Oregon Beach
Placers:
Beach placers along the Oregon coast were richly productive for a
time after their discovery in 1852 and have since yielded small amounts of
gold and
platinum annually. Renewed
interest in then was caused by the industrial depression that followed 1929.
A little
placer gold may be found in
almost any section of the beach, but the bulk of it is confined to certain
stretches south of Coos Bay. Along the Oregon coast gold and platinum
bearing deposits were discovered on the present beaches in 1852 and on tile
ancient elevated beaches 18 or 20 years later. In places the deposits were
rich, and for a time they were mined extensively. According to a popular
report a production of several million dollars, chiefly in gold but with a
minor content of platinum, was obtained. After the more profitable stretches
had been worked over mining activity decreased, out no season has passed
without some production. In 1930 and 1931 renewed interest in the deposits
was stimulated by the fact that the value of gold had become relatively
enhanced as the result of the depressed economic conditions throughout the
country. For this reason a field examination was made in June 3, 1931 of
parts of the coastal belt, chiefly between Coos Bay and the California line.
Increases in the price of gold since the field work was done gives the
deposits an added interest.
The generally mountainous Oregon coast is bordered in places by coastal plains that range from a quarter of a mile to 4 miles in width and are mostly less than 100 feet high. The plains are of two different geomorphic suites. 'One consists of lowlands composed of bay mouth bars or barrier beaches and the filled embayments behind them; the other is a group of slightly elevated marine terraces. The different terraces are capped with Pleistocene marine sediments, the largest area of which is between Port Orford and Cape Arago and is related to an ancient shore line at an altitude of 170 feet. Beds formed offshore compose a terrace plain about South Slough that is somewhat lower, and there are remnants of beaches in some of the other terraces. The placer deposits are wave-concentrated layers in the beaches and offshore beds and are generally called black sands for the reason that they are composed largely of magnetite, chromite, and other heavy minerals, most of which are dark-colored. Commonly these layers contain small particles of gold and platinum, and in places the metallic particles are abundant enough to be extracted profitably. The gold and platinum that are recovered from the beach deposits occur as particles most of which range in size from that of a small pinhead to microscopic specks. A sample of platinum from the Pioneer mine consists mostly of rounded flat grains from 0.8 to 0.05 millimeter or about 0.03 to 0.002 inch in diameter and from 0.05 to 0.005 millimeter or less in thickness. These grains weigh from 0.55 to 0.01 milligram.
Although a few specks of gold or platinum can be found almost anywhere along the present and ancient beaches, the workable deposits so far discovered form only a part of the whole and, as a rule are confined to the beaches bordering the shores that have receded under wave attack. In those beaches that are retreating under wave attack the deposits are variable end inconstant, but certain beaches are likely to be richer or more often workable than others. In the shores that are now retreating the beach varies in extent and composition from time to time as the result of wave action caused by storms and tides. Thus a stretch that is barren on one day or in one season may be productive at other times. There are, however, certain stretches that have been richer and are more often workable than the rest. These are, in order from north to south, in the vicinity of Newport, Whisky Run, Cape Blanco, Port Orford, and the beaches near the mouth of Rogue River.
Owing to the transitory character of the foreshores of the present beach no definite estimate of reserves can be made, but it is concluded that deposits suitable for small sca1e operators will continue to form here and there along certain parts of the coast. Ordinarily these deposits may be expected, under the working conditions possible, to yield from a few cents to 2 penneyweight a day per man. In places the backshore contains noteworthy amounts of gold and platinum, but in the decade immediately preceding 1932 attempts to mine the deposits apparently met with no success, and no basis for an estimate of their value exists. The backshore of the present beach and the ancient beaches up to an altitude of about 170 feet have been the most productive. The pay streaks generally ranges from a few feet to 200 or 300 feet in width, is 3 or 4 feet thick in the middle, and tapers toward the edges. It consists largely of alternating layers of black and gray sand with more or less cobbles, boulders, and drift wood and in the ancient beach, is mostly covered with a barren sand "overburden" 20 to 60 feet thick.
The immediate sources of the beach minerals, including gold and platinum, are the shores that are being cut back by the waves. Most of the gold-bearing beaches are south of Coos Bay, along the coast opposite the Klamath Mountain region, described by Diller, which contains several areas of gold-bearing lodes. The lodes of the interior were the ultimate sources of the gold from which it has been carried seaward at intervals since middle Tertiary time. In the past, as at present, the streams sorted the gold during its transportation, leaving the larger grains near the source and distributing progressively smaller and smaller particles downstream. As a result of stream sorting only the finer particles reached the coast. No definite source of the platinum has been found, but its distribution and its association with chromite suggests the abundant serpentinous and other basic intrusives of the region. However, no relation of the platinum and chromite of the beaches to any particular rock mass could be made out.
Pay streaks have been worked in the ancient elevated beaches or related offshore beds in the terrace p1ains north of Port Orford, north of the Rogue River, around South Slough, and in a terrace 800 feet above sea level at the Peck mine, on the spur north of the Sixes River. On the terrace plain north of Port Orford the deposits were formed when the sea stood about 170 feet higher than now. At that level the shore was cut back along two stretches one of about 4 miles between the Sixes River and Denmark, the other of about 4 miles extending north of Cut Creek. Pay streaks that were concentrated by the waves along parts of their stretches are exposed in the Majden and Butler mines, north of the Sixes River, and in the Pioneer, Eagle, Fletcher & Myers, and Rose mines, north of Cut Creek.
Continue on to:
Beach
Mining: Part I, Shore Deposits
Beach Mining: Part II, Alaska and California
Beach Mining: Part III, Oregon
Beach Mining: Part IV, Nome, Alaska
Return To:
All About Placer Gold
Deposits
