Copper Deposits of Part of Helvetia Mining District, Pima County Arizona Page: 301
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A CONTRIBUTION TO ECONOMIC GEOLOGY
COPPER DEPOSITS OF PART OF HELVETIA MINING
DISTRICT, PIMA COUNTY, ARIZONA
By S. C. CREASEY and GEORGE L. QuicK
ABSTRACT
This report presents the economic geology of four mines and the contiguous
area in the Helvetia mining district in the Santa Rita Mountains in south-
central Arizona. The four mines (Rosemont lease, Leader, Copper World,
and Narragansett) were selected for detailed study because they were considered
to be representative of the district. Production from the Helvetia district has
not been large.
The sedimentary rocks in the Helvetia district range from Cambrian to
Cretaceous. The Paleozoic rocks are chiefly limestone, dolomitic limestone, and
quartzite; the Mesozoic rocks (Cretaceous) comprise shale, sandstone, and im-
pure limestone. Although the structure largely controlled the mineralization,
most of the ore is found in Pennsylvanian and Permian limestones.
The igneous rocks consist of coarse-grained granitic rock ranging in compo-
sition from granite to quartz monzonite and monzonite, and a quartz monzonite
porphyry. The granitic rock is believed to be post-Paleozoic and pre-Comanche
in age, whereas the prophyry clearly intrudes the Cretaceous rocks.
The Helvetia district has been intensely deformed, and complex structures
resulted from high-angle normal faults, folds, and thrusts. Apparently thrust
faults.were active over a considerable period, for the quartz monzonite porphyry
is both older and younger than thrust faulting. The ore deposits in the four
mines appeared to be adjacent to or near both normal and thrust faults.
The ore deposits are chiefly of the pyrometasomatic or contact metamorphic
type, although some of them are not at the contact of intrusive rocks. In the
Copper World, Narragansett, and Leader mines, the mineralized zones in part
are in lime-silicate rocks developed in limestone along fault zones by silicating
solutions. The ore minerals are younger than the lime-silicate minerals, and the
ore is in shoots .largely within the silicated zones but not strictly coextensive
with them. In addition to the contact metamorphic deposits, there is a
brecciated area. in the porphyry sporadically stained with copper oxide minerals.
INTRODUCTION
LOCATION
The Helvetia mining district is in the northern Santa Rita Moun-
tains, Pima County, 28 miles southeast of Tucson, Ariz. (See fig. 48.)
301
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Creasey, S. C. & Quick, George L. Copper Deposits of Part of Helvetia Mining District, Pima County Arizona, report, 1955; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc1114950/m1/5/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.