MINES 



145 



rock) and a sudden inflow of water flooded the lower 

 80 feet of the shaft. This difficulty was quickly over- 

 come, however, and drifting along the contact soon 

 revealed a new body of ore 250 feet wide. During the 

 next 5 years this body, known as the No. 2 South 

 Randol ore body, was followed down the dip for about 

 600 feet to the 1500 level, and it furnished the bulk 

 of the 83,159 flasks recovered during that period. In 

 1877, when the ore had been found to extend down- 

 ward, the Santa Isabel shaft was started, some 1,300 

 feet northwest of the Randol shaft, to explore the 

 area at greater depths. Early in 1879, a crosscut was 

 extended on the 1700 level from the Randol shaft 

 toward the Santa Isabel shaft. Some disappointment 

 was felt when this crosscut had been driven through 

 solid serpentine far beyond the projected position of 

 the overlying ore body. Late in the year, however, 

 this crosscut finally reached silica-carbonate rock that 

 contained a substantial amount of cinnabar and native 

 mercury, and drifting soon revealed a new ore body 

 with a strike width of about 300 feet. During the 

 following 5 years the ore was followed from the 1700 

 level up to the 1450, and down about to the 2000, 

 which lies some 200 feet below sea level. As it was 

 developed, this new ore body was found to lie in a 

 narrow offshoot from the main sill, which contained 

 the other South Randol ore body, and crosscuts were 

 driven northward from the higher levels to reach the 

 upward extension of the new ore body. (See pis. 5-10, 

 and fig. 93.) In 1885, after this new ore body had 

 yielded more than 75,000 flasks of quicksilver and was 

 nearly exhausted, a connection between the Santa 

 Isabel and Washington shafts was started on the 1400 

 level to explore the entire western part of the hill at 

 that level. In the following year a drift from this 

 crosscut, running along the contact toward the old 

 depleted ore bodies, struck an entirely new ore body 

 lying west of the old South Randol stopes. Explora- 

 tion westward from the Randol shaft on several levels 

 proved that the new ore body was exceptionally wide, 

 but extended only from the 1550 level to the 1200 

 level. It was mined largely through the St. George 

 shaft, which was sunk in 1886 and 1887, and by 1889 

 it was fairly well mined out, after having yielded 

 about 30,000 flasks of quicksilver. Meanwhile, in 1885, 

 an attempt was made to extend a drift on the 1400 

 level from near the Santa Isabel shaft to the bottom 

 of the America shaft, which was then being sunk. 

 This work was diligently pursued, in spite of difficul- 

 ties caused by repeated floodings, huge quantities of 

 carbon dioxide, and caving ground, until June 1888, 

 when the America shaft caved and the drift was aban- 

 doned 475 feet short of its goal. 



After the Randol shaft was abandoned in 1896, ac- 

 cess to the stopes above the 1000 level could be gained 

 through the Victoria shaft. Since then some ore and 

 stope fill have been taken from these high-level stopes 

 at various times, but production from them has been 

 very small. 



Geology 



The same serpentine sill along whose upper surface 

 most of the large ore bodies of the New Almaden mine 

 were found is also the host for the South Randol ore 

 bodies. (See fig. 81.) In most of the South Randol 

 area the sill strikes nearly east-west and dips between 

 55-65 N. Above the 800 level, however, it flattens 

 abruptly to form the arch containing the Victoria and 

 Santa Rita West stopes, and along the southwest side 

 of the arch a large troughlike depression extends 

 northward past the St. George shaft. Near this shaft 

 the west limb of the trough steepens to nearly vertical, 

 and close to the surface, where it is cut by the shaft, 

 it is overturned to a steep westerly dip. Several thin 

 fin! ike apophyses project upward from the main ser- 

 pentine sill in the South Randol area. One of these 

 that contained ore extends from just above the 1600 

 level to the 1200 level, and is separated from the main 

 sill by a narrow wedge of graywacke, the keel of 

 which plunges westward at about 45. Below the 

 1900 level, downdip from this apophysis, is a second 

 thin fin which apparently extends downward at least 

 to the 2300 level. A third apophysis, which lies above 

 the main sill in the vicinity of the westernmost of the 

 South Randol ore bodies, extends downward from 

 about the 1450 level, but not enough information is 

 available to outline it fully. These intricacies of the 

 upper surface of the serpentine are shown by contours 

 in figure 81, by cross section C-C', plate 11, and by a 

 drawing of a model in figure 93. 



The thickness of the sill can be determined in only 

 a few places. The serpentine sill is about 350 feet 

 thick in the eastern part of the area, where it is 

 crossed by the Randol shaft. West of the St. George 

 shaft the long 1400-level crosscut penetrated only 60 

 feet of serpentine, but as a body of serpentine some 

 550 feet across horizontally was cut 150 feet farther 

 south, it is likely that this thin body was merely an- 

 other offshoot branching westward from the main sill. 

 On the same level a thousand feet farther west the sill 

 was penetrated for 500 feet. 



The rocks above the sill are largely sedimentary 

 rocks of the Franciscan group, but, as is revealed by 

 the workings on the 1400 level near the Santa Isabel 

 shaft, a few other thin sills, which are partly rimmed 

 by silica-carbonate rock, lie above those more fully 

 explored by the workings in the South Randol area. 



