Geology Reference
In-Depth Information
58
Klamath Mountains
ophiolite, one of the better exposures of a
massive sulfide deposit is in the Turner-
Albright mining district on the southern
Oregon border. Here hydrothermal depos-
its yield gold, silver, copper, zinc, and
cobalt from what has been interpreted as
an ancient ocean spreading ridge where
minerals precipitate from submarine hot
springs at temperatures up to 650 degrees
Fahrenheit.
A second important mineral-bearing
ophiolite sequence is the Jurassic Preston
Peak terrane of the Klamaths. Best ex-
posed in California, the Preston Peak has
been thrust into a position over the Jose-
phine ophiolite. Originally the Preston
Peak lay a distance to the east and was
either a poorly developed volcanic archi-
pelago or a piece of the Josephine interarc
basin.
The Rogue Valley subterrane forms
a five-mile wide strip just northwest of the
Smith River terrane. The Rogue Valley
consists of volcanic flows and ash of the
Rogue Formation covered by shales and
sands of the Galice Formation. The volc-
anics have been altered to greenstone
which in turn contain gold and other base
metals. The Briggs Creek subterrane, west
of the Rogue Valley, consists of folded
and altered garnet-bearing amphibolites.
The Dry Butte subterrane includes the
Chetco River complex of plutonic rocks,
locally known as the Illinois River gabbro,
and is considered to have been the roots
of the volcanic arc.
Over 20 miles west of the main expo-
sures of other Western Klamath terrane
rocks, the Elk subterrane is included
within the Western Klamath because it
contains the unmistakable sandy turbidit-
es, shales, and andesite volcanic flows of
the Galice Formation. Atop the Galice and within the
Elk subterrane coarse marine gravels of the lower
Cretaceous Humbug Mountain Conglomerate and
Rocky Point Formation are found.
Five slightly younger terranes, the Snow Camp,
Pickett Peak, Yolla Bolly, Gold Beach, and Sixes River
are separated from the overlying Western Klamath
terrane by a series of faults of early Cretaceous age.
The Snow Camp terrane is a disjunct group of rocks
including the Coast Range ophiolite which has been
overlain by the lower Cretaceous Riddle and fossilifer-
Oregon Klamath Mountain terrane stratigraphy (after
Blake, et al., 1985)
ous marine Days Creek formations of conglomerates,
silts, and sands. The highly folded Colebrooke Schist of
late Jurassic age makes up the Pickett Peak terrane.
Metamorphosed in early Cretaceous, the Colebrooke is
a blueschist that was originally a mixture of tuffs,
cherts, and pillow lavas in a deep sea, oceanic setting.
The Yolla Bolly terrane of upper Jurassic-lower
Cretaceous age has been divided into east and west
sections, both of which include the distinctive Dothan
Formation. Deriving its sand from continental and
