MINES 



169 



above the No. l 1 /^ level of the Old Mine, up the plunge 

 of the ore body mined in the Thayer Labor, and (2) 

 beneath a point 100 feet southwest of the East Hilltop 

 workings, where there appears to be an arch in the 

 footwall contact. 



Some stope fill and low-grade ore probably remain 

 in the Old Mine in the Thayer and Dore Labores. 

 These were reworked for the last time in 1884, and 

 the material then taken out failed to yield a profit 

 with quicksilver priced at about $30 per flask. At 

 times of high prices this material might possibly be 

 mined at a profit, especially if the old dumps and 

 the silica-carbonate rock breccia on the crest of the 

 hill were also utilized to support a large-scale low- 

 cost furnace operation. 



SANTA TERESA MINE 



The Santa Teresa mine is near the crest of the 

 north slope of the Santa Teresa Hills, close to the 

 957-foot summit and about 3.5 miles N. 30 E. of the 

 summit of Mine Hill. (See fig. 2.) It is one of the 

 two small mines developed many years ago on the 

 mineralized belt lying north of the main ore zone on 

 Los Capitancillos Ridge. As it has been inactive for 

 more than a score of years, it is virtually inaccessible, 

 and its present ownership is not known. 



The mine was active and apparently had been devel- 

 oped nearly to its present state when it was examined 

 by Forstner (1903, p. 186-187) in 1902. His report 

 includes a sketch map, which shows 3 main adits 

 within a vertical interval of about 300 feet and 2 con- 

 necting shafts. The aggregate length of these work- 

 ings is reported to be about 2,000 feet. 



A lens of silica-carbonate rock is explored by the 

 various workings of the mine. At the surface the 

 lens is separated by a septum of sediments from a 

 larger body of serpentine to the north, but under- 

 ground it apparently forms the southern border of the 

 serpentine. The lens dips steeply northward, and is 

 at least 90 feet thick where it is explored on the inter- 

 mediate level. It is described by Forstner as being 

 cut by many quartz-carbonate veins that contain nu- 

 merous vugs, and doubtless the ore occurred in and 

 along these veins. 



The property was equipped in 1903 with a 40-ton 

 Scott furnace (Bradley, 1918, p. 167), and in that year 

 the property had a recorded production of 9 flasks 

 of quicksilver. No other production is recorded, and 

 further exploration seems unwarranted. 



BERNAL MINE 



The Bernal mine is at an altitude of about 600 feet 

 on the north slope of the Santa Teresa Hills, about 



686-671 O 63 12 



1 mile east of the Santa Teresa mine. (See fig. 2.) 

 Its production is not recorded, and its present owner- 

 ship is not known. 



The mine is an old one, for Forstner (1903, p. 171- 

 172) described most of its workings in 1902. These 

 workings consist of 2 shafts, reported to be 65 and 

 20 feet deep, a 215-foot adit driven nearly 200 feet, 

 below, and another driven somewhat more recently 

 to a point about 10 feet under the bottom of the shal- 

 lower shaft. Very little is known of the early history 

 of the mine, but probably a small amount of quick- 

 silver was recovered from its ores by the early opera- 

 tions. In 1942, 4 drill holes, none of them more than 

 200 feet long, were put down from the surface into the 

 ground below the shafts. In 1946 the shallower adit 

 was extended to the area below the shaft, and a retort 

 was installed at its portal. In 1947 the mine was idle, 

 and no quicksilver appears to have been recovered 

 in the retort. 



The shafts explore a very thin nearly vertical lens 

 of silica-carbonate rock which is crossed by several 

 north-trending 1-inch veins of quartz and dolomite. 

 Some of the veins exposed in the shallower shaft con- 

 tain showy patches of cinnabar, which if present in 

 quantity would form good retort ore. These veins, 

 however, are thin and barren where they are cut in 

 the adit below the shaft, so that further development 

 is probably not worth while. 



PLACER CINNABAR DEPOSIT 



A remarkable placer deposit (Bailey and Everhart, 

 1947, p. 77-79) containing detrital nuggets of cinna- 

 bar was found just north of the dump of burnt ore at 

 the Hacienda, where Deep Gulch joins Almaden Can- 

 yon. The deposit was accidentally discovered by H. F. 

 Austin while he was sinking a shaft to bedrock to 

 search for native mercury, which commonly leaked 

 downward from the old brick Scott furnaces and came 

 to rest on the bedrock. With a few associates he 

 worked the placer deposit from the fall of 1945 to the 

 winter of 1947, recovering about 600 flasks of quick- 

 silver. 



The stream gravel of the area averages about 20 

 feet in thickness and is composed of 2 layers, which 

 can be distinguished by their color and pebble con- 

 tent. The upper layer, which is in places as much as 

 15 feet thick, has a yellowish cast due to iron stain- 

 ing, and as it contains many boulders from Upper 

 Cretaceous conglomerates of the Sierra Azul washed 

 down from the upper parts of Almaden Canyon, it is 

 believed to have been derived almost entirely from the 

 Almaden Canyon drainage area. The lower layer of 

 gravel, which contains almost all the nuggets, is blue- 



