1

Carlos Roberto De Souza Filho1

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University of Campinas Institute of Geosciences

Department of Geology and Natural Resources

PO Box 6152 13083-970

Ph: 55-19-3788-4535

Email: beto@ige.unicamp.br

Exercise 1: ENVI Spectral Libraries There are a variety of software packages for processing field/laboratory spectral data, including:

TSG (the Spectral Geologist) though CSIRO and AUSspec,

PIMAVIEW though Integrated Spectronics Pty Ltd; and

ENVI (Environment for Visualising Images) through KODAK RSI (Research Systems

Inc).

There are also a variety of accessible spectral libraries that can be used as a reference to help

interpret unknown sample spectra, including:

USGS;

NASA JPL;

The Johns Hopkins University;

University of Arizona; and

Specmin through Spectral International.

The first three of these libraries are available in the ENVI software package, which is what we

will be using to help interpret spectra of natural geological samples (Exercise 2).

TASK:

Open up ENVI to reveal the pull down menu.

>Spectral>Spectral Libraries>Spectral Library Viewer to show the:

Spectral Library Input File window

>Open Spec Lib>usgs_min>usgs_min.sli

Press OK to reveal a list of minerals. Left mouse click on any mineral name to open up a

spectrum (0.45 to 2.5 microns or 450 to 2500 nm). Left mouse click inside the spectral plot to

show a vertical line with channel number, wavelength position and reflectance level given at the

bottom left. Multiple minerals can be presented. Become familiar with both narrow and broad

absorption bands for a selection if important alteration minerals discussed in the associated PPT

presentation. Also explore other ENVI functionality using the pull down menus shown at the

top of the Spectral Library plot window including,

Wavelength zoom >Edit>Plot Parameters or control + left mouse click point drag

and drop

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Continuum removed spectra

Plot key (right mouse click in window) drag and drop to a new window

Using the USGS library spectra and the Figures 1 and 2, what are the colours and wavelength

peaks of:

COLOUR WAVELENGTH

Azurite……………….…………………………..………………

Hematite……………………….……………….………………..

Goethite……………………………….………..………………..

Magnetite………………………….…………..…………………

Malachite…………………………….…………………..………

Quartz ………………………………………………………..

Figure 1. Colour and wavelength Figure 2. Additive colour wheel

Exercise 2 – Spectral mineralogy and Alteration Zonation

The spectra provided below are from the hand samples on display. Interpret the mineralogy of

these samples using the USGS library:

BO_11B………………………………………………………….

T-7………………………………………………………….

PYROP………………………………………………………….

SER………………………………………………………….

BO_15…………………………………………………………..

BO 17A………………………………………………………….

BO 18A………………………………………………………….

CALC………………………………………………………….

red

blue

green

magenta

yellow

white

cyan

black

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6

The figure below stacks five of these samples in order of their location along a transect. What

can be said about the alteration facies shown by these minerals, including alteration zonation

(annotate of the figure) and likely style of mineralisation (see Appendix 1)?

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

Where would you locate the samples P, C and BO-11b along this transect: Show on above

figure.

………………………………………………………………………………………………………

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………………………………………………………………………………………………………

………………………………………………………………………………………………………

Which direction towards potential mineralisation (up or down)?

………………………………………………………………………………………………………

Exercise 3 : ENVI Mineral Alteration Facies

(I) montagem de bibliotecas espectrais para uso no estudo de:

mineralizações de ouro em greenstone belts Arqueanos

1. composição de rochas não alteradas hidrotermalmente: metamorfismo regional

- TALCO, SERPENTINA: rochas ultramáficas

- ACTINOLITA ou hornblenda clorita: rochas máficas

- sericita (paragonitica): rochas félsicas e alguns sedimentos

- kaolinita, montmorilonita, nontronita (maf – Fe-smectita), saponita (ultram – Mg-smectita):

produtos do intemperismo

2. Zona de alteração hidrotermal (mais externa) – ZONA DA CLORITA

- talco: rochas ultramáficas

- CLORITA, carbonato (calcita ankerita): rochas máficas e alguns sedimentos

- sericita: rochas félsicas e alguns sedimentos

3. Zona de alteração hidrotermal – ZONA DO CARBONATO

- FE-CARBONATO (siderita e ankerita)

- chlorita ()

- sericita ()

4. Zona de alteração hidrotermal (mais interna) – ZONA DA MUSCOVITA-PIRITA

- SERICITA (fengita)/MUSCOVITA

- biotita ()

- ankerita/siderita ()

- pirita

(II) montagem de bibliotecas espectrais para uso no estudo de:

mineralizações de cobre-porfiro em ambientes de cordilheira

- zonas de alteração clássicas:

(1) propilitica (mais externa)

- EPIDOTO, CLORITA, carbonato, actinolita – IMPORTANTES

- quartzo, zeolita, feldspato – não apresentam feições diagnósticas

- magnetita e sulfetos –mascaram feições de absorção no espectro.

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(2) argílica

- ILITA-ESMECTITA, ESMECTITA, , ILITA, kaolinita, clorita, carbonato -

IMPORTANTES

- quartzo– não apresenta feições diagnósticas

(3) argílica avançada

- ALUNITA, kaolinita, dickita, diásporo, pirofilita, mica – IMPORTANTES

- quartzo

(4) fílica (phyllic)

- ILITA 2M (muito cristalina; ‘quase’ sericita)

- sericita/mica; carbonato; clorita,

- quartz, feldspato

- sulfetos

(5) potássica

- BIOTITA

- K-feldspato

- magnetita

(Outros)

- GYPSO

- barita

- anidrita

‘TASKS’

(A) Construa uma biblioteca espectral, com base naquela do USGS, para cada associação,

salvando-as no disco rígido, num diretório criado previamente. Analise os espectros de

reflectância entre os minerais da associação e discuta qual a possibilidade de separação entre os

mesmos. Tente, finalmente, avaliar a separabilidade espectral entre as várias zonas de alteração

hidrotermal.

(A) TESTE DE MISTURAS ESPECTRAIS

- Faça uma análise, utilizando misturas representativas para o modelo de deposito,

sobre o aumento e/ou diminuição de contraste de algumas feições típicas de minerais

puros.

- Spectral => Spectral Math => enter an expression => s1+s2+s3+ ... Sn

Obs: Utilize recursos do ENVI para fazer essa análise, como por exemplo, a remoção do

contínuo, estaqueamento entre os espectros e etc.

(B) Re-amostre as bibliotecas que você constituiu para as resoluções do ASTER.

Para faze-lo:

1. Spectral => Spectral Libraries => Spectral Library Viewer

- Spectral library input file (carregue as bibliotecas que

voce montou anteriormente – uma de cada vez)

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2. Spectral => Spectral Libraries => Spectral Library Resampling

- Input file (use a biblioteca carregada)

- Spectral Resampling parameters

o user definied filter function

o open spectral library

o ASTER …. FILTROS

3. Spectral => Spectral Libraries => Spectral Library Viewer

- Spectral library input file (carregue o arquivo da

biblioteca reamostrada que voce acabou de criar)

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Exercise 4 – Mesothermal Alteration Mineralogy

The aim of this exercise is to spectrally map alteration mineralogy and zonation in a fresh rock

drill core taken from a mesothermal gold deposit in greenstone rocks.

Figure 6 presents a stacked profile of PIMA spectra taken from a diamond drill core (Figures 7

provides a selected wavelength expansions). Note that this drill core intersected only one rock

type that was variably altered during hydrothermal alteration

Using your Spectral Libraries, answer the following questions.

(a) What minerals or mineral groups are evident? (Note that there may exist mixtures of two

or minerals). Annotate your interpretation on one of the figures.

.....................................................……......................................................................................

...................................................……........................................................................................

(b) What evidence (if any) is there for the oxidation state of the iron and the type of water?

..............................................……............................................................................................

...........................................……...............................................................................................

...........................................……...............................................................................................

(c) Is there evidence for the mineral cation composition? Explain.

.................................................……........................................................................................

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(d) What was the likely composition of the host rock (give reasons)?

..................................................................…….......................................................................

........................................................................…….................................................................

.............................................................................…….............................................................

(e) Account for the alteration mineralogy and identify the most “prospective” samples.

...............................................................……..........................................................................

.....................................................................……....................................................................

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Figure 6 : Stacked PIMA reflectance spectra from a diamond drill core from the Eastern

Goldfields.

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Figure 7: The same spectra as Figure 6 though displayed from 2150 to 2500 nm.

Exercise 5 - Regolith Mapping

This exercise examines VNIR and SWIR spectral variations through a lateritic profile. A

schematic lateritic cross-section (Figure 9) shows the types of physicochemical changes that may

be expected to be evident in the spectral data.

A stack plot of IRIS VNIR reflectance spectra (Figure 10) spans samples from the top of the

lateritic duricrust down to the mottled zone. Broad "electronic" absorptions in the VNIR spectra

show variations in iron-related mineralogy.

(a) What is the dominant iron oxide mineralogy in the lateritic duricrust and mottled zone.

Apart from the feature at approximately 900 nm (0.9 µm), what other features appear to change

with the iron oxide composition (excluding the features at 1400 and 1900 nm).

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.........................................................................................................……..................................

...................................................................................................……........................................

.............................................................................................……..............................................

.......................................................................................……....................................................

Figures 11 to 14 present various zoom sections of stacked PIMA spectra measured from a

complete laterite profile similar to that shown in Figure 9.

(b) What minerals are evident in the PIMA spectra and how did you identify these?

...............................................................................................................……...........................

.....................................................................................................................…….....................

...........................................................................................................................……...............

.................................................................................................................................…….........

.......................................................................................................................................……...

..........................................................................................................................................……

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(c) Identify the primary and weathering minerals?

PRIMARY:...................................................................................................……......................

WEATHERING:.................................................................................................……...............

...................................................................................................................................……........

(d) What is the nature of the parent rock?

............................................................................................……...............................................

(e) What information is there about water, iron oxides, cation substitution and clay

crystallinity?

..................................................................................................…….........................................

........................................................................................................……...................................

..............................................................................................................…….............................

....................................................................................................................…….......................

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..........................................................................................................................…….................

................................................................................................................................……...........

......................................................................................................................................…….....

(e) Annotate the various lateritic units (lateritic duricrust, mottled zone, saprolite and fresh

rock) on Figure 11. What primary mineral coexists with the weathered minerals and

explain the significance?

..............................................................................................……............................................

....................................................................................................……......................................

..........................................................................................................…….................................

................................................................................................................……...........................

Figure 9: Schematic lateritic profile. The degree of iron oxide development is dependent on the

parent rock composition with granites generally producing less iron oxide than mafic and

ultramafic rocks.

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Figure 10: Stacked IRIS reflectance spectra taken from samples collected down a lateritic

profile.

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Figure 11: Stacked PIMA reflectance spectra of samples collected from a lateritic profile.

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Exercise 6 : ENVI ASTER Processing - Ratios

Coverage:

Image display and linking

Z-profiling

Contrast stretching

2-D scattergrams

Log residuals

Band maths and ratios

Masking

Open up the Cuprite ASTER reflectance image:

>File>Open Image File>*****

From the available bands list select RGB and three bands of your choosing. Three image

windows appear, including a Zoom, Scroll and (full resolution) Image.

Open a Z-spectral (spectral bands) profile for the Image pull down menu:

>tools>profiles>z-profile

Move the curser position around the image to check for changes in spectral shape.

Contrast enhance the image from the Image Pull down menu:

>enhance>[image] Linear 2%

Open a second image window (New Display) in “Gray Scale” from the available bands selecting

any single band.

Apply a colour density slice to the gray scale image using the Image Window pull down menu:

>Tools>Colour Mapping>ENVI Colour Tables. Select Rainbow.

Link the two image windows using the any one of the Image Windows pull down menu:

>tools>link>link display

Right mouse click inside the image window to reveal the second image.

Contrast stretch the single band image using:

>enhance>interactive stretching.

Experiment with changing the threshold values.

Generate band math or ratio ASTER products for the following :

3/2 : green vegetation

4/3 : iron oxide abundance

5/4 : ferric/ferrous iron (in silicate/carbonate) ratio

(6+8)/7 for chlorite, epidote

(5+7)/6 : Al-OH abundance

7/5 with mask of (5+7)/6 : Al-OH type (Group 1: alunite, pyrophyllite, kaolinite,

dickite); Group 2: muscovite; Group 3: phengite)

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(6+9)/(7+8) : Mg-OH + carbonate abundance

6/5 or 7/5 : pyrophyllite, alunite, kaolinite

11/(10+12), 11/10, 13/12 and 13/10 : SiO2 abundance

13/14 : carbonate abundance

7/8 mask with 13/14 for calcite vs dolomite

12/13 : “basic” minerals (garnet, CPX, epidote, chlorite)

To generate simple 2 band ratios:

>transform>band ratios

To generate multi-band bands ratios or “continuum” band ratios:

>basic tools>band math>enter and expression

To preserve sufficient dynamic range write:

Float(b1+b2)/float(b3)

Insert selected bands (recommend ASTER Bands V1: 5 V2: 7 V3: 6 for ALOH depth

calculation) into each available variable for a new image window.

Link image windows using ether image pull down menus:

>tools>link>link display

Apply density colour slice to the ratio products using image pull down menu:

>tools>colour mapping>ENVI colour tables>rainbow

To contrast stretch this product using the image window pull down menus:

>enhance>interactive stretching

Establish interactively suitable minimum and maximum threshold values. From Interactive

Stretch Window:

>Options>histogram parameters insert optimum min and max>apply

To generate a masked product which can remove those pixels that complicate the information

from a desired end product (e.g. green vegetation from AlOH depth), main ENVI menu:

>basic tools>mask>mask build>display (the image to build the mask)

From the Mask Definition window:

>Options>Import data range>Band Min Value (XXX determined from Interactive

histogram threshold assessment). Save file to disk (label with *_mask)

From the main ENVI window:

>basic tools>mask>mask apply Insert both image file and mask file accordingly and save

file (labelled accordingly).

Can coherent and interpretable alteration zonation be recognised from these images. These will

be compared with the Hourglass products generated later on so keep a good file naming

convention for these images.

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Appendix 1: Alteration Mineralogy. Summary of assemblages of alteration minerals, commonly used terminology, and the environment of formation.

Most of the key minerals in this table are dealt with individually in the Atlas; some minerals have multiple entries

because their characteristics change in different environments (from Atlas of Alteration, Editors AJB Thompson and

JFH Thompson, Special Publication, Geological Association of Canada, 119 pages, 1996).

Mineral Assemblage (Key minerals are in bold)

Standard

Terminology

Environment of Formation

Intrusion-related

biotite (phlogopite), K-feldspar

(orthoclase), magnetite, quartz,

anhydrite, albite-sodic

plagioclase, actinolite, rutile,

apatite, sericite, chlorite, epidote

potassic (biotite-

rich), K-silicate,

biotitic

Generally found in the core of porphyry deposits,

particularly those hosted by more mafic intrusions

(diorite, monzonite, granodiorite), or mafic to

intermediate volcanic/volcaniclastic wallrocks. May

form a large peripheral alteration zone in wallrocks

(without K-feldspar) that zones out to propylitic

alteration.

K-feldspar (orthoclase or

microcline), quartz, albite,

muscovite, anhydrite, epidote

potassic, K-silicate Found in the core of porphyry systems, particularly

hosted by felsic intrusions (granodiorite – quartz

monzonite, granite, syenite).

albite (sodic plagioclase),

actinolite, clinopyroxene

(diopside), quartz, magnetite,

titanite, chlorite, epidote,

scapolite

sodic, sodic-calcic Occurs with minor mineralisation in the deeper

(peripheral in some cases) parts of some porphyry

systems and is a host to mineralization in porphyry

deposits associated with alkaline intrusions.

sericite (muscovite-illite),

quartz, pyrite, chlorite, hematite,

anhydrite

phyllic, sericitic Commonly forms a peripheral halo around the core

of porphyry deposits; it may overprint earlier

potassic alteration and may host substantial

mineralization.

sericite (illite-smectite),

chlorite, kaolinite (dickite),

montmorillonite, calcite,

epidote, pyrite

intermediate

argillic, sericite-

chlorite-clay

(SCC), argillic

Generally forms a structurally controlled to

widespread overprint on other types of alteration

(potassic) in many porphyry systems; precursor

textures are usually preserved. Argillic is often used

for texturally destructive alteration that has a similar

clay-rich mineralogy, and which occurs in and

around structures in the upper parts of porphyry

systems.

pyrophyllite, quartz, sericite,

andalusite, diaspore, corundum,

alunite, topaz, tourmaline,

dumortierite, pyrite, hematite

advanced argillic Intense alteration, often in the upper part of porphyry

systems, but also form envelopes around pyrite-rich

veins that cross-cut other alteration types.

topaz, muscovite, quartz,

tourmaline

greisen Localized high-temperature alteration associated

with peraluminous granites and related

mineralization.

garnet, clinopyroxene,

wollastonite, actinolite-

tremolite, vesuvianite, epidote

calcic skarn Generally forms replacement zones in wallrocks

(exoskarn – typically in limestone or occasionally

mafic to intermediate volcanic rocks), or within

intrusions (endoskarn). Andradite and diopside occur

in oxidized assemblages related to porphyry Cu

systems; grossular and hedenbergite are more

common in reduced skarns (Au, W, and Sn).

forsterite-diopside or

serpentinite-talc, calcite,

magnetite, tremolite

magnesium skarn Magnesium skarns are developed as metasomatic

replacements of dolomitic limestone. High-

temperature magnesium skarns are characterized by

forsterite and diopside and low-temperature

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magnesium skarns contain serpentinite and talc, both

of which occur as retrograde minerals after forsterite

and clinopyroxene.

calcite, chlorite, hematite, illite-

smectite, montmorillonite-

nontronite, pyrite

retrograde skarn Commonly replaces earlier skarn alteration but may

also affect adjacent wallrock – limestone.

chlorite, epidote, albite,

calcite, actinolite, sericite, clay,

pyrite

propylitic Commonly forms the outermost alteration zone at

intermediate to deep levels in porphyry systems. In

some systems, propylitic alteration is mineralogically

zoned from inner actinolite-rich to outer epidote-rich

alteration.

Intrusion-related – High-sulphidation Epithermal

quartz, rutile, alunite, native

sulphur, barite, hematite, pyrite,

jarosite

vuggy silica,

vuggy quartz

Typically occurs in structural zones or as

replacement bodies in permeable lithologies, usually

in the core of zones of advanced argillic alteration.

This extreme form of leaching can occur in the upper

parts of porphyry systems (telescoped) but is more

common at higher (epithermal) levels.

quartz, chalcedony, alunite,

barite, pyrite, hematite

silicic Represents the addition of silica to the rock, resulting

in replacement or, more commonly, the fill to vugs

created during intense leaching. Silicification is

common in high-sulphidation systems at porphyry to

epithermal depths. It is sometimes confused with

intense quartz stockwork veining at the top of some

porphyry deposits.

quartz, kaolinite/dickite,

alunite, diaspore, pyrophyllite,

rutile, zunyite, alumino

phosphate-sulphates, native

sulphur, pyrite, hematite

advanced argillic –

acid sulphate

Forms widespread zones in the upper parts of some

porphyry systems (lithocap); also as more restricted

alteration haloes around high-sulphidation

epithermal deposits.

kaolinite/dickite,

montmorillonite, illite-

smectite, quartz, pyrite

argillic,

intermediate

argillic

May be present as a zone of alteration between

advanced argillic and propylitic alteration,

particularly in the high-sulphidation epithermal

setting.

calcite, chlorite, epidote,

albite, sericite, clay, pyrite

propylitic May occur as an outer regionally extensive alteration

zone in systems at moderate depths (>500m).

Low-sulphidation Epithermal – Geothermal

quartz, chalcedony, opal, pyrite, hematite

silicic Pervasive replacement of the rock by silica minerals.

Occurs in some epithermal and geothermal systems

as wallrock alteration around fractures and veins or

within permeable zones, usually at relatively shallow

levels. Also forms blanket-like zones of replacement

at the water table below steam-heated advanced

argillic alteration. Stratiform replacement

silicification may be mistaken for sinter.

orthoclase (?adularia”),

quartz, sericite-illite, pyrite

adularia” Varies from wallrock alteration around veins,

fractures and permeable zones to selective

replacement of plagioclase in alteration envelopes.

Common at shallow to intermediate depths in

epithermal or geothermal systems; may be associated

with boiling. Pervasive replacement by “adularia” is

difficult to distinguish from silicification.

-sericite (muscovite), illite-

smectite, montmorillonite,

kaolinite, quartz, calcite,

sericitic, argillic Occurs as wallrock alteration around veins and

replacement zones in permeable lithologies. May

exhibit progression from sericite to mixed layer clays

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dolomite, pyrite with increasing distance from mineralized (upflow)

zones. Blanket-like carbonate-bearing alteration

zones in the upper part of some

geothermal/epithermal systems may reflect the

condensation of gases (CO2) from deeper boiling

zones. Carbonate may also be important in some

deeper base metal-rich systems.

kaolinite, alunite, cristobalite (opal, chalcedony), native

sulphur, jarosite, pyrite

advanced argillic –

acid-sulphate

Forms extensive areas of alteration above the water

(paleowater) table related to the condensation and

oxidation of gases (H2S). Associated with mud pools,

fumaroles and deposits of native sulphur.

quartz, calcite silica-carbonate Replacement of ultramafic rocks in the shallow parts

(low temperature) or geothermal systems.

calcite, epidote, wairakite, chlorite, albite, illite-smectite,

montmorillonite, pyrite

propylitic, zeolitic

alteration

Regionally extensive alteration around epithermal

and geothermal systems. Mineralogical changes from

zeolite-rich to propylitic assemblages reflect

increasing depth and temperature. The concentration

of CO2 also influences the stability of zeolites and

the relative importance of calcite versus epidote.

Mesothermal

calcite, ankerite, dolomite,

quartz, muscovite (Cr-/V-rich),

chlorite, pyrite, pyrrhotite

carbonate Wallrock alteration in and around veins or shear

zones, and extensive replacement of ultramafic to

mafic rocks. Carbonate-rich alteration may be

regionally extensive and is not always related to

mineralization.

chlorite, muscovite, quartz,

actinolite, pyrite, pyrrhotite

chloritic Wallrock alteration in and around veins and shear

zones, particularly in mafic volcanic and

volcaniclastic sedimentary rocks.

biotite, chlorite, quartz, pyrite,

pyrrhotite

biotitic Wallrock alteration in and around veins or shear

zones, particularly in sedimentary rocks.

Sediment-hosted gold

quartz, pyrite, hematite jasperoid Complete replacement of limestone, and

occasionally other rock types, by fine-grained quartz;

often associated with brecciation. Jasperoids can

form as regionally extensive zones, as small bodies

related to sediment-hosted Au deposits (‘Carlin-

type’), and as the upper or outer alteration zones

associated with intrusion-related skarn/sulphide

replacement bodies. Depth of formation is probably

moderate (>2km – ‘mesothermal’), although

shallower zones of jasperoid may form; fluids may

be metamorphogenic (classic mesothermal), connate,

or magmatic.

Volcanogenic massive sulphide

sericite, quartz, pyrite, chlorite,

andalusite, chloritoid

sericitic Pervasive replacement of rocks in the footwall below

massive sulphide lenses; concentrated in stockwork

feeder zones but may be laterally extensive both

deeper in the footwall and extending into the hanging

wall in some deposits. Most common in intermediate

to felsic volcanic rocks but may also replace the

more mafic units in lower temperature systems.

Andalusite and chloritoid occur in metamorphosed

alteration zones.

chlorite, quartz, sericite, pyrite, chloritic Pervasive replacement of rocks in the footwall below

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cordierite, biotite massive sulphide deposits. Fe-rich chlorite occurs in

the core of stockwork feeder zones in mafic footwall

sequences (e.g. Archaean deposits) whereas Mg-rich

chlorite has a more erratic distribution, generally

around the periphery or upper parts of stockwork

zones. Cordierite ± biotite is common in

metamorphosed Mg-Fe-rich alteration zones.

quartz, pyrite, sericite, K-

feldspar

silicic Pervasive replacement of rocks in the footwall below

massive sulphide deposits; particularly common in

permeable siliceous ash-rich beds, where the

silicified rock may be mistaken for cherts (chemical

sediments). Also occurs as wallrock alteration in

some quartz vein stockwork zones.

dolomite, siderite, ankerite,

calcite, quartz, sericite, chlorite,

pyrite

carbonate Usually occurs as disseminated alteration in footwall

sequences, commonly over extensive lateral and

stratigraphic intervals. The composition of

carbonates may change with distance from ore zones.

Sediment-hosted massive sulphide

quartz, muscovite, siderite,

dolomite, garnet, celsian,

pyrrhotite, pyrite, barite

silicic Pervasive replacement of footwall strata below

massive sulphide; also of baritic facies of the

sulphide body and less commonly in the hanging

wall. Well developed within calcareous strata but

more cryptic in siliciclastic strata. Can be mistaken

for siliceous shale or chert. Occurs as “garnet

quartzite” in high grade metamorphic rocks.

tourmaline, muscovite, quartz,

pyrrhotite

tourmalinite Pervasive replacement of footwall strata below

massive sulphide. Associated with abundant

disseminated sulphide in shallow footwall. Limited

to feldspathic strata.

ankerite, siderite, calcite,

quartz, muscovite, pyrrhotite

carbonate Disseminated carbonate, often as euhedral crystals,

in the shallow footwall below massive sulphide and

baritic facies. Disseminated ankerite/siderite can be

very extensive within calcareous strata along major

structures.

sericite, chlorite, quartz,

pyrrhotite, pyrite, albite

sericitic Pervasive replacement of strata in broad halo around

massive sulphide deposit; forms discordant bodies in

structurally controlled vent areas. Occurs as

potassium feldspar in high-grade metamorphic rocks.

Best developed in feldspathic strata.

albite, chlorite, muscovite, biotite

albitic Pervasive replacement of strata, and massive

sulphide; more typically along structures and around

mafic intrusions. Limited to feldspathic strata.

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Appendix 3: Selected USGS library mineral spectra

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