DOCSLIB.ORG

The Orapa South Crater, Botswana

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Orapa South Crater, Botswana Open Research Online The Open University’s repository of research publications and other research outputs Pyroclastic flow deposits from a kimberlite eruption: The Orapa South Crater, Botswana Journal Item How to cite: Gernon, T. M.; Fontana, G.; Field, M.; Sparks, R. S. J.; Brown, R. J. and Mac Niocaill, C. (2009). Pyroclastic flow deposits from a kimberlite eruption: The Orapa South Crater, Botswana. Lithos, 112(1) pp. 556–578. For guidance on citations see FAQs. c 2009 Elsevier B.V Version: [not recorded] Link(s) to article on publisher’s website: http://dx.doi.org/doi:10.1016/j.lithos.2009.04.016 Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online’s data policy on reuse of materials please consult the policies page. oro.open.ac.uk ÔØ ÅÒÙ×Ö ÔØ Pyroclastic flow deposits from a kimberlite eruption: The Orapa South Crater, Botswana T.M. Gernon, G. Fontana, M. Field, R.S.J. Sparks, R.J. Brown, C. Mac Niocaill PII: S0024-4937(09)00152-2 DOI: doi: 10.1016/j.lithos.2009.04.016 Reference: LITHOS 1968 To appear in: LITHOS Received date: 8 September 2008 Accepted date: 19 April 2009 Please cite this article as: Gernon, T.M., Fontana, G., Field, M., Sparks, R.S.J., Brown, R.J., Niocaill, C. Mac, Pyroclastic flow deposits from a kimberlite eruption: The Orapa South Crater, Botswana, LITHOS (2009), doi: 10.1016/j.lithos.2009.04.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT 1 Pyroclastic flow deposits from a kimberlite 2 eruption: the Orapa South Crater, Botswana a;b;∗ c a a 3 T. M. Gernon , G. Fontana M. Field R. S. J. Sparks a;d c 4 R. J. Brown and C. Mac Niocaill a 5 Department of Earth Sciences, University of Bristol, Wills Memorial Building, 6 Bristol BS8 1RJ, U.K. b 7 Department of Geology, Trinity College, Dublin 2, Ireland. c 8 Department of Earth Sciences, University of Oxford, Oxford OX1 3PR, U.K. d 9 Department of Earth and Environmental Sciences, Open University, Milton 10 Keynes, MK7 6AA, U.K. 11 Abstract 12 The Orapa Diamond Mine (Republic of Botswana) exposes a bi-lobate kimberlite 13 pipe that erupted during the Late-Cretaceous epoch (∼93 Ma) through Archaean 14 basement and volcano-sedimentary rocks of the Karoo Supergroup. Geological map- 15 ping of the crater zone of the South Pipe has revealed a 15{25 m thick in-situ 16 kimberlite pyroclastic flow deposit. The pyroclastic deposit fills in the crater and 17 completely drapes lower units, indicating that the parent flow originated from an 18 adjacent kimberlite pipe. The unit comprises a basal coarse lithic concentration layer 19 exhibiting imbricated clasts, which grades upwards into massive poorly sorted lapilli 20 tuff. The tuff contains abundant sub-vertical degassing structures defined by lithic 21 enrichment and depletion in fine-grained material. Degassing structures commonly 22 emanate from blocks in the basal layer. The presence of degassing structures and a 23 coarse basal layer distinguishes this deposit from pipe-filling massive volcaniclastic 24 kimberlite, which is typically homogeneous in terms of texture and clast size over 25 distances onACCEPTED the order of 100s metres. StudiesMANUSCRIPT of the thermal remnant magnetism 26 in basalt clasts from the deposit, together with serpentine{diopside assemblages, ◦ 27 indicate that it was emplaced at elevated temperatures on the order of 200{440 C, 28 consistent with deposition from a pyroclastic flow. The lithofacies characteristics can 29 be explained by the interaction of the pyroclastic flow with the complex topography 30 of a pre-existing crater. 31 Key words: kimberlite, crater, pyroclastic flow, Orapa, fluidisation, degassing ∗ Corresponding author. Email address: [email protected] (T. M. Gernon). Preprint submitted to Elsevier 11 March 2009 ACCEPTED MANUSCRIPT 32 Introduction 33 Kimberlites are ultrabasic igneous rocks emplaced as pipes and dykes into 34 regions of stable cratonic crust (e.g. southern Africa, N.W.T. Canada and 35 Siberia, Russia). Downward tapering kimberlite pipes are typically divided 36 into a lower root zone, a central diatreme zone and an upper crater zone 37 (Hawthorne, 1975; Clement, 1982; Clement and Skinner, 1985; Mitchell, 1986; 38 Clement and Reid, 1989; Sparks et al., 2006). Kimberlite volcanoes are some- 39 what unique in that most of the deposits are preserved in the conduit. Unlike 40 at most other volcanoes, extra-crater deposits are not commonly preserved at 41 kimberlite volcanoes, due to protracted erosion in their cratonic settings. The 42 recognition of primary pyroclastic deposits preserved in a potentially distal 43 setting is unique and of great importance in trying to unravel the dynamics 44 of kimberlite eruptions. 45 Due to the extensive erosion that occurs in cratonic regions, kimberlite craters 46 are not commonly preserved. Exceptions include the Orapa (A/K1) kimberlite 47 pipes, Botswana (Field et al., 1997), the Mwadui kimberlite pipe, Tanzania 48 (Stiefenhofer and Farrow, 2004) and the Argyle (AK1) lamproite pipe, Western 49 Australia (Boxer et al., 1989). These craters typically contain re-sedimented 50 VK and crudely-layered pyroclastic units. The latter are envisaged by Boxer 51 et al. (1989), Field et al. (1997) and Stiefenhofer and Farrow (2004) to have 52 formed in-situ by sustained deposition from eruption columns. Sparks et al. 53 (2006) present an emplacement model in which primary pyroclastic processes 54 (i.e. pyroclastic fall and flow) are important throughout the life of a kimberlite 55 eruption. These can produce both layered and massive deposits. 56 Leahy (1997) and Leckie et al. (1997) describe crater-facies tuff deposits from 57 flat-lying crater deposits of the Fort `ala Corne kimberlite field, Saskatchewan, 58 Canada. Crystal-tuff and lapillistone units in this field are interpreted as py- 59 roclastic fall deposits (Leahy, 1997; Leckie et al., 1997). Pyroclastic flow de- 60 posits have also been identified in the Fort `ala Corne field, although there is 61 still considerableACCEPTED debate as to whether MANUSCRIPT these flows infilled an excavated crater 62 (Scott-Smith et al., 1994; Field and Scott-Smith, 1999; Berryman et al., 2004) 63 or whether some of these flows may have been deposited outside the vent in a 64 sub-marine environment where they have been preserved (Kjarsgaard et al., 65 2006; Pittari et al., 2008). Pyroclastic flow deposits have been reported from 66 the Orapa A/K1 kimberlite (Field et al., 1997; Gernon et al., 2009), and are in- 67 terpreted to have derived from a neighbouring pipe in the Orapa cluster (Ger- 68 non, 2007; Gernon et al., 2008, 2009). A similar style of cross-contamination 69 between kimberlite pipes has also been invoked for the Diavik Pipe (Moss 70 et al., 2008) and Ekati Fox Pipe (Porritt et al., 2008), NWT Canada. 71 In this paper we describe an unusual 25 m thick pyroclastic unit in the Orapa 2 ACCEPTED MANUSCRIPT 72 South kimberlite pipe that we interpret as a pyroclastic flow deposit. Thermal 73 Remnant Magnetism (TRM) analysis of lithic clasts within the deposit indi- 74 cate that it was emplaced at elevated temperatures and the geometry of the 75 unit, geological mapping and stratigraphic relationships with other units in 76 the pipe indicate that it must have been derived from an eruption at a neigh- 77 bouring kimberlite pipe after the cessation of volcanic activity at the Orapa 78 South Pipe. The novelty of this study is that we demonstrate how palaeo- 79 magnetic studies coupled with lithofacies analysis and geological mapping can 80 successfully distinguish between pyroclastic deposits and mass-flow deposits 81 within kimberlite craters (e.g. debris flow deposits): this is commonly diffi- 82 cult in volcaniclastic successions as both types of deposit can exhibit similar 83 lithofacies and features (Duyverman and Roobol, 1981; Cas and Wright, 1987; 84 Nocita, 1988; Best, 1989, 1992). 85 The discovery of a pyroclastic flow deposit within a kimberlite pipe, which 86 have been recently described elsewhere (Moss et al., 2008; Porritt et al., 2008), 87 places additional constraints on the dynamics of kimberlite eruptions and al- 88 lows comparisons with the deposits of pyroclastic flows from other better un- 89 derstood types of volcanoes. The success of the approach outlined here should 90 prompt re-examination of other kimberlite crater deposits. Additional merits 91 of this study are the economic ramifications of the cross-contamination of one 92 pipe by eruptions from a neighbouring pipe, because diamond grade commonly 93 varies significantly from one pipe to another, even within the same kimberlite 94 cluster. The ability to differentiate the provenance of pyroclastic units within 95 a kimberlite pipe is critical for the long-term planning of mining operations. 96 Thermal Remnant Magnetism (TRM) analysis 97 Palaeomagnetic determinations of emplacement temperatures of volcanic de- 98 posits are based on the fact that lithic clasts incorporated into a pyroclastic 99 deposit will originally have been magnetised in-situ prior to eruption and will 100 thus possessACCEPTED a primary or natural remnant MANUSCRIPT magnetisation (NRM) aligned with 101 the Earth's field (during their formation). If the deposits are emplaced above 102 ambient temperatures, the lithic clasts are heated during and after their in- 103 corporation into the deposit and then cool to an ambient temperature in their 104 present position.
Load more

Recommended publications
  • Volcanology and Mineral Deposits
    THESE TERMS GOVERN YOUR USE OF THIS DOCUMENT Your use of this Ontario Geological Survey document (the “Content”) is governed by the terms set out on this page (“Terms of Use”). By downloading this Content, you (the “User”) have accepted, and have agreed to be bound by, the Terms of Use. Content: This Content is offered by the Province of Ontario’s Ministry of Northern Development and Mines (MNDM) as a public service, on an “as-is” basis. Recommendations and statements of opinion expressed in the Content are those of the author or authors and are not to be construed as statement of government policy. You are solely responsible for your use of the Content. You should not rely on the Content for legal advice nor as authoritative in your particular circumstances. Users should verify the accuracy and applicability of any Content before acting on it. MNDM does not guarantee, or make any warranty express or implied, that the Content is current, accurate, complete or reliable. MNDM is not responsible for any damage however caused, which results, directly or indirectly, from your use of the Content. MNDM assumes no legal liability or responsibility for the Content whatsoever. Links to Other Web Sites: This Content may contain links, to Web sites that are not operated by MNDM. Linked Web sites may not be available in French. MNDM neither endorses nor assumes any responsibility for the safety, accuracy or availability of linked Web sites or the information contained on them. The linked Web sites, their operation and content are the responsibility of the person or entity for which they were created or maintained (the “Owner”).
    [Show full text]
  • VOLCANIC INFLUENCE OVER FLUVIAL SEDIMENTATION in the CRETACEOUS Mcdermott MEMBER, ANIMAS FORMATION, SOUTHWESTERN COLORADO
    VOLCANIC INFLUENCE OVER FLUVIAL SEDIMENTATION IN THE CRETACEOUS McDERMOTT MEMBER, ANIMAS FORMATION, SOUTHWESTERN COLORADO Colleen O’Shea A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August: 2009 Committee: James Evans, advisor Kurt Panter, co-advisor John Farver ii Abstract James Evans, advisor Volcanic processes during and after an eruption can impact adjacent fluvial systems by high influx rates of volcaniclastic sediment, drainage disruption, formation and failure of natural dams, changes in channel geometry and changes in channel pattern. Depending on the magnitude and frequency of disruptive events, the fluvial system might “recover” over a period of years or might change to some other morphology. The goal of this study is to evaluate the preservation potential of volcanic features in the fluvial environment and assess fluvial system recovery in a probable ancient analog of a fluvial-volcanic system. The McDermott Member is the lower member of the Late Cretaceous - Tertiary Animas Formation in SW Colorado. Field studies were based on a southwest-northeast transect of six measured sections near Durango, Colorado. In the field, 13 lithofacies have been identified including various types of sandstones, conglomerates, and mudrocks interbedded with lahars, mildly reworked tuff, and primary pyroclastic units. Subsequent microfacies analysis suggests the lahar lithofacies can be subdivided into three types based on clast composition and matrix color, this might indicate different volcanic sources or sequential changes in the volcanic center. In addition, microfacies analysis of the primary pyroclastic units suggests both surge and block-and-ash types are present.
    [Show full text]
  • ETD Template
    Syn-eruptive incision of Koko Crater, Oahu, Hawaii by condensed steam and hot cohesive debris flows: a re-interpretation of the type locality of “surge-eroded U-shaped channels” by Jessica Keri Bluth B.S., State University of New York at Binghamton, 2001 Submitted to the Graduate Faculty of Arts and Sciences in partial fulfillment of the requirements for the degree of Master of Science University of Pittsburgh 2004 UNIVERSITY OF PITTSBURGH FACULTY OF ARTS AND SCIENCES This dissertation was presented by Jessica Keri Bluth It was defended on June 25, 2004 and approved by Dr. Michael Ramsey Dr. Charles Jones Dr. Ian Skilling Committee Chairperson ii Syn-eruptive incision of Koko Crater, Oahu by condensed steam and hot cohesive debris flows: a re-interpretation of the type locality of “surge-eroded U-shaped channels” Jessica K. Bluth, M.S. Department of Geology and Planetary Science University of Pittsburgh, 2004 Phreatomagmatic fall, low-concentration PDC deposits and remobilized equivalents dominate the products of craters (tuff cones/rings) of Koko fissure, south-east Oahu. At Koko crater, Fisher (1977) described “U-shaped” channels, which he interpreted as due to erosion by low-concentration PDCs (surges), with minor modification by stream and debris flows. Similar channels on tuff cones and rings elsewhere in the world have been interpreted as “surge-eroded” by subsequent authors. However, no evidence for erosion by PDCs was observed during recent fieldwork, which suggested rather the following model. An important observation is that initial incision is always correlated with the emplacement of vesiculated ash layers (derived from Hanauma Bay), and is only very rarely associated with other facies.
    [Show full text]
  • Volcanic Glass Textures, Shape Characteristics
    Cent. Eur. J. Geosci. • 2(3) • 2010 • 399-419 DOI: 10.2478/v10085-010-0015-6 Central European Journal of Geosciences Volcanic glass textures, shape characteristics and compositions of phreatomagmatic rock units from the Western Hungarian monogenetic volcanic fields and their implications for magma fragmentation Research Article Károly Németh∗ Volcanic Risk Solutions CS-INR, Massey University, Palmerston North, New Zealand Received 2 April 2010; accepted 17 May 2010 Abstract: The majority of the Mio-Pleistocene monogenetic volcanoes in Western Hungary had, at least in their initial eruptive phase, phreatomagmatic eruptions that produced pyroclastic deposits rich in volcanic glass shards. Electron microprobe studies on fresh samples of volcanic glass from the pyroclastic deposits revealed a primarily tephritic composition. A shape analysis of the volcanic glass shards indicated that the fine-ash fractions of the phreatomagmatic material fragmented in a brittle fashion. In general, the glass shards are blocky in shape, low in vesicularity, and have a low-to-moderate microlite content. The glass-shape analysis was supplemented by fractal dimension calculations of the glassy pyroclasts. The fractal dimensions of the glass shards range from 1.06802 to 1.50088, with an average value of 1.237072876, based on fractal dimension tests of 157 individual glass shards. The average and mean fractal-dimension values are similar to the theoretical Koch- flake (snowflake) value of 1.262, suggesting that the majority of the glass shards are bulky with complex boundaries. Light-microscopy and backscattered-electron-microscopy images confirm that the glass shards are typically bulky with fractured and complex particle outlines and low vesicularity; features that are observed in glass shards generated in either a laboratory setting or naturally through the interaction of hot melt and external water.
    [Show full text]
  • Geology of Volcanic Rocks in the South Half of the Ishpeming Greenstone Belt, Michigan
    Geology of Volcanic Rocks in the South Half of the Ishpeming Greenstone Belt, Michigan U.S. GEOLOGICAL SURVEY BULLETIN 1904-P AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with the last offerings, are given in the current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey" Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated monthly, which is for sale in microfiche from the USGS ESIC-Open-File Report Sales, Box 25286, Building 810, Denver Federal Center, Denver, CO 80225 Order U.S. Geological Survey publications by mail or over the counter from the offices given below. BY MAIL OVER THE COUNTER Books Books Professional Papers, Bulletins, Water-Supply Papers, Tech­ Books of the U.S. Geological Survey are available over the niques of Water-Resources Investigations, Circulars, publications counter at the following U.S. Geological Survey offices, all of of general interest (such as leaflets, pamphlets, booklets), single which are authorized agents of the Superintendent of Documents. copies of periodicals (Earthquakes & Volcanoes, Preliminary De­ termination of Epicenters), and some miscellaneous reports, includ­ ANCHORAGE, Alaska-^230 University Dr., Rm.
    [Show full text]
  • Geologic Map of the North Cascade Range, Washington by Ralph A
    Prepared in cooperation with Washington State Division of Geology and Earth Resources, U.S. National Park Service, and U.S. Forest Service Geologic Map of the North Cascade Range, Washington By Ralph A. Haugerud and Rowland W. Tabor Nontechnical pamphlet to accompany Scientific Investigations Map 2940 Looking south from the North Klawatti Glacier [Mbse]. In the right foreground, the glacier breaks into a heavily crevassed icefall where it descends steeply. Rock in the foreground knob is Eldorado Orthogneiss (unit TKgo), a 90 million-year-old stitching pluton, which here includes numerous dikes of light- colored pegmatite. Mount Buckner on the left skyline and Mount Forbidden hidden in clouds are also eroded from the Eldorado Orthogneiss (photographed in 1987). 2009 U.S. Department of the Interior U.S. Geological Survey CONTENTS Introduction.....................................................................................................................................................1 Using this report ....................................................................................................................................1 Map preparation ...................................................................................................................................1 Major sources of new data .................................................................................................................1 Acknowledgments ................................................................................................................................2
    [Show full text]
  • Igneous Lab 1: Volcanic Rocks and Textures
    EESC 3000: Igneous and Metamorphic Petrology IGNEOUS LAB 1: VOLCANIC ROCKS AND TEXTURES Learning Objectives: Students will be able to identify volcanic textures in hand-sample Students will be able to classify volcanic rocks based on texture Key Minerals: None PYROCLASTIC ROCKS Pyroclastic rocks are classified principally based on grain size, and secondarily on composition: Ash <2mm Lapilli 2-64 mm Block/Bomb >64mm Examine the samples of tephra of various sizes: ash (Mt. St. Helens, WA), laplli (Flagstaff, AZ), and a bomb (Death Valley, CA). Then examine the three pyroclastic rocks. Determine the percentage of components (ash, lapilli, blocks/bombs) and classify each based on grain size. If possible, determine the composition of the tephra (glass, crystals, rock fragments) and add a modifier to each rock name (e.g., lithic Lapilli-tuff). Use a binocular microscope to aid in tephra identification. Pyroclastic Rock 1: __________________________________ Pyroclastic Rock 2: __________________________________ Pyroclastic Rock 3: __________________________________ 1 The temperature of tephra when deposited can affect the texture of the resulting pyroclastic rock. If the tephra is deposited while hot then the individual pieces will be welded together, and so is referred to as a welded tuff. Because the hot fragments are still ductile, the weight of the overlying rock material may cause the tephra to flatten to form a foliated texture referred to as eutaxitic texture. Examine the samples of unwelded and welded tuff from the same volcanic sequence in Shoshone, CA. Identify the composition of the lapilli in the unwelded lapilli tuff and find the corresponding clasts in the welded tuff.
    [Show full text]
  • A Proposed Classification Scheme for Pyroclastic Rocks
    71 A PROPOSED CLASSIFICATION SCHEME FOR PYROCLASTIC ROCKS By Joseph G. Wargo 1950, Hopi Road, Santa Fe, New Mexico INTRODUCTION The g eologist who works in the v ast volcanic fields of southwestern New Mexico and southeastern Arizona soo"n becomes aware of the large volume of volcanic rock that can be described generally as "pyroclastic". Each geolog ist will, in his mind's eye, have a slightly different :picture of the processes in­ v olv ed in the formation of such rocks, and of the point where the rock ceases to be pyroclastic and instead can be regarded as a flow. Most geologists will agree, howev er, that a pyroclastic rock (1), is produced by volcanic action or processes directly related to volcanism, (2) composed largely of broken rock, cry stalline and/ or glassy material, often cemented by a finer-g rained matrix and, (3) more or less indurated and compacted so that it forms a bedded unit. In the case of (3), some rocks otherwise regarded as pyroclastic may be very soft and friable, and perhaps would be better regarded as a "pile" of broken rock, rather than a bed. Another point soon realized in the study of such rocks is that a compositional name is often difficult to apply, especially if the fragments and matrix contain very little in the way of visible minerals. Even thin sections are apt to be mis­ leading because of sampling problems and because the mineralogy of the aphani­ tic portions of the rock may be difficult to resolve. In many instances chemical analyses or studies of the refractive index of the fused rock are necessary in order to decide whether a giv en rock is, for example, a rhyolite or a latite.
    [Show full text]
  • Fiamme Textures in Volcanic Successions: Flaming Issues of Definition and Interpretation ⁎ Katharine F
    Journal of Volcanology and Geothermal Research 164 (2007) 205–216 www.elsevier.com/locate/jvolgeores Fiamme textures in volcanic successions: Flaming issues of definition and interpretation ⁎ Katharine F. Bull , Jocelyn McPhie ARC Centre of Excellence in Ore Deposits and School of Earth Sciences, University of Tasmania, Private Bag 79, Hobart, TAS 7001, Australia Received 27 October 2006; received in revised form 29 March 2007; accepted 11 May 2007 Available online 24 May 2007 Abstract Fiamme are aligned, “flame-like” lenses found in welded ignimbrite. Fiamme also occur in welded pyroclastic fall deposits, secondary welded pumice-rich facies, diagenetically altered and compacted non-welded, pumiceous, volcaniclastic facies and lavas. Fiamme can be formed in a variety of ways. The common genetic use of the term fiamme for pumice clasts that have undergone welding compaction is too narrow. “Fiamme“ is best used as a descriptive term for elongate lenses or domains of the same mineralogy, texture and composition, which define a pre-tectonic foliation, and are separated by domains of different mineralogy, texture or composition. This descriptive term can be used regardless of the origin of the texture, and remains appropriate for flattened pumice clasts in welded ignimbrite. © 2007 Elsevier B.V. All rights reserved. Keywords: fiamme; pumice; welding; volcanic textures 1. Introduction need for a practical definition and a review of common volcanic facies in which fiamme occur. Widespread use of the term ‘fiamme’, Italian for As with many geological terms, ‘fiamme’ has ‘flames’, has ignited much confusion about its meaning acquired a genetic connotation, which, in many cases, in relation to interpretation of textures in volcanic rocks.
    [Show full text]
  • Glossary of Geological Terms
    GLOSSARY OF GEOLOGICAL TERMS These terms relate to prospecting and exploration, to the regional geology of Newfoundland and Labrador, and to some of the geological environments and mineral occurrences preserved in the province. Some common rocks, textures and structural terms are also defined. You may come across some of these terms when reading company assessment files, government reports or papers from journals. Underlined words in definitions are explained elsewhere in the glossary. New material will be added as needed - check back often. - A - A-HORIZON SOIL: the uppermost layer of soil also referred to as topsoil. This is the layer of mineral soil with the most organic matter accumulation and soil life. This layer is not usually selected in soil surveys. ADIT: an opening that is driven horizontally (into the side of a mountain or hill) to access a mineral deposit. AIRBORNE SURVEY: a geophysical survey done from the air by systematically crossing an area or mineral property using aircraft outfitted with a variety of sensitive instruments designed to measure variations in the earth=s magnetic, gravitational, electro-magnetic fields, and/or the radiation (Radiometric Surveys) emitted by rocks at or near the surface. These surveys detect anomalies. AIRBORNE MAGNETIC (or AEROMAG) SURVEYS: regional or local magnetic surveys that measures deviations in the earth=s magnetic field and carried out by flying a magnetometer along flight lines on a pre-determined grid pattern. The lower the aircraft and the closer the flight lines, the more sensitive is the survey and the more detail in the resultant maps. Aeromag maps produced from these surveys are important exploration tools and have played a major role in many major discoveries (e.g., the Olympic Dam deposit in Australia).
    [Show full text]
  • Transport Properties of Pyroclastic Rocks from Montagne Pelée Volcano (Martinique, Lesser Antilles) Marie-Lise Bernard, Maria Zamora, Yves Géraud, Georges Boudon
    Transport properties of pyroclastic rocks from Montagne Pelée volcano (Martinique, Lesser Antilles) Marie-Lise Bernard, Maria Zamora, Yves Géraud, Georges Boudon To cite this version: Marie-Lise Bernard, Maria Zamora, Yves Géraud, Georges Boudon. Transport properties of pyro- clastic rocks from Montagne Pelée volcano (Martinique, Lesser Antilles). Journal of Geophysical Research : Solid Earth, American Geophysical Union, 2007, 10.1029/2006JB004385. insu-01288783 HAL Id: insu-01288783 https://hal-insu.archives-ouvertes.fr/insu-01288783 Submitted on 15 Mar 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B05205, doi:10.1029/2006JB004385, 2007 Transport properties of pyroclastic rocks from Montagne Pele´e volcano (Martinique, Lesser Antilles) Marie-Lise Bernard,1,2 Maria Zamora,1 Yves Ge´raud,3 and Georges Boudon4 Received 10 March 2006; revised 23 September 2006; accepted 10 October 2006; published 5 May 2007. [1] The hydraulic and electrical properties of pyroclastic rocks have been investigated in laboratory on a representative sampling of Montagne Pele´e (Martinique, France) deposits with renewed interest in geophysical applications. This sampling covers all the lithologic units of this volcano: lava dome and lava flows, pumices from ash-and- pumice fall and flow deposits, lava blocks from block-and-ash flow and Pele´ean ‘‘nue´es ardentes’’ deposits, scoriae from scoria flow deposits.
    [Show full text]
  • 1981 203 Descriptive Nomenclature and Classification of Pyroclastic
    Downloaded from geology.gsapubs.org on October 17, 2013 Geology Descriptive nomenclature and classification of pyroclastic deposits and fragments: Recommendations of the IUGS Subcommission on the Systematics of Igneous Rocks R. Schmid Geology 1981;9;41-43 doi: 10.1130/0091-7613(1981)9<41:DNACOP>2.0.CO;2 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geology Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes Geological Society of America Descriptive nomenclature and classification of pyroclastic deposits and fragments: Recommendations of the lUGS Subcommission on the Systematics of Igneous Rocks R.
    [Show full text]