BOutwell.] ORE DEPOSITS OF BINGHAM, UTAH. 121 
extent. The Bingham porphyry is intrusive in origin. It was forced 
into the country rock from "below along the ways of least resistance 
when in a molten, semiliquid state, and on cooling assumed forms of 
irregular dome-like masses, laccoliths; roughly vertical wall-like bod- 
ies, dikes; and nearly flat bed-like bodies, sills. Thorough examina- 
tion of the form of the body on the surface should give the key to the 
type of the intrusive, and thus determine the most direct and economic 
method of attack. 
Again, faulting, that common and characteristic feature of Bingham 
structure, has caused loss through misdirected exploration. Exten- 
sive detailed underground work throughout the camp goes to show 
that the prevalent idea among Bingham miners, that faulting is 
systematically of one type, with the character of displacement uni- 
versally the same, is an error. Instances are at hand which x>rove 
that many types of faulting exist at Bingham, and that the character 
of the displacement is not restricted to one form, but includes many. 
In view of this fact each case must be worked out on its own evidence. 
Further, no little time and money have been lost by guessing on the 
direction of offset of ore bodies by faulting, and driving aimlessly in 
accordance with such guesses. When a lens of copper ore which lies 
along the strike of the beds and well within a thick limestone is found 
to be cut, displaced, and temporarily lost by faulting, it is usually 
advisable, in case the surface geolog} 7 does not afford a clue, to drive 
to the nearest wall, quartzite foot or hanging. There the member 
which lias been brought opposite to the contact may be found, the 
usual criteria indicative of the direction of movement observed, and 
the fault duly proved. The fact that a lens of copper sulphide 
pinches when followed down on its dip is not necessarily an indication 
that the ore has permanently disappeared. It is the habit of such 
lenticular bodies to thicken and thin irregularly. Accordingly con- 
tinued exploration in depth might reasonably be expected to be 
rewarded by the discovery of similar lenticular ore shoots. Although 
copper shoots of this type attain great size and value in the large 
limestones, they are erratic and should not be expected to prove as 
constant in extent, either perpendicularly or horizontally, as smaller 
but more faithful fissure ore bodies. 
The zinc contents of the Bingham ores have never received the 
attention they merit. Highly zinciferous ores have not onlj r been dis- 
dainfully rejected, but they have been regarded as losing proposi- 
tions, owing to extra smelting charges. 
In several cases Bingham ores are reported to have carried regularly 
15 pei' cent of zinc. In some instances values of 32 and 45 per cent 
zinc have been reported in Bingham. Although these ores may pre- 
sent some problems different from those encountered in camps where 
zinc ores are successfully worked, it would seem highly advisable to 
conduct more extensive experiments on them before abandoning ore 
