MINES 



167 



years would have been furnaced, it is not possible to 

 judge closely the relative quality of the ore bodies 

 found in the various parts of the mine. It is evident, 

 however, that the ore bodies, though they would be 

 considered rich at present, were not quite so rich as 

 those of the New Almaden mine. According to avail- 

 able records, the richest ore in the Guadalupe area 

 was found in the Old Mine, where large ore bodies 

 yielded from 2 to 5 percent mercury. Other large 

 ore bodies found adjacent to the New Guadalupe In- 

 clined shaft averaged from 6 to 12 pounds of mercury 

 per ton, and the surface pit above some of these 

 yielded, in recent years, about 6 pounds of mercury 

 per ton. The brecciated silica-carbonate rock near the 

 top of the ridge included 5-inch pieces of ore contain- 

 ing as much as 40 percent quicksilver, but the average 

 grade of the ore mined from the breccia was probably 

 not more than 1 percent. 



The ore bodies fall naturally into four groups lying 

 in different structural environments, and these groups 

 will be discussed in turn. The structures and the 

 workings that explore them are (1) the hanging- wall 

 side of the southern serpentine body, explored by the 

 workings of the Old Mine; (2) the area of coalescence 

 of the two serpentine bodies, explored chiefly by the 

 levels from the New Guadalupe Inclined shaft and 

 the adits to the northwest; (3) the footwall of the 

 northern part of the serpentine, explored chiefly by 

 the northern parts of the 100, 200, and 300 levels from 

 the New Guadalupe Inclined shaft and the East Hill- 

 top workings; and (4) the landslide area, explored 

 by the New Prospect and Kelly workings. 



The largest and richest ore bodies in the Guadalupe 

 mine were those lying along the hanging wall of the 

 southern intrusive mass, explored by the Old Mine 

 workings. These lay close to the intrusive contact, in 

 a continuous shell of silica-carbonte rock which in 

 places is at least 150 feet thick, and they extended 

 along the strike, according to the memory of 'one 

 miner, 15 beyond the limits of all the levels. The 

 greater part of the ore came from two great stopes or 

 labors the Thayer Labor and the Dore Labor. The 

 Thayer Labor plunges from the No. iy 2 level west 

 of the Engine shaft S. 30 E. to a place on the No. 6 

 level east of the shaft. Below the No. 6 level ore 

 bodies were mined in several small stopes, but at the 

 No. 7 level these merge into the Dore Labor, which 

 continues down nearly to the No. 9 level, still plung- 

 ing southeastward but becoming much flatter. The 

 southernmost pdrt of this stope is shown only vaguely 



Conversation with Mr. Alberto Garcia of Gilroy, California, who 

 was employed at the Guadnlupe mine during the period 1876-86. 



on available maps, but it appears to lie a little higher 

 than the flat part to the north. In the uppermost part 

 of the mine above the li/ 2 level the ore bodies were 

 scattered and were mined in several small stopes 

 adjacent to the Old Inclined shaft. 



The reason for the localization of the ore bodies in 

 this part of the mine are obscure because of the inac- 

 cessibility of the workings, but some interpretations 

 may be made on the basis of the positions of these 

 workings. The major ore bodies appear to have lain 

 along the hanging wall of the serpentine sill just 

 northeast of its intersection with a steeply dipping 

 contact, which may or may not be a fault, separating 

 greenstone from graywacke. This contact strikes 

 nearly northwest rather than west like the upper sur- 

 face of the sill, and its intersection with the south- 

 dipping sill results in the N. 30 W. elongation of the 

 ore bodies. The position of this contact from the 

 No. li/o level to the No. 6 level is indicated by abrupt 

 northward swings in the western parts of the levels, 

 bringing the lower levels beneath the upper levels. 

 In the deeper workings, it is suggested by short 

 branching drifts from the main workings on the No. 7, 

 9, and 10 levels and by the southwestern margin of 

 the Dore Labor. The nature of the contact is not 

 known, but if it is a fault separating greenstone from 

 graywacke, as seems likely, it is so poorly exposed on 

 the surface that it was nowhere recognized there as a 

 fault. However, the fact that the graywacke, which 

 has a wide surface exposure, gives way at depth to 

 greenstone as the hanging wall for the ore bodies lends 

 support to the fault hypothesis. A further structural 

 control for the ore body mined in the Thayer Labor 

 may have been effected by the slight bowing of the 

 contact, as indicated by the position of the No. 2, 3, 

 4, 5, and 6 levels, and at greater depth by a structural 

 nose near the No. 8 level, though on this level the 

 apparently irregular shape of the serpentine cannot be 

 deduced with certainty from the position of the work- 

 ings. The bottoming of the ore above the No. 9 level 

 nearly coincided, according to reports, with the change 

 of the hanging wall from greenstone to what was 

 known by the miners as the "lime ledge," which was 

 limestone of the Franciscan group. However, a 

 change in the shape of the intrusive body may have 

 been more effective than a change in the wallrock in 

 preventing the deposition of cinnabar. 



The ore bodies in the area of coalescence of the two 

 parts of the serpentine body, explored by workings 

 from the New Guadalupe Inclined shaft and the adits 

 to the northwest, were neither as large nor as rich as 

 those of the old mine. They lay in silica-carbonate 

 rock derived from the serpentine between the ends of the 



