Virgil W. Lueth
Mineralogist/Economic Geologist
Curator - Mineral Museum
Assistant Director for Public Outreach

Abstracts
 

2005

2004

2003

2002

2001

2000

1999

1998

1997

2005

Chemical Geology, v. 215, p. 339-360

“SOUR GAS" HYDROTHERMAL JAROSITE: ANCIENT TO MODERN ACID-SULFATE MINERALIZATION IN THE SOUTHERN RIO GRANDE RIFT, - Virgil W. Lueth, Robert O. Rye, Lisa Peters

As many as 29 mining districts along the Rio Grande Rift in southern New Mexico contain Rio Grande Rift-type (RGR) deposits consisting of fluorite–barite ± sulfide–jarosite, and additional RGR deposits occur to the south in the Basin and Range province near Chihuahua, Mexico. Jarosite occurs in many of these deposits as a late-stage hydrothermal mineral coprecipitated with fluorite, or in veinlets that crosscut barite.  In these deposits, many of which are limestone-hosted, jarosite is followed by natrojarosite and is nested within silicified or argillized wallrock and a sequence of fluorite–barite ± sulfide and late, hematite–gypsum. These deposits range in age from ~10 to 0.4 Ma on the basis of 40Ar/39Ar dating of jarosite. There is a crude north–south distribution of ages, with older deposits concentrated toward the south. Recent deposits also occur in the south, but are confined to the central axis of the rift and are associated with modern geothermal systems. The duration of hydrothermal jarosite mineralization in one of the deposits was approximately 1.0 m.y. Most D18OSO4–OH values indicate that jarosite precipitated between 80 and 240 °C, which is consistent with the range of filling temperatures of fluid inclusions in late fluorite throughout the rift, and in jarosite (180 °C) from Peña Blanca, Chihuahua, Mexico. These temperatures, along with mineral occurrence, require that the jarosite have had a hydrothermal origin in a shallow steam-heated environment wherein the low pH necessary for the precipitation of jarosite was achieved by the oxidation of H2S derived from deeper hydrothermal fluids. The jarosite also has high trace-element contents (notably As and F), and the jarosite parental fluids have calculated isotopic signatures similar to those of modern geothermal waters along the southern rift; isotopic values range from those typical of meteoric water to those of deep brine that has been shown to form from the dissolution of Permian evaporite by deeply circulating meteoric water.  Jarosite d34S values range from –24 to 5‰, overlapping the values for barite and gypsum at the high end of the range and for sulfides at the low end. Most d34S values for barite are 10.6 to 13.1‰, and many d34S values for gypsum range from 13.1 to 13.9‰ indicating that a component of aqueous sulfate was derived from Permian evaporites (d34S = 12 ±2‰). The requisite H2SO4 for jarosite formation was derived from oxidation of H2S which was likely largely sour gas derived from the thermochemical reduction of Permian sulfate. The low d34S values for the precursor H2S probably resulted from exchange deeper in the basin with the more abundant Permian SO42– at ~150 to 200 °C. Jarosite formed at shallow levels after the pH buffering capacity of the host rock (typically limestone) was neutralized by precipitation of earlier minerals. Some limestone-hosted deposits contain caves that may have been caused by the low pH of the deep basin fluids due to the addition of deep-seated HF and other magmatic gases during periods of renewed rifting. Caves in other deposits may be due to sulfuric acid speleogenesis as a result of H2S incursion into oxygenated groundwaters. The isotopic data in these “sour gas” jarosite occurrences encode a record of episodic tectonic or hydrologic processes that have operated in the rift over the last 10 m.y.

New Mexico Geological Society 2005 Spring Meeting, Abstracts and Programs and New Mexico Geology, v. 27, n. 2, p. 47.

SOIL PETROGRAPHY OF MULTIPLE SAMPLES FROM A PORTION OF THE GOAT HILL NORTH ROCK PILE, QUESTA MINE, NEW MEXICO - Phillips, E.H.1, McLemore, V.1, Lueth, V.1, Campbell, A.1, and Walker, B.2, (1) NM Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, ehp@nmt.edu, (2) Molycorp, Incorporated, Questa, NM 87556

Petrographic examination of a series of twenty-one soil samples collected at five foot intervals along Bench 9 of Trench LFG 006 in the Goat Hill North rock pile at the Questa molybdenum mine reveals significant differences in characteristics such as color and mineralogy.  This traverse crosses eight different mappable units, defined primarily based on color, stratigraphic position, and grain size.  Two of these units are classified as oxidized, one is intermediate, and five are unoxidized.  The color of secondary iron oxide minerals is variable among the twenty-one samples and includes black, orange, red, yellow, and brown material. 

Gypsum is present in all of the soils and occurs in different habits.  Stable isotope studies demonstrate that this petrographic observation can be used to distinguish gypsum as either detrital or authigenic.  A preponderance of clear, prismatic, authigenic gypsum grains is an indicator of a high degree of sulfide weathering after the material was emplaced in the waste rock pile. 

Significant differences in the abundance of carbonate in the soil samples exist and preliminary data suggest a positive correlation between carbonate abundance and paste pH values.  Seven samples contain no detectable carbonate and have paste pH values between 2.2 and 3.7, whereas four samples contain abundant carbonate and have paste pH values between 8.4 and 9.6.  The remaining ten samples contain trace to minor amounts of carbonate and have paste pH values ranging from 3.3 to 9.6.  All four samples with abundant carbonate are from unoxidized units. 

Goldschmidt Conference, Abs. No. 1207

SOURCE OF FLUORINE AND PETROGENESIS OF THE RIO GRAND RIFT TYPE BARITE-FLUORITE-GALENA DEPOSITS

F. PARTEY1, S. LEV3, R. CASEY3, E. WIDOM1, V. LUETH2 AND J.RAKOVAN 1Dept. of Geology Miami University, Oxford Ohio, 45056, U.S.A. (rakovajf@muohio.edu) 2New Mexico Bureau of Mines and mineral Resources, Socorro, NM, 87808, U.S.A. 3Dept. of Physics, Astronomy, and Geosciences, Towson University, Towson MD, 21252, U.S.A. (slev@towson.edu)

Abundant fluorite mineralization in the Rio Grande Rift (RGR) barite-fluorite-galena deposits is anomalous compared to typical Mississippi valley type deposits. The source of fluorine in these deposits is controversial. We have tested two hypothesized sources for the origin of fluorine in the RGR deposits. These include release of gaseous HF from magmas associated with rifting, and the leaching of fluorine from Proterozoic basement granites that underlie the Pennsylvanian limestones, which host much of the fluorite mineralization in the region.

In this study chlorine isotopes and Br/Cl were measured from fluorite fluid inclusions. Chlorine and fluorine exhibit chemically similar behavior, and therefore are likely to be derived from the same source if chlorine is associated with rift related magmatism. Sr and Nd isotopes were measured from fluorites, granites, carbonates, and asthenospheric basalts to aid in understanding the petrogenesis of RGR deposits.

Sr and Nd isotopic ratios from fluorites are distinctly more radiogenic than local basalts and Pennsylvanian limestones but similar to the Proterozoic granites. The radiogenic character of the fluorites indicates that the Sr and Nd were derived largely from a granitic source with some influence from a carbonate and/or asthenospheric source. δ37Cl values from fluorite fluid inclusions range from –0.003‰ to +3.069‰ relative to SMOC, and the Br/Cl ratio for all the fluorite samples ranges between 0.00008 and 0.00050, except for San Diego Mountain which has a relatively high Br/Cl ratio of 0.00242. There is a strong positive correlation between δ37Cl and Br/Cl in the fluorite data that indicates mixing of Cl from asthenospheric magmatic and evaporite sources. The calculated range of Cl derived from an asthenospheric source for the Mex-Tex deposit is 40% to 49%. Similarly, between 35% and 13% of the Cl in the Sunshine deposit is asthenospheric in origin. Since F and Cl likely exhibit similar chemical behavior in this system, the presence of asthenospheric Cl is consistent with an asthenospheric magmatic source of F in the RGR deposits.

New Mexico Bureau of Geology and Mineral Resources, Bulletin 161, p. 239-249.

AGE OF MINERALIZATION IN THE LUIS LOPEZ MANGANESE DISTRICT, SOCORRO COUNTY, NEW MEXICO, AS DETERMINED BY 40AR/39AR DATING OF CRYPTOMELANE. - Virgil W. Lueth, Richard Chamberlin, and Lisa Peters 
New Mexico Bureau of Geologys & Mineral Resources, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87808-4796

Cryptomelane, KMn8O16, samples from the Nancy and MCA mines in the Luis Lopez manganese district were collected in order to determine the age of mineralization using the 40Ar/39Ar isotopic method. Cryptomelane precipitation occurred at the onset of calcite mineralization following banded manganese ore deposition. X-ray diffraction analysis confirmed composition and sample purity.  40Ar/39Ar dating of two cryptomelane samples from the MCA mine yielded nearly concordant age spectra with a weighted mean age of 6.29 ± 0.08 Ma. Nancy mine cryptomelane yields a weighted mean age of 6.00 ± 0.09 Ma; argon spectra suggest that this is a minimum age of mineralization. These ages are consistent with age estimates for mineralization (3-7 Ma) based on geologic relationships in the area as established by previous workers.
These age determinations indicate manganese mineralization closely followed regional potassic alteration. Published 40Ar/39Ar ages of metasomatic adularia from jasperized fanglomerates north of the Nancy mine indicate metasomatism persisted until 7.4 Ma.  Minor manganese veins near the Nancy mine cut jasperized fanglomerates and cut numerous jasper veinlets in the Oligocene tuffs affected by this earlier alteration. A published model for the Luis Lopez district previously interpreted the mineralization to be derived from a manganese-depleted red alteration zone superimposed on thick intracaldera tuff (31.9 Ma) near the center of the district.  A coarsely porphyritic rhyolite dike, recently dated at 10.99 ±0.06 Ma, is unaltered where it cuts across the southern arm of the red zone. This indicates that the red zone is at least 4.7 million years older than manganese mineralization at the MCA and Nancy mines and genetically unrelated. Granitic intrusions that presumably fed rhyolite lava domes (8.7 to 7.0 Ma) in the Socorro Peak area, 8-9 km northeast of the Nancy mine, represent the most likely heat source for the hydrothermal system of the Luis Lopez district. 
 

25th Annual New Mexico Mineral Symposium - New Mexico Geology, v. 26, p. 126.

EARLY COMMERCIAL MINERAL COLLECTING IN NEW MEXICO AS REPRESENTED IN THE MINERAL COLLECTOR (1884-1909) - Virgil W. Lueth
New Mexico Bureau of Geology & Mineral Resources, New Mexico Institute of Mining & Technology, 801 Leroy Place, Socorro, NM 87801

The Mineral Collector, published from March 1894 until February 1909, was America’s first popular mineral magazine. The fifteen-year run recorded the mineral collecting history of the nation during a period of intense interest in the natural sciences. Articles and advertisements highlight the mineral specimens coming out of New Mexico. The information from this magazine, coupled with correspondence and reports found in the New Mexico Bureau of Geology and Mineral Resources Mining Archives, provides a record of the collecting history of New Mexico during the period.

The first New Mexico mineral specimen encountered in the magazine was in the 4th issue and it was the editor himself, Arthur Chamberlain, advertising “Peridotes, N.M., one-half carat 50cts.” Later that year Chamberlain advertised “Descloisite, N.M.” probably from Lake Valley. George English advertised “Shipments from New Mexico” and followed the ad with a list of material including “Cerussite from New Mexico in elegant groups of twins 50 c to $5.00; large museum specimens, $10.00 to $25.00.” “Yellow wulfenites” soon followed and along with the cerussite, probably came from the Stephenson-Bennett mine in the Organ Mountains. An article by Maynard Bixby mentioned silver specimens from Bullard Peak and the Solid Silver and Bremen mines near Silver City and the Bridal Chamber at Lake Valley. Some dubious localities were also advertised (not unlike today), such as the American Jewel Mines offering “Aquamarine that abounds in New Mexico and Arizona!” 

First mention of smithsonite, “of a color and and luster which exceeds that of the Grecian specimens” was first advertised by A.E. Foote in the first issue of 1895. F.G. Hillman offers quartz crystals from New Mexico in addition to an editorial note about their unusual shapes and colors that suggest they are the first offered from the Steeple Rock/Mule Creek area. The unusual pink chalcedony “buttons” from around Socorro also make their appearance in the magazine at this time. “Quartz, small red crystals from New Mexico, very pretty, 10c each, 3 for 25 c. postpaid” were offered in 1895 by Niven & Hopping marking the first documented sales of Pecos diamonds.

The “glory days” of New Mexico minerals in the popular literature and advertisements spanned the years of 1894 to 1899. Ads offered; wulfenite, cerussite, altaite, flos ferri and quartz from Organ, smithsonites and cerussites from Magdalena, red descloisite and silver vanadinite from the Commercial mine, graphite from Madrid, copper after azurite from the Copper Rose mine,  wolframite and helvite (probably from Victorio), and melanotekite and fine yellow endlichite from Hillsboro. New Mexico turquoise was commonly offered for sale. New Mexico almost disappears from the mineralogical scene from 1900 to 1907. Interestingly, aurichalcite from Magdalena does not show up until 1904, but when it does creates a sensation and rejuvenates interest in the minerals from the state. The last two issues of The Mineral Collector teem with New Mexico articles on meershaum and turquoise and ads that not only offer the “New Mexico staples” but also, molybdenum, bismutite, and a new find of red vanadinite from Kelley. 

More significant however, might be those items advertised yet never seen today or from what are now famous localities yet unmentioned. Of the latter, native copper and cuprite from Santa Rita are never mentioned although fine malachite specimens are noted! One of the more common mystery specimens is “drusy hematite on lava, NM” offered by George English. Embolite on quartz is also offered for sale but unfortunately with no location information was ever given. Most significant to modern collectors of New Mexico minerals is the complete lack of fluorite specimens in ads or articles. In fact, in an article discussing mineral products of the United States, New Mexico is not even mentioned in fluorspar production for 1908. However, it would soon achieve prominence as the largest producer in the west after 1909, the year the The Mineral Collector ceased to exist. 

25th Annual New Mexico Mineral Symposium - New Mexico Geology, v. 26, p. 130-131.

NEW MEXICO GOLD THROUGHOUT HISTORY
Robert W. Eveleth and Virgil W. Lueth,
New Mexico Bureau of Geology & Mineral Resources,
Socorro, New Mexico
 

   Gold, it can be argued, was a major driving force behind the early day exploration and development of southwestern North America. The Spaniards came here seeking it and stole it from the Aztecs in quantities they wrongly assumed to be inexhaustible. When the Aztecs could no longer continue to fill the specified store room full of gold, they met their fate at the business end of a sword or musket. Moving northward into present day New Mexico the conquerors voraciously continued their quest for the yellow metal. But the Native Americans were wise to their schemes by this time and kept the Spaniards forever on the march seeking the elusive, treasure-laden “Seven Cities of Cibola” always just beyond the next range of mountains.
   The Spanish eventually did manage to find a small quantity of gold in the Land of Enchantment but most of the major discoveries were made much later by their Mexican and American successors. What they did not fully appreciate at the time is that New Mexico, in truth, is not an area heavily blessed with the precious metal in the native state and the territory possessed few productive gold placers. Most of New Mexico’s gold, with but few exceptions, has been won from the by-product processing of other metals such as copper, lead, zinc, and silver. 
    Those few exceptions did produce some remarkable gold nuggets. Notable examples include the Old (Ortiz) and New (San Pedro) Placers districts of Santa Fe County, the Nogal-Bonito areas of Lincoln County, and the Elizabethtown-Baldy area of Colfax County. Many others, such as the Hillsboro-Las Animas area, Magdalena Mountains, Pinos Altos, White Oaks, Hopewell, have produced smaller but collectible specimens, all of which will be discussed in detail.

25th Annual New Mexico Mineral Symposium - New Mexico Geology, v. 26, p. 130-132.

THE WEALTH OF NEW SPAIN: CONQUISTADOR SILVER IN MEXICO
James McGlasson, Consulting Geologist, Tucson, Arizona (jimmcglasson@comcast.net)
Peter K. Megaw, IMDEX, Inc., Tucson, Arizona
Virgil W. Lueth, New Mexico Bureau of Mines and Geology, Socorro, New Mexico

In 1517 when Francisco Hernandez de Cordoba landed on the Yucatan Peninsula, he encountered the vestiges of the once-vast Mayan civilization. The Maya used substantial precious metals in decorative items as well as sacred ceremonial effigies. There was considerably more gold than silver in these objects, because the native gold could be worked without further refining, and the silver in this region is generally confined to complex minerals and not readily available in its native state.  Cordoba returned to Cuba telling of the great wealth of gold in the region as demonstrated by the objects that he had seen in the Yucatan. Two years later, 13 March 1519, Hernando Cortez landed at what is now Vera Cruz on the eastern Gulf shore.  Along with him he brought 10 stallions, 5 mares and at least one case of smallpox.  This date signifies the beginning of the end of the Aztec, Inca and other Native American civilizations in Latin America.  In the vicinity of Vera Cruz, Cortez encountered the thriving Aztec civilization, ruled by Montezuma II.  The Aztec at first thought that Cortez and followers were the reincarnation of a God - Quetzalcoatl, but soon determined that these “gueros” (light skinned people) were really there to conquer and plunder their people.  By November 1519 Montezuma was a captive of the Spanish, and was killed by his own people (30 June 1520) whilst trying to “calm” a crowd of Aztec lead by his son Cuauhtémoc as they drove Cortez and the invaders from the city.  Cortez returned to capture the city on 13 August 1521 and, with a relatively small force, defeated a civilization of approximately 25 million.  On 15 October 1522 Hernando Cortez was appointed governor of Mexico and thus began the reign of the Spanish Empire in the Americas.
The explorers / prospectors / conquerors were sent out from Mexico City to find the sources of the “Aztec Gold”.  What they discovered instead, was a vast wealth of silver.  During the next few years many of the “world class” silver districts of Mexico were “discovered”.  At least the conquistadores took credit for their discovery, because there is evidence in many districts that the indigenous people had known of these areas for years.  The discovery of this vast wealth in Silver financed the Spanish Empire for a long period of time, and to this day the mines of Mexico and Peru are the world’s leading producers of silver.  Silver production in Mexico has been affected by political events as well as technology.  

TAXCO  (Guerrero) – 1522 –
The Conquistadores (Juan de La Cabra, Juan Salcedo, Muriel and Hernan Cortez) began mining silver from the Socavon de Rey (Mina del Pedregal) in 1534.  Sporadic mining continued until 1747. In 1802 there were several “bonanza” discoveries in the district, but metallurgical problems curtailed major production.  In 1920 American Smelting and Refining Company (ASARCO) constructed a floatation plant to treat sulfide ores followed by amalgamation.  The property is currently controlled by Industrial Minera Mexico, S.A. (IMMSA), and in the late 80’s was producing 3,000 tons per day.  It has recently been put back into production after being idle for several years due to depressed metals prices.  

PACHUCA (Hidalgo) – 1524 - 
This area is located about 60 miles north of Mexico City and includes three areas (Pachuca, Real del Monte, and Moran). This is one of the most famous and productive areas in Mexico.  The area represents a confluence of the effects of technology as well as politics on the mining industry in Mexico.  The mines were worked continuously from 1524 to 1733, when they were abandoned due to high water flow.  Drainage tunnels were constructed and the mines re-opened and produced for an additional 140 years. 

GUANAJUATO (Guanajuato) – 152
The district was known as early as 1529, but the first recorded claim was filed by Juan Rayas, a muleskinner, in 1548.  On April 15, 1558 work began on the Mellado shaft resulting in the discovery of the Veta Madre.  This vein system underlies the eastern half of the city and mining continues to the present (555 years).  By the early 1600's the mines were well developed and numerous mines had been discovered and developed (Cata, Mellano, Rayas, and Sirena). In 1726 Don Jose de Sardaneta y Legaspi substantially increased production with the introduction of gunpowder to break rock.  In 1766 the Valenciana Shaft was developed to 230 meters, shortly thereafter (1770) production had commenced in the Peregrina, El Monte, San Nicolas, Santa Rosa and El Cubo areas.  Mining activity continued at a high level until 1821 when insurrectionists burned all mine operations, including the headframe of the Tiro Valenciana. The area became a harbor for thieves and criminals until 1868 when the Valenciana was re-opened and pumped using a Cornish steam hoist and leather buckets. 

FRESNILLO (Zacatecas) – 1553
The Fresnillo deposits were discovered shortly after the mineralization at Zacatecas by Francisco de Ibarra by miners traveling from Zacatecas to Sombrerete along the “Camino Real”  They noticed prominent hill on the western skyline and found rich siklver ores in outcrop on the flanks of th hill.  The  hill became known as Cerro Proaño, after Diego Fernandez de Proaño, who discovered some of the first small veins in the area.  Mining activities in the area continued until 1757 when they were suspended because of water problems in the mines.  The mines became property of the government in 1830 and re-opened with prison labor in 1833, until production was halted due to cholera and lack of capital.  An English Company – Compania Zacatecano-Mexicana took over operations in 1835 and installed two Cornish Pumps.  The Fresnillo Company was founded in 1910 in New York and leased the mine to the English – Mexican Corporation for operation.  The two companies eventually merged as the Fresnillo Company of New York.  This Company began changing structure in 1961 as the government required all foreign operations to reduce their ownership to 49% by 1975.  Industrias Penoles acquired the 51% majority ownership and  ultimately bought the remaining 49% in 1996.  However, the mine is still operated as Compania Fresnillo today.

CHARCAS (San Luis Potosi) – 1570
There were small mine workings being operated as early as 1570, but the main area of production was not discovered until 1583.  Open cut operations in the area of the San Bartolo Shaft yielded up to 1.5 kg / ton Silver.  

SANTA EULALIA (Chihuahua) –1593…first prod 1703
Santa Eulalia has been in continuous production for nearly 300 years (1703-present) and ranks as one of Mexico's chief silver and base metal producers with over a half billion ounces of silver recovered.   The City of Chihuahua was built by Spanish pioneers on the riches emanating from Santa Eulalia over the first 100 years of mining and, although modern industry now dominates Chihuahua's economy, the grand cathedral and palatial mansions of the old part of the city bear mute testimony to the wealth Santa Eulalia produced for those lucky enough to own the mines and not have to work in them.
Significant production from the district did not begin until the early 1700s, but the initial discovery of mineralization is shrouded in myth, romance, and speculation.  Several authors have suggested that, long before the Spanish Conquest of Mexico, indigenous peoples may have accidentally discovered that silver and lead could be obtained from mineralized outcrops in the district.  The mineralogy of the oxide ores would permit this, but no hard archeological evidence for it exists.  It is very likely that the indigenees found small pods of gaudy copper-oxide mineralization along the southern San Antonio Graben and mined it, with attendant ochre, for ornamentation.  
From 1709-1737 the district yielded a quarter of the silver produced in all of Mexico and remained the country's largest single silver producer until 1790.  By 1790, over 4 million tons of ore had been produced with grades that averaged 700 g/MT silver.  Ores from some mines were extremely high grade:  

MAPIMI [Ojuela] (Durango) – 1598 
The mineralization at the Ojuela Mine was first discovered in 1598 by Spanish Explorers who noticed the iron-stained outcrops on the canyon walls.  There are three possible derivations of the name “Ojuela”: 
1) The mine may have been named for a missionary, Don Pedro de Ojuela
2)  The name is possibly for a hole resembling the eye of a needle (ojuela, “little eye”) visible at on the north canyon wall at the mouth of the mine 
3) The third possible derivation of the name is from hojuela, an old Spanish mining term for argentiferous galena of a leafy texture.  The local miners consider this to be the source for the name.
The Ojuela Mine and others in the district operated until the beginning of the Mexican Revolution in 1810, and produced at very low levels under the new government from 1821 – 1867.  It was closed from 1867-1884.  Commercial mining at the Ojuela Mine continued , somewhat sporadically, until the 1940’s. Currently the Ojuela mine is operated solely for mineral specimens.
 In 1899, the district had 216 miners and produced $4 million (1899 dollars) of ore, the German Investors received $100,000 per month during the 1890’s and 1900’s.  During this period 6% of the total mine production in Mexico came from the Mapimi District.
There are 126 known mineral species from the Ojuela Mine, and type locality for five of them (lotharmeyerite, mapimite, metaköttigite, ojuelaite, paradamite) and the cotype locality for one (scrutinyite).  The mine has nearly 450 kilometers of workings. 

BATOPILAS (Chihuahua) – 1632
 High-grade native silver outcrops in the  Batopilas district were discovered around 1630 and production records begin in 1632.  The district contains over 65 mines, and experienced three major periods of activity during which approximately 300,000,000 ounces of silver were produced:  1632-1732, 1790-1819, and 1862-1914.  The last of these was the most sophisticated and organized, being run by A.R. Sheperd, former governor of Washington DC.  Sheperd was a good friend of Porfirio Diaz, president of Mexico from 1880-1910, who gave Sheperd carte blanche for the area. Sheperd opened the mines on a systematic basis and used the proceeds establish a fiefdom in the area.  He was very successful but used a large percentage of the profits to build himself a palatial residence and support a lavish lifestyle.  Sheperd died in 1902 and his sons took over until their world came to an end in about 1911 when Pancho Villa and company arrived in the area in search of silver and gold to support the Revolution.  The Sheperds refused to co-operate and Pancho devastated the area, including the hydroelectric plant which drove the pumps that kept dry the deep workings where mining was focused by that time.  Pancho and company did work the nearby Cerro Colorado deposit for gold which made it difficult for more than minor clandestine work to continue at Batopilas.  An attempt was made to put the mines back into production after the Revolution, but the destruction of the power plant made it impossible to pump out the deep workings.  It is believed that these efforts were directed to pillar and offshoots in the parts of the veins above the water table.  Sheperd’s son attempted to revive interest in the district in 1935 but was unsuccessful.  There are almost no production records for the period 1920-1975 so it is reasonable to infer that whatever work was undertaken during this period consisted of minor high-grading.  In the late 1970s-early 1980s,  miners reopened the New Nevada Mine and hit a high-grade breccia pipe which yielded a significant amount of native silver.  This work ended when the bottom dropped out of the silver market in 1983, leaving the lower extension of this body untouched.  An under-funded, but well-directed program in the early 1980s drove into the hangingwall of the Roncesvalles Fault-Vein and hit a vein carrying native silver ore.  This was the first discovery of mineralization in the hangingwall of this structure, but it was not systematically followed up.  No mining activity of note has occurred since 1983.    

NAICA (Chihuahua) – 1794 (first concession) – 1828 mining
The district was discovered in 1794 and small-scale mining occurred in 1828, but operations on the early oxide ores were limited to the “rainy seasons” because there was no water available.  In 1892 Compania Minera de Naica began commercial operations but suspended operations in 1911 as the mine reached the ground water level.  In 1954 the mine was acquired by the Fresnillo Company, and they erected a 400 ton/day sulfide processing plant to process sulfide ores discovered beneath the historic oxide zones.  By 1985 the mine was serviced by a 3,000 ton / day plant which has been expanded to produce approximately 100,000 tons per month by cut-and-fill mining techniques; recovering gold, silver, copper, lead, zinc and small amounts of tungsten and cadmium. 

BOLEO (Baja California South) – 1868
The Boleo was first exploited by the French El Boleo Company and produced 13.6 million metric tones of mineral containing 500,000 metric tones of copper.  The majority of the production occurred from 1886 – 1947, and the underground workings consist of nearly 600 kilometers of workings.  
 

25th Annual New Mexico Mineral Symposium - New Mexico Geology, v. 26, p. 128-129.

MINERALS OF THE QUESTA MINE, TAOS COUNTY, NEW MEXICO
Virginia T. McLemore and Virgil W. Lueth
New Mexico Bureau of Geology & Mineral Resources
New Mexico Institute of Mining & Technology
801 Leroy Place
Socorro, NM 87801

 The Questa Mine, Taos County, New Mexico, is a “Climax-type” porphyry molybdenum deposit. Recent development of the underground ore body and current studies of the rock piles, alteration scars and open pit have lead to the recognition of new minerals for the deposit. This presentation will highlight these new discoveries.

The deposit was first famous for collectable specimens of molybdenite and ferrimolybdite that were produced from old underground workings and the open pit that was abandoned in 1974. Minerals typically associated with the molybdenite mineralization include: fluorite, calcite, rhodochrosite (generally pale) and dolomite. As is typical of stockwork molybdenum deposits, these minerals typically were found in veins with limited amounts of open space and highly collectable minerals specimens were the exception.

New minerals discovered in the recent phase of mining breccia and vein type deposits in the underground workings include: beryl (aquamarine and emerald), anhydrite, celestine, and topaz. The greater abundance of open space in these deposits has lead to the discovery of a number of collectable pieces. In addition, exploration drilling has revealed significant tungsten mineralization, especially wolframite.

Geological Society of America - Cordilleran and Rocky Mountain Section Meeting 2004.

TRACING THE SOURCE OF FLUORINE IN THE FLUORITE MINERALIZATION OF THE SOUTHERN RIO GRANDE RIFT

Frederick Partey1, Elisabeth Widom1, Virgil Lueth2, Steve Lev3 John Rakovan1,
1Department of Geology Miami University, Oxford Ohio 45056.
2 New Mexico Bureau of Mines and mineral Resources, Socorro, NM 87808.
3 Department of Physics, Astronomy, and Geos. Towson University, Towson MD 21252

The Rio Grande Rift (RGR) is rich in fluorite mineralization, especially associated with Mississippi valley type (MVT) barite-galena deposits. The high abundance of fluorine deposits is anomalous but is similar to other anomalous MVTs such as the Illinois-Kentucky fluorspar district. We are in the process of testing two hypotheses for the origin of fluorine in the RGR MVT deposits, a.k.a Rio Grande rift type (RGRT) deposits. These include release of gaseous HF from magmas associated with rifting, and remobilization of fluorine from the Precambrian granites of the basement rocks that underlie the Pennsylvanian limestones, which host much of the mineralization in the region.

In this study chlorine is being used as proxy for determining the source of the fluorine because chlorine, unlike fluorine, has more than one isotope and can be used as an isotopic tracer. Chlorine and fluorine exhibit chemically similar behavior, and therefore are likely to be derived from the same source. Samples of fluorite from seven RGRT deposits, as well as granites, basalts and limestones were collected throughout the southern RGR. Chlorine is isotopically distinct in the two hypothesized potential reservoirs (d37Cl mantle~+4.7‰; crust 0‰), therefore it should be possible to distinguish between crustal and mantle sources of chlorine (Banks et al., 1999). Complimentary to chlorine isotopic studies, Sr, Nd and Pb isotopes and Br/Cl ratios are also being applied as additional tracers.

Preliminary results indicate that the fluorites have 87Sr/86Sri = 0.7314-0.7353, distinctly more radiogenic than local basalts (~0.7036) and carbonates (0.7266-0.7293). The radiogenic character of the fluorites indicates that the Sr was derived largely from a granitic source, possibly through interaction of the mineralizing fluids with the pre-Cambrian basement granites.
 
Reference

Banks, D.A., et al., Chlorine isotopes in fluid inclusions: Determination of the origins of salinity in magmatic fluids. Geochimica Et Cosmochimica Acta, 1999. 64(10): p. 1785-1789.

SULFURIC AND HYDROFLUORIC ACID SPELEOGENESIS ASSOCIATED WITH FLUORITE-JAROSITE MINERALIZATION ALONG THE RIO GRANDE RIFT, NEW MEXICO.

¹LUETH, Virgil W. and ²RYE, Robert O. 
 ¹New Mexico Bureau of Mines & Mineral Resources, New Mexico Institute of Mining & Technology, Socorro, NM 87801
 ²United States Geological Survey, Denver Federal Center, Denver, CO 80225

Caves associated with fluorite-jarosite mineralization in the Hansonburg and North Franklin Mountains districts may have formed from different solution types. These caves display spongiform and irregular walls and contain significant amounts of halloysite clay.
The caves at Hansonburg are mineralized and large masses of gypsum contain mineralized limestone rafts and textures indicating limestone replacement. The low d³⁴S values of gypsum (–7.2‰) and jarosite (– 25 ‰) are similar to those for gypsum and alunite, respectively, at Carlsbad Caverns, New Mexico and also to those of hydrothermal pyrite (-23‰), consistent with cave formation during ore deposition. The aqueous sulfate that formed jarosite and some of the primary gypsum was likely derived from the oxidation of isotopically light H₂S. Some of the later cave fill gypsum at Hansonburg has high d³⁴S values (6.5 to 13.9‰) indicating aqueous sulfate derivation from the overlying Permian formations.
The cave at the Copiapo deposit in the North Franklin district is unmineralized and is located below the level of ore, a feature commonly observed in the Illinois-Kentucky fluorspar district. The presence of prosopite, CaAl₂(F,OH)₈, and fluorite in the halloysite envelope around the deposit attest to the high F activity in the earliest mineralizing solutions. Exceptionally low d³⁴S values for some of the jarosite (~-25‰) and gypsum (-11‰) also indicate that aqueous sulfate formed from isotopically light H₂S, as it did at Hansonburg and Carlsbad. However, the occurrence of the cave below the level of jarosite formation, suggests that the fluids from depth were already acidic before H₂S was oxidized at higher levels that implies cave formation by hydrofluoric acid speleogenesis.
 
 

THE CHESS DRAW DEPRESSION, OTERO CO., NEW MEXICO: A HYDROTHERMALLY- ALTERED, SUBLACCOLITHIC, ALKALIC SYSTEM
Philip C. Goodell¹, Virgil W. Lueth² and Tina C. Willsie^3
1Department of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968
²New Mexico Bureau of Geology & Mineral Resources, Socorro, NM 87801
³814 Avon Rd., Oakdale, CA 95361

   The Tertiary alkalic intrusives of the Cornudas region of west Texas and southern Otero County, New Mexico, represent reasonable exploration targets rare earth elements, beryllium, and other metals. Erosionally resistant, unaltered intrusives are prominent on the landscape and have been extensively studied. This report presents data indicating that other portions of the intrusive complexes are also present in the region, but they form physiographically negative features. Three drill holes into the Chess Draw Depression, northwest of Wind Mountain, provide the evidence for the interpretation that Chess Draw is an example of a negative topographic feature caused by extensive hydrothermal alteration. 
 

23rd Annual New Mexico Mineral Symposium - New Mexico Geology, v. 24, p. 133.

RED GARNETS FROM LAKE JACO, MEXICO AND THE CHEMICAL CONTROLS OF COLOR IN GRANDITE SERIES GARNETS
Virgil W. Lueth
New Mexico Bureau of Geology & Mineral Resources, Socorro, NM 87801

 A recent find of garnets from the famous grossular garnet locality near Lake Jaco, on the Chihuahua-Coahuila border is unique for the bright red color exhibited by the specimens. The geology of the area and petrology of the rock types involved are not exceptionally unique for skarn type garnets of the grossular-andradite (grandite) series. These garnets typically exhibit colors ranging from pure white (grossular) to dark brown (andradite). Most grandite garnets are typically greenish in color and intermediate in composition. Occasionally andradite garnets are black (a variety known as melanite) when they contain significant amounts of titanium. Red colors are typically observed in pyrope-almandine-spessartine (pyralspite) series garnets and up to now, never observed in the grandite series. Pyralspite series garnets are never observed in skarn environments.

A detailed geochemical study of the garnets was undertaken to determine the cause of the red coloration using petrography and electron microprobe microanalysis. The cores of the garnets are typically black and contain elevated concentrations of titanium (up to 4.5 wt. %) consistent with the andradite (Ad15-29) variety of melanite. The immediate layer adjacent to the black core is white grossular. Minor variations in Ca and Fe indicate increasing amounts of andradite component outward from the core. The red coloration in the Lake Jaco garnets is due to elevated concentrations of manganese, 1.0 to 1.7 wt. %, (Sp 1.6–3.7) in the latest stage of garnet growth with a distinct change toward more grossular-rich compositions. Geiger et al. (1999) determined the red coloration in these garnets is due to the presence of Mn3+ in the octahedrally coordinated silicate site using spectroscopic analysis. They postulate that the color is derived from a similar mechanism that causes the red color in the mineral piemontite of the epidote group.
 

23rd Annual New Mexico Mineral Symposium - New Mexico Geology, v. 24, p. 133-134.

GEOLOGY, GEOCHEMISTRY, AND HISORICAL SIGNIFICANCE OF NATIVE COPPER AT THE CHINO MINE, SANTA RITA, GRANT COUNTY, NM
Robert M. North¹ and Virgil W. Lueth²
1Phelps Dodge Chino Mines Company, Hurley, NM, 88043
2New Mexico Bureau of Geology and Mineral Resources, Socorro, NM 87801

 The occurrence of native copper at Santa Rita resulted in some of the earliest mining in the Southwest.  Native copper artifacts from a Georgia archeological site dated at 880 AD have been identified by trace element chemistry as being from Chino and a copper bell dated ca. 1150 AD has been excavated from a Mogollon site.  Spanish explorers came north from Mexico to explore the area beginning with Don Juan de Oñate in 1598.  The exact time when the Spanish gained knowledge of the deposit is unknown, but ca. 1795 Captain Francisco Martínez stationed at El Presidio de Carizal mentions “El Cobre” near Santa Lucia Springs as a “Criadero”.  A criadero or nursery (where minerals “grow”) was at the time considered a natural wonder, with such occurrences of metals reserved to the Spanish Crown.  Consequently, there was little incentive to develop such deposits of native metal “growing” from the soil until Jose Manuel Carrasco, a soldier stationed about 150 miles south of Santa Rita at El Presidio de Janos, took the initiative to develop the deposit in the early 19th century.  By about 1801 Carrasco had interested his friend Don Francisco Manuel Elguea, a wealthy and influential merchant from Chihuahua, in Santa Rita copper, resulting in contracts to supply copper for Mexican coinage by 1804.
 Native copper is common in the oxidation zone of porphyry copper deposits, typically forming near the top of chalcocite enrichment.  Here, copper in chalcocite is reduced to the native state with accompanying oxidation of sulfur to sulfate, as suggested by Lindgren from observation of Morenci ore, by the reaction:
Cu+12S + 3Fe+32(SO4)3+ 4H2O = Cu0 + 6Fe+2SO4 + 4H2SO4
Even though ferric iron is responsible for the oxidation of chalcocite in this geologic setting, little hematite is present associated with native copper in recent finds at Chino perhaps due to the relatively low pyrite content in this area of the pit.  Much of the native copper at Chino occurs in the Santa Rita granodiorite stock to the west and beneath retrograde skarn mineralization in a “roof pendent” in the East Pit area of the mine.  Shiny, flattened specimens were collected in 1998 from fractures in skarn hosted by the Syrena Formation, suggesting a change in pH rather than Eh is responsible for the deposition of native copper from solution. 
 The best native copper specimens occur in the stock and, in the most recent finds, intimately associated with alunite. Additional associated minerals at Chino include quartz, sericite, gypsum, and minor orthoclase.  Pyrite and hematite are present, but in relatively small amounts. Cuprite is often found as an oxidation product on the native copper as coatings and in crystalline form as cubes, octahedrons, and dodecahedrons.  Native copper has also been found recently in the South Pit area of the Chino mine as finely crystalline masses in fractures associated with chryscolla and the chalcotrichite variety of cuprite. 
 The main body of native copper mineralization in East Pit was first encountered at about 700 feet below the original surface at an elevation of 5650 feet.  The best specimens have been found sporadically between an elevation of about 5500 feet and the current pit bottom on the 5150 bench.   Mining was stopped in 2001 about 50 feet above the bottom of the native zone that produced the most recent nicely crystallized specimens.  Copper mineralization extends in an adjacent zone to about the 4750 elevation, a total vertical extent of 900 feet, but current plans include mining only to the 5000 elevation. 
 The NMBGMR Mineral Museum contains specimens from at least as far back as the early part of this century (C.T. Brown Collection). Additions to the museum collections over time provide us a potential chronology for the production of fine specimens from the mine. The earliest documented specimens are typically massive vein fillings of native copper. A few early examples consist of arborescent growths of crystals. Later specimens, often dominated by spinel and polycyclic twinning, were produced in the 1970 up into the early 1980’s. A discovery in late 1993 had some nicely crystallized copper and cuprite and included some unusual forms.  More recently, a single specimen mined in March 2001 was recovered from an inactive concentrator stockpile that yielded some spectacular crystalline specimens sold in early 2002.  Crystal forms include spinel twins, dodecahedrons, and modified cubes.  Often single specimens show differing crystal habits.  Some finely crystalline copper “wool” occurred on some specimens as a secondary crystallization. Additionally, many good examples of crystalline copper of good quality, but reasonably priced, were found in the area. Additional discoveries are anticipated when mining resumes.
 

23rd Annual New Mexico Mineral Symposium - New Mexico Geology, v. 24, p. 132-133.

THE COLORS OF SMITHSONITE: A MICROCHEMICAL INVESTIGATION

Patricia L. Frisch¹, Virgil W. Lueth¹, & Paul F. Hlava²
1New Mexico Bureau of Geology & Mineral Resources, Socorro, NM 87801
2Sandia National Laboratories, Dept. 1822 – MS 0342, Albuquerque, NM 87185

We analyzed four smithsonite (zinc carbonate or ZnCO3) samples with electron microprobes in an attempt to decipher the origins of the different colors. We examined samples that were blue-green (Kelly Mine, NM), yellow (Hanover, NM), blue-purple-pink with white bands (Sinaloa, Mexico), and green-yellow (79 Mine, AZ). Previous authors have proposed, with some geochemical evidence, that the green color of smithsonite is due to copper (Cu), the yellow to cadmium (Cd), and the blue to cobalt (Co). However, until now, no one has used modern microchemical studies to investigate the chromophores in smithsonite. 
 The Kelly, NM sample exhibits strong color banding that corresponds to a change in solid solution of CuCO3 in the ZnCO3, with higher CuCO3 contents (up to 3 wt.%) occurring in the strongly colored green bands. No mineral inclusions occur in this sample and there is little variation of the other minor elements present (Ca & Pb). Therefore we believe that Cu is the coloring agent in the green smithsonite from the Kelly Mine. 
 “Cadmian” smithsonite from the Hanover mine contains inclusions of pyrite (iron sulfide or FeS2) approximately 300 µm on a side, Fe-rich sphalerite [(Zn,Fe)S], and CdS (either hexagonal greenockite or isometric hawleyite). The CdS occurs in brightly colored bands which are approximately 10 µm thick and contain about 17% of these ~1 µm diameter inclusions.  In addition, up to 19.5 wt.% FeCO3 (iron carbonate) is present in solid solution. From this evidence we hypothesize that both CdS inclusions and Fe in solid solution are the coloring agents in yellow smithsonite from this mine.
 The pink/purple-blue smithsonite sample from Sinaloa, Mexico contains Cu and Cd but no Co!  In addition to our work, others have found that pink “cobaltian” smithsonite lacks cobalt. Thus, the term “cobaltian” smithsonite should be abandoned. Linescans across the color zones show that CuCO3 is high in the purple-pink regions (1.5 wt.%) and even higher (3 wt.%) in the blue zones. Solid solution CdCO3 concentrations are fairly uniform at 1 to 1.5 wt.% in both blue and purple zones of the mineral. The coloring agents in this sample appear to be Cu and Cd but because CdCO3 is colorless, the Cd is not coloring the smithsonite directly but it must be altering the way Cu colors the mineral.  Where the copper concentration is highest, the smithsonite is blue instead of green.  As the concentration of Cu gets lower, the color goes to purple/pink in the presence of Cd. White zones are due to abundant inclusions of hemimorphite.
 The green smithsonite from the 79 mine, AZ, contains inclusions of hemimorphite, aurichalcite, and a Mn + Cu oxide and CuCO3 and MnCO3 in solid solution. The inclusions are up to 1 mm in size and are present mainly at the edges of the material. CuCO3 and MnCO3 have the greatest concentrations (up to 1.7 and 2 wt.%, respectively) of solid solution impurities and the strongest variation. The copper concentration is not as high as in the blue-green smithsonite from Kelly material. The combination of lower Cu and the presence of Mn may therefore account for the lighter green and yellow color of this smithsonite sample. 

Acknowledgements

Part of this work was supported by the US Dept. of Energy under Contract DE-AC04-94AL85000.  Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy.

Dr. Nelia Dunbar and Lynn Heizler (NMBG&MR) assisted with the electron microprobe analysis. The Cameca SX-100 electron microprobe at the New Mexico Institute of Mining & Technology was partially funded by the National Science Foundation, Grant STI-9413900. 
 

A GEOLOGIC MEMBRANE - MICROBIAL METABOLISM MECHANISM FOR THE ORIGIN OF THE SEDIMENTARY COPPER DEPOSITS IN THE PASTURA DISRICT, GUADALUPE COUNTY, NEW MEXICO

V. W. Lueth1 and T. M. Whitworth2
1New Mexico Bureau of Mines and Mineral Resources, 
New Mexico Institute of Mining & Technology, Socorro, NM  87801, vwlueth@nmt.edu
2Department of Geological & Petroleum Engineering, 
University of Missouri-Rolla, Rolla, MO  65409, mikew@umr.edu

  Examination of copper deposits in Pastura district shows that mineralization occurred at the sand/shale interface.  Mineralization was greatest adjacent to the thinnest shales and decreased with increasing shale thickness, becoming non-existent adjacent to the thickest shales.  This pattern of mineralization is consistent with geologic membrane effects that can occur in shales and clays in the subsurface.  We propose a conceptual model invoking solute-sieving effects to help explain the observed mineralization in the copper deposits in the Pastura district. We suspect that the role of the membrane-functioning shales was to concentrate the copper and the dissolved nutrients necessary for metabolic-functioning of sulfate reducing bacteria in “layers of increased solute concentration,” usually called the concentration polarization layer (CPL), adjacent to the shales.  The sulfate-reducing bacteria, as a part of their metabolic process, produce H2S, which precipitated the copper sulfides.  Experimental studies have demonstrated that the CPL can range from several to more than 100 times that of background concentrations within the aquifer.  Flux magnitude through shale is inversely proportional to its thickness and strongly affects CPL development.  For any given solute, there is a threshold flux value that must be exceeded before rejected solute becomes unable to effectively back diffuse into the reservoir.  Therefore, thick shales (with correspondingly low flux rates) typically do not form a CPL.  This physical fact corresponds with the field observation that the sands adjacent to the thicker shales in the Pastura district are not mineralized.  Our model explains why copper mineralization is localized in proximity to thin shale units and is not ubiquitous in the host rock

AGE OF HYDROTHERMAL MANGANESE MINERRALIZATION IN THE LUIS LOPEZ MANGANESE DISTRICT DETERMINED BY 40/39Ar DATING OF CRYPTOMELANE

Virgil W. Lueth, Lisa Peters and Richard Chamberlin
New Mexico Bureau of Mines & Mineral Resources, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87808-4796, vwlueth@nmt.edu

   Cryptomelane, KMn8O16, samples from the Nancy and MCA mines in the Luis Lopez manganese district were collected from a similar paragenetic stage of mineralization at both mines. The hydrothermal characteristics of these deposits have been documented by previous workers using fluid inclusion and stable isotope analysis. Cryptomelane precipitation occurred at the onset of calcite mineralization following banded manganese ore deposition. Both samples consisted of arborescent growths of acicular crystal bundles projecting into calcite. Composition and sample purity were confirmed by x-ray diffraction analysis.  40Ar/39Ar dating of cryptomelane at the MCA mine yielded well-behaved age spectra with a weighted mean age of 6.31 +/- 0.08 Ma. Age spectra from Nancy mine cryptomelane reveal a pattern suggestive of argon loss in the first 25% of 39Ar released during heating of the sample. A minimum age of 6.03 +/- 0.08 Ma for cryptomelane precipitation is calculated from the remaining 75% of the age spectrum. The 40Ar/39Ar apparent ages fall within the bracket of ages (3 to 7 Ma) proposed from geologic age relationships in the district by previous workers. Cryptomelane has previously been used to successfully date residual manganese deposits and manganiferous soil horizons in laterites by the 40Ar/39Ar method. This study demonstrates that the dating of hydrothermal manganese mineralization by this technique is accurate with respect to the geologic time constraints observed in the district.
. 
 

HYDROTHERMAL “SOUR GAS” JAROSITE: ANCIENT AND MODERN ACID SULFATE MINERALIZATION EVENTS IN THE RIO GRANDE RIFT
Topical Session T-37: Sulfate Minerals I. Hydrothermal Systems ( A Tribute to Robert O. Rye).

1LUETH, Virgil W., 2RYE, Robert O., AND 1PETERS, Lisa
1NMBGMR, New Mexico Tech, Socorro, NM 87801, vwlueth@nmt.edu
2United States Geologic Survey, Denver Federal Center, Denver, CO 80225

Fluorite-barite-jarosite deposits occur along the Rio Grande rift from central New Mexico to near Chihuahua, Mexico. Jarosite occurs as a late stage hydrothermal mineral co-precipitated with fluorite following gypsum-hematite mineralization. These deposits range in age from 10 to 0.4 Ma based on 40Ar/39Ar dating of jarosite. The duration of hydrothermal jarosite mineralization in one of the deposits is approximately 1 Ma. The mineralizing fluids had calculated isotopic signatures and high trace element concentrations (notably As and F) similar to modern geothermal waters. d34S values of < -15‰ imply an organic or “sour gas” origin for precursor H2S that exchanged with SO4=.  Calculated ?DH2O, ?18OH2O, ?34S SO4, and ?18OSO4 of parent fluids for these sour gas jarosites (SGJ) reveal a spectrum of values ranging from values typical of meteoric water to deep basin brine.  ?D and ?18O values are typical of steam heated jarosites. Mixing of acidic geothermal water with oxidized groundwater containing dissolved Permian sulfate appears responsible for SGJ mineralization. The low pH necessary for the precipitation of jarosite resulted from the oxidation of H2S derived from the thermochemical reduction of SO4= and/or the thermal degradation of organic matter in the Paleozoic rocks during renewed rifting accompanied by the introduction of deep-seated HF.  Jarosite formed after the pH buffering capacity of the host rock (usually limestone) was neutralized by precipitation of earlier minerals. ?18OSO4-OH temperatures of jarosite formation range from 80 to 200 °C similar to homogenization temperatures in late stage fluorite. A homogenization temperature of 180°C was determined from fluid inclusions in jarosite from Mexico. Sour gas jarosites encode a record of tectonic, hydrologic, and geomorphic processes that have operated in the rift over the last 10 Ma years. Models for sour gas jarosite mineralization have immediate application to the understanding of geologic controls on water resources, water quality, mineral exploration, paleoclimate, uplift rates and public health issues in this rapidly growing population corridor.

mineralization, jarosite, geochronology, stable isotopes, rift

THE ORIGIN AND NATURAL DESTRUCTION OF AN ORE DEPOSIT AS RECORDED BY JAROSITE: HANSONBURG MINING DISTRICT, NEW MEXICO.
Topical Session T-38: Sulfate Minerals II. Low-Temperature Environments

1LUETH, Virgil W., 2RYE, Robert O., AND 1PETERS, Lisa
1NMBGMR, New Mexico Tech, Socorro, NM 87801, vwlueth@nmt.edu
2United States Geologic Survey, Denver Federal Center, Denver, CO 80225

The Hansonburg galena-barite-fluorite deposits contain two types of jarosite based on occurrence, age, and stable isotopic characteristics: 1) an early hydrothermal jarosite that co-precipitated with fluorite and 2) two supergene (weathering) occurrences. The oldest jarosites encode the conditions of late stage hydrothermal mineralization localized in Pennsylvanian limestone. Younger jarosites record the timing and climatic history of the natural destruction of the deposit on the margin of a rift-related uplift. Hydrothermal jarosite occurs as a coating associated with purple fluorite and as late stage inclusions in blue-green to purple fluorite and quartz. Hydrothermal jarosite is characterized by 40Ar/39Ar apparent ages of 6.25 ± 0.1 to 6.54 ± 0.9 Ma and a wide range of negative ?34S values (-15 ± 6). ?D values also vary widely (-150 to -133). ?34S and ?18OSO4 values display strong covariance. The data suggest the jarosites formed by the mixing of geothermal brines containing H2S derived from Paleozoic sedimentary rocks with shallow oxidizing ground water containing Permian sulfate. Initial silicification effectively insulated later hydrothermal fluids from pH buffering by the host limestones and allowed for jarosite formation. The earliest episode of supergene jarosite formation is associated with complex copper sulfate minerals that are unusual for a carbonate hosted galena-fluorite-barite deposit. Jarosite with copper sulfate yield 40Ar/39Ar apparent ages between 3.43 ± 0.22 to 3.66 ± 0.48 Ma. ?34S values are uniform and cluster about -10‰. We speculate that the influx of copper accompanying extensive oxidation of the deposit was coincident with the weathering of the juxtaposed overlying Permian Abo Fm. containing red bed copper mineralization. A later supergene event (2.42 ± 0.02 to 1.63 ± 0.06) reflects surficial weathering characterized by positive ?34S values in jarosite similar to the pyrite precursor. ?D values in these jarosite increase over the last 3.5 Ma suggesting a warming and drying of climate during supergene mineralization similar to that reported in the Creede district 300 miles to the north.

mineralization, jarosite, geochronology, stable isotopes, paleoclimate

SYSTEMATIC VARIATION IN GALENA SOLID SOLUTION COMPOSITIONS AT SANTA EULALIA, CHIHUAHUA, MEXICO

Virgil W. Lueth1,  Peter K.M. Megaw2, Nicholas E. Pingitore3, and Philip C. Goodell3
1New Mexico Bureau of Geology and Mineral Resources, Socorro, NM  87801. vwlueth@nmt.edu
2IMDEX, Inc., Tucson, AZ  85728
3Department of Geological Sciences, University of Texas at El Paso, El Paso, TX  79968

 Argentiferous galena is the main silver-bearing phase at both the East and West Camps of the Santa Eulalia District, Chihuahua, Mexico. The silver occurs as a coupled substitution of Ag and Sb for Pb in PbS with compositions ranging from 0.04 to 5.9 atomic percent (at. %) Ag and 0.10 to 7.2 atomic percent Sb.  Correlation analysis between Ag and Sb resulted in r-values of 0.97 and 0.99 (significant at the 98% confidence level) for direct-current plasma – atomic emission spectroscopy (DCP-AES) and microprobe analysis of galena, respectively. Discrete and crystallographically oriented inclusions of diaphorite (usually 1 ? or smaller) were common in high silver/antimony galenas and rare in low silver types (when present, tend to be larger). These inclusions were most abundant in the core zones of the crystals and rare on the edges.
 Spatial and temporal variations in Ag-Sb concentrations and ratios in galena were found, mainly in the West Camp of the district.  High-silver galenas (maximum 5.9 at. %) are confined to skarn zones or deep manto and chimney areas.  The Ag:Sb ratio increases in galena from depth (0.88) to the surface (1.04) and from south (0.76) to north (0.94), following zonation and flow patterns established in previous investigations. Differences in Ag-Sb substitution in galena are also seen in different mineralization types: breccia zones, deep mantos and chimneys contain more Ag-Sb (3.5 at. % avg.) and have lower Ag:Sb ratios (avg. ratio = 0.88) than the upper mantos, silicate and calc-silicate orebodies, which have lower Ag-Sb concentrations (2.2 avg. at. %) but higher ratios (avg. ratio = 1.00).
 Silver and antimony substitution also correlates with sulfur isotope variation in the district.  Within individual orebodies, the del34S value increases with decreasing silver and antimony concentrations in galena.  The solid-solution compositional variations in galena coupled with sulfur isotope values are a useful tool for inferring fluid paths and appear to reflect fluid evolution.
At Santa Eulalia, silver is “disseminated” to various degrees throughout the ore bodies and galena solid solution concentrations appear to be controlled by subtle physical and/or chemical gradients. This contrasts with volcanic-epithermal systems in which significant physiochemical perturbations (large thermal and pressure gradients, boiling, etc.) lead to “dumping” of precious metals and semimetals as sulfosalts in bonanza zones. Relatively low concentrations of other potential ore-forming elements, namely copper and bismuth, also precluded the formation of a complex suite of silver sulfosalts and antimonian-argentiferous galena precipitated instead.  Sulfosalts at Santa Eulalia are localized to upper mineralized zones as breccia void fillings, indicative of limited zones of boiling.

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GEOLOGY AND MINERALOGY OF THE FIERRO AREA OF THE HANOVER-FIERRO MINING DISTRICT, GRANT COUNTY, NM:

Robert M. NORTH, Phelps Dodge Chino Mines Company Hurley, NM, 88043 & Virgil W. LUETH, Ph.D. New Mexico Bureau of Geology and Mineral Resources, Socorro, NM 87801

 The Hanover-Fierro (H-F) mining district extends from the community of Hanover north to mines in Shingle Canyon, northeast of the Continental mine. The host-rock stratigraphy consists of Paleozoic limestones, dolomites, and shales, overlain by Cretaceous siliceous sedimentary rocks, capped by mid-Tertiary volcanic rock.  The most important ore hosts are the Pennsylvanian Oswaldo Formation and the Mississippian Lake Valley Formation. Limestones in the Ordovician El Paso Formation also host chalcopyrite skarn. Late Cretaceous quartz diorite sills and Tertiary dikes intrude the stratigraphic section, with little or no associated mineralization.
 The major structural features of the district are the contacts of the stock and the Barringer fault zone, located near the northern end of the H-F stock near the community of Fierro.   The Barringer fault, which pre-dates the stock and mineralization, is a major feature that forms the northwestern edge of the Santa Rita horst.  The fault strikes north 75 to 80 deg. east, dipping steeply northwest on the west side of the stock, changing to a strike of about north 30 to 40 deg. east dip of 60 to 75? northwest to the northeast of the stock.  Displacement to the west is about 1600 feet, and 1400 feet on the northeast.  In the area of Hanover Mountain, the fault juxtaposes the Cretaceous Colorado Formation with the Paleozoic Lake Valley and Percha Formations, indicating about 1400 feet of displacement. The fault zone acted as an important conduit for mineralizing solutions in the district.  The important stock contacts run north-south on the east and west sides of the stock where the Paleozoic rocks have been domed by the force of the intrusion.  In the Fierro area, the lower Paleozoic rocks on the footwall of the Barringer fault and on the east side of the stock dip steeply (+80 deg.) to the east.  Upper Paleozoic rocks on the hanging wall of the Barringer on the west side of the stock dip more gently (20 to 25 deg.) while lower Paleozoic footwall rocks dip more steeply, especially near the stock contact (+60deg.).
 Copper mineralization in the Continental mines (open pit and underground) near Fierro is in skarns associated with the 57 Ma H-F granodiorite stock.  A large quartz-sericite-pyrite (QSP) hydrothermal alteration event involving large amounts of meteoric water did not occur at Hanover-Fierro as was the case at Santa Rita and Tyrone.  As such, the district has little supergene enrichment.  Most primary copper at H-F is hosted in skarns within the Paleozoic limestones and to a lesser extent, dolomites around the north end of the stock.  The skarns did not undergo a strong retrograde alteration event.  The differences between Santa Rita and H-F suggest a deeper level of emplacement for the Hanover-Fierro stock.  Weak to moderate QSP alteration is present in the Colorado Formation at Hanover Mountain which has resulted in the formation of a relatively small chalcocite enrichment blanket on the hanging wall of the Barringer fault northeast of the Continental pit.  The fault itself is also host of oxidized copper mineralization, most notably azurite roses from the Hanover #2 mine and a limited amount of turquoise.
 Iron skarns are common in dolomitic units of the lower Paleozoic section.  These units are in contact with the H-F stock in the middle stretches of the intrusive between the zinc deposits to the south and copper to the north.  The Fusselman and Montoya Formations are the most common hosts.  The iron occurs as magnetite, with much lesser specular hematite.  Copper as chalcopyrite has been produced from some of the iron mines from the El Paso Formation underlying the Fusselman and Montoya Formations.

AGE AND STABLE ISOTOPE GEOCHEMISTRY OF HYDROTHERMAL JAROSITE AT THE COPIAPO JAROSITE MINE, NEW MEXICO

1LUETH, Virgil W., 2RYE, Robert O., AND 1PETERS, Lisa
1New Mexico Bureau of Mines & and Mineral Resources, New Mexico Institute of Mining &Technology, Socorro, NM 87801, vwlueth@nmt.edu
2United States Geologic Survey, Denver Federal Center, Denver, CO 80225

The Copiapo jarosite deposit, mined for paint pigment in the 1920’s just north of El Paso, TX, occurs as a ~100 x 10 m vein in a north-south striking east dipping normal fault hosted by the Pennsylvanian Bishop Cap Limestone.  Mineralization is present as nested bands of variable thickness with the following paragenesis: 1) hydrated halloysite-prosopite-fluorite, 2) gypsum-hematite, 3) jarosite-fluorite, 4) natrojarosite-fluorite.  40Ar/39Ar age dating of jarosite and natrojarosite give apparent ages from 5.0 ± 0.12 to 4.5 ± 0.16 Ma, respectively.  del34S values for jarosite range from –22.8 in the main ore zone to –16.5 on the distal margins of the deposit where late barite has a value of 8.6.  ?34S values for gypsum show a similar pattern from –11.8 (ore zone) to 1.0 (margin).  del18OSO4 values of jarosite range 5.7 to 11.1 while most del18OOH values range from –4.8 to –0.9.  DeltaSO4-OH temperatures for jarosite average about 130°C.  ?18O values of hematite range from –3.4 to –1.9 in equilibrium with those for jarosite.  delD values of jarosite also vary from –146 for deep ore to –105 at the margin of the deposit.  Calculated delDH2O, del18OH2O, del34SSO4, and del18OSO4 of parent fluids are similar to modern geothermal and ground waters in the southern Rio Grande Rift and indicate mixing of acidic geothermal water with groundwater containing dissolved Permian sulfate.  The low pH necessary for the precipitation of jarosite resulted from the oxidation of H2S derived from the thermal degradation of organic matter during renewed rifting and introduction of deep-seated HF.  Jarosite formed after the pH buffering capacity of the limestone was inhibited by the precipitation of earlier minerals effectively insulating the vein. Copiapo is an end member of a series of fluorite-jarosite deposits that occur along the Rio Grande rift from central New Mexico to near Chihuahua, Mexico.  These deposits encode the record of tectonic, hydrologic, and geomorphic processes that have operated in the rift over the last 10 Ma years and continue to the present.  Information gained from the study of these deposits has immediate application to understanding geologic controls on water resources, water quality, and public health issues.

jarosite, hydrothermal, geochronology, stable isotopes, groundwater

THE APPLICATIONS OF JAROSITE GEOCHRONOLOGY AND STABLE ISOTOPE GEOCHEMISTRY TO ORE DEPOSIT GENESIS AND WEATHERING - SOME EXAMPLES FROM THE RIO GRANDE RIFT.

1LUETH, Virgil W., 2RYE, Robert O. and 1PETERS, Lisa
 1New Mexico Bureau of Mines & Mineral Resources, New Mexico Institute of Mining & Technology, Socorro, NM 87801
 2United States Geological Survey, Denver Federal Center, Denver, CO 80225

Jarosite, KFe3(SO4)2(OH)6, and other K-bearing minerals in the alunite group, can be dated by K/Ar and 40Ar/39Ar techniques and contain OH and SO4 groups that can provide four stable isotope analyses: delD, del18OSO4, del18OOH, and del34S. Age dating and analysis of these isotopic parameters can provide information on the genesis and natural destruction of the deposits by weathering.  This information in turn can provide insight into the climatic, geomorphic, and tectonic evolution of an area, as well as the hydrologic controls on present day water quality. A number of jarosite occurrences in the Rio Grande Rift have been studied and preliminary results are reported here.
Geochronologic and stable isotope studies of supergene jarosite are underway at the copper porphyry deposits in the Organ and Jarilla Mountains on the southeast margin of the rift. These studies are patterned after the work at Creede, Colorado, by Rye et al. (1993). Jarosite and alunite can be used to define the hydrogeochemical environment of supergene jarosite and alunite mineralization, record the age of paleowater tables, reconstruct climate, geomorphic, and tectonic history of the area. Sulfur isotopes trace sulfur to precursor sulfide sources. Hydrogen and oxygen isotopes can be used to infer climate changes during the course of supergene oxidation. The ages and distribution of jarosite and alunite in time and space define periods of uplift related to tectonic events.
An extensive geochronological and stable isotope study of jarosite at the Copiapo Mine, Dona Ana County, New Mexico has defined a new mode of occurrence - hydrothermal jarosite related to sour gas from sedimentary basins. Mineralization is hosted by a fault cutting Pennsylvanian-age limestone and consists of a replacement body with sequential deposition of halloysite, fluorite, prosopite, gypsum, hematite, jarosite and natrojarosite. 40Ar/39Ar age dates on hydrothermal jarosite and natrojarosite display a narrow range of apparent ages from 5.0 ± 0.12 to 4.5 ± 0.16 Ma with the natrojarosite consistently younger. Low sulfur isotope values for the jarosites (del34S = -16 to -24) indicate a basin-derived source of H2S with subsequent oxidation during mineralization.  Hydrogen (delDsmow = -64 to -96) and oxygen isotope (del18Osmow = -4 to -10) values of parent waters indicate an exchanged meteoric water origin typical of basin derived brines similar to the deep saline groundwaters found in the basins today.  Calculated temperature of formation, from the fractionation of 18O between the SO4 and OH sites in many of the jarosites, is approximately 130º C.
Analysis of jarosite from the Hansonburg deposits, Socorro County, New Mexico, reveals a range of apparent ages from 7.9 ± 0.85 Ma to 1.63 ± 0.06 Ma.  Each specific age of jarosite mineralization contains a unique mineral paragenesis and distinct stable isotope signatures. Both hydrothermal and supergene jarosites are present.  Hansonburg, Copiapo and many other jarosite-bearing deposits along the rift contain abundant hydrothermal fluorite suggesting that they have fundamentally similar origins controlled by tectonic events, climate and the evolution of brines and sour gas in sedimentary basins.

Reference:
Rye, R.O. Bethke, P.M. Lanphere, M.A., and Steven, T.A.. 1993, Age and stable isotope systematics of supergene alunite and jarosite from the Creede mining district, Colorado: implications for supergene processes and Neogene geomorphic evolution and climate of the southern Rocky Mountains: Geological Society of America Abstracts and Programs, v. 25, p. A-274

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A FLUID INCLUSION STUDY OF GEODES FROM RIO GRANDE DO SUL, BRAZIL: IMPLICATIONS FOR THE ORIGIN OF QUARTZ GEODES

LUETH, V. W. 1 and GOODELL, P. C.2, 1New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801, vwlueth@nmt.edu, 2Department of Geological Sciences, University of Texas at El Paso, El Paso, TX  79968, goodell@utep.geo.edu

Two types of quartz geodes are recognized from the Parana basalts of the Rio Grande do Sul region of Brazil. Mineralogic, morphologic, and fluid inclusion characteristics differentiate the two types although they are of similar size and shape.
   One group of geodes is characterized by dark gray to black exterior chalcedony and with particular chaledony-quartz stratigraphy. The stratigraphy from rim to center consist of: a rim of opal-C, often with a coating of heulandite; translucent gray chalcedony; flame-shaped milky white chalcedony that grows from the rim area and becomes prevalent toward the center; microcrystalline quartz; drusy quartz. Dark geodes contain pyrolusite and hollandite with variable textures ranging from large euhedral single crystals to acicular sprays and tufts. Fluid inclusion homogenization temperatures are low (less than 40? C) and salinities range between 0.0 and 0.7 weight percent equivalent NaCl.
   The other group of geodes is characteristically light-colored. The stratigraphy of these geodes is: opal-C outer layer (with no heulandite); white to yellow chalcedony; white chalcedony (distributed similarly to the dark geodes); microquartz; drusy quartz. Light-colored geodes have more abundant and coarser grained quartz, i.e., chalcedonic material is absent some samples. Manganese oxide mineralogy is limited to sparse, bladed pyrolusite crystals covered by drusy quartz. Fluid inclusion homogenization temperatures in quartz range between 140 to 175?C with low salinities (0 to 0.7 eq. wt. % NaCl).
   Based on the results of our study we infer the two populations of geodes formed as a result of different formation histories. The light-colored geodes may be the result of: 1) a hydrothermal heating event that occurred during or after geode growth or 2) deeper burial that lead to a greater degree of silica diagenesis.

Keywords: fluid inclusions, geodes, Brazil, quartz, chalcedony

“SCIENCE AND SERVICE,” THE New Mexico Bureau of Geology and Mineral Resources – MINERAL MUSEUM, SOCORRO, NEW MEXICO, USA

LUETH V.W. and Eveleth, R.W. (NMBGMR,  vwlueth@nmt.edu)

“Science and Service,” the motto of the New Mexico Bureau of Geology and Mineral Resources, requires the Mineral Museum to be one of the most important educational outreach programs of the Bureau. In addition, staff at the museum conduct and publish geological, historical, and mineralogical research.
The museum was established essentially at the same time as the NM School of Mines in 1889. The collection has grown to over 12,000 pieces, much of which is mineralogical material from New Mexico. The New Mexico Bureau of Mines & Mineral Resources (NMBGMR) assumed responsibility for the collections in 1961 and built a museum facility. A newly remodeled facility includes a large display gallery, education/ demonstration room, clean and dirty preparation labs, and a secure warehouse. Minerals are electronically cataloged and completely accessible.
Educational programs for the public include museum tours, lectures both on and offsite, exhibitions at major mineral shows and sponsorship of the New Mexico Mineral Symposium (now in its 19th year). The museum has an annual attendance of over 10,000. There is no charge for admission. Educational tours for groups ranging in age from preschoolers to senior citizens are routinely conducted and generally number over 25 per year totaling some 1000 visitors.
Mineralogic materials are available for researchers worldwide with over 20 requests processed in the past five years. Museum staff members also conduct research projects on a wide variety of topics. The museum is home to the type material of santafeite and native selenium in addition to a large amount of material from New Mexico type localities.

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TWO DIVERSE ORIGINS FOR TURQUOISE IN THE OROGRANDE MINING DISTRICT, OTERO COUNTY, NEW MEXICO

LUETH, VIRGIL W. New Mexico Bureau of Mines & Mineral Resources, Socorro, New Mexico 97801

Turquoise, Cu2+Al6(PO4)4(OH)8•4H2O, occurs in two distinctly different geological environments in the Orogrande district, Otero County, New Mexico.  The two deposits are hosted in different rock types. Associated vein mineral and gangue assemblages are also variable between the deposits.  Turquoise also has distinctly different physical character at each deposit.  The individual features at each deposit suggest a different mode origin for the turquoise.
     Providence (a.k.a. DeMueles) mine area -  The Providence mine is located near the terminus of an old railroad grade near the Cinco de Mayo and Iron Duke iron skarn deposits.  The turquoise is hosted by altered quartz monzonite.  The quartz monzonite represents the main stage plutonism in the district.  Alteration assemblages typical of porphyry copper systems are present.  The dominant hydrothermal alteration stage is quartz-sericite with a superimposed weathering assemblage of kaolinite and limonite (jarosite).  The turquoise occurs as vein fillings and nodules in veins.  Most of the material on the surface of the dumps is faded.  Freshly broken fractures containing  turquoise and unfaded material on the dump is deep sky blue.   The material tends to be thin but hard. Associated minerals are limited and consist mainly to kaolinite and mixed iron oxides (limonite) with minor gypsum.  On the margins of mineralization the turquoise grades into jarosite veins. This feature is similar to the reported turquoise occurrences at Hatchita, New Mexico.
     Iron Mask mine area - The Iron Mask mine approximately halfway between the Lucky and the Cinco de Mayo mines.  Most of the mining in this area was for iron, hosted in skarn and as large magnetite blocks cemented by caliche.  The turquoise deposits are immediately southwest of the Iron Mask workings.   Turquoise occurs as vein fillings and  nodules in a 7 meter thick shale unit within the Laborcita Formation (upper Pennsylvanian to lower Permian).  The most unusual feature of this deposit is the association of abundant gypsum and halite with the turquoise.  Most of the turquoise is chalky and light colored.  Occasional hard nuggets or veins are encountered but it is uncommon.  The material tends to be a lighter blue color than that from the Providence mine.  No turquoise was observed in rocks outside of the shale formation.   Jarosite and copiapite are found on the margins of turquoise mineralization as replacement masses.
     Three models have been presented for the origin of turquoise by previous investigators.  These models include: 1. Magmatic-related processes, e.g. hydrothermal alteration;  2. Contact metasomatic processes;  and 3. Weathering (supergene) related processes.  The geologic relationships and mineral assemblages suggest a weathering mode of formation for the turquoise at both deposits at Orogrande.
     At the Providence mine, weathering of disseminated pyrite and chalcopyrite in the monzonite porphyry lead to the formation of acid waters and provided a source of copper.  Percolating acid waters altered feldspar to kaolin and dissolved some aluminium.  The same acid waters weathered disseminated apatite as a source for phosphorous. The solutions were concentrated along fractures where the turquoise precipitated.  “Spent” solutions (lacking copper and phosphorus) precipitated jarosite and gypsum-goethite on the margins of the turquoise mineralized area.
     A different weathering model is required for the turquoise deposits at the Iron Mask locality.   Pyrite replacement deposits occur above and in the upper portions the host shale.  The oxidation of these pyrite deposits (which show copper staining) lead to the formation of acid-sulfate waters.  The acid sulfate waters percolated along fractures and through the shale and reacted with collophane-rich (probably carbonate-hydroxyapatite, Ca5(PO4,CO3)3(OH), since fluorite was not observed) zones to form the turquoise.  The abundance of gypsum is an artifact of the acid sulfate alteraton.   The presence of jarosite and copiapite on the margins of the shale are also reaction products of the pyrite oxidation.

LAZULITE OCCURRENCES IN SOUTHERN NEW MEXICO

1Phillip C. Goodell, 2Virgil W. Lueth and Mark Gresock
1UT El Paso, El Paso, TX  79968
2NMBGMR, Socorro, New Mexico 97801
 

During the end of the last century, a time of intense exploration in New Mexico, remote areas of the territory were reached by prospectors and more exotic resources were encountered.  One of these was recorded by Carrera (in Prince, 1891):  “There is said to exist up in the craggy peaks of the eastern slopes of the Organ Mountains large bands of lapis lazuli, a very valuable stone, made so both by its extreme rarity and matchless beauty.”  Farther east, in the Sacramento mountains around 1904, an unusual blue-banded stone was quarried for building stone.  The rock did not hold up to weathering and quarrying halted.  In both cases the blue mineral was mis-identified and its significance unexplored.

The location of the lapis lazuli (lazurite (Na,Ca)7-8(Al,Si)12(O,S)24 [(SO4),Cl2,(OH)2]) in the Organs was never properly reported in Prince (1891) and was repeated by Northrop (1944). When the area was mapped in some detail, Seager (1981) reported azurite present near the contact of the Granite of Granite Peak with a roof pendant.  Suspicious of the these early reports, the area was explored and lazulite MgAl2(PO4)2(OH)2, not lazurite or azurite, was found.  The lazulite occurrence in the Sacramento Mountains was mapped in detail by the United States Geological Survey during the White Mountain Wilderness study, but lazulite was not identified.  It was recently recognized during a reconnaissance geological trip.

In the Organ Mountains lazulite occurs in veins with muscovite (occasionally a dense blue-green variety), quartz, hematite, and jarosite hosted by a sericitized tuffaceous sandstone.  The lazulite occurs in a roof pendant in close proximity to a pyritized zone within the granite of Granite Peak, the latest stage of granitic plutonism recognized in the Organ batholith.  A red unidentified mineral is also associated with the lazulite.

At the Sacramento Mountains occurrence in Bluefront Canyon, the lazulite occurs in an altered quartzite.  The rock contains corundum (v. sapphire) and alunite in addition to the quartz.  The lazulite and corundum occur in bands which appear blue.  The light colored bands consist mostly of quartz.  The blue bands of lazulite have reaction rims on their margins.

The origin of the lazulite is still under study.  The geologic and mineralogic relationships suggest  phosphate metasomatism associated with late stage crystallization of a granitic magma gave rise to the lazulite veins.   However,  alteration of a phosphate-rich host rock is also possible.  Porphyry-type molybdenum mineralization is in close proximity in both instances.

40Ar/39Ar AGE  AND ORIGIN OF JAROSITE MINERALIZATION AT THE HANSONBURG DISTRICT, NEW MEXICO

LUETH, VIRGIL  W., and HEIZLER, MATTHEW T., New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801, vwlueth@nmt.edu and matt@nmt.edu
Jarosite [K2Fe63+(SO4)4OH)12] is formed in oxidized portions of sulfide ore deposits, precipitated as a primary mineral in some thermal springs and also as result of the production of H2S from organic matter.  Jarosite occurs late in the ore mineral paragenesis at the Snake Pit, Royal Flush, Mex-Tex, Portales, and Sunshine #2 mines where it coexists with fluorite, barite and quartz. Coarsely crystalline and euhedral jarosite is occasionally included in the quartz and fluorite. Petrologic and paragenetic relationships indicate the jarosite mineralization is hypogene.  Additional support for this hypothesis is seen in the paragenetic relationships displayed by the lead mineralogy.  The first formed lead mineral is galena (PbS) followed by anglesite (PbSO4) and finally by cerussite (PbCO3).  Mineral textures show sharp boundaries between galena and anglesite, characteristic of epitaxial overgrowth and not weathering.  The cerussite is probably of secondary origin.  The unusually diverse sulfate mineralogy at Hansonburg also suggests a possible “hypogene” oxidation event associated with the late stages of mineralization that resulted in the formation of complex sulfate mineral assemblage (anhydrite, antlerite, barite, beaverite, brochantite, caledonite, celestine, chalcanthite, creedite, corkite, cyanothrichite, goslarite, gypsum,  jarosite, langite, linarite, plumbojarosite, serpierite, spangolite, tsumebite). Putnam (1983) modeled the mineralization at Hansonburg based on fluid inclusion compositions and determined  that early sulfide mineralization was followed by a sulfate stage caused by precipitation of sulfides or cooling of the mineralizing fluids.  The coarse grained, euhedral jarosite also formed during this late sulfate stage of mineralization.
     40Ar/39Ar geochronologic analyses were performed on hand-picked jarosite separates (confirmed by x-ray diffraction) by both CO2 laser and resistance furnace incremental heating techniques.  The jarosite from the Snake Pit deposit gave well-behaved plateau age spectra and high radiogenic yields.  The simple systematics provide precise ages ranging from 6.36±0.1 to 5.98±0.06 (2?) Ma and are significant regardless of the of the mode of origin for the jarosite at Hansonburg.
If the jarosite is hypogene, consistent with the geologic evidence, then the age represents the time of late stage sulfate mineralization at Hansonburg.  Compared to other jarosite-bearing deposits such as the Copiapo jarosite deposit  (40Ar/39Ar age = 5.0±0.3 to 4.6±0.06 Ma) at Webb Gap, New Mexico, the ages are similar and result from rift-related pulses of mineralization. Interpretation of the data suggests that basin dewatering and/or migration of H2S up boundary faults resulted in sulfide and sulfate (including jarosite) mineralization.  Accordingly, galena-fluorite-barite mineralization probably correlates to major episodes of rift activity.  If the jarosite mineralization is due to weathering, then the age represents a time of significant oxidation weathering of the Hansonburg deposits.  Such a period of weathering would be due to significant uplift on the margins of Oscura Mountains during the late Miocene.

40Ar/39Ar AGE OF RIO GRANDE RIFT TECTONISM IN THE NORTH FRANKLIN MOUNTAINS, WEST TEXAS AND SOUTHERN NEW MEXICO

GOODELL, P. C., Department of Geological Sciences, University of Texas at El Paso, El Paso, TX  79968, goodell@utep.geo.edu
LUETH, V. W.2, and HEIZLER, MATTHEW T., New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801, vwlueth@nmt.edu and matt@nmt.edu

A quantitative age of tectonic events in the Franklin and Organ mountains (FOM) has not been previously determined, other than documentation of recent faulting. The study area straddles the Texas-New Mexico border and lies near the central portion of the Rio Grande Rift.  The FOM stand in geomorphic disequilibrium with respect to their surroundings, which suggests a young age of uplift.
In the Webb Gap area of the North Franklin mountains, New Mexico, the Copiapo jarosite deposit lies in a east-dipping listric fault. The jarosite orebody is crossed by at least three post-mineral faults that display slickensides with southeasterly plunge orientations. A second deposit of galena-fluorite and barite, two kilometers to the north named the Schneider #7, lies in a comparable structural setting. The geometry, mineralogy, and paragenesis of the deposits exclude a secondary origin for the jarosite.
Jarosite (KFe(SO4)2(OH)6) has recently been determined to yield geologically significant  40Ar/39Ar apparent ages. Geochronologic analyses were performed on hand-picked  mineral separates (confirmed by x-ray diffraction) by a three-step laser incremental heating technique. Three samples of jarosite gave a high radiogenic yield and flat age spectra. The 40Ar/39Ar ages range from 5.0 +/- 0.3 (early jarosite) and 4.6 +/- 0.06 Ma (late natrojarosite-jarosite solid solution) at the Copiapo Jarosite mine to 3.28 +/- 0.08 Ma at the Schneider #7 galena-fluorite-barite deposit. Interpretation of the data suggests that basin dewatering and/or migration of H2S up boundary faults resulted in jarosite mineralization.  Jarosite and galena-fluorite-barite mineralization probably correlates to a major episodes of rift activity. Post-mineralization faulting indicates significant rift tectonism occurred after 3.28 Ma in the Webb Gap area.

mineralization, jarosite, fluorite, normal fault, rift basin

VARIATION IN GALENA SOLID SOLUTION COMPOSITIONS AT SANTA EULALIA, CHIHUAHUA, MEXICO - IMPLICATIONS FOR METAL ZONING

LUETH, V. W., New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801, vwlueth @nmt.edu,
MEGAW, P.K.M., IMDEX, Inc., Tucson, AZ  85728,
PINGITORE, N.E. and GOODELL, P.C. Department of Geological Sciences, University of Texas at El Paso, El Paso, TX  79968

Argentiferous galena is the main silver-bearing phase at both the East and West Camps of the Santa Eulalia district, Chihuahua, Mexico.  Silver occurs in galena as a coupled substitution of Ag and Sb for Pb. Analysis by electron microprobe and direct current plasma - atomic emission spectroscopy (DCP-AES) determined a nearly 1:1 correlation between silver and antimony concentrations in galena. A coupled substitution: Ag+ + Sb3+ ? 2Pb2+ maintains charge balance. No discrete crystals of silver-antimony sulfide minerals were identified in galena grains indicating a limited solid solution exists between galena and miargyrite (AgSbS2).
Variations in Ag-Sb compositions in galena are documented in the deposits.  Differences in Ag-Sb substitution are seen in different types of mineralization.  Breccia zones, deep mantos, and deep areas of chimneys contain higher amounts of Ag and Sb and have lower Ag:Sb ratios than galena samples from upper manto zones, silicate and calc-silicate orebodies which display opposite ratios.  In areas with recognized silver-antimony sulfosalts, silver and antimony solid solution in galena is limited.  An increase in the Ag:Sb ratio in galena is noted from depth to the surface and from north to south and varies similarly to patterns of zonation and flow established by Megaw (1990).
The compositional variations in galena, occurrence of sulfosalts, and Ag-Sb ratio variation with respect to depth suggests a physiochemical control on the solid solution. These variations do not appear to be related to temperature gradients inferred in the district. The substitution must be controlled by metal ion activities, namely Ag and Sb, and not by temperature.  Compositional trends exhibited by galena follow the isotopic zonation pattern and Ag:Pb ratios determined by Megaw (1990) and are probably related to distillation/residuum trends created by ore deposition from a systematically evolving fluid.

galena, solid solution , zoning, Santa Eulalia, Mexico