Moose River Basin: geology and mineral potential - Geology Ontario

Petrography of Mesozoic and Pleistocene Sands
ABSTRACT
Study of Mesozoic and Pleistocene sands from drillholes in the James Bay Lowland indicates
that their petrography may be used to differentiate four sedimentary units. Properties of colour,
sorting, roundness, sphericity, purity, grain size, clay, organic and carbonate contents, granule li
thology, calcite-dolomite ratios and heavy mineral assemblages are important. The Middle Juras
sic Mistuskwia Beds consist of grey, calcareous, sorted, rounded, spherical, fine to medium, pure
quartz sand without organics and may be second-cycle sediments. Lower Cretaceous Mattagami
Formation sands are divided into older, white, calcareous, sorted, angular, spherical, medium, pure
quartz sand with abundant lignite fragments and authigenic pyrite, and younger, white, sorted,
angular non-spherical, fine, very pure quartz sand with abundant kaolin. Pleistocene sand is char
acterized as calcareous, unsorted, angular and impure, with little matrix, no organics and variable
granule lithology. Heavy mineral suites for these units have been determined, and an inverse rela
tion between blue-green hornblende and authigenic pyrite was identified.
INTRODUCTION
Stratigraphically useful criteria were sought to distinguish unlithified
Pleistocene, Lower Cretaceous, and Middle Jurassic sands known to occur in
the subsurface of the Moose River Basin. Various parameters of sedimentary
petrography, including heavy mineral analyses, carbonate analyses, and grain
descriptions were used and additional details were determined in the petrogra
phy and extent of the Mattagami Formation, and the newly-defined Mistusk
wia Beds (Telford et al. 1975; Telford, this report).
In a drillhole, if Cretaceous sands are overlain by Pleistocene sands rather
than till, the two may be difficult to distinguish. For many years the Matta
gami Formation was included in the Pleistocene, until Bell (1928) demon
strated by paleobotany that sediments of Mesozoic age were present. The Mat
tagami Formation and Mistuskwia Beds also have similar lithologies and
placing contacts has been tentative. The only fossils contained in these Meso
zoic deposits are a few lignitized twigs and branches, and palynomorphs requir
ing extensive specialized study. The unconformity between Pleistocene and
Cretaceous sequences spans probably 100 million years while that between the
Lower Cretaceous and Middle Jurassic is about 60 million years and both are
accompanied by palynological "gaps". The objective of this study was to estab
lish petrographical "gaps" at the contacts, if they exist, and define criteria to
differentiate the units in field examination.
Sand samples taken from four of six Ontario Geological Survey winter 1975
drillholes consisted of the finer fraction of interval samples from selected are
naceous segments of drillholes 75-02,75-03,75-05, and 75-06 (Table 3.1).
Five days of helicopter-supported field work allowed examination and sam
pling of a few Cretaceous outcrops in the southern Moose River Basin, includ-
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