Pumice Mining and Environmental Concerns in New Mexico
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Pumicemining and environmental concerns in New Mexico byGeorge S. Austin,New Mexico Bureau ol Minesand Mineral Resources, Socorro, New Mexico 87801 Abstract collected,and the miningcompany is releasedfrom its obligations outlined in the operationplan only afterall requiredreclamation hasbeen completed. A balancedapproach, in which the needfor mineralsis consideredalong with the needfor properreclamation of mining sites,is necessaryto maintaina productiveindustry in a scenicarea of New Mexico. Introduction Pumice is a light-colored, light-weight igneous rock with cel- lular structure and is formed by a processof explosive volcanism. It commonly has a rhyolitic (siliceous)composition but may have a rhyodacitic composition with increasing sodium content (Bates and fackson, 1987).Pumice occurs as fragmentalaggregates of volcanic glassfroth in which individual particlesrange from coarse- sand size to blocks meters in diameter. Very finely divided frag- ments are called pumicite (alsocalled volcanic ash or dust), which consists largely of angular and curved particles of the shattered vesicle(bubble) walls of pumice(Thrush, 1968). Pumicite has been subjected to additional explosive forcesduring the volcanic event whereby the previously formed cellular structure is broken down to form a very fine, unconsolidatedmaterial. Because of the cel- lular structure,light weight, and insulatingproperties, both pum- ice and pumicite have been used extensivelyas building materials since the Roman Empire (Meisinger, 1985).Before World War II, it was used largely as an abrasive;nearly all consumption since has been in the constructionindustry. Pumice and pumicite are currently mined by open-pit methods (Meisinger, 1985).Removal of overburdenis by standardearth- moving equipment and is usually kept to a minimum by careful selection of the mining site. Becausemost deposits are uncon- solidated (Fig. 1), mining equipment such as bulldozers, pan scrapers,draglines, and power shovelscan be usedwithout blast- ing. Modern highway constructionuses much the same equip- ment. Alsoin thisissue 1994summer volunteer programs p.6 Paleokarst,paleosols, cave fillings, and breccias at the FusselmanDolomitFPercha Shale unconformity,Silver City area p.7 1995NMGS Fall Field Conference p. 13 StuartA. Northrop(1904-1994) p.14 1993Mineral Symposium abstracts p. 15 Upcomingmeetings p.16 Galleryof Geology-ZuniSalt Lake maar p.17 Service/News p.18 Staffnotes p. 19 FIGURE l-General Pumice mine on the east flank of the Valles caldera showing unconsolidatedpumice that is moved by bulldozer to the screen- Topographicmaps p.19 ing plant (structure near center)that loads truckslor movement to market. in 1991 and 1992, but there was a reduction in the number of producersand operationsas well as in the number of employees engagedin pumice mining. In 1983,employment at U.S. pumice and pumicite mining and milling operations was approximately 60 workers, and averageannual productivity was approximately 7,500mt per production employee(Meisinger, 1985). However, office personnel, mechanics,and other serviceemployees greatly increase the number of paid employeesinvolved in pumice min- ing. Copar Pumice,Inc., has two mines in the |emez Mountains, Las Conchas and Guaje Canyon pumice mines, and in 1992they employed 12 people at those mines and two plants plus 9 indi- viduals as contact haulers; the same year total New Mexico em- ployment in the pumice mines and mills was 44 and included 13 contract haulers (K. S. Hatton, written communication 1993). Adding clericalstaff brings the number of individuals employed in mining of pumice by one company to a significant number. Pumiceproducers'salaries generate addition support jobs in nearby commercial centers. This multiplier effect is enhanced because many pumice operationsare rural. ductivity. New Mexico pumice Before the Spanish colonial period began in the 16th century, the Bandelier Tuff was used by Native Americans who carved or enlarged caves to form defensible living areas, as in Bandelier National Monument. Most of theseopenings are on south-facing canyon walls to take advantage of the sun for solar heating and light during colder months of the year. At Puy6 Pueblo on the east flank of the femez Mountains, tuff and pumice blocks from the Bandelier Tuff were used as building stone. The Bandelier Tuff is an extensive body of indurated volcanic ash that is thickest on the east and souih flanks of the Iemez . .Or9g91_ryasthe largest domestic producer of pumice and pum- icite in 1993,followed in descending order by New Mefco, Cal- ifornia, Atizona,Idaho, and Kansas.California, New Mexico, and Oregon produced about 85% of the national total (Bolen, oral communication 194). Inl992, New Mexico produced about 60,500 New A4exlc@ mt of pumice with a value of 91.5million (K. S. Hatton, written communication 1993). The U.S. construction industries con- GEOLOGV . Scienceand Seruice tssN (,196-94aX Volume 16, No. 1, February 1994 Editor:Carol A. Hiellming Published quarterly by New Mexico Bureau of Mines and Mineral Resources Domestic production in 1983was 407,000 a division of New Mexico lnstitute of - mtby 2L producers Mining & Technology from22 operationsin eight westem states(Meising6r, 19^85). fhese figures represent about the same tonnage of product produced BOARD OF REGENTS Ex-Officio Bruce King, Gooertor ol Nru Mexico Alan Morgan, Supoifttendentol Publiclnstruction Appointed Charles Zimmerly, Pres,191-197, Suorro Diane D Denish, SeclTreas ,1992-7997, Albuqwrque J- Michael Kelly, 1992-197, Rosuell Steve Tores, 199I-1997, Albuquerque Lt Gen. Leo Marquez, 1989-19%,Albuquerque New Mexico lnstitute of Minint & Tehnology President Daniel H L6pez New Mexico Bureau of Mines & Mineral Resources Directorand StateCeologist Charles E Chapin Sub{tiptiffi: I$ued quartedt FebMry May, Au8ust, November; subscription price $6 0O/calendaryear. Editorial Mttq: Articles submitted for Dublication should be in the editor'shands a minimum of five (5) months before date of pubtication (February May, August, or November) and shoLrldbe no longer than 20 typewritten, double-spacedpages Alt scientific papers will be reviewed by at least two people in the apprcpriate field of study. Address inquiies to Carol A Hjellming, Editor of Nru Merio Geology,New Mexico Bureau of Mines & Mineral Resources,Scono, NM 878014796 Publishedas pablic domoin, threfore reproduciblewithout permissionSource credit requsted FIGURE 2-Bags of siz4 pumice, covered with shrink-wrap plastic, on Circulation:7,m pallets_atthe American Pumice plant, SantaFe, ready for Ioiding on rail Printer: U^iversity of New Mexico Printint Seruices or truck transport. .. February 7994 Nrrt Mexico Geology FIGURE 3-A nearly vertical wall of grayish-white Guaje pumice Bed of FIGURE 4-Loosely consolidated, light-colored Guaie Pumice Bed of the the Otowi Member of the Bandelier Tuff in an abandoned mine on the Otowi Member of the Bandelier Tuff overlain by the welded Tshirege east flank of the Jemez Mountains. Horizontal orientation of the long axis Member at a road cut of NM-4 east of Los Alamos The Guaie Pumice of most pumice clasts is responsible for the indistinct bedding. Bed rests on the irregular upper surface of lava. FIGURE S-Coarse El Caiete pumice in Las Conchas mine near the south FIGURE 6-Screening plant in Las Conchas mine. Fragments in pile to rim of the Valles caldera, Jemez Mountains, New Mexico. Note hammer the left are about fist-size. The pile to the right has fragments two to three for scale at lower right times fist-size. Mountains in north-centralNew Mexico (Smith et al., 1970).It beds greater than 25 m thick adjacent to NM-4 (J. W. Hawley, was depositedfrom turbulent ash flows originating in the Valles oral communication 1993). Hoffer (in press) estimates El Cajete caldera on the crest of the femez Mountaiis. thJ t.+S-mithon- contains approximately 310,000 mt of minable pumice. The U.S. Forest Service classifies pumice into two varieties based on fragment size. If pumice has a large amount of material greater than 1.9 cm (">314 in."), recent case Iaw has held this to be designated as "uncommon" pumice and thus is considered Iocatable under the general mining laws (Verity and Young, 1973). This size material ensures that it can be sold for a premium market price for garment finishing, currently as high as 9286/mt in the El Paso market area (Hoffer, oral communication 1994). In addi- tion, no royalty fees are required on the pumice. The USFS can not prohibit mining locatable pumice, but it can require such reasonable measures as may be necessary to protect the surface environment. An even larger-size variet, "block" pumice, con- tains a large proportion of fragments greater than 5 cm (">2 in.") and is also designated "uncommon" or locatable. Common pum- ice, or nonlocatable pumice, has a larger proportion of material smaller than 1.9 cm and is considered a "mineral material." This designation gives the USFS the discretion to prohibit mining if it is in conflict with other uses of the forest, is publicly controversial, or would affect cultural resources or threatened and endangered species. The Guale Pumice Bed is considered to be "common" pumice and the Cajete Member of the Valles Rhyolite is consid- ered to contain "uncommon" pumice. (;r New Mexico Geology Febrtary 1994 RIOARRIBA I Vallesvolgo I caldera l------lo.17-1.4s7-1.45Ma L__ L. FIGURE8-Abandoned pumicemine on southeastflank of EastGrants Ridgewith light-coloredpumice below both thedark-colored overburden of scoriaand a volcaniccone.