In the summer of 1922, at the request of the Director of the United States
Geological Survey, I undertook an examination of the ore deposits in the Jerome
and Bradshaw Mountains quadrangles, Ariz. (See fig. 1.) The object of this work
was not a detailed investigation of each deposit but rather a coordination and
classification of the occurrences and an attempt to ascertain their origin and
economic importance. Almost all the deposits occur in pre-Cambrian rocks or in
rocks that are not readily differentiated from the pre-Cambrian. In the northern
part of the Jerome quadrangle there are large areas of almost horizontal
Paleozoic beds, and in both quadrangles there are also large areas of lava flows
of Tertiary age. Finally there are wide spaces occupied by Tertiary tuff and
limestone, or by Tertiary and Quaternary wash filling the valleys between the
mountain ranges. But all these rocks except the pre-Cambrian are practically
barren of ore deposits, and the problem therefore narrowed itself to an
examination of the pre-Cambrian areas. This task was greatly facilitated by the
careful work of Jaggar and Palache, set forth in the Bradshaw Mountains folio,l
in which the southern quadrangle of the two under present consideration is
mapped geologically and described, and which also includes a comprehensive
though brief discussion of the mineral deposits. There is no published geologic
map of the Jerome quadrangle, but I had the opportunity through the courtesy
of Dr. G. M. Butler, Director of the Arizona Bureau of Mines, to use a
manuscript map of this area prepared for the State by Mr. L. E. Reber, jr., and
Mr. Olaf Jenkins.
