MINES 



135 



the mineralization of thin overlying sills. The reason 

 for the localization of the other small ore body on the 

 700 level is not apparent. 



Suggestions for further development 



Most of the part of the Harry area lying either 

 adjacent to the main stopes or down the dip of the 

 intrusive contact beneath them appears to have been 

 adequately explored. One small part of this contact, 

 however, between the Machine stope and the Yellow 

 Kid workings, remains unexplored, though its rela- 

 tively low angle of dip above the 600 level should 

 have encouraged some further prospecting. Areas 

 lying to the west, northeast, and south of the explored 

 part of the Harry area appear promising for the 

 development of new ore bodies, but, as a discussion 

 of these outlying areas involves the geology of sur- 

 rounding parts of the mine, suggestions for their de- 

 velopment are placed in the section of this report that 

 deals with the outlook of the district (p. 170-176). 



VELA SCO AREA 

 Location and extent of workings 



The Velasco area, northwest of the Harry area (fig. 

 92), is named after the old Velasco mine, which was 

 developed in the earliest days of mining on Mine Hill. 

 Its main underground workings are a relatively com- 

 pact group of adits, drifts, and stopes, which extend 

 north and west from the vicinity of the Santa Maria 

 shaft for about 500 feet and go down about 300 feet 

 from the surface, or about to the 600 level of the 

 New Almaden mine. Practically all these workings 

 were inaccessible when the study for this report was 

 made. Before 1865 the workings were reached through 

 the Road tunnel and the Upper and Lower Velasco 

 tunnels, but after 1875 the deeper Great Eastern tun- 

 nel was used, and after 1892 some of the deeper lev- 

 els were reached through the Santa Maria shaft. The 

 Velasco workings were connected with the workings 

 of the central stope area to the west on the 600 level 

 by an incline from the Great Eastern tunnel and by 

 various stopes; they also were connected with the 

 Harry workings to the south by the Santa Maria 

 shaft and several winzes from nearby levels. (See 

 pi. 4.) 



The maps of the Velasco workings included with 

 this report are less complete and more confusing than 

 those of most of the other workings of the New Alma- 

 den mine. Many of the levels were driven from old 

 adits whose portals are caved and cannot be accurately 

 located, and they lie at irregular elevations that do 

 not coincide with the levels used in much of the rest 

 of the mine. Furthermore, as the workings were vir- 

 tually all inaccessible, those shown on the maps (pis. 



4-10) are copied from the old company maps. These 

 are believed to be fairly accurate in plan, but they do 

 not give many exact elevations. Since the old com- 

 pany maps were prepared, the area has been reex- 

 plored and mined, and some of the more recent work- 

 ings that were never surveyed are known to be missing 

 from the maps included with this report. The Velasco 

 workings shown on the maps are about 10,000 feet in 

 aggregate length, and those not shown perhaps as 

 much as 1,000 feet. 



History and production 



Ore is said to have cropped out at the surface in 

 this area, and during the very early development of 

 the New Almaden property, it was followed downward 

 in an isolated group of workings known as the Velasco 

 mine. Early records are too fragmentary and incom- 

 plete to give a detailed history of the subsequent de- 

 velopment of the mine or an accurate record of its 

 production. By 1864, however, the Upper and Lower 

 Velasco tunnels and the Road tunnel apparently were 

 serving as haulageways for ores that were being re- 

 moved in large quantity. In 1865 the daily yield was 

 reported as 7 tons of "very rich" ore, at a time when 

 the ore from the New Almaden mined averaged 12.4 

 percent quicksilver, and in order to explore the area 

 at greater depth the Great Eastern tunnel was driven 

 and connected with the existing workings. During 

 1866 and 1867 production from the area dwindled rap- 

 idly, and apparently there was almost none in 1868 

 and 1869. Between 1870 and 1874, however, some new 

 ore shoots probably were found, for during this period 

 a production of about 5,000 flasks was obtained. There- 

 after, production declined rapidly, and by 1877, the 

 area, which had yielded about 25,000 flasks of quick- 

 silver, was thought to be exhausted. With the sink- 

 ing of the Santa Maria shaft in 1892 some of the 

 workings were reopened, but no significant production 

 seems to have come from the Velasco workings at this 

 time. In 1908 and 1909, when ore was desperately 

 needed to maintain the operation of the New Almaden 

 mine, the old Mine Hill opencut, east of the Santa 

 Rita shaft, was excavated to remove the low-grade ore 

 left above the older Velasco workings, several adits 

 were driven below to find any 'remaining stope fill and 

 pillars, and the dumps at the mouths of the Bush and 

 Great Eastern tunnels were reworked. These opera- 

 tions, which apparently were the last undertaken in 

 the Velasco area, probably yielded between 2,000 and 

 3,000 flasks of quicksilver. 



Geology 



The rocks penetrated by the Velasco workings con- 

 sist in part of the extension of the greenstone tuffs of 



