PROJECT SUMMARY

INTERNATIONAL SMELTER SITE

STOCKTON DISTRICT

BAUER MILL SITE

DRAGON MINE SITE

Brief Description of Site

The Stockton (or "Rush Valley") mining district is located in north-central Utah, in the west-central Oquirrh Mountains, about 40 km southwest of Salt Lake City. The Bauer Mill processed ore from the lead-zinc deposits in the Stockton District and has remained essentially unreclaimed since it was de-activated.

The mill operated from 1900 to at least 1957 and was dismantled in 1976. The lead-zinc-silver sulfide ore of the adjacent Stockton Mining District made up the bulk of the material processed at Bauer, although ores from other mining districts were also processed there. The dried tailing impoundments cover an area greater than a square mile.

Much of the mine drainage from the Stockton District was through the Bauer Tunnel, which exited near the Bauer Mill approximately 2.5 km north of Stockton. The tunnel actually drained many large mines in the Stockton District and provided the mines the ability to greatly lower drainage and mining costs early in the 20th century.

The presence of pyrite in the ore indicates potential for acid generation and consequent heavy-metal leaching. This however is mitigated by the carbonates present, and the actual environmental liability from underground operations, where broken ore, waste, and wall rocks have been exposed to air and water, may be limited.

The historic mill tailings, however, do represent some hazard through potential transportation of fines into the drainages in and near the town; where separated from the carbonate-dominated substrate they may leach and release toxic metals into the environment. Similarly, concentrate spills and smelter fines are rich sources of toxic metals, which can be leached out of the sulfide matrix uninhibited by carbonate gangue.

Why Site Was Chosen

The Oquirrh Mountains study sites of interest to UDEQ and EPA were prioritized as #2 among the five general mining areas for study under the EPA Utah-Watershed AML project. The west-side districts and mill represent more varied waste conditions and proffered simpler access considerations then larger mines on the east side of the mountains.

The Stockton District is the oldest mining district in Utah and, therefore, has the longest mining and milling history and range of age of wastes. Although none of the mines were huge, some produced into the 1960s. Mills were started in the early days of the district and most did not survive more than a couple decades at most. However, the Bauer Mill remained active to some degree into the early 1970s, and represents a classic example of a totally unreclaimed tailings facility, with attendant potential surface and subsurface impacts.

The Bauer Mill site was chosen as a special section of the Stockton District study because of the raw nature of the site, which allows the evaluation of the hyperspectral technology for an unreclaimed and essentially unmodified site as compared to the almost far-endmember for mills and smelters of the International Smelter area, discussed above. The Bauer Mill primarily has tailings, accumulated from processing of both Stockton ores and ores from other parts of the Western United States.

The tailings ponds are of interest for waste characterization. However, there also are eolian tailings that have escaped from the facility and have the potential to impact areas to the north along the prevailing wind direction. The ore-processing tie between Stockton and Bauer is of interest of course, but the Bauer site in itself is a worthwhile study area for advancing the application of hyperspectral techniques to mill wastes and associated problems.

Both the Bauer and Stockton areas will continue to be studied as part of an M.Sc. thesis at the Colorado School of Mines. There are only preliminary results to date and these are are covered under the appropriate sections in other parts of this report.

SUMMARY OF STUDY AREA (INCLUDING SPECTRAL ANALYSIS)

	The tailings at the Bauer Mill contain pyrite, iron oxides, and iron sulfates in the area adjacent to the mill. Iron oxides dominate farther out into the tailings ponds. CASI data show the tailings have a distinctive signature from the surrounding valley-fill material, which suggests that these data may be useful for defining the limits of the iron oxides associated with the tailings.
	The dominant SWIR-active minerals in the tailings are silica, smectite, and gypsum. Silica and smectite are common components of both the lacustrine sediments that surround the tailings and of the tailings themselves and, therefore, probably will not be of use in discriminating between the tailings and the non-waste materials. Gypsum, however, may be found only in the tailings, and it does show a gradational pattern. Successful discrimination of the tailings and other wastes using the SWIR range probably will depend on devising a successful processing scheme for gypsum.
	The SWIR active minerals found in the waste rock in the mill dump near the drainage tunnel (alternately named the "Honorine" or "Bauer" Tunnel) are very similar to those found in the Stockton mining district. In addition to draining the mines of the district, ore was moved through the tunnel, and much of the dump material presumably came from the Stockton District. Ores (brought in by rail) from other mining districts also were processed at Bauer.
	Initial results from this site have already demonstrated an eolian distribution of tailings extended considerably further than predicted and visually observable.
	Studies at the Bauer Mill will be continued in Phase II as an M.Sc. thesis at the Colorado School of Mines. Interim and final results will be reported within the context of Phase II reports, as an unpublished thesis, and as presentations at both the Results Conference on the EPA Utah AML Project in June 2000 and at a remote sensing conference in November 2000, following the completion of this EOCAP project. It is expected that a refereed journal article also will be produced from this thesis work.

WATERSHED ASPECTS OF RESULTS

The Bauer Mill site is largely situated in a closed surface basin, so surface water impact is limited. However, there is significant potential for escape of contaminated ground waters. This has not been assessed (that we have been able to determine). Inquiries will be made with USGS, U.S. Army, UDEQ, and Tooele County officials during Phase II to determine if any ground water sampling has been done which could shed light on this issue. Eolian transport of tailings off site to the north and into the adjacent open surface drainages also is of interest.

COMMERCIAL IMPLICATIONS AND MARKET STRATEGY

The study areas, International Smelter, Stockton District and Bauer Mill, and the Dragon Pit, were chosen to address various mine/mill types and waste conditions as well as to address different segments of the mine and mill waste inventorying, characterization, remediation, and reclamation markets. The objective was to develop marketable cost effective tools for refined evaluation and monitoring methodologies and expertise through a cross section of applications case studies.

The Bauer Mill serves as an example of site characterization for long-active mill sites that are closing down or have been abandoned. Results from this site will help in convincing government agencies and the mining and environmental communities of the cost effectiveness and reliability of hyperspectral data and images to identify mineralogical and chemical conditions at such sites in advance of reclamation. The thoroughness of mineral mapping and identification of environmentally important constituents will allow reclamation of mill sites to be performed with the most economical and long-lasting methods, rather than applying incomplete or short-term solutions as is too often the case for such sites.

APPLICATION OF STUDY AREAS TO POTENTIAL COMMERCIALIZATION AND MARKETS

The Bauer Mill was the only mill that continued operation into the mid-20th Century. This is an example of the application of hyperspectral technology to fast inventorying and characterization of the wastes at the mill sites that remain wholly or partially exposed (i.e., not built upon by later residential and commercial construction). In this area, the old mills and smelters are associated with elevated to very high lead in their former wastes, which is of concern to government and current residents.

Stakeholders in this process include land management and environmental agencies at all levels and the mining industry. The mining industry has an interest in this technology and sites such as Stockton and Bauer as a means of identifying environmental risk for continued exploration and mining in historically mined areas.

The Bauer Mill presents a typical large mill site, which operated for a long period of time and produced large quantities of wastes, primarily in the form of tailings that still are mostly exposed. Little or no smelting occurred at this mill, but highly pyritic ore was processed and pyritic (i.e., acid-producing) wastes produced. Clearly this nearly totally unreclaimed site provided an excellent opportunity to evaluate waste characterization in a detailed manner using hyperspectral sensors.

Sites such as Bauer are of interest to land management and environmental agencies in terms of how they are impacting the surrounding and downstream environment, as well as for characterizing the sites to determine how they must be reclaimed to prevent future impacts. The Department of Defense also should have an interest in our results because of the proximity of the Bauer site to the Tooele Army Depot.

Bauer serves as the "starting" point on the mill site reclamation curve, with the International Smelter being somewhere between the middle and end of the curve, the end point being a site that requires no further remedial action or monitoring. Therefore, the Bauer site applies to the same market segment as the International Smelter site, but in the form of a mill that is just shutting down or has been abandoned (as at this site) and has had no reclamation done on it. Numerous mill site examples in the United States and elsewhere can be found where proven hyperspectral technology could find commercial application and a ready market for site characterization.

COMMERCIAL IMPLICATIONS OF RESULTS

The Bauer Mill site is under further investigation as part of a thesis at Colorado School of Mines. As a result, not all sample collection or analyses have been completed in Phase I. However, some preliminary results from field work and sample analyses can be used to assess commercial implications of work on this site. The Bauer Mill used primarily chemical and flotation processing, rather than smelting, so mill effluent was mostly in the form of tailings rather than combined tailings, slag, smokestack emissions, and acidic solutions such as at International.

It appears that the tailings and waste dumps can be differentiated mineralogically from the surrounding lacustrine gravels and soils. This may seem trivial, but the first question always of interest to potential users of a new data source is whether it has the ability to tell sites of interest from the background. If not, the method is dead from the start in terms of acceptance by nonexperts.

The second question is whether differences within the waste site can be discerned. That also appears to be the case based on preliminary iron mineralogy and presence of gypsum, which is not common in the background materials. Clay minerals, especially in the tailings, remain problematic and require further investigation, sampling, and image processing to determine if there are any differences that can be exploited to refine characterization of the wastes or among the wastes. With respect to tailings distribution, the main bare-surface ponds should be able to be easily delimited because of the high contrast with surrounding non-waste vegetated terrain, as well as mineralogically.

This site also has a unique feature in the form of tailings redistributed by the wind into partially stabilized dunes that have escaped the tailings ponds to varying degrees to the north, the prevailing downwind direction. This aspect of the site alone has significant implications for commercialization because a common complaint of neighbors in urban, suburban, and rural settings, even at some distance, of mills and tailings ponds (active, inactive, and abandoned) is blowing tailings escaping the sites.

An important point about such eolian tailings, which most people forget when discussing "fugitive dust", is just what the composition is of those tailings. Do the tailings present any chemical hazards or are they simply a dust and sedimentation hazard? The continued study of the Bauer tailings, dunes, and downwind impacts will help address this market segment which is on the minds of many growing urban areas in the Western United States that are encroaching on formerly isolated mill sites.