Cargill Township carbonatite complex, District of ... - Geology Ontario

CARBONATITE - ALKALIC ROCK COMPLEXES: CARGILL TOWNSHIP
placed on obtaining samples from the more homogeneous cores, or sections of
core which could be considered to be most representative of the lithologies pre
sent. The diamond drill core of Kennco Exploration (Canada) Limited is still at
the property; however, the numbers on the core boxes are unreadable due to
weathering.
The original version of this study was prepared in 1978. Brief summaries of
the conclusions or results of more recent studies (e.g. Twyman 1983, Kwon 1986
and Sharpe 1987) have been added to this study, but no major rewriting has been
done. Similarly, the results of exploration work from 1981 to 1987, supplied to
the author by Sherritt Gordon Mines Limited, have been consulted to revise the
exploration history and geology on the carbonatite complex.
Laboratory Technique
A suite of the texturally and compositionally most homogeneous rocks was se
lected for thin sectioning and chemical analysis. The thin sections were examined
only briefly and the major textural features noted. These observations are sum
marized in Table A-1 in Appendix A. Allen (1972) presented detailed micro
probe analyses of the various mineral phases, some of which is reproduced here
in Appendix B.
Nomenclature
The author uses names for the mafic to ultramafic rocks in the conventional
manner. The following terms are used to describe the carbonatite rocks.
Sovite: A carbonatite rock containing 509c or more calcite. Various
mineralogic modifiers are used to classify the sovite.
Rauhaugite: The dolomitic equivalent of sovite.
Silicocarbonatite: A carbonatite rock composed of 5096 or more oxide and
silicate minerals. Where the silicate mineralogy exceeds 9096 various other rock
names are applied, i.e., ijolite, biotitite, pyroxenite, etc.
The definitions of sovite and Silicocarbonatite are modified from Heinrich
(1966, p. 12). The author has found Heinrich's subdivision of the carbonate-rich
carbonatitic rocks generally suitable for field use when modified to a two-fold
subdivision at about 5096 oxide and silicate mineral contents. The two-fold subdi
vision is more convenient than the four-fold subdivision of Heinrich (1966, p. 12)
because carbonatites are extremely variable in mineral content over distances of
less than a few centimetres. It is difficult to rigorously classify such heterogeneous
rocks and they are not mappable at any convenient map scale.