MINES 



137 



tail the various developments during the history of 

 the mining of this, the greatest concentration of quick- 

 silver ore on the North American continent, is obvi- 

 ously impossible, and only the more significant facts 

 are touched upon. 



Mining was begun almost immediately after the 

 first recognition of cinnabar on Mine Hill, but during 

 the first few years it was conducted in a very erratic 

 fashion. In 1850, however, when the persistence of 

 the ores had been proved, the Main tunnel was begun 

 in an attempt to systematize the mining, and from it 

 the Main shaft was sunk a few years later. The in- 

 tricate and erratic workings above the tunnel are thus 

 described in the annual report of the New Almaden 

 Mining Co. for 1865 : 



The upper or old mine of Almaden continues to yield good ore 

 from pillars and hilos left unworked from the early days of the 

 mine. No description is possible of all this extent of ground 

 from the level of the Main Planilla up to the flagstaff on the 

 summit of Mine Hill. It is one mass of ruins with tunnels every- 

 where buried up, pillars crushed to pieces, and chambers caved in. 



Obviously no complete maps of these early work- 

 ings were made, but maps of some parts, which per- 

 haps were reopened older workings, were available to 

 the writers and have been incorporated in the accom- 

 panying maps of the mine. 



By 1857, when the ore had been followed to a depth 

 of 500 feet, the Day tunnel on the 800 level was be- 

 gun, largely in order to drain the upper levels. In 

 1858, when the tunnel had been driven only 508 feet, 

 the mine was closed by an injunction, and work was 

 not resumed until the winter of 1861. In August 1862, 

 the tunnel unexpectedly penetrated the ores that were 

 subsequently mined from the New Ardilla stope, and 

 in August 1864 a connection was made with the Junc- 

 tion shaft sunk from the 600 level. Up to this time 

 the ore was all taken out through the 300-level Main 

 tunnel, and even after the Day tunnel had been-eon- 

 nected with the workings, little ore was hauled through 

 it until 1870, because of the difficulty of transporting 

 the ore from its portal to the furnaces at the Hacienda. 



Meanwhile, in the mineralized area above the Day 

 tunnel, hilos had been followed from one ore body to 

 the next, and in 1865 the rich North Ardilla ore body, 

 which yielded a 7- months' supply of ore, was struck. 

 Next came the discovery of the great Santa Rita ore 

 body, which in 5 years yielded 70,000 flasks of quick- 

 silver. Up to 1870, when J. B. Randol took charge 

 of the mining, the ores of the central stope area had 

 yielded the major part of the 535,000 flasks that the 

 mine had produced. Most of the stopes, however, 

 were believed to be mined out, and there was little 

 ore in sight. Thin veinlets were therefore followed 



northward, and these led to the ore bodies of the 

 Victoria area, described on pages 135-136. 



In December 1884, the Santa Rita shaft was begun 

 in order to search for ore bodies above and below the 

 Santa Rita ore body. By 1886 it had reached the 800 

 level and was connected with the Day tunnel ; in the 

 following year it reached the 900 level, and crosscuts 

 were driven from it toward the downward continua- 

 tion of the New Ardilla ore body. These workings 

 failed to reveal any ore, and the shaft was allowed to 

 cave. In 1940 and 1941 it was reopened by C. N. 

 Schuette to the 800 level, but in 1948 it had again 

 caved from the 300 level to the surface and for an 

 unknown distance upward from the 800 level. 



In another attempt to find a downward continua- 

 tion of the New Ardilla ore body, a winze was sunk 

 in 1898 from a point 1,560 feet in from the portal of 

 the Day tunnel, and at the same time some ore was 

 underhanded in a winze from the 800 level nearby. 

 It soon became obvious that this winze would never 

 strike the continuation of the ore body, and a second 

 winze, which was known, like the first, as the New 

 Ardilla sink (winze), was started from the Santa Rita 

 shaft crosscut. This winze was sunk to a depth of 

 150 feet, and short drifts were run along a contact 

 near its bottom, but only a small amount of ore was 

 found. In 1901 the New Ardilla sink was abandoned, 

 and it quickly filled with water. 



Again and again since 1870, lessees and company 

 miners have returned to the huge cavern of the central 

 stope area to recover ore left in the walls or fill, but 

 no major attempt had been made to find new ore 

 bodies in the area or along its margins. How much 

 quicksilver was recovered by these sniping operations 

 is unknown, but it may have been considerable be- 

 cause very little ore remains in the stope walls and 

 floors. 

 Geology 



The central stope workings penetrated rocks of the 

 Franciscan group, and sills of serpentine whose mar- 

 gins were nearly everywhere altered to silica-carbon- 

 ate rock. These dip northward, in general, at moder- 

 ate angles, though locally there are radical departures 

 from this attitude. In the southern part of the area 

 one continuous mass of serpentine extends from the 

 surface down to below the 800 level, but farther north 

 it divides into several distinct and somewhat irregular 

 sills. (See section C-C', pi. 11.) The ore bodies lie 

 along the margins of some of these sills, and where 

 they are numerous the sills can be outlined with con- 

 siderable accuracy. But the sills that are cut only by 

 a few workings or a single crosscut cannot be projected 



686-671 063- 



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