Saginaw Hill, another old mine in a Tucson area neighborhood

Jonathan DuHamel — Thu, 05 Jan 2012 14:35:43 +0000

Saginaw Hill is located about 10 miles southwest of downtown Tucson. See general location on the map below.

The hill was home to several mines worked intermittently from the late 1800s to the mid 1900s. Mindat.org describes three of the major workings:

The Saginaw Mine:

A former small surface and underground Cu-Zn-Pb-Ag-Au-Mo (copper, zinc, lead, silver, gold, molybdenum) mine located in the NE ¼ sec. 11 & NW sec. 12, T.15S., R.12E. Owned at times, or in part, by the Saginaw Mining Co.; and the Tucson Arizona Copper Co.

Mineralization is sparse, spotty, partly oxidized base metal sulfides along fissure zones in limestone lenses in silicified Cretaceous Amole Arkose. Ore control was quartz veins as siliceous replacements along fractures. Alteration included limonite, quartz, sericite, clay, pyrite, and garnetization-epidotization. Associated rock units include the Saginaw Hill Porphyry, latite. Weakly mineralized. Chalcopyrite & pyrite on the W side of the Saginaw property, copper oxides on the E side of the property (Papago Queen). Cerussite & galena on the S end of the property along rhyolite-limestone contact. The identified ore zone is 330 meters long.

Local structures include NE-trending fractures, brecciation. On the SE side of the fracture and extending 300 meters away is propylitized quartz monzonite. Local limonite and partly oxidized pyrite with minor copper silicates along the fracture zone.

Workings include shafts, pits, and minor underground workings. Worked prior to 1900 with a possible 100 tons of low-grade ore produced. Production was sporadic. Production of smelter flux from 1956-1959. Has been prospected for porphyry copper. Prospect workings concentrated along N60E trend but no good fracture zone is exposed.

Palo Verde Mine:

Worked intermittently from 1918 through 1954. Total production amounted to some 2,300 tons of ore averaging about 13% Zn, 2.2% Pb, 0.7% Cu, 2.5 oz. Ag/T and 0.06 oz. Au/T.

Papago Queen Mine:

Mineralization is disseminated copper oxides and carbonates with minor molybdenum oxides in quartz veins and along fractures in a weakly altered, brecciated, and mineralized Laramide (?) porphyry stock.

Workings include tunnel and open cut operations. Sporadic production of copper ore occurred from 1917 to 1934, and of smelter flux in 1956 through 1959. Total output was some 3,700 tons averaging about 1% Cu and 0.5 oz. Ag/T.

This area had long been a favorite of mineral collectors. It is one of the few places in the world where peacock-blue cornetite is found. Cornetite is a copper phosphate with the formula Cu₃(PO₄)(OH)₃.

The Saginaw Hill mineralization is intimately related to the big copper mines west of Green Valley to the south. That will be the subject of a future post.

Because subdivisions were encroaching on the area, Pima County investigated Saginaw Hill in about 1988 with the view of turning it into a park. At the time, the mines were abandoned, there were mineralized dumps on the property. An assessment of the property by Pima County officials found (surprisingly to them apparently) that the area contained concentrations of toxic heavy metals.

The County made several more assessments and by 2003, the Bureau of Land Management (BLM) got involved. See the BLM report here, it provides many photographs. In 2005, the BLM was deciding what to do and there was much furor in the press. See examples from the Tucson Citizen here and here.

The BLM filled in the many mine shafts which did pose a danger. They also collected surface mineralization and dumps and buried the material on site to mitigate the imagined danger of heavy metal contamination. The Google Earth photo below shows how the area looks now. The orangish patch is were the material is buried. Saginaw Hill is closed to mineral collectors.

Wry Heat » toxic metals

Saginaw Hill, another old mine in a Tucson area neighborhood