MINES 



143 



FIGUKE 94. Tramming on the 1500 level In the North Randol area of the New Almaden mine In middle 1880's. Prom L. B. Bull- 

 more collection. 



backs of the large open chambers. (See fig. 94.) 



The ore mineral was chiefly cinnabar, though some 

 native mercury was found below the 1800 level. The 

 cinnabar occurred in and along hilos, which trended 

 nearly due north through the silica-carbonate rock 

 formed along the upper edge of the serpentine sill 

 and its upward-branching fin. The hilos were several 

 inches wide, and most persistent near the sharply de- 

 fined and locally 'slickensided upper contact; they 

 pinched and died out toward the serpentine footwall. 

 The ore is said to have been richest where the hilos 

 were most closely spaced. The average quicksilver 

 content of all the ore furnaced was about 2 percent, 

 and a rough comparison of the records of tonnage 

 that went to the furnace with the volume of the 

 stope, indicates that most of the rock taken out was 

 furnaced. 



The ore of the huge North Randol ore body appears 

 to have been localized mainly by the thin parallel 

 hilos, which here trend nearly down the dip of the 

 contact. (See fig. 95.) The lower part of the ore 

 body occupied a trough, in contrast to much of the 



ore in the mine, which is localized in arches or flats. 

 So far as can be deduced from available information, 

 the stopes were as wide and their ores as rich on steep 

 parts of the contact as on parts with lower dips, which 

 is another unusual feature. Little ore was found, 

 however, below the 1900 level, where the sill is very 

 steep or overturned. (See section B-B'. pi. 11.) 



Suggestions tor lurtner development 



Since the North Randol area appears to have been 

 so thoroughly explored in all directions that any con- 

 tinuation of the ore body can hardly have been missed, 

 no further exploration in the area seems warranted. 

 The Randol shaft, on the other hand, was closed down 

 at a time when the ore had to average more than 

 1 percent to yield a profit, and it is likely that a large 

 tonnage of ore containing several pounds of quick- 

 silver to the ton remains in the stope walls or in fill. 

 Whether or not it can be profitably mined, now that 

 the workings are inaccessible and probably caved, de- 

 pends on mining costs and the prevailing price of 

 quicksilver. 



