Roger Weller, geology instructor
Juniper Flats in the Mule Mountains, Cochise County, Arizona
Bisbee (from: Ransome, USGS Folio, 1914)
“The town of Bisbee, with an estimated population of 8,000, is crowded into a
few narrow, confluent ravines near the heart of the Mule Mountains, seven and
one half miles north of the international boundary. Within the Mule Mountains
may be distinguished two topographic divisions, based upon geologic structure
and roughly separated by a northwest-southeast line passing through Bisbee.
Northeast of this line, the mountains are sculpted from comparatively soft
Mesozoic beds striking approximately with the trend of the range and dipping at
moderate angles toward Sulphur Spring Valley. The slopes of these hills are
comparatively smooth, although the occurrence of a hard fossiliferous limestone
in the middle of the group has occasioned a conspicuous and persistent cliff of
Southwest of the divisional line, Paleozoic and older rocks prevail. These are
generally more resistant to erosion and more heterogeneous in character than the
Mesozoic beds, and have a far more complicated structure.
The fundamental rocks of the
Bisbee quadrangle are crystalline Pinal schists of Precambrian age, separated by
a profound unconformity from the overlying Paleozoic beds. The latter comprise
a basal Cambrian quartzite 430 feet thick (Bolsa Quartzite), succeeded by over
4500 feet of limestone representing portions of Cambrian (Abrigo limestone),
Devonian (Martin limestone and Mural limestone), Carboniferous (Escabrosa
limestone and Naco limestone).
At the close of the Paleozoic period and during the
Mesozoic, the rocks of the Bisbee area were deformed by faulting and folding and
were cut by intrusions of granitic magma. The principle mineralization of the
district dates in the early Cretaceous. The region as a whole was elevated above
sea level and subjected to erosion until the beginning of the Cretaceous
period. During the Cretaceous, the land again sank beneath the sea and over
4500 feet of sandstone, shales, and limestones were accumulated. Subsequent
elevation brought these sediments above sea level and exposed them to erosion.
During the Quaternary and probably during a part of the Tertiary, the higher
parts of the Bisbee quadrangle have been undergoing erosion, their waste
accumulating in the flat-floored valleys that surround the Mule Mountains.
Prior to 1880 Bisbee was an unimportant lead camp. The copper ore of the Copper
Queen Mine was discovered early in this year. This ore was free from sulfur and
averaged 23% copper. Ore minerals include: native copper, chalcopyrite,
sphalerite, cuprite, azurite, malachite, brochantite, tenorite, and aurichalcite.
The Bisbee copper ores occur as large masses in the limestones and intrusive
Published references on Bisbee Minerals
references on Bisbee mines and mining
Stratigraphic Section Bisbee Area- from Jan Wilt
Tour of the Bisbee Copper Queen Mine
Photos of Bisbee Minerals
student presentations on the Mule Mountains and Bisbee
The Special Relationship between Azurite and Malachite- Jesse Smith (Fall 2005)
The Worries of a Bisbee Copper Miner- Maria Ramos (Spring 2006)
Phelps Dodge Corporation- Robert Hardy (Fall 2007)
History of One of Bisbee's Families- Gina Thursby (Spring 2008)