4 Qz Pods Presentation 2004

7/30/2019 4 Qz Pods Presentation 2004

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QuartzQuartz PodsPods--AnAn ExplorationExploration GuideGuide toto IronIron

OxideOxide--CopperCopper--GoldGoldMineralisationMineralisation??

Prepared by:Prepared by:

Alberto LoboAlberto Lobo--Guerrero S.Guerrero S.

GeologistGeologist,, M.ScM.Sc.,., MinExMinEx

EconomicEconomic GeologyGeology ResearchResearch InstituteInstitute

UniversityUniversity ofofthethe WitwatersrandWitwatersrand

J ohannesburgJ ohannesburg,, SeptemberSeptember, 2004, 2004


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Quartz Pods - Exploration Guide to IOCG?

Contents

1. Description2. Environment and Extension

3. QP and Mineralization

4. Studies to be Done5. Practical Applications

6. Hypothesis on Origin


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-Goats-

common sight

during field work

in arid regions


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Goats with testicles

hanging from their neck


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That man is crazy!

Hes definitely nuts!


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Ive seen them.


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Now youve seen themtoo.

I discovered they are associatedto specific mineral enrichment in soils.

Mapping goats appendiceshelps explore for mineral deposits

Its a bitof animal geochemistry

Quartz pods are another strange feature that I noticed during

field work for doctoral research in Zambia & Namibia.


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Quartz pods = particular feature identifiedin most of Lufilian Arc study region

quartz pod= informal namefor massive or sugary QP of varying dimensions

Features differ fromvein qtz & pegmatitic qz bodies

most different = geometry

shape appears roughly cylindricaloutcrops of undeformed bodies = round to ellipticaldiameter varies fromfew to several hundred meters

some mapped bodies exceed 4 kmgeophysical evidence of even larger bodies

Quartz Pods 1


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Quartz Pods 2

Occur near intrusive bodies (at times just small apophysis)around iron oxide-copper-gold (IOCG) mineralized systems

Mostpods made of white qz, but color may vary greatlyExamples show changefrommilky white to dark gray smokey tonesand to light pink or yellow tints

colors probablydue to:abundant gassalt

micro-inclusions of:Fe oxideSulfides


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Quartz Pods 3

Both translucent + milky qz varieties occur togetherDifferent portions of single body

may be saccaroidal and/or massive

QP seldommapped in published geological maps

Field identification& particularphysico-chemicalfeaturesmay aid inexploration

of IOCG mnzn 1km


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QP surface expression E Solwesi, Zambia.Areal extension = few hundred m diameter

3.5 m


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Typical QP outcrop in Zambia.

Areal extension = 200 meters diameter


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Typical QP outcrop in Zambia.

Areal extension = 200 meters diameter

QP Outcrop

Host rock

= Katangan

carbonates


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Surface expression of very large QP.

Way to Oas farm, Khorixas inlier, Namibia.

Ground exclusively made of quartz.

Suface extends for tens of km.


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Interpreted airborne magnetometry + radiometrics, east of Kitwe, Zambia.

Expression of

quartz pods

10 km


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QP Environment and ExtensionQP Environment and Extension

QP = particular characteristicof Lufilian Arc

-may be related to rift environments-occur in many rk types:ls, dol, gtds,various schists & gneisses

NAMIBIA

ZAMBIA

500 km

NQP


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Quartz podoutcrop

500 km

QP outcrops in the Greater Lufilian Arc, Africa


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QP Environment and ExtensionQP Environment and Extension

NAMIBIA

ZAMBIA

500 km

N

QP occur in an extense regionroughly 2000 kmby 300 km

QP expected to be found in:SE Angola, Katanga provinceD.R. Congo, NW Botswana

QP


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500 km

IOCG deposits and prospects in the Greater Lufilian Arc, Africa


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Sometimes country rock is deformed upward around QPin a fashion similar to diapirs

-differential compaction?-disolution?

Some published geological sheets map QP

fewreferences describe QP

Maybe theywere consideredto be just qz veins of minor importance

QP


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Four Rock Association

Four-fold rk association observed in many parts of Lufilian Arcmade up by small bodies of:-massive Fe oxide bodies (mag and/or hem)

-red-tinted felsic intrusive rocks-gabbro or diorite-qz pods

1km


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Four Rock Association

Association seems to occur in rift environmentsTheir origin is not yet completely understood

Explaining ubiquitous presence of these 4 rk types

-ideas for origin ofLufilian Arc IOCG

mineralization

-more importantly,clues for

mineralisationelsewhere

1km


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QP and Mineralisation

QP host IOCG mnzn in many locations

At times QP actas brittle rocks

to hold massive mag and/or specular hemmnznw/ accompanying sulfs


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B

A

Braided veinsw/ hem+ oxidized sulfides

hosted by QP

Several fracture generationsintersecteach other

A = outcrop surfaceB = slabbed surface

FromOas farmKhorixas inlier, Nm


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Particles Enclosed in QP

On some locations, large QP containisolated spherical FeOx (hemand/or mag) inclusions

from10 cmto 1.5 cm.

Also perfect cubic FeOx crystalsxenoliths of any rk typealso included within QP


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Brittle character of qz allows it to hostbraided or sub-parallelsheeted veinletsystems filled by hem+sulfs.

Numerous field examples:

braided veinsstockworksvarious breccias

qz is both host rk& single clast componentin Tevrede, NW Namibia

rich Cu+Au IOCG prospect

QP and IOCG 1

Sheeted FeOx veins in QP

Hydrothermal bx from Tevrede, Nm


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Dense network of mag-py-cp veinlets in QP

outcrop at least150m


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Portion of cp-py rich,mag-filled stockwork in QP


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Slab of Cu sulf-rich, mag stwkhosted in QP

Brown stains = hemafter py


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Surface expressionof bo-cp-mag enrichedstwk in QP.Secondary Cu sulfs (bk)

Cu carbs (gn-bl)


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Slab of mineralised QP.Massive hem+minor py

overprintqz


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QP and IOCG 2Large QP, NE of Otjiwarongo, Namibiain environs of Otjikoto Au deposit

500m and over 350m deepcontains minor diss py & mag cubes

associated to Otjiwarongo batholith

KombatCu minealso related to batholith

Both = IOCG deposits

Quartz Pod

Fig 2650 km


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QP investigations might help to guideIOCG field exploration in southern Africa

detailed macroscopic analysisradioactivity & fluorescence, various wavelengthscathodoluminiscence studies

detailedspecific gravitychemical analysis (halogens, REE)

H & O isotopesFluid inclusions: salinity & emplacement T

3-D geometry of a fewsites using geophysical techniques

QP Studies to be done


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QP are related with Fe oxide-Cu-Au mineralized systems.

May be major breakthrough in mineral exploration

If QP detailed chemical signature

from mnzd IOCG systems is characteristic

= new exploration tool

Abundant white qz float in circular area= detected easilyon arid regions

QP outcrops offer good color contrast w/ country rockB/W air photos may help in location

large outcrop areas identifiable in ASTER images

Practical Applications of QP


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1) type of silicification alteration, notwell documented

2) hyper-alkaline fluids, disolve SiO2 & produce QP space problem

3) HF-rich extremelyalkaline fluids disolve SiO2replacing itby Fe oxidesSiO2 migrates further out & precipitates QP

space problemHow to detect F in qz?

4) Intrusiveevidence of some QP

Could QP be a qtz-only magma? (Quartzolites?)

Hypotheses About QP Origin

PregnantIOCG intrusive

body

Silica transported

by alkaline fluidFeOx

Silica

displaced

by FeOx

Silica deposited

as Quartz Pod


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Call to Other Geologists

Call attention of researcherswho might have come acrosssimilar QP

in other parts of the world

The author welcomes comments

& contributions to solve questions


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Now youve seen the quartz pods too.

C


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1. QP = massive/sugary qz body

roughly cylindrical in shape

round to elliptical outcropdiameter = few to 100s meterssome >4 square km

2. occur on or around IOCG

3. probably related to

hyperalkaline, F-rich hydrothermal fluids

4. may be new exploration tool

for IOCG mineralization

Conclusions


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QuartzQuartz PodsPods--AnAn ExplorationExploration GuideGuide toto IronIron

OxideOxide--CopperCopper--GoldGoldMineralisationMineralisation??

Prepared by:Prepared by:

Alberto LoboAlberto Lobo--Guerrero S.Guerrero S.

GeologistGeologist,, M.ScM.Sc.,., MinExMinEx

EconomicEconomic GeologyGeology ResearchResearch InstituteInstitute

UniversityUniversity ofofthethe WitwatersrandWitwatersrand

J ohannesburgJ ohannesburg,, SeptemberSeptember, 2004, 2004


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IOCG = recently-identified type of ore deposits

in zones of extensional tectonicsmainly along past rift zones or aulacogenssituated along major structural zones

Most related to anorogenicintrusive rocksNo direct relationship w/ intrusive rocks

-in small deposits-distalportions of mineralized systems

Mineralized deposits containFe oxide nucleus (mag and/or hem)replaced by py and cpy

IRON OXIDE-COPPER-GOLD MINERAL DEPOSITS


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Simplified Geological Map

Salobo Deposit, Brazil

From Requia et al, 2000

500 m

N

Ve ryalte redtyp eof minera lizationMediumaltered typeof minera lization

Very altered typeof mineralization

Medium altered type

of mineralization


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Mag might have been demagnetizedinto martite and/or hem

and later, part or all of the FeOx replaced by sulphides

May contain economic Au & light rare earth elements(LREE)

U content might be significantother metals may be economic: Ag, Co, Mn

Cu mnzn seems related to meteoric fluids & redoxreactions on/around FeOx

LREEs may be associated with apatite

IOCG MINERAL DEPOSITS, 2

Th K U Au Cu Ag F


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SimplifiedGeochemical Log

drill hole ALM-FD09

Alemao Deposit

Carajas, Brazil

From Ronze et al, 2000

FeOx (stars)

acts as nucleus for

Cu, Au, Ag, U, F

mineralization

Th K U Au Cu Ag F


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Uncertain issues:-origin of Au + LREEs

-causes ofhydrothermal alterationsilicate dissolutionmetal transportation

Source of halogens for highly alkaline and/or F-richsolutions

-evaporites formed in sabkha, playa or saltlake environments-basinal brines and/or mixing with sea water



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IOCG MINERAL DEPOSITS, ALTERATION

Zoned hydrothermal altn in mostmineralized IOCG depsAltn patterns depend on depth of emplacement & host rk chem

Gral alteration (shallow to deep): -albitization-scapolitization-K-alteration-sericitization

-silicification

Widespread massive hematitization, so-called red-rockaltnLarge-scale Na altn around mnzd rocks

Textural replacements of rock constituents are common

Alkaline and/or F-rich fluids seemto play important role inhydrothermal altn, metal transportation & silicate disolution.


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Common textural replacements of rock constituents

General order of hydrothermal altn/mnzn:

Country rock albitizationHigh T FeKCa altn

(Biot-garnet-Kfelds-amphybolite-cpx-mag)Mnzn+low T altn

(sulphsmaghem-carbser/chl) w/ CuAu

Explosive bxn in most known depositsMultiple explosive fragmentation in largest orebodies



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Geometry of mineralized bodies varies substantially

-Commonest deposits are veins-Some are massive replacements that grade

into stockworks

-Bx pipes or diatremes-Tabular bodies that run concordant w/ rock

foliation or stratification

Composite deposits comprising veins, bxs,stockworked zones & replacement mantosare common.


Major IOCG Deposits (from Pollard, 2000)


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j p ( , )

Major South American Deposits

4 Qz Pods Presentation 2004

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