pdac 2016 presentation by martini, carey, & witter

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


Sodic-Calcic• Albite/oligoclase• Actinolite• Magnetite• Diopside• Epidote• Garnet

Magnetite

Cu-Au

Low

Mineral match

High

Magnetite


Potassic• Biotite• K-spar• Actinolite• Epidote• Sericite• Albite• Carbonate• Tourmaline• Magnetite



Potassic• Biotite• K-spar• Actinolite• Epidote• Sericite• Albite• Carbonate• Tourmaline• Magnetite

~2325nm

~2250nm

~1380nm~2390nm

Biotite

Biotite

Actinolite

Mont.

Sericite

K-spar

Cu-Au


Propylitic• Chlorite• Epidote• Albite• Carbonate



Propylitic• Chlorite• Epidote• Albite• Carbonate

Chlo

rite

Chlo

rite

Chem

Epid

ote

Calc

ite

Plag

.

Cu-Au


Chlorite-Sericite• Chlorite• Sericite/Illite• Hematite• Martite, Specularite• Carbonate• Epidote• Smectite



Chlorite-Sericite• Chlorite• Sericite/Illite• Hematite• Martite, Specularite• Carbonate• Epidote• Smectite

Cu-Au

Sericite Chem.

Sericite Xtal.

Chlorite Chem.

Classification

Photography


Sericite (Phyllic)• Sericite• Quartz



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


Advanced Argillic• Kaolinite• Alunite• Pyrophyllite• Diaspore• Dickite• Jarosite• Topaz• Quartz• Vuggy Silica



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

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


Classification Map

Sulfide

Gypsum

Sericite

Chlorite + Clay



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




2196 nm 2212 nm


2185 nm 2225 nm

Porphyry A

Cu-Mo

Vein/Fracture Halos

Photo

Class

Sericite

Ser. Wav.

Gypsum

Low match

Mineral match

High match




2196 nm 2212 nm


2185 nm 2225 nm

Porphyry A

Cu-Mo

Vein/Fracture HalosPHOTOGRAPHY CLASS MAP WHITE MICA WM CHEM. WM XTAL.

Cu-Mo




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

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




2196 nm 2212 nm


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”

pdac 2016 presentation by martini, carey, & witter

Science