pdac 2016 presentation by martini, carey, & witter
TRANSCRIPT
HYPERSPECTRAL CORE IMAGING FOR CHARACTERIZATION OF CU-AU PORPHYRY7 MARCH 2016
Brigette A. Martini, PhD & Ronell Carey, PhDCorescan
Jeff Witter, PhDMira Geosciences
Presented at PDAC 2016
The mechanisms of Cu-porphyry formation (Harris and Golding, 2002; Richards, 2003; Sillitoe, 2010), theories of location (Tosdal and Richards, 2001), prediction and identification of type mineral assemblages (Lowell, 1970; Titley, 1982, 1993; Hedenquist at al., 1998; Seedorf et al., 2005; Halley et al., 2015), relative size and footprint (both vertically and horizontally) of alteration (Sillitoe, 2000,2010; Kerrich, 2000), grade in relation to size, age, lithology, location and fluid geochemistry (Singer, 1995; Cooke et al., 2005) have all been profoundly studied in the last 40+ years
“But more fundamentally, however, we require better and more detailed documentation of geologic relationships in porphyry Cu systems worldwide, at all scales from the thin section to the entire system, and with greater emphasis on the regional to district scale…[we] must further emphasize the relative timing of intrusion, brecciation, alteration and mineralization events…this geologic detail [will] hopefully further clarify the localization and evolutionary histories of porphyry Cu systems as well as the fundamental controls on large size and high hypogene grade.” (Sillitoe, 2010)
There are three goals:1. To expand current resource (less risk and highest reward/margins)2. To optimize current mine process (increasing margins by mining better ore)3. Greenfield discovery including potential new districts (high risk – low success) ;
Porphyry Alteration
Porphyry alteration variables from hyperspectral imaging
-Assemblage identification-subtypes Cu-Mo, Cu-Au
-Textures (veined, pervasive, porphyritic)-Paragenesis, vein selvages, cross-cutting, overprints-Sharpness of alteration boundaries-Scaling from fine resolution (cm’s) through to borehole scale (m’s) through to entire deposit scales (km’s)
Diagnostic spectral absorption features: VNIR & SWIR
500 1000 1500 2000 2500
Fe3+
Fe3+
Fe2+Unbound H2O
CO3
Unbound H2O
MgOH
AlOH(Mg,Fe)OH
(Al,Fe)OH, (Al,Mg)OH
CO3 CO3
(Al,Fe)OH
Cu NH4
AlOHOH
Mn
Cr Ni
500nm 1000nm 1500nm 2000nm 2500nm
Mobile, Automated, Hyperspectral Core Logging
HCI-3 System SpecificationsSpectrometers 3 (VNIR, SWIR-A, SWIR-B)Spectral range 450nm - 2500nmSpectral resolution ~4nmScan modes 0.5mm square pixels
Spectral calibration Detailed full width scan Reconnaissance profile scan
Radiometric calibration Spectralon reflectance standard, dark current
RGB image resolution 50 µmHeight profile resolution 20 µmCore tray sizes Up to 0.6m x 1.5m (WxL)
Scan rates200m to 1000m per day depending on operational constraints
Porphyry alteration: Typical assemblages
Sodic-Calcic• Albite/oligoclase• Actinolite• Magnetite• Diopside• Epidote• Garnet
Modified from Sillitoe, 2010
Porphyry alteration: Typical assemblages
Sodic-Calcic• Albite/oligoclase• Actinolite• Magnetite• Diopside• Epidote• Garnet
Magnetite
Cu-Au
Low
Mineral match
High
Magnetite
Porphyry alteration: Typical assemblages
Potassic• Biotite• K-spar• Actinolite• Epidote• Sericite• Albite• Carbonate• Tourmaline• Magnetite
Modified from Sillitoe, 2010
Porphyry alteration: Typical assemblages
Potassic• Biotite• K-spar• Actinolite• Epidote• Sericite• Albite• Carbonate• Tourmaline• Magnetite
~2325nm
~2250nm
~1380nm~2390nm
Biotite
Biotite
Actinolite
Mont.
Sericite
K-spar
Cu-Au
Porphyry alteration: Typical assemblages
Propylitic• Chlorite• Epidote• Albite• Carbonate
Modified from Sillitoe, 2010
Porphyry alteration: Typical assemblages
Propylitic• Chlorite• Epidote• Albite• Carbonate
Chlo
rite
Chlo
rite
Chem
Epid
ote
Calc
ite
Plag
.
Cu-Au
Porphyry alteration: Typical assemblages
Chlorite-Sericite• Chlorite• Sericite/Illite• Hematite• Martite, Specularite• Carbonate• Epidote• Smectite
Modified from Sillitoe, 2010
Porphyry alteration: Typical assemblages
Chlorite-Sericite• Chlorite• Sericite/Illite• Hematite• Martite, Specularite• Carbonate• Epidote• Smectite
Cu-Au
Sericite Chem.
Sericite Xtal.
Chlorite Chem.
Classification
Photography
Porphyry alteration: Typical assemblages
Sericite (Phyllic)• Sericite• Quartz
Modified from Sillitoe, 2010
Porphyry alteration: Typical assemblages
Sericite (Phyllic)• Sericite• Quartz
Seric
ite
Ser.
Chem
.
Ser.
Xtal
.
~2200nm
Sericite composition
10nm shift
~2210nm
~2200nm
Sericite crystallinity
~2200nm
~2200nm
High crystallinity
Low crystallinity
Cu-Mo
Porphyry alteration: Typical assemblages
Advanced Argillic• Kaolinite• Alunite• Pyrophyllite• Diaspore• Dickite• Jarosite• Topaz• Quartz• Vuggy Silica
Modified from Sillitoe, 2010
Porphyry alteration: Typical assemblages
Advanced Argillic• Kaolinite• Alunite• Pyrophyllite• Diaspore• Dickite• Jarosite• Topaz• Quartz• Vuggy SilicaAl
unite
G
ypsu
m
Kao
l.
Asp
ec.
Seric
.
Alunite
Pyrophyllite
Kaolinite
ClassificationCu-AuCu-Mo
Porphyry: Sulfides
Bornite Py/Cpy Moly
Sericite
Py/Cpy
Calcite
Silica
Bornite
Moly
• It is possible to map sulfides in the VNIR-SWIR spectral range
• However, unlike typical alteration mineralogy spectra, sulfide signatures are not unique and ambiguity between sulfides can be a problem
• Massive sulfide has higher accuracy than finely disseminated sulfides
Pyrite Spectral Signature
Assemblage – Alteration similarity across deposits (Cu-Mo)
Sericite
Sericite (Hi Xtal)
Kaolinite
Sulfide
Sericite + Chlorite
Chlorite
Montmorillinite
Phlogopite
Carbonate
Photo Class Sericite Ser. Wave Kaolinite Class Sericite Ser. Wave Kaolinite
Porphyry A Porphyry B
Porphyry alteration variables from hyperspectral imaging
-Assemblage identification-subtypes Cu-Mo, Cu-Au
-Textures (veined, pervasive, porphyritic)-Paragenesis, vein selvages, cross-cutting, overprints-Sharpness of alteration boundaries-Scaling from fine resolution (cm’s) through to borehole scale (m’s) through to entire deposit scales (km’s)
CorePhotography
Classification Map AspectralPhlogopite Sericite Kaolinite
Textural Mapping: Pervasive v. Veined
Low match
Mineral match
High match
Textural Mapping: Pervasive v. Veined
Photo Class Ser. Wave Kaolinite Alunite Gypsum Sericite
Sericite (Hi Xtal)
Kaolinite
Alunite
Gypsum
Tourmaline
Low match
Mineral match
High match
~17m
Texture: Primary Porphyritic
CorePhotography
Kaolinite Montmorillinite Aspectral
Porphyry alteration variables from hyperspectral imaging
Classification Map
Sulfide
Gypsum
Sericite
Chlorite + Clay
-Assemblage identification-subtypes Cu-Mo, Cu-Au
-Textures (veined, pervasive, porphyritic)-Paragenesis, vein selvages, cross-cutting, overprints-Sharpness of alteration boundaries-Scaling from fine resolution (cm’s) through to borehole scale (m’s) through to entire deposit scales (km’s)
Cu-Mo(Au)
Paragenesis: Vein/Assemblage
Low match
Mineral match
High match
Photo Class Sericite Kaolinite Alunite Gypsum Carbonate Atacam.
Cu-Mo
Paragenesis: Cross-Cutting Relationships
Low match
Mineral match
High match
2212 nmMuscovite2196 nm
White mica composition index (~2200 nm position)Increase in Na(Paragonite)
Increase in K/Al(Muscovite)
2196 nm 2212 nm
Fe substitution(Phengite)
2185 nm 2225 nm
Porphyry A
Photo Class Phlog. Kaolinite Chlorite Sericite Ser. Wav.
Cu-Mo
Vein Halos
Low match
Mineral match
High match
Photo Class Sericite Ser. Wav. Kaolinite
2212 nmMuscovite2196 nm
White mica composition index (~2200 nm position)Increase in Na(Paragonite)
Increase in K/Al(Muscovite)
2196 nm 2212 nm
Fe substitution(Phengite)
2185 nm 2225 nm
Porphyry A
Cu-Mo
Vein/Fracture Halos
Photo
Class
Sericite
Ser. Wav.
Gypsum
Low match
Mineral match
High match
2212 nmMuscovite2196 nm
White mica composition index (~2200 nm position)Increase in Na(Paragonite)
Increase in K/Al(Muscovite)
2196 nm 2212 nm
Fe substitution(Phengite)
2185 nm 2225 nm
Porphyry A
Cu-Mo
Vein/Fracture HalosPHOTOGRAPHY CLASS MAP WHITE MICA WM CHEM. WM XTAL.
Cu-Mo
Porphyry alteration variables from hyperspectral imaging
-Assemblage identification-subtypes Cu-Mo, Cu-Au
-Textures (veined, pervasive, porphyritic)-Paragenesis, vein selvages, cross-cutting, overprints-Sharpness of alteration boundaries-Scaling from fine resolution (cm’s) through to borehole scale (m’s) through to entire deposit scales (km’s)
Copper canyon
Photo Class Asp.Ser. Ser. Wav. Chl.
Cu-Au
Sharpness of Alteration BoundariesPhoto Class Gyp.Kaol. Tourm.Ser. Ser.
Wav.Mont. Chl.
Sericite
Sericite (Hi Xtal)
Kaolinite
Alunite
Gypsum
Tourmaline
Low match
Mineral match
High match
Cu-Mo
Sharpness of Alteration BoundariesClass
Sericite
Sericite (Hi Xtal)
Kaolinite
Alunite
Gypsum
Tourmaline
Low match
Mineral match
High match
Biotite/PhlogopiteCu-Au
~992
m
Sharpness of Alteration BoundariesPhoto Class
Sericite
Sericite (Hi Xtal)
Kaolinite
Alunite
Gypsum
Tourmaline
Cu-Au
~114
8m
Porphyry alteration variables from hyperspectral imaging
-Assemblage identification-subtypes Cu-Mo, Cu-Au
-Textures (veined, pervasive, porphyritic)-Paragenesis, vein selvages, cross-cutting, overprints-Sharpness of alteration boundaries-Scaling from fine resolution (cm’s) through to borehole scale (m’s) through to entire deposit scales (km’s)
Borehole-scale Alteration Domains: Cu-AuClass Chlorite Sericite
Kaolinite
Alunite
Gypsum
Tourmaline
Low match
Mineral match
High match
PhlogopiteSericite
~992
m
Borehole-scale Alteration Domains: Cu-MoClass Chlorite Sericite
Low match
Mineral match
High match
Phlogopite
~833
m
<<WHITE MICA (PHENGITE),HIGH XTAL WHITE MICA
PHLOGOPITE + CHLORITE (FE-RICH)
+ =
HIGHER CU-GRADE
Borehole-Scale Alteration Domains~1
69m
Borehole-scale Alteration Domains: Cu-Mo
Photo Class Kaol. ChloriteAlunite Ser. Wav. Phlog. Mont.
Argillic Lithocap Potassic CoreOverprintLow match
Mineral match
High match
~561
m
Borehole-scale Alteration Domains -> Deposit Scale
Photo Class AluniteMont.
Low match
Mineral match
High match
Export to downhole mineral% logs for databaseand 3D modeling
~561
m
Assemblage ID: Mineral Point Logs
Consistent, high resolution mineral point logs reveal basic (and sometimes subtle) mineral assemblages
Alunite Atacamite GypsumAsp. (Sericite)
Argillic
Assemblage ID: Mineral Point Logs
Consistent, high resolution mineral point logs reveal basic (and sometimes subtle) mineral assemblages
Chlorite Mont.Phlog (Sericite)Asp.
Potassic
Deposit-Scale Alteration Domains: Alunite
Alteration % point databrought into simple 3D models (e.g. Gocad)
• Point data represents % of minerals counted downhole, in specific depth intervals
• This model was created with 1m interval data which represents ~200,000 pixels/signatures per meter of core
• Color of model spheres relates to purity or ‘goodness’ of fit to verified mineral spectral signatures
• Size of model spheres also relates directly to purity of the identified mineral
Cu-Mo
Deposit-Scale Alteration Domains: Aspectral
• Aspectral refers to measured signatures that lack spectral absorption features
• They are related to either non-included, crystalline quartz OR un-altered feldspars
• Spatial mapping of this class is accurate – though identification can be ambiguous
• In this porphyry, most of the aspectral class relates to quartz (confirmed from previous traditional logging)
Deposit-Scale Alteration Domains: Atacamite
Deposit-Scale Alteration Domains: Carbonate
• While the chemistry of carbonates is possible to measure (e.g. dolomite v. calcite, ankerite, siderite, etc.), it is often useful to lump the carbonate classes in order to study gross patterns in alteration
• Further delineations such as crystallinity are also possible
Deposit-Scale Alteration Domains: Chlorite
Deposit-Scale Alteration Domains: Chrysocolla
Deposit-Scale Alteration Domains: Gypsum
Deposit-Scale Alteration Domains: Kaolinite
Deposit-Scale Alteration Domains: Montmorillinite
Deposit-Scale Alteration Domains: Phlogopite
• Discrimination between phlogopite and biotite is generally possible – though in some cases difficult
• In general, the higher the iron content (as measured directly from the spectral signatures) and the less water detected – the more biotitic the rock is
Deposit-Scale Alteration Domains: Sericite
Deposit-Scale Alteration Domains: Sericite Chemistry
2212 nmMuscovite2196 nm
White mica composition index (~2200 nm position)Increase in Na(Paragonite)
Increase in K/Al(Muscovite)
2196 nm 2212 nm
Fe substitution(Phengite)
2185 nm 2225 nm
Porphyry A
Deposit-Scale Alteration Domains: Tourmaline
• Distinction between tourmaline varietals is possible – though frequently of lesser importance
• Typically, tourmaline is lumped into a single class
Deposit-Scale Alteration Domains: RQD
• RQD data is derived using a laser profiling system with 15 micron vertical resolution
• Though very consistent and accurate, automated RQD data should be considered carefully based on age and condition of core
• Core that is old and/or been moved frequently may report different RQD values than those derived directly after drilling
• On-site deployment of automated core-logging during drilling solves this issue
Deposit-Scale Alteration: Alunite ≈ QS
Potassic - Bi Quartz-Sericite (QS)
• Alteration ‘cylinders’ derived from traditional core-logging data identified by on-site geologists
• Hyperspectral alteration (alunite) correlates to QS code
Deposit-Scale Alteration: Phlogopite ≈ KB
Potassic – Bi (KB) Quartz-Sericite (QS)
• Hyperspectral alteration (phlogopite) correlates to KB code
Deposit-Scale Alteration: Montmorillinite ≈ KB
Potassic – Bi (KB) Quartz-Sericite (QS)
• Hyperspectral alteration (montmorillinite) correlates to KB code
Deposit-Scale Alteration Domains: Alun+Kaol (+Gyp)
Alunite+Kaolinite(Gypsum)
• We can start to create initial assemblage classifications and model these relationships in 3D
Deposit-Scale Alteration Domains: Phlog+Chl+Mont
Alunite+Kaolinite(Gypsum)
Phlogopite+ChloriteMontmorillinite
Deposit-Scale Alteration Domains: Argillic
Alunite
• Minerals thought to correlate to particular alteration domains are modeled in 3D space
Deposit-Scale Alteration Domains: Alunite – Mont.
Alunite
Montmorillinite• Such modeling shows presence
of (late-stage?) montmorillinite overprint at depth
Deposit-Scale Alteration Domains: +Phlogopite
Alunite
MontmorillinitePhlogopite
• Montmorillinite co-located with Phlogopite (Potassic) domain
Cu-Au Porphyry: Borehole-scale AlterationClass Epidote ChloriteActin. SericitePhlog. Kaol.Chl+Clay Chl Wav. Ser. Wav. Mont.
~114
8m
Cu-Au Porphyry: Borehole-scale AlterationClass Epidote ChloriteActinolite SericitePhlog. Kaolinite Mont.
~995
m
Deposit-Scale Alteration Domains
Montmorillinite
Phlogopite
%Cu
• Similar modeling in a Cu-Au porphyry highlights the more expected alteration domains as well as expected correlation of Cu with the Potassic (represented by phlogopite)
“From Microns to Kilometers”
Spectral Signatures (“microns”)
Core-scale “meters”
Core-hole scale “kilometers”