DOCSLIB.ORG

Fe-OS Redox Reactions and Kinetics in Hydrothermal Systems

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Fe-OS Redox Reactions and Kinetics in Hydrothermal Systems A major purpose of the Techni- cal Information Center is to provide the broadest dissemination possi= ble of information contained in NE’s Research and Development Reports to business, industry, the academic community, and federal, state and local governm~ents. Although a small portion of this report is not reproducible, it is being made avaiiable to expedite the availabilityof information on the research discussed herein. LA-lJR -86-1330 (’!fNF”wy.y5f”--] LA-uR--86-133O DE86 010187 AuTHORIS) D. N. .liin~~cky, LNC-7 V. K. Scy Fr+d, Jr, , U. of ?linnwolm Mm K. lh’rlld L, 11. n r ?41nnwmtn WBMITTED TO 5LII I nt’ 1 tlo~~tirlg on Wntrr-ttnrk Intrrmt [cm llc~vk.!nvl k, I I’ll I nnd AIIIWH1 H- 12, I l)HfI INSCI,AIMUR Thisrqmrrwu pqmrcdu ● mom d WA npnmral hy ● apncy m“k I Mild Hhlm (IownmmN. Ndkr k { Idld SImn (kwerrr~l rmr any ~my IIMIOA.. rmrrsuy d lldf cm- nmka ●ry ummrny, cqwcu w implld, w U- ●ry al I; thllhy Irt ~- IMly k k ncwwy, crrm~, w Al- d mry Idhmrmlirm, qqmrmu pzdwl, w pltrxm Illuhd. w ~ml, Ihil Iln w Wrdd WI ld’rl~ pdvmdy @d *IL Raw. mw Irmdn m mry @k ~mcrdd pmkl, p- IU ● wk by id ntrrk W*- mnnufwwmr, rx IrrkrwU rb rrd ~rlly ~llulc m Impy k ~rrt, ~ mddnn, w ram b Ik Ilnhd ?Ma (km- w ●y UEnCV Ilwarr, !hE + ●d ~rrb d ~ulhm cEX Imrdrr da MI ~rily SIAM IW rekr Ib d ik Ilnlld Sm@OCkRrmnral or my ~ Ikrdm %0-S REOOX REACTIONS AND KINETICS IN HYDROTHERMAL SYSTEMS D. R. Janeckyl, W. E. Seyfried, Jr., and M. E. Berndt Department of Geology and G-physics, University of Minneseta. Minneapolis, MN 55435 ‘ now at: INC-7. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 INTRODUCTION Oxidation-reduction reactions are important in many hydrothermal systems, predominantly in- volving the elements O, H, C, S, and Fe. but also significantly a~ecting a wide variety ~f minor and trace components. Fe-bearing silicate. oxide. and ,sulfide minerals are commonly used in hydrothermal experiments and petrographic studies to define the redox state of a system, We have experimentally investigated reactions of magnetite, hematite, pyrite. and pyrrhotite with 0.5 molal NaCl solutions. at temperatures of 30&425’C and pressures of 400-5@0 bars, using flex;~le cell hydrothermal equipment [Seyfried et a/.. 1986), These experiments allow reversible steady state solution compositions and the rates of equilibration of various redox couples (including HZ-H20, HaS-SOd. and CC)S-CH4) to be determined, MAGNET1-fE-HEMATITE EXPERIFJIENTS Magnetite-hematite-solution equilibria is characteristic of mineral assemblages used to control system redox state. or other potential variables, in a hydrothermal experiment to simplify the analyses necessary and to constrain the ex~eriment to geologically reasonable conditions. We have performed ~Yoeriments to evaluate equilibration of solution redox couples at 300’C, 500 bars. with a mind assemblage of magnetite and hematite, and a 3.5 wt.% NaCl solution (pH=-5.4, total dissolved CO, =-6 mM), To confirm reversible redox equilibrium, two experiments were run simultan~ously, one starting with excess 00 dissolved in solution and the other with excess Ha and CH4, Concentrations of Ha in solution for both experiments reached a consistent steady state concentration after ‘2000 hours of reaction (Figure la). 02 initially present in the oxidised experiment was rapidly consumed by the reactions to below analytical detectian limits. In contrast, concentrations of CFi4 did not reach a consistent steady state between experiments (Figure lb). S04 concentrations in solution decreased slightly, while sulfide was produced. in both experimmts (Figure lc), Dissolved Fe increased rapidly to ~ maximum in the reduced experiment, and then decreased to achieve a steady state concentration consistent with the oxidised experiment (Figure Id), The steady state H, concentration observed in the experiments is consistent with ●quilibrium concentrations of H: calculated for magnetite-hematite equilibria using SUPCRT (Helg,eson et d., 1978, 1981 and references therein and data for H, volubility (Himmelblau, 1959: Drumnwnd, 1982: Naumov et al,, 1971) (Figure la), \ he data of Kashima and Sakai (1984) for dissolv~d Ha i~ oagnettte- hematite. solution cxperimants at 300’IC is also consistent with our experimental data set, but does not represent steady state or ●quilibrium con:entlations (Figure la), SOt-H2S reacticms, (!vJluated by distribution of ~pecies in aqueous solution using SOLVEQ (Reed, 1982) and the aqueous sperne dissociation constant data set of Janecky (1982), Jlso indicate a r,fose approach to equilibrium with the magnetit~hematita assemblage. CHf concentrations in both experiments are, however, fir~atly In excess of that which would be in equilibrium with the C0,2 present, ~t the measured concentrations of H.], CH4 in tho oxidised experiment was apparently Benerated by breakdown of a small amount of organic carbon dissolved in the deionized w,lter used, These results are consistent with stlldies of nat~ral systems in which the redox couples HJ-H,10 and S04-H4S, and Fe-bearing minerals onulllhr,ltc, . while CH4-COj does not (Arnorsson and Cmmlaugsson, 1985: Jarwcky and Seyfri~d, 1984), - SULFIDE-BEARING SYSTEMS Sulfide is an important reactive component of rcdox rctictions in hydrothermal systcnls at wI. evated temperatures. For example, in high temperature oceanic ridge crest hydrothermal systems, sulfide alteration rnirmrals form within the basalts am.1sulfide deposits are produced whe) hydmttwr mal solutions exit into seawater, To vnderstilnd [he source and re;lction controls on high twnprvature hydrotlwrrnii! solutions, such o~ those nt 21’ N, E~st P,)cific Rise VOI1 Damm et d,, 1985), thr rela tionship~ betwctm solution composition, twnperature, pressure, anA krsalt alteration pathway Inust h under~tood, Two typas of experiments can ba used to examine these rclationship~ 1) SIIIIPIC mincrd raactlon exmwiments fe,~,. magnetita-llerntitite-py rite reactiorr with 3,5 wt, % NaCl solution), w,rf 2) Janecky, D. R. 2 LOS M -r-- Figure 1. Concentrations of analyzed species in solut on versus IOK hours of reaction for hematite- magne~ite- solution experiments with initial excessesof 0~ (open circles), and H I and CH4 (closedcircles), Uncertainties for the analysm are shown by vertical lines, if larger than iyrnbol dh ter. Circleswith attached arrows r~present maximum or detection limit concentrations, (a) Dissolved H? data with respect to calculated ●quilibrium With hematile-magnetite and equivalent log f,,1. Open square is data of Kashima and Sakai, (1984). (b) Dissolved CH4 data. (c) Dissolved sulfate and sulfide data. (d) Dissolved Fe data. basalt reaction with evolved seawa!er compositions (Seyfrled and Janecky, 1985), Magnetitt+pyrite and magnetite-hematite-pyrite experirwnts at 3501C and 4001’C approach re- versible equilibrium wiih solution. although slowly at 350’C (Figure 2), In contrast, at 400 C Fe- bearing assemblages of pyrite-pyrrhotite-magnetite appear tc equilibrate metastablv with pyrrbotlte and magnetite, within the pyrh fdd (Figure 2), At 31511C, however. the pyrite- pyrrhotite- m~gnetlte ass~mblage equilibrates with pyrite and magnetite (Figure 2), Mineralogical relationships observed In the charges at the completion of the experiments are consistent with these relationships, Basalt-solution ex eriments at 375 and 409”C. appeai tu equilibrate or closely a~p~o,~ch e.qull~- bration with F*oxide [and sulfide) assemblages (Figuro 2. A! 350’C, equilibration was .~ppatently slow and at the end of the experiment sulfide remained slig1lt!y below pyrite saturation (Figlire 2) At 4251C, sulfide cw~~entrations are abovo pyrrhotite and/or ma~petite stah;lity with pyrite, evvn though -- magnetite was present, Sinlilarly, at 400’9C and water-rock ~aticr of 0.5, the solution colnposltmn IS at metastabla ●quilibrium with rragrwtite-pyrl hotite and heaagona! oyrrhotite c[ystals wwe observed with several ragged margins and overgrowths of smaller pyriu? crystals (!3eyfried and Janecky, 1985), Water-rock ratio is also important in determining the stability of sulfide minerals, with those 400 C experiments at ratios greater than ‘2 Lwking observable pyrite and indicating undersaturatlon with pyrite (Figure 2), CONCLUSIONS AND APPLICATION The exper;mwtal data on solutmn compositions and mmerals for simple bufier assemblages and ● bti~i]lt-.. “solution interaction provide a very important check on rodox quilibria Ciagrarns [or the Fc-O- -1 .---------- :- .I-- -.;0:--1 ●-”:nm u*II k=uam~ *k- ~nnumntinnal limit- Janecky, D. R. logf(OJ bg f (OJ -w -Vs -m -MS -ma -SM -ss -ns -m -! .s -1 -1A -2 “ -2- ~., - :.,. I El. I 1 S75”c -. -s, 4 -2 -1 -5 + -a I “ kg J-Q bg J-Q IaJ f (0,) bg f (o,) -i~ -+~i= Wlh . -2- ● ~-, .’ 3’ 4 -! Figuru 2, Stability fields for Fe oxide and sulfide minerals with respect to Hll,,,,l and hqS acr~vi:ies In e~pef. imental solutions at 400 bars (Solid Squares — EPR ferrobasalt-solution interaction: Solid Circles -- MAR olivine-normative basalt-solution interaction: Open Squares — magnetite-pyrite experiments at 500 bar? op~n Diamonds — magnetite-pyrite-hematite experiments at !;00 bars, Open Circles and Open Triangles — pvfll Q- pyrrhotite-magnetite experiments) and ●rid-member hydrothermal solutions at 21’ N EPR (X) (Craig ●t J/ l)CIO Welhan, 1980; Welhan and Craig. 1983) In the 400”C diagram, pyrite-magnetite-hematite relation~hlps .~Ic JI\O shown for 500 bars pressure, the rnctastable pyrrhotitc magnetite boundary is shown, and basalt -~CIUIIm CQ. perlments with water-rock ratios of O S dnd 5 are l~heled Thermochemical data for mineral (JiSSr)lUtit>~~~A{ll~n\ from Helgeson et ●l. (1978, 1981, and referencestherein), for H? volubility from Hirnlnel’~l~u(1959) ~rurnrn,>nd (1982), and Naumov ●t d (1971) and for H2S(,,,,I dissociation from Ellis and ~~ge~,lba~h (1971] for most solution equilibria computations (Figure 2).
Load more

Recommended publications
  • Modeling the Shape of Ions in Pyrite-Type Crystals
    Crystals 2014, 4, 390-403; doi:10.3390/cryst4030390 OPEN ACCESS crystals ISSN 2073-4352 www.mdpi.com/journal/crystals Article Modeling the Shape of Ions in Pyrite-Type Crystals Mario Birkholz IHP, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany; E-Mail: [email protected]; Tel.: +49-335-56250 Received: 13 April 2014; in revised form: 22 August 2014 / Accepted: 26 August 2014 / Published: 3 September 2014 Abstract: The geometrical shape of ions in crystals and the concept of ionic radii are re-considered. The re-investigation is motivated by the fact that a spherical modelling is justified for p valence shell ions on cubic lattice sites only. For the majority of point groups, however, the ionic radius must be assumed to be an anisotropic quantity. An appropriate modelling of p valence ions then has to be performed by ellipsoids. The approach is tested for pyrite-structured dichalcogenides MX2, with chalcogen ions X = O, S, Se and Te. The latter are found to exhibit the shape of ellipsoids being compressed along the <111> symmetry axes, with two radii r|| and describing their spatial extension. Based on this ansatz, accurate interatomic M–X distances can be derived and a consistent geometrical model emerges for pyrite-structured compounds. Remarkably, the volumes of chalcogen ions are found to vary only little in different MX2 compounds, suggesting the ionic volume rather than the ionic radius to behave as a crystal-chemical constant. Keywords: ionic radius; ionic shape; bonding distance; ionic volume; pyrite-type compounds; di-chalcogenides; di-oxides; di-sulfides; di-selenides; di-tellurides 1.
    [Show full text]
  • Pyrite Roasting, an Alternative to Sulphur Burning
    The Southern African Institute of Mining and Metallurgy Sulphur and Sulphuric Acid Conference 2009 M Runkel and P Sturm PYRITE ROASTING, AN ALTERNATIVE TO SULPHUR BURNING M Runkel and P Sturm Outotec GmbH, Oberursel GERMANY Abstract The roasting of sulphide ores and concentrates is often the first step in the production of metals or chemicals. In many processes, the production of sulphuric acid is viewed as a by-product, while in some plants production is an important economic factor. Regardless of the purpose, a pyrite roasting plant consists of mainly three plant sections: roasting, gas cleaning and sulphuric acid. With the addition of air, the pyrite concentrates are transformed into solid oxides and gaseous sulphur dioxide at temperatures of 600 - 1000° C. After cleaning and cooling, the sulphur dioxide in the roasting gas is further processed to sulphuric acid. Two types of reactors are used depending on the application: stationary or circulating fluid bed . For over 60 years, Outotec has progressively been developing the principle of fluidised bed technology in several different reactor types for a multitude of process applications. The versatility of the fluidised bed reactor system has manifested itself in the treatment of minerals, including solid fuels, and for metallurgical processes both in the ferrous and non-ferrous fields. Process applications have included roasting, calcining, combustion and charring of coals, as well as off-gas treatment. This paper provides a summary of the pyrite roasting technology currently used along with a simple cost comparison of pyrite roasting and sulphur burning processes. Introduction Pyrite roasting and sulphur burning plants are built for the production of sulphuric acid.
    [Show full text]
  • Ultrafast Band-Gap Oscillations in Iron Pyrite
    Ultrafast band-gap oscillations in iron pyrite The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Kolb, Brian, and Alexie Kolpak. “Ultrafast Band-Gap Oscillations in Iron Pyrite.” Phys. Rev. B 88, no. 23 (December 2013). © 2013 American Physical Society As Published http://dx.doi.org/10.1103/PhysRevB.88.235208 Publisher American Physical Society Version Final published version Citable link http://hdl.handle.net/1721.1/88761 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. PHYSICAL REVIEW B 88, 235208 (2013) Ultrafast band-gap oscillations in iron pyrite Brian Kolb and Alexie M. Kolpak Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA (Received 7 August 2013; revised manuscript received 17 October 2013; published 20 December 2013) With its combination of favorable band gap, high absorption coefficient, material abundance, and low cost, iron pyrite, FeS2, has received a great deal of attention over the past decades as a promising material for photovoltaic applications such as solar cells and photoelectrochemical cells. Devices made from pyrite, however, exhibit open circuit voltages significantly lower than predicted, and despite a recent resurgence of interest in the material, there currently exists no widely accepted explanation for this disappointing behavior. In this paper, we show that phonons, which have been largely overlooked in previous efforts, may play a significant role. Using fully self-consistent GW calculations, we demonstrate that a phonon mode related to the oscillation of the sulfur-sulfur bond distance in the pyrite structure is strongly coupled to the energy of the conduction-band minimum, leading to an ultrafast (≈100 fs) oscillation in the band gap.
    [Show full text]
  • The Electrical Resistivity of Galena, Pyrite, and Chalcopyrite
    American Mineralogist, Volume61, pages248-259, 1976 The electricalresistivity of galena,pyrite, and chalcopyrite Doneln F. PnlorrronreNn RnlpH T. Suurv Departmentof Geologyand Geophysics,Uniuersity of Utah Salt Lake Cily, Utah 84112 Abstract. The sulfidesgalena, chalcopyrite, and pyrite are semiconductorswhose electrical resistivity and type are controlled by deviationsfrom stoichiometryand impurity content,and henceby their geochemicalenvironment. We measuredelectrical resistivity,type, and the impurity content (emissionspectrograph and microprobe) on small volumesof sample.Our results, together with those obtained from a comprehensiveliterature analysis, are usedto construct histogramsof the natural variability in carrier density and resistivity. Sulfur deficiency is the dominant defect in chalcopyrite and hence almost all natural samplesare n-type. lt appearsthat the copper/iron ratio is also important electrically,the copper-richsamples being the more resistive. lmportant donor deiectsin galena(z-type samples)are antimony and bismuth impurities, and sulfur vacancies;acceptor defects(p-type samples) include silver impurities and lead 'Mississippi vacancies.P-type samplesappear to be restrictedto Valley' and argentiferous deposits. In pyrite, electricallyactive impurities include cobalt, nickel, and copper as donors, and arsenicas an acceptor.Deviations from stoichiometry,in the same senseas galena,may be important. Pyritesfrom sedimentaryand epithermaldeposits are usuallyp-type if cupriferous sulfidesare not present.Samples from hypothermaldeposits
    [Show full text]
  • Banded Iron Formations
    Banded Iron Formations Cover Slide 1 What are Banded Iron Formations (BIFs)? • Large sedimentary structures Kalmina gorge banded iron (Gypsy Denise 2013, Creative Commons) BIFs were deposited in shallow marine troughs or basins. Deposits are tens of km long, several km wide and 150 – 600 m thick. Photo is of Kalmina gorge in the Pilbara (Karijini National Park, Hamersley Ranges) 2 What are Banded Iron Formations (BIFs)? • Large sedimentary structures • Bands of iron rich and iron poor rock Iron rich bands: hematite (Fe2O3), magnetite (Fe3O4), siderite (FeCO3) or pyrite (FeS2). Iron poor bands: chert (fine‐grained quartz) and low iron oxide levels Rock sample from a BIF (Woudloper 2009, Creative Commons 1.0) Iron rich bands are composed of hematitie (Fe2O3), magnetite (Fe3O4), siderite (FeCO3) or pyrite (FeS2). The iron poor bands contain chert (fine‐grained quartz) with lesser amounts of iron oxide. 3 What are Banded Iron Formations (BIFs)? • Large sedimentary structures • Bands of iron rich and iron poor rock • Archaean and Proterozoic in age BIF formation through time (KG Budge 2020, public domain) BIFs were deposited for 2 billion years during the Archaean and Proterozoic. There was another short time of deposition during a Snowball Earth event. 4 Why are BIFs important? • Iron ore exports are Australia’s top earner, worth $61 billion in 2017‐2018 • Iron ore comes from enriched BIF deposits Rio Tinto iron ore shiploader in the Pilbara (C Hargrave, CSIRO Science Image) Australia is consistently the leading iron ore exporter in the world. We have large deposits where the iron‐poor chert bands have been leached away, leaving 40%‐60% iron.
    [Show full text]
  • A Sulfur Isotope Study of Pyrite Genesis: the Mid-Proterozoic Newland Formation, Belt Supergroup, Montana
    A sulfur isotope study of pyrite genesis: The Mid-Proterozoic Newland Formation, Belt Supergroup, Montana HARALD STRAUSS' and JORGEN SCHIEBER 2 'Ruhr-Universitat Bochum, Institut fur Geologie, Postfach 102148, 4630 Bochum 1, FRG 2University of Texas at Arlington, Department of Geology, Arlington, TX 76019, USA Abstract-Different generations of sedimentary pyrite from the Mid-Proterozoic Newland Formation, USA, have been analysed for their sulfur isotopic compositions. The results indicate bacterial sulfate reduction as the pyrite forming process. The V'S values for early diagenetic pyrite, around -14%o, are in contrast to dominantly more positive values for many other Middle Proterozoic units. A progressive reduction of sulfate availability during diagenesis can be recognized by an increase in 34S content (Rayleigh Distillation) as well as through detailed petrographic observations. Contemporaneous seawater had a sulfur isotopic ratio between +14 and +18%o as measured from sedimentary barite within the unit. INTRODUCTION deposited between 1450 and 850 Ma ago (HARRISON, 1972), and the Newland Formation accumulated early in basin history. OBRADOVICH and PETERMAN THE MID-PROTEROZOIC Newland Formation (Belt Supergroup) contains (1968) defined a 1325 Ma Rb-Sr isochron in Belt rocks (including the Newland horizons of pyritic shale. These and surrounding sediments have been Formation) of the Big Belt and Little Belt Mountains. Because the whole Lower investigated in detail by SCHIEBER (1985) and a continuous spectrum of pyrite Beltian sequence shows the 1325 Ma age, it is likely that this age represents the types from early diagenetic fine crystalline to late diagenetic eudedral and approximate time of diagenetic smectite-illite trans concretionary pyrite has been distinguished.
    [Show full text]
  • Eg9601814 Supergene Alteration of Magnetite And
    EG9601814 SUPERGENE ALTERATION OF MAGNETITE AND PYRITE AND THE ROLE OF THEIR ALTERATION PRODUCTS IN THE FIXATION OF URANIUM FROM THE CIRCULATING MEDIA. BY MA EL GEMMIZI Nuclear Materials A uthority Cairo- Egypt. ABSTRACT. In most of the Egyptian altered radioactive granites, highly magnetic heavy particles were found to be radioactive. They are a mixture of several iron oxide minerals which are products of supergene alteration of the pre-existing hypogene iron-bearing minerals especially magnetite and pyrite. The end products of this supergene alteration are mainly hydrated iron oxide minerals limonite hematite and geothite. During the alteration, deformation and defects in the minerals structure took place , thereby promoting diffusion of the substitutional and interstitial ions (uranium) to words these sites The mechanism of the alteration of the hypogene iron-bearing minerals; magnetite and pyrite to form the secondary minerals hematite, limonite and geothite; the role of these minerals in fixing uranium from the ciculating media as well as the applicability of these minerals as indicators to the radioactivity of the host rocks were discussed. INTRODUCTION It is quite common that in all the altered rocks magnetite and to some extent pyrite which are present as accessories are suffering from some degrees of alteration. Magnetite and pyrite in the altered granite of Wadi Nugrus, El Missikat and £1 Aradyia, Eastern Desert was found by (1 & 2) to possess several degrees of alteration and crystal deformation. This means that both minerals are sensitive to postdepositional environmental changes. The granites of the present study were described as altered granites overlained by metasediments and underlained by magmatic bodies which invaded the granites itself by sills.
    [Show full text]
  • Pyrite's Evil Twin Marcasite and Pyrite Are Two Common Minerals. Both Fes2 Chemically, Making Them Polymorphs. Polym
    Marcasite - Pyrite's Evil Twin Marcasite and pyrite are two common minerals. Both FeS2 chemically, making them polymorphs. Polymorphs are minerals with the same chemical composition but different crystal structures. Diamond and graphite are polymorphs, both minerals being pure carbon. In diamond and graphite the different arrangement of carbon atoms gives these two minerals of very different physical properties. Pyrite and marcasite, on the other hand, have almost identical physical properties, making them tough to tell from each other. Let's go through their properties. Both are metallic and pale yellow to brassy yellow. Both can tarnish and be iridescent. Both are 6-6.5 on the Mohs' hardness scale. Neither have a particularly prominent cleavage, although marcasite does have one that occasionally shows up. Both have densities of about 5 grams per cubic centimeter (pyrite is a bit denser, but not enough to be detectible without delicate measurements). They can even be found together in the same rock. Fortunately these minerals often show good outer crystal shapes that are quite different. Pyrite crystals are generally equant, and dominated by cubes, octahedrons and 12-sided pyritohedrons. Marcasite crystals are usually rectangular (tabular) with wedge-shaped ends and tend to form in star shaped, radiating or cockscomb groups. Marcasite is also much more restricted in occurrence than pyrite, forming only in low temperature, near surface, very acidic environments. It is found in some ore deposits, in sediments formed under somewhat stagnant conditions and as ground water precipitates in rocks such as in limestone and shale. Although pyrite can also be found in many of these same environments, the crystal shapes are diagnostic.
    [Show full text]
  • Skarn Related Mineralization in the Magnetite-Pyrite-Hematite Deposit of Brosso (Ivrea, Italy)
    ©Geol. Bundesanstalt, Wien; download unter www.geologie.ac.at Verh. Geol. B-A. Jahrgang 1978 Heft3 S. 321-346 Wien, Dezember 1979 Proceed. 3 rd ISMIDA (Leoben, Oct. 7-10, 1977) S. 147-172 Wien, Dezember 1979 Skarn Related Mineralization in the Magnetite-Pyrite-Hematite Deposit of Brosso (Ivrea, Italy) By ALBERTO GIUSSANI*] With 8 figures Italien: Aostatal: Brosso skarnähnlicbe Vererzungen Magnetit-Pyrit-Hämetit- Erzlagerstätten Traversella Pluton Sesia-Lauro Zone 3 Metallogenese Index Introduction , 323 (149) Regional geological setting 323 (149) Geology of the mining area 324 (150) a) Structural setting 324 (150) b) Igneous rocks 326 (152) c) Metamorphic rocks 328 (154) d) Contact aureola 328 (154) The ore deposit 330 (156) a) Quartz-arsenopyrite veins 330 (156) b) Hematite-pyrite lenses : 331 (157) c) Skarn related mineralization 332 (158) • The first mineralizing stage 332 (158) • The second mineralizing stage 335 (161) • The third mineralizing stage 337 (163) Ore genesis in relation to orogeny and to magmatic evolution 340 (166) Conclusion 344 (170) Acknowledgements 344 (170) Riassunto La miniera di Brosso, situata alio sbocco della Valle di Aosta, ё stata coltivata in passato per galena argentife ra poi per ossidi di ferro ed infine per pirite. Le mineralizzazioni si trovano lungo il margine Orientale del plutone di Traversella intruso nelle formazioni metamorfiche della zona Sesia Lanzo, sub­ ito a nord della linea del Canavese. L'intrusione, di etä Alpina, ha ripiegato e metamorfosa to per contatto sia le metamorfiti della Zona Sesia-Lanzo che i filoni di porfirite, intrusi negli scisti. *) Author's address: MONTEDISON S. p. A., Divisione Prodotti per l'Industria Attivitä Minerana.
    [Show full text]
  • Crystal Systems and Example Minerals
    Basics of Mineralogy Geology 200 Geology for Environmental Scientists Terms to Know: •Atom • Bonding • Molecule – ionic •Proton – covalent •Neutron – metallic • Electron • Isotope •Ion Fig. 3.3 Periodic Table of the Elements Fig 3.4A Ionic Bonding Fig 3.4B Covalent Bonding Figure 3.5 -- The effects of temperature and pressure on the physical state of matter, in this case water. The 6 Crystal Systems • All have 3 axes, except for 4 axes in Hexagonal system • Isometric -- all axes equal length, all angles 90ο • Hexagonal -- 3 of 4 axes equal length, three angles@ 90ο, three @ 120ο • Tetragonal -- two axes equal length, all angles 90ο (not common in rock forming minerals) • Orthorhombic -- all axes unequal length, all angles 90ο • Monoclinic -- all axes unequal length, only two angles are 90ο • Triclinic -- all axes unequal length, no angles @ 90ο Pyrite -- an example of the isometric crystal system: cubes Galena -- an example of the isometric crystal system: cubes Fluorite -- an example of the isometric crystal system, octahedrons, and an example of variation in color Garnet -- an example of the isometric crystal system: dodecahedrons Garnet in schist, a metamorphic rock Large masses of garnet -- a source for commercial abrasives Quartz -- an example of the hexagonal crystal system. Amethyst variety of quartz -- an example of color variation in a mineral. The purple color is caused by small amounts of iron. Agate -- appears to be a noncrystalline variety of quartz but it has microscopic fibrous crystals deposited in layers by ground water. Calcite crystals. Calcite is in the hexagonal crystal system. Tourmaline crystals grown together like this are called “twins”.
    [Show full text]
  • Causes of Variation in Crystal Morphology in Metamorphogenic Pyrite Deposits of the Cameros Basin (N Spain)
    Causes of variation in crystal morphology in metamorphogenic pyrite deposits of the Cameros Basin (N Spain) J. ALONSO-AZCÁRATE'*, M. RODA~, L. FERNÁNDEZ-DíAz2, S.H. BOTTRELe, J. R. MAS" and S. LÓPEZ-ANDRÉ~ 1 Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Toledo, Spain 20epartamento de Cristalografía y Mineralogía, Universidad Complutense de Madrid, Madrid, Spain 30epartment of Earth Sciences, University of Leeds, Leeds, UK 40epartamento de Estratigrafía, Universidad Complutense de Madrid, Madrid, Spain The low-grade metasediments of1the Cameros Basin, northem Spain, host a number of deposits of spectacular quality pyrite mineralization. These formed dunng regional metamorphism and the pyrite crystals exhibit a wide range of morphologies. On the basis of pyrite crystal habit, the deposits can be classified into two groups: Group 1 comprises deposits with cubic, elongated or platy crystals; Group II comprises deposits characterized by pyritohedra and cubo-pyritohedra with striated faces, along with blocky crystals and fine-grained aggregates. Group 1 deposits are formed in sequences dorninated by meandriform fluviatile sediments, while Group 11 is hosted by deltaic plain and lacustrine metasediments. Temperature differences between deposits and As content are possible causes of the different pyrite morphologies in the deposits, but no significant variation exists between the two groups for either factor. Comparison with experimentally grown pyrite crystals suggests that Group 1 deposits have morphologies indicative of lower degrees of pyrite supersaturation than pyrite crystals in Group II deposits. The sedimentary facies hosting Group II deposits provides a greater availability of sedimentary sulphur (pyrite and sulphates). Moreover, reactions involving sulphate during metamorphism may have modified fluid chernistry, which would also act to produce higher degrees of pyrite saturation in fluids derived from the sulphate-rich deltaic plain and lacustrine metasediments hosting the Group 11 deposits.
    [Show full text]
  • Millerite and Other Nickel Sulfides from the Siderite Deposit „Steirischer Erzberg“, Styria, Austria
    MITT. ÖSTERR. MINER. GES. 164 (2018) MILLERITE AND OTHER NICKEL SULFIDES FROM THE SIDERITE DEPOSIT „STEIRISCHER ERZBERG“, STYRIA, AUSTRIA Eugen Libowitzky*1, Anton Beran1 & Richard Göd2 1Institut für Mineralogie und Kristallographie 2 Department of Lithospheric Research Universität Wien, Althanstrasse 14, 1090 Wien / *[email protected] Abstract Millerite, NiS, has been identified for the first time in cinnabar- and pyrite-bearing siderite ore samples from „Steirischer Erzberg“, Styria, Austria. In addition, the occurrence of other nickel sulfides has been confirmed, such as siegenite-violarite solid-solutions (ss), CoNi2S4- FeNi2S4, and Gersdorffite, Ni[AsS]. Whereas milleri- te and gersdorffite are close to ideal chemistry with only minor Co and Fe contents, siegenite-violarite ss show a wide range of compositions. Almost pure siegenite with Fe below detection limit occurs in separated crystals within cinnabar or mil- lerite. In contrast, small grains (sometimes in equilibrium with millerite) within a pyrite host contain up to ~14.1 wt% Fe and thus plot in the compositional field of violarite. Zusammenfassung Millerit, NiS, wurde zum ersten mal in Zinnober- und Pyrit-führenden Sideriterz- proben vom Steirischen Erzberg, Steiermark, Österreich, nachgewiesen. Zusätzlich wurde auch das Vorkommen weitere Nickelsulfide wie Siegenit-Violarit-Mischkri- stalle (ss), CoNi2S4-FeNi2S4, und Gersdorffit, Ni[AsS], bestätigt. Während Millerit und Gersdorffit nahe der Idealchemie mit nur geringen Co- und Fe-Gehalten sind, zeigen Siegenit-Violarit ss einen weiten Zusammensetzungsbereich. Nahezu reiner Siegenit mit Fe unter der Nachweisgrenze kommt in separaten Kristallen innerhalb von Zinnober und Millerit vor. Im Gegensatz dazu enthalten kleine Einschlüsse (manchmal im Gleichgewicht mit Millerit) im Pyrit bis zu ~14.1 Gew.-% Fe und fallen damit in das Zusammensetzungsfeld von Violarit.
    [Show full text]