82 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



of rock is about 50 feet think the copper- bead a jj poitioris are frotn 10 

 to 15 feet thick. 



Ill going across the formation we find first a dark gray, fine-grained 

 trap rock, having an irregular jointage iu four directions. Near the 

 vein these joints are "filled with brilliant sheets of copper, and this is 

 especially so where the vein is barren. Xext to this conies a variable 

 hiyer, 5 to 25 feet thick, of open porous amygdaloid, the amygdules and 

 cracks being filled by calcite, laumontite, epidote, i)rehnite, and various 

 zeolitic minerals, together with metallic copper, the most abundant 

 mineral being calcite. Beyond this layer the rock gradually changes 

 to a close-grained compact trap, with only an occasional amygdule. 

 Small masses are occasionally found, but they seldom exceed 100 pounds 

 in weight. Silver often occurs on and with the copper, occasionally 

 beautifully crystallized. 



The mine is opened by four shafts that have developed it to a depth 

 of 1,350 feet on the dip, and for a distance of 2,750 feet along its strike. 

 The shafts follow the general dip of the bed, but owing to the irregu- 

 larities they will sometimes be above, sometimes in, and sometimes 

 below the bed, but never depart very far from it. N'ot only is the bed 

 irregular, butthe distribution of the copper within the bed is also irregu- 

 lar, so that a great deal of care and judgment is necessary in planning 

 the work of the mine so as to keep np a continual supply of good ore, 

 and to keep the development work ahead to j^rovide for the future. 



In the distance of 1,350 feet on the dip fourteen levels have been 

 run off to open uj) and work the mine. These levels follow along the 

 irregular contact of the amygdaloid and the hanging wall. Whenever 

 a promising piece of ground is struck a stope is started, which is car- 

 ried ni)wards as long as paying ore is found. If no promising ground is 

 struck in running the levels, then winzes or risers 5 feet square are 

 run np into the rock in order to search for the ore. 



The location of these winzes is a very important matter, and every 

 point in any way likely to give any indication of the presence and posi- 

 tion of an ore body must be carefully studied. In some cases the first 

 investigation would seem to indicate that a given block of ground was 

 barren, but the subsequent working out of surrounding blocks has 

 given new indications to work by in the barren ground, and it is again 

 attacked, and generally successfully, although occasionally three and 

 four attacks have been made on the same block before ore was found. 



As much as possible of the drilling in the mine is done by machine 

 drills, hand drilling being confined to exploratory work, and the work- 

 ing out of small bodies of ore. Nitroglycerin is used almost entirely 

 as an explosive. As the rock is broken out at the working face it 

 travels down the stope to the level, where it is loaded on to tram cars 

 and hauled to the shaft ; it is then hoisted through the shaft to the 

 rock house iu a skip. Nearly all the rock broken out is hoisted to the 

 surface, and while the stopes are confined as much as possible to the 

 copper bearing rock, yet considerable barren material has to be hoisted. 



