The Pontatoc mine in a north Tucson neighborhoodby Jonathan DuHamel on Jan. 02, 2012, under Geology
Sometimes mines just vanish. Such seems to be the case with the Pontatoc mine located near the north end of Pontatoc Road in Tucson and just south of Pontatoc Ridge. The map below shows the general location (at the balloon).
The Pontatoc mine was discovered in 1906 and worked until 1917. It produced about 5,000 tons of copper, silver, gold, and molybdenum ore. Mindat.org reports that handpicked ore assayed at 4% copper, 0.5 oz./T silver, and a trace of gold.
Mineralization occurred in a wide altered breccia zone along the Catalina foothill fault dividing Catalina Gneiss, a Laramide metamorphic, from Tertiary to Quaternary Pantano conglomerate beds. “Ore occurred in the fault zones wherever rock alteration is intense. Alteration included silicification, propylitization, spordic dolomitization and epidote. Sulfides precipitated with quartz,” according to Mindat.org.
Workings consisted of two shafts, one 105 feet deep, the other 125 feet deep, plus a pit and tunnel operations. The following graphic from the Pusch Ridge wilderness study by George S. Ryan shows again the general location and location of mine workings on Pontatoc Ridge to the north.
According to Ryan, Pontatoc Ridge was intensely prospected shortly after the production from the Pontatoc mine itself. There were several shows of oxide copper on the ridge, but apparently they didn’t amount to much.
So far I’ve shown rather vague locations for the Pontatoc mine and it may surprise you where it was. The map below shows the mine location with current development.
The following graphics show where I think the mine was, just west of the intersection of E. La Paloma Dr. and E Coronado Dr. There is no trace of the pit or shafts, presumably they have been filled in. The detailed picture does show what is presumably the scarp of the fault in which the mineralization developed.
Some mines just disappear and houses are built along or near fault zones. This particular fault is apparently inactive, homeowners shouldn’t worry.
By the way, Ryan reports that gypsum was mined from Tertiary lake beds in the same area and used for plaster in the Tucson building industry prior to 1966.
Ryan, George S., 1982, Mineral Resources Investigation of the Pusch Ridge Wilderness
Pima County, Arizona, U.S.B.M. open file report MLA 118-82.
http://www.mindat.org/loc-35539.html (Note this reference erroneously lists the Township as 12S rather than 13S.)