placer mining in oregon and california

[whats4supper]

While I would normally relegate such postings to Nevada Nugget Hunters, under the historical tidbits heading, summer is around the corner and likely everyone with means is looking for a new twist on old works.

Though the treatise below deals with flour gold, the tail end of the article has some fairly surprising news regarding gold, gems, and platinum values that may be your ticket to further success.

The article is transcribed from a March 15, 1931 issue of the [AZ] Mining Journal.

THE MINING JOURNAL

VOL. XIV. No. 20

MARCH 15. 1931

The Origin of Flour Gold in Black Sands

By A. E. KELLOGG, Geologist, Medford, Oregon.

A discussion of the cause of flour gold, or very fine gold, with examples of its attrition in Southwestern Oregon and Northeastern California.

Flour gold, or gold too light, or in too fine particles to save, has long been the "bugbear" of the placer miner and prospector. All sorts of devices have been tried to save it, with usually poor success. It may be so light and fine as to float over riffles, or by adhering to accompanying black sand, or particles of magnetic iron, or, by a certain coating of iron or sulphur, refuse to amalgamate with quicksilver, and be lost.

The origin and cause of this elusive gold may be various. In the first place, it may have been originally minutely disseminated through crystalline, or other rocks, not locally concentrated, or run into solution with quartz, in vein fissures, or wrapped up within, or chemically combined with other so-called gold-bearing ores, but is practically free. Such is probably the origin of much of the tantalizing gold in the gold sands of the Pacific Coast.

Another cause for flour gold is undoubtedly its attrition by waves and other violent waters. As a rule, the further we recede from the crystalline and igneous rocks of the mountains, with their quartz-fissure veins, which are assumed to be the proper habitat of gold in-place, and pass out to the plains, the finer, and more flour, does gold become. This is clearly the effect of the winnowing-grinding action of the streams and other bodies of water, flowing toward the low lands, from the mountains.

A fine example of this grinding and natural milling is to be seen in the very ancient Siskiyou Island, situated in that large area of Southwestern Oregon and Northwestern California, designated as the Klamath Mountains. These lofty mountains were an island in the ocean during Cretaceous times, long before the Cascade Mountains rose above the surface of the water, and by geologists, termed the "Great Siskiyou Batholith." It is, perhaps, one of the oldest pieces of terra firma on the western continent, and compares favorably in age, with the Alps in Europe.

The ancient island is located on the site of the Sierra Nevada, Cascade, and Coast Range, of mountains, a plexus of mountains, including the Klamath Mountain group. The Klamath mountains extend from the fortieth, to near the forty-fourth parallel, and include the Yallo Bally, Bully Choop, South Fork, Trinity, McCloud, Scott, and Salmon Mountains of California, and the Siskiyou, Rogue River, and others, in Oregon. The outline of the 'Island in Cretaceous Sea" and the "Klamath" mountain group is indicated by heavy broken lines on accompanying map.

The major part of the mass of the ancient island is granite, or granitic in character, accompanied with other intrusive igneous rocks, such as diorite, porphyry, and other intrusions of ancient origin, such intrusions having lifted from the depths of the ocean, the sediments that had settled there. These elevations have reached an altitude in some places of 7,000 to 8,000 feet. These sediments thus lifted, were changed from their original horizontal character, to various angles of inclination, and accommodated easy erosion.

Hence we find now only fragments of these early sediments, at the tops of the rather higher elevations, such as limestone, often metamorphosed into marble. These sediments were originally very deep, and erosion carried them away—some back to the ocean, while others were deposited in the valleys as the valleys were formed. These intrusions, and the necessary broken fissured condition in which they, and their beddings have been left facilitated the settling of such minerals as were held in position, or suspended, and all other matter susceptible of being carried downward into seams and fissures as the mass slowly rose. After the whole had arisen above the ocean water, and valleys were formed, or in process of forming, much of the residue resulting from this disintegration was deposited around the shore-lines of the old Siskiyou Island, resulting in the heavy placer deposits, which employed the pioneer placer miners.

Observations will show that all of these deposits were formed along the shore-line of this old island, and that the gold came from it. Thus, into these mountains, as judgment dictates, we must look for the source of the gold. The searches thus prompted have proven correctly that the heavy mineral deposits are found in the seams and fissures of this ancient island.

The Rogue and Klamath rivers drain, by their profound canyons, a vast area in the valley regions of the Klamath group of mountains. These valleys are largely composed of conglomerates of the Siskiyou Batholith. The pebbles, sand, or gravel components of these rocks are derived from many sources, but principally from granite or igneous rocks from the Klamath Mountains. These cementing sands doubtless carried the gold, which, having traveled far from its source, is naturally fine, and must have been reduced still finer by the angry waves and torrents that aided in laying down the Siskiyou batholith. From these cemented rocks, by a stupendous system of erosion and canyon cutting, the gold has, with sand and pebbles, found its way into the bottom of these rivers, and in some cases been deposited in bars and beaches, or along the banks of the streams.

Of the kind of additional milling and comminuting treatment it has received for untold centuries in the depths of the rivers, we may have a vivid object lesson, which will leave no wonder in our minds as to the flour condition of the gold, or as to one of the causes of its particle sizing. The streams, at the time of their annual freshets, are on rampages and impassable. They have narrow passages through solid rock banks, where the boiling waters are forced between narrow walls, as through a pipe. The centers of these narrows become heavily charged with gravel, which piles up a temporary sand and gravel bank, then a sudden and terrific roar, and the roaring is over. In a few minutes, the obstacle is washed away, to re-form again in another point down stream, and the temporarily checked stream rushes on its course. During the floodwater times there are frequent repetitions of the same phenomena in these narrow gorges. Imagine this gravel to carry a percentage of gold and its ultimate grinding by such a terrific milling process is obvious.

The gold found on the beaches of the Pacific Ocean near the deltas of these rivers, has received and is receiving daily, much the same treatment from the waves and tides, let alone what grinding it received in being washed from its source in crystalline rocks, far back in the Klamath Mountains, and on its way toward the sea. There it is deposited and redeposited in beaches, ultimately consolidated into conglomerates, and gradually raised above the sea, and from these again washed out seaward, and daily milled and turned over, deposited and covered, and re-deposited by the waves of the sea. Is it any wonder that such gold is very floury? What metal could withstand such a process and not become so?

Gold, as it has been said, is one of the widest disseminated minerals in the world, despite its rarity in veins, or in concentrated form. It is safe to say that most of the flour gold found in the various river and sea sands of the world, was never at any time in a concentrated form such as we understand it, in gold-bearing veins and the like, but is derived from gold particles minutely and widely disseminated through the rocks of the world, primarily in the igneous and crystalline series, and secondarily, in the sedimentary rocks derived from these, and lastly in loosely consolidated modern placers, and alluvial deposits.

The analysis of almost every igneous rock bears evidence to this minute gold dissemination. In this respect some igneous rocks are richer in gold than in others: as, for instance, the "pyritiferous porphyry" of Leadville, Colorado, in which the gold may have originally been contained within the pyrites, which are a constituent of that rock, just as mica and hornblende are of many igneous rocks.

In some cases gold has been detected in combination with some common rock forming minerals, and again it appears to occur free, or freed, in certain porphyries, especially in zones of brecciation and decomposition of these. Slates are notorious for carrying gold, sometimes disseminated within their mass, but generally concentrated within minute veinlets, and lenses of quartz, probably segregated from the materials of the slates themselves, or derived from solution from outside, and deeper sources.

Gold disseminated in sandstone, conglomerates, and metamorphic quartzites is not uncommon, sometimes even in commercial quantities. These rocks being consolidated in river or sea beach placers, the presence of gold is naturally to be expected, but commonly in a fine or flour condition. In fact in all cases, either by original deposition, or by combination chemically or mechanically, with other rock-forming minerals, or by long travel or attrition, the gold is in the minute and flour state, and appears so when rocks are broken up, and reduced to sand or gravel by wave or stream, and re-deposited in bars, beaches, placers, and river beds.

In most placers, there is a large proportion of this flour gold, and when coarser gold occurs, even up to small or large nuggets, it is traceable to concentration in veins or veinlets in the vicinity, which may be very small and inconspicuous, such as those traversing the schists of the Nome and Klondike areas, in which there is a notable absence of large workable gold-bearing veins.

Others, as in the Breckenridge region of Colorado, are doubtless derived from concentration in brecciated and decomposed porphyries, or from peculiar veins in place carrying crystallized gold, as in some of our local mines, leaf-gold deposited in shales. With the exception of those derived from these sources of concentrated gold, the gold so universally found and so widely disseminated is in the flour or fine state, and there are many good reasons why it should be so.

An indirect evidence of the wear and tear of the flour gold, experienced in its travel from the parent source, is shown by the character of the minerals associated with it in this region. These are usually the hardest, heaviest and most insoluble known, and in minute state in which they are found, are the relics and sole survivors of the tremendous abrasion by water, which has destroyed all other associated minerals. The common rock minerals associated with placer, beach, or alluvial gold, are quartz sand, the hardest insoluble residium of the disintegration of granite and igneous rocks, and of the sandstones and porphyries formed from these.

Mingled with these are all sorts of heavy and hard silicates and metals, some of them known as gems, such as garnets, rubies, beryls, tourmalines, and even rarer and more valuable stones, from sapphire and topaz, to the diamond. In the metalliferous series, the specimens accompanying placer gold are fragments of the hardest, heaviest, and most insoluble metallic minerals known, such as magnetite, wolframite, etc., and the platinum series, palladium, rhodium, iridium, ruthenium, osmium and iridosmine. Iridium is a hard metal, and 20 percent heavier than gold, while osmium is also a very hard metal, quite infusible and twenty-two and one-half times heavier than water. Iridosmine is of such extreme hardness that it is used for pointing non-wearing pens. In such hard and tough company, it is somewhat remarkable that gold actually exists or remains, considering its comparative softness, and its not absolute insolubility.

Soluble minerals are generally wanting in a placer, although at one time may have been in the placer rocks, the close associates of gold, such as lead, zinc pyrite, and silver-bearing ores. The sorting down and reduction to the heaviest, hardest, and most insoluble class, is somewhat wonderful, and is comparable on a grand scale with the most insignificant processes of artificial jigging and separation in our concentration mills.

Anyone who can invent a reliable means of saving this flour gold will be a benefactor to the mining world, and have a wide area for his operations.

On the coast beaches, the river bars, the irregular values of the deposits, the fineness of the gold, and the difficulty of separating the minute particles of it from magnetic, or black sands, are the main difficulty. The sands are limited as to extent and ephemeral in their nature. In river and dredging placer deposits, the flour gold is apt to be carded over and beyond the plates, by an overwhelming amount of heavy, black sands often accompanying it, or else it is too fine to save and declines to amalgamate. In addition to its fineness, the microscope shows the tiny grains are flat, boat, or cup shaped, causing an air vacuum, permitting them to float and they are consequently lost in the clean-up.

An unusually severe storm raging along this Oregon and California coast lasts for several days. Huge breakers lash the shores, making sweeping changes in the beach modeling, tearing up and tossing about large areas of shingly beach, and piling up the sands in new places and shapes to suit the angry mood of the lashing sea. At last, the angry waves having spent their vengeance, lap peacefully along the shores.

From South Slough, in Coos County, Oregon, to Gold Bluff, Humboldt County, California, the beach miners, following the storm, swarm on the newly made beaches to gather their golden harvest.

The origin and causes of fine or flour gold may be summed up to the original deposition of the metal, in a minute, and disseminated condition and, secondly, travel and attrition.

For more than 70 years the black sands of the Pacific Coast have been delved and tossed about by man as well as nature. At the beginning of beach mining, the reward was aimed at the golden contents of the sands. However, at an early date, platinum, iridium, palladium, and associate metals, were known to exist in these beach placers. In those days platinum was given little attention by miners on account of its then small value in limited market. Many old clean-up dumps have been re-worked for their platinum contents in recent years, with gratifying results.

Government experts, making search for war-metals during the war in this region, said: "There is but little doubt that from the early days of placer mining in South­western Oregon, more values in platinum went through the sluice boxes, and was lost, than were ever taken out in gold."

The first record of beach mining was at Gold Bluff, California. The '49ers from middle California were already drifting northward on new quests. Shortly afterward, the northward trek found the Oregon Coast, equally rich. In 1854, an authority, Blake called attention to the occurrence of platinum with the gold at Cape Blanco, Oregon, and stated that platinum was present at a ratio of from 10 to 80 percent of the gold.

In the late 1850's and early 1860's, beach and placer mining was at its height along the Oregon coast, as far north as Coos Bay. The Rogue River Indian war, which was raging made it a very precarious undertaking at the time, however. When easy takings had been cleaned up, the advancing horde of miners moved northward to the Idaho diggings. However, the Old Man of the Sea has since, and still, is generous to the beach miners.

Many ingeniously designed devices for extracting gold, platinum, and associate metals from the black sands on these beaches have been tried with indifferent success. The old-time devices, the sluice box, and the long tom, still remain the tried and trusty method used by successful beach miners.

[Uncle Ron]

Just north of Gold Beach, OR, there's an inlet and an old island in the middle of the inlet...There's a good running stream coming in there and the sands are solid black...I've set up a sluice there and shoveled in....That black sand is loaded with gold, but there so much black sand that your riffles get clogged within minutes...I tried magnetic separation, rather crudely, but it just sucks that flour gold right up with the magnetics...Very frustrating...I was told there was an old man back in the day who claimed the island and ran an amalgamation operation...Unfortunately, he died of mercury poisoning....We ended up just combing the beach for agates, of which there are some good ones...Cheers, Unc

[whats4supper]

Yeah Ron, pretty much my experience too. I tried sluicing along a lot of beaches. I did have better results with synthetic miner's moss and a fairly open riffle system, and flatter angles. It takes a special breed to deal with fine gold though, and a lot of patience. My better returns were near reedsport, brookings, and north of crescent city, and parts around eureka, but the water there is cold, along with the weather. Still, I got quite a mix of stuff, and after sending the lot out to someone else for cleanup, still made $4000 in 1980. Though I did a solo operation, this is one effort that would be better with 3 or 4 guys, each with their own particular job.

I did a little better with a keene's dredge prior (one of their first models that you couldn't get wet), up along the Umpqua watershed, east of Roseburg. One of the 'glamorous' jobs I sought right out of highschool was logging in the woods. That 24 year old greeney on AxMen pretty much mirrors my experience setting chokers, high-leading (yarder), and helicopter logging later on near Red Bluff, CA, and time in a redwood sawmill at Scotia. A lot of work, ornery boss and work partners, ticks, extreme accidents, and bad deals working with a cat skinner; not to mention not all that great paychecks.

I never really knew about the whole scope of placer mining in southwestern oregon, and northern california till decades afterwards, and that there were sizeable nuggets and hydraulicking like there was in the siskiyous and west of grants pass. Oh well...

[fishbone]

I have'nt posted in a while, ( had a electrical injury 6 months ago so I've been offline for a while ). Nonetheless. I have used them since they came out, and used them on California Beaches, and it works. Check out cleangold.com. They make a very cool product. Some may know of it, but most do not. I use them for clean ups, and end stage Dredge sluice, but mostly for Beach placers.

Cheers, John