Asbestos technical reports

There are many technical reports regarding Gila County asbestos deposits and mining operations. It's totally out of the scope of this blog to attempt to list and excerpt each of the available reports.  This particular report, however, should be #1 on your list to download and digest.  It was published in the mid-1950's by the US Bureau of Mines.  Consequently, the information contained in the report was probably collected beginning in the late 1940's through the early 50's.  The report represents a snapshot of Gila County asbestos near the peak of its "popularity".  Below are a few excerpts from the report. The report is located here:

 https://digital.library.unt.edu/ark:/67531/metadc67066/Arizona asbestos mines are the only sources on the American continents of naturally iron-free chrysotile spinning fiber that is so urgently needed for electric-cable coverings, especially on warships.

Asbestos was first recorded and recognized in Arizona in 1872, and a minor amount was produced from a deposit in the Grand Canyon in 1900. The discovery of a deposit in the Salt River district in 1912 initiated intensive prospecting, and deposits soon were developed. The total Arizona production of all grades of asbestos through 1953 is estimated at 30,000 to 35,000 tons.

The deposits of the Central Arizona region, which are discussed in this paper, are scattered over nearly 2,000 square miles. The annual output is relatively small, because the asbestos occurs in thin, discontinuous veins and only in areas where intrusions of diabase are adjacent to or crosscut certain favorable units of the pre-Cambrian Mescal limestone. This stratigraphic limitation, combined with other essential geologic conditions, tends to restrict the size of the deposits.

Virtually all of the deposits are in rugged, mountainous country, and many of the mines are on steep canyon walls • In the average mine, production of 1 ton of commercial asbestos requires removal of 30 to 4o tons of waste rock. Mining and transportation costs consequently are high.

Diallase intrudes all members of the Apache group and is particularly prevalent in the Mescal limestone, where it is predominantly in the form of sills that vary from a few inches to several hundred feet in thickness. Some of the larger sills extend laterally for several miles. There was no stoping or assimilation of the limestone; the diabase pushed the beds apart. Consequently, the same stratigraphic units may occur at different elevations within a relatively small area.

Chrysotile is the fibrous form of serpentine, and the other five are amphi -boles. Because it is superior to other types of asbestos for textile processing, as well as for industrial purposes generally, about 95. percent of the total world production of natural mineral fibers is chrysotile . As chrysotile is the only variety of asbestos found in commercial quantities in Arizona, a discussion of the amphibole varieties is not considered necessary.

As already mentioned, Arizona asbestos is of the chryaotile variety, a hydrous magnesium. silicate with the same composition as serpentine. The fibers of chrysotile occur as crossfiber; that is, the fibers of which the material is composed and into which it may readily be separated lie approximately  perpendicular to the walls of the vein.

Crossfiber chrysotile occurs as two distinct types, soft and harsh. Soft fiber feels smooth or soapy and can be twisted and bent between the fingers. The individual fibers usually are extremely flexible and strong. Harsh fiber is splintery, prickly, and somewhat brittle, so a small bundle of it breaks if twisted a number of times.

Arizona asbestos mines are the only sources of the American continent of naturally low-iron chrysotile SJ)inning fiber that meets the Navy specifications for asbestos fiber for use in covering electrical cables.

Arizona asbestos is found invariably in veins within bands of serpentine. The veins vary in thickness from a fraction of an inch to several inches and roughly parallel the borders of the enclosing serpentine. They are seldom continuous over long distances but split into smaller veins or coalesce and form larger veins. The thicker veins frequently have longitudinal partings that reduce the apparent fiber length. Because of the tendency of asbestos veins to pinch or swell suddenly, their continuity and probable volume are difficult to predict.

The serpentine bands vary in thickness from a few inches up to 2 feet or more and may contain l to 20 or more fiber seams • Local occurrences show as much as 4 or 5 feet of serpentinized zone, containing over 100 veinlets of asbestos. Often two or more asbestos zones are separated by a few feet of limestone, so that both can be mined in one heading. Elsewhere, multiple zones may be 10 to 30 feet apart.

The unique fibrous structure of chrysotile asbestos, combined with its high tensile strength, incombustibility, and high electrical resistance, is the prime factor that makes this mineral of commercial importance.

History of Chrysotile claims

The first locations upon this ground were made in 1913 by Albert end William West, who took up 10 claims , During the following 2 years !bell & Fiske operated the claims for the Arizona Asbestos Association of Globe, apparently added 14 more claims to the group, end produced a moderate amount of asbestos, In 1916 the Arizona Asbestos Association became a subsidiary of the H. W, Johns-Manville Co, other claims were located, until 76 claims were owed by the association, 22 of which ;,ere patented in 1922, The camp was known as Chrysotile, and a post-office, established in 1916, was in existence until the mid-1930's. About 1915 a small experimental mill was erected, which had a capacity of approximately 10 tons of mill feed per 8 hours, It consisted of a Blake crusher, hammer mill, Torrey separator, end sizing trommels, producing four grades of mill fiber in addition to the Nos, 1 and 2 crudes, Apparently this mill was unsatisfactory, as it was taken out of service in 1921, and the operator reverted to hand cobbing the two longer grades, Under the ownership of Johns-Manville the property became the largest producer of asbestos in the district, and the workings developed into the largest asbestos mine in the United states, In 1936 the name of the association was changed to the Johns-Manville Products Corp, A modern fiberizing mill was completed in 1942. This plant treated a large amount of material from old dumps end mine fills end also newly mined ore until the mines were considered exhausted for large-scale mining. The mill and mine plant were dismantled in 1945, end all but the 22 patented claims were relinquished.

Late in 1951 the property was acquired by the Western Chemical Co, A small temporary plant was erected to clean end fiberize dump material. In 1952 the company constructed a cruding and fiberizing mill to beneficiate its ow production, Custom milling also was accepted.

Note: We found reference to the US Bureau of Miles report via this article.  It's a great read:
https://tucson.com/news/local/minetales/mine-tales-arizona-has-huge-deposits-of-asbestos/article_bb645592-75f9-5453-b3aa-c93d78548808.html