Teaching an old dog new tricks:Stable isotopes in mineral exploration

Noranda Area, Abitibi Belt. Cathles (1993)

Shaun Barker, Department of Earth and Ocean Sciences,

University of Waikato, New Zealand and Mineral Deposit

Research Unit, UBC e-mail: sbarker@waikato.ac.nz

Dilbert, Nov 4, 1989

Summary

• Stable isotope alteration haloes are real

• Isotope alteration haloes well outside traditional alteration vectors, providing larger targets and vectors to ore

• Now have a tool for the job - mineral industry relevant and accessible via ALS Minerals - tick the assay form!

• Potential exploration impacts:

• Near miss?

• Target ranking (e.g. bigger halo = bigger hydrothermal system = more fluid = more ore)?

• Ground sterilization?

• Vectoring up fluid pathways towards ore?

Acknowledgements

• With many thanks to many contributors:

★ Greg Dipple, Craig Hart, Ken Hickey - MDRU

★ Will Lepore - MDRU and Pilot Gold

★ Jeremy Vaughan - MDRU and Barrick Gold Corp

★ Paul Dobak - Barrick Gold Corp

Distal Alteration Footprints

Kelley et al, 2006, Econ. Geol.

FIG. 1. Schematic cross section through a typical porphyry copper deposit showing (A) common primary features that maybe identified within the obvious limits of mineral deposits and (B) primary far field features discussed in the text. Horizon-tal bars show spatial distributions, which are poorly constrained for far field features. AFT = apatite fission track, BR = bi-tumen reflectance, CAI = conodont color alteration index, VR = vitrinite reflectance, ZFT = zircon fission track.

Kelley et al, 2006, Econ. Geol.

Distal Alteration Footprints

Kelley et al, 2006, Econ. Geol.

FIG. 1. Schematic cross section through a typical porphyry copper deposit showing (A) common primary features that maybe identified within the obvious limits of mineral deposits and (B) primary far field features discussed in the text. Horizon-tal bars show spatial distributions, which are poorly constrained for far field features. AFT = apatite fission track, BR = bi-tumen reflectance, CAI = conodont color alteration index, VR = vitrinite reflectance, ZFT = zircon fission track.

Kelley et al, 2006, Econ. Geol.

Normal

“Everything”

Distal Alteration Footprints

Kelley et al, 2006, Econ. Geol.

FIG. 1. Schematic cross section through a typical porphyry copper deposit showing (A) common primary features that maybe identified within the obvious limits of mineral deposits and (B) primary far field features discussed in the text. Horizon-tal bars show spatial distributions, which are poorly constrained for far field features. AFT = apatite fission track, BR = bi-tumen reflectance, CAI = conodont color alteration index, VR = vitrinite reflectance, ZFT = zircon fission track.

Kelley et al, 2006, Econ. Geol.

Normal

“Everything”

mineralogicalalteration

Isotope halo,δ188888O

heat

ore

Haloes and vectoring

mineralogicalalteration

Isotope halo,δ188888O

heat

ore

Haloes and vectoring

http://www2.bnl.gov/CoN/

Pro

ton N

um

ber

(Z

)

Isotopes

Neutron Number (N)

What are isotopes?

δ18O for Earth Materials

Hoefs, 2009

What isotope systems?

• Most hydrothermal fluids are very water (H2O) rich, so hydrogen and water should have most significant isotopic alteration

• Carbon and sulfur may capture important redox gradients (Alkalic porphyries - Dave Cooke and coworkers, Orogenic gold - John Walshe)

Epithermal Au-Ag

Kilometer-scale 18O halo to the General Custer

Mine.

Criss et al, 1985

Mineralization in Comstock Lode coincident with steep gradients in 18O-depletion.

Epithermal Au-Ag

Epithermal Au-Ag

Stable Isotopes in Mineral Exploration

Noranda Area, Abitibi Belt. Cathles (1993)Noranda Area, Abitibi Belt. Cathles (1993)

VHMS Systems

Carbonate-hosted Pb-Zn

7MAKK-1

δ18OSMOW (‰)

10

7.5

5

10

7.5

5

EWAtotsugawa Ichi-go Fault

Drill hole collar

Atotsugawa Ni-go Fault

Atotsugawa Fault

Hydrothermal fluid

Ore bodies

Crystalline limestone

Skarn

Fault

5MAHS-7

0 200 m

Fig. 13 Schematic profile with drill holes 5MAHS-7 and 7MAKK-1 in the Sakonishi area.

Morishita, 1991,

Resource Geology

Carbonate-hosted ore depositsPb-Zn-Ag Skarn, Kamioka, Japan

discovery hole

contours of whole rock carbonate δ18O

Naito et al. (1995)

knownmineralization

• Carbonate-hosted ore bodies often have subtle visual and lithogeochemical alteration

• Carbonate-hosted ore deposits are particularly suited for isotopic analysis - large signals, easiest analytical approach

The old way......

INN

OV

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IVE

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The inXitu iX-T “Terra” is the first truly portable XRD system designed specifically for rock and mineral analysis. Now “field work” can really be done in the field. Terra can be configured with everything you need to acquire and analyze diffraction data in a rugged compact case. With our pat-ented sample handling system not only is sample prepara-tion time minimized but accuracy in peak identification pre-viously only available using laboratory based systems can be achieved. XRD is the technique of choice for accurate identification of minerals. XRD data from Terra can be readily ana-lyzed using the software of a laboratory XRD instrument, or third party applications like Jade (MDI), XPowder, Match! (Crystal Impact), CrystalSleuth (Univ. of Arizona), etc. Identification of phases also requires the use of a li-brary such as the ICDD Powder Diffraction Files or the American Mineralogist Crystal Structure Databases.

Terra XRD two-theta display Terra XRF energy spectrum

The iX-T “Terra” operates off software embedded in the unit itself. The user accesses the operating system through a wireless connection (802.11 b/g). This unique method of operation allows for a wide degree of flexibility in controlling the instrument and subsequent data handling

+,(-)./'%"#0)1%2!33()4-!,5%6%"#0)1%7/8,('94'54'%

inXitu Inc. 2251 Casey Ave, Ste A, Mountain View, CA 94043 USA Tel (650) 567 0081 FAX (650) 567 0082 www.inXitu.com email: Sales @inXitu.com

There have been advances in light stable isotope analysis that are based on infrared absorption laser

spectroscopy.

Barker et al, Analytical Chemistry, vol 83, pp 2220-2226

Long Canyon Gold Deposit, Nevada

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Will Lepore, MSc Thesis, 2012

Use of different sampling scales and materials to evaluate hydrothermal fluid flow pathways and

alteration haloes

Carbonate-rock hosted gold deposit

Hand sampling vs pulps

y=0.6822x+5.3741

y=0.6816x+3.7435

y=0.7472x+4.8141r2=0.46

r2=0.32

r2=0.66

y=0.6857x+4.9978r2=0.66

LC555C

LC533C

LC556C

LC555C

LC533C

LC556C

All Drillholes

Ha

nd

Sa

mp

le P

ulp

δ1

8O

VS

MO

W (‰

)

Drill Assay Pulp δ18O VSMOW

(‰)

• Spatial correlation is strong between pulp and hand samples

• Distal - Fluid flow becomes isolated to highly permeable beds

• Pulps become background, individual hand samples still altered

LC480

LC733C

LC537C

LC541C

LC46

2C

LC452C

LC53

3C

LC737C

LC446

LC548C

LC445C

LC524C

LC67

3C

LC564C

LC55

6C

LC666C

LC555C

LC44

2

LC396

LC516

LC448

LC53

3C

LC55

6C

LC555C

3.74 - 8.00

8.00 - 12.00

17.50 - 19.00

19.00 - 25.16

16.00 - 17.50

12.00 - 16.00

MDRU-MIA Oxygen Isotope

18O/16O Drillhole Values Qal

Opls

Cnpd

Oplw

Cambrian Notch Peak Group Lithologies

Ordovician Pogonip Group Lithologies

Oplsm

Cnplbu

Cnplonc

Cnplw

Cnplus

Alluvium/Colluvium

Quaternary Lithology

Laminated to thin-bedded silty limestone and limy

siltstone

Massive dolomite

Massive limestone with silt wisps

Silty limestone alternating with thick-bedded massive

limestone and $at pebble conglomerates

Massive, burrowed, bioturbated, mottled limestone,

often dolomitizedMassive oncolitic limestone, often dolomitized

Massive limestone with silt wisps

Upper siltstone, 0.5-1 m beds of silty limestone

Alteration

Opdl

Au

Replacement Dolomite of Pogonip Limestone

Cnpdl Hydrothermal Replacement Dolomite of

Notch Peak Limestone

Gold mineralization outline greater than 0.1 ppm

Structure Breccia Brecciation including Fault Breccia, Solution Breccia and

Post-ore Calcite Cement Breccia

Long Canyon

Section L12800N

Looking N40E

12800N

12750N

500 metres

Section Location

3 g/t Au Cuto%

100 metres 1000 mX800 mX

1750 mRL

Fig

ure 1

28

00N

Han

dsam

pleP

ulp

25

LC480

LC733C

LC537C

LC541C

LC46

2C

LC452C

LC53

3C

LC737C

LC446

LC548C

LC445C

LC524C

LC67

3C

LC564C

LC55

6C

LC666C

LC555C

LC44

2

LC396

LC516

LC448

LC480

LC733C

LCC55373 CCC37C3

C

3.74 - 8.00

8.00 - 12.00

17.50 - 19.00

19.00 - 25.16

16.00 - 17.50

12.00 - 16.00

MDRU-MIA Oxygen Isotope

18O/16O Drillhole Values Qal

Opls

Cnpd

Oplw

Cambrian Notch Peak Group Lithologies

Ordovician Pogonip Group Lithologies

Oplsm

Cnplbu

Cnplonc

Cnplw

Cnplus

Alluvium/Colluvium

Quaternary Lithology

Laminated to thin-bedded silty limestone and limy

siltstone

Massive dolomite

Massive limestone with silt wisps

Silty limestone alternating with thick-bedded massive

limestone and $at pebble conglomerates

Massive, burrowed, bioturbated, mottled limestone,

often dolomitizedMassive oncolitic limestone, often dolomitized

Massive limestone with silt wisps

Upper siltstone, 0.5-1 m beds of silty limestone

Alteration

Opdl

Au

Replacement Dolomite of Pogonip Limestone

Cnpdl Hydrothermal Replacement Dolomite of

Notch Peak Limestone

Gold mineralization outline greater than 0.1 ppm

Structure Breccia Brecciation including Fault Breccia, Solution Breccia and

Post-ore Calcite Cement Breccia

Long Canyon

Section L12800N

Looking N40E

12800N

12750N

500 metres

Section Location

3 g/t Au Cuto%

100 metres 1000 mX800 mX

1750 mRL

Fig

ure 1

28

00N

IsoP

ulp

Au

Case study - isotopic alteration around Carlin-type gold deposits, northern Carlin Trend, Nevada

Vaughan, 2013 PhD Thesis

Significant gold intercepts

Most distal drilling available

BackgroundAltered

~ 1 km ~ 500 m ~ 500 m ~ 500 mBarker et al, Economic Geology, 2013, vol. 108 pp 1-8

> 2 km halo laterally around mineralization

~ 1 km ~ 500 m ~ 500 m ~ 500 mBarker et al, Economic Geology, 2013, vol. 108 pp 1-8

> 2 km halo laterally around mineralization

Au

~ 1 km ~ 500 m ~ 500 m ~ 500 mBarker et al, Economic Geology, 2013, vol. 108 pp 1-8

> 2 km halo laterally around mineralization

• Stable isotope alteration haloes are real (lots of case studies) - strong theoretical understanding from 60 years of academic research

• Isotope alteration haloes well outside traditional alteration vectors, providing larger targets and potential vectors to ore

• Now have a tool for the job - mineral industry relevant

• Substantial case studies still required to determine best practice, where most value can be extracted for exploration

• Potential exploration impacts:

• Near miss?

• Target ranking (e.g. bigger halo = bigger hydrothermal system = more fluid = more ore)?

• Ground sterilization?

• Vectoring up fluid pathways towards ore?

Conclusions

• Approach appears to have value in carbonate-hosted deposits - but what about the rest? - literature says useful, but methods lacking - S, O, H not yet available

• Potential to look at propylitic alteration that involves formation of secondary carbonate minerals (see work of Kyser group in South America on porphyry deposits)

• Orogenic gold?? Not many case studies relevant to exploration.

• Work just beginning on applying similar technology at U of Waikato to analyze O and H in O-H-bearing minerals (relevant to epithermal, porphyry, orogenic?).

• Emphasis on fast, cheap and easy - relevant cost and utility for industry

The next step(s)?