58) m per platinum-group minerals attained their final year, where D is the particle diameter (cm) and sizesafter having been deposited. pr is the particle density (g.cm"). The size data reported in Table 1 were Strictly, the densities should have been cor- collected by different workers and are usual'ly rected for temperature, but in view of the larger the sizes as seen in polished sections without influence exerted on settling velocity by grain any allowance for sectioning. The averages sizes, it was decided that this correction would were calculated from a few tens to a few not have influenced the results undulv. A hundreds of grains and are usually close to the PLATINI'M DEPOSITS IN THE BUSHVELD COMPLBX 471 T^8[r l. GRArt{.STZES 0F SotECoI{STITUEI{TS til nE i€nSrSKYnEEF TlgL[ 2. SFtTUile lELoClTlEsmR S0r qilEnALSFnoil IllE I'ERt[Sfr IEEF tf,llslTl 0F liAOlA. 2.58 s,@-' VISOSIIY3 lo00 P Rock mtt/localtty Range Average,/Slze Yclslty. Hlneral lbnslry Slzs. @ q A.ttt ot Pl tanesDgtg 'l.6rD p$ yolr Chrwlio T@ lqyer 0.1-1.6m ChroElte EottoE layer l,0m 2'| (e.9. In p€g@told) 52gI (0.9. ln Fgstold) t3 u0 Pyrorene Porphyrlti c 2-3m 1.5@ 0.3 (s.9. ln porphyrltlcpyrcEnlto) I 189 pyrorenl ts 0.1 (e.9. In por?hyrltlcpyrcEnlte) 132 Pt-Fo 6llay Pegmtold 16 !m Chrgdlto 4.5 0.3 2 967 0.2 I 319 !.)quu oT rr tanesErg 0.1 w Orrorlte Top layor 0.3. 2.5m 1.0 m 0.05 v, Braggdte 3.5-47 !E 12.5 |lm Bnggltg 8,9 0.03 (u. val6 lablo l) 98 Laurl tE 5.5-27 un 13.25um 0.0012(dv.Atot ud S. of Pllmberg) 0.16 Sperrylits 6 -50 un 20.0 !n C6p€r{ta 10.2 0.01 (Mr. valE Tabl€ l) l3 0.0@8(!Y. fru rear R6tenburg) 0.08 Spedyllte 10.59 0.015 (Er, 6l@ Tlble l) 3l Brdgglte sl ll6te' rrca A 9,hn 0.0m (av. S. of Pll@3berg) Bragglte &rodt€, arca A 6. tllm Pt-F€ rIloy 15 0.0115(Er. valE Tlble l) 28.20 Coopsrlte Slllcats' arca A I 1.lum 0.0016([E of Pl lmesb€rg] 0.54 Cooperlt6 Chr@lte' arca A 8. lum 5Utn@ Co@erlte ChroElts' ar€a B 4.9un droplets 4.5 0.05 e. 0,C03 (UL'z @dlil) 0.s Laurl te Sllicater area.A 6'9um lm Ftrl 7.8 0,03 v Laurlte Sillcate, ar€a I 7.4um Laurite Chroullo, arca A 4.9!n Laur'lte B - chro0lte, ar€a 6.lum minerals from a u.tesEm Ptaunm mne (2, The settling of platinum-group Sperylite 6-150|ln crystallizing magma, on the assumptionthat they Braggilte 37-300!n in the sizes in whioh they are en- L.
Load more

Recommended publications
  • Podiform Chromite Deposits—Database and Grade and Tonnage Models
    Podiform Chromite Deposits—Database and Grade and Tonnage Models Scientific Investigations Report 2012–5157 U.S. Department of the Interior U.S. Geological Survey COVER View of the abandoned Chrome Concentrating Company mill, opened in 1917, near the No. 5 chromite mine in Del Puerto Canyon, Stanislaus County, California (USGS photograph by Dan Mosier, 1972). Insets show (upper right) specimen of massive chromite ore from the Pillikin mine, El Dorado County, California, and (lower left) specimen showing disseminated layers of chromite in dunite from the No. 5 mine, Stanislaus County, California (USGS photographs by Dan Mosier, 2012). Podiform Chromite Deposits—Database and Grade and Tonnage Models By Dan L. Mosier, Donald A. Singer, Barry C. Moring, and John P. Galloway Scientific Investigations Report 2012-5157 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2012 This report and any updates to it are available online at: http://pubs.usgs.gov/sir/2012/5157/ For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Suggested citation: Mosier, D.L., Singer, D.A., Moring, B.C., and Galloway, J.P., 2012, Podiform chromite deposits—database and grade and tonnage models: U.S.
    [Show full text]
  • A New Occurrence of Terrestrial Native Iron in the Earth's Surface
    geosciences Article A New Occurrence of Terrestrial Native Iron in the Earth’s Surface: The Ilia Thermogenic Travertine Case, Northwestern Euboea, Greece Christos Kanellopoulos 1,2,* ID , Eugenia Valsami-Jones 3,4, Panagiotis Voudouris 1, Christina Stouraiti 1 ID , Robert Moritz 2, Constantinos Mavrogonatos 1 ID and Panagiotis Mitropoulos 1,† 1 Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Panepistimioupolis Zografou, 15784 Athens, Greece; [email protected] (P.V.); [email protected] (C.S.); [email protected] (C.M.); [email protected] (P.M.) 2 Section of Earth and Environmental Sciences, University of Geneva, Rue des Maraichers 13, 1205 Geneva, Switzerland; [email protected] 3 School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; [email protected] 4 Department of Earth Sciences, Natural History Museum London, Cromwell Road, London SW7 5BD, UK * Correspondence: [email protected] † Professor Panagiotis Mitropoulos has passed away in 2017. Received: 6 April 2018; Accepted: 23 July 2018; Published: 31 July 2018 Abstract: Native iron has been identified in an active thermogenic travertine deposit, located at Ilia area (Euboea Island, Greece). The deposit is forming around a hot spring, which is part of a large active metallogenetic hydrothermal system depositing ore-bearing travertines. The native iron occurs in two shapes: nodules with diameter 0.4 and 0.45 cm, and angular grains with length up to tens of µm. The travertine laminae around the spherical/ovoid nodules grow smoothly, and the angular grains are trapped inside the pores of the travertine.
    [Show full text]
  • Heazlewooditeand Awaruite in Serpentinites of The
    HEAZLEWOODITEANDAWARUITE IN SERPENTINITESOF THE EASTERN TOWNSHIPS,QUEBEC J. A. CnaUBERLATN Geological,Suraey of Canail,a,Ottawa Awaruite of composition approximately NiaFe was shown by Nickel (1959) to be a common accessory phase in most serpentinites of the asbestos-producing belt in the Eastern Townships, Quebec. Nickel demonstrated that awaruite developed during the serpentinization process from nickel and iron already present in these rocks. Work on the distribution and genesis of native metals in the Muskox intrusion (Chamberlain, et aI, 1965) indicated that native metals could form by the decomposition of earlier-formed sulphides. For example, pentlandite was shown to decomposeto form avraruite plus iron sulphide, and chalcopyrite to native copper plus pyrrhotite. Some native iron may have been formed by the reduction of magnetite. Such reactions suggested that awaruite in the Eastern Townships could also have been formed by the decomposition of primary sulphides. This theory was checked by examination of 44 polished sections made from samples donated by A. S. Maclaren of the Geological Survey, and from samples collected during the 1965 field season*. The observed distribution of awaruite, heazle- woodite and magnetite in these sections is summarized in Table 1. Magnetite is present in g4 per cent of the sections in amounts exceeding 0.1 per cent. Most sections contain 1 per cent or more. It occurs as threads between ghost olivine or pyroxene crystals, as discrete, weakly euhedral grains, or as rims around primary chromite crystals. It is invariably in contact with serpentine. Magnetite is believed to have formed by reaction of magnesium-iron olivine or pyroxene with water to give magnesium serpentine plus magnetite at temperatures below 550o C.
    [Show full text]
  • Washington State Minerals Checklist
    Division of Geology and Earth Resources MS 47007; Olympia, WA 98504-7007 Washington State 360-902-1450; 360-902-1785 fax E-mail: [email protected] Website: http://www.dnr.wa.gov/geology Minerals Checklist Note: Mineral names in parentheses are the preferred species names. Compiled by Raymond Lasmanis o Acanthite o Arsenopalladinite o Bustamite o Clinohumite o Enstatite o Harmotome o Actinolite o Arsenopyrite o Bytownite o Clinoptilolite o Epidesmine (Stilbite) o Hastingsite o Adularia o Arsenosulvanite (Plagioclase) o Clinozoisite o Epidote o Hausmannite (Orthoclase) o Arsenpolybasite o Cairngorm (Quartz) o Cobaltite o Epistilbite o Hedenbergite o Aegirine o Astrophyllite o Calamine o Cochromite o Epsomite o Hedleyite o Aenigmatite o Atacamite (Hemimorphite) o Coffinite o Erionite o Hematite o Aeschynite o Atokite o Calaverite o Columbite o Erythrite o Hemimorphite o Agardite-Y o Augite o Calciohilairite (Ferrocolumbite) o Euchroite o Hercynite o Agate (Quartz) o Aurostibite o Calcite, see also o Conichalcite o Euxenite o Hessite o Aguilarite o Austinite Manganocalcite o Connellite o Euxenite-Y o Heulandite o Aktashite o Onyx o Copiapite o o Autunite o Fairchildite Hexahydrite o Alabandite o Caledonite o Copper o o Awaruite o Famatinite Hibschite o Albite o Cancrinite o Copper-zinc o o Axinite group o Fayalite Hillebrandite o Algodonite o Carnelian (Quartz) o Coquandite o o Azurite o Feldspar group Hisingerite o Allanite o Cassiterite o Cordierite o o Barite o Ferberite Hongshiite o Allanite-Ce o Catapleiite o Corrensite o o Bastnäsite
    [Show full text]
  • Sulfide Dissolution and Awaruite Formation in 10.1029/2021JB021758 Continental Serpentinization Environments and Its
    RESEARCH ARTICLE Sulfide Dissolution and Awaruite Formation in 10.1029/2021JB021758 Continental Serpentinization Environments and Its Special Section: Implications to Supporting Life Ophiolites and Oceanic Lith- 1 1 1 1 1 osphere, with a focus on the E. M. Schwarzenbach , J. C. Vrijmoed , J. M. Engelmann , M. Liesegang , U. Wiechert , Samail ophiolite in Oman R. Rohne1, and O. Plümper2 1 2 Key Points: Institute of Geological Sciences, Freie Universität Berlin, Berlin, Germany, Department of Earth Sciences, Utrecht • High disequilibrium conditions University, Utrecht, The Netherlands induce skeletal awaruite growth during continental serpentinization • Pentlandite dissolution creates fluid Abstract Serpentinization environments are key locations that support microbial communities by pathways and nutrients for microbial the abiogenic formation of reduced species associated with peridotite alteration. Here we studied partially life • Sulfur isotope compositions serpentinized peridotites from the Chimaera seeps (Turkey), an active continental serpentinization system document ocean floor and that vents highly methane-rich fluids, to investigate the impact of water-rock interaction on the sulfide subsequent continental and metal mineralogy and its implications on supporting microbial communities. Using high-resolution serpentinization processes scanning electron microscopy, electron microprobe analysis, and transmission electron microscopy we found diverse pentlandite decomposition features with precipitation of secondary sulfides including Supporting Information: millerite, heazlewoodite, as well as Cu-bearing sulfides, native Cu, and awaruite (Ni3Fe). Awaruite forms Supporting Information may be found in the online version of this article. dense veinlets to single crystal platelets tens of nanometers in size, which is formed by desulphurization of pentlandite. In addition, the nanometer-sized awaruite platelets are intimately intergrown with serpentine suggesting its growth during peridotite alteration by a dissolution-precipitation process, Correspondence to: E.
    [Show full text]
  • Plagioclase-Spinel-Graphite Xenoliths in Metallic Iron
    THE AMERICAN MINERALOGIST, VOL. 51, MAY_JUNE, 1966 PLAGIOCLASE-SPINEL-GRAPHITEXENOLITHS IN METALLIC IRON-BEARING BASALTS, DISKO ISLAND, GREENLAND Wrr,rrau G. MBr.soNeNo Gnoncp Swrrzrn Departmentof Mineral Sciences, U. S. l{ational Museum,Washington, D. C. Ansrnac:t Tertiary basalt flows from west Greenland commonly contain metallic iron and graph- ite. They are thus some of the most reduced of terrestrial basalts, and are of interest in con- nection with basalt studies in general, and in connection with the origin of certain meteor- ites (Lovering, 1964). Xenoliths composed mainly of plagioclase (Anzo-zu), graphite, rose-colored spinel and rarely corundum are included in these basalts on Disko Island. The xenoliths are remark- ably similar to reconstituted shale xenoliths in basaltic rocks from other localities except for the presence oI graphite and in the composition of the spinel. The spinel has n:1.747 +0.001, o:8'119+0.002 and D:3.81 +0.01, and electron microprobe analysis gave Mg : 13 and Fe:8.9/6. These data indicate a spinel with composition about spzaHezz.This un- usually low Fe content compared to spinels from other aluminous xenoliths in basaltic rocks is evidently related to the low oxygen fugacities ln basaltic magmas in contact with graphite, particularly in an environment such as Disko, where active reduction of ferrous iron to iron evidently occurred. The close similarities in the mineralogy of the xenoliths from specimen to specimen indi- cate complete equilibration of magma and xenoliths. This equilibration involved mainly loss of K and Si, and gain of Ca, Mg, Al and Na by the xeno.liths.
    [Show full text]
  • Structure-Magnetism Correlations and Chemical Order-Disorder Transformations in Ferrous L10-Structured Compounds
    STRUCTURE-MAGNETISM CORRELATIONS AND CHEMICAL ORDER-DISORDER TRANSFORMATIONS IN FERROUS L10-STRUCTURED COMPOUNDS A Dissertation Presented By Nina Cathryn Bordeaux to The Department of Chemical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the field of Chemical Engineering Northeastern University Boston, Massachusetts April 15, 2015 ACKNOWLEDGMENTS There are so many people I am grateful to for getting me to this point. First and foremost, I would like to thank my advisor, Professor Laura H. Lewis for taking me on and teaching me so much. You’ve challenged me to “ask the right questions” and I am a better scientist for it. Thank you for believing in me and for all of the ways you’ve gone beyond the expected for me, from taking me to the Taj Mahal to attending my wedding! Many thanks to my committee members, Professor Sunho Choi, Professor Teiichi Ando, and Professor Katayun Barmak, for taking the time to read my Dissertation and to serve on my committee. Thanks to Dr. Ando for teaching such a wonderful kinetics course that provided me with the foundational knowledge for much of this Dissertation. Special thanks to Dr. Barmak for being a collaborator in this research and for all of the time you’ve invested in discussing results and analysis methods. Thank you for your patience and your guidance. I want to thank Professor Joseph Goldstein for serving on my proposal committee. You provided invaluable guidance in this project and I am so grateful for all that you taught me about meteorites and scientific research.
    [Show full text]
  • Occurrence of Graphite-Like Carbon in Podiform Chromitites of Greece and Its Genetic Significance
    minerals Article Occurrence of Graphite-Like Carbon in Podiform Chromitites of Greece and Its Genetic Significance Maria Economou-Eliopoulos *, George Tsoupas and Vasilis Skounakis Department of Geology and Geoenvironment, University of Athens, Athens 15784, Greece; [email protected] (G.T.); [email protected] (V.S.) * Correspondence: [email protected]; Tel.: +30-2107274214 Received: 21 December 2018; Accepted: 26 February 2019; Published: 3 March 2019 Abstract: The role of post-magmatic processes in the composition of chromitites hosted in ophiolite complexes, the origin of super-reduced phases, and factors controlling the carbon recycling in a supra-subduction zone environment are still unclear. The present contribution compiles the first scanning electron microscope/energy-dispersive (SEM/EDS) data on graphite-like amorphous carbon, with geochemical and mineral chemistry data, from chromitites of the Skyros, Othrys, Pindos, and Veria ophiolites (Greece). The aim of this study was the delineation of potential relationships between the modified composition of chromite and the role of redox conditions, during the long-term evolution of chromitites in a supra-subduction zone environment. Chromitites are characterized by a strong brittle (cataclastic) texture and the presence of phases indicative of super-reducing phases, such as Fe–Ni–Cr-alloys, awaruite (Ni3Fe), and heazlewoodite (Ni3S2). Carbon-bearing assemblages are better revealed on Au-coated unpolished sections. Graphite occurs in association with hydrous silicates (chlorite, serpentine) and Fe2+-chromite, as inclusions in chromite, filling cracks within chromite, or as nodule-like graphite aggregates. X-ray spectra of graphite–silicate aggregates showed the presence of C, Si, Mg, Al, O in variable proportions, and occasionally K and Ca.
    [Show full text]
  • Cais CAI AOA AOA AOA
    50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 1033.pdf THE FORMATION CONDITIONS OF CHONDRITES: INSIGHTS FROM NORTHWEST AFRICA 10850 – AN OXIDIZED CV3 CHONDRITE. M. M. Jean1,2, A. Patchen1, M. B. Sueilem3, L. A. Taylor1, 1Planetary Ge- osciences Institute, Dept. Earth and Planetary Sciences, University of Tennessee Knoxville. 2University of Alaska- Anchorage, Dept. of Geological Sciences, Anchorage, AK 99508. 3Smara Refugee Camps of Western Sahara, Tin- douf, Algeria. ([email protected]) Introduction: For the first time, data are presented lected from Algeria, in the Tindouf province. Approx- from a detailed investigation of all components of the imately 50.3 g were recovered on August 2015, and Northwest Africa (NWA) 10850 carbonaceous chon- acquired by us shortly thereafter. Its classification as a drite. NWA 10850 is a newly classified meteorite col- carbonaceous chondrite was recently approved [1]. chondrules matrix chondrule matrix AOA chondrule CAI AOA matrix CAIs matrix AOA chondrules matrix AOA 2 mm Figure 1. Combined Mg Kα (blue) + Al Kα (green) + Ca Kα (red) X-ray maps showing chondrules, CAIs (cal- cium-aluminum inclusions), amoeboidal olivine aggregates (AOA), and other features found in NWA 10850 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 1033.pdf We have undertaken a comprehensive study to pro- Di Hd vide an overview of the petrography and geochemistry of this meteorite. Based on these results, we add NWA 10850 to the Allende-like subgroup (CV3oxA), which typically contains approximately 40 vol % matrix ma- terial (with little phyllosilicate), 40–50 vol % intact En Fs chondrules, and ~ 0.2 vol % metallic FeNi.
    [Show full text]
  • Highly Reducing Conditions During Alpine Metamorphism of The
    Contrib Mineral Petrol (1992) 112:329-340 Contributions to Mineralogy and Petrology 9 Springer-Verlag 1992 Highly reducing conditions during Alpine metamorphism of the Malenco peridotite (Sondrio, northern Italy) indicated by mineral paragenesis and H 2 in fluid inclusions Adolf Peretti 1 *, Jean Dubessy 2, Josef Mnllis 3, B. Ronald Frost 4, and V. Trommsdorff 5 1 Institut ffir Mineralogie und Petrographie, ETH, Sonneggstrasse 5, CH-8092 Zurich, Switzerland 2 CREGU, GS CNRS 077, BP 23, F-54501 Vandoeuvre-Les-Nancy Cedex, France 3 Mineralogisch Petrographisches Institut der Universit/it, Bernoullistrasse 30, CH-4056 Basel, Switzerland 4 Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA 5 Institut fiir Mineralogie und Petrographie, ETH, Sonneggstrasse 5, CH-8092 Zurich, Switzerland Received April 12, 1991 / Accepted June 19, 1992 Abstract. During regional metamorphism of the Malen- has evidenced mineral parageneses (formation of awar- co serpentinized peridotite (Sondrio, northern Italy), the uite) indicative of highly reducing conditions during the mineral assemblage pentlandite-awaruite-magnetite-na- prograde alpine metamorphism. The aim of this study tive copper-antigorite-brucite-olivine-diopside is formed. is to obtain information about the prograde metamor- The opaque assemblage indicates very reduced fluids phic fluids at the site of dehydration reactions of serpen- with fO2 values 4 log units below QFM. Primary fluid tinite (olivine-in isograd) and the contemperaneous for- inclusions were trapped in diopside overgrowth, contem- mation of awaruite. poraneous with the opaque assemblage. These metamor- phic fluids are saline aqueous solutions (about 10.4 mol% NaC1 equivalent) and contain molecular H2 Geological setting of approximately 1 mol%, as shown by micro-Raman analysis and microthermometry.
    [Show full text]
  • Crystal-Structure of a Natural Nickel-Iron Alloy. by Professor E
    415 Crystal-structure of a natural nickel-iron alloy. By Professor E. A. OWEN, M.A., Sc.D., and B. D. BURNS, M.Sc. University College of North Wales, Bangor. [Read June 8, 1939 ; communicated by the editor.] 1. Introduction. ATU,RAL nickel-iron alloys have been found in several places on the N earth s surface. In addition to alloys containing a low percentage of nickel (about 3%), there are others which contain much higher per- centages of nickel (about 70o/o). To alloys of the latter group the name awaruite is now generally given and it may include josephinite, souesite, and other alloys possessing high nickel content so long as they belong to the same phase and possess identical crystal-structures. It is of interest to the mineralogist to know whether these alloys con- form to the structure of nickel-iron alloys prepared in the laboratory and whether they fit into the accepted phase diagram of the nickel-iron system. It is of interest also to the physicist and the metallurgist to obtain information concerning these natural alloys, because some nickel- iron alloys made in the laboratory are difficult to prepare in a state of true equilibrium. Data derived from the study of the natural alloys may help to throw light upon the structure of these artificial alloys. 2. Previous Work on Natural Nickel-iron Alloys. Several investigations of natural nickel-iron alloys have been de- scribed. W. H. MelvillO records the examination of magnetic pebbles discovered in large quantities in the gravel of a stream in Josephine and Jackson Counties in Oregon.
    [Show full text]
  • NEPHELINE SYENITE and IRON ORE DEPOSITS in GREENLAND by Richardbogvad*
    NEPHELINE SYENITE AND IRON ORE DEPOSITS IN GREENLAND By RichardBogvad* HE voyages of exploration toGreenland at the beginning of the Tseventeenth century aroused interestin the possibilities of mineral wealth in the country. As a result King Christian IV in 1605 and 1606 equipped two expeditions to collect silver, which was supposed to have been found in large quantities, but only valueless mica was brought home. After this disappointment thematter was allowed to rest for barely a century,when fresh investigations werestarted; these have-sometimes withlong intervals-been continueduntil today (2; 4). Much time has been devoted tothe investigation of copperand graphite occurrences; coal (lignite) has been mined fortwo centuries, andmarble has been quarried. But so farthe only mineral foundwhich can be profitablv minedis cryolitefrom Ivigtut. Recently, however, nepheline syenite and iron ore deposits have been investigated. NEPHELINESYENITE In GreenlandIn nepheline syenite' occurs in the Kangerd- lugssuaq district onthe east coast (18, p. 38; 19, p. 41); be- tween the Arsuk and Ika fjords onthe west coast (17, p. 387; 6) ; and between Julianehaab and Kagssiarssuk in southern Green- land (15, p. 35; 16, p. 132; 17; 20, p. 60). Only inthe last- mentioneddistrict, which can be divided into the Igdlerfigsalik and Ilimausak-Kangerdluarsuk massifs, are there large quantities of thezirconium-bearing min- eral eudialyte'. K. L. Giesecke (1 O), who made the first sys- tematic mineralogical investiga- tion of Greenlandfrom 1806 to 1813, visited the deposits in Fig. 1. the Kangerdluarsuk district but ~ "Chief geologist, Kryolitselskabet Oresund A/S (The Cryolite Company), Copenhagen. 'Igneous rocks characterized by thepredominance of alkalifelspar, and nephelite, NaAlSiO,.
    [Show full text]