Moose River Basin: geology and mineral potential - Geology Ontario

Petrography of Mesozoic and Pleistocene Sands
for the unusual minerals gold staurolite and pale brown tourmaline. There are
very low values of magnetite and ilmenite, epidote and altered pyroxene, only a
trace of hornblende, and near absence of all other common minerals. Only the
most stable and authigenic minerals are abundant indicating at least a second
cycle deposit. Sorting, rounding and purity increase and grain size decreases
from drillhole 75-03 to 75-02, implying a gross direction of transport from north
to south.
Drillhole 75-05
Original logging by Rogers et al. (1975) placed a Pleistocene-Mesozoic con
tact at 22.5 m depth between samples 27 and 28. This petrographic analysis in
dicates instead that a geological boundary occurs in the 4.5 m interval between
samples 28 and 39, and may be interpreted as an unconformity separating
Pleistocene and Lower Cretaceous deposits. Between samples 28 and 39 signifi
cant changes in total carbonate content, colour, sorting, purity, grain size, ma
trix composition and pebble lithology occur. Clays underlying sample 28 are or
ange or reddish brown and typical of Cretaceous age sediments in other areas.
The Pleistocene-Lower Cretaceous boundary is placed, therefore, immediately
below sample 28 at a depth of 22.8 m.
Drillhole 75-06
A Pleistocene-Mesozoic contact was placed at 51.2 m depth, samples 61 and
63, by Rogers et al. (1975). Parameters studied in this project support this
"pick" and indicate that it is an unconformity between Pleistocene till and un
derlying Lower Cretaceous sand and clay. It is defined on the basis of carbonate
analysis, heavy mineral analysis, colour and especially sediment type since all
Pleistocene samples are till. Those samples below sample 67 contain typical
Mattagami Formation sands with a distinct mineral assemblage, low carbo
nate content (and dolomite dominates calcite), and black lignite occurrences.
Samples 63 and 67 are grouped with the underlying Lower Cretaceous on the
basis of carbonate and heavy mineral content, colour and descriptions of con
tained sand.
In the lower part of this hole, from sample 93 to 138, carbonate content sud
denly becomes very high (with equal calcite and dolomite), clay matrix content
drops and several heavy minerals change proportions. Sorting, sphericity,
grain size, purity, and pebble-granule lithology are also affected and from sam
ple 99 to 115 the lignite content is quite high. Though these sands maintain a
generally similar colour, mineralogy and appearance to overlying Mattagami
Formation sands, the differences are enough to warrant separation of the two
units at a depth of 93.8 m.
In summary, Pleistocene sands of the southern part of the Moose River Ba
sin (drillholes 75-05 and 75-06) consist of calcareous, greyish, poorly sorted, an
gular, low sphericity, impure coarse sand containing minor calcareous clay ma
trix, no organics and abundant limestone, Precambrian and quartz granules.
Till in drillhole 75-06 contains a medium heavy mineral percentage of high
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