boutwell.] ORE DEPOSITS OF BINGHAM, UTAH. 113 
ECONOMIC GEOLOGY. 
General. — The principal mines of this district are located on the 
slopes of Bingham Canyon, of its tributaries, and of the head ward 
portions of the northeastern tributaries of Butte rfield Canyon. They 
have revealed valuable ore bodies of two great types, those which 
occur as lenses, roughly parallel to the bedding, and those which 
occur in fracture or fissure zones. Under each of these forms of 
occurrence ores of copper, lead, silver, and gold occur, though the 
copper lies mainly in the lenses in limestone, and the lead and silver 
in fissures. For the purpose of this abstract the economic geolog3 T 
may best be considered with regard to character and occurrence of 
ores, placers, and commercial considerations. 
Character of the ores. — The ores of Bingham include a valuable 
variety of the desirable metals. Thus mining activity has been devoted 
successively to oxidized gold ores, carbonate ores of lead and cop- 
per, sulphide of lead, and finally sulphides of copper. The oxidized 
^old ores carried good values, but were not commercially profitable. 
Although some of the gold was free, no satisfactory treatment of its 
ares was obtained, the commonly accepted explanation being that the 
presence of copper required too much cyanide to leave a profit. The 
carbonates of lead and silver carried high values and were treated 
with comparative success, but are to-day worked out. Lead-silver 
sulphides later assumed commercial importance, and under the influ- 
ence of good market values lead is still extensively mined. This ore 
is made up of galena, tetrahedrite, considerable zinc sulphide, pyrite, 
and chalcopyrite, with a gangue of quartz and calcite. The mainstay 
3f the district, however, is copper sulphide ore. This is composed of 
cupriferous pyrite, chalcopyrite, and the black sulphides of copper, 
which may prove to be chiefly tetrahedrite and chalcocite, with occa- 
sionally a little galena, zinc, and a siliceous gangue. 
Pyrite (sulphide of iron with copper as an impurity: iron pyrites), 
-he most common metallic mineral known in Bingham, forms the bulk 
)f immense replacement ore bodies in limestone, plays a secondary 
*61e in fissure ores, and is freely disseminated through the igneous 
*ocks. Although large masses of perfect crystals of exceptional purity 
tfere found, its more prevalent occurrence is in massive form inti- 
nately combined with chalcopyrite, small amounts of bornite, pyrrho- 
ite, and alteration products of primary sulphides. Chalcopyrite 
sulphide of copper and iron : copper pyrites) occurs scattered in small 
)atches throughout bodies of massive pyrite in limestone associated 
vith pyrite bands; in fissures of lead-silver ores, and in grains dis- 
eminated through the main porphyry bodies. It appeal's, from 
cached and unleached specimens, and from a study of thin sections, 
hat much of the copper of cupriferous pyrite occurs as chalcopyrite 
n the state of a i)hysical mixture with pyrite. Certain samples of 
Bull. 213—03 8 
