project 3.3 the platinum value chain -...

Project 3.3The platinum value chain

7th Inkaba yeAfrica Workshop GFZ Potsdam, Germany

1 – 5 November 2010

M. Tredoux, D. Reid, R. Trumbull,T. Obertür, D. Chetty, C. Ballhaus

AND STUDENTS

UFS, UCT, GFZ, BGR, Mintek and Univ. Bonn

What are the platinum-group elements (PGE)?

21 – 5 November 20107th Inkaba yeAfrica Workshop - GFZ Potsdam, Germany

Why investigate the Pt value chain in Inkaba?

• RSA is the World’s largest producer of the PGE

• Germany is one of • Germany is one of the largest users of PGE

• Can address a wide range of questions about processes


What processes are being addressed?

• Are the fundamentals and models well understood?

• Basic geochemistry

• Ore formation

• Exploration

• Resource extraction

• What are the environmental impact(s)?

• Resource extraction

• Beneficiation

• Purification and alloying

• Uses, especially in catalysis and nano applications


Specific research questions

• PGE in the mantle: Where from? How emplaced? How much? In what form?

• PGE in the crust: What is their geochemistry during partial melting and fractional crystallization during partial melting and fractional crystallization and/or hydrothermal and sedimentary processes?

• How can the beneficiation and processing of the PGE be optimized?

• Investigation of new industrial uses of the PGE.• Investigation of the environmental impact of the

PGE at various stages of the surface cycle.


Established research

Explorationand

extraction

Experimental petrologyand

beneficiation


Coming online in 2010

• Petroleum industry and reprocessing

• New alloys with novel propertiesnovel properties

• PGE in nano manufacture

• Emphasis on Ir, Os and Ru

• OsO4 is very volatile and toxic


Pt value chain w.r.t goals of IyA

� German and South African institutions are both actively involved

� Next-generation science and technology� New exploration and mining models/techniques� refining of the beneficiation circuits� refining of the beneficiation circuits� Development of new nano-technological applications

� Multi-disciplinary and intercultural� Involves expertise from 7 distinct scientific fields� Students are from very diverse cultures

� Training and capacity building in scare skills� 8 graduates this year, and 6 more in 2011

7th Inkaba yeAfrica Workshop - GFZ Potsdam, Germany

A PGE-rich rock from the Barberton greenstone belt: core formation or

extraterrestrial?

7th Inkaba yeAfrica Workshop GFZ Potsdam, Germany

1 – 5 November 2010

extraterrestrial?

M. Tredoux et al. (N. Chabangu and F. Madala)(with extensive acknowledgement of the work done

by M. de Wit et al.)

Department of GeologyUniversity of the Free State

The Barberton greenstone belt

Based on mapping done by Maarten de Wit and some of his post-grad students in the period 1980 to


period 1980 to 1995.

The results of this work was to turn the then accepted model completely on its head.

Stratigraphy of the Barberton Supergroup

• Onverwacht Group– 3.5 Ga basement: granites with CFB– Coarse-grained peridotites– Ultramafic volcanics (including

komatiites), increasingly interleaved with sedimentary rocks towards the top of the Hoogenoeg FmHoogenoeg Fm

– Evidence for rapid cooling: pillow structures, gas-escape vesicles, spinifex textures

• Fig Tree and Moodies Groups– Marine sedimentary rocks, increasing in

grain size upwards.– Deep sea conditions (turbidites) in the

lower Fig Tree Gp, shallowing upwards


The Jamestown ophiolite


Characteristics of the Jamestown ultramafite

• Mineralogical– Highly silicified (white smoker?)– Original mineralogy visible

• Olivine• Minor orthopyroxene• Minor orthopyroxene

• Geochemical– Very depleted in the LILEs– REE chondrite normalized patterns which are flat or

negative for the HREE• Sm-Nd systematics indicate that the depletion is Archaean

– Apparent Re depletion event at 3.5 Ga


Bon Accord farm: view east toward the Sheba sincline


Local geology of the Bon Accord farm

• A very Ni-rich (>30% whole rock NiO) was discovered in the 1920s

• Completely removed, but proved to be unsmeltable

• Investigated by S. de Waal in the 1960s-1970s: he found 6 new Ni mineralsminerals

• De Waal subdivided the body into 4 zones, ranging from massive (centre?) to highly sheared and altered (rim?)

• The host rock is a coarse-grained depleted ultramafite

• A zone of stratiform Ni sulphide mineralization is associated with the zone of talc schist


MINERALOGY OF THEBON ACCORD OXIDE BODY

• SILICATES• Liebenbergite Ni2SiO4 *• Nepouite Ni3Si2O5(OH)4

• Willemseite (NiMg)3Si4O10(OH)2 *

• OXIDES• Trevorite NiFe2O4

• Chromite FeCr2O4

• Nichromite NiFe2O4 *• Cochromite NiFe2O4 *• Willemseite (NiMg)3Si4O10(OH)2 *

• Nimite (NiMgFe)5Si3AlO10(OH)8 *

• OTHER• Gaspeite (NiMg)CO3

• Bonaccordite Ni2FeBO5 *

• Cochromite NiFe2O4 *• Magnetite (NiFe)3O4

• Bunsenite NiO

• SULPHIDES• Millerite NiS• Pyrite (NiFe)S2


Texture of ‘Bon Accord’ rock

Core (more oxides) Rim (more silicate)


0.5mm 0.1mm

0.1mm


Chemical composition of the oxide body (‘BA’)

NiO and FeO/Fe2O3 are the major components, accounting for 85% of the chemistry of the massive core region, and 70% of the shistose rim

SiO2 and MgO (and Al2O3 in the rim) account for SiO2 and MgO (and Al2O3 in the rim) account for almost all of the rest

The alkalis and CaO are present at permil levels in the rim but only at trace levels in the centre

The body is highly enriched in the PGE, Sb and As; moderately enriched in Cr and Au

S is very low (< 500 ppm)


The age of ‘BA’


Models for formation

• Oxidized iron meteorite (de Waal)• Lateritic NiO body, as is found (much smaller) in

e.g. New Caledonia• Desulphurized • Desulphurized

– magmatic Ni-Cu sulphide ore– hydrothermal Ni-Cu sulphide associated with the

implacement of the Stentor pluton– massive volcanic exhalative Ni-Cu sulphide deposit

• Oxide alteration of olivine and auto-oxidation-reduction of Fe2+ (e.g. awaruite after fayalite)


PGE patterns of ‘BA’

• Although the patterns have similarities to iron meteorites, the inter-element ratios are extremely different

• Ditto with respect to the PGE patterns of komatiitic PGE ores

• Absolutely different to awaruite

• Core pattern mirrors the pattern of the host rock


New rock type?

• We propose that the present rock is an oxidized remnant of an original metallic precursor

• As the mineralogy and geochemistry of the Ni oxide seem to be decidedly different to any other oxide seem to be decidedly different to any other known rock type, we propose that it should be recognised as a new rock type

• As it is found in an ophiolite sequence, we suggest following the convention set by J. Bird and co-workers, who named a metallic assemblage JOSEPHINITE, after the ophiolite in which it was found


JAMESTOWNITE

• Ni+Fe oxides account for ≥70% of the major chemistry

• CaO+Na2O+K2O ≤ 1• S ≤ 1 permil, and so remnant sulphide mineral • S ≤ 1 permil, and so remnant sulphide mineral

morphology• Ni end-members of common silicate and oxide

minerals are present• Trace element

– Total PGE ≥ 1ppm– As+Sb ≥ 1 permil


Hard to swallow?

• When the idea was originally made, the then current models did not accept material transfer across the 670 km across the 670 km ‘boundary’

• Now we quantitatively know that whole mantle convection is a reality, so

…. watch this space


ET or home? A difficult question…


‘Mystery mineral’ (Ni-As-Sb)


100 µm

7th Inkaba yeAfrica Workshop GFZ Potsdam, Germany1 – 5 November 2010

Thank you for your attention.


project 3.3 the platinum value chain -...

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