124 TRANSACTIONS OF THE 
The ore deposits of the San Pedro Mountains present a 
typical example of deposits attending igneous activity. At 
the contact copper deposits with a garnet gangue are formed. 
Narrow gold veins are abundant both in the porphyry and 
the altered sediments. Then in the unaltered limestones 
farther away from the contact, galena of the replacement 
deposit type is found. Then as a result of erosion gold 
bearing gravels have accumulated at the base of the moun- 
tains and have been worked since the time of the Spaniards 
200 years ago. 
The workings of this company are confined entirely to 
the copper deposits of the garnet zones. There are three 
well defined ore bearing zones, known locally as Nigger 
Heaven, Middle, and Lower zone. These garnet zones are 
separated one from another by a white quartzese porphyry. 
These quartzese porphyries are facies of the main igneous 
mass. The distribution of the pay ore in the garnet beds 
is extremely irregular. At places the ore shoots are 30 - 40 
feet high and several hundred feet long. The average height 
of the stopes are 5 - 6 feet. The ore is mostly calcopyrite 
with some bernite, cuprite, and a little malacite and azurite 
in the upper workings where oxidizing conditions have pre- 
_vailed. The oxidized zone however is very shallow, not more 
than 150 feet. The calcopyrite is invariably associated with 
the yellow garnet, andradite, and in a few places with also 
a little pyrite, specularite, and wollastonite. 
Mining is almost entirely by the overhand stoping 
methods. The shaft is 220 feet deep and is tapped 180 
feet from the collar by a tunnel to the surface. Most of the 
workings are above the tunnel level. Hence all ore is 
dumped in shoots to this level where it is trammed to the 
shaft and hoisted to the surface. All waste is trammed out 
the tunnel, the hoist not being large enough to handle both 
the ore and waste tonnage. The hanging wall of all the 
stopes is hard and tough and stands extremely well. Tim- 
bering is practically unknown. In a few of the very large 
stopes pillars of low grade are left for support. If timbering 
had to be used in the stopes it would increase the cost of 
mining to such a degree, that from an economic standpoint, 
mining the ore at a profit would be out of the question. 
