Cargill Township carbonatite complex, District of ... - Geology Ontario
Cargill Township carbonatite complex, District of ... - Geology Ontario
Cargill Township carbonatite complex, District of ... - Geology Ontario
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R. P. SAGE<br />
A crandallite-rich blanket near the top <strong>of</strong> the apatite residuum is high in rare<br />
earth values which may ultimately prove <strong>of</strong> economic interest (Sandvik and Er-<br />
dosh 1977; Erdosh 1979). Sandvik and Erdosh reported that the apatite<br />
residuum may exceed 170 m in thickness in preglacial troughs within the car<br />
bonatite <strong>complex</strong> and may be only a few metres thick on ridges between the<br />
troughs.<br />
Even though apatite is present in all phases <strong>of</strong> the <strong>complex</strong>, the protore for<br />
the apatite residuum is principally sideritic and dolomitic <strong>carbonatite</strong> (Sandvik<br />
and Erdosh 1977).<br />
EARLY PRECAMBRIAN (ARCHEAN)<br />
GRANITIC GNEISSES<br />
Outcrops <strong>of</strong> the granitic host rocks that enclose the <strong>Cargill</strong> <strong>Township</strong> <strong>complex</strong> are<br />
rare. Several very small outcrops <strong>of</strong> gneissic granitic rock occur along the access<br />
road to the property. These rocks are mottled white and black on the weathered<br />
surface and have a banded pink and black appearance on fresh surface. Banding<br />
up to 2 cm in width is present and is defined by the variation in the relative<br />
amounts <strong>of</strong> the mafic and felsic components. Biotite is the dominant mafic min<br />
eral. The banding has a northeast trend and dips steeply northwest.<br />
Sandvik and Erdosh (1977) reported that rock chips, obtained from drill<br />
holes west <strong>of</strong> the south sub<strong>complex</strong>, consist <strong>of</strong> a medium-grained rock that is<br />
likely a banded gneiss. Both amphibole-rich and quartz dioritic chips are present<br />
implying the presence <strong>of</strong> a mixed or banded rock beneath the overburden.<br />
Sandvik and Erdosh (1977) reported that fenitization is absent in the gneissic<br />
rocks bordering the south <strong>complex</strong> but outcrops around the west sub<strong>complex</strong> are<br />
distinctly fenitized.<br />
MIDDLE PRECAMBRIAN (PROTEROZOIC)<br />
CARGILL TOWNSHIP COMPLEX<br />
The <strong>Cargill</strong> <strong>Township</strong> <strong>complex</strong> consists <strong>of</strong> a suite <strong>of</strong> Middle Precambrian rocks<br />
which have been dated by K-Ar isotopic techniques at 1740 Ma (Gittins et di.<br />
1967). Using U-Pb techniques, the age was determined as 1907 4 Ma (S.T.<br />
Kwon, Department <strong>of</strong> <strong>Geology</strong>, University <strong>of</strong> California, Santa Barbara, Califor<br />
nia, personal communication, 1987).<br />
The rock suite studied by Allen (1972) and the rock suite studied by the<br />
author are from drill core and thus are incomplete. Neither likely represent all<br />
the phases present in the body. The samples examined by each author were the<br />
best and most representative that were obtainable at the time <strong>of</strong> the respective<br />
sampling. It would appear that most <strong>of</strong> the samples examined by Allen (1972)<br />
were from Kennco Exploration (Canada) Limited hole No. 2. This hole is in<br />
clined (45 0) and located such that it represents a cross-section <strong>of</strong> a small portion<br />
<strong>of</strong> the body. The author examined core obtained from vertical drill holes com<br />
pleted by the International Minerals and Chemical Corporation (Canada) Lim<br />
ited. Presumably these vertical holes in a probably vertically dipping body would<br />
not be as likely to provide cross sectional information on the intrusion nor are<br />
they likely to provide information on all rock types present.<br />
Twyman (1983, p.73) used samples from Kennco Exploration (Canada) Lim<br />
ited holes 4 and 6 and both Kwon (1986) and Sharpe (1987) used surface and<br />
drill core samples provided by Sherritt Gordon Mines Limited.