Gold Placer Prospecting

Placer gold has tantalized many a person who has tried his luck and skill in the hope of striking it rich. Separating gold from embedded materials is basically simple, and can be done effectively on nearly any scale, depending upon the deposit and the capital available for investment. The final product is consistently in demand at a relatively stable price. Historically, however, one must be advised that rewards for the majority of small-scale miners those who operate “on a shoestring” have been depressingly small.

First of all, the placer miner must know where placer deposits are located and he must have the technical knowledge to extract the gold. Additionally, he must face problems of land ownership, water supply, and water pollution, all of which have grown in complexity with the population. The costs of labor and equipment are relatively high now, although this may not seem significant to an individual mining a small deposit. Second hand equipment may become available at relatively low cost because of a slowdown in construction or as surplus at the end of a war. By taking advantage of such opportunities, one can sometimes make an otherwise unprofitable operation successful, at least as long as the equipment holds up.

To the novice or “weekend prospector,” the more complex features of placer mining may seem hard to comprehend. At any rate, the novice is often more interested in the recreational values offered by gold placering than in its profitability. Thus, the search for and discovery of even a small grain or nugget of gold is an achievement worth considerable effort. As a start, the beginner may gain some benefit from visiting one of the many pan-for-a-fee tourist establishments typically found in gold-mining areas.

The small-scale miner may sell his gold, but often he keeps it as a souvenir, or for use in some kind of jewelry, or in the hope that its value will appreciate. Seldom is a placer gold venture truly profitable when all costs are considered under existing circumstances. On the other hand, an individual or a family can gain a great deal of pleasure and satisfaction from the experience of producing your own gold. Producing your own, even on a small scale, involves a number of problems which this publication attempts to discuss. Because the subject is so extensive, the reader is referred to other reports in the bibliography for more detailed information.

Where to Find Placer Gold

Figures 1 and 2 show general areas of the conterminous United States and Alaska, respectively, where placer gold has been produced. Placers can be found in virtually any area where gold occurs in hard rock (lode) deposits. The gold is released by weathering and stream or glacier action, carried by gravity and hydraulic action to some favorable point of deposition, and concentrated in the process. Usually the gold does not travel very far from the source, so knowledge of the location of the lode deposits is useful. Gold also can be associated with copper and may form placers in the vicinity of copper deposits, although this occurs less frequently.

Geological events such as uplift and subsidence may cause prolonged and repeated cycles of erosion and concentration, and where these processes have taken place, deposits may be enriched. Ancient river channels (referred to as

the “Tertiary channels” in California) and certain river bench deposits are examples of gold-bearing gravels that have been subjected to a number of such events, followed by at least partial concealment by other deposits, including volcanic materials.

Residual placer deposits formed in the immediate vicinity of source rocks are usually nut the most productive, although exceptions occur where veins supplying the gold were unusually rich. Reworking of gold-bearing materials by stream action leads to the concentrations necessary for exploitation. In desert areas deposits may result from sudden flooding and outwash of intermittent streams.

As material gradually washes off the slopes and into streams, it becomes sorted or stratified, and gold concentrates in so-called pay streaks with other heavy minerals, among which magnetite (black, heavy, and magnetic) is almost invariably present. The gold may not be entirely liberated from the original rock but may still have the white-to-gray vein quartz or other rock material attached to or enclosing it. As gold moves downstream, it is gradually freed from the accompanying rock and flattened by the incessant pounding of gravel. Eventually it will become flakes and tiny particles as the flattened pieces break up.

Some gold is not readily distinguishable by the normal qualities of orange-yellow to light yellow metallic color and high malleability, where it occurs in a combined form with another element, such as tellurium. Upon weathering, such gold may be coated with a crust, such as iron oxide, and have a rusty appearance. This “rusty gold,” which resists amalgamation with mercury, may be overlooked or lost by careless handling in placer operations.

As mentioned before, the richest placers are not necessarily those occurring close to the source. Much depends on how the placer materials were reworked by natural forces. Streambed placers are the most important kind of deposit for the small-scale operator, but the gravel terraces and benches above the streams and the ancient river channels (often concealed by later deposits) are potential sources of gold. Other types of placers include those in outwash areas of streams where they enter other streams or lakes, those at the foot of mountainous areas or in regions where streams enter into broader valleys, or those along the ocean front where beach deposits may form by the sorting action of waves and tidal currents. In desert areas, placers may be present along arroyos or gulches, or in outwash fans or cones below narrow canyons.

Because gold is relatively heavy, it tends to be found close to bedrock, unless intercepted by layers of clay or compacted silts, and it often works its way into cracks in the bedrock itself. Where the surface of the bedrock is highly irregular, the distribution of gold will be spotty, but a natural rifflelike surface favors accumulation. Gold will collect at the head or foot of a stream bar or on curves of streams where the current is slowed or where the stream gradient is reduced. Pockets behind boulders or other obstructions and even moss-covered sections of banks can be places of deposition. Best results usually come from materials taken just above bedrock. The black sands that accumulate with gold are an excellent indicator of where to look.

It should be kept in mind that each year a certain amount of gold is washed down and redeposited during the spring runoffs, so it can be productive to rework some deposits periodically. This applies chiefly to the near surface materials such as those deposited on the stream bars or in sharp depressions in the channels. The upstream ends of stream bars are particularly good places for such deposits. Where high water has washed across the surface by the shortest route, as across the inside of a bend, enrichment often occurs. A rifflelike surface here will enhance the possibility of gold concentration.

In prospecting areas with a history of mining, try to find places where mechanized mining had to stop because of an inability to follow and mine erratic portions of rich pay streaks without great dilution from nonpaying material. Smaller scale selective mining may still be practical here if a miner is diligent.

Placer gold occurs in so many areas that it would be impractical to try to identify each of them here. One of the best recent publications covering individual districts and areas is U.S. Geological Survey Professional Paper 610 Principal Gold Producing Districts of the United States, published in 1968. Also, a series of reports is being written describing the individual placer gold deposits of various States or portions of States, to be published as Geological Survey Bulletins. For general areas of occurrence the maps in figures 1 and 2 may be consulted. Specific locations and names of mines can often be found on the detailed maps prepared by the U.S. Forest Service, the U.S. Bureau of Land Management, the U.S. Army Corps of Engineers, or the U.S. Geological Survey. Various State agencies may also have appropriate maps on hand.

Prospect for Placer Gold in California

California has led all other States in placer mining and as would be expected has many gold-producing areas of interest, particularly including the deposits on the Feather, Mokelumne, American, Consumnes, Calaveras, and Yuba Rivers and their tributaries. These rivers reach into the famous Mother Lode area of the Sierra Nevada Mountains from which much of the gold is derived. Deposits are also found in the drainages of the Trinity and Klamath Rivers in northern California and at scattered points in the southern part of the State. Ancient Tertiary channels and gravels of the Sierra Nevada Range have been especially productive sources of gold, and maps have been published by the California Division of Mines and Geology showing approximate routes of these features. Two U.S. Forest Service maps that the prospector would find of particular value in considering the Sierra deposits are of (a) the Downieville, Camptonville, and Nevada City districts, Tahoe National Forest; and (b) the Foresthill and Big Bend districts, also in the Tahoe National Forest. Maps covering the Trinity and Klamath National Forests of northern California might also be of interest.

Placer Gold Prospecting in Alaska

Most of Alaska’s gold production has come from placers, principally chose in the Yukon River Basin, although deposits are known on nearly all major rivers or their tributaries. Beach deposits in the Nome district have been notably productive, as have the river and terrace or bench placers in the drainages of the Copper and Kuskokwim Rivers. Figure 2 shows the main placer districts of the State. Climatic conditions play a great part in mining in Alaska, and the season for hydraulic operations of any kind is relatively short.

Find Placer Gold in Montana, Idaho, Oregon, & Washington

Montana’s principal placer mining districts are in the southwestern part of the State. The Helena mining district and the many placers along the Missouri River in the vicinity of Helena and upstream are among the more important areas. The headwaters and tributaries of the Missouri in Madison County, particularly near Virginia City and Bannock, are noted for early placer production. Placer gold has also been produced on the headwaters of the Clark Fork of the Columbia River at a number of points.

The Boise basin, northeast of Boise, Idaho, is most noted for the dredging of placers. Other well-known placer areas lie along the Salmon River in Lemhi and Idaho Counties and on the Clearwater River and its tributaries particularly in the vicinities of Elk City, Pierce, and Orofino. Placer gold is also found along the Snake River, but this is commonly fine-grained or “flour” gold that is difficult to recover.

Oregon’s placers are located mainly in the southwestern part of the State on tributaries of the Rogue River and on streams in the Klamath Mountains. Main gold-producing areas are the Greenback district in Josephine County and the Applegate district in Jackson County. Placer gold also occurs in many of the streams that drain the Blue and the Wallowa Mountains in northeast Oregon. The Sumpter area and the upper Powder River have had important production. Other areas include the Burnt River and its tributaries and the John Day River Valley.

Washington is not noted for placers, although gold has been found along a number of its streams, including some on the western slope of the Cascade Mountains. Generally, the few productive placers have been confined to the north-central part of the State.

Look for Placer Gold in Nevada

Nevada has not been a large placer gold producer, although lode gold deposits—potential sources—are widely distributed throughout the State. The problem has been chiefly one of too little water. In the past, dry washers were used extensively, as well as other methods that were very conservative of water. Producing areas were largely found in the western half of the State and included American Canyon and Spring Valley in the Humboldt Range, Pershing County, and the Manhattan and Round Mountain areas of Nye County. Placers were also worked below Virginia City and in northern Elko County near Charleston. Signs of limited placer diggings may be seen in many parts of the State.

Discover Placer Gold in Colorado

A few important Colorado placers of the residual type are found on slopes and hillsides in the immediate vicinity of gold veins. However, placers in Colorado are generally confined to narrow canyons below lode gold mining areas within the Rocky Mountains in a belt which extends northeast across the western part of the State. Almost every gold district has had some placer production. Many of the streams emerging from the Front Range, the headwaters of the South Platte River, and the Arkansas River and its tributaries as far upstream as California Gulch contain placer gold. Historically, placers were mined first and led to development of Colorado’s rich lode deposits.

Prospecting for Placer Gold in USA

Among the other Western States, placer raining has been limited to only a few localized areas. In South Dakota, the Black Hills (particularly the Deadwood area) and French Creek, near Custer, have been productive sources. Arizona and New Mexico placers are in some instances related to copper deposits that carry gold.

In the Eastern States some of the streams draining the eastern slopes of the southern Appalachian Range have yielded gold. Saprolite deposits (rock decomposed at the original site) have been a source of placer gold in Georgia and the Carolinas. Generally, the eastern placers are sparsely distributed and the gold is low in grade. Thus, few serious efforts have been made at mining them since the early 1800’s. Nevertheless, many locations offer possibilities for small operations intended primarily for recreational purposes.

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How to Look for Gold Placer Deposits

Once decided on the area of search and armed with some knowledge of the characteristics of deposits to look for, then you are ready to explore. Most areas are relatively settled today and are accessible by car, or at least lie within a few miles of a road. A possible exception is Alaska, where an aircraft or boat might be needed to reach the site. Regardless of the type of transportation, you will need adequate supplies and equipment to sustain you and your companions for an extended stay in the field. With a gold pan for each and setting out from a base camp it should be possible to determine within several days if the potential for the area is good.

Prospecting Equipment

Camping and outdoor recreation in general have become so popular that many commercial sources of equipment and information are now available. Some stores appeal to the budget-minded, while others, such as the specialty shops for camping supplies, have a wider selection of usually more durable products. Books on camping are available at the library, and reliable merchants will recommend the equipment best suited for a particular use. Many of the comforts of home can be found in the ordinary camp today. Backpacking has benefited from developments in lightweight materials and foods. The amounts and types of goods and equipment selected will depend on the remoteness of your location and accessibility of a resupply point. The prospector might wish to travel with a mobile home, trailer, or camper, or he might simply pack his gear on his back and head up the trail. A few suggestions are in order here, but the individual must do much of his own planning, since requirements and tastes vary so greatly.

Basic Gold Prospecting Equipment

Among the essential implements needed for prospecting are a pick; a long- handled, round-pointed shovel; and a gold pan, preferably a 10- or 12-inch- diameter pan which can usually be purchased at hardware stores in gold-mining areas. A small prospector’s pick is also useful, and a magnet and a small amount of mercury should be carried to separate the gold from black sand after panning. Specialty stores and manufacturers can provide the more elaborate equipment, such as skindiving gear, ready-built sluices, and mechanical gold separation devices, if desired.

In some cases, a bucket or wheelbarrow may be needed to transport materials to the washing site, and in addition, a heavy ¼- to ½-inch-mesh screen is handy to separate out coarse materials. A small screen cut to nest in the upper part of a gold pan can be useful for the same purpose in panning. A gold pan the same size as the one used for panning will make a most efficient nesting screen if a close pattern of holes is drilled in the bottom. Holes usually should be ¼ to 3/8 inch in diameter, depending on the average size of the material being sampled. Distance between holes should be about the same as the diameter of the holes. In some areas these pans can be purchased readymade. For weighing gold, a small balance scale graduated in milligrams may be desirable. A compact, folding type of balance is available for this purpose.

A compass will be needed for establishing claim lines and for finding your way out of the woods if lost. Adequate maps should be carried. A hand magnifying lens is helpful in identifying minerals. Bags may be needed to carry out samples; plastic bags are the best because samples may be damp. A rocker may be transported to the site either assembled or in a knocked-down condition. If mining is planned, lumber and other materials to build a sluice may be carried to the site. (See construction details under respective headings.) More elaborate equipment such as pumps, pipes, hoses, and light plants might be taken in by pack animals if desired.

Personal gear includes a good pair of boots, sturdy clothing, weather-proof gear, sleeping bag, tent, and such other things as one might want for comfort and sanitation. A foam pad or air mattress adds comfort to sleeping. A length of rope is useful for many purposes around camp, from raising the food out of reach of animals to extracting a car from a mudhole. For hiking, all necessary equipment for the period away from camp should fit into a manageable backpack of some kind.

An ax, a flashlight, a knife, and matches are almost indispensable. (Fires in the National Forest should be made only in designated areas or after consulting the local forest ranger.) A water bucket is often required, and a good crosscut saw will be found useful. Guns and fishing equipment can be taken to supplement the food supply and to provide some additional recreation. Guns are seldom necessary for protection from animals. A canteen with a 2-quart or larger capacity is advisable in many areas, depending on dryness of the climate. You will need water-purification tablets where streams are contaminated, whether by grazing stock or for other reasons. A miner’s lamp, which consumes calcium carbide, is sold at some hardware stores and can be used for a serviceable light, although most people when away from electricity prefer gasoline or propane lamps. A carbide lamp will also be useful for any underground work. The special miner’s safety lamp is recommended wherever air may be bad. Stoves that burn gasoline or pressurized gas are in wide use in camping and even gas refrigerators may be taken along “to cool the beer.” (For low-budget operations, a swift-running stream will serve this same purpose well.) For any length of time in the field, an oven for baking is a valuable amenity. A reflector oven for use next to a campfire can be made of light sheet metal and will give excellent results, also serving as a place to keep food warm.

Supplies

Freeze-dried foods are generally good and easy to carry and prepare, although somewhat more expensive than most other foods. For estimating pack weights, about 2 pounds of dehydrated and freeze-dried foods is needed per person per day. Canned foods should be avoided when backpacking because of their weight, but they are otherwise satisfactory. Disposal of empty containers should be done with consideration to others who may follow and wish an uncluttered landscape; burial is usually recommended.

Suggested food supplies for a prospector’s camp include the following: bacon, beans, cheese, salt, baking powder and soda, coffee, tea, onions, potatoes, fruits, corn, peas, raisins, rice, flour, crackers, cereals, butter or margarine, powdered milk, eggs, pancake and waffle mix, sugar, syrup, and fresh meat and vegetables as practicable. Many other items can be added to the list, but these are most of the basics. Utensils should include a variety of dishes, silverware, a sharp knife, spatula, can opener, frying pan, coffee pot, and several different sizes of pots and pans. Towels, both paper and cloth, soap, scouring pads, and metal or plastic tubs or basins will be needed for cleaning up.

Extra clothing should be included in your supplies for warmth and for changes. Mosquito netting may be a virtual necessity in some areas, and adequate amounts of a good insect repellent should be packed.

Safety Needs

Probably the most troublesome and at times the greatest hazard in the wilds today is the bear. People may argue which type of bear has the meanest temperament, but any type may leave your camp a shambles when in search of food, and under certain circumstances any bear will attack a person. Placing food out of reach or in a secure container will help reduce the attraction. Fortunately, most bears will turn and run when frightened by loud noises.

Other wild animals are seldom dangerous except when provoked, but smaller ones such as packrats can inflict considerable damage on camp gear and foodstuffs. Poisonous snakes, spiders, ticks, scorpions, and the like should be treated with traditional caution; their presence should be anticipated in most areas. Learn to identify and avoid poison oak and poison ivy! Knowledge of first aid is essential for dealing with emergencies that might arise on an outing, and a study or review of the subject should be included in any preparations.

Some of the personal hazards faced in the out-of-doors include twisted ankles, lacerations from falling in brush, falls from slippery rocks or crude bridges when crossing streams, breaking through floors in old building ruins, and falls or cave-ins in old mine workings. Beware of bad air in any old workings! Danger of drowning is always present when working around the deeper streams or pools when placer mining.

Many types of first aid kits and equipment are on the market. The choice of kit is one of size and variety of content. A snakebite kit is usually a separate accessory and should be carried, even though it is rarely put to use. Disinfectants, aspirin, fungicides, bandages, and similar items should be included. For areas of considerable sunshine, tanning lotion, sunglasses, and a hat are needed, and salt tablets should be taken as designated to prevent heat prostration. Wearing a safety hardhat and safety glasses may be advisable at times.

Should you Invest and Mine

This question becomes more difficult to answer as the size of the planned operation increases. Estimation of the amount of gold recoverable and the overall costs of investment and mining is no simple matter and calls for highly experienced engineering skills for any moderate- to large-scale project. Elaborate procedures of sampling and evaluation cannot be followed by the small-scale operator because of the cost. Thus, his decisions must be based on a variety of factors, not the least of which is intuition. Needless to say many mistakes have been made, with much resultant waste of money and effort. Do not let what started out as a recreational activity become your master instead of your servant.

Sampling Techniques

Many methods of sampling are possible, including the simple panning of gravel from surface exposures, churn drilling, test pitting and trenching, shaft sinking, and drifting. As an aid in tracing possible gold-bearing channels, geophysical techniques have been employed with some success, but proper use of the typical instruments involved is generally reserved to experts. Moreover, interpretation of results is seldom adequate to provide any quantitative estimates, although the information gained can be useful in planning an exploration program.

For a thoroughgoing discussion of exploration and sampling techniques the reader is referred to the recent Bureau of Land Management publication by John H. Wells, entitled Placer Examination: Principles and Practice. Wells description of panning is particularly recommended.

Panning and rocking (described later) are the basic means of determining the recoverable gold content of placer materials. A fire assay, sometimes made on a concentrate, provides a relatively complete estimate of the gold content of the material, but a poor estimate of how much gold can actually be extracted by conventional washing methods. Thus, placer gold is seldom assayed, except to determine its fineness (measure of gold purity). In estimating the value of gold in the pan after washing a quantity of gravel, the technique of counting nuggets and “colors” is normally followed. Generally, pieces worth more than 5 or 10 cents are considered as nuggets; smaller particles are colors. When skill is developed in estimating the various sizes of particles, a good degree of consistency can be achieved in the results.

Where samples can be obtained across a section of the bank exposed along a creek, it is good practice to cut a vertical groove or channel of fairly con sistent width and depth. The sample may be cut from top to bottom, or in segments comprising several different samples if the bank shows distinct changes in materials. Bars may be sampled by digging a vertical hole, clear to bedrock if possible, and panning the product. For surface mining of “skim bars,” sampling consists of simply taking a panful from a favorable point and visually estimating the amount of similar material In the vicinity. Clearly, there is not much accuracy in any of these methods, but the deposition of gold in such locations is bound to be erratic anyway. More representative sampling is usually possible in the larger deposits where deposition and size of gold particles is more uniform or consistent.

How to Calculate the Value of a Gold Placer

For the small-scale miner, sampling will usually be limited to taking a panful here and there and possibly running a larger sample through a rocker or sluice if panning discloses any gold. If colors are found, a record should be made of the number and estimated size of colors per pan and the approximate location. The sampling then progresses until one is assured the prospects are good enough to warrant a mining operation of some sort.

A scale of sizes and approximate values of colors based on pure gold at $35 an ounce is as follows: (Note: Mesh = screen size in openings per square inch; minus 10- plus 20-mesh material will pass screen with 10 openings per square inch but be stopped by screen with 20 openings.)

• Coarse gold, plus 10 mesh: should be picked out and weighed individually, value about $1 per gram.
• Medium gold, minus 10 mesh but plus 20 mesh: 2,200 colors per troy ounce, value about two-thirds of a color to 1 cent.
• Fine gold, minus 20 mesh but plus 40 mesh: 12,000 colors per troy ounce, value about 3 colors to 1 cent.
• “Flour” gold, minus 40 mesh: 40,000 colors per troy ounce, value about 10 colors to 1 cent.

Differing fineness or price will affect the values somewhat.

It is common to report panning results in cents per pan. So, assuming you have determined that a “pan factor” of about 400 pans per cubic yard (bank measure) for the 12-inch pan is a suitable figure, multiplying the cents-per- pan figure by 400 gives the estimated value per cubic yard.

Another means of estimating is to rank the colors into three groups, as follows.:

• Number 1: colors weighing over 4 milligrams
• Number 2: colors weighing between 1 and 4 milligrams
• Number 3: colors weighing less than 1 milligram

(Note: 31,103 milligrams equals 1 troy ounce.)

Scales will be needed to check the weights until the eye can judge the sizes properly. It is recommended that particles over 10 milligrams be weighed individually. A rough measure of value is one-tenth of a cent per milligram. Thus, the value in a pan can be calculated using your visual count and tally of the number of colors of each rank. After sufficient practice, good estimates will come easily. Thickness has a great bearing on weight: For instance, some gold might look large, but actually be flat, flaky, and hence very light.

Determining the overall value of a deposit with any accuracy calls for a knowledge of accepted practices and mathematical procedures for weighting the values and sample intervals it is important also to understand the statistical principles of variation and distribution, which are beyond the scope of this report. Generally, the practical prospector will take a few measurements, make some crude calculations using his panning results, and decide to stay or move on.