126 



GEOLOGY AND QUICKSILVER DEPOSITS, NEW ALMADEN DISTRICT, CALIFORNIA 



tain some gold. The rock seen in the outcrops and on 

 the dumps shows far too little copper deposition to 

 be rated as copper ore. 



CHROMITE 



Chromite occurs sparingly in small lenses and ir- 

 regular stringers in the serpentine of the New Alma- 

 den district. These bodies measure only a few inches 

 in length, and are generally widely spaced. Typical 

 examples are well exposed in the serpentine near the 

 foot of the cable raise which goes up from a branch 

 of the 800 level Day tunnel in the New Almaden 

 mine (pi. 6). At the surface in a few nearly flat areas 

 the serpentine containing widely scattered chromite 

 lenses has weathered and been eroded, leaving a natu- 

 ral concentration of the resistant heavy chromite in 

 the thin residual soil. 



Short adits have been driven into the serpentine in 

 search of chromite ore at two places in the district, 

 but none of these revealed more than a few scattered 

 pods. One of these places is close to the end of the 

 east branch of the road leading from Guadalupe Can- 

 yon toward El Sombroso; the other is in the Santa 

 Teresa Hills, near the narrow saddle three-fourths of 

 a mile south of Coyote Peak. From the surface in the 

 latter area one carload of ore was collected and shipped 

 during World War I. In a third area, 8,000 feet east 

 of the Senator mine at the northern base of Los Capi- 

 tancillos Ridge, many pieces of massive chromite float, 

 the largest nearly 1 foot in diameter, have been piled 

 along fence lines, and it seems likely that some chro- 

 mite ore was collected here also during World War I. 



MANGANESE 



Manganese-bearing chert lenses of the Franciscan 

 group have been prospected by means of a few shal- 

 low cuts near the top of Fern Peak, 1 niile S. 40 E. 

 of the Hacienda and also on a spur extending from 

 Fern Peak, 0.35 mile S. 75 E. of the Hacienda. In 

 each of these places the manganese minerals are of 

 supergene origin; they consist of psilomelane, pyro- 

 lusite, and the more nondescript material generally 

 called wad. These minerals fill cracks in the chert 

 to form irregular veins, and locally they form small 

 pods of nodular ore. Although selected specimens rich 

 enough to constitute manganese ore can be collected 

 at both places, in neither does there appear to be any 

 chance of obtaining more than a few sacks of usable 

 ore. 



NONMETALXJC MINERAL RESOURCES 



BUILDING STONE 



The sandstone of Late Cretaceous age in the Santa 

 Teresa Hills has been quarried in several places on 



the southwest flank of the hills for use as a building 

 stone. Seven of the larger quarries are indicated on 

 plate 1, but all of these, and some smaller ones not 

 shown, appear to have been abandoned many years 

 before 1948. The quarries were first opened in 1866 

 (Irelan, 1888, p. 546-547) and were intermittently 

 operated at least until 1906. During this period they 

 supplied the building stone for several well-known 

 public buildings in San Francisco and San Jose and 

 for all the older buildings of Stanford I'niversity. 



This sandstone was particularly desirable as build- 

 ing stone for several reasons. Its color where un- 

 weathered is gray, but, owing to the great depth of 

 oxidation in the area, most of the rock that has been 

 quarried had an attractive buff color. Of particular 

 importance, especially in the days of ornately carved 

 buildings, was the fact that the sandstone when first 

 quarried was soft and easily carved but became harder 

 on exposure to the air (Forstner and others, 1906, 

 p. 134). One unfavorable feature of the sandstone is 

 its tendency to crumble on repeated wetting and dry- 

 ing. This is especially well displayed by many of the 

 sandstone columns around the quadrangle of Stanford 

 University; in places as much as an inch of rock has 

 crumbled off the lower parts of these columns, which 

 have been exposed to water sprinklers, whereas the 

 higher parts of the columns, which remained dry. are 

 so little eroded that they still clearly show the marks 

 of the stonemasons' tools. For further statistical data 

 bearing on the suitability of this sandstone us a build- 

 ing stone, the reader is referred to the work by Forst- 

 ner and other (1906). 



The cavernous- weathered silica-carbonate rock of 

 the New Almaden district is sold locally for decorative 

 use in gardens. Fresh serpentine, limestone of the 

 Franciscan group, and siliceous shale of the Monterey 

 have also been used for ornamental rock walls in and 

 around Los Gatos and San Jose. 



LIMESTONE 



Limestone of the Franciscan group was quarried 

 before 1900 in several places in the area anil converted 

 in nearby kilns to lime. The more productive quarries 

 were those of the Guadalupe Lime Co. about a mile 

 southeast of the Guiulalupe quicksilver mine, the Old 

 Douglass Ranch quarries (Logan, HUT. ]>. .".!_') south 

 of Los Gatos in tin- NWVi sec. 27, T. 8 S., R. 1 W.. 

 and the quarries on the north slope of Limekiln Can- 

 yon. The largest of these, the Guadalupe Lime Co. 

 quarry, was first opened in 1864 (Irelan, 1888, p. 544) 

 and remained in operation for more than 20 years. 

 The limestone, which contained many lenses of chert, 

 was apparently hand sorted at the quarry and trans- 



