HISTORY OF PLACER MINING 



By CHARLES \ 



Methods for the recovery of gold even today depend largely on the 

 high specific gravity of that metal. A particle of gold of a certain size 

 is so much heavier than a particle of associated rock of the same or even 

 larger size, that a current of water washes the particles of dirt and 

 rock away and leaves the gold behind. At Sutler's sawmill, water turned 

 through the ditch to operate the water wheel washed away the dirt and 

 gravel and left the bright flakes of gold. These were caught on the rough 

 bottom of one of the ditches where Marshall found them. 



The earliest efforts to recover gold, after Marshall's discovery, were 

 directed toward those places where flakes and nuggets of gold had been 

 concentrated on rough bedrock and in crevices by the natural flow of 

 the streams. Small tools were used to dig in the crevices and to pick up 

 the flakes of gold. Soon the miner's pan came into use. An ordinary 

 frying pan can be used to concentrate gold providing it is free of grease, 

 but the familiar miner's pan with gently sloping sides is more efficient. 

 It is a simple device for washing away the lighter dirt and fine gravel, 

 and concentrating the heavy gold in the bottom of the pan. The capacity 

 of the pan is so limited that gravel very rich in gold is needed to pay 

 by this method. A skilled operator is able to pan less than one cubic 

 yard of gravel during a day's work. The batea is a wooden version of 

 the miner's pan that was introduced into California at a very early date 

 by Mexican miners. 



Rockers or cradles and sluice boxes were the next devices used by 

 the early-day miners. The rocker is a crude concentrating machine made 

 of wood that combines the shaking motion of the pan with some of the 

 features of the sluice. Riffles or obstructions are placed across the bottom 

 to catch the heavy flakes of gold. The dirt and gravel are washed over 

 the tops of the riffles. With the rocker, both the gravel and the water are 

 introduced by hand. With the sluice, the water flows by gravity, but 

 the gravel is shoveled in by hand. The miner is able to wash several cubic 

 yards per day still a small amount of gravel. By 1860, gravel that would 

 pay to work by these methods was getting hard to find, and production 

 of gold declined. 



In the meantime the hydraulic method of mining was developed. 

 Great jets of water were directed against banks of gravel hundreds of 

 feet in height. Some of the jets of water were 9 inches in diameter as they 

 left the nozzles. After the proper ditches and pipe lines had been installed, 

 thousands of cubic yards of gravel could be washed without hand labor. 

 The gold was recovered in riffle-sluices, and quicksilver was usually 

 added to aid in its recovery. The debris deposited in streams by hydraulic 

 miners became so objectionable to agricultural interests that the method 

 was stopped by injunction in 1884, and placer production dropped to a 

 very low level. 



Evidence of hydraulic mining in the form of old gravel banks may 

 be seen on Highway 49 at Mokelumne Hill in Calaveras County and 



(19) 



FOR GOLD IN CALIFORNIA 



. AVERILL 



near Camptonville in Yuba County near the Sierra County line. The 

 Depot Hill mine near Camptonville has been worked quite recently. 

 The Bullard Bar dam of the Pacific Gas and Electric Company is avail- 

 able for the storage of tailings ; hence this mine can be operated legally 

 at the present time. Other dams that were constructed primarily for the 

 purpose of restraining such tailings are located on the North Fork 

 American River about two miles above its confluence with Middle Fork 

 American River near Auburn, and on the Yuba River about li miles 

 above its confluence with Deer Creek near Smartsville. 



Some of the largest hydraulic mines ever operated are a few miles 

 east of North San Juan. Leaving Highway 49 at this point, one may travel 

 for 15 miles practically along the course of an ancient river channel in 

 which gold-bearing gravel was deposited many millions of years ago to 

 a depth of about 500 feet. The climate was semi-tropical at that time, and 

 the elevation was much lower. The region has been raised by tilting so 

 that the bed of the ancient river now occupies the top of a high ridge. The 

 largest mine was the Malakoff at North Bloomfield. and it was the injunc- 

 tion against this mine in 1884 that practically put a stop to hydraulic 

 mining in this region. 



The lode mines with their quartz veins and stamp mills took over the 

 major output of gold, and the production curve rises gradually until 

 about 1900 when connected-bucket dredges were introduced and made the 

 curve rise a little faster. These great machines contain a continuous chain 

 of buckets for digging the gravel and taking it aboard the floating barge. 

 Such a chain of buckets and the support for it (the ladder) may weigh 

 1,000 tons. The entire outfit including the digging machinery and the 

 equipment for washing out the gold may weigh 3,750 tons. Riffle sluices 

 and quicksilver are still used to recover the gold on the dredges, but 

 sluices are gradually being replaced by jigs, which are mechanical devices 

 for concentrating the gold. The dragline type of dredge is a later develop- 

 ment that was introduced in the 1930 's. The heavy digging equipment is 

 an ordinary dragline excavator that travels on the bank. The floating 

 barge carries only the screen, equipment for concentrating the gold, and 

 the tailing-stacker." Placer gravel is handled so cheaply on these dredges 

 that gravel running 10 cents to 20 cents per cubic yard can be mined at 

 a profit. 



Inflation following World War I stopped the rising trend of gold 

 production, and it declined until the early 1930 's, when the increase in 

 price from $20.67 to $35 per fine ounce caused production to rise until 

 1940. In October 1942 Limitation Order L-208 of the War Production 

 Board stopped all gold mining with few exceptions. This caused great 

 damage to California mines in the form of flooded and caved workings, 

 and gold production is now at a very low level. It cannot be expected to 

 rise very fast under present conditions of high costs of labor and supplies, 

 unless a way can be found so that the miner will receive more than $35 

 per fine ounce for his gold. The price is higher than this in many countries 

 today. 



