AMGAMGMineralogical Society

Applied MineralogistThe

Edited by: William Smith Georgian Manuc Stefan Horn

Web: www.minersoc.org/amg.htmlTwitter: www.twitter.com/amg_minEmail: amgminsoc@gmail.com

The Bulletin of the pplied ineralogy roupA M G

Sept 2019Volume 4Number 3

From the AMG committeeHello and welcome to the September edition of Applied

Mineralogist! In this issue, we bring you a special feature from

Dr. Rob Chapman, University of Leeds, on tracing Au back to its

source, together with a round-up from the SGA biennial

meeting. We also have the winner of our #AppliedMineralogy

competition and a calendar for all upcoming events so you

don’t miss out!

In this issue:

Ÿ From the AMG committee (p. 1)

Ÿ Round-up for the SGA (p. 1)

Ÿ Panning back to the source (p. 2-3)

Ÿ #AppliedMineralogy (p. 3)

Ÿ MDSG winter meeting (p. 4)

Sept 2019, 6(1). Page 1

Academics, industry professionals, and students gathered in thGlasgow's striking Gilbert Scott Building for the 15 biennial

meeting of the Society of Geology Applied to Mineral Deposits.

The conference was preceded by a number of short courses

and field trips, including a trip to the Scottish Highlands, to visit

sites of classic geology and mineral deposits and another to

Ireland, to visit base metal deposits, such as the famous Navan

Pb-Zn mine.

Of the many short courses on offer, my personal bias was

toward the exploration targeting for magmatic Ni-Cu-PGE

mineral systems course, organised by Dr. Dave Holwell and

Prof. Marco Fiorentini. Over the two-day course, we saw

fantastic magmatic sulphide ores from world-class ore

deposits, including Voisey's Bay and the Bushveld, together

with a number of talks on the mineralising system, sulphide

textures, and case studies. The course was a great precursor,

and got participants excited for the magmatic sulphide and

oxide system session occurring later on in the conference

programme.

Conference delegates were welcomed to the Hunterian

Museum for the pre-conference ice breaker event, allowing

participants to browse the museum's collection, whilst

catching up with old friends and colleagues. The conference

programme began with plenary speakers Cam McCuaig (BHP),

Sarah Gordon (Satarla), and Mike Russell (CalTech), who set

the tone of the conference, with insightful talks regarding

mineral systems, mining evaluation, and the relationship

between life and ore deposits. From the afternoon onwards,

the cohort was divided into different sessions, where I was

able to attend talks outside of my subject area. I particularly

enjoyed talks from Cyril Chelle-Michou on the role of chlorine

in porphyry systems and from David Mole on the crustal

architecture of the Superior Craton, as seen through isotope

mapping. Later that evening was the Student-Industry

Round-up: SGA Biennial Mee�ng, Glasgow, 27�� to 30�� August 2019William Smith, Cardiff University

networking event, which allowed myself and my fellow

student attendees to talk to those working in the mining and

metals industry. Throughout this evening, there was a lot of

opportunity to get advice and perspectives from those in the

early and later stages in their career, and on behalf of the

student attendees, I thank the organisers of this event.

Wednesday gave me another opportunity to attend talks

outside of my 'comfort zone', where I enjoyed the 'fertility

assessment' morning in the porphyry to epithermal session.

This session gave a nice insight into ongoing research

regarding ways to assess mineral fertility of large-scale

regions, using geochemistry, minerals, and mineral inclusions.

After the break, SGA-Newmont Gold Metal awardee Richard

Sillitoe spoke about the role of breccias in porphyry copper

formation, imparting many years of fieldwork experience. Two

poster sessions were held over the course of Wednesday and

Thursday afternoons, allowing presenters to talk about their

research over a drink or two.

Most of my time over Thursday and Friday was dedicated

to the magmatic sulphide and oxide session, where I was

particularly interested in talks on the Grasset Ultramafic

Complex (Michael Tucker) and the Nova-Bollinger Ni-Cu ore

deposits in Western Australia (Valentina Taranovic). Following

the magmatic sulphide and oxide session, was the session on

the Co-evolution of Life and Ore deposits, were I was

fascinated by John Parnell's presentation on the importance of

carbon in ore deposits.

Following on from the conference are field trips to visit the

mineral deposits of Milos Island (Greece) and the Skellefte Belt

(Sweden), and we hope that participants enjoy these trips.

From all SGA participants from the AMG, we thank the

organising committee, session conveners, course and field trip

hosts, and sponsors for putting together a wonderful

conference, and we congratulate the deserving award

winners; thank you Glasgow!

Sept 2019, 6(1). Page 2

A new take on ‘panning back to the source’Rob Chapman, Senior Lecturer, School of Earth & Environmental Sciences, University of Leeds

There is a cultural stereotype for prospectors: they tend to be sartorially challenged, bearded and generally ancient. They have inherited the alchemist's obsession with obtaining gold, and pursue it to the exclusion of most other things in life. The methodology is simple - detrital gold forms a dispersion trail from its source, so when the gold cuts off upstream it's �me to look for the motherlode.

Unfortunately this method has some limita�ons, which have become amplified as the 'search for the motherlode' has evolved to the point where explora�on companies may seek a specific style of gold mineral-isa�on in areas where outcrop is non- existent.

The increasing challenges facing explora�onists are well documented. New discoveries demand techniques which can iden�fy the presence of a rela�vely small target, o�en obscured by surficial deposits. An array of geophysical and geochemical approaches has been developed, enabling us to predict the presence of prospec�ve bedrock geology. Indicator minerals have enjoyed much publicity in the literature as specific erosional products of mineralisa�on may either clearly indicate the presence or direc�on of a target. Gold has chemical and physical a�ributes required by indicators, in that it is inert and rela�vely easy to isolate on account of its high density. However, there are drawbacks too: chemical stability permits recycling into genera�ons of surficial sediments removed from the original erosional context, and par�culate gold may be generated in a range of geological environments, such that the presence of gold in a panned concentrate is not indica�ve of a specific style of mineralisa�on. In many parts of the world, explora�on is focussed in geologically complex areas, where different sources of gold are possible. Explora�on campaigns rely on deposit models

but the source of most/all detrital gold is o�en unclear. Various locali�es (in the UK at least) proudly proclaim

that their local gold is the 'purest in the world', despite all natural gold being predominantly an alloy of gold and silver. It has long been recognised that the silver content varies with loca�on; data describing placer gold comp-osi�ons from different locali�es may represent bulk composi�ons, which can mask contribu�ons from different sub-popula�ons.

The advent of the electron microprobe (EMP) facilitated screening of large numbers of individual gold par�cles and the iden�fica�on of component popula�ons. These studies (e.g., Knight et al. 1999) sought to match composi�ons of detrital gold with that of known sources and to speculate on whether there may be other sources yet to be discovered.

The approach met with success on an empirical 'same or different' basis but it proved difficult to link alloy composi�on to a style of mineralisa�on. The silver content of gold alloy is a func�on of fluid composi�on

-(Au/Ag , fS , aCl and pH) and temperature (Gammons & aq 2

Williams-Jones 1995). The net effect of these controls is that silver content is only poten�ally diagnos�c where it is very high, or very low because the majority of gold par�cles exhibit a silver content between 5 and 30% Ag irrespec�ve of source.

In the early 1990s the Bri�sh Geological Survey (BGS) began to record systema�cally the presence of opaque inclusions of other minerals within detrital gold par�cles. Mineral inclusions (Figure 1) have been shown to represent the mineralogy coeval with the phase of gold precipita�on (Chapman et al., 2000). Consequently an inclusion suite derived from a detrital gold popula�on can be used to reconstruct the source vein mineralogy.

30 µm200 µm

Arsenopyrite

Pyrite

25 µm

Arseno-pyrite Niccolite

25 µm

Pyrite

Galena

A C DB

Figure 1. Examples of inclusions within gold par�cles. A: rela�onship between vein mineralogy and inclusions: gold liberated from crushed ore, Bralorne, BC, Canada, B: swarm of pyrite inclusions in a detrital gold par�cle Thistle Ck, Yukon, Canada, C: different inclusions within the same detrital grain: Dolly Creek, Victoria, Australia, D: inclusions of unusual minerals may represent extreme par��oning rather than vein mineralogy; detrital par�cle from Atlin, BC, Canada.

Sept 2019, 6(1). Page 3

#AppliedMineralogy

@freyargeorge

A combina�on of inclusion and alloy data on a grain-by-grain basis permits 'microchemical characterisa�on' of a popula�on, where the two datasets provide independent parameters to iden�fy any sub-popula�ons. This approach has found applica�on both in refining the 'same or different' approach for use in establishing placer-lode rela�onships, but also in establishing composi�onal templates for gold derived from different styles of mineralisa�on. Dis�nc�ve inclusion signatures have been established for gold derived from alkalic porphyries, (Pd- Hg signature) calc-akalic porphyries (Bi-Te-Pb-S signature) and their associated epithermal expressions through study of samples of vein gold and detrital gold from adjacent placers (Chapman et al., 2018).

Gold from orogenic se�ngs usually yields a simpler signature comprising base metal sulphides and sulph-arsenides (e.g., Chapman & Mortensen 2016). Gold par�cle studies have the poten�al to be extremely helpful in various explora�on scenarios. In areas of complex geology, characterisa�on of detrital gold may indicate the styles of mineralisa�on present within the catchment. At brownfield sites, the signature of local detrital gold can be compared with that derived from the resource already exploited to evaluate whether further reserves are present. Finally, ascribing a style of source to detrital gold can avoid fruitless pursuits pinned to an incorrect deposit model.

Further analy�cal techniques are being applied to natural gold to establish the rela�onship between gold crystallography and composi�onal heterogeneity, and the heterogeneity of gold alloy with respect to trace elements. Such studies will both contribute to our understanding of gold mineralisa�on processes and facilitate more sophis�cated approaches to designing

indicator methodologies based on gold.

ReferencesChapman R.J., Mortensen J.K. (2006) Applica�on of

microchemical characteriza�on of placer gold grains to explora�on for epithermal gold mineraliza�on in regions of poor exposure: J Geochem Explor. 91: 1-26.

Chapman R.J., Leake R., Moles N.R., Earls G., Cooper C., Harrington K., Berzins R. (2000) The applica�on of microchemical analysis of alluvial gold grains to the understanding of complex local and regional gold mineraliza�on: a case study in the Irish and Sco�sh Caledonides. Econ Geol 95:1753-1773.

Chapman R.J., Mortensen J.K. (2016) Charact-riza�on of gold mineraliza�on in the northern Cariboo gold district, Bri�sh Columbia, Canada, through integra�on of composi�onal studies of lode and detrital gold with historical placer produc�on: a template for evalua�on of orogenic gold districts. Econ Geol 111:1321-1345.

Chapman R.J., Allan M.M., Mortensen J.K., Wrighton T.M., Grimshaw M.R. (2018). A new indicator mineral methodology based on a generic Bi-Pb-Te-S mineral inclusion signature in detrital gold from porphyry and low/intermediate sulfida�on epithermal environments in Yukon Territory, Canada. Miner Deposita, 53: 815-834.

Gammons C.H., Williams-Jones A.E. (1995) Hydroth-ermal geochemistry of electrum; thermodynamic constraints. Econ Geol 90:420-432.

Knight J.B., Mortensen J.K. Morison S.R. (1999). Lode and placer gold composi�on in the Klondyke District, Yukon Territory, Canada: Implica�ons for the nature and genesis of Klondyke placer and lode gold deposits. Econ Geol 94: 649-664.

Check out this awesome #ThinSec�onThursday entry of

garnet-mica schist from the Sikkim Himalaya (40 mm) curtsey of metamorphic

petrologist Dr. Freya George.

Interested in joining the Mineralogical Society and Applied Mineralogy Group? Go to: for membership details.http://www.minersoc.org/

Mineralogical Society

SEP ‘19 22-25

Calendar

AMGAMG

About UsFounded in 1963 by Norman F.M. Henry, the AMG is a special interest group of the Mineralogical Society of Great Britain and Ireland. We encourage and promote the study and research of mineralogy applied to ores and related industrial mineral materials. This encompasses: ore microscopy, fluid inclusions, nuclear minerals, coals, refractories, slags, ceramics, building materials, nuclear waste disposal, carbon capture and storage, down-hole borehole alteration, and mineral-related health hazards.

Editorial

Thank you to those who have contributed to this issue of

Applied Mineralogist. Please forward any articles, comments or

notices of events and conferences to . amgminsoc@gmail.com

All previous issues of Applied Mineralogist are available at

www.minersoc.org/amg-applied-mineralogist

Thanks for reading; our next Applied Mineralogist will be

out in December. Keep up on what is happening in the

meantime by following us on twitter .@amg_min

Notices

Get Involved

If you would like to become more involved in the AMG,

elections are held yearly at the AGM. Spaces for Student

Representatives come up regularly. If you would like to be

considered for a committee spot please email Eimear Deady.

AMG Postgraduate Bursaries

The AMG provides bursaries for postgraduate students in

the disciplines of Applied Mineralogy, Crystallography, and

Petrology and Geochemistry. Bursaries are intended to support

conference attendance and associated travel costs, although

other activities may be considered. Application guidelines can

be found at www.minersoc.org/amg-bursaries

Please note there are two bursary application deadlines

each year: 1st March and 1st September. Requests for funding

must be received well in advance of the event to allow for

consideration by the committee.

Funding

We welcome applications from both individuals or

organisations for funding in support of events covered in the

AMG remit. Further guidelines on how to apply can be found at

www.minersoc.org/amg-funding

OCT ‘1913 - 19

JAN ‘2006 - 08

MAR ‘2001 - 04

MAY ‘20 03 - 08

Mineral Deposits Studies Group

6th to 8th January 2020Natural History Museum, London

Confirmed keynotes: Prof. John Dilles (Oregon State)Prof. Sarah Gleeson (GFZ-Potsdam)

Pre-conference porphyry workshop: Dr. Richard Sillitoe

Registration and abstract details to follow

43rd Annual Winter Meeting

EGU Annual CongressVienna, Austria

PDACToronto, Canada

Mineral Deposits Studies Group Mee�ngNatural History Museum, London

Interna�onal Earth Science Week

Geological Society of America Mee�ngPhoenix, USA

SEP ‘20 06 - 10

European Mineralogical ConferenceKrakow, Poland