Wednesday, August 29, 2012

Arizona's other mineral resources - iron ore

Arizona has a variety of iron ore deposits ranging across the center of the state.  There have been quiet exploration programs underway by a number of companies for the past several years.   I offered a brief overview of the deposits to the Arizona Mining Association Board on Monday at their annual strategic planning retreat.
AZGS Chief Geologist Jon Spencer provided these descriptions. The banded-iron formation (BIF) northwest of Prescott is comprised of quartz-hematite-magnetite rock precipitated out of slightly oxygenated ocean water 1.7 billion years ago [right, circled area in the center of the state].  Ore-grade BIF rocks are referred to as “taconite.” This is the same type and age of rock that forms the huge iron deposits in the Lake Superior region.

The Buckskin and Plomosa replacement iron deposits [right, western Arizona] were produced by basin brines ascending along fault zones during middle Tertiary tectonic extension. Many of these deposits also contain copper that was mined in the early 20th century. The Copperstone gold deposit, also one of the replacement iron deposits, has been mined intermittently since the 1980s.

Both the Apache bedded iron in the Mesoproterozoic Mescal Limestone [right, northeast of Phoenix] and the Seligman replacement iron in the Devonian Martin Limestone [right, south of I-40] formed where reactive limestone was intruded by basaltic igneous rocks.

The magnetite placer deposits [between Phoenix and Tucson] are magnetite heavy-mineral sands in modern washes and Quaternary alluvium. These were derived from Precambrian granitic rocks that contain abundant magnetite. Sands contain up to 15% magnetite. Commercial iron production from magnetite placer sands was attempted in the 1960s but did not prove economic at the time.


  1. Anonymous4:49 PM

    I live in Flagstaff and need about a hundred pounds of magnetite sand for home use in water traps. Can anyone tell me where in this general are there are some reasonably accessible magnetite deposits I could get two or three buckets full?

    1. Hhere are a couple of resources describing iron-bearing deposits in the region. We caution that you need to be respect ownership of surface and mineral rights i.e. private, state, federal, etc. Federal agencies have restrictions of what can be taken from public lands.

      IC 8236 Reconnaissance of Iron Resources in Arizona: C. M. Harrer, 1964.

      The Iron chapter p 168 here