The Arizona Geological Survey has just published a new paper on the fault:

Citation: Hoxie, D.T., 2012, Exhuming the Remains of the Inactive Mountain-Front Pirate Fault, Santa Catalina Mountains, Southeastern Arizona. Arizona Geological Survey Contributed Report CR-12-F, 18 p. You can download the 24Mb report here.

The Arizona Geological Survey describes the Pirate fault system as follows:

Not so long ago, mountain building was alive and well in southern Arizona. [The Pirate] fault demarcates uplift of the Santa Catalina structural block to the east, from the down-dropped, alluvial Cañada del Oro basin to the west. Vertical displacement on the nearly 16 mile long fault is about ~ 2.5 miles or 13,200 feet, which occurred over a six million year span from ~ 12 to 6 million years before the present.

Once buried under detritus eroded from the uplifted Santa Catalina Mountains, the Pirate fault is currently being exhumed by the downcutting Cañada del Oro and its tributaries. “This field examination reveals the fault to have left a sparse but diverse collection of remains implying a varied history of fault development and evolution”, says Hoxie. In detailed mapping of the trace of the Pirate fault zone, he identified a number of sites of exposed fault rocks and fault-related features, ten of which are described in detail. Key observations include identifying local, hematite-rich zones and noting the presence of small-volume, mafic dikes that intruded fault breccia near the end of active uplift on the Pirate fault.

The report includes an annotated satellite image of the Santa Catalina Mountains – Cañada del Oro Basin and a suite of maps showing the distribution of geologic units – alluvium, granites (emplaced between about 70 to 26 million years before the present), and the Pinal Schist, a 1.6 billion-year-old metamorphic rock – that crop out along the fault.

The photo on the left shows an outcrop of the steeply dipping Pirate fault. The photo above shows several faults in the Santa Catalina Mountains including the Catalina detachment fault which forms the scarp on the north side of Tucson.

Some other posts on work by the AZGS:

A guide to the geology of the Sedona & Oak Creek Canyon area of Arizona

Earthquakes shake Morenci, Arizona area

Arizona is earthquake country

Earthquake videos from Arizona Geological Survey

Arizona earthquakes, 1852-2011, a video time line

Arizona earthquakes numbers saw a large increase in 2011

Helium potential of Arizona may help fill shortage

Petroleum and Natural Gas Potential of the Paradox Basin

Arizona may become a major producer of potash

Arizona Geological Survey Leads Geothermal Energy Study

The ore is predominantly bornite ( Cu₅FeS₄) hosted by limestone. Chalcopyrite ( CuFeS₂) occurs in the lower reaches. Ore grade is considerably higher than that at the open pit mines in the area. The ore also contains silver and gold.

Exploration in the area may have begun as early as 1870 and the first major operation dates from 1881 according to the Department of the Interior. The Oracle Ridge mine is principally a contact metamorphic skarn similar to the Rosemont deposit.

The company anticipates employing about 200 people, running the mine 24 hours per day, 365 days per year. The anticipated mine life is 11 years.

The ore will be mined and crushed underground, then conveyed to a plant immediately outside the mine. The mine will produce 140 tons of concentrate (about 30% copper) a day which will be trucked off the mountain and transported to a smelter. The company has not announced which smelter, but ASARCO’s Hayden smelter is the closest.

Tailings will be contained by a double-lined, dry stack method with water reclaimed and recycled. The old tailings will be incorporated in the new tailings piles on private land. The entire operation would be contained within 45 acres. The water supply will come from underground workings and wells.

The photo below shows the mine area. The gray areas are tailings from past operations. The company claims that new operations would not increase the existing footprint.

See also:

Old mines of the Tucson Mountains

Rosemont’s dry-stacked tailings will be greener than those near Green Valley

Saginaw Hill, another old mine in a Tucson area neighborhood

Sierrita Mine is only U.S. source of Rhenium

Surprising Structure of the Copper Deposits near Green Valley, Arizona

The I-10 copper deposit

The Pontatoc mine in a north Tucson neighborhood