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VOL. 1   ISSUE 1

THIS ISSUE:

____________________________________

By William B. Clark

California Division of Mines and Geology

    Diving for gold in the streams of California has been a popular hobby for some years. Diving was first done in the state by the “Forty Niners” during the days of the gold rush, but apparently only in a few areas and for short periods of time. Self-Contained Underwater Breathing Apparatus (known as scuba) was developed by French and U.S. Navy frogmen during the 1940s. Soon afterward all types of recreational and sport diving became popular. Apparently diving for gold in California with this type of equipment began in the late 1940s or early 1950s.

    This interest in diving for gold in California is associated with the general interest in the historic gold-bearing regions and in gold prospecting and small-scale mining by amateur prospectors, tourists, snipers, and pocket miners. A few “strikes” have been made where small but rich deposits of placer gold have been found in deep cracks or crevices in the streams that were missed by the early-day miners. Most of the rivers and larger creeks in the gold-bearing regions of California have been prospected by diving in recent years. Diving for gold has been done in some other states such as Alaska, Colorado, Idaho, and Montana, several provinces in Canada, and several countries in South America. Undoubtedly diving has been done in Asia and Africa, too. In Columbia, South America gold-and-platinum-bearing placer deposits have been worked by several generations of divers and continue to be worked at the present time.

HISTORY

    In the early part of the gold rush, miners first worked the shallow placers and high sand and gravel bars along the margins of the streams by small-scale methods. The equipment used in those operations included the miner’s pan, batea, sluice, rocker, and long tome. Soon the miners realized that the deeper gravels in the river beds were rich in gold and as early as 1849, attempted to recover gold from the bed of the American River near Sutter’s Mill at Coloma by diving. Shortly afterward, they dived in several other streams in the gold regions.

    Some of the early-day divers were probably “Kanakas” or native Hawaiian sailors who left their ships in San Francisco to work in the gold fields. There may have been South American and Chinese divers, too. There probably was some diving later, in the 1870s through the 1890s, when thousands of Chinese were active in the gold regions reworking the placer tailings deposits and re-mining the rivers.

    In the 1880s, several crude steam-powered suction dredges were active in the Feather, Stanislaus, and Yuba Rivers. In those operations divers worked on the bottoms of the streams to clear away boulders from the dredge’s pipe intake and to loosen well-packed gravels. Around 1904, an operation on the Sacramento River near Redding had a steel shaft or caisson that extended from a barge to the bed of the river. A diver working in the bottom of this shaft removed gold-bearing gravel with a nozzle which was attached to a hose and a pump mounted o the barge. Other short-lived diving operations in the early 1900s took place on the American and Feather Ri8vers. In most of these operations, divers employed deep-sea diving suits with metal helmets. Older publications sometimes referred to these diving suits as “sub-aqueous armour.”

    Lightweight and flexible diving equipment including various types of “wet” suits and scuba are now widely used in diving for gold.

    The equipment used in diving for gold varies considerably. The occasional or beginning underwater prospector and miner may have only a face mask, snorkel, and a gold pan while others may have complete scuba outfits, suction dredges, compressors, pumps, gasoline motors, and various types of gold recovery equipment. The outlay for equipment can range from a few dollars to more than $10,000. Because it often is necessary to hike over steep trails or climb down steep banks to the streams, durable equipment that can be carried by two men is the most satisfactory.

    Several experienced gold divers have recommended the following as the minimum equipment needed: diving suit, snorkel, face mask, fins, weighted belt, diver’s knife, gold pan, and crevicing tool. Although a diving suit isn’t absolutely necessary, low water temperatures in California’s streams make it difficult to do much work without one.

    There are two types of diving suits, wet and dry. Dry suits, which are composed of sheet rubber, prevent the water from having any contact with the body and are used mostly in very cold water. Wet suits are most commonly used by gold divers in California. They are close fitting but allow a little water to enter the space between the suit and diver’s body. Once inside the suit, the water is warmed by the body and serves as an insulating layer. Wet diving suits today are composed of neoprene foam rubber. Most divers wear gloves, the most practical being those with separate thumbs and forefingers. When moving around, divers wear fins; when working in one place, they wear boots or shoes. The amount of weight required to hold the diver underwater varies with the buoyancy of the diver. All weighted belts have quick-releases so they can be discarded in case of emergency.

    When a diver works in one place for a considerable length of time during an underwater gold operation and when a sustained air supply is required, many operators employ what is known as a “hookah.” A hookah consists of a long air hose connected to the diver’s breathing apparatus (regulator and mouthpiece) and an air compressor on the surface. In a hookah operation, the air hose allows the diver to move around freely within the length of the hose. The air compressor can be located either on shore, or as in many operations, mounted on floats so it can be towed after the diver as he moves around underwater. The compressors are of the diaphragm type and are operated by small gasoline motors. From the compressor, the air goes to a tank or receiver and then to the diver. This tank or receiver allows the air to cool, and also allows the diver a margin of safety in case the motor stops. If the compressor suddenly stops, the air in the receiver tank acts as an emergency supply, giving the diver enough air to reach the surface.

    All types of diving equipment can be purchased from any of the numerous dive ships in California. There are dive shops in most coastal cities as well as in Sacramento, Stockton, Fresno, and Bakersfield. At nearly all of them it is possible to get air tanks recharged.

GOLD RECOVERY EQUIPMENT

    Many different types of gold saving and concentrating devices have been invented and used over the years. Some have been successful, but many have been worthless. The most useful by far for the prospector and small-scale placer gold miner are the sluice box and the miner’s pan. Gold divers use both. They also use other items of equipment which include small suction dredges and jet dredges. A number of gold diving operations employ suction dredges and sluice boxes mounted on floats. As underwater mining operations are conducted, the suction dredge discharges into the sluice box. Later, during cleanup, the concentrates from the sluice are further concentrated by panning.

    A  device that has been used for some years in gold diving is a jet dredge which is sometimes known as a “sucker.” This is a pipe-like device that is curved at one end. They range from 4 to 8 feet in length and weight up to 20 pounds. The jet dredge is usually made of galvanized sheet metal, and the curved or intake end is of stainless steel or some other resistant material. At the upper end of the intake there is a valve that is connected with a hose which in turn is connected to a motor-driven water pump on the surface. Water under pressure is fed through the hose to the head. As the water is injected, a vacuum is created at the mouth which sucks in and then blows out the discharge end.

Keene Engineering 4" 6.5 HP Intek Pro Jet Flare Dredge with T80 Compressor 

    Although the jet dredges have a small riffle box at the discharge end, apparently they are most widely used now for removing overburden. After the overburden has been removed, the area is then mined with a suction dredge or by hand with crevicing tools. A useful device for prospecting and working narrow cracks and crevices is a large syringe known as a gold sniffer. This can be made from a grease gun, the best ones being those that unscrew on the front or nozzle end. Also, there are sniffers on the market which are plastic tubes connected in a large rubber bulb.

    Crevicing tools are needed to work the deep and often narrow cracks where the gold is most likely to be found. These tools include large spoons, knives, screw drivers, crowbars, and special types now on the market.

    Other useful equipment includes shovels, buckets, screens, prospector’s pick, hand magnifying glass for inspecting small gold particles, tweezers, gold scales, and small bottles or vials for storing gold. A number of divers attach small bags to their belts for placing gold nuggets that are found when working underwater. Underwater mining equipment is available for purchase at some of the dive shops in the San Francisco Bay area, Sacramento, Stockton, and the Los Angeles area. Equipment such as miner’s pans and prospector’s picks are available at many hardware stores.

    Sluices should be of sturdy construction, and yet light enough to be easily carried or set on floats. The portable sluice box most commonly used in gold diving is composed of sheet metal and is mounted on a float which is an inflatable rubber tube. The vacuum hose of the suction dredge is attached. Sand and gravel from the vacuum hose are discharged into a hopper at the upper end of the sluice box and from there pass over a screen. The material that passes through the screen then goes to the riffle section where the gold and other heavy minerals are deposited. Underlying the riffles is heavy cloth matting which helps to seal the riffles and to catch the find gold particles. The riffle section and matting can easily be removed by loosening the quick release latches which are along the sides.

PROSPECTING

    When prospecting, the diver should look for the most favorable places for the occurrence of gold. The first step involves a careful examination of the streams and the adjacent terrain. Natural features that should be noted are topography, nature of the bedrock including joint and crevice systems, stream currents, bends in the stream, and visible underwater features such as crevices, large boulders, or any other type of barrier that might act as a trap for gold. The deposition of gold is the result of the action of flowing water coupled with the shape of the stream channel and stream bed which have acted as natural traps. The processes involved in the action of flowing water are complex as they are dependent upon a number of variable factors which include shape of the channel, volume of water, and the slope of the stream channel.

    Wherever the natural features or a change in the volume of water flow have caused a sudden decrease in stream velocity, conditions are favorable for gold deposition. A decrease in velocity lowers the carrying power of the stream which then begins to deposit its sediment load. The heaviest particles, including gold, will be dropped first. Thus, concentration of gold can be expected where the stream widens, near quiet pools below rapids, or along bends in the channel. In a straight channel, the current is swifter near the middle than near the sides, and swifter above mid-depth than below. At bends the transportation and deposition of gold becomes complicated. Velocities within the stream change so that the greatest velocity is near the outer or concave part of the bend.

    The diver should then examine the stream bank for gold between the high water mark and the water level. The sediment in narrow cracks and crevices should be removed with a crevicing tool and panned. Material from the downstream side of the half-buried obstructions also should be examined. Small roots, moss, or other vegetal material near the water should be examined as they may trap fine gold particles. If gold or “colors” are found in the pan, that area of the stream is a good place to prospect further.

    Initial underwater exploration in the stream can be done with the snorkel. This avoids the large amount of work involved in setting up mining equipment in case the stream proves to be unfavorable. The initial underwater trip is to determine the configuration, location of natural gold traps, and the nature of currents. Deep narrow crevices and cracks, especially those that occur in steeply dipping rocks whose strike or trend is perpendicular to the stream flow, are particularly favorable for the occurrence of gold. A series of parallel deep narrow cracks at right angles to the direction of stream flow are especially good because they form natural riffles. Such traps are most likely to be found in slate, schist, gneiss, and heavily jointed granitic and volcanic rocks. In some cases, long trough-like crevices that are parallel to the stream flow act as natural sluice boxes. Natural irregularities at the bottom act as traps to catch the gold.

    Sometimes deep potholes are good gold traps. Potholes have been scoured out in the bedrock by gravels being spun around by eddying currents. They are most common below falls and rapids and are most abundant in crystalline limestone and granitic rocks. However, the scouring action also may tend to grind up and dissipate the gold. The downstream side of large boulders or any type of obstruction may be a favorable site because the eddying motion on the downstream side facilitates the deposition of gold.

    The gold is almost always concentrated near or at the bottom of such natural traps. It occurs as flat or rounded grains and flakes ranging from microscopic size to nuggets several inches across. The coarser gold usually is found at the greatest depths. Because many of the streams were mined in past years and the gold usually was recovered by amalgamation with mercury, some of the gold found at the present time may have been partially amalgamated with mercury and be nearly white in color. Also native mercury occasionally is found at the bottom of such streams.

    The gold is always associated with black sands that are composed chiefly of magnetite and smaller amounts of ilmenite, zircon, and garnet. Small amounts of pyrite or “fools’ gold” may be present in black sands. Small grayish-white grains of platinum may be present but usually only in extremely small amounts. Also present in stream beds are lead shot, old nails, small bits of scrap iron, and occasionally old coins. The presence of metal should be carefully noted when prospecting. The gold-bearing black sands are near or at the bottom of the natural traps and usually are covered by accumulated sands, gravels, cobbles, boulders, and wood fragments. Sometimes the overburden itself will contain values. The particles of gold found in the streams originally came from veins, mineralized zones, and older placer deposits from which they were released by weathering and disintegration of the rock.

    When prospecting a crevice underwater, the loose overburden can be partially removed by “fanning” it with cupped hands, and the heavier gold bearing black sands at the bottom can be removed with the crevicing tool. The gold sniffer is especially valuable here. Efforts should be made to determine the exact spot for mining operations. There is no magic formula to determine the presence of gold. The finding of gold is partly luck and observation. A knowledge of the gold-bearing regions in the state is extremely important.

    After the area to be mined has been determined, the equipment is then carried down to the stream and set up. If suction and jet dredges are to be employed, the first step is to remove overburden. It is easiest to work upstream when mining a deposit because the overburden and tailings can be deposited downstream from the operation by the natural flow of water in the stream. Summer and fall are the best times of the year to dive for gold because the water in the stream is low and clear. The deep and narrow crevices should be completely cleaned out, particularly the lowest and deepest parts because it is here where most of the gold is found. A rugged crevicing tool is most useful here.

    If the deposit is small and the diver has no suction or jet dredge, he can mine by hand and place the excavated material in a bucket that he takes underwater with him The material in the bucket is later concentrated by sluicing and panning.

    In any sluicing operation, it is important to “clean up” as soon as the riffles become full. During the cleanup, the riffles are removed and all the concentrates in the bottom of the sluice box are carefully washed into a bucket. The material on the cloth matting is also carefully washed into the bucket. If a jet dredge is used to recover values, its riffle box is dumped into the bucket. Usually the concentrates are further concentrated by panning at the end of the day. All nuggets, of course, should be kept separate from the fine gold, because they have the most value and are easiest to sell.

    If there is difficulty in concentrating very fine gold, it can be recovered by amalgamation with mercury. This can be done in a copper-bottomed pan, available on the market for this purpose. Also, it can be done in a revolving drum known as an amalgamating barrel. If a barrel is used, it is a good idea to have several steel grinding balls in it. Sometimes quartz cobbles are used in the barrel if the gold is rusty, that is, coated with limonite. A small concrete mixer makes an excellent amalgamating barrel. The gold is separated from the mercury by distillation, usually in a small iron-pot retort with a condenser so the mercury be reused. Caution should be used because the mercury fumes are very poisonous. The final product is called gold sponge.

    Very fine or “flour” gold is not abundant in California’s streams, and most divers will find that sluices and pans are adequate for retrieval of the gold. It should be emphasized that there are no magic or secret formulas for recovering gold-it is just hared work and a knowledge of how it is done.

    The most favorable areas for the occurrence of gold are the streams that flow through the gold-bearing regions. Although gold has been recovered in many areas in California, the most productive region by far has been the west slope of the northern and central Sierra Nevada. This region, which often is referred to as the Mother Lode area, extends from Butte and Plumas Counties on the north to Mariposa County on the south. Many millions of dollars worth of placer gold have been recovered from the streams in this region. The richest streams have been the Feather, Yuba, and American Rivers and their tributaries. Substantial amounts of gold also have been recovered from the Bear, Consumnes, Mokelumne, Stanislaus, Tuolumne, and Merced River in the southern Sierra Nevada. All of these streams have been mined one or more times so the amount of unworked or “virgin” ground is small.

    Large amounts of gold have been recovered from the Klamath Mountains in northwestern California. The placers of the Klamath-Trinity River system have been the largest sources of gold in that area. Both the gravels in the present stream channels and the adjacent older terrace gravels have yielded gold. The older terrace deposits were mined chiefly by hydraulics.

    Placer gold has been found in many other areas in the state, but the total output is small as compared to the Sierra Nevada and the Klamath Mountains. Water is scarce in many districts, and the streams are dry much of the year. The most productive placer mines in Southern California were in the San Gabriel Mountains north of Los Angeles and the dry desert placers of Kern, San Bernardino, and Imperial counties. Small amounts of placer gold were recovered years ago from a few streams in widely scattered areas in the Coast Ranges and in the Peninsular Ranges east of San Diego.

    Safety rules and precautions should be observed when diving for gold as they should in all diving operations. The buddy system should always be used, and a person should never dive alone. If you are out of sight of your buddy, you are diving alone. The gold diver should have sufficient experience so that he can handle the various situations and hazards that may be encountered in mountain streams. He should have a thorough understanding of the use and limitations of his equipment and a complete first aid kit should be taken on any gold diving expedition.

    Hazards that may be encountered include swift and treacherous currents, chilling water temperatures, snags, floating debris, caving banks, deep holes, shifting boulders, and old mine excavations. Diving usually is done in isolated areas often far from help. Because most gold diving is at depths of less than 30 feet, there usually are no decompression problems or danger of the bends. If diving is below 33 feet the U.S. Navy Standard Decompression Tables should be followed.

    Air embolism can be a hazard, even at shallow depths. If it is necessary to ascend rapidly, the diver must exhale continuously. This is necessary because the higher pressure in his lungs as he ascends into water of lower pressure will force the air in the lung’s air sacs into the blood vessels surrounding them and thence into the heart and brain causing unconsciousness or death. Published reports indicate that in scuba diving, air embolism is a close second to drowning as a cause of death.

    Because of the great amount of exertion in gold diving coupled with often chilling water temperatures, the diver should be in reasonably good health. On any expedition he should get adequate rest. Those who suffer from asthma, chronic bronchitis, emphysema, cardiac conditions, ear trouble, or have a perforated ear drum should not dive. Persons with colds or a sinus condition should not dive until they have recovered. Ear plugs should never be used in scuba diving. It is advisable to adhere to a high protein diet and avoid heavy gas-forming foods, alcoholic beverages, and drugs. Cuts and bruises should be treated promptly.

    When prospecting the diver should be acquainted with the various regulations that govern mineral rights and prospecting and mining operations. Much land belonging to the United States is open for mineral exploration. This includes land in the national forests, but this land is subject to U.S. Forest Service regulations. Land not open for mineral exploration includes privately owned land, national parks, military reservations, Indian reservations, land belonging to the State of California, county-or-city-owned land, reservoirs, permanent lake beds, certain wilderness and primitive areas, national monuments, most power sites, land situated below mean high tide, and the beds of navigable streams. Most mountain streams in California are not navigable.

    No maps exist that show the locations of land open for mineral exploration. The ownership status of land in a given area can be determined by looking for ownership signs, monuments, and location markers and searching the property records at the county seat. Deed and patent records in the office of the county assessor, and records pertaining to unpatented mining claims are in the county recorder’s office. Records of patented land also are in the Land Office of the U.S. Bureau of Land Management, Sacramento and Riverside.

    If the land is privately owned it may be possible to negotiate a lease or obtain a prospecting permit from the owner. If the land is owned by the State of California and was granted to the state for school purposes, it possibly can be leased from the State Lands Division of the State Lands Commission.

    Mining on the public domain without the benefit of a legally located claim is called “sniping” and initiates no legal right to the property. A “sniper” risks the possibility of dispossession by later claimants.

    Placer-mining operations are subject to the California Fish and Game Code and Water Code and county and city ordinances regulating discharge of debris into streams. The Porter-Cologne Act pf 1969 added new strength to the Water Code and the Regional Eater Quality Control Boards, which now have the power to prescribe severe restrictions for mining waste discharges. It is necessary to obtain a permit from the Department of Fish and Game to operate a suction dredge. Although there is hardly any hydraulic mining in the Sierra Nevada now, it is allowed only under permit from the California Debris Commission of the U.S. Army Corps of Engineers.

SELECTED BIBLIOGRAPHY

Averill, Charles V., 1946, Placer mining for gold in California: California Division of Mines Bulletin 135, 477 pp.

Boericke, William F., 1941, Prospecting and operating small gold placers, 1^{st edition, John Willey and Sons, Inc., New York.}

Council for National Cooperation in Aquatics, 1957, The new science of skin and scuba diving, Association Press, New York, 224 pp.

California Division of Mines & Geology, December 1963, Basic placer mining: Mineral Information Service, Special Supplement, 16 pp.

Clark, William B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, 186 pp.

Gilmore, Charles L. and Stewart, Richard M., 1970, Legal guide for California prospectors and miners: California Division of Mines and Geology, 133 pp.

Jenkins, Olaf P., and others, 1948, Geologic guidebook along highway 49-Sierran gold belt–the Mother Lode Country: California Division of Mines Bulletin 141, 221 pp.

Jenkins, Olaf P., 199694, Geology of place deposits: California Division of Mines and Geology Mineral Information Service, January through September, 1964.

Leopold, L.B., and Maddock, T. Jr., 1953, The hydraulic geometry of stream channels and some physiographic implications: U.S. Geological survey Professional Paper 252, 57 pp.

Lundgren, Waldemar, 1911, The Tertiary gravels of the Sierra Nevada of California: U.S. Geological Survey Professional Paper 73, 226 pp.

Pages of History, 1960, Diving and digging for gold, Naturegraph Publishers, Healdsburg, California, 24 pp.

Underwater Enterprises, 1960, Diving for gold: Underwater Enterprises, Sacramento, California, 39pp.

U.S. Navy, 1970, Diving manual: Navships 0994-001-9010, Navy Department, Washington, D.C., 687 pp.

von Bernewitz, M.W., 1943, Handbook for prospectors and operators of small mines, 4th edition, McGraw-Hill Book Company, New York, 547 pp.

By Eugene Nielsen

    In 1565, 43 years after Portuguese explorer Ferdinand Magellan discovered the Philippine Islands, Felipo de Salcedo sailed his tiny ship, the San Pablo, eastward from the Spice Islands of Indonesia with a cargo of cinnamon. Instead of trying to head straight towards Mexico, Salcedo, with Fray Andres de Urdaneta as navigator, set a northerly course across the vast and then uncharted Pacific Ocean, taking full advantage of the prevailing westerly winds. During the voyage, Salcedo discovered what is known today as the Japanese current. From then on, galleons returning from the Far East rode the current until they were near Cape Mendocino before turning south and following the coastline to Acapulco.

    Thus began a trading institution that would last for the next two and a half centuries. No other line of ships in history has endured as long. The Manila Galleons or Nao de China (China Ships), as they were called by the Spaniards, were the richest ships to sail the oceans. To the Spanish, they gave some substance of reality to the dream of empire over the Pacific.

    Indeed, it is questionable whether or not Spain could have retained control over the Philippines for as long as it did had it not been for the galleon trade. The enormous demand for goods from the Orient in Spanish America and for Mexican and Bolivian (Alto Peruvian) silver in the Orient assured Manila merchants of over 200 percent profits.

    The galleon trade flourished until the last half of the eighteenth century, when competition at Canton by the British and other European merchants began to seriously erode the profitability of the galleon fleet. In 1815, the last Manila Galleon put into port.

    In the early years of the galleon fleet, there was no uniformity in the number or size of the vessels. From one to four galleons of various tonnage set out for the Philippines from Acapulco each year. This changed, at least officially, with a decree in 1593 that restricted to two the number of vessels that might cross yearly and the tonnage of each ship to 300 tons. From 1593 until 1720, one or two galleons made the voyage each year. In 1720, it was expressly prescribed by Spain that two vessels should be dispatched annually and the permissible tonnage was increased to 560 tons. Restrictions on tonnage were never enforced and most Manila Galleons greatly exceeded the official maximum.

    The Manila Galleons were not the most seaworthy of ships. They were immense for their time and were too high and top-heavy to weather storm churned seas. They were slow, hard to maneuver and could not sail to windward or run away from storms. Regulations against overloading were disregarded and the ships were often inadequately careened and repaired for the long and arduous voyage. Captains with little or no experience often bought their positions and incompetent officers and crew were commonplace. Not surprisingly, many galleons, thousands of lives, and untold millions of pesos in treasure were lost.

    The exact monetary losses will probably never be known. Although each cargo of treasure was recorded in triplicate, illegal cargos were common. In addition, each sailor was allowed to carry on board the equivalent of up to a year’s pay in gold or silver and officers were allowed even more. The result was that the Manila Galleons often carried twice as much precious cargo as was listed on the official manifests.

    Very little of the treasure that went down with the galleons was salvaged by the Spanish. Since most Spanish sailors could not swim, Indian divers were brought in to recover that they could under the watchful eyes of Spanish armed guards. Buy necessity, the efforts were limited to shallow depths and very little treasure was ever recovered.

    Treasure hunter and author John S. Potter states: “If a diver wants to assure himself of an absolute 100 percent certainty of a rich salvage, there is a way to do so: find a Manila Galleon. Shipwreck for shipwreck, with very few exceptions, none of the Spanish (Mexico to Spain) galleons could approach these Pacific giants for volume and richness of cargo…The Manila Galleons are a new, untapped treasure trove. Although most lie off accessible shores not one has been salvaged in recent years.”

    Although, as respected nautical archaeologist R. Duncan Mathewson III once stated, California is still pretty sleepy when it comes to shipwreck research. A number of Manila Galleons are known to have been wrecked off its coast.

THE SANTA MARTA

    One of the earliest of the Manila Galleons, the Santa Marta, ran aground on Santa Catalina Island in 1582 after a rough return voyage from the Philippines. Although the crew and passengers were able to save some of her valuable cargo, an estimated 200 tons of treasure went down with the ship. It is possible that a salvage expedition was dispatched from Acapulco the following year, since the location of the wreck was known to the survivors. However, there are no records of the Santa Marta ever being salvaged.

THE SAN AGUSTIN

    In 1595, after returning from Manila, enroute to Acapulco, Captain Sebastian Rodriguez Cermeno (Cermeho) anchored his galleon, the San Agustin, off present day Drakes Bay on the California coast. The previous year, the Casa de Contratacion had issued orders to all captains and navigators of the Manila Galleons to chart the areas through which they sailed. Following his orders, Captain Cermeno went ashore with most of his crew to find out if the bay connected to a navigable river. Only a skeleton crew was left aboard the ship. A strong storm suddenly struck from the southwest and caught the San Agustin in its grips. As the shore crew watched helplessly, the San Agustin dragged anchor and smashed into the treacherous rocks off Point Reyes. All of the San Agustin’s cargo and most of the crew who were on board were lost. Florida treasure hunter and archaeologist Robert F. Marx believes that the remains of the San Agustin are buried under the sands of Drakes Bay in Marin County. Marx believes that the wreck may contain up to 130 tons of valuable artifacts, including large quantities of gold and jewels.

THE CAPITANA

    In 1600, the Capitana (flagship) of General Juan de Velasco disappeared with all hands. The Capitana had been on a trading and exploratory mission to the South Seas and was headed towards California when it was last seen.

THE NUESTRA SENORA DE AYUDA

    The 230 ton Nuestra Senora de Ayuda struck a rock and sank west of Santa Catalina Island in 1641. None of the rich cargo from Manila was ever recovered. The wreckage lies somewhere on a shallow reef awaiting discovery by a lucky diver.

THE CORTEZ BANK GALLEON

    According to several written accounts, in 1717, a Spanish galleon hit a 15 foot deep shoal, now called Bishop’s Rock, on the outer point of Cortez Bank, southwest of the Coronado Islands, off San Diego.

THE SAN SEBASTIAN

    According to Potter, the San Sebastian was a Spanish merchant ship, quite possibly a Manila Galleon, that sank off the west shore of Santa Catalina Island during the winter of 1754. She had been sailing through the outer Santa Barbara Channel when she was attacked by the English pirate George Compton. While attempting to escape, the San Sebastian ran aground and quickly sank. Potter believes that the wreckage is buried deep under shifting sands in 170 feet of water.

    In the 250 years that the Manila Galleons sailed, over 30 ships were lost. All but four of the losses occurred on the eastward passage from Manila to Acapulco. How many Manila Galleons await discovery off the California coast? No one really knows for certain.

REFERENCES

Gibbs, James A., Shipwrecks of the Pacific Coast, Binford and Mort Publishing, Portland, OR 1971.

Marshall, Don B., California Shipwrecks, Superior Publishing Company, Seattle, WA, Seattle, WA 1978.

Marx, Robert F., Shipwrecks of the Western Hemisphere, David McKay Company, NY, 1971.

Potter, John S., The Treasure Diver’s Guide, Florida Classics Library, Port Salerno, FL, Revised 1988.

Schurz, William Lytle, The Manila Galleon, E. P. Dutton & Company, NY, 1939.

Williams, John Hoyt, “Tapping the Orient,” Oceans, July 1982.

A Spanish galleon of the seventeenth century as depicted by by Gustave Alaux

A TREASURE HUNTER’S GUIDE TO UNDERWATER METAL DETECTORS

By Eugene Nielsen

An ever increasing number of recreational divers are being beckoned by the lure of sunken treasure. The lure of sunken treasure is beckoning may treasure hunters to become divers. While many divers may dream of finding a sunken galleon loaded with gold and silver, the discovery of coins and jewelry lost daily by those who use the water for recreation and commerce can be almost as exciting.

Metal detectors work in a manner similar to that of a radio transmitter and receiver. Electronic circuitry generates an electromagnetic field through antenna windings in the detector's searchcoil. When metal, and, in some cases, certain minerals come into contact with the field, eddy currents and electromagnetic distortion occur. The detector is able to sense these distortions and alert the operator. Metal can be detected through any non-metallic material.

The first metal detector was patent was issued in 1937 to Dr. Gerhard Fisher.  Dr. Fisher's "Metallascope," as he called it, was a big, awkward device, consisting of two flat wooden boxes which contained copper coils, five vacuum tubes and a few other assorted components. Metal detectors have come a long way since then.  Excellent underwater metal detectors are available from a number of manufacturers.

Five different types of circuitry have been used in metal detectors. They are the beat frequency oscillator (BFO), transmitter-receiver (TR), very low frequency (VLF), automatic VLF and pulse induction (PI).

Most underwater metal detectors manufactured today utilize either automatic VLF or pulse induction circuitry. Automatic VLF and pulse induction metal detectors are extremely easy to operate, since they do not need to be manually adjusted to compensate for ground mineralization and salt water. Although there are pros and cons to both, either type will serve the recreational diver well.

Automatic VLF metal detectors are extremely versatile and work well on land or underwater. They automatically tune themselves to changing ground conditions and salt water. They are "motion" detectors. This means that the searchcoil must be kept in motion for detection to take place. The motion required is slight on many of today's better VLF metal detectors, allowing you to almost stop the coil for accurate pinpointing.  Some underwater VLF metal detectors, such as Fisher Lab’s  CZ-20, have a pinpointing feature that allows for motionless detection for precise pinpointing. The dual-frequency CZ-20 allows the operator to switch between automatic VLF and manual ground-balanced VLF modes.

Pulse induction metal detectors perform well under adverse conditions and are generally known for their deep seeking capabilities, making them popular with many professional treasure salvors. Black sand and salt water have no effect on the signal. However, pulse induction metal  detectors generally require more battery power, which results in them often having a shorter battery life and/or being somewhat heavier than other types of metal detectors.

Some people find that pinpointing small objects which have been detected is often slightly more difficult with a pulse induction metal detector since peak audio signals aren't generated, at normal scanning speeds, until after the center of the searchcoil has passed over the target. Newer pulse induction metal detectors provide almost instantaneous target response and greatly improved battery life.

CZ-20 underwater metal detector (left).   CZ-20 control panel (right).
Photos courtesy Fisher Research Laboratory.

Many metal detectors have the ability to selectively eliminate undesirable or "trash" targets from detection. This is known as target elimination or discrimination. It is made possible by the fact that more desirable metals, such as silver, copper or gold have higher conductivity than iron, tin and less desirable metals.

Target elimination can be used to quickly survey a site to locate only coins, jewelry and other non-ferrous objects. Also, since identifying stamps, insignia and markings are usually affixed to non-ferrous metals, target elimination can often be used to hasten the identification of a particular wreck.

Although target elimination has become quite sophisticated, target elimination isn't completely foolproof with any metal detector. For example, platinum is a relatively poor conductor and may be eliminated along with the trash. Small jewelry items of gold or silver may also be rejected because there are minimal flat surfaces for eddy currents to take place. It's often best to first search an area without target elimination. After digging a few targets, you'll be better able to adjust the control to reject only undesirable objects at the site.

Most pulse induction metal detectors don't have the ability to eliminate trash from detection. Those that do generally have good target elimination capabilities, although small, elongated iron objects, such as nails or hairpins, might not be rejected. All automatic VLF metal detectors have fully adjustable target elimination capabilities.

Most underwater metal detectors are sold with 8- to 10.5-inch diameter searchcoils as standard equipment. Searchcoils of this size give good ground coverage and depth and are sensitive to a wide range of target sizes. Other sizes may be used for more specialized applications.

Larger searchcoils provide the ability to search to a greater depth, but aren't as effective for use in detecting smaller objects, such as coins. They also have a wider scan, allowing you to cover a wider area with each sweep. Precise pinpointing of targets is more difficult with a large searchcoil. In loose sand it is often advantageous to use a larger searchcoil in the initial search, due to its enhanced depth capabilities.

Smaller searchcoils have a intense magnetic field which gives excellent detection of small objects, although they don't detect as deeply as do the larger searchcoils. The narrow detection pattern of a small searchcoil allows targets to be isolated and pinpointed with great precision, a necessity when digging in coral or clay. A small searchcoil also permits scanning in close proximity to other metal objects, which is often an important plus especially in areas with a high density of trash or in tight spots.

Searchcoils designed for underwater use should be neutrally or slightly negatively buoyant. They should be of an open coil design to minimize drag due to water resistance. Open coils also make the pinpointing of targets easier.

An underwater metal detector should have both audio and visual target indication. Audio target indication can be provided either through special headphones or bone conductors. Visual indication may be provided by a meter, LCD bar graph and/or a LED (Light Emitting Diode).

Most underwater metal detectors are equipped with submersible headphones. Properly designed headphones produce more audio power than bone conductors. Headphones with dual ear-cups also reduce outside noise interference. Headphones which are designed for use while diving are vented to allow for the equalization of pressure.

Bone conductors are smaller than headphones and are held against the ear or temple by the mask strap or hood. Bone conductors don't get in the way as much as headphones do, but any convenience here may be offset by problems with outside noise interference. They also aren't suited for use on land and thus limit the versatility of a metal detector.

Visual target indicators generally operate in synchronism with the audio. They provide parallel indication, which is especially important in situations where there is a weak audio response. Without a visual indication, weak signals might easily be missed. Visual indicators also greatly enhance the ability to pinpoint objects that have been detected. Although it is easier to measure signal strength with a meter or LCD bar graph, LED indicators are easier to see in waters with limited visibility.

Most problems with underwater metal detectors result from accidental flooding. Flooding can easily ruin the circuitry of a metal detector. The common cause of flooding is failure to exercise care when changing batteries. Metal detectors which have the electronics sealed off from the battery compartment, or are factory sealed with rechargeable batteries, provide an extra degree of security.

The majority of underwater metal detectors are designed to be used to depths far beyond those recommended for recreational divers. There are a few "underwater" metal detectors which are designed only for shallow water use, however, so check the manufacturer's depth rating before you buy.

You should always visually check a metal detector prior to use. Special attention should be paid to all seals and connections. After underwater use, all sand and salt residues should be immediately washed off with freshwater.

Some manufacturers recommend that underwater metal detectors be returned to the factory every two years to have the O-rings and other seals replaced and have the detector retested and recertified.

Compare different models of underwater metal detectors before buying. Expect to pay somewhat more for an underwater metal detector than you would for a comparable metal detector designed for use only on land. If at all possible try out different metal detectors before buying.

SEARCHING WITH A METAL DETECTOR

Good search techniques are the same for both land and underwater. When searching with a metal detector, the searchcoil should be moved from side to side in front of the operator, scanning in a straight line. A scanning speed of about one-foot per second is about right. The searchcoil should be kept parallel to, and as close to the ground as practical (a distance of approximately one to two inches above the surface being scanned is ideal). A methodical scanning pattern should be employed, making certain that each sweep of the searchcoil slightly overlaps the previous sweep.

The searchcoil should always be kept at least several feet from the body to avoid false signals. Metal gear, such as scuba tanks, gauges, and weights, will be detected if the searchcoil is held to close to the body.

It is important to hunt in a systemic manner. A haphazard approach to searching reduces efficiency and often results in failure. Clearly define your search area. Always follow a pattern. Begin at a known point. Cover a known area. End at a known point.

Marking the bottom is often very useful and may be necessary where there are few underwater reference points. This may be as simple as a stick stuck in the sand or a line drawn on the bottom.

Don't disregard any signals from your metal detector. Dig all targets. If you believe that the signal is coming from a trash target, remove the trash and scan over the area again.

It's important to always carefully examine trash before discarding it. What at first appears to be trash may in fact turn out to be a valuable find. Encrustation and corrosion often make valuable items difficult to discern from trash. When in doubt, it is far better to take it home for cleaning and identification. It's also a good idea to make a habit of logging your finds, since potentially valuable patterns may emerge.

The tools used for recovery will depend on the prevailing conditions at the site, and your own personal preferences. A dive knife will generally be sufficient in mud or small rocks. Most divers prefer to use their hands in loose sand. Although professional treasure salvors often use giant airlifts, water dredges or prop blasters to vacuum up or blow away sand gravel or mud, your objective, should be to leave the area as you found it with no sign of excavation and no damage to marine life.

The recovery of small, lightweight objects is simply a matter of picking them up. Objects that significantly affect a diver's buoyancy should be recovered using a lift bag or a line brought down from the surface. As a good rule-of-thumb, always use a lift bag or line on any object weighing over 15 pounds.

Heavy objects should first be marked with a buoy. In many instances, divers have surfaced to get salvage gear and then been unable to relocate the object to be recovered. It is also not uncommon for an object to re-sink after it has been raised. A buoy makes relocation simple. Without a buoy, another search may become necessary.

All recovered objects must be handled with care if they are expected to survive. Keep all recovered items wet until the proper method of cleaning and preservation can be determined. Many materials will begin to disintegrate if allowed to dry without proper preservation.

Sites of archeological or historical significance should not be disturbed. The acts of a few irresponsible treasure hunters have resulted in laws restricting the use of metal detectors becoming more commonplace. Act responsibly. Check with the appropriate authorities if you are unsure of the laws as they apply to your intended activities. It's your responsibility to determine what those laws are.

Thorough research is the key to success to any form of "treasure hunting." Study the history of your local waterways. Don't neglect to search out information on popular beaches of past and present, either. Valuables are bound to have been lost wherever people have congregated. One of the best places to begin your search is your local public library. The reference librarian will be happy to help you. The Internet has also become an invaluable reference tool. The U.S. Coast Guard has a useful guide, Researching Shipwrecks, on the Web.

Nautical charts are also an important research tool. Many of the wrecks which are shown have never been dived. Also, a spot which is marked as an obstruction may turn out to be a shipwreck.

An underwater metal detector will add new excitement to your diving. It will provide the necessary key to unlock a fascinating world of exploration and discovery.

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