Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1932-07-23
Radersburq Offers Promise

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cambrian, with an average ehick-
ness OF about t25 fegt. out
cropping In a loop around the
s or z square miles Of spokaHe
shale.
Cansbrian 20 Carbonlferoua
H.imestOnes. Above the Blathead
QuartzHe (Camlbrian) ara series
of six additional Cambrian strata,
named wolsey shale, Meagher
limestone, Park shale, Pilxrim
limestone, Dry Greek shale, and
Yogo limestone.
The Devonian period Is repre-
scented by the Jefferson lime
stone and the Three Forks shale.
Above these Is the Madison
limestone OF the carboniferous,
or Mississippian period. The to-
tai thickness Of these entire series
OF CambrianlCarbonHerous lime
stones and shades is about 1000
feet.
Quadrant Quartzite. Upper
Carboniferous or Pennsylvanian. }
overiying the Madison limestone
is the Quadrant quartzite. some
200 to 500 feet thick. Its Night
gray color, density and cherry
texture distinguish It from ali the
other quantities Of the region.
IL forms a hogsback ridge which
extends from Johnny guich in an
irregular northwest line to the
vicinity OF Elkhorn peak.
CretaceOus shaIes. Next above
the quadrant quartzite and under-
lying the andesite to the east
are a series OF shales. sandstones
and limestone OF Cretaceous
age. They are probably the
Morrison and Benton formations
which are recognized further east.
Tertiary lake beds. These are
seen in a small area south OF
the Keating mine. and east Of the
Black Friday mine. The valley
OF the Missouri 70 the east OF the
district is the bottom Of an old
lake in which these clay beds
were deposited.
Volcanic or Igneous Rocks
In late Cretaceous or early
Tertiary times. volcanic erup-
lions. possibly from Grow and
Elkhorn peaks, covered the area
to a depth OF at least 1000 feet.
Alta later date, granite, called
the Boulder batholith. formed a
great dome to the west Patches
OF granite appearing here and.
there In the vicinity Of Raiders
burg lead us to believe that the
batholith is underlying the terri
tory Immediately east Of Elk
horn. These granite masses are,
OF course, very much younger In
age than the granite core Of the
earth. and are slightly different
in composition. Feldspar and
quartz are, however. the principal
constituents OF both old and
young GRANTEES.
Andesite is a rock with mainly
soda-lime feldspar, with little
or no quartz. When the rock
shows large crystals OF one min
eral embedded In an intimate
mixture Of the other minerals,
It Is called a porphyry. Rock OF
this coarse grained type is a re-
suit Of slow cooling from liquid
to a solid state, which happens
when the molten mass does not
reach the surface. Many Of the
metal deposits, especially gold,
in the Rocky Mountains, are
associated with the porphyry in
trusions Of one kind or another.
Andesite rocks outcrop on the
eastern side OF the area from
Radersburg to Hassel and farther
north. These vary in character.
depending on whether they cooled
on the surface (eStrusive). or
underneath other rock masses
(intrusive); n the rocks were
elected from the volcano as dust
and fragments, they consolidate
to tufts and breocta. All these
varieties OF andaaite are found IN