Virgil W. Lueth

Terrestrial analogs of martian jarosites: Major, minor element systematics and Na-K zoning in selected samples

Abstract Natural jarosites selected for study have mixed domains of jarosite, KFe33+ (SO4)2(OH)6, and natrojarosite, NaFe33+(SO4)2(OH)6. Minor elements include Al in the octahedral B-site, and P, As, Mo, and V in the tetrahedral T-site. High abundances of As are detected in some samples. Oscillatory zoning of Na and K in a subset of these samples has been explored using BSE images, X-ray maps, and a 1 μm EDS beam. Our work shows that zoning is composed of less than micrometer-sized bands of near end-member compositions. This agrees with the XRD work of Desborough et al. (2006), where 32 natural hypogene and supergene jarosites were found to be mixtures of near end-member compositions and showed <5% solid solution. This indicates a wide solvus (miscibility gap) between jarosite and natrojarosite. It also suggests that special crystallization effects are active in solid-solution and aqueoussolution interactions. Here, the optimal conditions for the crystallization of end-member compositions are at low temperatures (<100 °C), and when the two end-members of a binary solid-solution series have different solubilities, as do jarosite and natrojarosite (Glynn 2000). These conditions are commonly found in supergene environments, and are best illustrated by spectacular oscillatory zoning of jarosite and natrojarosite in samples from the Apex Mine, Arizona and Gold Hill, Utah.

CHARACTERIZATION OF GOATHILL NORTH MINE ROCK PILE, QUESTA MOLYBDENUM MINE, QUESTA, NEW MEXICO 1

Rarely do rock pile characterization methods allow for examination and sampling of the interior of large rock piles in-situ. The regrading of the Goathill North (GHN) rock pile at the Questa mine provided a unique opportunity to examine and sample the interior of a large rock pile through the construction of trenches cut into the rock pile as earth-moving progressed. Maps of each bench were created to document the different stratigraphic units, including the thickness, dip, and extent of the units. Units were defined based on grain size, color, and other physical properties. Units were correlated between benches and downward through the series of successively excavated trenches. Typically, paste pH increased with distance from the outer, oxidized zone (west) towards the interior units (east) of the GHN rock pile. The outer zone was oxidized (weathered) based upon the white and yellow coloring, low paste pH, presence of jarosite and gypsum, and absence of calcite. However, the oxidation/reduction (weathering) state in the interior zone is not yet determined. The base of the rock pile closest to the bedrock/colluvium surface represents the oldest part of the rock pile since it was laid down first. Portions of the base appeared to be nearly or as oxidized (weathered) as the outer, oxidized zone, suggesting that air and water flow along the basal interface occurred and possibly was an active weathering zone. Analyses of samples from unweathered, unoxidized drill core samples and from the GHN rock pile are similar in clay mineralogy as determined by XRD and electron microprobe analyses, which suggests that the majority of clay minerals in the GHN samples were derived from the original, pre-mined hydrothermal alteration and not post-mining weathering.

PETROGRAPHIC, MINERALOGICAL AND CHEMICAL CHARACTERIZATION OF GOATHILL NORTH MINE ROCK PILE, QUESTA MOLYBDENUM MINE, QUESTA, NEW MEXICO 1

Tachie-Menson, Vanesssa Viterbo, Virgil W. Lueth, and Andrew R. Campbell Abstract. Rarely do rock pile characterization studies allow for petrographic, mineralogical, and geochemical characterization of the undisturbed interior of large rock piles in-situ. The regrading of the stable portion of Goathill North (GHN) rock pile at the Molycorp Questa molybdenum mine, New Mexico, provided an opportunity to examine and sample rock pile material in-situ through the construction of trenches cut into the rock pile as earth-moving progressed. Maps of each bench were created to describe the different stratigraphic units, including the thickness, dip, and extent of the units. Units were defined based on grain size, color, texture, stratigraphic position, and other physical properties that could be determined in the field. Units were correlated between benches and to both sides of each trench, and several units were correlated downward through the excavated trenches in the rock pile. Characterization of original rock pile material was accomplished by petrographic, mineralogic, and chemical analysis and includes descriptions of rock fragment lithology, mineralogy, texture, and alteration type and intensity. Rock fragment lithology is generally consistent within mapped units and correlates well with mineralogy and chemistry. Typically, paste pH and carbonate abundance increases with distance from the outer, oxidized zone (west) towards the interior, unoxidized zone (east) of the GHN rock pile. Conversely, authigenic gypsum, which is likely a product of in-situ weathering, usually exhibits a decrease in abundance from the outer to the inner portion of the rock pile. CaO and Sr also typically increase in concentration from the outer, oxidized zone (west) towards the interior, unoxidized zone (east) of the GHN rock pile, suggesting dissolution of feldspars and calcite to form gypsum in the outer, oxidized portions of the rock pile. Clay mineral and electron microprobe analyses of soil samples and unweathered drill core imply that the majority of clay minerals in the GHN samples are derived from the original pre- mining hydrothermal alteration and not by oxidation of minerals within the rock pile.

A History of Mineral Collecting at the Chino Mine Grant County, New Mexico

*The Mogollon (named after the mountain range in southwestern New Mexico) were an ancient Native American group that inhabited the area and built the structures at the Gila Cliff Dwellings National Monument around Silver City. They abandoned the region, much like the Anazazi left the Four Corners, around 1400. The Apache later moved into the area and made it their homeland. The Chino mine is probably one of the oldest collecting sites in North America. A copper bell, dated ca. 1150, has been excavated from a nearby Mogollon site.* Though yet to be studied in detail by archeological scholars, Chino copper and turquoise doubtless have been collected at the site since prehistoric time. The mine derives its name from the Spanish term for chalcopyrite (formally, copper pyrite), not as an allusion to the Chinese, as has long been reported. The Chino mine is located in eastern Grant County, New Mexico, approximately 12 miles east of Silver City, the county seat. The town of Santa Rita, once nearly surrounded by the mine (hence the name Townsite Island on many mine maps), served for many years as the center of mining activity until it was completely engulfed by the open pit in the 1970s. The deposit is often referred to as the Santa Rita deposit, or some reference is made to the former town, in geological literature. Mining has progressed nearly continuously in the area of the Chino mine for more than the past two hundred years and is still active today. From 1911 to 2006, the mine produced more than 5.9 million tons of copper and 500,000 ounces of gold (McLemore 2008). Chino was the fifthlargest copper producer in the United States in 2005, producing 104,800 tons. Although production dropped to 92,900 tons in 2006, the mine rose to third in U.S. production for the year (Phelps Dodge, company annual reports). Chino Mines Company, a wholly owned subsidiary of Freeport McMoRan Copper and Gold, currently owns and operates the mine. Collecting of mineral specimens has been continuous for many years, with punctuated finds of minerals of significant