Bisbee daily review., 1906-08-05
PLACERS IN SONORA
 FIELD
Antigua Workings Are Netting Large Returns Under Mod
 ern Methods.

have no hesitation in stating afford excellent opportunities for gold dredg- ing on a larger scale. at low cost and at an exceedingly high net profit.
 Beginning at Imuris,- on the Sonora railway and some ten miles northeast of the city of Magdalena, and thence through the Magdalena and Altar dis tricts, the Magdalena river passes through or close to placer deposits that have been worked by hand over and over again for centuries-by na- tives before the Spanish occupation. by Spaniards and finally by Mexicans for their rich gold content. Even to- day, so defective has been the past work. these placeS; will yield good wages by dry washing which is the most advanced yet applied.
 The rich placer deposits of this sec tion of Mexico extend from the Arizona line south, over a wide belt into the tres district; but the most valuable are in the great valley of the Mazda lena.
 Through development of the Llanos de Orc mine, owned by Colonel Epes Randolph and associates of Los An geles. it has been shown that in this region there are two placer beds ly- l ing one alsve the other and separated by false bedrock. The upper bedrock ! is at a depth varying from fifteen to | fifty feet.A bed 105 feet in the Llanos de Orc mine was opened by the lower gravel bed, made up of sharply broken | fragments of country rock and ex- tremeiy rich ore which had not trav- eled far enough to be water worn, to- gether with fine, shot and nugget gold throughout the cemented mass. This deposit has been very thoroughly ex- plored by drift mining methods, and it is reliably stated that over SS,oOO,- 900 are now in sight ready for extrac- ! tion and treatment in the company 100 stamp mill, now almost completed. 1 The surface deposit, which has been worked over many times and by many races. is still of high grade and will probably be worked by the company either by a dredge or by steam shovel To this end the company has com pleted a ten inch pipe line from Las Trinchiras, fourteen miles distant whence water for sluicing purposes IS obtained.
 The chief source of these extremely rich placer deposits is found in the low porphyry ranges traversins the country. which are scanned closely in every direction with small quartz strin-
 gers that are very rich in gold. Erosion from these has evidently been tremendous though interrupted by al least one period of false bedrock dep- osition throughout the region. The surface deposits are comparatively free from clay and large boulders and' whenever occurring sufficiently near to the present river, offer almost ideal opportunities for gold dredging; while more distant lands, to which siulce water must be piped, may be adVan- ltageously worked by steam shoVels.
 Gold dredging, has been attempted in many places during the past halt century, but it is only within elsht years that the industry has been mark edly successful. It has been not only necessary to perfecS mechanical metn- ods, but to arrive at correct un. derstanding of the various types or dEedges required for working deposlIs
 of differing character.
 In the Sacramento valley of Cali fornia, particularly at Oroyille, the ped rock is soft and may be readily
 scooped up, as to its upper layer py bucket chain dredges Of the Bucyrus or Riston types. Gold deposited upon or within seams of the bedrock IS thereby effectually saved. Where bed
 rock is hard, suction dredges must be used with a hydraulic jet to clean
 the bottom thoroughly of it's concen- trated gold values. Dredges of any sort are suitable only where there is ex'
 cessiye water: for fairly dry ground may be more cheaply worked by steam
 shovels than by artificially creating
 conditions suitable for dredging-a
 course which has in some instances
 bt en followed in spite of it's obvious
 waste.
 i Through and by reason. Of many ltyears of failure, the science Of gold
 lredging as practiced today has been evolved, and there are now hundreds of dredges in California, Colorado. Ida, ho. Montana, Oregon, Alaska and New Zealand that are working very low lgrade placers at a profit. - T
 The average value of the California ] placers now being worked by this method is under twenty-one cents a cubic yard, with about fifteen and thirty cents a yard as the minimum tvalues. The average cost Is six cents
 cubic yard. though the new and
 largest machines recently built are
 handling gravel at cost of three
 cents and less. It is estimated by the : state mining bureau that the 25.OOO . acres of proven dredging lands of the
 Sacramento valley will produce an av'
 craze of fifteen cents cubic yard and an aggregate of $163, 900, 900, of which nearly two-thirds will be profit. The placer of the Magdalena and ! Altar districts should be divided into , three classes.
 : CD Surface deposits which lie so iclose to considerable living streams, , as the Magdalena and Altar rivers
 and water in quantity to float the dredge will readily follow its progress , through the deposit as worked,
 l (2) Surface deposits more distant ; from living streams but to which wa
 ter for sluicing may be readily piped