When a site where gold is known to occur has been found, and after it has been sampled and judged worthy of further effort, the ownership status should be checked to assure that the ground is open for claiming. Then, after staking adequate claims (or arranging to lease if the ground is not open to claim), you are ready to consider mining. Whether mining permits are required by those State agencies involved with fish and game or watersheds should be investigated, because placer operations of any size may drastically change the local water quality. A simple operation may have virtually no effect on a stream or surroundings, but when materials amounting to more than a few cubic yards a day are handled, the possible effects begin to become significant.

Choosing a Gold Placer Mining Method

Among the simpler hand methods of recovering gold are the gold pan, the rocker, the dip-box, the long tom, and the sluice. Panning has been described in a previous section, entitled “How to Look for Placers,” and will only be discussed briefly here. The pan is generally too slow to be effective for anything more than prospecting. The rocker is a time-honored device of the small-scale miner with limited means. The dip-box and long tom might be considered more like simplified sluicing methods than distinct methods in themselves. As a method, the long tom has never been very popular but is described here for its possible historical interest. Other methods used in specific circumstances would include the surf washer, the dry washer, and skindiving.

The simpler methods all normally involve hand-mining operations (shoveling and/or picking of the gold-bearing materials). Limited mechanization is sometimes practical for moving and washing gravels in even the smallest operation, and this possibility should not be overlooked. Even motorized devices for panning are marketed by several manufacturers. Pumps and small excavators can often be adapted to the small mining operation by the enterprising miner.

The more complex methods, such as ground sluicing, hydraulicking, drift mining, excavation using powered equipment, and dredging, require considerable investment, knowledge, and experience; a full discussion of these methods is beyond the scope of this report.

The choice of method depends primarily on the scale of operation and the availability of water. These and other characteristics of the different methods are discussed below.

Gold Panning

 

Gold Rocker & Cradle

 

Dip-Box

The dip-box is useful where water is scarce and where an ordinary sluice cannot be used because of the terrain. It is portable and will handle about the same quantity of material as the rocker.

Construction is relatively simple. The box has a bottom of 1- by 12-inch lumber to which are nailed 1- by 6-inch sides and an end that serves as the back or head. At the other end is nailed a piece approximately 1 inch high. The bottom of the box is covered with burlap, canvas, or thin carpet to catch the gold, and over this, beginning 1 foot below the back end of the box, is laid a 1- by 3-foot strip of heavy wire screen of about ¼-inch mesh. The fabric and screen are held in place by cleats along the sides of the box. Overall length may be 6 to 8 feet, although nearly all gold will probably collect in the first 3 feet. The box is placed so the back is about waist high; the other end is ½ to 1 foot lower. Material is simply dumped or shoveled into the upper end and washed by pouring water over it from a dipper, bucket, hose, or pipe until it passes through the box. The water should not be poured so hard that it washes the gold away. Larger stones (after being washed) are thrown out by hand, or a screenbox can be added to separate them. Riffles may be added to the lower section of the box if it is believed gold is being lost.

Long Tom

 

Sluice

 

Additional Methods Sometimes Used

The methods described below, particularly the surf washer, are limited in application, but interest in them revives from time to time, so they are included hero. Many kinds of dry washers have been developed, some very elaborate. Most dry-washing operations have a short lifespan, owing to the erratic character if the deposits. Skindiving for gold is not new, but development of better diving equipment in recent years has stimulated interest in the method, although restricted in practice to a few select stream areas. Shaft and drift mining are also among methods used in extracting placer gold gravels, but because techniques are more related to other types of mining, discussion is not included in this report.

Dry Washer 

 

Surf Washer Gold Beach Deposits

Few sea-beach-type placer gold deposits have been mined successfully. The most important producers have been in the vicinity of Nome, Alaska, but gold is also known to occur in a few other shoreline locations of States bordering the Pacific Ocean. Special techniques have been developed to utilize the action of the surf in recovering gold from these deposits.

Surf washers are similar to long toms, but wider and shorter. They can be used only when the surf is of proper height. They are set so the incoming surf rushes up the sluice, washes material from the screen box or hopper, and retreating, carries it over the riffles and plates. One man can attend to two surf washers, and about 8 cubic yards can be handled per 10 hours.

An example of a simple surf washer is a riffled sluice 3 to 4 feet wide and 8 to 10 feet long, set on the sand at the water’s edge so that the incoming waves wash through it to the upper end, and retreat below the lower end. The sluice is made of boards nailed to sills at either end which can be weighed down with rocks or otherwise. The sides are 4 or 5 inches high. The riffles in the example are made in sections of about 1- by 1-inch strips spaced about 1 inch apart. The end sections are transverse riffles, the center section longitudinal. The box preferably is set on a grade of 8 to 10 inches per 12 feet. Best results are obtained by using mercury in the riffles. When the surf is strong, the washer treats as much as two men can shovel, but at other times it has to be fed very slowly.

Skindiving Gold

In recent years skindiving enthusiasts have taken up small-scale placering as both a hobby and a sometimes, though seldom, profitable venture. Various kinds of apparel and equipment are used, but the investment is usually not great. Wet suits and canvas shoes are almost a necessity for entering cold mountain streams to search the streambed for pockets that might contain gold. Beginners should be equipped with a snorkel, a face mask, gloves, a weighted belt, fins, a gold pan, and a crevicing tool. More experienced divers may use the popular scuba equipment, but this calls for special knowledge to insure safety. Crevicing tools include large spoons, tire irons, crowbars, etc. almost anything that can reach into tight places and dislodge nuggets from the stream bottom. The pan should be used to test sands from various places where gold would be expected to settle, such as the downstream sides of obstructions. Where colors in the pan indicate a favorable area of the stream, a more intense search may be made.

Mining equipment may include various combinations of pumps, miniature dredges, and riffle boxes that can be built from salvage by the operator or purchased from commercial sources. A number of manufacturers have produced special equipment for the purpose. One of the popular kinds is the jet dredge a pipelike device made of sheet metal curved at the intake end and with a water jet entry to propel the water and gravel through the straight portion. The jet is supplied from a portable pump and in effect causes gravel and sand to be sucked into and through the pipe. A riffle box built into the end section collects the gold and other heavy particles while the rest of the material discharges. The riffle box may be enclosed so it can function while submerged. Usually, a 6- to 10-horsepower pump is adequate; the hose to the jet may be 1½ to 2 inches in diameter.

Manipulating the device underwater requires skill and patience, since the riffle section must be kept nearly horizontal during the mining operation. Floating platforms are sometimes used to support equipment. In this case, riffle boxes and other units may be installed on the platform. The usual operation includes moving many large boulders to get at the trapped gold underneath or alongside. Conventional equipment such as a rocker or a sluice may be employed to carry selected material from the streambed to a shoreline site for processing. Concentrates are then panned to recover the gold.

Problems in Placer Mining

Besides the many problems already discussed, such as where and how to find a placer deposit, how to locate a claim, and how to sample and mine, a few special operational problems should be considered. These relate to the physical nature of placer materials and the climatic conditions under which they may be found.

Streams with steep gradients often have poorly sorted sands and gravels, meaning a wide range of size will be encountered, up to cobbles and large, irregularly shaped boulders. Other debris and tree roots may be present too. Materials that have lain in place for long periods become indurated (that is, bound up tightly with clay, or cemented sometimes almost to the point of being solid rock), which makes them exceedingly difficult to break up with water. Irregularities in the rock surface underlying placer materials become important in mining because this is the zone where the richest values usually are found. A very uneven surface can be particularly difficult to work on. In addition, there is difficulty in Alaska where ground may be frozen a large part of the year. It may be impractical for the weekend or vacation prospector to tackle placers where such adverse conditions prevail. How these problems are normally dealt with in larger operations is discussed briefly under the headings to follow.

Boulders

Boulders are best left in place if it is at all possible to work around them. Sometimes, particularly in sluicing, it becomes necessary to move the boulders out of the way. A derrick operated by a hand winch or steam, gasoline, or electric power may be used for this purpose. Possibly several such derricks will be needed if many boulders are present. Boulders may be drilled with a jackhammer and blasted using dynamite, or more simply blasted with an explosive plastered onto the rock, a technique called “mudcapping.” Platform skips may be swung from a derrick boom or cableway; the larger rocks are then pried out and rolled into the skip for removal. A small bucket-loader vehicle may be useful for handling boulders, provided it can operate over the type of surface exposed on the pit floor. Sections of the pit where bedrock has been cleaned up may be reserved for stacking large rocks. Future operations should be planned so repeated handling is avoided.

Trouble With Clays and Cemented Gravels

Clays and cemented gravels usually require the cutting force of the hydraulic giant for effective mining. In some nonfloating washing plants the gravel is delivered to the head of the sluice where a giant is used to break up the clay. Indurated or clayey materials are normally dredged with little difficulty, but if gravels are tightly cemented, they may best be rained by shaft or drift methods using explosives and timbering as required. This presumes they are rich enough to stand the high cost of such mining and are not exposed enough for open pit mining. Clay lumps must be broken up quite thoroughly before passing through gold-recovery equipment because of their capacity to imbed gold particles and carry the gold out with the discharge. The breaking of clays can be accomplished using the puddling box (previously described on p. 29) or with a trommel, which quickly reduces the lumps by its rotation and abrading action. Exposure of clays to air is also effective in breaking them down, although the time required may be a matter of days or weeks.

Cleaning Bedrock

Cleanup of the last remaining materials from bedrock is an important step in gold placering, and if the surface is soft, fractured, or uneven, this can be a painstaking chore. Where bedrock is soft; and fractured, gold particles can be embedded as much as several feet, so it often is advisable to also excavate this kind of bedrock material for its gold content. Usually, it is best to clean the bedrock as the work progresses upstream. A final cleaning of the surface may be left until the end of the season, when there is more time to spend on this activity and when the water is short for other work.

Where bedrock is hard it must be cleaned largely by hand, and the soft seams and cracks invariably present should be cleaned out with handtools. A hose and small pump are almost necessities for a good cleanup. Sometimes a separate sluicebox smaller than that used in the main operation will be employed for handling materials from a cleanup operation.