Mapping and Modeling Geochemical Dispersion Above a Till Concealed Polymetallic VMS Deposit

Bodnar, M.M and Winterburn, P.A.IAGS 28 / RFG, Vancouver, 21 June 2018

EGI

Felix Ng

Content

• Rationale

• Location and Setting

• Methodology

• Results

• Integration and Interpretation

• Implications and Recommendations

The Reality – the future is under cover

• ~75% of the glaciated Canadian landscape is covered by quaternary sediments representing a challenge to discovery

• Enhanced methods in exploration geochemistry, capable of detecting mineral deposits through complex cover, must be developed to satisfy global resource demands.

Geochemical Dispersion Mechanisms

? ?

Concealed Deposit - Lara VMS

• Polymetallic massive sulphide

• Well defined by drilling

• Widespread glacial sediment cover

• Minimal anthropogenic disturbance (undeveloped)

• Heavily forested by mature 2nd growth

VMS in the Sicker Group

Ice Flow Indicators

Direction known

Direction unknown

Blyth and Rutter (1993)

Lara VMS - Geology

Py – Cpy stringer zone

Andesite

Rhyolite

Rhyolite

Sandstone

Andesite

(Co, Se, Bi and Te) (As, Sb, Cd, Se, In, Mo, Hg and Ga)

Lara VMS - Geology

(Photo: Barry Smee)Exposure of Pyrite Stringer Zone Lara Discovery Trench

Methodology• Upper B horizon soil (n=150)

• Aqua regia digestion, ICP-MS (-180 μm)

Py-CpyZone

Zinc

B horizon, aqua regia, -180 μm Robust linear regression

Copper

B horizon, aqua regia, -180 μm Robust linear regression

Cadmium

B horizon, aqua regia, -180 μm

Residence - Sequential Extraction

Sequence

DIWAmmonium

Acetate

Cold 0.1M

HA-HC

Hot 0.25M

HA-HC

Na Pyro-

phosphateAqua Regia 4-Acid

Clastic signatureHydromorphic signatureOrganic matter

ResidenceSequential Extraction

High Zn residual

B horizon, 2 - 6.3 mm fraction, Kappameter KT-10

High Zn residual

(>55 ppm)

(>38 ppm)

(>22 ppm)

(>5.3 ppm)

Landscape and Surficial Material IntegrationTb

Tb

Tb

Cv

Cv

Cv

Cv

Cv

Cv

CzAv

GFb

Av

GFb

Tb

GFv GFv

GFb

Tv

Tv

Steep slope

Geochemical Dispersion Vectors

• Establish clastic and hydromorphic geochemical dispersion pathways

Lara Adit

ICE FLOW

Summary of Geochemical ResponsesPyrite Horizon Stringer Zone• Thin cover • strong response of Zn, Cu,

Cd, Mo, Se, Hg, Te• clastic dispersion of bedrock

Lara VMS • Thick cover• strong response of Zn• clastic dispersion of exotic

mafic rock, not VMS

Alluvial Basin • displaced clastic

signature due to erosion and redisposition of till

• Zn and Cu response from primary minerals in till

• More labile elements collect in alluvial basins (Cd, etc.)

• No evidence of metal migration from VMS

Mineral Exploration Strategy

Surficial material and landscape mapping is strongly recommended to be completed as an integrated component of:

• Sampling survey design

• Geochemical data interpretation

• Drill target selection

When exploring in recently glaciated terrain,

must ESTABLISH:

• Pathways of paraglacial and modern erosion / re-deposition

• Pathways of surface runoff drainage

• Characterization of bedrock units using same digestion and analysis as soil program

Acquire Lidar or HR-DEM as EARLY as possible!

Rhyolite

Andesite

Gabbro(altered)

Gabbro(fresh)

Till A (early)

Over Lara

High Zn Residuals

Surficial Material

Over pyrite

Till D (late)AlluviumColluvium

Ga (ppm) - aqua regia

Cr

(ppm

) -

aqua r

egia

Thank-You

Chris BennConsulting

Smee & AssociatesConsulting Ltd.

Colin DunnConsulting

Landscape Integration of archived data:B Horizon soil geochemistry completed in1979,Aqua Regia, -180 μm

Matthew.Bodnar@csaglobal.com

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