integrated interpretation of anaconda-style mapping and core …€¦ · marco einaudi john dilles...

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Integrated interpretation of Anaconda-style mapping and core logging, trace element geochemistry and short wave infrared spectroscopy for the exploration of porphyry copper deposits.

Federico Cernuschi | [email protected] the collaboration of Scott Halley, John Dilles, Dick Tosdal, Marco Einaudi, Phil Gans among many others

Contributors:

29 September 2020

This presentation has also benefited by the extensive collaboration with:

Ore deposit models

What the community understands (empirically and scientifically) of the geology, mineralogy, petrology and geochemistry of discovered ore deposits is used to explore for others.

From exploration to geometallurgy

Abundant “mappable” features that inform and guide the exploration and geometallurgy!

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Why is so difficult to make useful maps and cross-sections?

• Correctly identify minerals is difficult.• Overprint in hydrothermal alteration.• Geologists commonly not properly trained on what to look for.• Diverse teams with different training and experience.• Making a map is a subjective task. It is a craft.

3 geologist = 5 opinions

We have to minimize the interpretation during the data gathering process.

A. Anaconda mapping and core-logging. Map what you can see:1. Descriptive lithology, structure and veining,2. Sulfides and oxides,3. Mineral replacements to track hydrothermal alteration.

B. Whole rock and soil compositional and SWIR-data:1. Lithogeochemical units using immobile trace elements, 2. Sulfide mineralogy, 3. Hydrothermal alteration using mobile major elements and SWIR-data, 4. Trace element anomalies and depletions.

C. Integration in hand made maps, cross-sections and in 3D space:• Lithology, structure, alteration, veining, mineralogy, footprints, oxidation front, etc. • Use 3D software to visualize data. Detailed models are often unrealistic and

misleading.• This is the time to bring in the geophysics.

The Scott Halleymethod

Kudos for Marco EinaudiJohn DillesDick Tosdal

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Whole rock and soil geochemistry

Consider this:• Digestion technique

(which minerals are dissolved)

• Assay method (detection limits, precision, accuracy)

• 4 acid digestion (HCl, HNO3, HF, HClO4) and ICP-MS• Dissolves most minerals (except extremely refractory). For soils and whole rock.• Great detection limits.• Does not report Si, but it can be back calculated.• Assay it all!

• Li-metaborate fusion and ICP-MS• For selected samples for lithogeochemistry (Zr, Hf, REE)• More accurate but less precise. No so good for subtle trace element

variations.

My preferred assays:

Whole rock and soil geochemistry

Aqua Regia

4 acid

Aqua Regia

4 acid

Plot by Scott Halley

Aqua regia digested whole rock or soil samples are much less useful

W (ppm)

W(ppm

)

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1. Lithogeochemistry

Fined grained basalts and rhyolites


Instead of Si, use Sc in the X-axisSc substitues for Fe. Immobile proxy for fractionation

X-sections

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Fractional crystallization of magnetite

Pattern recognition supported by petrology and mineralogy

Fractional crystallization of ilmenite

Fractional crystallization of hornblende

PCD

EpiVMS

BasaltAndesiteDaciteRhyolite

Fractionation trends

Implications for magma fertility

Lithogeochemistry vs lithology: feedback to core logging

1. LithogeochemistryWorks for sedimentary rocks too

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Cu5FeS4

CuFeS2

FeS2

2. Sulfides, Oxides and sulfates

(almost any assay type with Cu, Fe, S works for this)

Bn

Cpy

2. Sulfides, Oxides and sulfates

FeS2

SulfatesPyrite: FeS2

Anhydrite: CaSO4

Alunite: KAl3(SO4)2(OH)6

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Sulfi

des

and

oxid

es

Leapfrog video: www.eclectic-rock.com/haquira-movies (password: Haquira-2015-)

Sulfi

des

and

oxid

es


http://www.eclectic-rock.com/haquira-movieshttp://www.eclectic-rock.com/haquira-movies

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KAl3Si3O10(OH)2

Al2Si2O5(OH)4

KAlSi3O8

NaAlSi3O8CaAl2Si2O8

3. Hydrothermal alteration


Hyd

roth

erm

al

alte

ratio

n

http://www.eclectic-rock.com/haquira-movies

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Hyd

roth

erm

al

alte

ratio

n


3. Hydrothermal alteration

Kaolinite: Al2Si2O5(OH)4

Biotite: K(Mg,Fe)3AlSi3O10(F,OH)2

Orthoclase: KAlSi3O8

Muscovite: KAl2(AlSi3O 10)(F,OH)2

K-silicate

Sericitic

Advanced Argillic

Intermediate ArgillicClinochloro: (Mg5Al)(AlSi3)O10(OH)8

Montmorillonite: (Na,Ca)0,3(Al,Mg)2Si4O10(OH)2•n(H2O)

SWIR!


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Short wavelength Infrared Spectrometer:

Systematic and fast: Measure 1000 m of drill core/chips per day.

3. SWIR for hydrothermal alteration

• Export TSA/aiSIRIS mineral identification and scalars

• Equally fast to process 10 or 10.000 spectra

The Spectral Geologist or aiSIRIS


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TSA identifications of Ankerite, Siderite, Mg Chlorite, Tourmaline, Diaspore and Zeolite are not very reliable.

Simplify the TSA mineralogy in ioGAS:

3. SWIR for hydrothermal alterationSW

IR m

iner

alog

y



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Example of use of scalars: Mixtures of kaolinite and muscovite

The Spectral Geologist


Example of use of scalars: Solid solution: muscovite, epidote, alunite, chlorite

The Spectral Geologist


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SWIR imaging systems


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SWIR imaging is a great learning tool and provides feedback for Anaconda logging


CoreScan data: • Better agreement with compositional data. • More and better identifications of biotite. • Quantification of mineralogy by intercept.

K-silicate

Plots by Scott Halley


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4. Trace element footprints

Halley et al., 2015

• Targeting and erosion level.• Anomalies are typically a few

ppm, but 10x average crustal abundance.

Sn, Te, Tl

Mn, Co, Ni

Oxyanions: Low pH outflow zones of magmatic hydrothermal system and distance from the source. Immobile during weathering.Chloride complexes: Stripped from low pH centers and precipitated upon neutralization

Mostly immobile during weathering

~1 km

~2 km

PCD footprint


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~1 km

~2 km

PCD footprint


~1 km

~2 km

PCD footprint


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~1 km

~2 km

PCD footprint


~1 km

~2 km

PCD footprint

RGB


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~1 km

~2 km

PCD footprint

RGB


~1 km

~2 km

PCD footprint

RGB


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~1 km

~2 km

PCD footprint

RGB


Trace element footprints and Anaconda map

Where exactly to park the drill hole rig to maximize chances of hitting ore?

• A veins with Fe-oxidessurrounded by D veins with pyrite. • Drill perpendicular toA

vein sets.

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Lithology

Alteration

SWIR

3D m

odel

Sulfide, oxides, sulfates

Geometallurgy

2- Input: 1000’s of assays throughout the deposit

Output: BlocksEconomic value of each block:

• Contained metal• Recoverable %• Mining cost• Grinding cost

1- Input: 10’s to 100’s of geomet tests: point load pressure, flotation, etc.

3- Input: Geophysics (now it has a context)

integrated interpretation of anaconda-style mapping and core …€¦ · marco einaudi john dilles...

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