Robert Linnen, Department of Earth Sciences, University of Western Ontario

Metallogeny of Lithium Pegmatites

Acknowledgements: Laurisha Bynoe, Paul Kremer, Marieke Van LichterveldeDon Burt, Don Davis, Carey Galeschuk, David London, Gary Pearse, David Trueman

TANCO Tantalum Mining Corporation of Canada, Ltd.

Structure of the Talk

Review of Pegmatite Types and Classification Structural Controls of Pegmatite Emplacement

(focus on Tanco and Whabouchi) Exploration for Pegmatites, Traditional and

Novel Techniques

Pegmatite Classification

after Cerny (1991) in Simmons and Weber (2008)

Greenbushes, Quebec Lithium

Tanco (squi), Big Whopper

Wodgina

Whabouchi, Mt. Cassiterite, Kings Mtn

petalite – LiAlSi4O10

spodumene – LiAlSi2O6

squi: spod-qtz intergrowthPet = Spod + 2 Qtz

Spodumene Indicates Higher Pressure or Undercooling

from Linnen et al. (2012) after London (2005)

Multiple Commodities versus Single Commodities

Greenbushes PegmatiteCentral Lode Stage 1 at 11150 mNfrom Freeman and Donaldson (2004)

Long Section of the Tanco pegmatite

Černý et al., 1996

Lithium Pegmatites Have Extreme CompositionsWhat Processes Control this?

Granite pegmatites have granite compositions and are controlled by magmatic processes

London (2008)

London (2008) after Stewart (1978)

1.85% Li2O at eutectic

An Anatectic Origin?

Extreme Fractional Crystallization

from Breaks et al. (2005)

PeraluminousSedimentary sourceLi-Rb-Cs-F in micasBe in cordierite, muscoviteTa-Nb-Sn in Ti minerals

Separation Rapids Plutonfrom Breaks et al. (2005)

Extreme Fractional Crystallization

from Breaks et al. (2005)

Located at Margins of Major Subprovinces

also located at the boundary between major tectonic Sub-Provinces

Whabouchi Pegmatite

Houle (2003)

Greenbushes pegmatite Western Australia

Pegmatite-Shear Association

after Partington (1990)

after Duguet (2007)

Bernic Lake Pegmatite Group

• Tanco pegmatite

– Tabular, shallowly-dipping

– Hosted in prominent fracture set

– Rheologically competent lithologies

• Oompa Loompa

– Folded and/or boudinaged

– Hosted in highly deformed metavolcanics/volcaniclastics

Fracture-hosted, tabular

pegmatite, Tanco mine

Folded pegmatite, Bernic Lake

Pegmatite Emplacement Styles

from Kramer (2009)

Tanco2640 ± 7 Ma

Oompa Loompa2647 ± 2 Ma

• Doubly-dipping body

• Hosted in metagabbro

• Occurs in conjugate fracture set

Fracture-hosted tabular pegmatite at Tanco

Conjugate fracture set in gabbro at Tanco

From Stilling, 1995

From Kremer, 2009

From Kremer, 2009

Tanco Pegmatite

from Kramer (2009)

Model for the Emplacement of the Tanco Pegmatite

from Kremer (2009)

WhabouchiPegmatite

from Nemaska 2009 NI 43-101 report

(after Hocq, 1994)

Measured and Indicated Resource

of 27.99 Mt of 1.57% Li2O

(0.43 % Li2O cutoff)Nemaska Lithium

Inc. (2016)

WhabouchiGeology

from Bynoe (2014)

Granite monazite 2649 ±10 MaGranite zircon age

2704 ±8.6 Ma

Whabouchi zircon age 2577 ±13 Ma

Pegmatite zircon age 2594 ±11 Ma

Pegmatite monaziteage 2621 ±9.5 Ma

Pegmatite zircon 2530 ±14 monazite 2578 ±14 Ma

Pegmatite monazite 2584 ±7 to 2579 ±8 Ma

from Bynoe (2014) and unpublished data

Metabasites at Whabouchi

Distal to the pegmatite Turbulent shear zone with smeared leucocratic component

from Bynoe (2014)

Structural Analysis

Crosscutting relationship between the pegmatite and host rocks showing evidence of dextral sense of shear

Crosscutting relationship between the pegmatite and host rocks showing emplacement of the Li pegmatite after the onset of deformation

from Bynoe (2014)

Metabasite interpreted to be the preferred host and

shearing controlled pegmatite emplacement

from Bynoe (2014)

Whabouchi Pegmatite Emplacement

London (2008), after Cerny (1990)

Emplacement in Pegmatite Fields

London (2008), after Cerny (1990)

from Černý (1989)

Emplacement in Pegmatite Fields

Exploration - Prospecting

Whabouchi Pegmatite

Lithogeochemistry

from Fetherston, 2004

Lithogeochemistryat Whabouchi

from Bynoe (2014)

Recent Drilling

Nemaska press release (2016)

from Morgan & London (1987)

Most Indicator

Mineral Studies Have

Concentrated on

Pegmatite Minerals

Wallrock Minerals

Have Received Much

Less Attention

Rb in Biotite Around Tanco

from Galeschuk and Vanstone (2005)

Indicator Mineral Study of the Dibs Pegmatite

The Dibs pegmatite is completely buried, at a depth of ~ 70m

Found by lithogeochemistry, but Tanco had many false positives from lithogeochemistry

Lithogeochemistry from Drill Holes(Classic elements)

- Mobility of Li>Rb>Cs, similar to previous studies

- Note enrichment at the bottom

- Top of whole ~ 30 ppm Li (2x threshold), ~15 ppm Rb

& 5 ppm Cs (both values near threshold)

Cs anomaly

Linnen et al (2009)

Metabasite Mineral Chemistry

Linnen et al (2009)

Fracture Geochemistry

Late syn-kinematic

Amphibole±Plag±ZoisiteChlorite-Carbonate-Titanite

±Zoisite ±Amphibole

Late syn- to post-kinematic

Linnen et al (2009)

Chlorite

Note scale for Li, 100’s of ppm distal to pegmatite

Linnen et al (2009)

Summary of Li data (distal to pegmatite - 60m)

Whole-rock: 30 ppm Li

Fracture chlorite: 200 to 400 ppm Li

-Fracture chlorite may explain false-positive lithogeochemical anomalies- By contrast fracture chlorite shows promise as an exploration tool

Thank you