Printer Friendly

Huancavelica Group.


Angaraes Province Huancavelica Department


The Julcani district is located about 65 km by road southeast of the city of Huancavelica, at an elevation of 4,200 meters. The district has been mined discontinuously since Spanish colonial times. Serious mining has been conducted since about 1907, and large-scale mining commenced in 1936. The present operator is Alberto Benavides Q., who founded the Compania de Minas Buenaventura S.A. in 1953. Julcani is one of Peru's largest producers of silver and bismuth.


Goodell and Petersen (1974) and Petersen et al. (1977) have described the geology and mineralogy of the Julcani area. The mineralogy in these papers, as well as one published by Goodell (1974), is used as background for the following synopsis of the district geology and ore deposits.

The Julcani district is dominated by a series of rhyodacitic to dacitic dikes, volcanic domes with related eruptive rocks, and pyroclastic material described as the Julcani volcanic center. There were three phases of activity. The first or main stage activity is characterized by explosive pyroclastic eruptions. The second stage resulted in the formation of a series of domes, and the third and final stage consisted of recurrent doming and dike formation. Hydrothermal alteration and mineralization occurred more or less simultaneously with the intrusion of the third stage volcanic domes and dikes.

Ore mineralization is generally confined to fracture filling, with limited replacement of the country rock within the vein structures. The mineralized area, containing the major mines of the district, measures approximately 3 x 5 km. Ore solutions appear to have spread upward and outward from several centers. This resulted in clearly defined zoning patterns. These centers are also the location of the major mines today. Some of the more important mines are the Herminia (in the south) and Mimosa (in the north), followed by the Estela, Tentadora, Lucrecia, Rita, Sacramento (Sacramento Otoni), Acchilla, and Manto mines.

Generally, as the ore-bearing solutions moved upward and outward from the innermost centers of the Herminia vein system, they first deposited pyrite-wolframite-enargite-barite, then enargite-pyrite-tennantite/tetrahedrite, then a zone of complex silver and bismuth sulfosalts with bismuthinite (Robinson et al., 1997; Vajdak, 1995), and at a greater distance they deposited galena, followed by lead sulfosalts, orpiment, and realgar. Pyrite was deposited first throughout the vein system, particularly in association with enargite; smaller amounts of pyrite also crystallized later. Barite commonly crystallized with, or slightly after, enargite and extends beyond the area of enargite deposition. In the outermost fringes of the zoning sequence, barite precipitated with tennantite/tetrahedrite, followed by bismuth sulfides and sulfosalts, then galena, followed by orpiment, realgar, and lead sulfosalts. Galena is the main ore mineral in the distal parts of the zoning sequence.

Pyrite-gold-tungsten mineralization is the dominant mineralization in the Tentadora mine, which is thought to be in the innermost zone of the Herminia vein system,

The Mimosa vein system is in the northern part of the district. In this vein system, tennantite/tetrahedrite is the dominant mineral in the innermost assemblage, with galena being the dominant mineral in the outer zones. The Mimosa system is similar to, and somewhat simpler than, the Herminia system. Pyrite was the first mineral to crystallize, followed, in order, by tennantite/tetrahedrite, sphalerite with chalcopyrite, and siderite. This first stage of mineralization was followed by crystallization of bismuth-bearing minerals, followed by galena, then lead sulfosalt-bearing mineral assemblages. In both the Herminia and the Mimosa vein systems, the final mineralization phase was a crystallization of sphalerite and siderite.

Southwest of the Mimosa mine is the Estela vein system. The inner zone of this system is dominated by pyrite-wolframite mineralization, followed by tennantite/tetrahedrite-chalcopyrite-arsenopyrite-bismuthinite, and finally by galena-sphalerite mineralization.


The reader is referred to Goodell (1974) for an excellent short description of the minerals reported from Julcani.

A help in distinguishing mineral specimens from Julcani is the matrix rock. If the matrix is country rock, it will be an altered, siliceous volcanic rock, usually with anhedral quartz phenocrysts, originally rhyolitic to dacitic in composition.

Aikinite PbCuBi[S.sub.3]

Aikinite has been identified by one of us (JAC) in two specimens provided by two individuals, both specimens attributed to Julcani. It occurs as coatings of tiny, acicular, steel-blue, metallic-lustered crystals up to 3 mm long associated with chalcopyrite, tetrahedrite and enargite. It could easily be mistaken for boulangerite or bismuthinite. Identification was made by X-ray powder diffraction analysis.

Arsenopyrite FeAsS

Arsenopyrite occurs as brilliant, silvery, prismatic crystals with fiat, triangular or wedge-shaped terminations. The crystals are usually on the order of a few centimeters in maximum dimension. According to Goodell (1974), arsenopyrite is restricted to the Estela mine. In 1993 a small find of arsenopyrite was made at Julcani, presumably from the Estela mine. The specimens are in flat to mounded plates composed of near-solid coatings of bright, silvery, simple prismatic crystals up to 6 mm diameter and about 1 cm long. Colorless or very pale yellow to yellowish green apatite crystals up to 2 cm long are frequently implanted on the arsenopyrite.

Barite BaS[O.sub.4]

Barite is relatively common at Julcani as bladed crystals and mound-like crystal aggregates. This latter habit is similar in shape to barite from the Mibladen, Morocco vanadinite area. Barite is frequently associated with the sulfides and sulfosalts. Crystals may exceed 5 cm in size and, according to Goodell (1974), have been recorded up to 25 cm in size from the Herminia mine.

Commonly white, barite can also be gray-blue, pinkish or colorless. Julcani produced some quite attractive thin, flake-like or wafer-like barite in 1987. A substantial amount of very pretty and choice barite, covered with siderite and associated with galena crystals, was produced in 1988. In the early 1990's, Julcani produced a small amount of attractive yellow barite which is associated with siderite.

Bismuthinite [Bi.sub.2][S.sub.3]

Bismuthinite is found as lustrous, steel-gray, needle-shaped prismatic crystals that superficially resemble stibnite. Bismuthinite can achieve crystal lengths up to several cm, which make excellent specimens for the species, White bladed barite is a common associated mineral.

Boulangerite [Pb.sub.5][Sb.sub.4][S.sub.11]

Boulangerite occurs in hair-like, sometimes matted, crystals.

Bournonite PbCuSb[S.sub.3]

Bournonite usually occurs as splendent black to steel-gray crystals up to 2.5 cm across. It frequently occurs with bladed barite, bismuthinite, boulangerite and jamesonite (these last three identifications are questionable as they are visual observation only).

Cosalite (?) [Pb.sub.2][Bi.sub.2][S.sub.5]

Cosalite (?) has been tentatively identified by one of us (JAC) in one specimen attributed to Julcani. It occurs as long, thin, prismatic crystals with metallic luster and typical arsenopyrite-gray color where crystals have been broken; the cosalite (?) is partially covered with drusy quartz. It is also associated with tetrahedrite and chalcopyrite. Identification was made by X-ray powder diffraction analysis.

Fluorapatite (?) [Ca.sub.5][(P[O.sub.4]).sub.3]F

Apatite occurs in sharp crystals, usually as simple hexagonal prisms with flat terminations. They are near-colorless to a pale yellow, greenish yellow, or yellowish green color. Larger crystals are frequently zoned. In the case of single-terminated crystals, the base is white or colorless and the termination may be greenish in color. In the case of doubly terminated crystals, the midpoint is white or colorless and both terminations may be greenish in color. Julcani apatite fluoresces a cream-yellow color that varies in intensity due to zoning within the crystals. Rarely, apatite crystals may exceed 2.5 cm in length. Associated minerals are usually white to near colorless, tapered crystals of quartz and small crystals of siderite and pyrite. Arsenopyrite, frequently found in drusy crusts, often forms the matrix mineral for the apatite crystals.

Galena PbS

Galena occurs as shiny gray crystals. These are usually highly modified cubes tending toward the octahedron or dodecahedron forms, sometimes to the degree that the cube is no longer distinguishable. Some galena has a "crinkly" surface, possibly due to etching.

Jamesonite [Pb.sub.4]Fe[Sb.sub.6][S.sub.14]

Jamesonite is megascopically indistinguishable from boulangerite and bismuthinite.

Orpiment [As.sub.2][S.sub.3]

Orpiment occurs in bright orange, glassy, lustrous, pencil-shaped crystals that are up to at least 2.5 cm in length. They are distinctly different in appearance from the orpiment crystals found at Quiruvilca.

Pyrite Fe[S.sub.2]

Pyrite, commonly in pyritohedrons, is usually a minor constituent on most mineral specimens. Where present, crystals may reach 1 cm across. During the past several years botryoidal pyrite specimens, typical for Julcani, have been produced in small numbers in handsized specimens.

Quartz Si[O.sub.2]

Quartz is usually present on Julcani mineral specimens, commonly as very small, white to colorless drusy crystal coatings and as the matrix for other minerals. Quartz also occurs as milky white, nearly opaque crystals which have a strong triangular development when viewed along the c-axis. Crystals can also be slightly barrel-shaped and at least 2 cm long.

Siderite [Fe.sup.+2]C[O.sub.3]

Siderite is common as a minor accessory mineral and also as good specimens in its own right. It is beige to brownish in color, and is usually found in flattened rhombohedral crystals that are quite discoidal in appearance. Siderite commonly occurs on barite, sometimes with galena. Very nice stalactites and "worms" of siderite up to 15 cm long were recovered from 1988 to 1990. These make rather interesting specimens.

Stibnite [Sb.sub.2][S.sub.3]

Stibnite in the specimens seen occurs as typical, acicular, metallic luster crystals up to several mm in length. Barite is a common associated mineral.

Tennantite/Tetrahedrite [(Cu,Fe).sub.12][As.sub.4][S.sub.13] - [(Cu,Fe).sub.12][Sb.sub.4][S.sub.13]

Tennantite/tetrahedrite crystals are usually complex in form, though such complexity is more typical of the As-rich end member, tennantite. It rarely occurs in simple tetrahedrons. Crystals are usually lustrous and black to silvery black in color. It also occurs as casts after enargite.

Table 19. Minerals reported from the Julcani district.

Major Mines and Common to Locally Abundant Minerals

Herminia Mine

Andorite Aramayoite Arsenopyrite (*)Barite (*)Bismuthinite (*)Bournonite (*)Chalcopyrite (*)Enargite Galena (*)Pyrite Semseyite (*)Siderite Sphalerite (*)Stibnite (*)Tennantite-tetrahedrite Wolframite

Lucrecia Mine

(*)Barite Galena (*)Tennantite-tetrahedrite

Tentadora Mine

Galena Pyrite Quartz Sphalerite Wolframite

Estela Mine

(*)Apatite (*)Arsenopyrite (*)Bismuthinite Chalcopyrite Galena Pyrite Sphalerite Tennantite-tetrahedrite Wolframite

Mimosa Mine

(*)Bismuthinite (*)Boulangerite Chalcopyrite Galena Siderite Sphalerite Tennantite-tetrahedrite

Sacramento Mine

(*)Orpiment Realgar

Minerals reported with no specific mine listed

(*)Aikinite Bornite Calcite (*)Cosalite (?) Friedrichite Gustavite Hammarite HodrushiteKrupkaite Marcasite Pavonite Scheelite

* Collector-quality specimens


Castrovirreyna Province Huancavelica Department


The Castrovirreyna district [ILLUSTRATION FOR FIGURE 105 OMITTED] is located along the road which leads from the city of Huancavelica to Pisco on the Pacific coast. The district is named for the town of Castrovirreyna.

The Castrovirreyna district is composed of a series of volcanic peaks that average about 5,000 meters in elevation. There are 18 peaks exceeding 4,700 meters in the district. Snow in the winter months is common. The Western Cordillera divides the district into two halves. Many large glacial lakes are present. Orcococha, one of the largest, is in the Atlantic watershed and Pacococha, about 7 km to the west over the divide, is in the Pacific watershed. The terrain is strongly glaciated, which creates sharp angular relief. The dark volcanic rocks are colored by areas of manganiferous and limonitic alteration and weathering. Masias (1924) described the area from atop 5,000-meter Monserrate Chico hill:

As no wind blew, the lakes appeared as extensive surfaces of lead. To the front, the snowed-under ribbon of the cordillera peaks extended like a rampart, an immense wall with its scarps and parapets. It seemed like a cyclopean fortress placed by God to defend our native soil. Above the level of the lakes the different mineralized hills rise to a great elevation, some forming great masses and others, volcanic cones or needles of varied forms.


The district's mineral deposits were discovered in 1590, but the mines closed a short time later in response to the occurrence (according to legend) of various supernatural events (Purser, 1971). Serious mining operations began again in 1946.


The Castrovirreyna district is briefly described by Masias (1924) and Purser (1971) and the following geological discussion is abstracted from their papers. Very little other information on the district is available.

Rocks in the district are flat-lying Cenozoic andesitic volcanics with some dacite and rhyolite present. A buried intrusion is inferred from the mine geology.

There are four major mines in the district. The largest are the Caudalosa and Candelaria mines, which are found in the Caudalosa vein-group. Another major mine is the San Genaro mine, east of the Caudalosa mine near the village of Choclococha, in the San Genaro vein-group area. The third is the Carmen-Lira mine in the La Virreyna vein-group. The Carmen-Lira mine is the source for most of the sulfide-bearing mineral specimens from the district. Near the Caudalosa mine are several smaller mines including the Reliquias, Dorito, San Pablo and Madona. The Reliquias is the largest of these.

The Pb-Cu-Zn-Ag veins in the district run more or less east-west in the andesite-to-rhyolite country rock. They frequently contain proustite, pyrargyrite and other rarer silver sulfosalts. Silver content of the ores from the district increases from west to east. There are three main groups of veins; the La Virreyna group, just east of Pacococha Lake, the Caudalosa group, at the northwest end of Orcococha lake, and the San Genaro group, a few km north of the eastern part of Orcococha Lake. Veins vary from 30 cm to 3 meters wide, with quartz usually the dominant gangue mineral. The Caudalosa mine veins have been traced a horizontal distance of 1,500 meters. In the La Virreyna group, the Carmen-Lira veins usually contain tetrahedrite, chalcopyrite, galena, sphalerite, pyrite and quartz. The Huachacolpa district, several km to the northeast, is considered to be an extension of the Castrovirreyna district by Masias (1924).

The Caudalosa mine ores are composed of Ag-rich galena, sphalerite and pyrite, plus or minus stibnite. Gangue minerals are quartz, manganoan calcite and rhodochrosite. Deposition in the Caudalosa mine occurred in four stages. In the first stage, pyrite, galena, sphalerite and enargite were deposited. In the second stage, pyrite, sphalerite and chalcopyrite were deposited, galena was replaced by boulangerite and bournonite, and enargite was replaced by famatinite. In the third stage, conversion of lead-beating minerals to jordanite, replacement of copper-bearing minerals by tetrahedrite, and deposition of pearceite and proustite took place. In the fourth stage, deposition of stibnite, rhodochrosite, pyrargyrite and polybasite occurred.

At San Genaro, on the east side of the divide, there are three stages of mineralization. The first stage is marked by the deposition of pyrite, sphalerite, galena and chalcopyrite. The second stage is marked by proustite. The third stage is marked by pyrargyrite, polybasite and other sulfide/sulfosalts in small amounts.

Neither Masias (1924) nor Purser (1971) discuss the Carmen-Lira mine.


Most mineral specimens from the Castrovirreyna district are simply labeled "Castrovirreyna," with no specification as to which mine they came from. Confusion also exists regarding mineral specimens collected from the Castrovirreyna vs. the Pacococha mining district. This confusion, related to geographic location, is the result of there being a Pacococha district and mine near Millotingo; in the Castrovirreyna district, there is a Pacococha Lake, and hill, with mines adjacent to both, located in the western part of the district. Specimens from the Carmen-Lira mines are frequently labeled as "Pacococha, Huancavelica." To add to the location problems for the district, there is another large, operating, Caudalosa mine in the Huachacolpa district, just north of the Castrovirreyna district. The majority of good specimens of chalcopyrite, sphalerite, galena and tetrahedrite labeled "Pacococha" are actually from the Castrovirreyna district. A help in differentiating the two locations labeled as "Pacococha" is that the Pacococha mines near Millotingo have produced (in comparison to the Castrovirreyna district) very few mineral specimens. Generally, the Caudalosa and Carmen-Lira mines produce mixed sulfide specimens, and the San Genaro mines produce silver and silver-sulfosalt minerals. The San Genaro mines produced a significant number of very fine-quality sulfosalt specimens, primarily miargyrite and pyrargyrite associated with aramayoite, native silver, proustite and barite, in the mid-1970's through the middle 1980's.

Ankerite Ca([Fe.sup.+2],Mg,Mn)[(C[O.sub.3]).sub.2]

Ankerite is a common accessory mineral in the west side of the district, and is one of the last minerals to have formed. Ankerite crystals occur as poorly formed rhombohedra usually having a dull beige or tan color and a chalky appearance. It is present as small crystals and aggregates which coat the other minerals. Larger ankerite crystals commonly have pinkish cores; this may reflect a change from kutnohorite(?) to ankerite as the crystals grew. Ankerite from the Pacococha area of Castrovirreyna is distinctive enough to help identify specimens from there. Specimens from the Pacococha district near Millotingo do not have this distinctive-appearing ankerite.

Aramayoite Ag(Sb,Bi)[S.sub.2]

Aramayoite is a relatively common but minor accessory mineral on specimens of miargyrite and pyrargyrite. It occurs as iron-black, crystalline, platy masses on the sulfosalts. It can be easily overlooked as it resembles miargyrite.

Barite BaS[O.sub.4]

San Genaro is the most prolific location for barite in Peru. Barite occurs in the San Genaro mine as translucent to opaque, white to off-white bladed crystals in good and sometimes large groups associated with sulfides and quartz. These groups are often damaged. The barite crystals may have white centers which are less transparent when compared to the white edges; this creates a two-tone effect on the crystals. The barite crystals average about 2 cm in size, but may be up to 10 cm long, and occur in plates up to about 22 cm across, associated with milky quartz. These large barite specimens may weigh up to several kilograms. Most of these specimens have been purchased by European mineral dealers. Barite also occurs at the Caudalosa mine.

Calcite CaC[O.sub.3]

Pink manganoan calcite has been visually identified as fine-grained pink coatings on stibnite and other sulfides from the Caudalosa mines.

Chalcopyrite CuFe[S.sub.2]

Chalcopyrite at Castrovirreyna is dark yellow-gold in color, with a bright and shiny luster. It occurs in the better specimens as sharp crystals over 2 cm across. Some crystal faces are mirror-bright with no striations, while opposing faces are striated and very slightly etched. The crystals are frequently twinned. Tetrahedrite may occur on the chalcopyrite. In the Carmen-Lira mines, chalcopyrite crystals may exceed 2 cm in size. The crystals have a bright luster, sometimes with an iridescent tarnish. One Carmen-Lira specimen, about 5 x 6.5 cm in size, has very sharp, bright, gold-colored chalcopyrite crystals 2 cm across on a bed of clear glassy quartz crystals which average about 2.5 cm long.

Galena PbS

Galena occurs both as dull, etched-looking crystals and as lustrous bluish-silvery cubes and cubes modified by the octahedron. It occurs both on and with sphalerite or chalcopyrite. Galena frequently has triangular surface growth features on some faces. It also occurs as crystals with a "melted" look, The melted-appearing galena has considerably brighter luster than the etched-looking galena.

Kutnohorite Ca(Mn,Mg,Fe)[(C[O.sub.3]).sub.2]

Kumohorite has been tentatively identified in pale pink rhombic crystals with a satiny to dull luster. They have also been found at the core of ankerite crystals.

Miargyrite AgSb[S.sub.2]

Miargyrite occurs at Castrovirreyna in crystals up to 3 cm in size. Most specimens, however, consist of botryoidal miargyrite coated with microscopic to small red-black miargyrite crystals with other minor associated minerals.

Pyrargyrite [Ag.sub.3]Sb[S.sub.3]

Found at Castrovirreyna in magnificent crystals to over 4 cm in size, pyrargyrite is more common as microscopic crystals up to a few millimeters in size. The best pyrargyrite specimens have 2 x 4-cm crystals. San Genaro has produced some of the largest pyrargyrite crystals in the world. The best specimens are described as "golfball"-sized crystals which are lustrous and deep ruby-red to red-black in colon Perhaps the best specimen of pyrargyrite collected from San Genaro is now in the Houston Museum of Natural Science,

Pyrite Fe[S.sub.2]

Pyrite occurs at Castrovirreyna as lustrous pyritohedrons up to 1 cm in size, frequently associated with tetrahedrite in the Caudalosa mine. The Carmen-Lira mines commonly produce pyrite associated with various ore minerals, but it does not generally form good specimens there by itself.

Quartz Si[O.sub.2]

Quartz from the district is usually opaque milky white in color. Other than the strong milky-white color, they are typical in crystal appearance. Quartz has been collected from the Caudalosa mine as drusy quartz which forms molds of now-absent tabular barite. The Carmen-Lira mine has quartz that occurs both as drusy coatings and as individual crystals exceeding a few centimeters in length. These crystals are typically clear to colorless, with a very slight taper and somewhat triangular cross-sections. The San Genaro mine produces milky quartz crystals which typically exceed 1 cm in length.

According to Dan Belsher (personal communication, 1992), amethyst occurs in fairly nice specimens from the San Genaro mine, as "milky amethyst which looks like Guanajuato, Mexico amethyst, with some occurring in plates to 9 inches square with crystals to 5 or 6 inches long, fairly lustrous, sometimes sceptered, and very pretty."

Silver Ag

In the San Genaro mine native silver occurs as wiry aggregates mixed with the silver sulfosalts.

Sphalerite (Zn,Fe)S

In splendent dark brown to light yellow crystals, sphalerite in reflected light often has a silvery look, particularly in the lighter colored crystals. Crystals vary from well-formed to subhedral cubic shapes, and to poorly formed tetrahedrons. The best of these crystals can be up to about 2 cm across, associated most commonly with quartz and galena. Sphalerite tends to be gemmy in the pale straw-yellow, yellow-green or dark reddish-amber colored crystals. Sphalerite from the Carmen-Lira mines occurs in good crystals; these vary from a dark brown to amber-yellow color in transmitted light, and possess a silvery to iridescent luster. Crystals generally do not exceed 2.5 cm in size, even in the best specimens. In the Carmen-Lira mine, the sphalerite crystal habits are complex, giving rise to rather rounded crystals. Better specimens are usually dominated by orange to amber-yellow crystals about 1 cm in size, associated with white quartz, galena, chalcopyrite and siderite.

Stibnite [Sb.sub.2][S.sub.3]

Stibnite occurs as needle-like crystals in fan-shaped sprays on milky quartz crystals. The crystals are generally on the order of 7 cm or less in length, with the sprays at least 7 cm across. In rare cases the stibnite has been replaced by finely crystalline galena; this creates unusual and pretty specimens. Probably erroneously labeled as from the San Genaro mine, the stibnites are most likely from the Caudalosa mines. Stibnites from the Caudalosa mine are sometimes coated with tiny, pale pink crystals of manganoan calcite forming a solid covering over the stibnite. The underlying stibnite has a frayed look to it. Stibnite crystals from the Caudalosa mine can reach several centimeters long.

Tetrahedrite [(Cu,Fe).sub.12][Sb.sub.4][S.sub.13]

Tetrahedrite in good specimens is not common in the Castrovirreyna district. The Carmen-Lira mines have produced simple tetrahedrons, 1 cm or so in size, with dark gray color and a satiny to bright metallic luster. Tetrahedrite crystals are usually slightly modified by other forms. The satiny crystals are usually slightly etched and pitted when viewed under the microscope. Tetrahedrite comes with a variety of associated minerals including chalcopyrite, sphalerite, quartz, siderite and dolomite.

Table 20. Minerals reported from the Castrovirreyna district.

Common or Abundant

(*)Barite (*)Boulangerite (*)Bournonite (*)Chalcopyrite Enargite Famatinite (*)Galena Jordanite (*)Miargyrite Pearceite (*)Polybasite (*)Proustite (*)Pyrargyrite (*)Pyrite (*)Quartz (*)Rhodochrosite (*)Native silver (*)Sphalerite (*)Stibnite

Rare or Locally Abundant

(*)Aramayoite Acanthite Arsenopyrite Calcite Hematite Marcasite Realgar (*)Tetrahedrite

* Collector-quality specimens
COPYRIGHT 1997 The Mineralogical, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1997 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:mining district in Peru
Publication:The Mineralogical Record
Date:Jul 1, 1997
Previous Article:Morococha-Casapalca Group.

Terms of use | Privacy policy | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters