Geology Reference
In-Depth Information
Hanna Nickel Mine and smelter in Douglas County (Photo courtesy of Oregon Dept. Geology and Mineral
Industries)
sulfide ores are found in veins, and the coarse crystals
in the ores and adjacent rocks suggest that cooling of
the hydrothermal fluids proceeded very slowly at
considerable depth below the sea floor to deposit ores
of pyrite, chalcopyrite, sphalerite, and pyrrotite.
Economic amounts of gold as well as silver,
copper, zinc, and cobalt along the California border
southwest of Takilma have been identified as part of
the Turner-Albright sulfide deposit in the Western
Jurassic belt. The Turner-Albright occurs in the
Josephine ophiolite, a section of oceanic crust that was
impregnated with minerals by superheated oceanic
waters. No production of base metals has yet been
reported, but serious efforts to examine the sulfide
deposit began in 1954. Since then these mineral-rich
deposits were the focus of intensive exploration in the
1970s and 1980s, and drilling programs indicate signifi-
cant reserves of minerals exist here.
In the mining district along the upper Illinois
and Chetco River watersheds, most of the gold was
extracted from placers. After discovery in 1850, placer
mining was most active on Josephine Creek and Briggs
Creek in the upper Illinois River. Workings on these
creeks are the principal producers, but incomplete
records from both placer and lode mines make it
almost impossible to accurately estimate how much
gold was ultimately removed from this district. Gold in
this district appears along shear zones within the
Galice Formation in association with the Josephine
ophiolite.
Small quartz veins have been responsible for
limited amounts of gold from northeast Curry and
southeast Coos counties on Mule and Cow creeks
where mineralization is associated with an ophiolite of
the Snow Camp terrane. Although some of the veins
are rich sources of lode gold, others contain only low
grade ore. The Red River Gold Mining Company on
Mule Creek, one of the largest placers in this district,
had an hydraulic operation for a brief time in the late
1800s. Total production for the Mule Creek district was
around $100,000.
Nickel
Along with gold and chromite, nickel is one of
the most important economic minerals in southeast
Oregon where it is mined from peridotites that have
been deeply weathered leaving the isoluble nickel as a
by-product in the soil. Formed deep within the ophio-
litic sequence, peridotites containing the characteristic
minerals olivine and pyroxene decompose quickly upon
exposure to surface geologic processes. The soft laterite
residue from deep weathering is relatively easy to
excavate.
The only operating nickel mine in the United
States is at Nickel Mountain, a few miles west of
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