A Eulogy for the Underground Workings of the Gold Hill Mine: Tooele County, Utah
By Haynes, Patrick E
For decades, wonderful, rare, and usually microscopic minerals have been found by hundreds (thousands?) of enthusiastic mineral collectors, both on the surface and in the underground workings of the Gold Hill mine in Tooele County, Utah. On 6 August 2007 the Utah Mined Land Reclamation Program started closing off holes related to former mining and prospecting activity within the Gold Hill mining district, beginning with the Gold Hill mine itself. In anticipation of the mine’s closure, a friend, Erich Laskowski, and I made some collecting trips to the mine to investigate the underground workings and recover specimens of interest to collectors. There were many good targets, so the question of what to collect became a matter of personal interest, which changed by the day, depending upon what was found. Semiquantitative EDS and/or powder XRD analysis confirmed the identities of most of these minerals. Only species personally collected on these recent trips are mentioned here.
For many years there have been reports of “mixite” with weird chemistry occurring on the 30-foot level of the Gold Hill mine. Mixite may indeed occur there, but we collected material identified as zalesiite, an acicular, pale blue mineral that closely resembles mixite. Zalesiite and mixite are chemically identical, except that zalesiite is a calcium copper arsenate instead of a bismuth copper arsenate. The analyzed material showed calcium to be significantly greater than bismuth. It was found associated with calcite, conichalcite, quartz, and chrysocolla.
The 300-foot level has a quartz vein that is rich in conichalcite and sulfides/sulfosalts. Less common are malachite and azurite. This level lacked the variety of minerals found (in the same vein?) on the 150-foot level.
The mine’s largest stoped-out area is adjacent to one of the tunnels on the 300-foot level. The bottom of it had a wall with common brown jarosite microcrystals. Another area had colorless aragonite crystals to about 4 cm.
Most of our collecting activities were on or via the 150- foot level, where adamite, austinite, and conichalcite were locally abundant. One altered scorodite pod had scorodite in four different colors: pale blue, yellowish, white, and pink. Associated with it are green crystals and groups of olivenite, some of which have tiny yellow cubes of alumopharmacosiderite. The olivenite can have zinc substituting for the copper, resulting in changes in the crystal habit, opacity, and luster. It becomes more like adamite, so much so that one can label it olivenite/adamite. White halloysite partially or wholly filled some cavities. Some of the halloysite has a curious platy texture. Tiny green crystals of phillipsburgite were found associated with crystals of brochantite, mixite, cornwallite, chrysocolla, and sulfides/sulfosalts.
Juanitaite was described as a new mineral in 2000 by Kampf, Wise, and Rossman (2000). In 1986 it was found in a quartz vein in a small stope off the 150-foot level. We revisited this area and found juanitaite, connellite, conichalcite, tyrolite, chrysocolla, mixite, cornwallite, and sulfides/sulfosalts.
Bariopharmacosiderite crystals were found in one area above the 150-foot level. They are typically orange, but the color is variable: some are brick-red, others are a dark, dull red. The vugs of a few of the specimens have a thin gray coating of an untested translucent mineral (arseniosiderite?), which although covering the bariopharmacosiderite crystal’s sharp edges, creates attractive and unique specimens. Nearby were nice austinite specimens, some a green cuprian color. Arseniosiderite as variously shaded brown crusts was commonplace. They typically formed before the other zinc minerals, offering a place for the other minerals’ precipitation. Conichalcite as minute crystals and crusts was common.
Purple adamite crystals to 8 mm were found! This adamite typically has purple cores overgrown with colorless adamite, making attractive phantoms. Manganese was determined to be the cause of the purple color. These crystals are associated with tiny druses of shiny black chalcophanite and dull black to brown aggregates of hydrohetaerolite. Nearby were white talmessite crystals to 8 mm.
Another area, above the 150-foot level, had gorgeous green cuprian adamite crystals associated with conichalcite. They are commonly sitting on crusts of mammillary, or sometimes crystallized, arseniosiderite. One small, localized area, also above the 150-foot level, had tiny colorless cubes of natropharmacosiderite associated with olivenite and massive white scorodite.
Accessible via a connecting shaft is the 110-foot level. One wall had massive scorodite with red carminite and colorless to white mimetite, which resembles cerussite. The mimetite crystals can reach 6 mm in size. Some of the scorodite is orange, perhaps due to included carminite. Various tiny yellow, orange, and brown minerals were seen in the vugs. We expected to find thometzekeite but instead found that some of the carminite was intimately associated with yellow aggregates of finely crystallized segnitite. Beudantite occurs as tiny yellowish-brown to brown aggregates, some of which are spherical. The beudantite can sometimes be slightly iridescent. It was the most common of the brownish microscopic minerals. Root- beer-brown to orangish-colored cubes of pharmacosiderite were generally sparse.
Another wall had scorodite with finely crystallized yellow to yellowish-green gartrellite. Elsewhere we found little splays/disks of bright green conichalcite crystals, some associated with crystals and crusts of brown beudantite. In the gossan matrix were completely oxidized galena crystals. One of the galena grains was replaced with fine-grained yellowish mimetite, tiny blue linarite laths, and a colorless glassy grain of leadhillite showing perfect cleavage.
Although the Gold Hill mine’s underground workings clearly had numerous mineral collecting opportunities at one time, these areas are now inaccessible. However, the mine’s open pits and, to some extent, the dumps remain a treasure-trove for the micromineral collector.
I thank Anthony Kampf for all of his invaluable work identifying several dozen specimens; Erich Laskowski for his camaraderie and sound collecting suggestions; and Forrest Cureton for his years of mineralogical enthusiasm and friendship, which inspire field collectors to seek out rare species. I also thank Anthony Kampf and Robert Cook for reviewing the manuscript and William Besse for preparing the map.
This article is dedicated to David Eugene Cureton (1952-1971). The Gold Hill mine’s 80- foot level cut short David’s life while he was doing what he loved-collecting.
Kampf, A. R., R. W. Wise, and G. R. Rossman. 2000. Juanitaite, a new mineral from Gold Hill, Utah. Mineralogical Record 31:301-5.
Kokinos, M., and W. S. Wise. 1993. Famous mineral localities: The Gold Hill mine, Tooele County, Utah. Mineralogical Record 24: 11- 22.
PATRICK E. HAYNES
6468 Jackrabbit Run Avenue
Las Vegas, Nevada 89122
Patrick E. Haynes, after whom the mineral haynesite is named, has field-discovered eight new mineral species.
Copyright Heldref Publications Sep/Oct 2008
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