Moose River Basin: geology and mineral potential - Geology Ontario

Lignite and Industrial Mineral Resources
greater amount of organic impurities than the white clays, are less likely to
have been affected by post-depositional weathering than kaolinitic clays asso
ciated with quartz sand. The latter kaolinitic clays may well be due entirely to
post-depositional weathering of the feldspathic component of the sands. Under
these circumstances individual beds of kaolinitic clay may result from minor
washing and transport at surface or they may be due to vertical migration of
fine clay particles through the sand and concentration at certain levels. The
latter process is believed to have been responsible for beds with 92 to 93 percent
kaolinite in residual deposits in North Carolina (U.S. Bureau of Mines Bull.
No.53,1913,p.l6).
Silica Sand
Weathering of rocks and transport of the weathered material leads to accu
mulation of weathering-resistant particles. The accumulation may occur at the
site of weathering or weathering-resistant particles may be washed away by
rain or flood waters and selectively deposited downstream. If quartz is^the pre
dominant weathering resistant mineral in the original rock, the resulting sedi
ment is a nearly pure quartz sand. Quartz is a ubiquitous mineral. In granite
the quartz content often ranges from 20-359fc (Hewitt 1972, p.57), and it is par
ticularly abundant in rhyolites, granites, granite-gneisses and clastic sedi
ments. Quartz, with formula SiO2 , hardness 7 (Moh's scale), and specific grav
ity 2.65, lacks cleavage. Prolonged physical abrasion results in perfect
rounding of the grains. Quartz is insoluble in acids except hydrofluoric acid. It
is constant in composition and, by nature, of high purity.
In source rocks quartz occurs in a wide range of grain sizes, from large bod
ies measured in metres in pegmatites to the size of rock flour in the clay frac
tion of sediments. Deposits of quartz sand are characterized by a specific grain
size distribution corresponding to their origin. The effective grain size is occa
sionally influenced by cementing of the sand grains. The cementation agent
may be silica or carbonate. Silica cement permits the use of sandstone as a
source of lump silica required for the manufacture of ferrosilicon.
SILICA SAND - KAOLIN CLAY ASSOCIATION
Unconsolidated quartz sands associated with kaolinitic clay are frequently
of high purity ^29c impurities). The weathering process responsible for kao
linization has simultaneously depleted the deposit of iron, magnesium, calci
um, and alkalies, particularly in areas where kaolinization is complete. The
major remaining source of impurities is a residue of heavy minerals, e.g. rutile,
zircon, magnetite, staurolite. Heavier than quartz, some of these minerals have
been incorporated in lighter grains or failed to respond to gravity separation
over the distance of transport from the source rock. This distance is characteris
tically short for material in a quartz sand - kaolinitic clay association.
Size sorting of quartz grains is also a function of the distance of transport.
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