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Abstracts of the 24th Annual Tucson Mineralogical Symposium. (Minerals of the Andes).

Introduction

The 24th Annual Tucson Mineralogical Symposium, sponsored by the Mineralogical Society of America, the Friends of Mineralogy, and the Tucson Gem and Mineral Society, will be held on Saturday, February 15, 2003 at the Tucson Convention Center. Admission is free and everyone is welcome. "Gems and Minerals of the Andes" is the theme of this year's Tucson show and also the subject of the 2003 symposium.

The Andes Mountains are an enormous range comprising a variety of active tectonic environments that have given rise to some of the world's most important mineral deposits. Scattered among the thousands of miles of mountains are great batholiths and related stocks, cupolas, and skarns; active hot springs; mineralized red beds; and a variety of volcanogenic occurrences, all of which host one or more classes of mineral deposit. These include the phenomenal porphyry copper systems and historically important silver veins of Chile, the tin-silver vein systems of Bolivia, the polymetallic deposits of Peru, and Colombia's somewhat enigmatic emerald occurrences. The wide range of climates has resulted in wonderfully diverse zones of supergene enrichment and an array of curious surficial deposits that include lithium-rich brines and the famous nitrates of the Atacama Desert. Less well-known are the recently developed gold deposits of southern Peru, unusually rich near-surface gold associated with certain porphyry coppe r systems, and even peculiar gold deposits in the far southerly reaches of Chile's Punto del Fuego area.

Wonderfully productive Andean specimen occurrences are quite familiar to the mineral community, and visitors to the Tucson show will have ample opportunity to view an unusually wide suite of competitive displays and dealer stocks that illustrate the breadth of these deposits. The list of classic occurrences is quite long and includes emerald and parisite from Chivor, Muzo and nearby Colombian sites; hubnerite and rhodochrosite from Pasto Bueno, spectacular Huanzala pyrite, San Genero pyrargyrite; native silver and rhodochrosite from Uchucchacua, Peru; Bolivian localities such as Llaguagua and its variety of phosphates; Potosi phosphophyllite; tin sulfosalts from Oruro and Poopo; Quimsa Cruz wolframite and Japan-law twinned quartz; proustites from Chanarcillo, Chile; and the unusual suites of ore-related minerals from porphyry copper deposits such as Chuquicamata. Exciting recent discoveries include epidote and Japan-law twinned quartz from Pampa Blanca, Peru; danburite and boracite from the Alto Chapare distr ict, Bolivia; vivianite and ludlamite from Morococala, Bolivia; cassiterite from Viloco, Bolivia; and new minerals from Chile including szenicsite, lemanskiite, cristelite, and gordaite.

Despite the amazing mineral wealth of the Andes, English literature of interest to the mineralogist or collector (other than technical papers related to specific ore deposits) is relatively sparse. This is due, in part' to the predominance of the Spanish language in these countries and the locally confusing mix of indigenous Indian languages. Nevertheless, modem descriptive works focused on specimen and gem occurrences are beginning to emerge in such periodicals as Mineralogical Record (for example Crowley and others, 1997; Wilson and Petrov, 1999; and Petrov and Smith, 2001). These and slightly older works such as those of Cook (1975, 1978, and 1979) augment the classics of Ahlfeld and Munoz Reyes (1943), Bandy (1944) and Domeyko (1879) and are still available.

The papers presented at this year's symposium reflect both the great mining heritage of the Andes as well as the incredible potential for future discovery. They include descriptions of recent museum acquisitions and previously undescribed holdings, detailed accounts of classic localities, descriptions of unusual new occurrences, detailed species mineralogy, and chronicles of systematic mineral discoveries. They have all been prepared by persons with first-hand knowledge of a wide variety of the area's deposits, including many of those listed above, and include professors, geologists, curators, and professional mineral specimen collectors and dealers. Each talk will be illustrated with locality and specimen photographs, and each promises to be both enjoyable as well as informative.

REFERENCES

AHLFELD, F., and MUNOS REYES, J. (1943) Los Minerales de Bolivia. Published by Direccion General de Minas y Petroleo, LaPaz, 276 p.

BANDY, M. C. (1944) Mineralogy of Llallagua, Bolivia. LaPaz, 67 p.

COOK, R. B. (1975) Mineralogy of the Department of Oruro, Bolivia. Mineralogical Record, 6, 125-137.

COOK, R. B. (1978) Famous Mineral Localities: Chuquicamata, Chile. Mineralogical Record, 9, 321-333.

COOK, R. B. (1979) Famous Mineral Localities: Chanarcillo, Chile. Mineralogical Record, 10, 197-204.

CROWLEY, J. A., CURRIER, R. H., and SZENICS, T. (1997) Mines and Minerals of Peru. Mineralogical Record, 28, 1-98.

DOMEYKO, I. (1879) Mineralaojia. Liberia Central de Servat, Santiago, 760 p.

PETROV, A, and SMITH, B. (2001) A guide to the mineral localities of Bolivia. Mineralogical Record, 32, 457-482.

WILSON, W. E. and PETROV, A. (1999) Famous mineral localities:

Cerro Rico de Potosi, Bolivia. Mineralogical Record, 30, 9-36.

The Polymetallic Capillitas Deposit, Catamarca, Argentina

Fernando Colombo

Museo de Mineralogia y Geologia

"Dr. A. Stelzner" Facultad de Ciencias Exactas, Fiscas, y Naturales Av. Velez Sarsfield 299

(5000) Codoba, Argentina

The Capillitas deposit, located in Argentina's Catamarca province, has been the source of rhodochrosite for more than 50 years. It is noted for particularly fine rhodochrosite stalactites and massive banded rhodochrosite known as "Inca Rose." Capillitas, exploited since pre-Columbian times, is a sulfide-rich epithermal deposit with Cu, Pb and Zn ores that contain lesser amounts of As, Sb, Au and Ag. There are approximately 20 km of historical workings distributed throughout 18 levels; today only a small percentage of these is accessible.

In the area of the Capillitas deposit, volcanic rocks (rhyolite, porphyritic dacite, and rhyolitic and granitic breccias) form an elliptical, 900 x 1500-meter diatreme surrounded by a granitemonzonite belonging to the Capillitas batholith. K-Ar age dating of a dacite and a rhyolite gives ages of 5 [+ or-] 0.5 million years.

Capillitas is a polymetallic vein system composed of 19 veins up to 600 meters long. The veins form two sets which strike ENE and WNW, and dip 50[degrees]-70[degrees] or more towards the south. They are lenslike or tabular, with an average thickness between 50 and 70 cm.

More than 120 mineral species have been found at Capillitas. Rhodochrosite occurs rarely as euhedral rhombohedral crystals, isolated or in groups, up to 1 cm across. Its most common habit is as crusts formed by a large number of thin layers. Less frequently it can be found as masses with no banding and showing a distinctive reddish pink coloration (from the Ortiz vein). Straight or bent stalactites to more than 30 cm long and 8 cm in diameter were found in the 25 de Mayo vein. According to official statistics, the rhodochrosite output between 1951 and 1971 was 1,986 metric tons, with a maximum annual production of 309 tons in 1966; no production was reported for several years (e.g. 1952 and 1962-1964).

Llallagua, Bolivia: Mineral Associations and Habits Exhibited by Micromounts in the Collection of the National Museum of Natural History (Smithsonian Institution)

Robert B. Cook

Department of Geology and Geography

Auburn University, Alabama 36849

Paul Pohwat

Department of Mineral Sciences

U.S. National Museum of Natural History

Washington, DC 20560

The enormous tin deposit of Llallagua, Potosi, Bolivia, exploited by the famous Siglo XX mine, is historically among the best-known Andean mineral specimen producers, thanks in part to the efforts of such notable collector-scientists as Samuel Gordon (1922; 1924), Mark Chance Bandy (1944), and Federico Ahlfeld (1943; 1954). Phenomenal specimens of Llallagua purple fluorapatite, wavellite, stannite and the rarer tin sulfosalts, pyrrhotite. the vauxite family minerals (for which it is the type locality), wolframite, vivianite, wurtzite, complexly twinned cassiterite, and Japan-law twinned quartz are well-represented as miniature to cabinet-sized specimens in both private and museum collections the world over. Less well-known are the phenomenal suites of microminerals once available from the mine and still locally present to a limited extent on the surrounding dumps. A previously undescribed, generally representative collection of Llallagua micromounts is housed in the U.S. National Museum of Natural History, co nsisting in part of specimens contained in the Neal Yedlin collection. Of particular interest are assemblages such as rose-pink monazite-tourmaline-cassiterite-quartz; complexly twinned red greenockite with wavellite; childrenite with vauxite, paravauxite, and wavellite; wavellite with fluorapatite; and vauxite with metavauxite. Fine suites of pyrite, arsenopyrite, tetrahedritetennantite, wurtzite, stannite, vivianite, and cassiterite reflect a wide variety of crystal forms and habits.

REFERENCES

AHLFELD, F. (1954) Los Yacimientos Minerales de Bolivia. Bilboa, Imprenta Industrial, S.A., 227 p.

AHLFELD, F., and MUNOS REYES, J. (1943) Los minerales de Bolivia. Published by Direccion General de Minas y Petroleo, LaPaz, 276 p.

BANDY, M. C. (1944) Mineralogy of Llallagua, Bolivia. LaPaz. 67 p. (reprinted in 1976 as Special Paper 1 of the Tucson Gem and Mineral Society).

GORDON, S. G. (1922) Preliminary notes on vauxite and paravauxite, two new minerals from Llallagua, Bolivia American Mineralogist, 7, 108.

GORDON, S. G. (1924) Crystallographic notes on six minerals from Peru and Bolivia. Proceedings of the Academy of Natural Science, Philadelphia, 76, 335-341.

Refreshing a Regional Focus at Harvard: The Szenics Collection of Chilean Minerals

Carl A. Francis

Harvard Mineralogical Museum

24 Oxford Street

Cambridge, Massachusetts 02138

Terry Szenics

4 Manchester Drive

North Massapequa, New York 11758

Chilean minerals became important at Harvard with the addition of a suite collected by Mark Bandy in northern Chile in 1935. Bandy studied 76 species including seven new minerals from Chuquicamata and other mines for his PhD dissertation. Thereafter interest at Harvard waned and Chilean minerals have only been acquired incidentally. Interest was revived in the early 1990's when Terry Szenics, who had relocated to Santiago in order to acquire specimens and lapidary materials to be marketed through Aurora Mineral Corporation, began submitting unidentified specimens for study. The May 2002 purchase of Szenics's nearly 800 contemporary mineral and ore specimens from Chile was a logical extension of that relationship. It neatly complements the museum's holdings of classic Chilean minerals. Its acquisition is focusing curatorial attention on Chilean minerals and creating an unusually large and well-documented representation of minerals from Chile.

The Szenics collection is mostly focused on minerals from the copper mines near Copiapo in the Atacama Desert. Highlights include: (1) Showy specimens of chrysocolla coated with a druse of quartz from mines in the Inca del Oro area, one clearly showing that the chrysocolla has replaced malachite. (2) Atacamite in the form of flat radiating crystal clusters along joints in highly fractured andesite host rock from Mira Flores at La Farola near Tierra Amarilla. (3) Fine azurite crystals, in part altered to malachite, from Manto Cuba in the San Pedro de Cachiyuyo district near Inca de Oro. (4) Secondary arsenates including adamite, erythrite, karibibite, parasymplesite, pharmacosiderite, olivenite, schneiderhohnite, and villyaellenite from the Veta Negra mine near Los Loros. And (5) molybdenite, powellite and ore specimens from the Jardinera #1 Mine near Inca de Oro that supplement material previously acquired for the description of szencisite.

Japan-Law Quartz Twins from Bolivia and Peru

Jaroslav Hyrsl

Heverova 222, 280 00 Kolin

Czech Republic

Bolivia and Peru have yielded a significant percentage of the Japan-law quartz twins discovered in the past decade. Interestingly, many of the most productive localities are tungsten vein-type deposits. In Bolivia, these include: (1) The Kami tungsten mine, which produced hundreds of specimens in 1993-1998. The twins are typically in the 3 cm range but can reach 8 cm across. They often contain inclusions of arsenopyrite, pyrrhotite, or marcasite, and are sometimes covered by a scorodite or pitticite crust. At one location within the mine, a one-meter-square area was covered entirely by thousands of small twins. (2) The abandoned Chicote Grande tungsten mine near Kami, which is a past producer of excellent water-clear Japan-law twins to 10 cm across, often accompanied by lustrous, black, V-shaped ferberite twins, arsenopyrite, and lenticular siderite. (3) The Siglo XX tin mine at Llallagua, which sporadically produced good Japan-law twins to about 5 cm across. These are often covered by thin crusts of wavellit e or, less commonly, fluorapatite. (4) The Chambillaya and Tasna tungsten mines, which have also produced Japan-law twins but not in the prodigious amounts of the previous occurrences.

Peruvian Japan-law quartz twin occurrences include: (1) The Pasto Bueno tungsten mine, which has historically been the source of rather typical Japan-law twins to 5 cm across. (2) The Mundo Nuevo tungsten mine, where, in 1998. a major find of Japan-law twins was made in. Many of the twins are milky and unflattened, and reached sizes up to 11 cm across. Multiple twins and specimens with numerous twins were common. (3) The Alimon polymetallic mine near Huaron, which has been the source of transparent twins to 5 cm across associated with sphalerite, chalcopyrite, and pyrite. (4) The well-known epidote locality at Pampa Blanca (originally the Rosario Mabel claim and now the Flor de Peru II claim), where good Japan-law quartz twins have been found since 1997. This skam-type occurrence contains abundant andradite and epidote in addition to transparent, flattened quartz twins that reach widths of 10 cm. The twins are, in rare cases, covered by calcite crystals. (5) An abandoned Cu (?) mine at Ollupac, near Pampa Bla nca, which is the most productive Japan-law quartz twin locality in Peru and perhaps in the world. Thousands of specimens have been recovered there since 1999. Most are characterized by a milky white color and thin overgrowths of younger quartz. Untwinned crystals to 20 cm have been found, whereas twinned crystals rarely exceed 10 cm. The twin habit varies from the typical flattened V-shaped, through heart-shaped to almost square-shaped crystals. Multiple twins and chlorite-dusted phantoms are common. One vein produced specimens composed entirely of groups of thick Japan-law twins to 8 cm wide.

Strange Minerals of a Salt Dome Caprock in Cochabamba Department, Bolivia

Alfredo Petrov

531 North James Street

Peekskill, New York 10566-2401

Salt dome caprocks are very mobile, chemically active features that are little known to most mineralogists and mineral collectors. They deserve more attention. When salt is deeply buried, high pressure renders it plastic, forming a salt dome which slowly punches its way upwards through kilometers of overlying strata, entraining blocks of exotic rocks along the way. As the dome approaches the surface, circulating groundwater dissolves halite away, greatly concentrating the traces of insoluble minerals present in and with the salt, such as anhydrite, clays and other silicates, various carbonates, borates, and sulfides, all of which tend to accumulate on top of the salt as an insoluble "hat" or caprock. The continuous upward movement of the salt "conveyor belt," and the constant formation and collapse of solution cavities; makes the caprock highly brecciated. Hot brine circulates through lower zones of the breccia, reacting with the exotic blocks of sedimentary and volcanic rock to form new minerals and recrysta llize old ones. Most crystals in this environment form complete, euhedral "floaters."

One of the world's oldest salt dome caprocks (Cambrian or Proterozoic), the "Locotal Breccia' crops out at several places on the lower slopes of the Andes, at elevations ranging from 400 to 2,000 meters, in the Alto Chapare district of Cochabamba Department, Bolivia. It is the type locality for povondraite and magnesioriebeckite, and has also produced abundant sharply-formed, doubly-terminated danburite crystals, the world's largest boracite crystals, and interesting specimens of ericaite, dolomite, magnesite, and several other species. Potential new tourmaline group species are being studied. Industrial dolomite, magnesite, and magnesioriebeckite asbestos are mined on a small scale. Most of the breccia is hidden under dense jungle, but new specimen finds are exposed every year by landslides in this area of intense periodic rain and steep topography.

Bolivian Minerals in the Bandy Collection

Anthony R. Kampf and Dorothy L. Ettensohn

Department of Mineral Sciences

Natural History Museum of Los Angeles County

900 Exposition Boulevard

Los Angeles, California 90007

The mineral collection assembled by Mark Chance Bandy was donated to the Natural History Museum of Los Angeles County by his wife Jean in 1977. This collection is rich in specimens from Bolivia, which were collected by Bandy between 1936 and 1947. During this period Bandy worked in Bolivia for the Patino family, first doing mineral exploration and then at Llallagua serving as chief geologist, chief engineer, and finally general manager of the Siglo XX mine. Bolivian tin mining was at its peak and the Siglo XX was the world's largest producer.

Not surprisingly, the minerals of Llallagua are especially well represented in the Bandy Collection, but also prominent are minerals from other Bolivian mines active during the period, especially those at Araca, Chocaya, Colavi, Colquechaca, Huanuni, Monserrat, Oruro and Poop6. The sulfides and Sulfosalts are very well represented, most notably arsenopyrite, bismuthinite, bournonite, cylindrite, franckeite, pyrargyrite, pyrite, stannite, stibnite, teallite, and wurtzite Among the oxides, cassiterite and quartz are most important and siderite is the most important carbonate. Llallagua phosphates, including childrenite, crandallite, fluorapatite, metavauxite, monazite, paravauxite, sigloite, vauxite, vivianite and wavellite, were actively collected by Bandy. He particularly appreciated the fluorapatite crystals and on some he noted a "whatsit" that was described by Kampf in 1982 as the new mineral jeanbandyite.

Exceptional Apatites from the Siglo XX Mine, Llallagua, Bolivia

John Rakovan

Department of Geology

Miami University

Oxford, OH 45056

The Siglo XX mine, Llallagua, Bolivia is well-known as a classic location for beautiful fluorapatite specimens of varying habits (some quite complex) and colors (Bandy 1944). Many crystals from Llallagua exhibit compositional heterogeneities that lead to unusual and beautiful luminescence and optical properties. During growth of the apatite, trace elements are preferentially incorporated on different crystal faces, leading to sectoral zoning in the bulk crystal (Rakovan and Waychunas 1996). Sectoral zoning is often evidenced by differing fluorescence colors on different faces of the same crystal (Rakovan 2002). For example many crystals exhibit a lavender fluorescence from {001} faces and orange fluorescence from {100} faces. Genetically related to sectoral zoning, intrasectoral zoning of trace elements is also found (Rakovan and Reeder 1996). Intrasectoral zoning is often evidenced by different cathodoluminescence colors on different vicinal faces of growth hillocks. Variations in purple, blue and yellow cat hodoluminescence are found among vicinal faces of hillocks on {100} and {001} faces. Sectoral and intrasectoral zoning are the result of different atomic arrangements among regions of the crystal surface that are not symmetry-related. The differences in surface structure lead to dissimilar affinities for the incorporation of a given trace element. Differential incorporation also leads to optical anomalies in apatites from Llallagua. Crystal sections observed under crossed polars on a petrographic microscope show concentric, sectoral and intrasectoral variations in optical character and orientation, indicating domains of different bulk atomic structure (Rakovan and Reeder 1994; Rakovan 2002). The complex structural and compositional zoning is not only a source of aesthetic and mineralogical interest but has been used to determine the age of formation of these crystals to be 43.8 [+ or -] 4.7 Ma (Rakovan et al. 1997).

REFERENCES

BANDY, M. C. (1976) Mineralogy of Llallagua, Bolivia. The Tucson Gem and Mineral Society Special Paper #1.

RAKOVAN, J. (2002) Growth and surface structure of apatite. In KOHN, M., RAKOVAN, J., and HUGHES, J. M. (eds.), Phosphates: Geochemical, Geobiological and Materials Importance. Reviews in Mineralogy. Mineralogical Society of America, Washington, DC.

RAKOVAN, J., MCDANIEL, D. K., and REEDER, R. J. (1997) Use of surface-controlled REE sectoral zoning in apatite from Llallagua, Bolivia, to determine a single-crystal Sm-Nd age. Earth and Planetary Science Letters, 146, 329-336.

RAKOVAN, J., and REEDER, R. J. (1996) Intracrystalline Rare Earth Element distributions in apatite: Surface structural influences on zoning during Growth. Geochimemica et Cosmochimica Acta, 60, 4435-4445.

RAKOVAN, J., and WAYCHUNAS, G. (1996) Luminescence in Minerals. Mineralogical Record, 27, 7-19.

RAKOVAN, J., and REEDER, R. J. (1994) Differential incorporation of trace elements and dissymmetrization in apatite: The role of surface structure during growth. American Mineralogist, 79, 892-903.

Mineral-Producing Mines of Peru

R. Scott Werschky and Alan R. Day

5655 Riggins Court, Suite 15

Reno, Nevada 89502

Peru has a long history of base and precious metal mining. Most of Peru's mines occur in the high cordillera of the Andes Mountains but, contrary to common thought, these mines are not associated with andesitic volcanism. The vast majority of mines in the Andes are actually replacements and skarn-type deposits hosted by Cretaceous limestones. Replacement deposits are known worldwide as prime environments for the formation of crystallized minerals, and the deposits of Peru are no exception. Foremost among the mineral-specimen-producing mines are Uchucchacua, Morococha, Casapalca, Huanzala, Chiurucu, Pachapaqui, Raura, Animon, Quiruvilca, Pasto Bueno, Pampa Blanca, Salinas de Paracas, and Julcani. World-class-caliber specimens of many species have been found at Peruvian sites in the last few decades, including pyrite, sphalerite, galena, chalcopyrite, tetrahedrite, tennantite, hubnerite, fluorite, rhodochrosite, gypsum, atacamite, quartz, epidote, rhodonite and silver.

A Decade of Mineral Discoveries in the Atacama Desert of Northern Chile

Terry Szenics

4 Manchester Drive

North Massapequa, NY 11758

Of the hundreds of mines scattered over the 1200-km length of the Atacama Desert of northern Chile, only a relatively small percentage have potential for mineral specimen production. However, over the past decade a few adventurous individuals have made a series of important discoveries. These began with the identification of the new mineral species szenicsite at a small copper mine near the oasis town of Inca de Oro. In 1994, at the Santa Catalina mine in Sierra Gorda, the finest known specimens of the rare mineral sampleite were found, occurring as pearly, pale blue, platy crystals on rock matrix. Collecting periodically since 1994 at the San Samuel mine near Carrera Pinto has produced exceptional microcrystalline lindgrenite. Other areas of the mine produced powellite and wulfenite. Two new minerals, christelite and gordaite, were identified in 1995 from material collected at the San Francisco mine in the Sierra Gorda lead-silver district. The only known South American spangolite was collected in 1996 at th e Rosalia mine, far to the east of Inca de Oro. Collecting in 1997 and 1998 in the Veta Negra mine, Pampa Larga district near Tierra Amarilla, produced a small quantity of the world's finest specimens of villyaellenite in attractive pink to pinkish-orange crystals. Associated minerals were olivenite, conichalcite, scorodite, erythrite, roselite, brandtite, parasymplesite, pharmacosiderite, adamite, cuproadamite, schneiderhohnite, and karibibite. Collecting in the gold mining district of Guanaco near Taltal since 1998 has produced a host of desirable minerals. These include ceruleite, olivenite, mansfieldite, relatively large amounts of the rare mineral lammerite, and pale blue, platy crystalline masses of the new mineral lemanskiite (the tetragonal dimorph of lavendulan). Good specimens of erythrite and clinoclase microcrystals were discovered in the Freirina area near Vallenar in 2000. A surprising quantity of the rare mineral penfieldite as small, sharp, pyramidal crystals lining vugs in galena and associat ed with powdery boleite was found in 2001 at the Margarita mine in Sierra Gorda. Finally, in August 2002 exceptional specimens of bellite as bright orange-red crusts of needle-like microcrystals were found at the Ponderosa mine south of Sierra Gorda.

Silver Minerals of Peru

Terry C. Wallace

Department of Geosciences

University of Arizona

Tucson, AZ 85721

Peru has historically been one of the largest producers of silver, ranking second behind Mexico over the past decade. During this period Peru has produced more than 70 million ounces annually. Despite this enormous wealth in silver, there are relatively few localities that have produced world-class specimens of silver-containing minerals. Presently there are two districts producing fine specimens: Uchucchacua and Castrovirreyna.

Uchucchacua is located at the southern end of the Cordillera Blanca, which is one of the most impressive mountain ranges in the world. The Cordillera Blanca is about 20 km wide and 180 km long; within this small region there are 50 peaks with elevations in excess of 5700 meters (18,500 feet). Uchucchacua is a skarn-rich deposit in which limestones are cut by numerous sheets and stocks of porphyritic dacite. Veins and the metamorphic halos associated with the intrusions are typically rich in Ag, Mn, Pb and Zn. In addition to the veins, there are massive orebodies associated with faults in the wall rock. As the fluids moved out from the intrusions, hypogene mineralization progressed in four stages. First, skarn developed; this is characterized by anhydrous Mn-Fe-Ca silicates. Next the main stage of mineralization occurred, which is primarily Zn-Mn-Fe, Pb and Cu-Fe sulfides, and Mn-Ca carbonates. This unique chemistry makes for some very unusual minerals and mineral assemblages. Uchucchacuaite ([AgPb.sub.3][MnSb .sub.5][S.sub.12]), a very rare manganese mineral, was discovered here in the early 1980's, and Uchucchacua remains the only known locality for the species. Some of the most spectacular wire silvers are found on a pale pink rhodochrosite. Recently large arsenopolybasite crystals have been sold that are on balls of kutnohorite.

Castrovirreyna is located 350 km south of Uchucchacua in a similarly spectacular, high-altitude setting. The Castrovirreyna district is on the margin of a collapsed caldera, surrounded by 18 peaks in excess of 4,700 meters elevation. The rocks In the area are all andesitic volcanics, and the major mines all exploit Pb-Cu-Zn-Ag veins. The most prolific specimen producer in the district is the San Genaro mine. Pyrargyrite is found here in crystals to 6 cm in length. Miargyrite is frequently associated with pyrargyrite, typically as botryoidal clusters of crystal. Some of the world's best aramayoite comes from this Peruvian district.
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Author:Cook, Robert B.; Eriksson, Susan
Publication:The Mineralogical Record
Geographic Code:9JAPA
Date:Jan 1, 2003
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