Regional basement to the Flin Flin Flon Flon arc and Burntwood ...

Regional basement to the Flin
Flon arc and Burntwood
Group: A progress report
Joe Whalen, Bill Davis, Nicole Rayner
John Percival and Herman Zwanzig

• Why:
– characterizing crust that FFB formed on/or proximal to is
directly relevant to tectonic-metallogenic models which in
turn impact on VMS exploration.
– a low cost subcomponent with potential for providing
valuable input toward achieving TGI3 objectives.

Why:
– characterizing crust that FFB formed on/or proximal to is
directly relevant to tectonic-metallogenic models which in
turn impact on VMS exploration.
– a low cost subcomponent with potential for providing
valuable input toward achieving TGI3 objectives.
How?
1. utilize NATMAP legacy datasets especially Nd isotopes
and geochemistry
2. evaluate additional tools, such as Pb isotopes and U-Pb
zircon SHRIMP inheritance ‘fingerprints’
3. possibly some field work on known or potential
basement rocks (e.g. ca. 1910 Mystic Lake ‘evolved arc’
plutonic rocks near Flin Flon)

Progress?
1. Assemble Shield Margin NATMAP
legacy datasets?
- expected to be an easy task

But……no Nd isotopic data.

Action:
1. Located an archived preliminary version of a Nd
compilation begun by Richard Stern and myself
2. Obtained assistance and input from:
a. various former NATMAP participants (R. Stern, K.
Ashton, B. Simmons) helped fill ‘data holes’
b. published (Stern et al., various) Nd isotopic data
c. NATMAP CD geochemical data
3. Assembled an integrated GIS compatible Nd-isotopic –
geochemical flatfile for NATMAP legacy data

TGI3: Nd Isotopic-Geochemical Compilation
of Shield Margin NATMAP Data
GSC (+MGS, SIR?) Digital Open File (in prep. 2007 release)
Authors: J.B. Whalen, R.A. Stern, N. Rayner,
MGS and SEM contributors
• GIS compatible spreadsheet format
• contains 182 Nd isotopic analyses
• 91 Nd analyses represent previously unpublished data
collected by the senior authors.
• most geochemistry previously released on NATMAP CD
but not previously integrated with Nd isotopic data
• @ $625 sample, represents >90K of Nd isotopic data

FEATURES:
1. Volcanic samples mainly
from 3 areas – Flin Flon,
Elbow Lk & Snow Lk….how
representative are they???
2. Data from SK is very scarce
3. Sedimentary rock analyses
also scarce
Box includes 21
post-NATMAP
samples

FEATURES OF

Why employ Pb as an addition isotopic tool?:
• more sensitive than Nd to detecting involvement of
older crustal components
• initial Pb isotopic compositions obtained from Pb-
bearing but ‘U-free’ minerals such as galena and K-
feldspar

Why Pb as an addition isotopic tool?:
• more sensitive than Nd to detecting involvement of
older crustal components
• initial Pb isotopic compositions obtainabled from Pb-
bearing but ‘U-free’ minerals such as galena and K-
feldspar
Progress:
• Organized collaborative work with Bill Davis and
Doreen Ames
• Assembled existing sulphide and feldspar Pb isotopic
datasets

FEATURES:
1. Enough existing Pb data to evaluate usefulness to FFB
2. All 3 data sets exhibit similar dispersion trends
3. Steeply increasing 207/204 relative to 206/204 best
explained as mixing between at least 2 components

Why Pb as an addition isotopic tool?:
• more sensitive than Nd to detecting involvement of
older crustal components
• initial Pb isotopic compositions obtainable from Pb-
bearing but ‘U-free’ minerals such as galena and K-
feldspar
Progress:
• Organized collaborative work with Bill Davis and
Doreen Ames
• Assembled existing sulphide and feldspar Pb isotopic
datasets
Conclusions:
• Preliminary evaluation suggests mixing between old
(2.7-3.0 Ga) upper crustal- and mantle-derived Pb.
• Whether the old Pb component is from subducted
sediment or arc basement, Pb isotopes argue for FFB
formation proximal to a continental margin

50 Ma
Another Tool For Basement Characterization
HR-SIMS/SHRIMP (U-Pb)
In situ micro-
sampling by
charged O or Ce
beam
1.8 Ga
1. Unpublished (Stern & Machado)
data from Gants Lk batholith found
ca. 2.6 Ma zircon inheritance
2. More recent work on 3 pre-1.87 Ga
FFB pluton samples by N. Rayner
yielded no evidence for
significantly older zircon
inheritance