FUTURE PRODUCTION 



175 



ern one passed directly from serpentine to alta, but 

 may have failed to reach the true contact. This area 

 also lies close enough to the surface to be readily ex- 

 plored by drilling from the surface, or it could be 

 reached by relatively short underground drifts, pro- 

 vided the nearest old workings are accessible. 



The third place on contact 1 that is worthy of at 

 least some exploration lies between the southernmost 

 Harry and Cora Blanca workings and the workings in 

 the San Francisco area. Geologic information about, 

 this area is not sufficient to locate accurately any small 

 structure that might contain an ore body, but the geo- 

 logic relations both on the surface and in underground 

 exposures indicate that a structural "nose" of the up- 

 per contact of the intrusive mass extends between the 

 two groups of workings. On the surface in this area 

 there is no silica-carbonate rock along the margin of 

 the serpentine mass, but underground a shell of silica- 

 carbonate rock has been formed along both flanks of 

 the supposed "nose." This structural feature also lies 

 close enough to the surface to be explored by surface 

 drilling, or it might be better explored by drifting 

 along the contact from the south end of the Harry 

 600 level. 



Contact 2 



Contact 2 is the lower contact of the upper serpen- 

 tine sill, and its relation to contact 1 is indicated in 

 sections B-B' and C-C', of plate 11. It is believed 

 that the best places to look for ore along this contact 

 lie below the 900 level, but there has been so little 

 exploration at this depth that it is hard to predict what 

 parts of the contact would prove most favorable. If it 

 be assumed that the serpentine body is more or less 

 sill-like in shape, a favorable arch on this contact 

 should lie below the arch on the upper contact of the 

 sill, along which the Victoria ore bodies were localized. 

 And if the hilos are developed along the lower side 

 of the sill nearly underneath those on the upper side, 

 this area would also contain hilos. The part of con- 

 tact 2 below the Victoria stopes, together with a part 

 of contact 3 at greater depth, could best be tested by 

 drill holes put down from the 800 level near the Santa 

 Eita shaft. . Although much uncertainty exists as to 

 what part of contact 2 will be most likely to border on 

 ore bodies, the chance of finding extensive ore bodies 

 above this contact is thought to be good enough to 

 warrant the expense involved in extensive explora- 

 tion. If a careful study is made of the geologic struc- 

 ture indicated by the rocks penetrated by the first few 

 drill holes, the number of holes necessary to explore 

 the contact should not be very large. 



Contact 3 



Contact 3 might be considered to offer at least as 

 good possibilities for ore as contact 2; it even has a 

 possible advantage in being overlain by alta, and on 

 the 1800 level south of the Randol shaft it is under- 

 lain by a shell of silica-carbonate rock cut by hilos 

 containing cinnabar. The explored parts of this con- 

 tact on and above the 800 level, however, have not 

 been as productive as the explored parts of contact 2. 

 On contact 3 as on contact 2, it is not possible to de- 

 duce from the available geologic data what places be- 

 low the 800 level offer the best structural setting for 

 the localization of ore, but the Victoria-Velasco arch 

 may affect contact 3 as well as contact 2. (See sec- 

 _tion A-A', pi. 11.) This contact, because it offers such 

 a large unexplored area along which ore bodies may 

 have formed, is believed to provide good enough pos- 

 sibilities to justify the cost of exploring it. 



Contact 4 



What has been said about the uncertainty of the 

 exact position of contacts 2 and 3 is even truer of the 

 almost completely unexplored contact 4. One part of 

 this contact, however, is so exceptionally promising, 

 and could so easily be tested, that it probably offers 

 one of the best chances in the district for the finding 

 of new ore bodies. This is the part beneath the south- 

 ern part of the Day tunnel ; for the arch in the silica- 

 carbonate rock here penetrated by the tunnel indicates 

 that this underlying contact is also arched. As the 

 thickness of the silica-carbonate rock is not known, we 

 cannot state exactly how far below the tunnel the con- 

 tact with the underlying alta may be, but judging 

 from the usual thickness of the shells of silica-car- 

 bonate rock in the mine area, the distance is likely to 

 be only a few tens of feet. From the distribution of 

 the rocks east and west of the tunnel, the arch is in- 

 ferred to be a section along the west flank of a domal 

 structure whose apex is east of the Day tunnel, but 

 the position of this favorable apex cannot be exactly 

 located from the available data. One reason for be- 

 lieving that this domal structure is likely to contain 

 ore is found in certain records of the mine superin- 

 tendent, written when the tunnel was driven; these 

 contain the statement that in the area of the "mule 

 barn" (1630 N.-5120 W.) a flow of water containing 

 fragments of cinnabar was encountered. Subsequently 

 the source of this cinnabar was sought by putting up 

 a raise, which passed into the overlying serpentine 

 without finding cinnabar; but the geologic structure 

 indicates that the possible ore body was more likely 



