168 



GEOLOGY AND QUICKSILVER DEPOSITS, NEW ALMADEN DISTRICT, CALIFORNIA 



two septa of graywacke and along other small inclu- 

 sions of rocks of the Franciscan group, and, conse- 

 quently, they were not localized along an extensive 

 hanging wall or footwall. In the Mason stope and the 

 pit above, however, a relatively thin inclusion of 

 country rock acted as a footwall, and in the Water, 

 Moreno, and McGurk stopes there are isolated ex- 

 posures of alta. The ore bodies appear to have been 

 formed in the silica-carbonate rocks at places where 

 steep northeastward-trending hilos are abundant, and 

 they were richest where the hilos are closely spaced. 

 The mineralized zone, though it extended along the 

 surface for a distance of 1,200 feet, has been followed 

 downward for only about 200 feet. The deepest ore 

 body yet found along this zone extended up from the 

 intersection of the New Guadalupe Inclined shaft with 

 the 150 level, but the rest of the mineralized zone has 

 not been extensively explored even down to this rela- 

 tively shallow depth. 



The ore bodies in the silica-carbonate rock that 

 borders the northern or lower contact of the northern 

 part of the serpentine have been mined in stopes from 

 the 100, 200, and 300 levels by way of the New Gua- 

 dalupe Inclined shaft and in the East Hilltop work- 

 ings. These bodies were small, erratically distributed, 

 and about as rich as the ore bodies mined near the 

 shaft. The largest was mined in the No. 2 stope, 

 which extended from near the surface at the Air 

 shaft down almost to the 100 level. It lay in silica- 

 carbonate rock more than 50 feet from the contact, 

 under a shear that dipped northward toward the 

 south-dipping footwall, and the inaccessible stope on 

 the 300 level appears to have been similarly situated. 

 In contrast, one small body of ore was found right 

 against the footwall contact below the 100 level, close 

 to the downward continuation of the No. 2 stope. 

 Hilos were abundant in all these ore bodies, and they 

 may have been important in localizing the ore, al- 

 though this silica-carbonate body is so little explored 

 that hilos may, for all we know, be as abundant else- 

 where. The silica-carbonate rock containing the ore 

 bodies was of the carbonate-rich variety, which con- 

 tains ore elsewhere in the mine, but where the exten- 

 sion of the same body of silica-carbonate rock reaches 

 the surface it is of the silica-rich variety, which is 

 apparently unfavorable for ore deposition. At depth 

 extensions of this footwnll mass of silica-carbonate 

 rock may well contain undiscovered ore bodies. Those 

 that have beeii discovered were found largely by 

 dinnce, for even the largest of them was not exten- 

 sive and was not localized along the footwall contact; 

 a systematic search for additional ore bodies near this 



contact, therefore, would probably entail prohibitive 

 expense. 



The ore mined from the landslide of silica-car- 

 bonate rock breccia in the Kelly workings and in the 

 shallow pits to the southwest was unique in the dis- 

 trict. It contained small angular pieces of very rich 

 ore scattered through a breccia that consisted mainly 

 of barren silica-carbonate rock, and in places the 

 interstices in the breccia contained native mercury. 

 The fragments of ore were not equally distributed 

 through the breccia, but were concentrated in certain 

 parts that were several tens of feet in length. Ac- 

 cording to G. F. Kirk (oral communication, 1947), one 

 of the operators, these rich parts were marked by 

 thin films of a yellow mineral, apparently a solid 

 hydrocarbon, that was used as a guide to the ore con- 

 centrations. One of these concentrations, mined in a 

 glory hole 28 feet in diameter and 18 feet deep lying 

 above the Upper Kelly workings, averaged between 1 

 and 2 percent quicksilver. The average quicksilver 

 content of the entire breccia mass, however, as deter- 

 mined by samples taken by the U.S. Bureau of Mines 

 (Bedford and Ricker, 1950, p. 6, 7-9), is between 2 and 

 3 pounds per ton. 



Suggestions f Or further development 



Further development of the Guadalupe mine might 

 be directed toward finding new ore bodies and re- 

 covering quicksilver from stope fill or dumps. 



The most favorable area for the discovery of new 

 ore bodies lies beneath the old stopes and cuts ex- 

 tending northwest from the New Guadalupe Inclined 

 shaft below an altitude of 400 feet. This area, as yet 

 almost unexplored, may reasonably be expected to 

 contain ore bodies localized along swarms of hilos. 

 Judging by the positions of the ore bodies already 

 found, near the surface new ore bodies are most likely 

 to be in the silica-carbonate mass tens of feet from 

 the contact, and at greater depth they would prob- 

 ably dip southward along the footwall of the southern 

 part of the serpentine. In two other places on the 

 surface near the New Guadalupe Inclined shaft small 

 quantities of ore could probably be obtained with 

 little effort. The first of these is an extension of the 

 ore mined in the large pit east of the shaft, where ore 

 on and behind the north wall has been left lx>cause 

 of the hazard involved in attempting to remove it 

 from the base of the overhangling cliff. The other 

 place offering promise is in the mass of silica-car- 

 bonate rock extending under the modern furnace 

 building: this rock is reported to contain some cin- 

 nabar near the surface l>ut remains unexplored. Still 

 other places where ore might be developed are (1) 



