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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
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Felix Ng
Content
• Rationale
• Location and Setting
• Methodology
• Results
• Integration and Interpretation
• Implications and Recommendations
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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.
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Geochemical Dispersion Mechanisms
? ?
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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
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VMS in the Sicker Group
Ice Flow Indicators
Direction known
Direction unknown
Blyth and Rutter (1993)
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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)
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Lara VMS - Geology
(Photo: Barry Smee)Exposure of Pyrite Stringer Zone Lara Discovery Trench
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Methodology• Upper B horizon soil (n=150)
• Aqua regia digestion, ICP-MS (-180 μm)
Py-CpyZone
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Zinc
B horizon, aqua regia, -180 μm Robust linear regression
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Copper
B horizon, aqua regia, -180 μm Robust linear regression
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Cadmium
B horizon, aqua regia, -180 μm
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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
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ResidenceSequential Extraction
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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)
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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
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Geochemical Dispersion Vectors
• Establish clastic and hydromorphic geochemical dispersion pathways
Lara Adit
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ICE FLOW
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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
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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
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Thank-You
Chris BennConsulting
Smee & AssociatesConsulting Ltd.
Colin DunnConsulting
Landscape Integration of archived data:B Horizon soil geochemistry completed in1979,Aqua Regia, -180 μm
Contact: