MINES 



161 



level, about 480 feet from the portal. Although large 

 parts of this sill have been converted to silica-car- 

 bonate rock, no ore has been found in it. 



The next serpentine sill to the southwest is a com- 

 paratively large body, which is barren of ore in the 

 Senator mine, though it contains small ore bodies in 

 the Guadalupe mine. This sill extends northwestward 

 from the Senator mine across the Guadalupe mine 

 property and reaches the canyon of Guadalupe Creek 

 at Shannon Road; it also extends eastward from the 

 mine for about 1,500 feet along the ridge. Within the 

 Senator mine area the sill trends from the Guadalupe 

 property line about S. 55 E., following the crest of 

 the ridge to a point 400 feet southeast of the Nones 

 shaft, beyond which it trends nearly east. Its general 

 dip is about 50 SW., though along certain flexures 

 its dip may vary as much as 25 from that figure. 

 The serpentine body appears to pinch out completely 

 at depth. Its thickness is greatest at the surface, 

 where it has an outcrop width of 270 feet, but on the 

 260 level it is only 80 feet in horizontal width and 

 its contacts converge downward. The deepest level 

 at which the width of this body is known is the 500 

 level, where a nearly horizontal diamond-drill hole 

 passed through it within an interval of 100 feet, and 

 a crosscut on the 800 level extends northward beneath 

 the body without striking either serpentine or silica- 

 carbonate rock. These facts, taken together, indicate 

 that the body pinches out a little below the 600 level, 

 and this conclusion is further strengthened by the 

 fact that the northwestward extension of the same 

 body in the Guadalupe mine also appears to pinch 

 out at a slightly lower level (pis. 16-18). The north- 

 east or footwall margin of this serpentine body has 

 been partly altered to a shell of silica-carbonate rock, 

 which the miners refer to as the "No. 1 vein" (pi. 14, 

 section B-W). It crops out about 400 feet northeast 

 of the Nones shaft, is exposed underground on the 

 260 level just north of the shaft, and probably is cut 

 on the 125 level about 200 feet from the portal. Al- 

 though this shell of silica-carbonate rock has been 

 but little explored on the surface and underground, 

 it appears to be barren. The southwest or hanging- 

 wall border of the serpentine body is virtually un- 

 altered except for thin selvages of silica-carbonate 

 rock, penetrated by diamond-drill holes from the 400 

 and 500 levels. 



The third serpentine body in the Senator mine (go- 

 ing south west ward) is important economically, for it 

 is almost completely sheathed with silica-carbonate 

 rock, and this sheath contains all the productive ore 

 shoots that have been found in the mine. (See sec- 

 tion B-B', pi. 14.) This body strikes N. 60 W. and 



extends as a fairly regular sill from the deepest part 

 of the mine nearly to the surface. At the surface, 

 however, its presence is indicated only by three thin 

 elongate bodies of silica-carbonate rock and serpen- 

 tine cropping out in the vicinity of the Nones shaft. 

 Underground, where every level in the mine explores 

 this body, its width is well known to the 1000 level, 

 and in the deeper levels its contacts can be inferred 

 from the position of the workings. It is discontinu- 

 ously exposed at the surface, but in the mine it is 

 nearly 200 feet wide between the 500 and 800 levels, 

 and below the 800 it tapers downward. Wherever it 

 is exposed by the mine workings the serpentine has 

 been extensively altered to silica-carbonate rock all 

 along its periphery, but serpentine cores are preserved 

 between the 125 and 300 levels and between the 400 

 and 800 levels. 



The most southwesterly of the serpentine bodies in 

 the Senator mine area crops out as bulbous body 

 measuring 1200 by 750 feet, and extends northwest- 

 ward into the Guadalupe property (pi. 14). It is 

 bordered everywhere except on the north by green- 

 stone tuff or by amphibolite derived from tuff. In 

 general it is not .altered to silica-carbonate rock, 

 though a few small outlying bodies of that rock crop 

 out within a 300-foot marginal zone to the south. 

 The general dip of the serpentine body can be roughly 

 inferred from the dips of the shear planes within the 

 serpentine; these average about 60 to 65 SW., being 

 steeper than the known dips of the extension of the 

 body in the Guadalupe area. This inference regard- 

 ing the dip cannot be confirmed by information gained 

 from the records of the driving of the 260-level tun- 

 nel ; for the records indicate merely that much of the 

 rock along the course of the tunnel was serpentine and 

 alta, without giving any exact locations for the con- 

 tacts. The part of the tunnel lying within 300 feet 

 of the southern portal is reported to have been in 

 "vein" (silica-carbonate rock), but this is probably 

 the downward extension of one of the small masses 

 exposed on the surface. 



Ore txxlles 



The descriptions of the ore bodies included in the 

 following paragraphs are necessarily based on obser- 

 vations of others, including John Drew, who served 

 as foreman of the Senator mine during most of its 

 period of large production. Consequently, although 

 the size, shape, distribution, and general grade of the 

 ore bodies are well known, their geologic character 

 and occurrence are partly inferred. 



The ore bodies of the Senator mine were comparable 

 to those of the New Almaden mine in size, but their 



