Indicator Mineral Morphology UBC Graduate Course Diamond - - PDF document

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Indicator Mineral Morphology UBC Graduate Course Diamond - - PDF document

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MCC Indicator Mineral Morphology UBC Graduate Course Diamond Exploration November 2013 Dr. Tom E. McCandless MCC Geoscience Inc. www.mccgeoscience.com

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  • MCC

Indicator Mineral Morphology

UBC Graduate Course – Diamond Exploration November 2013

  • Dr. Tom E. McCandless

MCC Geoscience Inc. www.mccgeoscience.com

www.mccgeoscience.com

MCC

(Four (Four-

  • Carat Diamond, Renard 65, Quebec)

Carat Diamond, Renard 65, Quebec)

Commercial diamonds do not form in Commercial diamonds do not form in kimberlite kimberlite -

  • they are xenocrysts in kimberlite.

they are xenocrysts in kimberlite.

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Most diamonds originate in mantle peridotite Most diamonds originate in mantle peridotite and eclogite and eclogite -

  • the parent rocks of diamond.

the parent rocks of diamond.

  • eclogite parent rock

eclogite parent rock

  • mphacite

pyrope-almandine

peridotite parent rock peridotite parent rock

pyrope forsterite

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  • D

Disruption – the diamond parent rock is removed

from its mantle stability field.

Disaggregation – the diamond parent rock (xenolith)

is physically broken apart and attacked by fluids in the igneous host rock (kimberlite)

Dissemination – diamonds, parent rock minerals

(indicators) and parent rock fragments (xenoliths) are physically mixed into the igneous host rock.

Dispersion – surviving indicator minerals are eroded

from the igneous host by weathering, and by alluvial, fluvial, glacial, and/or marine processes.

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50 100 150 200 250 depth, km

crust

kimberlite genesis graphite diamond

mantle

1 cm

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  • (after Hawthorne, 1975)

(after Hawthorne, 1975)

Present Present-

  • day surface of

day surface of Kimberley pipes and Kimberley pipes and sills. sills. Erosion of 1.4 km Erosion of 1.4 km

  • f kimberlitic material
  • f kimberlitic material

Mantle indicator minerals are Mantle indicator minerals are dispersed into the secondary dispersed into the secondary environment environment

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! " ! "

Quebec, Esker sampling Quebec, Esker sampling Botswana, Deflation surface Botswana, Deflation surface sampling sampling

Indicator mineral sampling Indicator mineral sampling accounted for over 80% accounted for over 80%

  • f kimberlite discoveries from
  • f kimberlite discoveries from

1872 1872 – – 1981 1981

Brazil, Stream sediment sampling Brazil, Stream sediment sampling

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Cr Cr-

  • diopside (CD)

diopside (CD) Cr Cr-

  • spinel (chromite

spinel (chromite)

""# ""#" "$ $

eclogite garnet (e eclogite garnet (e-

  • type)

type) peridotite garnet (p peridotite garnet (p-

  • type)

type) Mg Mg-

  • Cr ilmenite (

Cr ilmenite (picro picro) ) unique appearance, high specific gravity, limited magnetic unique appearance, high specific gravity, limited magnetic susceptibility, susceptibility, ubiquitous in the mantle ubiquitous in the mantle

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pressure, temperature pressure, temperature diamond cogenesis, diamond cogenesis, temperature temperature

""# ""#" "$ $

diamond cogenesis diamond cogenesis diamond preservation diamond preservation indicator minerals allow for prioritization of exploration indicator minerals allow for prioritization of exploration samples and igneous host rocks samples and igneous host rocks diamond cogenesis, diamond cogenesis, temperature temperature

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"" % "" %

Assessment of the shape and surface features of indicators that are developed in the primary primary and secondary secondary environments – primary primary environment – the mantle parent rock and the igneous host rock; secondary secondary environment – the near surface (marine) and surface of the earth; weathering – physical and chemical transport – alluvial, fluvial, glacial, and marine. – with the goal of establishing proximity to source.

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& %#'$ & %#'$

Primary Environment Primary Environment

Kelyphitic rim Kelyphitic rim – a mix of hydrous silicate and oxide minerals formed as a reaction product between the igneous host and the parent rock mineral. Sub Sub-

  • kelyphitic surface

kelyphitic surface – ‘orange peel’ texture on garnet developed beneath the kelyphite. Reaction surface Reaction surface – dendritic texture on garnet along planes in the garnet. Sculpturing Sculpturing – dissolution along crystallographic planes that produce systematic pyramidal features.

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& %#'$ & %#'$ & %#'$ & %#'$ & %#'$ & %#'$ & %#'$ & %#'$ Secondary Environment Secondary Environment

Weathering Weathering – (chemical) etching of the garnet surface. (physical) fracture due to stress release. Transport Transport – frosting, pitting, abrasion, conchoidal breaks. Both primary surfaces and secondary surfaces are modified in the secondary environment.

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! ()*+

  • physical search of libraries (no

physical search of libraries (no GeoRef GeoRef) )

  • gleaned from 181 public & private sources

gleaned from 181 public & private sources

  • 124 kimberlites, 15 countries

124 kimberlites, 15 countries

  • entered all mineral analyses to 1984:

entered all mineral analyses to 1984:

  • 4,002 garnets

4,002 garnets

  • 976 chrome

976 chrome diopsides diopsides

  • 949 chromites

949 chromites

  • 1,691

1,691 picroilmenites picroilmenites

  • 326 other mineral analyses

326 other mineral analyses

  • also 3,519 minerals from

also 3,519 minerals from ‘ ‘non non-

  • kimberlite

kimberlite’ ’

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! ()*+ A total of A total of 11,463 analyses collected, 11,463 analyses collected, all data entered by hand. all data entered by hand. Linked reference, kimberlite, Linked reference, kimberlite, mineralogy, occurrence, association mineralogy, occurrence, association

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,()*+

Mobil Oil buys out Superior Oil, dismantles the Superior Minerals Division. Data etc., were ‘discarded’

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()*+- )+).

(Supco Database)

10 20 30 40 50 60 70 80 2 4 6 8 10 12 14 16 18 20

MgO wt % Cr2O3 wt %

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  • /01//

!

10 20 30 40 50 60 70 80 2 4 6 8 10 12 14 16 18 20

MgO wt % Cr2O3 wt % kimberlites (n = 2017) kimberlites (n = 2017)

(Roeder Database; 1994)

groundmass groundmass (n = 291) (n = 291) xenoliths xenoliths (n = 409) (n = 409)

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2 #34/($

(Roedder database, 1994)

10 20 30 40 50 60 70 80 2 4 6 8 10 12 14 16 18 20

MgO wt % Cr2O3 wt % inclusions in olivine inclusions in olivine in basalts (n = 305) in basalts (n = 305)

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!!56

(Renard 3, Quebec) www.mccgeoscience.com

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!!5

1 2 3 4 5 6 7 8

0.001 0.001 0.01 0.01 0.1 0.1 1 1 10 10

grain size, mm grain size, mm

  • phiolites

layered ultramafics komatiites basalts

  • kimb. gmass
  • kimb. macrocrysts

mantle xenoliths

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% 7

(Renard 3, Quebec) www.mccgeoscience.com

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!%

(Renard 3, Quebec)

  • Know the regional geologic history of the AOI, including changes

Know the regional geologic history of the AOI, including changes in in stream direction, capture etc. stream direction, capture etc.

  • Sample the dominant clastic lithologies for indicators, and iden

Sample the dominant clastic lithologies for indicators, and identify tify contributions from contributions from paleo paleo-

  • deposits

deposits

  • Use associated non

Use associated non-

  • kimberlitic minerals as indicators of transport

kimberlitic minerals as indicators of transport when possible when possible

  • Document primary morphology on the indicators

Document primary morphology on the indicators

  • Document the morphology of known kimberlites and

Document the morphology of known kimberlites and lamproites lamproites in in the region the region

  • Check non

Check non-

  • geologic literature for human effects on mineral

geologic literature for human effects on mineral dispersion, e.g. ancient farming or modern road dispersion, e.g. ancient farming or modern road-

  • building

building

  • Characterize the sedimentary nature of

Characterize the sedimentary nature of paleo paleo-

  • sediments in the area

sediments in the area

  • Use regional garnets as monitors of

Use regional garnets as monitors of sedimentological sedimentological conditions conditions

  • Systematically classify each anomalous grain or grain population

Systematically classify each anomalous grain or grain population, , paying attention to size and other characteristics paying attention to size and other characteristics