Carbonatites and Alkaline Rocks in the Southern Canadian Cordillera by Dr. Leo J. Millonig, Axel Gerdes and Dr. Lee A. Grout:

1. CARBONATITES AND ALKALINE ROCKS IN THE
SOUTHERN CANADIAN CORDILLERA
Leo J. Millonig1*, Axel Gerdes2, Lee A. Groat1
1. DEPARTMENT OF EARTH AND OCEAN SCIENCES, UNIVERSITY OF BRITISH COLUMBIA, 6339 STORES ROAD,
VANCOUVER, BC, CANADA, V6T 1Z4 [*CORRESPONDENCE: LMILLONIG@EOS.UBC.CA]
2. INSTITUT FUER GEOWISSENSCHAFTEN, ALTENHOEFERALLEE 1, D-60438 FRANKFURT AM MAIN, GERMANY
SCOPE AND GEOLOGICAL SETTING
In British Columbia (B.C.) carbonatites, nepheline and sodalite syenite gneisses and related alkaline rocks are found in a zone which is parallel to,
and on either side of the Rocky Mountain Trench. From the 14 known carbonatite occurrences in B.C. (Fig. 1) 7 have been dated with reported
intrusion ages between 356 Ma (Ice River Complex) and 202 Ma (Howard Creek). Associated syenite complexes are either ~coeval (Trident Moun-
tain) or significantly older (Mount Copeland Syenite). However, most of the intrusion ages cluster around Mississippian time. Subsequently all
carbonatites and alkaline rocks were affected by (multiple?) greenschist to amphibolitefacies metamorphism. The scope of this study is to provide
reliable age data through LA-ICP-MS U-Pb age dating of zircons of previously undated and/or unknown carbonatites and accompanying alkaline
rocks in British Columbia in order to better understand the mineralogical and chemical differences between the individual magmatic bodies and the
geodynamic setting during their emplacement. 10 carbonatite, 2 mafic and 4 syenite samples are currently being processed in this study.
FIG. 1:
a) Carbonatites (black) and
associated alkaline rocks (blue)
in B.C. with their interpreted
intrusion ages (modified after
Woolley & Kjarsgaard, 2008).
b) Distribution of miogeoclinal
sediments in B.C. in which the
carbonatite and alkaline rocks
intruded (Lund et al., 2010).
How old are the undated carbonatites/alkaline rocks?
Is the spread in interpreted intrusion ages (202-356 Ma) real?
GEODYNAMIC BACKGROUND
• Miogeoclinal sediments of the Windermere Supergroup were deposited during the
initial break-up of Rodinia in the Neoproterozoic at <750 Ma (Fig. 2).
• Final separation of Siberia and Laurentia occurred during the Early Cambrian at
~540 Ma and during the Middle Devonian the passive continental margin of western
Laurentia became an active margin (Fig. 3).
• Extensional tectonics in the Early Carboniferous lead to back-arc basin formation at
~355-320 Ma (Fig. 3).
FIG. 2: The Windermere Supergroup FIG. 3: Geodynamic evolution of the western margin of Laurentia during Early
(Nelson & Colpron, 2007). Paleozoic to Permian time (modified after Monger, 2008).

2. CARBONATITES AND ALKALINE ROCKS IN THE
SOUTHERN CANADIAN CORDILLERA
Leo J. Millonig1*, Axel Gerdes2, Lee A. Groat1
1. DEPARTMENT OF EARTH AND OCEAN SCIENCES, UNIVERSITY OF BRITISH COLUMBIA, 6339 STORES ROAD,
VANCOUVER, BC, CANADA, V6T 1Z4 [*CORRESPONDENCE: LMILLONIG@EOS.UBC.CA]
2. INSTITUT FUER GEOWISSENSCHAFTEN, ALTENHOEFERALLEE 1, D-60438 FRANKFURT AM MAIN, GERMANY
SAMPLE LOCALITIES AND LA-ICP-MS U-PB DATING
Blue River area Perry River area
FIG 4.: Carbonatites in the Blue River area.
Carbonatites in the Blue River area (Fig. 4) are numerous and widely dispersed with
interpreted intrusion ages between 202 Ma (Howard Creek) and 351 Ma (Paradise Lake).
In the Perry River Area (Fig. 5) carbonatites and alkaline rocks intruded the mantling
gneiss succession of the Frenchman Cap Dome and are either of Cryogenian age FIG 4.: Carbonatites and syenites in the
(Mount Copeland syenite) or Cambrian age (Mount Grace carbonatite) based on Perry River area.
stratigraphic relationships.
Serpentine Creek carbonatite – Blue River Area
FIG 7.: Concordia
diagram of U-Pb
zircon analyses
from the Serpentine
Creek carbonatite
with aninterpreted
intrusion age of
FIG 6.: Zircons from the Serpentine Creek ~340 Ma and
carbonatite. a) Image of euhedral transparent short Pb-loss during a
prismatic zircons. b+c ) CL - images of the zircons metamorphic
revealing oscillatory magmatic zoning in some cores overprint at ~80
and alteration/zircon growth along the rims. Ma.
Little Chicago carbonatite – Blue River Area
FIG 9.: Concordia
diagram of U-PB
zircon analyses
from the Little
Chicago carbonatite
with an interpreted
intrusion age of
FIG 8.:Zircons from the Little Chicago carbonatite
~490 Ma and
a) Image of euhedral transparent to yellow short
Pb-loss during
prismatic zircons. b+c) CL - images of the zircons
metamorphism at
revealing oscillatory magmatic zoning in some cores and
~156 Ma.
various forms and degrees of alteration and/or zircon
growth.

3. CARBONATITES AND ALKALINE ROCKS IN THE
SOUTHERN CANADIAN CORDILLERA
Leo J. Millonig1*, Axel Gerdes2, Lee A. Groat1
1. DEPARTMENT OF EARTH AND OCEAN SCIENCES, UNIVERSITY OF BRITISH COLUMBIA, 6339 STORES ROAD,
VANCOUVER, BC, CANADA, V6T 1Z4 [*CORRESPONDENCE: LMILLONIG@EOS.UBC.CA]
2. INSTITUT FUER GEOWISSENSCHAFTEN, ALTENHOEFERALLEE 1, D-60438 FRANKFURT AM MAIN, GERMANY
Perry River syenite
FIG 10.: Zircons from the Perry River syenite. a) Image of ±euhedral slightly
elongated prismatic zircons. b+c) CL-images of the zircons revealing oscillatory
magmatic zoning and different degrees of alterartion in some cores as well as
alteration/zircon growth along the rims. d) Concordia diagram of U-Pb zircon
analyses from the Perry River syenite with an interpreted intrusion age of ~800
Ma and Pb-loss during a metamorphic overprint at ~50 Ma.
RESULTS AND DISCUSSION
• The Serpentine Creek carbonatite was emplaced during extensional tectonics in Mississipian
times at 340 Ma.
• The intrusion of the Little Chicago carbonatite at 489 Ma is interpreted to be related to the
separation of Laurentia and Siberia. No carbonatites of comparable age have been
documented in the Canadian Cordillera yet, but are known from the Cordillera in the USA!
• The Perry River syenite is interpreted to be part of the Mount Copeland syenite and intruded
during the initial stages of the break-up of Rodinia at ~800 Ma.
Carbonatitic and alkaline magmatism in the Canadian Cordillera spans ~460 Ma and is
linked to several episodes of extensional tectonics.
REFERENCES
Lund, K., Aleinikoff, J.N., Evans, K.V. duBray, E.A., Dewitt, E.H., Unruh, D.M., 2010: SHRIMP U-Pb dating of recurrent Cryogenian and Late
Cambrian–Early Ordovician alkalic magmatism in central Idaho: Implications for Rodinian rift tectonics. GSA Bulletin, v. 122, no. 3/4, p. 430–453.
Monger, J.W.H., 2008: Evolution of Canada’s Western Mountains. Geological Survey of Canada, Open File 5804, 1 poster. Nelson, J., and Colpron,
M., 2007: Tectonics and metallogeny of the British Columbia, Yukon and Alaskan Cordillera, 1.8 Ga to the present. In Goodfellow, W.D., ed.,
Mineral Deposits of Canada: A Synthesis of Major Deposit-Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration
Methods: Geological Association of Canada, Mineral Deposits Division, Special Publication No. 5, p. 755-791. Woolley, A.R. & Kjarsgaard, B.A.,
2008: Carbonatite occurrences of the world: Map and database. Geological Survey of Canada, Open File 5796.
ACKNOWLEDGMENTS
The author is grateful to Zimtu Capital Corp. for funding this project and the geologist from Dahrouge Geological Consulting whose work in the Blue
River area dicovered several new carbonatite occurences. Special thanks go to Rob Bergman who dicovered the Little Chicago carbonatite in 2008.
Support and help during sample preparation from the geochronolgy unit at the Earth and Ocean Science Department of the UBC is gratefully
acknowledged.