Geology Reference
In-Depth Information
Coal
Although coal deposits are scattered across
Oregon, there are only two significant coal producing
regions in the state, the Coos Bay and Eden Ridge
fields, both in Coos County. Of these, only the Coos
Bay field has been extensively mined. Eocene coal beds
formed as a result of a chronically swampy environ-
ment that existed along the edge of the ocean covering
western Oregon. As plants growing in the lowland
swamps accumulated in the brackish water, layers of
peat developed. With the land sinking locally, sedi-
ments covered the bogs compressing and compacting
the organic material into coal. Where there was not
enough compression and the coal contains too much
water, it is ranked as sub-bituminous and of little
economic value. Most of Oregon's coal is of inferior
quality, even though deeper parts of the basin have
bituminous zones where pressure and heat have reacted
with the sub-bituminous material to make a higher
rank of coal capable of generating in excess of 9,000
B.T.U.'s. In spite of its low rank, coal here spontane-
ously combusts. Coal loaded in a bunker or gondola
A bucket line dredge mounted on a wagon
with 6-foot steel wheels was designed to
work beach placers in and out of the tide
(photo courtesy Oregon Dept. Geology and
Mineral Industries).
had sprung up only to be abandoned after a disasterous
storm destroyed most of the mining operations on the
beach in 1854. Shortly after that, prospecting here was
only carried out sporatically. Although gold remains in
the thin layers of black sands today, it is doubtful if the
amounts are economic.
North of the Coquille River the two largest
placers occur on the uplifted Seven Devils and Pioneer
terraces. Here north-flowing longshore currents carried
the minerals to be deposited near old seacliffs. At the
Pioneer Mine, the 3-foot thick placers atop the terrace
are covered by recently deposited sand dunes. Cutting
three long tunnels, the longest of which was 1,340 feet,
miners recovered gold and platinum from the mineral-
rich layers. The Seven Devils or Last Change Mine
south of Cape Arago was originally opened for gold
and platinum, but from 1942 to 1943 chromite was
extracted before the operation closed after World War
II.
Production amounts from Coos and Curry
county beach placers were never systematically report-
ed, but $60,000 in gold and platinum is estimated to
have been extracted between 1903 and 1929. In 1988 a
joint federal and state Placer Task Force examined the
Oregon shelf for economic deposits of metalliferous
black sands, but few mineral resources were discovered.
The search for economic minerals in the black sands
was pursued as recently as 1992 when a mineral
resources company leased the rights on 4,000 acres
south of Coos Bay to investigate the possibility of
extracting chromite, garnet, zircon, and titanium.
Historic Libby Coal Bunker on Coos Bay (photo
courtesy of J. L Slattery)
