150 



GEOLOGY AND QUICKSILVER DEPOSITS, NEW ALMADEN DISTRICT, CALIFORNIA 



offshoot from the lower part of the larger sill con- 

 taining the Randol ore bodies to the north. Near the 

 crest of the ridge the sill is nearly flat ; but in the 

 vicinity of the San Pedro workings it dips about 40 

 NE., and it has about the same dip where it is cut by 

 the levels from the Almaden shaft. Between the San 

 Pedro and Almaden workings it either steepens to 

 nearly vertical or has a jagged surface resulting from 

 the protrusion of apophyses. (See section A-A', 

 pi. 11.) The lower margin of the sill is extensively 

 altered to silica-carbonate rock, which is about 40 feet 

 thick in the upper workings and more than 100 feet 

 thick on the lower levels. The upper part of the sill 

 is likewise altered to silica-carbonate rock near the 

 surface. 



Ore bodies 



The only real ore body found in the area was devel- 

 oped through the San Pedro adits. It was compara- 

 tively small and lay in the silica-carbonate rock along 

 the lower margin of the sill. The stoped area is bor- 

 dered by rock containing a few well-developed hilos 

 and scattered irregular quartz-carbonate veins. Ex- 

 cept for a local flattening of the contact, no structural 

 reason for the localization of the ore is apparent. 



Suggestions for further development 



The extensive workings on the upper levels in the 

 area have probably exhausted the possibilities for find- 

 ing additional ore there, but cinnabar is reliably re- 

 ported to have been found on the 500 and 600 levels 

 along the lower margin of the sill. At a time when 

 the price of quicksilver is high this deeper material 

 might perhaps be profitably mined. An inclined shaft 

 going down the dip of the contact seems to offer the 

 best means for reaching the ore, as it would also ex- 

 plore the interval between the lowest San Pedro and 

 the highest Almaden workings. 



AMKRICA MINE 



Location ana extent of workings 



The America mine lies close to the top of Los Capi- 

 tancillos Ridge, a little more than 3,000 feet west of 

 the Randol shaft on Mine Hill. (See pi. 3.) It is the 

 nearest to the New Almaden mine of the so-called out- 

 side mines, and at one time an unsuccessful attempt 

 was made to reach it by extending a crosscut from the 

 New Almaden mine. The workings, which were al- 

 most entirely inaccessible in 1948, include an old shaft 

 216 feet deep, adits and connected drifts, known as 

 the Upper and Lower America workings, on the 300 

 and 500 levels, and extensive drifts from the 700-foot 

 America shaft on the 600 and 700 levels. The total 

 length of the level workings is a little, more than a 

 mile. (See pis. 4, 13.) 



History and production 



The early history of the American mine is known 

 only from fragmentary records. One early company 

 report mentions that between September 1863 and 

 July 1866 the mine was worked through the old shaft 

 and the Upper and Lower America tunnels, and that 

 stopes developed from each of these levels yielded 

 about 1,000 flasks of quicksilver from 1,037 tons of 

 hand-sorted ore. After 1866 the America mine was 

 apparently abandoned until 1885, when the upper 

 levels were reopened and a decision was made to at- 

 tempt to develop the America workings into a large 

 mine. The proposed program involved the sinking 

 of the America shaft to a depth of 1.100 feet and the 

 driving of a 2,000-foot crosscut on the 1400 level from 

 near the Santa Isabel shaft. The America shaft was 

 begun in October 1885, and at about the same time the 

 long crosscut was started from near the Santa Isabel 

 shaft. When the America shaft reached the level of 

 the Lower America tunnel, a crosscut was driven to 

 reach this adit, which had been simultaneously re- 

 opened from the portal. The level was also extended 

 east of the shaft for 450 feet, where it reached appar- 

 ently barren silica-carbonate rock. When the shaft 

 had been deepened another hundred feet, the 600 level 

 was driven westward to tap an ore body mined in the 

 old stopes above, but although ore was found on the 

 level, only a small amount of raising showed that the 

 old stope extended downward virtually to the 600 level. 

 In March 1887 a 700 level was driven westward from 

 the America shaft, and a connection between the 600 

 and 700 levels tested the downward extent of the ore 

 body. Ore was cut in the first 35 feet of a winze from 

 the 600 level, and a short drift along the contact 80 

 feet below the level also was reported to have l>een 

 run in "fair-grade ore." 



Meanwhile the shaft was being deepened under con- 

 siderable difficulty, owing to the large amount of water 

 pouring into it, and in February 1888, at a depth of 

 701 feet, the shaft struck "boulders of silica-carbonate 

 rock" and an inflow of water that the pumps were 

 unable to keep pace with. The sinking of tb* shaft 

 was temporarily abandoned, and although new pumps 

 capable of pumping 50,000 gpd (gallons per day) were 

 installed, the water continued to rise in the shaft, 

 causing it to cave from the bottom upward. In .June 

 1888, when the shaft had caved to within 20 feet of 

 the 600 level, it was closed down, and the long cr<>>- 

 cut from the Santa Isabel shaft, which had been driven 

 through heavy and gassy ground to within 47o feet 

 of the projected bottom of the shaft, was abandoned. 

 During the revival of the America mini' lu-tween 

 1885 and 1888, about 500 flasks of quicksilver was re- 

 covered from ore mined chiefly above the 600 level. 



