Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1932-07-16

/ reaches lOurlsheo-
The periods from the canabrian
to and including the carboni-
ferrous, which have been briefly
described above. are called
PaIeozic fold life). The follows
ing era is called MesOzOic (inter-
mediate life.l
/ Triassic, yurassic and Creta-
ceous. Duration 100000 yeau.
During this period the North
American coutinent continued %
rise; great masses Of molten
granite called batholiths pushed
up from great depths in British
Columbia, Montana and Idaho.
accompanied by cracking and
folding OF the rock layers above.
Enormous lava flows issued
from volcanoes and cracks, COW
ering the region in the vicinity
Of the Columbia and Snake
rivers.
Sedimentary rocks we're in-
vaded by other numerous ig-
neous magmas Of smaller size
which did not reach the surface
Hot waters from these molten
magmas deposited veins OF gold,
silver. lead, copper and zinc, ores
in the assures and cracks in the
vicinity OF the intrusive rocks.
The Rocky Mountain ranges were
produced by the folding and fault
ing OF the strata along great
trOughs. The crests Of these
folds are called anticIines. and
the trOughs which form our
intermountain valleys are called
synclines.
The climate became much cold
er, and animal life on the land
developed from the great egg
laying reptiles, the dinosaurs. 20
birds and warm-bIooded nam
mails, the ancestors OF our pre-
sent-day animals The next era
is called CenezOic (recent times }
Tertiary and Quarternary. Dur
alton 10000, 900 years. The con-
tinent continued to rise, and the
climate became more arid, with
high winds blowing desert and
volcanic dust across the plains.
These wind deposits covered great
areas in the west, often killing
the forests and animals. Great
ice sheets came down from the
North or formed on the noun
tain tops. Our modern animals
such as the horse, elephant, and
other hoofed animals were
evolved from more primitive
forms. Finally man appeared
possibly 100000 years ago.
Origin OF Ore Deposits.
The metallic ore deposits are
derived from 6he batholiths and
smaller masses OF igneous rocks
buried far under the surface
The hot waters squeezed out o.
these slowly cooling rocks carry
the dissolved metals into the
crevices above, and as the waters
are further cooled by contact Will
the strata above, they deposi-
their load in the veins and along
contacts of igneous and sedi
mentary formations. The latte
type Of ore body is called a re
placement deposit.
Mineral deposits are classi
fled according to the zones o
temperature and pressure. as FOL
lows:
1 Deep high temperature de
posts. Gold, copper, tin tungsten
ores are found under these con
ditions with the minerals game
magnetic, pyorrhotite.
2. Deposits formed at moder
ate depths by only moderately
hot solutions. The gold. silver
copper. lead and zinc ores OF tn,
Rocky Mountains are OF thii
type. The associated mineral,
are pyrite (sulDhide Of iron.I
chalcopyrite (sulphide OF iroI
and copper gaiena (sulphide o
lead,) sphalerite (sulphide o
zinc,) Quantz (silica). calcit,
Carbonate of Hme.) siderit,
carbonate OF iron.)
3. Shallow deposits fOrme,
by warm solutions. These ar
: found near the smaller instru
, sives OF igneous rocks or nea
surface flows OF lava in region
where volcanoes have recent
lbeen active. The gold silve