148 



GEOLOGY AND QUICKSILVER DEPOSITS, NEW ALMADEN DISTRICT, CALIFORNIA 



The smaller ore bodies mined from the jagged in- 

 trusive contact above the 600 level included, in as- 

 cending order, the Warren, Arcial, 500-level, 400-level, 

 Curasco, and Manilla ore bodies. The first two of 

 these were in well-defined thin apophyses that appear 

 to have been mineralized throughout, the 400-level 

 and Curasco ore bodies were on the lower contacts of 

 branching apophyses, and the other smaller ore bodies 

 were found in silica-carbonate rock near the junctions 

 of adjacent apophyses. The scattered occurrence of 

 ore bodies along this irregular contact on both upper 

 and lower sides of apophyses made prospecting diffi- 

 cult, as is emphasized in the following quotation from 

 the company superintendent's report of 1885: 



The peculiarity of this portion of the mine even In the rich 

 upper works of the San Francisco and New World is that the 

 ore masses are capriciously distributed, and do not have con- 

 necting links. Some of the ore chambers like the New World, 

 found when almost all hope was abandoned, are rich and exten- 

 sive and others again are nothing but mere pockets. Difficulty 

 of prospecting in this portion of the mine is vastly increased 

 from the fact that the faithful guide, the black alta hanging 

 wall so reliable and comparatively uniform In the main "New 

 Almaden" and "Randol ore territory" is In this section as fickle 

 and uncertain as the ore chambers themselves, sometimes not 

 occurring at all on the hanging wall and at others abruptly 

 ceasing and giving place to serpentine. 



SANTA MARIANA AREA 



Location and extent or workings 



The Santa Mariana area includes the scattered sur- 

 face cuts, shallow adits, and connected workings that 

 explore a body of serpentine and silica-carbonate rock 

 lying along and near the crest of Mine Hill between 

 the Washington shaft and the San Pedro workings 

 (pi. 3 and fig. 92). The many opencuts are all small 

 and appear to have been excavated by hand in the 

 early days of mining on the hill. The underground 

 workings, which lie at and above the 200 level, con- 

 sist mainly of 3 adits totaling only a little more than 

 2,000 feet in length on the company maps and known 

 as the Lower Santa Mariana, Upper Santa Mariana 

 (or Carler), and the Mariana Road (or Upper Mari- 

 ana No. 2) tunnels. The Lower and Upper Santa 

 Mariana tunnels were driven from the south side of 

 the hill and the Mariana Road tunnel from the north 

 side. (See pi. 4.) Several other adits were driven 

 in this area, but they are not plotted on any avail- 

 able maps and apparently failed to develop any ore. 

 During this study only the surface cuts and a part 

 of the Mariana Road tunnel were accessible; infor- 

 mation on the rest of the other underground workings 

 is therefore based on company maps and surveyors' 

 records. 



History and production 



All that is known of the early history of mining in 

 the Santa Mariana area is that in 1864, 10 tons of ore 

 was mined from some workings in the area, that by 

 1871 about 218 tons had been mined, and that in 1888 

 and 1889 another 557 tons was mined. The main 

 period of production, however, was brought about by 

 the reopening and extension of the three principal 

 adits, which began in 1897. For the period 1898-1902 

 the recorded yield of ore was !>.7-_'5 tons. In 1897, also, 

 the small Santa Mariana shaft was put down, some 

 800 feet west of the Lower Mariana tunnel, to a depth 

 of 62 feet. Company records indicate that in the fol- 

 lowing years several new adits were driven to prospect 

 the area further, but some of these workings can no 

 longer be identified. The Refanni tunnel, on the 

 "southwest side of the hill," was driven in 1898; the 

 Chabolla tunnel, "200 feet west of the Lower Santa 

 Mariana," and the Bernal tunnel, on the "north side 

 of the hill," in 1899; the Payson tunnel, "on the south- 

 west slope," in 1900; and the Tank tunnel, "near the 

 Lower Santa Mariana," in 1901. All of these, how- 

 ever, were abandoned after a few months, and none 

 contributed to the production of the area. Virtually 

 no mining has been carried on in the area since 1902, 

 although several unsuccessful exploratory trenches 

 were dug in 1941 and 1942. 



No figures showing the amount of quicksilver pro- 

 duced from the Santa Mariana area are available, for 

 its ores apparently were mixed with those from other 

 parts of the New Almaden mine. Any estimate of its 

 production, therefore, depends largely on the assumed 

 grade of the ore. If the ore from this area during 

 each of its productive years was of the same grade 

 as the average ore furnaced at New Almaden during 

 the same years, the production of the Santa Mariana 

 area was somewhat more than 2,600 flasks; but because 

 of the ready accessibility of the area it is likely that 

 ores of lower than average grade were mined, in which 

 case the production was less. 



Geology 



The principal geologic feature of the Santa Mariana 

 area is a tabular intrusive body of serpentine partly 

 replaced by silica-carbonate rock, which forms a south- 

 eastward extension of the body explored by the San 

 Pedro workings. (See pi. 3.) On the surface the 

 general trend of this tabular body across the top of 

 the ridge is N. 32 W.; underground its strike, as de- 

 lineated by both sides of the body on two levels, is 

 about N. 20 W. The dip can be determined only 

 down to the 200 level, but the contacts on the two 

 sides in the Upper and Lower Santa Mariana tunnels 

 lie directly below those on the surface, indicating that 



