MINES 



147 



was started in November 1881. From the first the 

 miners felt it was cursed with bad luck, for it was 

 repeatedly caved, flooded, or beheaded by landslides; 

 but by August 1883 it had been sunk below the 900 

 level and had passed through a little ore. In June 

 1884 the Garfield shaft was renamed the Washington 

 shaft, with elaborate ceremony, in the hope of lifting 

 the curse, but its bad luck persisted. By January 1885 

 the shaft had been sunk below the 1100 level, and a 

 connection was made, in August 1885 through a long 

 drift and incline, with the 1400-level crosscut from 

 the Santa Isabel shaft. Prospecting in the lower levels 

 continued for the next few years without results, and 

 in September 1890 the Washington shaft was closed 

 down. 



In that same year, however, an attempt was made 

 to recover more ore from the abandoned upper stopes 

 and to explore laterally from them. For this purpose 

 the San Francisco branch from the Main tunnel was 

 reopened, and the internal San Francisco shaft was 

 extended from the 300 level up to the surface and 

 provided with a hoist. Some ore was recovered near 

 the upper level by this new work, but no sizable new 

 ore bodies were found. In 1899 the Washington shaft 

 was again reopened, only to be almost completely 

 obliterated by another landslide in June 1901. The 

 San Francisco shaft remained passable for many 

 years, but with the excavation of the large San Fran- 

 cisco opencuts in 1944 and 1945 it was covered over 

 and probably largely filled. The surface operations 

 during World War II yielded ore at the prevailing 

 high price for quicksilver, but no ore bodies com- 

 parable in grade to those mined underground were 

 struck. In 1948 some ore was being taken by H. F. 

 Austin from adits driven into the opencut area. The 

 entire production from the ores of the San Francisco 

 area cannot be computed from the available records, 

 but it is estimated to have been about 50,000 flasks. 



Geology 



The rocks explored by the San Francisco workings 

 are serpentine, the silica-carbonate rock derived from 

 it, and various sedimentary rocks and greenstones of 

 the Franciscan group. The serpentine forms the 

 southern continuation of the two sills explored in the 

 rest of the New Almaden mine, which in this area are 

 apparently joined to form a single mass. (See section 

 C-C', pi. 11.) In general the contact between the ser- 

 pentine and the country rock from the surface down 

 to the 600 level strikes about N. 35 W. and stands 

 nearly vertical. In detail, however, it is extremely 

 complex : many sill-like apophyses, ranging in thick- 

 ness from a hundred feet to less than a foot, branch 

 southward and downward from it, following rather 



closely the southward dip of the beds of the rocks of 

 the Franciscan group. In many places along the con- 

 tact, also, there are small pods and lenses of carbon- 

 atized serpentine entirely isolated in the bordering 

 alta. Locally the serpentine and the shaly alta inter- 

 penetrate in so complex a fashion that it would not 

 be possible to tell from the field relations which rock 

 was intruded into the other. A very unusual compli- 

 cation in this area is the presence of faults of a few 

 feet displacement that are later than the silica-carbon- 

 ate rock. These complexities in the details of the 

 geology have made the area a difficult one in which 

 to carry on exploration and development work. 



Below the 600 level the roughly vertical but highly 

 complex intrusive contact gives way to an arching 

 contact dipping gently southwestward, formed by the 

 extension of a single thick sill beyond the general 

 limit of the intrusive contact in the higher levels. 

 (See fig. 81 and pi. 12.) Exploration below the 800 

 level was nearly all directed toward searching for ore 

 along the upper margin of this sill, which therefore 

 is fairly well outlined by workings down to the 1100 

 level. The sill extends westward below the south end 

 of the 1400 level driven from the Santa Isabel shaft, 

 but farther south it must pinch out at a higher level, 

 for it was not struck by the south crosscut on the 

 1000 level. The arched lower contact of the sill was 

 cut on the 1100, 1000, and 900 levels, but as it was not 

 cut on the 800 level it is believed to reach the highest 

 point on its arch not far below that level. (See sec- 

 tion C-C', pi. 11.) 



Ore bodies 



Most of the ore bodies mined in the San Francisco 

 area were small, but the largest, the New World ore 

 body (fig. 81), was comparable in size to some of those 

 in the central stope area. It extended down below the 

 850 level and up to about the 600 level ; it had a maxi- 

 mum plunge length of about 500 feet, an average strike 

 width of less than 100 feet, and a thickness of 10 to 20 

 feet. It lay mostly along the upper margin of the 

 thick sill that extended southwestward beyond the 

 general limits of the intrusive contact above, but some 

 ore lay in a higher sill which extended out over the 

 lower ore body. (See section C-C', pi. 11.) A third 

 sill, only 6 feet thick, contained near the 600 level a 

 small but rich extension of the New World ore body. 

 The ore apparently was localized by a sharp roll in 

 the contact of the larger sill, which formed a well- 

 defined inclined inverted trough, and the overlying 

 thinner sill apparently had a similar shape. The ore 

 lay just beneath the alta hanging walls, and extended 

 along numerous hilos that had a strike of N. 30-50 E. 



