teaching an old dog new tricks: stable isotopes in mineral ... - barker.pdf · teaching an old dog...
TRANSCRIPT
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: [email protected]
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
AT
IVE
!"#$%&$'(()*%
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
!"#$ %$ &'()*"'+,'-,&'+#,.)+/'+,01'231*/ 4)-*31,5'67)8,3*,)8$9,:;;;<$,,5=3,>1,;$?;@,8"+3,"6,A637,)6,)+,
!"#$%$
!"#$%&$'
!"#$%&%'
(")*+
,#&%'-#
(")*+
&'$(
)%$(*
.//012
+,-./,001
'2,34
)34,5,34,3.,1
'2,34
67381
9:3;73
$<)=*!$
3%4&56"5+&"575-#80
9"%'*-+-5'%4
(")*+
..:..;..< 555
<=5
</5
>:5
>; 5
..=5
9:20>31
'2,34
!"#$%&'()(*'S+$,0"+#*+/*07(*S+#<*I,#.+#*'(1+)"0*"#*#+-07(,)0(-#*T(4,',9*=H,1*,/0(-*
:+)',%*(0*,%95*,#'*U2"07*(0*,%95*@AD@B9*:7(*U-*A9VAL*%"#(*-(1-()(#0)*07(*('<(*+/*07(*-"/0('*
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)?