DOCSLIB.ORG

11. Hydrothermal Alteration

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
11. Hydrothermal Alteration 11. Hydrothermal Alteration By W.C. Pat Shanks III 11 of 21 Volcanogenic Massive Sulfide Occurrence Model Scientific Investigations Report 2010–5070–C 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 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 Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Shanks III, W.C. Pat, 2012, Hydrothermal alteration in volcanogenic massive sulfide occurrence model: U.S. Geological Survey Scientific Investigations Report 2010–5070 –C, chap. 11, 12 p. 167 Contents Relations among Alteration, Gangue, and Ore .....................................................................................169 Mineralogy, Textures, and Rock Matrix Alteration...............................................................................170 Mineral Assemblages and Zoning Patterns ..........................................................................................170 Alteration in Modern Seafloor Volcanogenic Massive Sulfide Systems ................................170 Alteration Zoning in Ancient Volcanogenic Massive Sulfide Deposits ...................................173 Lateral and Vertical Dimensions .............................................................................................................175 Alteration Intensity ....................................................................................................................................175 References Cited........................................................................................................................................178 Figures 11–1. Representative cross sections of alteration related to hydrothermal activity or fossil hydrothermal activity on the modern seafloor .....................................................172 11–2. Representative examples of alteration zoning in volcanogenic massive sulfide deposits .........................................................................................................................174 11–3. Fluid flow modeling showing water/rock ratios during hydrothermal circulation at A, the Panorama volcanogenic massive sulfide district and B, beneath the seafloor at the Lau Basin hydrothermal system ...............................176 11–4. Graphs showing geochemical techniques for quantifying hydrothermal alteration effects using (A) the Gresens mass balance approach and (B) the alteration box plot approach .....................................................................................................................177 Table 11–1. Diagnostic minerals in hydrothermally altered volcanogenic massive sulfide deposits at different metamorphic grades ..........................................................................171 11. Hydrothermal Alteration By W.C. Pat Shanks III The geochemical reactions that produce hydrothermal Relations among Alteration, Gangue, alteration in host rocks of VMS deposits are critically important for a number of reasons. First, three-dimensional and Ore distributions of hydrothermal alteration zones are produced by circulating hydrothermal fluids and thus provide evidence Ore is traditionally defined as a valuable mineral or for pathways of fluid travel and geochemical evidence for the chemical commodity that can be extracted at a profit. In VMS physical and chemical conditions of alteration. The chemical deposits, ore generally consists of sulfide or sulfosalt minerals and mineralogical distributions of hydrothermal alteration that contain Cu, Pb, Zn, Ag, and (or) Au. Gangue is defined zones are generally the only direct evidence of fluid circulation as any noneconomic mineral deposited together with ore; in patterns related to VMS ore formation. Second, systematic VMS deposits this means essentially all nonsulfide miner- arrangement of hydrothermal alteration zones, and recognition als (see “Hypogene Gangue Characteristics,” Chapter 9, this of this arrangement, may provide information useful in volume) and some hydrothermal sulfide minerals (typically mineral exploration and may in some cases provide vectors pyrite or pyrrhotite) that lack economic value. Hydrothermal to undiscovered deposits. Third, hydrothermal alteration can alteration is defined as any alteration of rocks or minerals provide key information on the origin of metallic elements by the reaction of hydrothermal fluid with preexisting solid in VMS deposits. For example, depletion of key elements in phases. Hydrothermal alteration can be isochemical, like meta- altered rocks, combined with measured or inferred estimates morphism, and dominated by mineralogical changes, or it can of the volume of altered rock, can constrain possible be metasomatic and result in significant addition or removal of sources of ore metals. Finally, identification and recognition elements. Where alteration is intense, it can result in signifi- of hydrothermal alteration assemblages and their zonal cant volume changes such that mass balance approaches using relationships in the field may provide important evidence that immobile elements are required to fully understand the altera- a terrane under assessment is favorable for occurrence of VMS tion process (Gresens, 1967). deposits. Some authors include gangue and hydrothermal alteration Hydrothermal alteration varies widely from district to together (Beane, 1994) but, in the context of VMS deposits, it district and among individual deposits, and the literature on seems useful to continue distinguishing gangue from altera- this topic is voluminous. A detailed review is beyond the scope tion. Alteration is by definition an epigenetic process that of this report; the interested reader is referred to the following modifies preexisting rocks (or sediments), whereas gangue summary references and additional citations therein: Slack is generally a syngenetic mineral deposited on or near the (1993), Ohmoto (1996), Carvalho and others (1999), Galley seafloor along with the ore minerals. However, distinctions and Koski (1999), Large and others (2001a), Herrington and between gangue and alteration become difficult in cases where others (2003), Gifkins and others (2005), Peter and others VMS mineralization occurred by replacement and open space (2007), Galley and others (2007), Gibson and Galley (2007), filling in porous and permeable rocks in shallow zones beneath and Goodfellow (2007). the seafloor. Fortunately, alteration zones related to VMS deposits In some cases, the bulk of the massive sulfide ore may do show characteristic zonal arrangements (proximal, distal, be deposited in shallow subseafloor environments. In this comformable) that may be related to fluid flow and water/ mode of mineralization, hydrothermal fluids flow into highly rock interaction processes (upflow, recharge, burial metamor- permeable, high-porosity rocks, where sulfide precipitation is phism). In addition, fairly standard alteration assemblages, triggered by mixing with cold ambient seawater in the pore defined by alteration mineralogy, also occur in country rocks space. The prime example of this style of mineralization is the around many deposits, and even metamorphosed alteration giant Kidd Creek deposit, where most mineralization occurred zones produce predictable assemblages. below the seafloor in permeable, fragmental felsic volcanic 170 11. Hydrothermal Alteration rocks by infill and replacement (Hannington and others, 1999). (Zierenberg and others, 1988). The completely silicified A similar origin is inferred for the Horne mine (Kerr and Gib- rocks were originally mapped as “chert exhalite,” but careful son, 1993), the Ansil deposit where laminated felsic ash flows/ mineralogical, geochemical, and isotopic studies showed the turbidites were replaced by sulfides and silica (Galley and presence of relict igneous chromium spinel, proving massive others, 1995), and for the Turner-Albright ophiolitic deposit hydrothermal replacement. Similar extreme alteration has where massive sulfide formed below the seafloor within basal- been documented locally in the amphibolite-facies wall rocks tic hyaloclastite (Zierenberg and others, 1988). Hannington to the Elizabeth VMS deposit, Vt., where assemblages such and others (1999) suggested that subseafloor mineralization as quartz-white mica-calcite and quartz-white mica-albite- also formed some of the Bathurst (New Brunswick) deposits. staurolite-garnet-corundum contain uniformly high Cr/Zr and Ti/Zr ratios, which reflect protoliths of tholeiitic basalt that were pervasively metasomatized during seafloor hydrothermal Mineralogy, Textures, and Rock Matrix mineralization (Slack, 1999; Slack and others, 2001). These studies underscore the importance of under- Alteration standing the nature and effects of hydrothermal alteration in VMS systems, including overprinting
Load more

Recommended publications
  • Editorial for Special Issue “Ore Genesis and Metamorphism: Geochemistry, Mineralogy, and Isotopes”
    minerals Editorial Editorial for Special Issue “Ore Genesis and Metamorphism: Geochemistry, Mineralogy, and Isotopes” Pavel A. Serov Geological Institute of the Kola Science Centre, Russian Academy of Sciences, 184209 Apatity, Russia; [email protected] Magmatism, ore genesis and metamorphism are commonly associated processes that define fundamental features of the Earth’s crustal evolution from the earliest Precambrian to Phanerozoic. Basically, the need and importance of studying the role of metamorphic processes in formation and transformation of deposits is of great value when discussing the origin of deposits confined to varied geological settings. In synthesis, the signatures imprinted by metamorphic episodes during the evolution largely indicate complicated and multistage patterns of ore-forming processes, as well as the polygenic nature of the mineralization generated by magmatic, postmagmatic, and metamorphic processes. Rapid industrialization and expanding demand for various types of mineral raw ma- terials require increasing rates of mining operations. The current Special Issue is dedicated to the latest achievements in geochemistry, mineralogy, and geochronology of ore and metamorphic complexes, their interrelation, and the potential for further prospecting. The issue contains six practical and theoretical studies that provide for a better understanding of the age and nature of metamorphic and metasomatic transformations, as well as their contribution to mineralization in various geological complexes. The first article, by Jiang et al. [1], reports results of the first mineralogical–geochemical Citation: Serov, P.A. Editorial for studies of gem-quality nephrite from the major Yinggelike deposit (Xinjiang, NW China). Special Issue “Ore Genesis and The authors used a set of advanced analytical techniques, that is, electron probe microanaly- Metamorphism: Geochemistry, sis, X-ray fluorescence (XRF) spectrometry, inductively coupled plasma mass spectrometry Mineralogy, and Isotopes”.
    [Show full text]
  • Download PDF About Minerals Sorted by Mineral Name
    MINERALS SORTED BY NAME Here is an alphabetical list of minerals discussed on this site. More information on and photographs of these minerals in Kentucky is available in the book “Rocks and Minerals of Kentucky” (Anderson, 1994). APATITE Crystal system: hexagonal. Fracture: conchoidal. Color: red, brown, white. Hardness: 5.0. Luster: opaque or semitransparent. Specific gravity: 3.1. Apatite, also called cellophane, occurs in peridotites in eastern and western Kentucky. A microcrystalline variety of collophane found in northern Woodford County is dark reddish brown, porous, and occurs in phosphatic beds, lenses, and nodules in the Tanglewood Member of the Lexington Limestone. Some fossils in the Tanglewood Member are coated with phosphate. Beds are generally very thin, but occasionally several feet thick. The Woodford County phosphate beds were mined during the early 1900s near Wallace, Ky. BARITE Crystal system: orthorhombic. Cleavage: often in groups of platy or tabular crystals. Color: usually white, but may be light shades of blue, brown, yellow, or red. Hardness: 3.0 to 3.5. Streak: white. Luster: vitreous to pearly. Specific gravity: 4.5. Tenacity: brittle. Uses: in heavy muds in oil-well drilling, to increase brilliance in the glass-making industry, as filler for paper, cosmetics, textiles, linoleum, rubber goods, paints. Barite generally occurs in a white massive variety (often appearing earthy when weathered), although some clear to bluish, bladed barite crystals have been observed in several vein deposits in central Kentucky, and commonly occurs as a solid solution series with celestite where barium and strontium can substitute for each other. Various nodular zones have been observed in Silurian–Devonian rocks in east-central Kentucky.
    [Show full text]
  • Geologic Atlas of Blue Earth County, Minnesota
    Prepared and Published with the Support of COUNTY ATLAS SERIES THE BLUE EARTH COUNTY BOARD OF COMMISSIONERS AND ATLAS C-26, PART A MINNESOTA GEOLOGICAL SURVEY the Minnesota ENVironment and Natural Resources Trust Fund Blue Earth County Harvey Thorleifson, Director as recommended by the LEGislatiVE-CitiZen Commission on Minnesota Resources Plate 2—Bedrock Geology NIC OLL ET COU NTY 7 Minnesota B BEDROCK GEOLOGY Ka 44°15' N. 285 300 R. 29 W. Kd m STRATIGRAPHIC COLUMN River 285 By 240 s 94° W. e i Lithostratigraphic r Composite natural gamma log 255 NICOLLET LE SUEUR COUNTY R. 26 W. COUNTY R. 25 W. e unit S 270 - e 315 Increasing count 330 Era m Lithology Kd e T. 109 N. sl Os 315 Julia R. Steenberg t Group, 0 100 s 24 Map symbol 19 y 300 300 24 24 Formation 270 lr 19 S API-G units Oo Thickness (in feet) 300 River 285 LIME JAMESTOWN 345 94°15' W. 255 Kd Wita Kd Creek 315 2012 315 )68 j Kd Lake j Dakota Kd 5-90 m.y.) Upper Formation Os Y 300 (99.6-93.5 T Duck Cretaceous 300 lr Morgan Os Lake N T. 109 N. CAMBRIA U 315 O 300 Minnesota 240 Ballantyne C LOCATION DIAGRAM Oo 300 Lake R 270 Madison MESOZOIC R. 28 W. U 31 Kd 300 31 Oo Unnamed Ka Os E Kd 30-90 36 31 Eagle Lake lr lr 36 315 36 U 36 S Cretaceous 300 ) 31 300 22 (112-93.5 m.y.) (112-93.5 Gilfillin 315 E Lower to Upper Lake L Judson Lake 315 300 lr 240 1 6 Y 6 240 Os Platteville Formation 255 315 T Opg 6 Madison 5-20 1 1 N 6 Glenwood Formation Ph 1 255 U sl 255 1 CORRELATION OF MAP UNITS O )60 Upper 315 315 C Lake A j (450 m.y.) 315 C ? E Kd Upper Cretaceous 285 14 Kd S Lithology Key 315 A St.
    [Show full text]
  • PARAGONITE PSEUDOMORPHS AFTER KYANITE from TURKEY HEAVEN MOUNTAIN, CLEBURNE COUNTY, ALABAMA1 Tnonnron L. Noarnnnu, Geological Su
    THE AMERICAN MINERALOGIST, VOL, 50, MAY_JIJ'}IE, 1965 PARAGONITE PSEUDOMORPHS AFTER KYANITE FROM TURKEY HEAVEN MOUNTAIN, CLEBURNE COUNTY, ALABAMA1 TnonNroN L. Noarnnnu, GeologicalSuraey of Alabama, Uniaersity, Alabama. ABSTRACT Paragonite pseudomorphs after kyanite have been found in the Turkey Heaven Moun- tain kyanite prospects. The pseudomorphs range in size from microscopic grains to mega- scopic prisms, which resemble andalusite crystals Optical, o-ray and petrographic studies indicate direct hysterogenic paragonite alteration of the kyanite. INrnolucrroN An investigationof kyanite prospectsin Sections22 and29,T.17 5., R. 11 E., at Turkey Heaven Mountain, Cleburne County, Alabama, discloseda unique mineral occurrence.The mineral assemblageincludes hysterogenicparagonite pseudomorphsafter kyanite, which resemble andalusite.The geneticphysicochemical parameters are consideredas a function of retrogrademetamorphism within a restrictive water environ- ment. GBor-ocrc SB:rrrNc The Turkey Heaven Mountain areais underlain by two metamorphic rock units: 1) the WedoweeFormation, a highly resistantgraphite-mica schist,and 2) a unit of the Ashland Mica Schist,an extensivelyweathered garnet-muscovite schist. Fresh rock exposuresindicate a retrograde metamorphic cycle from an almandine-amphibolite facies to a green- schist facies. At the crest of Turkey Heaven Mountain, the Wedowee Formation over-liesthe Ashland Mica Schist.The resistantgraphite-mica schist of the WedoweeFormation and associatedquartz veins contribute to the physiographic configuration of the area. The generalregional strike in the Alabama crystalline belt is about N. 45o E., and the dip is generally southeast.The crystalline area has undergoneprimary deformationfrom the stressesapplied generallyfrom the southeast,which producedisoclinal folding and thrust faulting to the northwest. Geologic studies at Turkey Heaven Mountain indicate a secondperiod of deformation in which the stressdirection can be ex- pressedaS a northeast shear couple that formed nonplanar, non-cylin- drical left lateral drag folds.
    [Show full text]
  • Minnesota's Mineral Heritage
    MINNESOTA'S MINERAL HERITAGE CONSERVATION BULLETIN NUMBER TWELVE MINNESOTA OF CONSERVATION This document is made available electronically by the Minnesota Legislative Reference Library as part of an ongoing digital archiving project. http://www.leg.state.mn.us/lrl/lrl.asp (Funding for document digitization was provided, in part, by a grant from the Minnesota Historical & Cultural Heritage Program.) Author's Foreword Our natural resources constitute the foundations· of our well-being. the means of our protection, the hope of our future. The resources of any region determine to a marked degree .the activity of its inhabitants. Minnesota, though known as an agricultural state, has great mineral wealth and many of its citizens are engaged in mineral industries. Only ten states exceed Minnesota in the value of their annual mineral output. Of these ten, six are the great oil-producing states, three are the coal-producting states of Pennsylvania, West Virginia and Illinois, and one is California with its oil and gold. All of the mineral substances produced from the rocks of the states may be considered industrial minerals. Some are metals and others are non-metals. Metal mining· is restricted to the iron ranges, but the non-metals include a great variety of materials, such as limestone, agricultural lime, dolomite, marl, sand and gravel, clays and shales, wool rock, structural and architectural stone, etc., which are excavated and processed at many different places in the state. In the preparation of the articles in this bulletin, the main objective of the author was to acquaint the citizens of the state with the nature and extent of our mineral heritage.
    [Show full text]
  • Limestone & Dolomite
    Issue Number: 20 Limestone & Dolomite Date: March 2009 1. IDENTIFICATION OF THE SUBSTANCE / PREPARATION AND Both materials may contain trace OF THE COMPANY / UNDERTAKING quantities of other minerals, metal salts, halides. 1.1 Identification of the substance or preparation This datasheet applies to the following products: 3.1.1 Limestone Composition 1.1.1 Limestone: Limestone Aggregates, Granules and Powders Calcium Carbonate Substance Tradenames: Superlon, Longcal and Longcliffe CaCO3 Trivial Chemical Description: Natural Calcium Carbonate Limestone Name 1.1.2 Dolomite: Magnesium Limestone Aggregates, Granules and Powders CAS 1317-65-3 Tradenames: Golconda Number EINECS Chemical Description: Natural Calcium Magnesium Carbonate 215-279-6 Number 1.2 Use of the substance/preparation Powders and granules typically used as inert filler material in applications such 3.1.2 Dolomite Composition as plastics and rubber and building products. Also used in soil stabilization, Calcium Magnesium animal and pet feeds, and glass manufacture. Aggregates used in concrete, Substance Carbonate construction and landscaping. CaMg(CO3)2 Trivial Dolomite 1.3 Company identification Name Longcliffe Quarries Ltd CAS 16389-88-1 Brassington, Matlock, Derbyshire, DE4 4BZ Number EINECS Telephone : +44 (0)1629 540284 Fax :+44 (0)1629 540569 240-440-2 Number E-mail: [email protected] 3.2 Components presenting a 1.4 Emergency telephone health hazard Emergency telephone number available during office hours: 01629 540284 The products contain no Emergency telephone number available outside office hours: No components classified as dangerous according to EC 2. HAZARDS IDENTIFICATION directive 1999/45/EC. The products contain no substances classified as being hazardous to health according to EC directive 1999/45/EC.
    [Show full text]
  • THE PARAGENETIC RELATIONSHIP of EPIDOTE-QUARTZ HYDROTHERMAL ALTERATION WITHIN the NORANDA VOLCANIC COMPLEX, QUEBEC R' the PARAGENETIC RELATIONSHIPS of EPIDOTE-QUARTZ
    TH 1848 THE PARAGENETIC RELATIONSHIP OF EPIDOTE-QUARTZ HYDROTHERMAL ALTERATION WITHIN THE NORANDA VOLCANIC COMPLEX, QUEBEC r' THE PARAGENETIC RELATIONSHIPS OF EPIDOTE-QUARTZ HYDROTHERMAL ALTERATION WITHIN THE NORANDA VOLCANIC COMPLEX, QUEBEC Frank Santaguida (B.Sc., M.Sc.) Thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Earth Sciences Carleton University Ottawa, Ontario, Canada May, 1999 Copyright © 1999, Frank Santaguida i The undersigned hereby recommend to the Faculty of Graduate Studies and Research acceptance of the thesis, THE PARAGENETIC RELATIONSHIPS OF EPIDOTE-QUARTZ HYDROTHERMAL ALTERATION WITHIN THE NORANDA VOLCANIC COMPLEX, QUEBEC submitted by Frank Santaguida (B.Sc., M.Sc.) in partial fulfillment of the requirements for the degree of Doctor of Philosophy ,n. cGJI, Chairman, Department of Earth Sciences \ NW Thesis Supervisor /4, ad,/ External Examiner ii ABSTRACT Epidote-quartz alteration is conspicuous throughout the central Noranda Volcanic Complex, but its relationship to the Volcanic-Hosted Massive Sulphide (VHMS) deposits is relatively unknown. A continuum of alteration textures exist that reflect epidote abundance as well as alteration intensity. The strongest epidote-quartz alteration phase is represented by small discrete "patches" of complete groundmass replacement that are concentrated in discrete zones. The largest and most intense zones are spatially contained in mafic volcanic eruptive centres, the Old Waite Paleofissure and the McDougall- Despina Eruptive Centre. Therefore, epidote-quartz alteration is regionally semi- conformable and is not restricted to the hangingwall or footwall of the VHMS deposits. Epidote-quartz alteration is absent from the alteration pipes associated with sulphide mineralization.
    [Show full text]
  • Part 629 – Glossary of Landform and Geologic Terms
    Title 430 – National Soil Survey Handbook Part 629 – Glossary of Landform and Geologic Terms Subpart A – General Information 629.0 Definition and Purpose This glossary provides the NCSS soil survey program, soil scientists, and natural resource specialists with landform, geologic, and related terms and their definitions to— (1) Improve soil landscape description with a standard, single source landform and geologic glossary. (2) Enhance geomorphic content and clarity of soil map unit descriptions by use of accurate, defined terms. (3) Establish consistent geomorphic term usage in soil science and the National Cooperative Soil Survey (NCSS). (4) Provide standard geomorphic definitions for databases and soil survey technical publications. (5) Train soil scientists and related professionals in soils as landscape and geomorphic entities. 629.1 Responsibilities This glossary serves as the official NCSS reference for landform, geologic, and related terms. The staff of the National Soil Survey Center, located in Lincoln, NE, is responsible for maintaining and updating this glossary. Soil Science Division staff and NCSS participants are encouraged to propose additions and changes to the glossary for use in pedon descriptions, soil map unit descriptions, and soil survey publications. The Glossary of Geology (GG, 2005) serves as a major source for many glossary terms. The American Geologic Institute (AGI) granted the USDA Natural Resources Conservation Service (formerly the Soil Conservation Service) permission (in letters dated September 11, 1985, and September 22, 1993) to use existing definitions. Sources of, and modifications to, original definitions are explained immediately below. 629.2 Definitions A. Reference Codes Sources from which definitions were taken, whole or in part, are identified by a code (e.g., GG) following each definition.
    [Show full text]
  • 06Metamorphs.Pdf
    Clicker • The transformation of one rock into another by solid-state Metamorphism and recrystallization is known as Metamorphic Rocks – a) Sedimentation – b) Metamorphism – c) Melting – d) Metasomatism – e) Hydrothermal alteration Metamorphism • Metamorphism is the solid- state transformation of pre- existing rock into texturally or mineralogically distinct new rock as the result of high temperature, high pressure, or both. Diamond is Metamorphic Metamorphism • The mineralogy of a metamorphic rock changes with temperature and pressure. • In general, the highest temperature mineral assemblage is preserved. • It is possible to infer the highest P- T conditions from the mineralogy. 1 Metamorphic Environments Metamorphic Environments • Regional metamorphism • Where do you find metamorphic involves the burial and rocks? metamorphism of entire regions • In the mountains and in continental (hundreds of km2) shield areas. • Contact metamorphism results from local heating adjacent to • Why? igneous intrusions. (several meters) • Because elsewhere they are covered by sediments. Metamorphic Environments Regional Metamorphism • Because the tectonic forces required to bury, metamorphose, and re- exhume entire regions are slow, • most regionally metamorphosed terranes are old (> 500 MY), and • most Precambrian (> 500 MY) terranes are metamorphosed. Regional Metamorphism Regional Metamorphism • Regional metamorphism is typically • Regional metamorphism is typically isochemical (composition of rock isochemical (composition of rock does not change), although water does not change), although water may be lost. may be lost. • Metasomatism is a term for non- • Metasomatism is a term for non- isochemical metamorphism. isochemical metamorphism. • Contact metamorphism is typically • Contact metamorphism is typically metasomatic. metasomatic. 2 Effect of Increasing Conditions of Metamorphism Temperature • Changing the mineralogy of a sediment requires temperature > • Increases the atomic vibrations 300ºC and pressures > 2000 • Decreases the density (thermal atmospheres (~6 km deep).
    [Show full text]
  • Schists of the Central Alaska Range
    Schists of the Central Alaska Range By CLYDE WAHRHAFTIG CONTRIBUTIONS TO STRATIGRAPHY GEOLOGICAL SURVEY BULLETIN 1254-E Distribution of schists within Fairbanks A-2, A-3, and A-4 quadrangles and Healy 0-2, 0-3, and 0-4 quadrangles UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968 UNITED STATES DEPARTMENT OF THE INTEKIOK STEWART I,. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington. D.C. 20402 - Price 15 cents (paper cover) CONTENTS Page Abstract-..---------------------..-----..-----.----------------------- E 1 Introduction---------..-------------------------------------------- General structural and areal relations- - _ _------ ----..-- ------------ --- Birch Creek Schist----___--_-_------------------------------------- Keevy Peak Formation ............................................. Totatlanika Schist-----__--_-_------------------------------------- Moose Creek Member ----_--------------- ...................... California Creek Member ..................... --- ---------- -- -- - Chute Creek, Mystic Creek, and Sheep Creek Members ------------ Age and origin of the Totatlanika Schist -------- ----__-------- -- --- Metavolcanio schists and associated rocks south of the Birch Creek Schist- References cited-___--_-_-__--------------------------------------- ILLUSTRATIONS Page FIGURE1. Index map of Alaska _----_____---------------------------E3 2. Generalized geologic map of part of the central Alaska Range- Fairbanks A-2, A-3, and
    [Show full text]
  • Iligh Resolution Solid-State Sodium-23, Aluminum-27, and Silicon-29
    American Mineralogist, Volume 70, pages 106-123,I9E5 Iligh resolution solid-statesodium-23, aluminum-27, and silicon-29nuclear magnetic resonancespectroscopic reconnaissance of alkali and plagioclasefeldspars R. JeMes Ktnrpernrcr Department of Geology University of lllinois at Urbana-Champaign l30l West Green Street. Urbana. Illinois 61801 Ronnnr A. KrNsev. KeneN ANN SuIrn School of Chemical Sciences University of lllinois at Urbana-Champaign 505 South Mathews Avenue, Urbana, Illinois 61801 Donelo M. Hr,NoBnsoN Department of Geology University of lllinois at Urbana-Champaign 1301 West Green Street. Urbana. Illinois 61801 eNo Enrc OlorrBI-o School of Chemical Sciences University of Illinois at Urbana-Champaign 505 South Mathews Avenue. Urbana, Illinois 61801 Abstract We presentin this paperhigh-resolution solid-state magic-angle sample spinning sodium- 23,aluminum -27 , andsilicon-29 nuclear magnetic resonance (NMR) spectraof a varietyof plagioclaseand alkali feldsparsand feldsparglasses. The resultsshow that MASS NMR spectracontain a great deal of informationabout feldspar structures. In particular,we observethe following.(l) AUSiorder/disorder and exsolution effects in alkalifeldspars are readily observable.(2) To our presentlevel of understandingthe publishedstructure refinementsof anorthiteare not consistentwith the NMR of spectraof anorthite.(3) The spectraofthe intermediateplagioclases are interpretable in termsofe- and/-plagioclases, with much of the signalapparently coming from strainedsites between albiteJike and anorthite-likevolumes
    [Show full text]
  • Metasomatic Alteration Associated with Regional Metamorphism: an Example from the Willyama Supergroup, South Australia
    Lithos 54Ž. 2000 33±62 www.elsevier.nlrlocaterlithos Metasomatic alteration associated with regional metamorphism: an example from the Willyama Supergroup, South Australia A.J.R. Kent a,),1, P.M. Ashley a,2, C.M. Fanning b,3 a DiÕision of Earth Sciences, UniÕersity of New England, Armidale, NSW, 2351, Australia b Research School of Earth Sciences, The Australian National UniÕersity, Canberra, ACT, 0200, Australia Received 20 October 1998; accepted 12 May 2000 Abstract The Olary Domain, part of the Curnamona Province, a major Proterozoic terrane located within eastern South Australia and western New South Wales, Australia, is an excellent example of geological region that has been significantly altered by metasomatic mass-transfer processes associated with regional metamorphism. Examples of metasomatically altered rocks in the Olary Domain are ubiquitous and include garnet±epidote-rich alteration zones, clinopyroxene- and actinolite-matrix breccias, replacement ironstones and albite-rich alteration zones in quartzofeldspathic metasediments and intrusive rocks. Metasomatism is typically associated with formation of calcic, sodic andror iron-rich alteration zones and development of oxidised mineral assemblages containing one or more of the following: quartz, albite, actinolite±hornblende, andradite-rich garnet, epidote, magnetite, hematite and aegerine-bearing clinopyroxene. Detailed study of one widespread style of metasomatic alteration, garnet±epidote-rich alteration zones in calc-silicate host rocks, provides detailed information on the timing of metasomatism, the conditions under which alteration occurred, and the nature and origin of the metasomatic fluids. Garnet±epidote-bearing zones exhibit features such as breccias, veins, fracture-controlled alteration, open space fillings and massive replacement of pre-existing calc-silicate rock consistent with formation at locally high fluid pressures and fluidrrock ratios.
    [Show full text]