MINES 



165 



are connected by stopes. (See pi. 15 and section A-A', 

 pi. 14.) 



In the newer parts of the mine there are 17,000 feet 

 of underground workings, widely distributed beneath 

 the crest and southern slope of Los Capitancillos 

 Eidge. (See pis. 14, 15.) Most of the workings lying 

 more than 300 feet above sea level were accessible 

 when this study was made, but most of those below 

 that level were inaccessible. In 1942, however, when 

 the pumps were working in the Guadalupe Inclined 

 shaft, a Survey field party was able to reach the 200 

 level, which is only 235 feet above sea level. Most of 

 the newer workings were reached through adits, but 

 four important levels and connected stopes were ac- 

 cessible only through the New Guadalupe Inclined 

 shaft. The collar of this shaft is 504 feet above sea 

 level, and it bottoms on the 300 level at an altitude of 

 about 90 feet. The most extensive workings from it 

 are on the 100 level; these extend 600 feet southwest 

 from the shaft to reach the surface near the camp, 

 and 1,300 feet northeast to points under the New 

 Prospect tunnel area. Most of the other adits lie 

 between 420 and 530 feet above sea level and were 

 driven northeastward into the ridge along a zone ex- 

 tending 1,000 feet northwest of the shaft, but a small 

 group of adits were driven southward into the north 

 slope of the ridge at altitudes of 600 to 670 feet. 



Other important parts of the newer mine workings 

 are the open pits, which are clustered in two areas. 

 One area, which extends northwestward from the 

 modern reduction plant for about 1,200 feet, includes 

 at its southeastern end the pit from which the greater 

 part of the ore mined in recent years was taken. This 

 pit, which is about 220 feet long, 60 feet wide, and 

 60 feet deep in its deepest part, is connected by a 

 raise with the 100 level from the New Guadalupe 

 Inclined shaft. The other cluster of pits lies on the 

 north slope of Los Capitancillos Ridge near its crest 

 and extends for about 800 feet parallel to the trend 

 of the ridge. Most of the pits in this area are shallow 

 bulldozer cuts, but the two known as the Kelly cuts 

 are larger. The western one of these is 125 feet in 

 diameter and 25 feet deep, whereas the other is only 

 80 feet in diameter but nearly 60 feet deep on its 

 upslope side. One other large pit, known as the Office 

 Mine pit, lies outside the two main areas of opencuts, 

 between the reduction plant and the bridge across 

 Guadalupe Creek. 



Geology 



The dominant geologic feature of the Guadalupe 

 mine area is a complex composite serpentine body, 

 which is intrusive into deformed clastic sedimentary 



rocks and greenstones of the Franciscan group. The 

 general strike of this irregular intrusive body is N. 

 55 W., roughly conformable with the strike of the 

 rocks of the Franciscan group (pi. 14), and its south- 

 westerly dip of 35-50 also is probably parallel to 

 that of these rocks. (See pi. 14.) The intrusive 

 body is therefore roughly sill-like, but in its surface 

 exposure it is split lengthwise by two narrow highly 

 irregular but roughly wedge-shaped septa of gray- 

 wacke, which nearly converge in the area northwest 

 of the New Guadalupe Inclined shaft. The eastern 

 septum, which extends beyond the Senator mine, does 

 not dip gently southwestward with the sill, but ap- 

 pears to extend downward almost vertically, thus 

 separating a rootless northern serpentine body from 

 a more sill-like southern body. The marginal parts 

 of this complex serpentine body, which have been 

 hydrothermally converted to silica-carbonate rock, 

 have contained most of the ore. A little additional 

 ore, however, was obtained from a landslide of brec- 

 ciated silica-carbonate rock near the crest of the ridge. 



The southern part of the intrusive body crops out 

 as a band of serpentine and silica-carbonate rock that 

 extends through the camp area along the southwest 

 base of Los Capitancillos Ridge and slants upslope to 

 the southeast. Underground these rocks were exten- 

 sively explored by the now inaccessible workings of 

 the old mine. (See pis. 16-18.) The upper surface 

 of the serpentine body is fairly well delineated by the 

 workings of the old mine that apparently followed 

 it, but the position of the lower surface is known in 

 only a few places. In general, however, the body is a 

 sill about 500 feet thick with extensive shells of silica- 

 carbonate rock along both sides. The character of the 

 silica-carbonate rock formed along different parts of 

 the intrusive mass in the mine area varies from place 

 to place, even though the serpentine shows no ap- 

 parent variation, being all sheared and bouldery. The 

 silica-carbonate rock formed along both borders of the 

 southern serpentine mass contains a relatively high 

 proportion of carbonate, and is cut by a large number 

 of steep northeastward-trending carbonate-quartz 

 veins or hilos. These hilos, which are exceptionally 

 abundant where the northern and southern serpentine 

 masses coalesce, were of great importance in localizing 

 ore bodies, though in some places the localization was 

 also affected by rolls and irregularities in the shape of 

 the hanging- wall contact. (See fig. 89.) 



The northern part of the composite intrusive body 

 crops out along the crest and upper southwestern slope 

 of the ridge from a place beyond the northwest corner 

 of the Guadalupe mine area to the Senator mine area. 

 (See pi. 14.) The extent of this northern body at 



