Sub-Division of Kimberlites: Mineralogical and Textural

© 2012 Scott-Smith Petrology Inc.

Sub-Division of Kimberlites:Mineralogical and Textural

Barbara H. Scott Smith

• Mineralogical Classification• identifies different batches of magma

- mineralogy of a rock or a unit reflects composition of melt

• Textural Classification• identifies facies

- characteristics of a rock or a unit reflect the conditions of its origin, i.e. near surface final emplacement processes

Kimberlite Sub-Division

A B CMonticellite 58 41 11Phlogopite 2 29 23Calcite <1 0 25Serpentine 13 14 22Spinel 17 8 13Perovskite 9 6 4Apatite <1 2 2

Total 100 100 100

• Main Subdivision: most dominant groundmass mineral

• Further subdivision: other groundmass minerals which exceed 2/3 modal % of the dominant mineral

A: monticellite kimberliteB: phlogopite-

monticellite kimberliteC: serpentine-phlogopite-

calcite kimberlite

Kimberlite Mineralogical ClassificationModal Analyses Calculated on an Olivine-Free Basis

Skinner and Clement 1979


Kimberlite MagmasAscend to Surface as Separate Batches of Magma

• Mineralogical Classification• identifies different batches of magma

- mineralogy of a rock or a unit reflects composition of melt

• Textural Classification• identifies facies

- characteristics of a rock or a unit reflect the conditions of its origin, i.e. near surface final emplacement

Kimberlite Sub-Division

Kimberlite Textural-Genetic Classification

• Textures result from final emplacement processes

• Near surface kimberlite magmas comprise

Solids: xenoliths, macrocrysts, phenocrysts

Silicate melt: groundmass

Volatiles: CO2 and H2O

• Each behaves differently in contrasting processes


Pu’u ‘O’o, Hawaii 1986 Photo: USGS JD Griggs

Hypabyssal Kimberlite: 25% Mixed Grain Sizes of Olivine Macrocrysts (>1mm)

Schematic Olivine Macrocryst Distributions


Kimberlite Textural-Genetic ClassificationKimberlite Magma Texture

Coherent Magmaclastic

Magmaclasts Interclast MatrixUniform Groundmass

± Segregations of Fluid in Melt (FiM) Non-MagmaticMagmatic

ICK

KPK FPK RVK

Segregations ofMelt in Fluid (MiF)

DiscreteOlivines

Melt-bearingPyroclasts

Interpretation: Rock TypesCK ECK - Extrusive Coherent (mainly lava)

ICK - Intrusive Coherent (mainly HK)VK KPK - Kimberley-type Pyroclastic

FPK - Fort a la Corne-type Pyroclastic RVK - Resedimented Volcaniclastic after Scott Smith 2007

after Field and Scott Smith 1998

(Xenoliths)ECK

HKlava

KPK-type FPK-type

Coherent(replaces magmatic)

Fort a la Corne 175Finlay, Hardy Lake, Lac de Gras

Magmaclastic


Magmaclastic

Magmaclasts Interclast Matrix

Fort a la Corne 175 Slab FOV=13mm FalC 118 Thin section FOV=4mm FalC 169



FPKFOV=4mm FalC 152

HKFOV=10mm Finsch, RSA

KPKFOV=0.6mm Camsell Lake

RVKFOV=13mm Hardy Lake 02


Magmaclastic


Non-MagmaticMagmaticSegregations ofMelt in Fluid (MiF)


KPK-type FPK-type

DiscreteOlivines

DiscreteOlivines

FPKKPK RVKHK


Magmaclastic


Non-MagmaticMagmaticSegregations of Melt in Fluid (MiF)


KPK-type FPK-type





ICK

KPK FPK RVK


DiscreteOlivines






(Xenoliths)ECK

HKlava

KPK-type FPK-type


Kimberlites in CanadaTextural Classification

HK (only)• Snap Lake, NWT • Doyle Lake, NWT• MZ Lake, NWT• Wales Island, Nunavut• Cross, BC• Wemindji, Quebec

1: KPK (+HK)• Gahcho Kue, NWT • Camsell Lake, NWT• Renard, Quebec• Aviat, Nunavut• Qilalugaq, Nunavut

2: FPK• Sturgeon Lake, Saskatchewan • Fort a la Corne, Saskatchewan • Victor/Attawapiskat, Ontario• Candle Lake , Saskatchewan• Mountain Lake, Alberta • Buffalo Hills, Alberta• Birch Mountains, Alberta• Jericho, Nunavut• Knife Lake, Nunavut

3: RVK• Lac de Gras, NWT

TerminologyHK - Hypabyssal (intrusive)

(1) KPK - Kimberley-type PK(2) PK - Fort a la Corne-type PK (3) RVK - Resedimented

Volcaniclastic

Pipe Classes after Skinner and Marsh (2004)

Canadian Kimberlite Geology: OverviewBased on First Decade of Data

Updated 2003

HK

2: FPK 3: RVK 1: KPK 2: FPK2: FPK

Scott Smith 2006

FPK

KPKKPKHK

RVK

Volcaniclastic Kimberlites 1:Fort à la Corne-type

Pyroclastic Kimberlites (FPK)



Fort à la Corne, SaskatchewanType Area Fort a la Corne-type Pyroclastic Kimberlite - FPK

(A) (B) Emplacement Processes

(1) Crater excavation(2) Crater infill

(C) Diamond distribution

FPK

Scott Smith et al. 1996, 1998; Scott Smith 2008

FPK

= FPKkimberlite

magma

= PK

= VK

Fort à la Corne, SaskatchewanMagmaclastic Kimberlite

Thin section FOV=4mm FalC 169Slab FOV=13mm FalC 118

Fort à la Corne, SaskatchewanMagmaclasts = FPK-type Melt-Bearing Pyroclasts

TS FOV=4mm FalC 145

as above xN

TS FOV=4mm FalC 122

TS FOV=4mm FalC 152


Fort à la Corne, Saskatchewan What are the Magmaclasts?

• Evidence• Fluidal fragments of typical kimberlite magma• Smooth and often amoeboid shapes indicating surface tension

control (low viscosity as a few basalts and carbonatites)• Vesicles• Quenched to ‘glassy’ groundmass• Composite magmaclasts• Rare broken magmaclast• Adjacent examples of overall similar magmaclasts are different• (Different to KPK-type magmaclasts or melt segregations)

• Conclusions• extrusively formed fragments of fluidal magma, or• melt-bearing pyroclasts• liberated FPK-type melt-bearing pyroclasts

FalC 121

Fort à la Corne, SaskatchewanOlivine = Discrete Crystals

Fort à la Corne, SaskatchewanOlivine = Discrete Crystals

Slab FOV=13mm FalC 145


Fort à la Corne, SaskatchewanMagmaclasts = FPK-type Melt-Bearing Pyroclasts

TS FOV=4mm FalC 145

as above xN

TS FOV=4mm FalC 122

TS FOV=4mm FalC 152

Fort à la Corne, Saskatchewan What are the Discrete Grains?

• Evidence• associated with melt-bearing pyroclasts containing similar olivines,

garnets etc.• derived from same kimberlite-magma• some broken grains• sorted• clast supported textures

• Conclusions • crystal pyroclasts dominated by olivine • separated from fluidal magma (both melt and fluids) during eruption • pyrocrysts• subaerial liberated pyrocrysts

Fort à la Corne, SaskatchewanMode of Deposition

Note: deposition is within pipe below original surface

• Limited Options are • Primary pyroclastic (FPK)• Resedimented / Reworked (RVK)


Fort à la Corne Bedding

Fort à la Corne, SaskatchewanWind Winnowing of FPK

Slab FOV=6mm Body 145, Fort a la CornePu’u ‘O’o, Hawaii 1986 Photo: USGS JD Griggs

Fort à la Corne, SaskatchewanEmplacement Processes


Evidence

• Clast-supported textures

• Loosely packed textures

• Planar bedding, normal grading

• Megagraded beds, marker horizons

• Ballistic impact fragmentation and dropstone

• Lack of abrasion, breakage and fines

• Composite melt-bearing pyroclasts

• Clustering of xenolith type

• Phases of kimberlite representing batches of magma

Conclusion• primary pyroclastic fallout (column collapse)

Fort à la Corne, SaskatchewanMode of Deposition

Fort à la Corne, Saskatchewan Interclast Matrix: Carbonate Cement

• Contrasts with groundmass in melt-bearing pyroclasts

• Composed of carbonate, serpentine and some magnetite of magmatic origin

• Similar mineralogy to late-stage fluids of kimberlite magmas thus likely derived from kimberlite fluids

• Void infill crystallisation textures

• Pore space infilling by crystallisation of later kimberlitic fluids rising from vent through an uncemented pile of pyroclasts

• Rapid cementation indicated by lack of weathering

Fort à la Corne, Saskatchewan Interclast Matrix: Conclusions


Fort à la Corne, Saskatchewan-type PK (FPK) Summary of Textures (and Geology)

• 25% olivine macrocrysts• 25% olivine phenocrysts• 50% melt + fluids

Typical Erupting Kimberlite (= HK)

Snap Lake Sheets 80km W of Gahcho Kué

Melt-Bearing Pyroclast-dominated FPK


Fort à la Corne, SaskatchewanEmplacement Processes

Olivine Pyrocryst-dominated FPK

macrocrysts

phenocrysts

(ash from melt)

macrocrystic ol pyrocryst FPK

70-103 Ma.

FPK Summary


Volcaniclastic Kimberlites 2:Resedimented

Volcaniclastic Kimberlites (RVK)


Canadian Kimberlite Geology: OverviewField And Scott Smith (1999) Based On First Decade Of DataPipe Classes (1,2,3) From Skinner And Marsh (2004)

Updated 2003

HK


Scott Smith 2006

FPK

KPKKPKHK

RVK

Lac de gras, NWTMode of Deposition

Note: deposition is within pipe below original surface

• Limited Options are • Primary pyroclastic (FPK)• Resedimented / Reworked (RVK)

• major from crater rim/wall – shallow large bodies• minor within crater – unlikely to be detected


PK

Koala PK FOV=7mm

DO27 PK FOV=1.6mm xN

FPK

Lac de Gras Pipe Infill

Scott Smith 2006

RVK

Hardy Lake 2 FOV=12mm


Scott Smith 2006

Mudstone

Ekati


Scott Smith 2006


RVK

Hardy Lake 2

RVK


Scott Smith 2006

RVK

Hardy Lake 2

RVK


Scott Smith 2006

Panda Open Pit, Ekati

RVK


Scott Smith 2006


RVK


Scott Smith 2006

Moss and Russell 2006

FPK


Scott Smith 2006


Scott Smith 2006

After Nowicki et al. 2004 Dyck et al. 2004

McKinlay et al. 1998


RVKSummary

48-75 Ma.

After Nowicki et al. 2004 Dyck et al. 2004

McKinlay et al. 1998

macrocrystic ol pyrocryst FPK

kimberlite magma

Canadian Kimberlite GeologyEmplacement Summary: Graded Olivine Pyrocryst FPK

ol pyrocryst FPK

Canadian Kimberlite GeologyEmplacement Summary: Olivine Pyrocryst FPK


ol pyrocryst FPK

country rock (shale)

FPK

RVKRVK

Canadian Kimberlite GeologyEmplacement Summary: RVK

Kimberlite Textural-Genetic ClassificationStage 3a: Step 1 - Kimberlite Magma Texture




ICK

KPK FPK RVK


DiscreteOlivines






(Xenoliths)ECK

HKlava

KPK-type FPK-type

Canadian Kimberlite Geology: OverviewField And Scott Smith (1999) Based On First Decade Of DataPipe Classes (1,2,3) From Skinner And Marsh (2004)

Updated 2003

HK


Scott Smith 2006

FPK

KPKKPKHK

RVK


Canadian Kimberlite GeologySummary of Textures

Scott Smith 2008

Canadian Kimberlite GeologySummary Based on Second Decade of Data

Kimberlite Terminology and ClassificationSystematic Framework: Description, Classification, Interpretation


Kimberlite Terminology and ClassificationExample Rocks Illustrating the Application of The Scheme

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Sub-Division of Kimberlites: Mineralogical and Textural

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