116 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
proposition. Thus in certain instances it is the accessory gold, lead, 
and silver contents which raise the total value of low-grade copper 
ores safely above the commercial limit. It has been reliably esti- 
mated that a profit can not be guaranteed on a mixed copper ore 
from Bingham whose aggregate value falls below $6. It is under- 
stood, however, that this minimum limit has been lowered and may 
reasonably be expected to be still further reduced. The combination 
of a few higher grade bodies, several of medium grade, and many 
of low grade, together with the variety of types of ore, including cop- 
per, lead-silver, and gold, has proved most essential. This fact, by 
providing the mining industry against early exhaustion, baseless 
speculation, and market fluctuations, has made possible practically 
continuous mining operations from the date of the earliest mining in 
Utah to the present. 
Little reliable information regarding the copper values is available. 
The aA^erage of the assays of three characteristic shipments from a 
typical fissure mine shows a copper content of G.5 per cent. In the 
limestone replacement ore bodies the copper values are understood to 
run somewhat lower. Thus the average of three averages of a great 
number of assays on ore from two of the great copper properties shows 
a copper content of between 3 and 4 per cent. An assay of an average 
shipment from ore in a fissure in quartzite and porphyry gave 44.25 per 
cent lead, and the average of shipments for three years from a mine 
on a fissure in limestone is reported to be 45 per cent. These facts] 
la ken in connection with assays from many mines, warrant, the con- 
clusion that the average of typical lead ore in Bingham is about. 45 
per cent lead. The silver content in two famous lead bonanzas ^aver- 
ages 25.18 ounces per ton. In sulphide-copper ore from the replace- 
ment bodies silver runs from 2 to 4 ounces, and in fissure ores it 
ranges from 18 to several hundred, while ore from a fissure in quartz! 
ite and porphyry affords an average, based upon assays of three nor- 
mal shipments, of 8U) ounces. Gold values from the crests of the] 
great replacement bodies average $10 to 1-12 a ton. Those in cuprif- 
erous pyritic ores average about $2, and those in the porphyry ore! 
average about 25 cents. The pay in detrital deposits is stated in the 
description of placers. 
Occurrence of the ores. — The productive area in the Bingham dis- 
trict is not restricted to any local ore deposit nor to a single zone of; 
deposits. The most important productive belt comprises those mas- 
sive limestones described under "Area! geology" as the middle and 
upper series of the lower great division. They have been found to 
be productive from the desert on the east to West Mountain on the 
west, a distance in a direct line of about 3| miles. The known pro-] 
ductive area of Bingham extends from the Richmond mine on the 
east to the Star mine on the west and from the Midland and Broad 
