The Reef Ridge supergene nionsulphide zinc mineralization, Alaska

21

st

meeting of the International Mineralogical Association

1-5 September 2014

Johannesburg, South Africa

ABSTRACTS

Edited by:

Deshenthree Chetty (Chief Editor)

Lesley Andrews

Johan de Villiers

Roger Dixon

Paul Nex

Wolf Uwe Reimold

Jill Richards

Bertus Smith

Craig Smith

Sabine Verryn

Fanus Viljoen

A joint publication of the Geological Society of South Africa and the Mineralogical Association of

South Africa

Abstracts for the IMA2014 conference were collated into 58 topical sessions convened after proposals

for sessions were approved. All abstracts were subjected to a review process by convenors, prior to

editing and collation of the abstract volume. The sessions were grouped into ten themes. Themes,

sessions, codes and convenors are listed as follows:

Code

Session

Convenors

CLAY SCIENCE

CS1

General Session: Clay science

Birgit Schampera, Rosa Torres, Sabine Verryn,

Jean-Louis Robert, Maguy Jaber

CS2

Scientific and industrial applications of green rust

related compounds and layered double hydroxides

Andrew Christy, Jean-Marie Genin, Stuart Mills

CS3

Structural characterisation of lamellar compounds

Bruno Lansen, Eric Ferrage, Douglas McCarty

DEEP EARTH

DE1

Cratons and diamonds

Thomas Stachel, Graham Pearson, Fanus Viljoen

DE2

Fluid in the Earth

Pei Ni, Ronald J. Bakker (IMA-WGIM)

DE3

Mineralogy in the Deep Earth

Catherine McCammon, Toru Inoue, Paola

Comodi, Eiji Ohtani, Fanus Viljoen (IMA-CPM)

DE4

Theoretical and Compositional mineral physics

for Deep Earth

Taku Tsuchiya, Razvan Caracas, Jun Tsuchiya

(IMA-CPM)

DE5

Water and hydrous phases in the Earth's interior:

geological, geophysical and geodynamic

implications

Istvan Kovacs, Jannick Ingrin, Qunke Xia

ECONOMIC GEOLOGY/MINERALOGY, APPLIED MINERALOGY

EG1

Critical metals and Rare earth elements

Frances Wall, Kathryn Moore, Judith Kinnaird,

Kathryn Goodenough (Critical Metals Alliance;

Applied Mineralogy Group, Mineralogical

Society of Great Britain and Ireland)

EG2

General Session: Applied Mineralogy

Hans-Joachim Kleebe, Lesley Andrews

EG3

General Session: Economic Geology/Mineralogy

Paul Nex, Judith Kinnaird, Brian Hoal, Thomas

Oberthür, Frank Melcher (SEG)

EG4

Gold deposits

Lynnette Greyling, Hartwig Frimmel (SGA)

EG5

Non-sulphide Pb-Zn deposits

Maria Boni, Suzanne Paradis

EG6

Platinum group minerals (PGMs) from the mantle

to the crust

Federica Zaccarini, Maryse Ohnenstetter, Anna

Vymazalova (IMA-COM, SGA)

EG7

Process Mineralogy and Geometallurgy

Dee Bradshaw, Megan Becker (IMA-CAM)

EG8

Sediment-hosted ore deposits

Bertus Smith, Lynnette Greyling, Jens Gutzmer

EG9

Sulphide mineralogy and Geochemistry

Nigel Cook, Martin Reich, Joël Brugger (IAGOD,

IMA-COM)

EG10 Zeolites and porous materials

Maria Giovanna Vezzalini, Thomas Armbruster,

ENVIRONMENTAL MINERALOGY/GEOCHEMISTRY

EM1

Applied Geochemistry and Geomicrobiology for

the Remediation of inorganic pollutants

Manuel A. Caraballo, Esta van Heerden, Harish

Veeramani, Julio Castillo

EM2

CO

storage: Mineralogical Implications

Jordi Cama, Linda Luquot, Sebastian Fischer

EM3

Environmental mineralogy and geochemistry of

mine waste

Juraj Majzlan, Karen Hudson-Edwards, Dogan

Paktunc

EM4

Environmental Mineralogy and the Carbon Cycle

Ben Gilbert, Glenn Waychunas

EM5

General Session: Environmental Mineralogy and

Geochemistry

Christian Mavris, Mihály Pósfai, Theophilus

Davies, Benjamin Mapani, Hassina Mouri,

Tsutomo Sato

EM6

Inorganic fibres, biosphere, and risk assessment

Elena Belluso, Alessandro Gualtieri, Mickey

Gunter, Caterina Rinaudo

EM7

Mineralogy on Radioactive waste disposal,

decontamination of radioactively contaminated

sites and decommissioning of nuclear power

plants

Tsutomo Sato, Anhuai Lu, Jordi Cama

(IMA-WGEMG)

EM8

Minerals and Microbes

Anhuai Lu, Hailiang Dong

EM9

Role of Mineralogical Sciences in Sustainable

Cement-based materials

Gilberto Artioli, Joseph Biernacki, Luca Valentini

GEOCHEMISTRY AND PETROLOGY

GP1

Africa-A Mecca of kimberlite, alkaline rock and

carbonatite geology

Frances Wall, Craig Smith

GP2

Aqueous and carbonic fluids in ultramafic rocks:

From vein precipitation to channeled and

pervasive wall-rock reaction

Walter Maresch, Hans-Peter Schertl, George

Harlow

GP3

Dating Metamorphic Processes: Promise and

Pitfalls of Geochronology

Hao Cheng, Tatsuki Tsujimori, Patrick O'Brien,

Hafiz UrRehman

GP4

General Session: Geochemistry and Petrology

Paul Nex, Jean-Louis Robert

GP5

Geologic fluids in the deep crust and upper mantle

Dirk van Reenen, Oleg Safonov, Daniel Harlov

(IMA-WGME)

GP6

Magma differentiation and ore formation

processes

Ilya Veksler, Rais Latypov, Jakob Keidling

GP7

Magma mixing - from macro to micro scale

Ewa Slaby, Diego Perugini

GP8

Magmas and Melts under extreme conditions

Grant Henderson, Daniel Neuville, Roberto

Moretti (IMA-CPM)

GP9

Mineral Inclusions - their genesis and fate

Alexander Proyer, Shah Wali Faryad, Tzen-Fu

Yui

GP10 Pegmatites, and pegmatite mineralogy

Paul Nex, Robert Martin, William 'Skip' Simmons

GP11 Petrologic Pathfinders: Trace elements and stable

isotopes in tourmaline, rutile and other accessory

minerals

Robert Trumbull, Horst Marschall

GP12 The Geology of Gems and their Geographical

Origin

Gaston Giuliani, Lee Groat, Daniel Ichangi

(IMA-CGM)

GP13 Timing and genesis of mineralisations: the isotope

record

METHODS AND APPLICATIONS

MA1

Computed tomography – pushing frontiers in

imaging of the third and fourth dimensions

Deshenthree Chetty, Cecil Churms, David Reid

(IMA-CAM)

MA2

General Session - methods and applications

Sabine Verryn, Simon Clark, Klaus-Dieter

Grevel, Artur Benisek

MA3

Mineral microanalysis

Michael Wiedenbeck, Roger Dixon

MA4

Remote mapping of minerals

Eric Pirard, VDM Van der Meer, Erick

Ramanaidou, Paul Linton (IMA-CAM)

MINERALOGICAL CRYSTALLOGRAPHY

MC1

Crystallography and its importance in applied

mineralogy

Volker Kahlenberg, Johan de Villiers

(IMA-CAM)

MC2

General Session: Mineralogical Crystallography

Johan de Villiers

MC3

Modular aspects of mineral structures

Massimo Nespolo, Marco Pasero, Sergey

Krivovichev

MC4

Physics, Chemistry and Crystallography of

Minerals

Stefan Stöber, Christoph Berthold (German

Minerological Society, Section: Physics,

Chemistry and Crystallography of Minerals)

MC5

Recent progress in the crystal chemistry of

minerals: systematising mineral properties and

behaviour

Georges Calas, Frank Hawthorne

MINERALS, MUSEUMS, CULTURE AND HISTORY

MM1 Archaeometry and Geosciences: facing the

cultural heritage challenges

Corina Ionescu, Gilberto Artioli, Patrik Degryse,

Ãkos Torok, Richard Prikryl

MM2 General Session: Minerals, museums, culture and

history

Roger Dixon, Bruce Cairncross, Peter Davidson,

Suzanne Miller, Eric Pirard (IMA-CM)

OPEN THEME

OT1

Education and skills development

Megan Becker, Gillian Drennan, Rene Toerien

(IMA-CAM)

OT2

New minerals, nomenclature and classification

Stuart Mills, Frédéric Hatert, Peter Williams

(IMA-CNMNC)

OT3

General Session: Open Theme

Deshenthree Chetty

PLANETARY AND COSMIC MINERALOGY

PC1

Challenges in Asteroidal, Lunar and Martian

mineralogy

Jesús Martínez-Frías, Fernando Rull-Pérez

PC2

General Session: Planetary and cosmic

mineralogy

Uwe Reimold, Ansgar Greshake, Razvan Caracas

PC3

Impact cratering, high pressure shock

metamorphism and luminescence studies

Uwe Reimold, Roger L Gibson, Ansgar

Greshake, Jörg Fritz, Arnold Gucsik

PC4

Mineralogical Co-evolution of the Geosphere and

Biosphere

IMA 2014 ORGANISATION

CONFERENCE CHAIR: Sabine Verryn, XRD Analytical Consulting, South Africa

Vice Chair: Deshenthree Chetty, Mintek, South Africa

Vice Chair: Craig Smith, GSSA, South Africa

Organising bodies:

Mineralogical Association of South Africa (MINSA)

The Geological Society of South Africa (GSSA)

LOCAL ORGANISING COMMITTEE

Scientific Programme Committee:

Deshenthree Chetty (Chair)

Mintek, South Africa

Lesley Andrews

Private Consultant, South Africa

Johan de Villiers

University of Pretoria, South Africa

Roger Dixon

University of Pretoria, South Africa

Paul Nex

University of the Witwatersrand, South Africa

Wolf Uwe Reimold

Museum für Naturkunde and Humboldt Universität zu Berlin, Germany

Jill Richards

Exxaro Resources, South Africa

Bertus Smith

University of Johannesburg, South Africa

Craig Smith

Geological Society of South Africa

Sabine Verryn

XRD Analytical and Consulting, South Africa

Fanus Viljoen

University of Johannesburg, South Africa

Sponsorship, Marketing and Exhibition Committee:

David Long (Chair)

Sci-Ba, South Africa

Siksha Bramdeo

Anglo American, South Africa

Deshenthree Chetty

Mintek, South Africa

Annegret Lombard

SGS Minerals Services, South Africa

Chazanne Long

Sci-Ba, South Africa

Craig Smith

Geological Society of South Africa

Darren Tiddy

Anglo American, South Africa

Sabine Verryn

XRD Analytical and Consulting, South Africa

Bursary Committee:

Bertus Smith (Chair)

University of Johannesburg, South Africa

Megan Becker

University of Cape Town, South Africa

Grant Bybee

University of Witwatersrand, South Africa

Annegret Lombard

SGS, South Africa

Luke Longridge

VMIC, South Africa

Jodie Miller

University of Stellenbosch, South Africa

Hervé Wabo

University of Johannesburg, South Africa

Field trips:

Finance:

Craig Smith, Geological Society of South Africa

Social Events:

Wiebke Grote, University of Pretoria, South Africa

Additional LOC members:

Erica Barton

Nelson Mandela Metropolitan University, South Africa

Byron Bezuidenhout

Anglo American, South Africa

Grant Cawthorn

University of the Witwatersrand, South Africa

Louise Coney

De Beers, South Africa

John Dunlevey

University of Limpopo, South Africa

Christoph Gauert

University of the Free State, South Africa

Johan Krynauw

Consultant, South Africa

Hassina Mouri

University of Johannesburg, South Africa

Musarrat Safi

Anglo American, South Africa

Igor Tonzetic

Consultant, South Africa

Brandon Youlton

SGS, South Africa

CONFERENCE SECRETARIAT: Scatterlings Conference and Events

Carolyn Ackerman

Project manager

Jeanne Day-Spriesterbach

Programme, speakers, field trips

Shelley-Ann Abrahams

Registration

Carina du Plessis

Sponsorship and Exhibition

Rowan Moss

Technical

Juanita Males

Speaker preparation room

INTERNATIONAL ADVISORY COMMITTEE:

Walter V. Maresch

President of the International Mineralogical Association, Ruhr Universität Bochum,

Germany

Dee Bradshaw

University of Queensland, Australia

Georges Calas

Université Pierre et Marie Curie, France

Jens Gutzmer

Helmholtz Institute Freiberg for Resource Technology, Germany

Hannah Horsch

Hazen Research, Inc., USA

Sergey Krivovichev

St. Petersburg State University, Russia

Anhuai Lu

Peking University, China

Stuart J Mills

Geosciences Museum Victoria, Australia

Aberra Mogessie

President of the Geological Society of Africa (GSAf), Karl-Franzens-Universität Graz,

Austria

Massimo Nespolo

Université de Lorraine, France

Eric Pirard

Université de Liège, Belgium

Herbert Pöllmann

University of Halle-Saale, Germany

Wolf Uwe Reimold

Museum für Naturkunde and Humboldt Universität zu Berlin, Germany

Ekkehart Tillmanns

Universität Wien, Austria

Frances Wall

University of Exeter, UK

CONTENTS

PLENARY

1

SPECIAL TALK

5

CLAY SCIENCE

CS1

General Session: Clay science

6

CS2

Scientific and industrial applications of green rust related compounds and layered double

hydroxides

13

CS3

Structural characterisation of lamellar compounds

16

DEEP EARTH

DE1

Cratons and diamonds

20

DE2

Fluid in the Earth

33

DE3

Mineralogy in the Deep Earth

37

DE4

Theoretical and Compositional mineral physics for Deep Earth

45

DE5

Water and hydrous phases in the Earth's interior: geological, geophysical and geodynamic

implications

49

ECONOMIC GEOLOGY/MINERALOGY, APPLIED MINERALOGY

EG1

Critical metals and Rare earth elements

57

EG2

General Session: Applied Mineralogy

66

EG3

General Session: Economic Geology/Mineralogy

73

EG4

Gold deposits

86

EG5

Non-sulphide Pb-Zn deposits

97

EG6

Platinum group minerals (PGMs) from the mantle to the crust

101

EG7

Process Mineralogy and Geometallurgy

113

EG8

Sediment-hosted ore deposits

125

EG9

Sulphide mineralogy and Geochemistry

129

EG10

Zeolites and porous materials

138

ENVIRONMENTAL MINERALOGY/GEOCHEMISTRY

EM1

Applied Geochemistry and Geomicrobiology for the Remediation of inorganic pollutants

143

EM2

CO

storage: Mineralogical Implications

149

EM3

Environmental mineralogy and geochemistry of mine waste

154

EM4

Environmental Mineralogy and the Carbon Cycle

161

EM5

General Session: Environmental Mineralogy and Geochemistry

163

EM6

Inorganic fibres, biosphere, and risk assessment

174

EM7

Mineralogy on Radioactive waste disposal, decontamination of radioactively contaminated

sites and decommissioning of nuclear power plants

179

EM8

Minerals and Microbes

183

GEOCHEMISTRY AND PETROLOGY

GP1

Africa-A Mecca of kimberlite, alkaline rock and carbonatite geology

192

GP2

Aqueous and carbonic fluids in ultramafic rocks: From vein precipitation to channeled and

pervasive wall-rock reaction

197

GP3

Dating Metamorphic Processes: Promise and Pitfalls of Geochronology

204

GP4

General Session: Geochemistry and Petrology

208

GP5

Geologic fluids in the deep crust and upper mantle

218

GP6

Magma differentiation and ore formation processes

229

GP7

Magma mixing - from macro to micro scale

237

GP8

Magmas and Melts under extreme conditions

241

GP9

Mineral Inclusions - their genesis and fate

245

GP10

Pegmatites, and pegmatite mineralogy

253

GP11

Petrologic Pathfinders: Trace elements and stable isotopes in tourmaline, rutile and other

accessory minerals

271

GP12

The Geology of Gems and their Geographical Origin

278

GP13

Timing and genesis of mineralisations: the isotope record

286

METHODS AND APPLICATIONS

MA1

Computed tomography – pushing frontiers in imaging of the third and fourth dimensions

292

MA2

General Session - methods and applications

301

MA3

Mineral microanalysis

310

MA4

Remote mapping of minerals

315

MINERALOGICAL CRYSTALLOGRAPHY

MC1

Crystallography and its importance in applied mineralogy

319

MC2

General Session: Mineralogical Crystallography

323

MC3

Modular aspects of mineral structures

327

MC4

Physics, Chemistry and Crystallography of Minerals

333

MC5

Recent progress in the crystal chemistry of minerals: systematising mineral properties and

behaviour

345

MINERALS, MUSEUMS, CULTURE AND HISTORY

MM1

Archaeometry and Geosciences: facing the cultural heritage challenges

353

MM2

General Session: Minerals, museums, culture and history

361

OPEN THEME

OT1

Education and skills development

369

OT2

New minerals, nomenclature and classification

372

PLANETARY AND COSMIC MINERALOGY

PC1

Challenges in Asteroidal, Lunar and Martian mineralogy

382

PC2

General Session: Planetary and cosmic mineralogy

389

PC3

Impact cratering, high pressure shock metamorphism and luminescence studies

393

PC4

Mineralogical Co-evolution of the Geosphere and Biosphere

402

IMA2014 SPONSORS AND EXHIBITORS

410

AUTHOR INDEX

423

PLENARY

__________________________________________________________________________________________________________________________________________

The valuable role of process mineralogy in the future of

the mining industry

Bradshaw D

Julius Kruttschnitt Mineral Research Centre, University of Queensland, Australia d.bradshaw@uq.edu.au

Process mineralogy is at the centre or heart of the Mining Industry, where its very purpose or 'raison d'etre' is to extract value from the defined ore deposit. Each deposit is made up of a distinct set of minerals; their location, type, abundance, association and texture are determined by its formation. In the past, as noted by early twentieth century authors, a working knowledge of applied mineralogy was intrinsic to effective extraction and value creation and so was a skill acquired by any metallurgist or mineral processor.

As the years progressed, processes were to some extent standardised, company structures became formalised, with different disciplines and groups becoming more specialised and less integrated and 'professional silos' were created. With notable exceptions of course, less mineralogical knowledge became inherent to mineral processing, which has resulted in the steady weakening of the discipline's position and contribution of value to the industry.

While at first this did not diminish success, this has all changed recently and unexpected surprises resulting from inadequate ore body knowledge have resulted in reduced economic returns for the Mining Industry. More and more, ores have become complex and lower grade, containing more deleterious elements, resources such as energy and water need to be conserved, and skills shortages have resulted in a wider range of people entering the industry, often with inadequate preparation and less equipped to deal with the more difficult operating environment.

For the future of the Mining Industry to be sustained, the discipline 'Process Mineralogy' needs to be returned to its central, core position. This will provide foundational support for mineral processing circuit design and optimisation, appropriate research and technology development, as well as effective waste and tailings disposal strategies. This requires an articulation of the value as well as the appropriate education and training at all levels to establish and develop our 'Process Mineralogy' communities of practice.

Cross-fertilization of mineralogy and crystallography:

a tribute to the International Year of Crystallography at

IMA 2014

Depmeier W

Institute of Geosciences, University of Kiel, Germany wd@min.uni-kiel.de

It goes without saying that mineralogy as a scientific discipline depends strongly on crystallographic knowledge, techniques and methods, such as structure determination, refinement of site occupancies, or indexing of crystal faces. On the other hand, it is clear that crystallography has its roots in mineralogy, although it is fair to say that nowadays much crystallographic work pertains to objects related to biology.

In this contribution several examples shall be described and discussed where sine qua

non conditions between mineralogy and crystallography, or vice versa, have been

decisive for substantial progress in one of the two fields to be made. Examples include, but are not necessarily restricted to, boracite, charoite, icosahedrite and calaverite. The type locality of boracite, Mg3B7O13Cl, is Lüneburger Kalkberg, Lüneburg, Lower Saxony, Germany where it occurs within the gypsum cap rock of a salt dome. The story has it that the children of Lüneburg liked to play dice with the cube-shaped boracite crystals. Idiomorphic quartz crystals occur together with boracite in this deposit and since both minerals show similar hardness and lustre, boracite was described as "cubic quartz" before it was discovered that it contains boron (hence the name). Later this mineral played a notable role in crystal physics, because it was one of the materials on which J. and P. Curie first demonstrated piezoelectricity. The structure of boracite, in both its cubic and orthorhombic phase, had been determined in the 1950s and it is characterized by chains of corner-sharing asymmetric O4Cl2-octahedra around the Mg2+ ions running along all three cubic <100> directions. Note that a variant of boracite, named ericaite, exists where Fe2+ _{substitutes for Mg}2+_{. In the sixties of the last century} the question was raised whether materials exist, which are simultaneously ferroelectric and ferromagnetic. There were no reasons based on symmetry considerations why such materials should be forbidden. At that time it was believed that a "good" ferroelectric material, such as certain perovskites, should contain d0 cations (Ti4+, Nb5+, etc.), e.g. at the centre of symmetric octahedra in the structure of perovskite. Obviously, d0 _cations do not allow for ferromagnetism. In order to overcome this dilemma scientists proposed to prepare materials containing paramagnetic cations in an asymmetric octahedral environment. First attempts with oxyfluorides failed. Input from mineralogy drew the attention to boracites and after a long and arduous way the first ferroelectric - ferromagnetic, i.e. multiferroic material, Ni-I-boracite, could be prepared. This is how mineralogy helped crystallography.

Likewise, the recent confirmation of a natural quasicrystal, icosahedrite, was only possible with the help of mineralogy. On the other hand, the 50 years old enigma of the structure of charoite could only be solved with the help of a newly developed method of electron crystallography. Another long-standing enigma in mineralogy, namely the indexing of the crystal faces of calaverite, succeeded after application of superspace group theory.

PLENARY

__________________________________________________________________________________________________________________________________________

Petrography in 3D: using X-ray computed tomography to

amplify geological intuition

Ketcham R A

Jackson School of Geosciences, University of Texas at Austin, USA ketcham@jsg.utexas.edu

Three-dimensional imaging using high-resolution X-ray computed tomography (CT) transforms petrographic analysis. An early and persistent critique of X-ray CT for geological applications was that it only produced "pretty pictures", and great progress has been made developing tools to extract 3D quantitative data from voxel data sets. However, the opportunities inherent in doing fundamental petrography in 3D through visualization and geological intuition have remained relatively overlooked. Three examples of the power of CT are presented from the fields of planetary geology and igneous petrology, featuring insights derived from 3D visualization and leveraged by 3D image analysis.

In the first, 3D analysis of a fragment of the famous Murchison meteorite reveals a flattening texture in the chondrules [1]. This flattening may be caused by impact events or a more steady process akin to sediment compaction. Volumetric imagery allows investigation for textural clues of which process may be responsible, and provides a unique opportunity to estimate porosity loss, which may be responsible for the divergent densities of asteroids and meteorites derived from them.

Next, CT analysis of vesicles and phenocryst fragments within pumice provides a fresh look at pre-eruption dynamics [2]. The discovery of welded pumice with vesicles and phenocrysts aligned in a planar fabric that cross-cuts the weld suggests a sequence of fragmentation, welding, strain, and re-fragmentation that is more complex than previously proposed simple end-members for the eruption process. 3D interrogation allows vesicles formed by explosive decrepitation to be easily distinguished from those formed by nucleation of vapour bubbles and enables in situ access to fragment size distributions, providing further insight into the development of eruptive textures. Finally, 3D inspection of a 27-carat carbonado provides numerous insights critical to unraveling the origin of this enigmatic diamond variety [3]. CT data reveal a texture in the porosity that evolves across the sample, suggesting a link between the through-going porosity and the patinaed surface on the specimen. A shear fabric in the pores suggests a shearing event immediately prior to solidification. In-situ examination of the unusual inclusion suite indicative of crustal conditions (e.g., kaolinite, hematite, florencite, etc.), normally accessed by crushing specimens, shows that they all have textures indicating disequilibrium formation. Abundant pseudomorphs reveal a megacrystic euhedral dodecahedral phase (Figure 1) never previously described in carbonado, which has been entirely eradicated but may have provided the raw materials for REE- and U-rich inclusions.

These examples point to the tremendous potential for scientific discovery with more widespread dissemination and utilization of CT data, and the importance of lowering the technical, educational, and financial barriers to it.

Figure 1: 3D visualization of dodecahedral pseudomorphs in carbonado diamond.

[1] Hanna R.D. and Ketcham R.A. ( 2013). Ann. Meet. Meteor. Soc., 75, abstract #5031. [2] Ketcham R.A., Gardner J.E. and Abbott S. (2011). Am. Geophys. Union Fall Meet., abstract EP52C-05.

[3] Ketcham R.A. and Koeberl C. (2013). Geosphere, 9 (5), 1336-1347.

Photoelectrons from the mineral and microbial world:

a new perspective on the interactions between the

geosphere and biosphere

Lu A

School of Earth and Space Sciences, Peking University, China ahlu@pku.edu.cn

The Earth surface is a multiple open system. It is obvious that the interaction among solar light, semiconducting minerals, photoelectrons/photoholes, organics, inorganics, valence electrons and microorganisms occurs continuously on our planet. Semiconducting minerals, including most metal oxides and sulfides, absorb visible light of the solar spectrum. Microorganisms evolve varied pathways to obtain carbon and energy sources. In a recent study [1], evidence was presented demonstrating solar energy mediated by semiconducting mineral photocatalysis, acting as energy source, promoting the growth of some non-photosynthetic bacteria. This revealed that the ternary system of microorganisms, minerals and solar light has played a critical role in the history of life on our planet. In a simulated system, under simulated solar light, semiconducting minerals generate photoelectrons that could be used by non-phototrophic microorganisms to support their metabolisms. The growth of microorganisms was closely related to photon quantity and energy and the microorganism growth and mineral light absorption spectra were fitted well under different light wavelengths. The overall energy efficiency from photon to biomass was 0.13‰ to 1.9‰. Further studies revealed that in natural soil systems, semiconducting mineral photocatalysis could influence the microbial population. Solar energy

utilization pathways by non-phototrophic microorganisms, mediated by

semiconducting mineral photocatalysis, provide a new concept to evaluate the origin and evolution of life. Semiconducting minerals are ubiquitous on Earth's surface and widely participate in redox reactions following photoelectron-photohole pairs excited by solar light. As photoholes can be easily scavenged by environmental reductive substances and microorganisms possess multiple strategies to utilize extracellular electrons, the highly reductive photoelectrons serve as potential energy source for microbial life. The discovery of this pathway extends our knowledge on the use of solar energy by nonphototrophic microorganisms, and provides important clues to evaluate life on the early Earth. Microorganisms, minerals and solar light constitute a complex but important ternary system through Earth history. The discovery of the novel energy conversion pathway in this system demonstrates how non-phototrophic microorganisms directly or indirectly utilized photoelectrons as the solar energy source. The full comprehension of non-phototrophic bacterial solar energy utilization conducted by semiconducting minerals in present environments will greatly help us to better understand the energy transform mechanism among interfaces of lithosphere, pedosphere, hydrosphere and biosphere.

[1] Lu A. et al. (2012). Growth of non-phototrophic microorganisms using solar energy through mineral photocatalysis. Nature Communications, 3(4), 768-775.

PLENARY

__________________________________________________________________________________________________________________________________________

To be or not to be an eclogite, that is the question:

the amphibolite-eclogite transition revisited

Maresch W

Institute of Geology, Mineralogy and Geophysics, Ruhr-University Bochum

IUGS guidelines recommend that the term eclogite be used only for rocks of basic composition, in which garnet + sodic pyroxene exceed 75 vol%. Consequently, the eclogite facies is a P-T region in which eclogite is stable. It is a broad field clearly characterized by high pressures but also highly variable temperatures. Thus the eclogite facies grades into the blueschist, the epidote-amphibolite, the amphibolite and the granulite facies with rising temperatures. However, typical compositions of garnet and sodic pyroxene in low-temperature basaltic eclogites often lead to modal amounts of garnet + pyroxene much less than 75%. Therefore significant amounts of additional amphibole, epidote-group mineral, mica, etc. are common [1]. According to IUGS, these are not eclogite sensu stricto, but "amphibole-eclogite", "zoisite-amphibole eclogite", etc. Although the geodynamic significance of the high-pressure rock eclogite is immense, the precise P-T definition of eclogite facies boundaries is not straightforward. Exhumation from great depths often dismembers coherent high-pressure rock sequences. Basic rocks as evidence of eclogite formation may only constitute minor fragments of these units. Ambiguity of the role of water fugacity adds uncertainty.

This presentation analyzes a case study of a rare metamorphic array spanning the transition between the epidote-amphibolite and eclogite facies as exposed in a coherent 15 km sequence of tholeiitic rocks on Margarita Island, Venezuela. From south to north, the following assemblages are encountered in low-variance metabasaltic rocks (Ab = albite; Bar = barroisite; Chl = chlorite; Ep = epidote; Czo = clinozoisite; Grt = garnet; Omp = omphacite; Pg = paragonite; Qtz = quartz):

Bar + Grt + Ep/Czo + Ab + Chl + Qtz (Omp,Pg absent) Bar + Grt + Ep/Czo + Ab + Pg + Qtz (Omp,Chl absent) Bar + Grt + Ep/Czo + Omp + Pg + Qtz (Ab, Chl absent)

where the assemblages (Omp,Pg) and (Ab,Chl) represent the epidote-amphibolite and eclogite facies, respectively. The assemblage (Omp,Chl) corresponds to the paragonite amphibolite stage discussed by Konzett and Hoinkes [2] as a transitional stage towards the eclogite facies. The reaction leading to eclogite, or in IUGS compatible terminology Ep/Czo-amphibole eclogite, can be formulated by mass balance from the Margaritan array as Bar + Ab + Ep/Czo => Omp + Pg + Grt + Fluid and is essentially analogous to a reaction derived by Molina and Poli [3] from phase petrological considerations. In the present analysis, the two reactions linking the three assemblages by mass balance are strongly pressure dependent, with low dP/dT slopes, and indicate dehydration with increasing pressure. Best estimates for the exposed metamorphic array suggest 500 - 550°C and 10 to 14 kbar, with the eclogite-forming reaction located at approximately 12 kbar. Conspicuous reequilibration textures of omphacite, paragonite and garnet (essentially a reversal of the S - N metamorphic array), as well as Ca-rich overgrowths on barroisite, monitor a return to epidote-amphibolite conditions during exhumation. This metamorphic array is thought to have been produced in young oceanic crust during closure and subduction of a back-arc basin, followed by arc-continent collision and exhumation.

[1] Schliestedt M. (1990). in, Carswell, ed., Eclogite Facies Rocks, Blackie, 160-179. [2] Konzett J. and Hoinkes G. (1996). J. met. Geol., 14, 85-101.

[3] Molina J.F. and Poli S. (1998). J. Petrology, 39, 1325-1346.

Feldspars on the inside: reading their record

Parsons I

School of Geoscience, University of Edinburgh, UK ian.parsons@ed.ac.uk

Alkali feldspar is the third most abundant mineral in the continental crust, growing from magma, during metamorphism, and in hydrothermal systems and diagenesis. Individual grains exhibit a range of intracrystal microtextures, unique in the mineral world, that record both, their thermal history and replacive fluid-feldspar reaction events, sometimes multiple, that they have experienced over geological time. This talk will concentrate on the characterization and interpretation of the microtextures from the standpoint of the petrologist or geochemist.

Only rare, very rapidly cooled volcanic crystals, and some near end-member grains that grew at low T, are strictly single crystals that can be described by a single lattice. Most 'single crystals' are complex intergrowths based on many lattices. The geometrical relationships within the microtextures, many of which are sub-optical, were established in the 1950s in pioneering single-crystal X-ray diffraction work by W.S. MacKenzie and J.V. Smith. Since the 1970s, transmission and scanning electron microscopy, in combination with electron probe analysis, experimental work on diffusion rates, two-feldspar geothermometry and observations on crystals from well-constrained geological settings, have allowed the mechanisms of microtexture formation and their thermochronology to be deduced. The most complex crystals known contain 8 chemically distinct phases, some twinned in 4 different orientations.

Factors leading to the microtextures are exsolution (giving perthitic intergrowths), framework Si-Al ordering (leading to the sanidine-microcline phase transition, with orthoclase as a metastable intermediate structure, and to high- and low-albite) and the shearing phase transition in albite. A nanoscale peristerite intergrowth has been found recently in a mesoperthite. Perthitic intergrowths formed wholly by diffusion are initially coherent (have a continuous Si-Al-O framework) and have regular morphologies constrained by minimization of elastic coherency strain energy, which defines the orientation of exsolution lamellae and repeated twinning. Misfit dislocations sometimes develop during cooling and these are important in replacement reactions and weathering. Preservation of elastic strain in coherent intergrowths is a robust indicator of structure that has remained chemically (and isotopically) undisturbed since the microtexture formed. Their periodicity has been used to calculate cooling rates in volcanic rocks using experimental diffusion coefficients and to estimate relative cooling rates in plutonic rocks. The coarsest coherent intergrowths have periodicities (~10 µm) in order-of-magnitude agreement with measured diffusivities.

Plutonic crystals are usually mixtures of coherent and replacive microtextures. Replacive textures are coarser, relatively irregular, with 'patch' or 'vein' morphology, and are associated with the development of optical turbidity, caused by µm-scale micropores. At the electron microscope scale they have a sub-grain microtexture on scales from 10s of nm to >100 µm. In some examples replacement reactions have occurred twice and in evolved igneous rocks some euhedral primocrysts are entirely pseudomorphs. Cathodoluminescence has revealed extraordinary concentric oscillatory zoning of trace-elements in sub-grains. Replacement may be isochemical (driven only by decrease of coherency strain energy) or non-isochemical, a common feature widely ignored by petrologists and geochemists. Replacive microtextures have recently been produced experimentally. Vein intergrowths are sometimes periodic, on scales >100 µm, but for kinetic reasons cannot have formed by diffusion, and cannot be used to estimate cooling rates. The cause of their regularity is an enigma. Once formed, all microtextures exercise a strong control on feldspar dissolution and mechanical degradation during sedimentary transport, diagenesis and soil formation. Microtextures can be used as provenance indicators in clastic sedimentary rocks. Misfit dislocations, enlarged by dissolution to form networks of 'nanotunnels', would have provided ideal reactors for the emergence of life.

PLENARY

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Natural controls of platinum group mineral formation and

distribution: new insights from recent advances in

nanomineralogical analysis

Reid D L

Department of Geological Sciences, University of Cape Town, South Africa david.reid@uct.ac.za

Recently developed techniques in high resolution mineralogical analysis include Focussed Ion Beam and High Resolution Transmission Electron Microscopy (FIB/HRTEM) [1] and microfocus X-Ray Computed Tomography (XRCT) [2]. Both approaches have been driven primarily by the search for new materials and industrial applications, but as is often encountered in science, provide the opportunity for returning full circle to studies of a more fundamental nature. The platinum group metals are immensely important in numerous technologies and thus have received much attention from a wide spectrum of industries. Their strategic importance and high cost have motivated numerous efforts at gaining a better understanding of their properties, more effective usage and ensuring a continuous and sustainable supply. We review recent research using these techniques developed by the materials industry on seeking a better understanding of the natural controls that govern the concentration and distribution of platinum group elements (PGE) in the world's largest repository of these strategic metals in the Bushveld Complex of South Africa.

Despite a voluminous literature on PGE chemistry, geology, exploration, mining, beneficiation and recovery, we still debate some of the most fundamental features of the fabulous Bushveld deposits, including the perennial question of how they acquired their incredibly high concentrations that range between a thousand to a million times typical crustal levels. Previous research has highlighted the relationship between base metal (Cu-Ni-Fe) sulphides and the PGE, which has led to the popular theory involving preferential concentration in sulphide melts due to their chalcophile and siderophile nature. Not so obvious from this theory is an explanation for the close relationship between PGE and chromite, since this oxide seemingly possesses no tendency to accommodate base and precious metals into its internal structure. Thus the traditional orthomagmatic collection model suffers from serious deficiencies in its successful application to the Bushveld ores, which has led to alternatives that challenge the assumption of simple thermodynamic partitioning between sulphide, silicate and oxide phases. One such alternative highlights the potential for the PGE to experience an early phase of atomic scale aggregation into nanometre-sized crystalline and non-crystalline particles or clusters, even under conditions of extreme undersaturation [3]. Should this occur in natural magmatic systems then the distribution of PGE between silicate, sulphide and even metal melts will be controlled by the surface properties of the nano-associations, more so than by the chemical properties of the elements and conventional mineral species.

Experimental work designed to explore the behaviour of the PGE in magmatic systems has produced results confirming the self-organisation into nanoparticles, well before the melt has reached elemental concentrations at which discrete minerals become stable phases [4]. Similar to minerals crystallizing from aqueous solutions, magmatic minerals may nucleate by using pre-existing nanophases and nanoparticles as building blocks. The importance of As in the experimental Fe-Cu-S melts was emphasized, as this component was responsible for the preferential aggregation of Pt.

Preservation of very similar PGE-bearing arsenide and sulphide nanocrystals in host base metal sulphides has been reported in a recent FIB/HRTEM study of the Merensky Reef [5]. This particular population of PGE-bearing phases has never been detected before and could prove to be crucial to the concentration of precious metals in not only the Bushveld ores but also other deposits.

[1] Wirth R. (2009). Chemical Geology, 261 (3-4), 217-229. [2] Godel B. (2013). Economic Geology, 108 (8), 2005-2019.

[3] Tredoux M. et al. (1995). South African Journal Geology, 98, 157-167. [4] Helmy H.M. et al. (2013). Nature Communications, 4, 2405 [5] Wirth R. et al. (2013). Canadian Mineralogist, 51, 143-155.

Ultrahigh pressure mineralogy of the continental

lithosphere

Sobolev N

Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Russia sobolev@igm.nsc.ru

Coesite and diamond are principal index minerals of ultrahigh pressure (UHP) metamorphic and igneous rocks equilibrated at depths greater than 100 km. In spite of a long time knowledge of both minerals associated with silicates and oxides in kimberlites and their eclogite xenoliths, their occurrence in situ in crustal metamorphic rocks was detected relatively recently in 1984 (Italian Alps and Norway for coesite) and in 1990 (Kokchetav massif, Kazakhstan for diamond). Following these discoveries, an intense search was performed and resulted in numerous new findings. Zircon is shown to be the best and perfect container of coesite, diamond and coexisting minerals in UHP metamorphic rocks since the early 1990's and successfully used to date almost for all new UHP localities. Nitrogen isotope data and negative δ13_{C values of metamorphic} diamonds as well as oxygen isotope data of coexisting minerals indicate the metasedimentary origin of coesite and diamond bearing metamorphic rocks. Eclogite (E-type) diamonds and associated minerals (e.g., Na-bearing garnets and K- bearing clinopyroxenes) of several kimberlitic and placer localities worldwide demonstrate similar specific compositional features, probably caused by subduction. Diamond occupies a unique position in discussion on the igneous and metamorphic aspects of the Earth's carbon cycle. This talk will also review research on naturally occurring diamonds and their mineral and fluid inclusions. Comparison of mineralogical features of coesite- bearing UHP crustal and mantle rocks will be performed and relative significance of subducted and deep mantle assemblages of the continental lithosphere will be estimated. We conclude that only through careful investigation and interpretation of often sub-millimetre and even sub-micrometre scale observations it is possible to derive large-scale orogenetic processes.

SPECIAL TALK

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Hypatia: from unusual carbonado to cometary nucleus

Andreoli M1*, Belyanin G2, Block D3, Kramers J2, Pischedda V4, Sigalas J3, Westraad J5 1 – Necsa, South Africa *marco.andreoli@necsa.co.za 2 - University of Johannesburg, South Africa 3 - University of the Witwatersrand, South Africa 4 - University of Lyon, France 5 - Nelson Mandela Metropolitan University, South Africa

Of all rocks on earth, carbonados consisting of polycrystalline diamond, found in Brazil and the Central African Republic, are arguably the only ones for which their ultimate place of origin, this world or the stars, remains open to discussion. Stimulated by the controversy, research was initiated in the early 1980s at the University of the Witwatersrand on stones supplied by the late Prof H Meyer of Purdue University. Two features of carbonado attract special attention, namely porosity and the fact they tend to host elements in native or in highly reduced state (i.e. TiN, Ni). These features have been considered to point unquestionably to a cosmic origin. However, doubt about this arose from observing the similarly porous nature of the spherical, radially textured "ballas" recovered from kimberlite pipes, and the occurrence of TiN (osbornite) inclusions in chromite from an ophiolite in Tibet [1]. Later on, an expanding collaboration with scientists working on the enigmatic Libyan Desert Glass found in SW Egypt led to the study of a new carbonado-like stone previously collected by Dr Aly Barakat in that region. Petrographic, mineralogical and isotopic studies of subsamples of this stone (named Hypatia) have shown that it only superficially resembles carbonados. The latter are extremely tough yet porous, with diamond the only carbon mineral present, whereas Hypatia lacks porosity, is pervaded by open fractures that make the stone exceedingly brittle, and most of the carbon is in an amorphous, glassy state (Figure 1) hosting graphite and containing appreciable oxygen and nitrogen. Further, carbonados have δ13_{C values between -30 and -20 ‰ (PDB) like organic} matter, whereas Hypatia's value is close to 0 ‰. If carbonado failed so far to provide unequivocal diagnostic signatures of its origin, a growing list of isotopic and mineralogical features brand Hypatia as uniquely cometary in origin. Noble gas analyses provided crucial evidence. 40_Ar/36_{Ar ratios range down to 30, between the} atmospheric value of 298 and all meteoritic material, which has 40_Ar/36_{Ar ratios <1. This} betrayed an extra-terrestrial object that had captured atmospheric gases before impact, in accord with the presence of high pressure atmospheric gas inclusions in the stone. Other noble gases (neon, krypton and xenon) yielded more subtle indications of a material very different from chondritic meteorites [2]. Further differences from all known meteorites are the major element chemistry dominated by carbon (the most carbon-rich carbonaceous chondrites have only 3% carbon) and the δ13_{C value} mentioned above, which differs from the range of -25 to -10 found in chondrites. Last but not least, the non-carbon mineralogy of Hypatia is totally different from that in all known meteorites [3], and from sediments close to Hypatia's discovery site grains of metallic Ti were recovered, which may be regarded as debris from exploded parts of the bolide [4]. We thus conclude that Hypatia represents part of an impacted fragment of a cometary nucleus that exploded over the SW Egyptian desert, causing the surface melting that produced the Libyan Desert Glass, and that shock-induced modification of the matrix led to its extraordinary preservation.

Figure 1: Bright-field transmission electron microscope image from Hypatia; "dark" specs: cubic diamond domains (in non-diamond carbon matrix) oriented to produce electron diffraction. Lamellar nature of the domains is reminiscent of shock diamonds from the Popigai impact site [5].Image by Johan Westraadt.

[1] Dobrzhinetskaya et al. (2009). PNAS-0905514106. [2] Kramers et al. (2014). IMA2014 abstracts volume. [3] Belyanin et al. (2014). IMA2014 abstracts volume. [4] Andreoli et al. (2014). IMA2014 abstracts volume.

[5] Koeberl et al. (1997). Diamonds from the Popigai impact structure, Russia.

CS1 – GENERAL SESSION: CLAY SCIENCE - ORAL

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Clay stratigraphy at the Vaalputs low level radioactive

waste disposal site, Namaqualand, South Africa

Andreoli M1*_{, Clarke C}2_{, Cloete M}3_{, Evans M}4_{, Harris C}5_{, Logue A}1_{, Majodina O}2_, McCarthy T4_{, Netterberg F}6_{, Stengel I}7_{, van Blerk J}8_{, van Rooy L}9 1 - Necsa *marco.andreoli@necsa.co.za 2 - University of Stellenbosch 3 - Council for Geoscience 4 - University of the Witwatersrand 5 - University of Cape Town 6 - Private Consultant 7 - Private Consultant, Windhoek; Polytechnic of Namibia 8 - AquiSim

Consulting 9 - University of Pretoria

The first nuclear power station in Africa is situated at Koeberg, near Cape Town and has been a reliable producer of electricity to the South African power grid since 1984. Whereas the spent fuel is currently stored at the utility, the low level radioactive waste is trucked over 600 km north to Vaalputs, a licensed facility located in Bushmanland being a sub-arid and sparsely populated area. Over the past 30 years Vaalputs has been the site of continuous, detailed investigations of most aspects of the earth and environmental sciences. In simple outline, the geology of the area consists of a sequence of Late Mesozoic to Cenozoic continental clastic sediments of the informally termed Koa Plateau Group (KPG) overlying a Mesoproterozoic granitic-granulitic basement. Mesozoic igneous activity at the site is represented by numerous explosive pipes of melilitite and non-diamondiferous kimberlite ~67 Ma in age. The KPG comprises three formations, the oldest being the Dasdap (fluvial conglomerate and arkosic sandstone) followed by the Lower Vaalputs Formation (lacustrine siltstone) and later by the Upper Vaalputs formation (unconsolidated, argillaceous fluvial sediments). Sedimentation occurred under changing climate conditions in shallow basins developed eastward of the receding Great Escarpment, which was initiated by the breakaway of South America ca.130 Ma ago. The Dasdap sediments are saprolitic and kaolinite-rich as a result of a prolonged hot and humid Cretaceous episode. Little is known of the unexposed Lower Vaalputs Formation, but much research has been conducted on the Upper Vaalputs Formation, which is exposed in the 8 m deep trenches in which the radioactive waste is placed. Most trenches show a subdivision of the Upper Vaalputs Formation in a beige, pebbly bottom member and a light grey, gritty member above. The most distinctive clay mineral of the pebbly member is palygorskite. When this mineral coats the surface of peds, it gives the impression of a white bed at the base of the trenches (see A, Figure1). Illite is, instead, the characteristic clay of the overlying gritty member (B, Figure 1). In the top 2 to 3 m of the trenches the gritty member is increasingly fractured, with fractures stained red by Fe oxides. Veins of calcium carbonate and, less frequently, gypsum become common, locally coalescing into thick calcrete duricrusts (C, Figure. 1). However, up to 40 percent of what appears to be calcrete is actually a sepiolite duricrust or sepiocrete, and nodules of this mineral are common near the base of a thin, near surface siliceous and ferruginous duripan, locally called dorbank, within which barite-bearing veins also occur. Dorbank also fills funnel-shaped karstic embayments within the calcrete (D, Figure. 1). Finally, a thin veneer of unconsolidated to semiconsolidated, weathered red sand is draped over these palaeosols (E, Figure 1). Silt and clay-size material derived from the excavations is used to backfill the trenches once packed with radioactive waste drums. Ongoing studies of the Vaalputs geohydrology and sediments, their mineralogy, age and palaeoenvironmental significance are aimed to assess the overall safety of the disposal operations for the current and future generations.

Figure 1: Photo of the NE wall of trench B.

Origin and petrophysical behaviour of clay minerals in

faults affecting deeply buried reservoirs: example of

Annot sandstones (Southern Alps, France)

Buatier M1*_{, Cavailhes T}2_{, Leclère H}3_{, Lerat J}4_{, Charpentier D}1_{, Sizun J}1_{, Labaume P}5_, Gout C6

1 - Chrono-Environnement, UFC Besançon *martine.buatier@univ-fcomte.fr 2 - DNO International ASA, Norway 3 - University of Liverpool, UK 4 - Université de

Nancy, France5 - Geosciences Montpellier, France 6 - TOTAL Pau, France

Clay minerals are ubiquitous minerals in fault zones in a broad range of geological contexts, particularly in sedimentary basins. The presence of clay minerals in fault zones and their structural arrangement can play a critical role on fault mechanics and on fluid-flow properties of faults.

The present study focuses on clay mineral assemblages from two normal faults located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep, SE France. The Annot sandstones were buried below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The studied faults are located in the internal part of the basin (Moutière-Restefond area), where the sandstone formation reached 8-10 km burial depth attested by vitrinite reflectance. The faults affect arkosic sandstone alternating with pelitic layers, and display throws of a few cm to tens of meters.

A mineralogical investigation (XRD, optical and SEM observations) combined with chemical analyses (microprobe analyses) has been performed to investigate the origin of clay minerals and their conditions of formation. Shear deformation of sandstone beds in fault zones is mainly achieved by the combination of pressure-solution (and precipitation) of quartz and alteration of feldspar giving rise to the formation of illite. The foliation in the fault core zone of the faults is underlined by preferentially oriented newly-formed phyllosilicates (illite and chlorite) and cross-cut by mineralized veins of quartz and calcite. Chemical analyses of chlorites and thermodynamic calculations suggest that fault deformation occurred at temperatures around 220-250°C in accordance with the peak temperature of the host rock estimated from vitrinite reflectance. These data suggest that synkinematic clay minerals registered the early stages of the fault deformation close to the maximal burial of the sandstones between 6.5 and 8 km, assuming a mean geothermal gradient between 25 and 30 °C/km. One of the two studied faults (Point Vert) displays a core zone including intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The gouge samples have a higher illite crystallinity index than the foliated sandstones, which could be explained by a reactivation of the fault at lower temperature.

The petrophysical properties of sandstones from the core zone and the hanging and foot walls of the fault were determined on drilled plugs following three spatial directions. The permeability of the highly-deformed sandstone from the core zone is anisotropic, about one order of magnitude higher than in the host rock in the direction parallel to the foliation. This permeability increase is explained by the occurrence of well-connected micropores localized between platy phyllosilicates. This study shows that the fault petrophysical properties are mostly controlled by the precipitation of synkinematic phyllosilicates under deep burial conditions.

CS1 – GENERAL SESSION: CLAY SCIENCE - ORAL

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Mineralogical characterization of clays involved in the

Termini-Nerano slow moving landslide (southern Italy)

Cesarano M1*_{, Bish D}2_{, Cappelletti P}3_{, Belviso C}4_{, Cavalcante F}4_{, Fiore S}4 1 - Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse *mara.cesarano@unina.it 2 - Indiana University 3 - DiSTAR - Università degli Studi di Napoli Federico II 4 - Institute of Methodologies for Environmental Analysis-CNR

"Slow moving landslides" are downslope movements of rock masses, characterized by low rates of displacement (some mm to 1/2 m per year). External phenomena, such as long-duration rainfall or earthquakes, can increase their velocity (which can reach 50 cm/hour - 5 m/day) and consequently their hazard. These slope movements in southern Italy involve sedimentary formations characterized by arenaceous and clayey successions. Physical-chemical weathering, which alters shallow zones of these rock masses, favours the development of slow moving landslides. Another factor promoting these phenomena is their water content (i.e., groundwater). Both weathering and water cause a general decrease in material strength [1]. The occurrence of weathering-related clay minerals (e.g., smectites), able to trap significant quantities of water, has been generally considered a triggering factor of these landslides [2]. The main goal of this research was to carry out a mineralogical characterization of clay minerals occurring in the Termini-Nerano landslide (Massalubrense, Naples) in order to assess this statement. Five bore holes were drilled in the study area on the rocks involved in the landslide. Several samples were selected at different depths along the cores and were analyzed by quantitative X-ray powder diffraction (QXRPD) to investigate their mineralogical composition. Bulk-rock chemical analyses were used to calibrate the quantitative mineralogical analyses. Samples were also treated to separate the clay fraction from the more coarse-grained mineral phases.

The material involved in the landslide is an association of sandstone and siltstone, mainly constituted by quartz, mica, feldspars and variable amounts of clay minerals. Calcareous sandstone layers are also frequent. Quantitative analysis of the bulk samples showed that the clay fraction is on average the 50 wt.% of the material involved in the landslide. Specific analysis of the clay fraction revealed kaolinite, chlorite, mixed-layer illite/smectite (I/S), and mixed-layer chlorite/smectite (C/S). Using the Moore and Reynolds approach [3], the percentage of illite in the mixed-layer illite/smectite and the stacking order, R, were determined. The amount of illite in the mixed-layer I/S had a mean value of 57% and varied between 21% and 83%. The stacking order of the I/S was R0 and R1.

According to literature data [4], the total amount of clays, and specifically the amount of smectite in the mixed-layer I/S, could have played an important role in the landslide development.

A geotechnical study on these samples is ongoing, to investigate any possible relationships between the clay mineral properties and the geomechanical parameters of materials.

[1] Taylor K.R. and Cripps J.C. (1987). Weathering effects: slopes in mudrocks and over consolidated clays. p.40. In Slope Stability: Geotechnical Engineering and Geomorphology (M.G. Anderson and K.S. Richards, editors). Wiley, New York. [2] Calcaterra D., Calò P. Cappelletti, de' Gennaro M., Di Martire D., Parise M. and Ramondini M. (2007). Mineralogical and geotechnical characterization of a large earthflow in weathered structurally complex terrains of the Molise region, Italy-Geophysical Research Abstracts, Vol.9.

[3] Moore D.M. and Reynolds R.C., Jr. (1997). X-Ray Diffraction and the Identification and Analysis of Clay Minerals, 2nd ed. XVII + 378 pp.

[4] Uneno H., Jige M., Sakamoto T., Balce G.R., Deguchi I. (2008). Geology and clay mineralogy of the landslides area in Guisaugon, southern Leyte Island, Philippines. University Bulletin of Chiba Institute of Schenze, No 1, 9 pp.

Asbestiform sepiolite wrapped by aliphatic

hydrocarbons from Perletoa, Aosta Valley (Western Alps,

Italy): characterization, genesis and possible hazards

Giustetto R1*_{, Seenivasan K}2_{, Belluso E}3 1 - Department of Earth Sciences, University of Turin (Italy) roberto.giustetto@unito.it 2 - NIS, Centre of Excellence, Turin 3 - University of

Torino

An atypical asbestiform sepiolite was found in the Gressoney Valley (Italian Western Alps), with exceptionally long fibres coated by an aliphatic hydrocarbons sheath - an association never reported before in literature. This sepiolite was characterized with a multi-analytical approach with the aim to infer its genesis, the role of its organic coating and its potential noxiousness for human health.

Microscopic and FT-IR analyses proved that these fibres, apparently up to several cm long, are formed by bundles of thinner fibrils (average length: 150 mm) potentially dispersible in the environment. When observed with TEM, these fibrils show a rhomboidal to parallelogram cross section (< 1 mm) with surfaces covered mostly by a thin film of aliphatic hydrocarbons (Figure 1).

The sepiolite fibrils and their organic coating originated in sequential steps from precipitation of Si/Mg rich hydrothermal fluids, resulting from serpentinization of olivine and clinopyroxene and Fischer-Tropsch-type reaction in the Combin Zone (Aosta Valley). Presence of a hydrocarbons sheath implies serious consequences on the sepiolite habit: the organic matter, in fact, interacts with the fibrils surface reducing the amount of adsorbed water and favouring fragmentation of thicker units into thinner ones, due to an 'opening' process implying separation along z and cleavage on (110). Similar mechanisms were observed in several sections of amphibole asbestos and fibrous serpentine wrapped by organic matter.

This progressive 'defibrillation' of the Perletoa sepiolite, triggered by the hydrocarbons sheath, not only causes a significant increase in the interfibrillar (open) porosity but also affects the fibre morphology enhancing its aspect ratio (length vs. thickness) from 'high' to 'very high'. The thinner and exceptionally long fibrils (rods and/or laths), therefore, potentially become more dangerous for human health due to their carcinogenic potential if dispersed in air and breathed in high doses.

Figure 1: TEM micrographs of sepiolite fibres in cross section, observed along [001]. a) At medium magnification, fibrils show a rhomboidal to parallelogram-like contour and a large open texture. (b) At high magnification the incipient 'opening' process is evident (split surfaces: dashed white lines); a roughly continuous and scarcely electron-dense organic film (indicated by arrows) surrounds the fibres.