162 



GEOLOGY AND QUICKSILVER DEPOSITS, NEW ALMADEN DISTRICT, CALIFORNIA 



average quicksilver content was only about 0.5 per- 

 cent, as compared with averages of from 1 to more 

 than 10 percent in the New Almaden bodies. Some 

 of the Senator ore was like that taken from the New 

 Almaden mine in having been formed by the replace- 

 ment of silica-carbonate rock along hilo fractures. 

 Where replacement was extensive the ore is said to 

 have been almost pure cinnabar, and one body of this 

 extremely rich ore found below the 500 level measured 

 9 by 12 feet in plan and extended 30 feet down the 

 dip. Judging from the dump material and the aver- 

 age grade of the furnace feed, the ore formed by 

 replacement was less abundant than ores formed by 

 the intermittent encrustation of cinnabar during the 

 growth of layered dolomite veins. These veins, which 

 ranged in width up to 14 inches, may be exceptionally 

 large hilos, but they more closely resemble the large 

 northwest-trending veins of the New Almaden mine, 

 which only very locally contain cinnabar, and which, 

 as far as is known, were nowhere mined as ore in the 

 New Almaden mine. It appears likely that the dif- 

 ference in grade between the ores of the two mines 

 results from this difference in the character of most 

 of the ore. 



The two main ore shoots of the mine lay in silica- 

 carbonate rock on each side of a serpentine sill, and 

 both sides plunged S. 20 to 30 E. The ore bodies 

 in these shoots had similar horizontal dimensions; 

 most had stope lengths of less than 200 feet, though 

 on the 500 level the footwall stope is nearly 300 feet 

 long. They varied in width from a few feet to as 

 much as 30 feet in exceptional places, the average 

 width being about 15 feet. The mass of silica-car- 

 bonate rock on the northeast or footwall side of the 

 serpentine was known to the miners aa the "No. 2 

 vein," and that on the southwest or hanging-wall side 

 as the "No. 3 vein." In vertical dimension the ore 

 bodies in the No. 2 vein were the more extensive, 

 for they cropped out at the surface near the Nones 

 shaft and have been mined to a varying extent on all 

 the levels down to the 1200. The ore bodies in the 

 hanging-wall, or No. 3 vein, have been mined only 

 between the 260 and 1200 levels. No stopes were de- 

 veloped on the 1300 level, and rumors concerning the 

 occurrence of ore on that level are contradictory. 

 Since the geology of that part of the mine can only 

 be inferred, we do not know whether the ore shoots 

 were bottomed or whether they were of such low grade 

 as not to be worth mining. The exploration done in 

 the area appears, however, to have been properly 

 directed to meet the downward projection of the ore 

 bodies found on higher levels. 



Huggestlons for furtuer development 



The geology and history of the Senator mine, so 

 far as they are known, indicate that the ore bodies 

 found were fully exploited and that little marginal 

 ore or stope fill remains in the mine. However, be- 

 cause of the strict economy practiced during much of 

 its development, little lateral exploration was done 

 except on the 260 and 1000 levels, and on the deeper 

 levels where the contacts were followed in driving 

 from the inclined winzes to the ore bodies. It is 

 therefore possible that other ore bodies may lie close 

 to workings and yet have escaped discovery. If so, 

 there is no way of accurately predicting the location 

 of such bodies from the limited geologic data avail- 

 able. 



On the other hand, we can suggest a few places 

 where one might mine submarginal ore at times when 

 prices were abnormally high. These are (1) near the 

 surface west of the Nones shaft, along the upward 

 continuation of the ore shoots mined at depth; (2) 

 near the south portal of the 260 level in the small 

 body of silica-carbonate rock reported in the com- 

 pany records to have contained some cinnabar; and 

 (3) below the known ore bodies on the 1300 level or 

 deeper. The first two of these places are readily ac- 

 cessible from the surface and may easily be tested, 

 but the last would be hard to reach because of caving, 

 and probably would not be worth testing unless the 

 mine were also reopened for further lateral explora- 

 tion on the intermediate levels. 



GUADALUPE MINE 



The Guadalupe quicksilver mine is in the valley 

 of Guadalupe Creek and along the adjacent Los Capi- 

 tancillos Ridge in the west-central part of the New 

 Almaden district. The property, which includes about 

 1,800 acres in the northeastern part of sec. 30, T. 8 S., 

 R. 1 E., Mount Diablo base and meridian, is owned 

 jointly by the estate of Mrs. ,1. S. Gregory, the law 

 firm of Young, Hudson, and Rabinowitz of San Fran- 

 cisco, and the law firm of McKee, Tashiera, and Wahr- 

 haftig of Oakland. In 1948 it contained several 

 dwellings and a modem reduction plant with a rotary 

 furnace having a daily capacity of 60 to 80 tons. 



The total recorded production of the Guadalupe 

 mine to the end of 1947 is 92,623 flasks. If we add 

 the 20,000 flasks reported to have been produced be- 

 t \\oen 1854 and 1875 (Bradley, 1918, p. 156-157) but 

 not recorded, the total claimed production comes to 

 more than 112,600 flasks, and places the Gundalupe 

 mine sixth among California quicksilver mines. Like 

 many other old quicksilver mines in the Coast Ranges, 



