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Corresponding author: e-mail, cesarvid@buenaventura.com.pe

Abstract

The Marcapunta enargite-Au deposits are located in the center of the Colquijirca mining district, 310 km northeast of Lima and 10 km south of the Cerro de Pasco mine. The regional geology comprises folded Permo-Triassic red-bed deposits of the Mitu Group succeeded by Pucará Group limestone and dolomite of Triassic to Jurassic age, which are overlain by carbonate breccia, conglomerate, and fresh-water limestone of the Eocene Calera Formation. These units are intruded and overlain by dacitic domes and pyroclastic rocks of the Marcapunta volcanic center. The north-trending Longitudinal fault controlled basin morphology during both the Pucará and Calera Formation sedimentation as well as emplacement of the Cerro de Pasco and Marcapunta Miocene volcanoes.

The Marcapunta Cu-As-Au deposits are zoned symmetrically northward into the Zn-Pb-Ag ores of Colquijirca and southwestward into the Zn-Pb-Ag San Gregorio deposit. The Miocene volcanic center at Marcapunta is intensely altered to advanced argillic alteration assemblages in the form of quartz-alunite ledges with argillic halos. Alunite mineral separates have been dated at 11.6 ± 0.1 Ma by K-Ar and 10.6 ± 0.1 Ma by 40Ar/39Ar methods. The main silicification and quartz-alunite alteration are controlled by several prominent east-west fractures and attain thicknesses from a few centimeters to ~50 m. Mineral assemblages are zoned outward from a central zone of vuggy quartz to quartz-alunite ± dickite, illite-kaolinite ± montmorillonite and external chlorite-calcite envelopes. Copper mineralization surrounds an interpreted subsurface diatreme vent and flares outward along the base of the dacitic domes comprising the Marcapunta volcanic center. Semimassive to massive quartz-pyrite bodies preferentially replaced limestone breccia and conglomerate of the Calera Formation and are sandwiched between the underlying Mitu Group sandstone and the overlying lava domes.

The northern, western, and southwestern flanks of the Marcapunta volcanic center are characterized by a recently determined and drill-tested, crescent-shaped gravimetric high. Ore zones attain thicknesses as much as 100 m adjacent to the steep diatreme walls and thin laterally into discrete strata-bound manto and breccia horizons. Ore mineralogy is dominated by enargite, covellite, native gold, and several precious metal-bearing telluride phases. Hypogene chalcocite and digenite occur in a discrete lower manto beneath the enargite zone of western Marcapunta. Gold appears to be concentrated in the southwestern parts of the replacement bodies. Cu/As ratios increase from a homogeneous value of 3/1 in the Smelter area, immediately north of the volcano, to variable values of 4 to 40/1 in the western Marcapunta enargite and digenite-chalcocite mantos.

Exploration and Mining History

The Colquijirca district was known as “mountain of silver” by the original Quechua-speaking inhabitants of the region. Native Ag, stromeyerite, and acanthite in gossanous outcrops were probably hand sorted by artisanal miners between the 10th and 15th centuries. Later, shallow adits, raises, and serpentine declines were constructed for the colonial mining of high-grade silver ore from the then-called Minas del Cerro Bombon (Pérez-Arauco, 1996). It was not until the early 20th century, when operated by Sociedad Minera El Brocal headed by Eulogio Fernandini de la Quintana, that Colquijirca became one of America’s most important and best studied primary Ag producers (Lindgren, 1935; McKinstry, 1936). Railroad connection with the La Oroya metallurgical complex was in place by 1906 and was fundamental in future mine development.

From 1945 to 1975, strata-bound Pb-Zn-Ag mantos, in the Mercedes Chocayoc anticline, were stoped west of Colquijirca from underground sublevels accessed by three main shafts. An aggressive exploration campaign from 1968 to 1974, including induced-polarization surveys and diamond drilling, led to the discovery of extensive open-pittable reserves in areas west and southwest of Colquijirca. From 1992 to 1994, the San Gregorio Ag oxide and Zn-Pb sulfide deposits were rediscovered and partially delineated. A drilling campaign during the 1930s revealed the San Gregorio zoning pattern: from near-surface Bi-rich argentiferous oxide ore to low pyrite, high-grade Zn and Pb sulfide ore at depth.

Since 1978, open-pit methods have been applied at Colquijirca, where current production is 3,500 metric tons (t) per day of polymetallic sulfide ore, assaying 6 percent Zn, 2 percent Pb, and 100 to 150 ppm Ag. The waste/ore stripping ratio is currently 7/1, and the Zn-Pb-Ag ore is valued at US$35 to US$45/t.

This paper reports the geologic, mineralogic, and geochemical findings provided by the 2002–2003 exploration campaign led by Compaóía de Minas Buenaventura S.A.A. The exploration program was designed in collaboration with Alberto Benavides de la Quintana, chairman of Compaóía de Minas Buenaventura S.A.A., and Sociedad Minera El Brocal S.A.A. More work, currently underway, is necessary to fully explore these and other pyritic, enargite-Au deposits within and around the Marcapunta volcanic center.

Structural, Stratigraphic, and Volcanologic Framework of Marcapunta in Relationship to Cerro de Pasco

Tectonic inversion is documented on the north-south-trending Longitudinal fault, the most prominent structure in the Colquijirca-Cerro de Pasco region. During the Late Triassic to Jurassic, the fault separated a shallow-water carbonate platform to the west from a subsiding riftlike basin to the east (Sempere et al., 2002). During the Eocene, a lacustrine basin formed west of the Longitudinal fault (e.g., Calera Formation). Other faults and lineaments of the north-south system are indirectly indicated by the elongate form of the Colquijirca mineral occurrences (Petersen and Vidal, 1996). The Cerro de Pasco and Marcapunta volcanic centers are 10 km apart and both seem to be controlled by the Longitudinal fault system. Other volcanic centers, such as Yanamate, are controlled by a set of northeast-trending strike-slip structures, including the Yurachuanca and Chancay faults (Fig. 1).

Fig. 1.

Location and geologic map of the Cerro de Pasco-Colquijirca region. Modified from Angeles (1999).

Fig. 1.

Location and geologic map of the Cerro de Pasco-Colquijirca region. Modified from Angeles (1999).

Principal faults and volcanic centers of the región cut across and pierce folded metamorphic and sedimentary sequences of early Paleozoic, Permian, Triassic to Jurassic, and Eocene ages. Folds are generally symmetric and open but exhibit exceptional complexity and tightness in proximity to fault zones, such as the La Llave and La Pampa isoclinal folds at Colquijirca, as shown schematically in the geologic section (Fig. 1).

Regional stratigraphy was thoroughly documented and described in the pioneer works of McLaughlin (1924) and Noble and Butz (1931) and, more recently, by Mégard (1978) and Angeles (1999). Early Paleozoic schists and phyllites of the Excelsior Group were deformed and metamorphosed to low-grade greenschist facies; they form the wall rocks to the Cerro de Pasco diatreme and occur as lithic fragments in both the Cerro de Pasco and Marcapunta diatreme breccias. Permian red beds of the Mitu Group uncomformably overlie the Excelsior. The red-bed sequence comprises fine-grained, hematite-stained sandstone with localized beds of quartzpebble conglomerate, interpreted to have been deposited in an arid and desertic mudflow-plain environment (McLaughling, 1924). The Pucará Group carbonate sequence transgressed a partially reworked unconformity carved on the Mitu sandstone. The western, shallow-water carbonate facies consists of 300 to 400 m of dolostone breccia and laminated algal mats with minor intercalations of waterlain tuff. The eastern basinal facies of the Pucará Group includes 2,400 m of massive gray micritic limestone and minor shale (Mégard, 1978; Angeles, 1999).

Cretaceous Goyllarisquizga Group sandstone, shale, and limestone are absent in the Colquijirca district but present farther north at Cerro de Pasco (Fig. 1). The district may have been uplifted at this time or, alternatively, the Cretaceous sequence was eroded prior to Eocene basin development. During the Eocene, uplift of the eastern facies of the Pucará Group promoted rapid erosion and formation of fanglomerate and lacustrine calcareous deposits known as the Pocobamba Group or, locally, as the Calera and Shuco Formations (McLaughlin, 1924; Boit, 1962; Angeles, 1999).

Miocene volcanism produced two large composite domediatreme centers at Marcapunta and Cerro de Pasco and a small volcanic vent at Yanamate (Vidal et al., 1984; Rivera, 2002). Cerro de Pasco and Marcapunta are steep-sided, inward-dipping, conical diatremes in the sense of Lorenz (1986); they were intruded, and partially covered, by dacitic flow domes and pyroclastic breccia. Cerro de Pasco is exposed at subvolcanic levels and the diatreme structure is filled by crudely bedded maar tuff and breccia (Silberman and Noble, 1977), known locally as the Rumiallana Agglomerate; dikes and cone sheets of younger dacitic magma intruded along east-west fractures and up the western and northern flanks of the diatreme structure. Ten kilometers south, at the Marcapunta volcanic center, dacitic flow domes predominate at surface with related carapace breccia and minor tuff; diatreme-related, bedded sedimentary rocks and tuff breccia, believed to have accumulated in a maar setting, are observed in core from several deep diamond drill holes. Intense and pervasive acid-sulfate alteration affects the domes (Fig. 2a) and indicates a shallow environment affected by vapor-dominated plumes (e.g. Stoffregen, 1987). The contrast in exposure level is believed to reflect a combination of the older age of the subvolcanic Cerro de Pasco vent (Silberman and Noble, 1977; Rogers, 1983) and post mid-Miocene uplift to the north, with shallower exposure levels and both more widespread lakes and subsurface meteoric water reservoirs preserved to the south, in the Marcapunta volcano area. A half graben of Eocene to Miocene age is defined by the Río San Juan-Venenococha and Longitudinal faults (Fig. 1).

Fig. 2.

Plans of the Marcapunta volcano. a. Hydrothermal alteration. b. Residual Bouger gravity contours, showing inferred outline of diatreme. North-south and east-west sections shown in Figures 3 and 4.

Fig. 2.

Plans of the Marcapunta volcano. a. Hydrothermal alteration. b. Residual Bouger gravity contours, showing inferred outline of diatreme. North-south and east-west sections shown in Figures 3 and 4.

Mineral Deposits of the Colquijirca District

The Colquijirca mining district has produced Ag-rich ore since precolonial Inca times, particularly since the beginning of the 20th century, from hypogene tennantite-polybasite ore and rich, near-surface, gossanous stromeyerite and native Ag ore. From 1974 to 1982, underground room and pillar mining in the Smelter area produced arsenical sulfide ore to produce Au- and Ag-bearing Cu concentrates (Table 1).

Table 1.

Copper Concentrate Production from the Smelter Area, 1974 to 1982 Period

YearMetric tonsCu (%)As (%)Au (ppm)Ag (ppm)
197412,94725.15nana325
197513,68726.08nana180
19769,87622.93nana118
19775,54924.53nana104
19782,15025.288.652.40130
19793,81925.788.603.50130
198080324.388.294.63171
19815,75024.588.394.08116
19822,38132.6210. 095.41134
1974–198256,96225.228.944.08181
YearMetric tonsCu (%)As (%)Au (ppm)Ag (ppm)
197412,94725.15nana325
197513,68726.08nana180
19769,87622.93nana118
19775,54924.53nana104
19782,15025.288.652.40130
19793,81925.788.603.50130
198080324.388.294.63171
19815,75024.588.394.08116
19822,38132.6210. 095.41134
1974–198256,96225.228.944.08181

Notes: na = not available

Notwithstanding its zoned polymetallic character at the district scale, silicification and sulfide mineralization are predominantly stratiform in geometry and tend to form replacement mantos that follow folded beds of either the Calera or Pucará Formations (Vidal et al., 1997). Historical underground and open-pit production of polymetallic ore in the Colquijirca part of the district estimated to be 13 million metric tons (Mt); current reserves are 8 Mt, averaging 6.4 percent Zn, 2.4 percent Pb, and 95 ppm Ag.

Over the last 20 yrs, several drilling campaigns totaling 35,000 m have extended the known Cu mineralization for 2.5 km south from the Smelter area around the periphery of the Marcapunta volcanic center, coinciding with a crescent-shaped gravimetric high (Fig. 2b).

Alteration-Mineralization and Paragenesis

The main constituents of the massive sulfide ore at Marcapunta are pyrite and enargite together with quartz, alunite, and minor barite. The early sulfide stage is characterized by intense silicification and massive pyrite replacement of limestone breccia and, to a lesser extent, the overlying dacitic domes and sills (Figs. 35). Pyrite with cataclastic texture is overgrown by a second stage of zoned pyrite crystals (Fig. 6a). Main-stage enargite occurs as open-space fillings of vugs and fractures in massive pyrite and in close association with minor covellite and tetrahedrite (Fig. 6b). A large number of minute, <5-μm inclusions and hairline fractures with native gold, native tellurium, and telluride species, such as hessite, guanajuatoite, and goldfieldite, are ubiquitous in the more Au-rich portions of the Marcapunta deposit. Barite, galena, and sphalerite are present only marginally to the enargite mineralization. Further mineralogic details, based on studies by Bendezú (2003) and Sáez (2003), are synthesized in a paragenetic sequence of mineral deposition, subdivided into three hypogene stages and a fourth supergene event (Fig. 7).

Fig. 3.

North-south section, showing Marcapunta geology and mineralization. Section marked in Figure.

Fig. 3.

North-south section, showing Marcapunta geology and mineralization. Section marked in Figure.

Fig. 4.

East-west section of Marcapunta geology and mineralization. Symbols as in Figure 3.

Fig. 4.

East-west section of Marcapunta geology and mineralization. Symbols as in Figure 3.

Fig. 5.

Photographs of the Marcapunta area and drill core. a. Western flank of Marcapunta volcano. b. Flow-foliated dacitic lava. c. Argillic-altered dacite. d. Massive quartz-pyrite-enargite-Au limestone-breccia replacement. e. Bleached, but largely unaltered Mitu Group sandstone. f. Silicified and mineralized dacitic sill. g. Digenite, chalcocite, and covellite replacing alunitized dacite. Note alunite, pseudomorphous after prominent sanidine phenocrysts.

Fig. 5.

Photographs of the Marcapunta area and drill core. a. Western flank of Marcapunta volcano. b. Flow-foliated dacitic lava. c. Argillic-altered dacite. d. Massive quartz-pyrite-enargite-Au limestone-breccia replacement. e. Bleached, but largely unaltered Mitu Group sandstone. f. Silicified and mineralized dacitic sill. g. Digenite, chalcocite, and covellite replacing alunitized dacite. Note alunite, pseudomorphous after prominent sanidine phenocrysts.

Fig. 6.

Ore microscopic features. a. Quartz (qtz), pyrite (py-1 and py-2) matrix. b. Pyrite (py-l)-enargite (en) assemblage. c. Pyrite (py) replaced by hypogene chalcocite (cc) and digenite (dg). d. Pyrite (py-1) replaced by hypogene covellite (cv) and digenite (dg). e. Late-stage colloform pyrite (py-3) with marcasite (mc) veinlet cutting covellite (cv) and sphalerite (ef). f. Late-stage colloform pyrite (py-3) with marcasite (mc) cut by late-stage enargite (en) and covellite (cv).

Fig. 6.

Ore microscopic features. a. Quartz (qtz), pyrite (py-1 and py-2) matrix. b. Pyrite (py-l)-enargite (en) assemblage. c. Pyrite (py) replaced by hypogene chalcocite (cc) and digenite (dg). d. Pyrite (py-1) replaced by hypogene covellite (cv) and digenite (dg). e. Late-stage colloform pyrite (py-3) with marcasite (mc) veinlet cutting covellite (cv) and sphalerite (ef). f. Late-stage colloform pyrite (py-3) with marcasite (mc) cut by late-stage enargite (en) and covellite (cv).

Fig. 7.

Paragenetic sequence of the Marcapunta enargite-Au deposit.

Fig. 7.

Paragenetic sequence of the Marcapunta enargite-Au deposit.

The pyrite, enargite, and covellite mineralization is clearly followed by deposition of digenite in close association with chalcocite. Coarse-grained crystalline aggregates and veins of digenite and chalcocite are considered to be of hypogene origin and occur as cement to microbreccias that crosscut pyrite, enargite, and barite. Replacement by these sulfide minerals blurs the rectilinear fracture patterns in the preexisting sulfide mineral and results in an anastomosing network (Fig. 6c-d). Occasionally, replacement is complete. Thus, the main-stage hypogene paragenesis may be subdivided into enargite-covellite followed by digenite-chalcocite substages. The Smelter and northern Marcapunta orebodies consist of relatively homogeneous enargite. The recently discovered western Marcapunta mineralization has both enargite- and digenite-bearing zones (Figs. 34). Late-stage hypogene veinlets of colloform pyrite, with marcasite cores and cut by enargite-covellite veinlets, are known only from the recently drilled western Marcapunta extensions (Fig. 6e-f).

Dacitic sills, emplaced between the Mitu Group red beds and the silicified Calera Formation, are also altered and mineralized in western Marcapunta. Porphyritic textures are preserved with alunite and pyrite psedomorphous after relict quartz and sanidine phenocrysts. The sanidine pseudomorphs are, in turn, selectively replaced by digenite and chalcocite plus subordinate covellite and enargite (Fig. 5f-g).

Supergene oxidation and precious metal enrichment affected the uppermost parts of the Marcapunta sulfide bodies. The oxide zone is selectively developed along fractures and within porous portions of the silicified hanging-wall dacite. Vuggy quartz rock, with trace to 15 percent limonite fillings and coatings, typically assay 0.5 to 5 ppm Au and 10 to 200 ppm Ag and occur as lenticular bodies varying from 5 to 35 m in thickness above the massive sulfide limestone-replacement deposits (Figs. 34). Supergene Cu enrichment, immediately below the oxide zone, is characterized by sooty chalcocite coatings on pyrite, with or without supergene sphalerite, but does not give rise to a widespread blanket. Most of the digenite and chalcocite are located below the massive pyrite-and enargite-dominated mantos, indicative of hypogene deposition (Figs. 34, 7). Similar overprinting of strongly developed hypogene Cu enrichment has been noted in other deep, high-sulfidation systems in the southwestern Pacific región (Sillitoe, 1999).

Geochemical Zonation

Enargite-Au deposits worldwide are magmatic-hydrothermal Fe-Cu-As-Au systems with a complex geochemical signature that includes Ag, Bi, Sb, Te, Ba, W, and Pb. They are particularly abundant in the Cerro de Pasco and Cajamarca regions of Peru, which host numerous Miocene deposits of this type (Vidal and Cedillo, 1988). Figure 8 shows the metal content contours for Cu and Au in the Marcapunta deposits. The Marcapunta Cu-Au system is 3 km north-south, with widths varying from a few hundred to ~1,500 m. Copper contents increase as the volcanic center is approached. The northern Marcapunta area has the highest arsenic and copper contents (Fig. 9a). Similarly, Au is clearly related to the volcanic center and appears to be enriched in the southwestern part of the system. Localized areas of ≥2 ppm Au are known in the Smelter and northern Marcapunta areas, with up to 6 ppm in the western Marcapunta zone. Underground in the Smelter zone, an elongate shoot shows Au enrichment southward toward the Marcapunta center (Fig. 9b). Gold contents in sulfide ore are typically <10 ppm and, based on present knowledge, do not seem to be as enriched as in epithermal telluride-bearing ores elsewhere, such as Orcopampa in southern Peru and Vatukoula in Fiji (Mayta et al., 2002; Pals et al., 2003).

Fig. 8.

a. Copper distribution at Marcapunta. b. Gold distribution at Marcapunta. Grade × thickness contours; same area as shown in Figure 2a-b. Smelter inset shown in Figure 9. Sections of Figures 3 and 4 shown in (b) for reference.

Fig. 8.

a. Copper distribution at Marcapunta. b. Gold distribution at Marcapunta. Grade × thickness contours; same area as shown in Figure 2a-b. Smelter inset shown in Figure 9. Sections of Figures 3 and 4 shown in (b) for reference.

Fig. 9.

Geochemical distribution in the upper enargite manto of the Smelter area. a. Copper. b. 100 Au/Ag ratio.

Fig. 9.

Geochemical distribution in the upper enargite manto of the Smelter area. a. Copper. b. 100 Au/Ag ratio.

Implications for Exploration

All genetic models proposed for the Colquijirca mining district recognize Marcapunta as the main hydrothermal center (McKinstry, 1936; Lehne, 1980; Vidal et al., 1984, 1997; Rivera, 2002; Bendezú et al., 2003). Discussion and controversy have mostly surrounded the structure of the volcanic edifice, formerly considered as a high-level intrusive stock (Lacy, 1953; Cobbing et al., 1981). Other matters of current debate include the age and duration of the magmatic-hydrothermal system, its metal zoning, and the ultimate mineral potential. Geochronologic knowledge remains incomplete despite increased precision in recent dating of volcanic rocks and alteration minerals from Marcapunta. Biotites were dated at 11.5 ± 0.4 Ma using the K-Ar method (Vidal et al., 1984) and 12.4 ± 0.1 Ma by the 40Ar/39Ar method (Bendezú et al., 2003). Structural and geochemical similarities are apparent with other Au-bearing enargite systems, such as Bisbee in Arizona and Lepanto in the Philippines (Sillitoe, 1988; Hedenquist et al., 1998).

The high-sulfidation, limestone-replacement, massive to semimassive pyritic, enargite-Au deposits discovered at Marcapunta are open and untested both at depth and laterally to the south and southwest toward San Gregorio (Fig. 1). Chalcocite stringers, with only traces of pyrite and quartz, are found in sandstone of the Mitu Group along the western diatreme wall and possibly indicate deeper, porphyry copper-type mineralization. To date, however, no direct evidence of such mineralization has been found. Nevertheless, a buried hydrothermal system associated with a blind porphyry copper-bearing stock remains a possibility at depth. Such mineralization, however, is not the prime objective of current exploration programs and its hypothetical occurrence needs to be tested first by additional geologic and geophysical modeling.

Effective exploration for high-sulfidation epithermal deposits at Marcapunta relies on detailed structural mapping and selective sampling of mineralized veinlets, breccia dikes, and reactivated faults. At surface, 100 to 300 m above the massive sulfide deposits, geochemical leakage has produced anomalies for Cu, Au, As, Bi, and Te with high Cu/Au and Cu/As ratios. These, in conjunction with geologically constrained residual gravity maps, have been used to design and prioritize exploration drilling. Targeting for, and delineation of, higher grade orebodies and extensions to known ones is largely a trial-and-error drilling exercise. Buried Cu-Au deposits are still believed to exist, with prospectivity increasing along the western diatreme walls in the center of an 8-km-long, north-south mineralized belt defined by the Colquijirca, Marcapunta, and San Gregorio deposits (Fig. 1).

Hydrothermal fluid migrated upward around and away from the diatreme, with replacement of the carbonate rocks beneath the dacitic flow-dome complex. The fluid became neutralized as it progressed from the strongly acidic Cu- and Au-depositing environment to the near-neutral Zn- Pb- and Ag-enriched zone, as discussed in the case of nearby Cerro de Pasco by Graton and Bowditch (1936). Carbonate rocks dissolved by acidic fluid formed a widespread halo rich in pyrite and quartz and is further characterized by the occurrence of hematite or siderite with minor sphalerite and trace to 1 percent Zn. Such district-scale zoning is the most compelling feature for guiding exploration in the Colquijirca, Cerro de Pasco, and other limestone-hosted, enargite-bearing districts in the Andes of Peru.

Conclusions

The Marcapunta volcanic center generated multiple hydrothermal cells, which formed an extensive blanketlike horizon of enargite-Au mineralization in the core of a zoned base and precious metal district. Gold-enriched, arsenical Cu deposits in limestone-replacement quartz-pyrite mantos were emplaced in a subvolcanic setting around a central diatreme. Strata-bound Cu mantos flare laterally from beneath below the northern, western, and southwestern flanks of the Marcapunta volcanic center. This central or proximal Cu mineralization grades to both north and south through high-grade Pb and Zn sulfide ore into distal zones rich in Ag- and Sb-bearing sulfosalts. The outermost halo in the well-developed, district-scale zoning pattern is characterized by low-grade Zn in association with abundant siderite or hematite.

Hypogene enargite and digenite zones occur only beneath the western flanks of Marcapunta. Hypogene Cu enrichment with Au gave rise to a nonarsenical, low Au, Cu-enriched horizon emplaced deep in the high-sulfidation epithermal column, as discussed for other comparable deposits worldwide (Sillitoe, 1999). Such hypogene Cu enrichment may result from meteoric water ingress to the core of the magmatichydrothermal system, thus generating deep hypogene oxidation, as proposed by Brimhall (1980).

The total resource inventory for the Colquijirca mining district is estimated to be about 2 Mt of contained Cu with 3 Moz of Au at Marcapunta, surrounded by 9 Mt of Zn and 300 Moz Ag in San Gregorio and Colquijirca. Often, as recognized by McLaughlin (1939), the magnitude of mining districts is only appreciated after decades of research and exploration. The major precious metal-bearing Cu and Zn deposits of Marcapunta and San Gregorio, respectively, would be defined as giants using the criteria of Singer (1995), and the district remains open for the discovery of new orebodies and deposit extension.

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Gold telluride-native gold veins of the Chipmo zone, Orcopampa district, southern Peru [abs.]
:
Congreso Peruano de Geología, 11th, Lima, 2002
 ,
Sociedad Geológica del Perú
,
Resúmenes
, p.
240
.
McKinstry
,
H.E.
,
1936
,
Geology of the silver deposit at Colquijirca, Peru
:
Economic Geology
 , v.
31
, p.
619
635
.
McLaughlin
,
D.H.
,
1924
,
Geology and physiography of the Peruvian Cordillera, Departments of Junín and Lima
:
Geological Society of America Bulletin
 , v.
35
, p.
591
632
.
McLaughlin
,
D.H.
1939
,
Geological factors in the valuation of mines
:
Economic Geology
 , v.
34
, p.
589
621
.
Mégard
,
F.
,
1978
,
Etude géologique d’une transversale des Andes au niveau du Pérou Central. Contribution a l’étude géologique du Pérou Central
 :
Paris
,
ORSTOM, Memoires
86
,
310
p.
Noble
,
J.A.
Butz
,
W.
,
1931
,
Colquijirca examination 1930–31: Cerro de Pasco Copper Corporation, Geological Department, Exploration Division
 ,
unpublished report
.
Pals
,
D.W.
Spry
,
P.G.
Chryssoulis
,
S.
,
2003
,
Invisible gold and tellurium in arsenic-rich pyrite from the Emperor gold deposit, Fiji: Implications for gold distribution and deposition
:
Economic Geology
 , v.
98
, p.
479
494
.
Pérez-Arauco
,
C.
,
1996
,
Cerro de Pasco. Historia del pueblo mártir del Perú. Siglos XVI, XVII, XVIII y XIX
 :
Perú
,
Instituto Nacional de Cultura de Pasco, Cerro de Pasco
,
449
p.
Petersen
,
U.
Vidal
,
C.E.
,
1996
,
Magmatic and tectonic controls on the nature and distribution of copper deposits in Peru
:
Society of Economic Geologists Special Publication
 
5
, p.
1
18
.
Rivera
,
N.
,
2002
,
Metalogenia del distrito mineral de Cerro de Pasco
:
Boletín de la Sociedad Geológica del Perú
 , v.
94
, p.
71
97
.
Rogers
,
R.
,
1983
,
Structural and geochemical evolution of a mineralized volcanic vent at Cerro de Pasco, Peru
:
Unpublished Ph.D. thesis
,
Tucson
,
University of Arizona
,
116
p.
Sáez
,
J.
,
2003
,
Estudio al microscopio de 20 muestras (14 secciones pulidas y 6 secciones delgadas) del proyecto Marcapunta, distrito minero de Colquijirca
 :
Lima
,
Sociedad Minera El Brocal S.A.A.
,
unpublished report
,
85
p.
Sempere
,
T.
Carlier
,
G.
Soler
,
P.
Fornari
,
M.
Carlotto
,
V.
Jacay
,
J.
Arispe
,
O.
Néraudeau
,
D.
Cárdenas
,
J.
Rosas
,
S.
Jiménez
,
N.
,
2002
,
Late Permian-Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics
:
Tectonophysics
 , v.
345
, p.
153
181
.
Silberman
,
M.L.
Noble
,
D.C.
,
1977
,
Age of igneous activity and mineralization, Cerro de Pasco, central Peru
:
Economic Geology
 , v.
72
, p.
925
930
.
Sillitoe
,
R.H.
,
1988
,
Gold and silver in porphyry systems
, in
Schafer
,
R.
Cooper
,
J.J.
Vikre
,
P.G.
, eds.,
Bulk mineable precious deposits of the western United States. Symposium Proceedings
 :
Reno
,
Geological Society of Nevada, Proceedings
, p.
233
258
.
Sillitoe
,
R.H.
1999
,
Styles of high-sulphidation gold, silver and copper mineralisation in porphyry and epithermal environments
:
Pacrim ’99 Conference, Bali, Indonesia, 1999
 ,
Melbourne
,
Australasian Institute of Mining and Metallurgy, Proceedings
, p.
29
44
.
Singer
,
D.A.
,
1995
,
World class base and precious metal deposits: A qualitative analysis
:
Economic Geology
 , v.
90
, p.
88
104
.
Stoffregen
,
R.
,
1987
,
Genesis of acid-sulfate alteration and Au-Cu-Ag mineralization at Summitville, Colorado
:
Economic Geology
 , v.
82
, p.
1575
1591
.
Vidal
,
C.E.
Cedillo
,
E.
,
1988
,
Los yacimientos de enargita-alunita en el Perú
:
Boletín de la Sociedad Geológica del Perú
 , v.
78
, p.
109
120
.
Vidal
,
C.E.
Mayta
,
O.
Noble
,
D.C.
McKee
,
E.H.
,
1984
,
Sobre la evolución de soluciones hidrotermales desde el centro volcánico Marcapunta, en Colquijirca, Pasco
:
Sociedad Geológica del Perú
 , Volumen Jubilar
600
Aniversario, Fascículo 10
, p.
1
14
.
Vidal
,
C.E.
Proaño
,
J.A.
Noble
,
D.C.
,
1997
,
Geología y distribución hidrotermal de menas con Au, Cu, Zn, Pb y Ag en el distrito minero Colquijirca, Pasco [ext. abs.]
:
Congreso Peruano de Geología, 9th, Lima, 1997, Sociedad Geológica del Perú, Resúmenes Extendidos
 , Volumen Especial
1
, p.
217
219
.

Acknowledgments

Sociedad Minera “El Brocal” S.A.A. is gratefully acknowledged for permission to publish and for the continued support provided by its Board of Directors and General Manager, Ysaac Cruz. El Brocal geologists Ivan Monteagudo, Carlos Yacila, and Marco Panez, together with Mario Rosas and Juan Carlos Sarmiento of Compaóía de Minas Buenaventura S.A.A., comprise the exploration team and are recognized for their combined efforts in the mapping, logging, sampling, and information processing during this fascinating discovery.

An original draft was reviewed and much improved by Noel White and Steve Turner, while a later version was edited by José Perelló and Richard Sillitoe. We thank them all for their constructive editorial suggestions, which turned a draft contribution into a readable paper.

Figures & Tables

Fig. 1.

Location and geologic map of the Cerro de Pasco-Colquijirca region. Modified from Angeles (1999).

Fig. 1.

Location and geologic map of the Cerro de Pasco-Colquijirca region. Modified from Angeles (1999).

Fig. 2.

Plans of the Marcapunta volcano. a. Hydrothermal alteration. b. Residual Bouger gravity contours, showing inferred outline of diatreme. North-south and east-west sections shown in Figures 3 and 4.

Fig. 2.

Plans of the Marcapunta volcano. a. Hydrothermal alteration. b. Residual Bouger gravity contours, showing inferred outline of diatreme. North-south and east-west sections shown in Figures 3 and 4.

Fig. 3.

North-south section, showing Marcapunta geology and mineralization. Section marked in Figure.

Fig. 3.

North-south section, showing Marcapunta geology and mineralization. Section marked in Figure.

Fig. 4.

East-west section of Marcapunta geology and mineralization. Symbols as in Figure 3.

Fig. 4.

East-west section of Marcapunta geology and mineralization. Symbols as in Figure 3.

Fig. 5.

Photographs of the Marcapunta area and drill core. a. Western flank of Marcapunta volcano. b. Flow-foliated dacitic lava. c. Argillic-altered dacite. d. Massive quartz-pyrite-enargite-Au limestone-breccia replacement. e. Bleached, but largely unaltered Mitu Group sandstone. f. Silicified and mineralized dacitic sill. g. Digenite, chalcocite, and covellite replacing alunitized dacite. Note alunite, pseudomorphous after prominent sanidine phenocrysts.

Fig. 5.

Photographs of the Marcapunta area and drill core. a. Western flank of Marcapunta volcano. b. Flow-foliated dacitic lava. c. Argillic-altered dacite. d. Massive quartz-pyrite-enargite-Au limestone-breccia replacement. e. Bleached, but largely unaltered Mitu Group sandstone. f. Silicified and mineralized dacitic sill. g. Digenite, chalcocite, and covellite replacing alunitized dacite. Note alunite, pseudomorphous after prominent sanidine phenocrysts.

Fig. 6.

Ore microscopic features. a. Quartz (qtz), pyrite (py-1 and py-2) matrix. b. Pyrite (py-l)-enargite (en) assemblage. c. Pyrite (py) replaced by hypogene chalcocite (cc) and digenite (dg). d. Pyrite (py-1) replaced by hypogene covellite (cv) and digenite (dg). e. Late-stage colloform pyrite (py-3) with marcasite (mc) veinlet cutting covellite (cv) and sphalerite (ef). f. Late-stage colloform pyrite (py-3) with marcasite (mc) cut by late-stage enargite (en) and covellite (cv).

Fig. 6.

Ore microscopic features. a. Quartz (qtz), pyrite (py-1 and py-2) matrix. b. Pyrite (py-l)-enargite (en) assemblage. c. Pyrite (py) replaced by hypogene chalcocite (cc) and digenite (dg). d. Pyrite (py-1) replaced by hypogene covellite (cv) and digenite (dg). e. Late-stage colloform pyrite (py-3) with marcasite (mc) veinlet cutting covellite (cv) and sphalerite (ef). f. Late-stage colloform pyrite (py-3) with marcasite (mc) cut by late-stage enargite (en) and covellite (cv).

Fig. 7.

Paragenetic sequence of the Marcapunta enargite-Au deposit.

Fig. 7.

Paragenetic sequence of the Marcapunta enargite-Au deposit.

Fig. 8.

a. Copper distribution at Marcapunta. b. Gold distribution at Marcapunta. Grade × thickness contours; same area as shown in Figure 2a-b. Smelter inset shown in Figure 9. Sections of Figures 3 and 4 shown in (b) for reference.

Fig. 8.

a. Copper distribution at Marcapunta. b. Gold distribution at Marcapunta. Grade × thickness contours; same area as shown in Figure 2a-b. Smelter inset shown in Figure 9. Sections of Figures 3 and 4 shown in (b) for reference.

Fig. 9.

Geochemical distribution in the upper enargite manto of the Smelter area. a. Copper. b. 100 Au/Ag ratio.

Fig. 9.

Geochemical distribution in the upper enargite manto of the Smelter area. a. Copper. b. 100 Au/Ag ratio.

Table 1.

Copper Concentrate Production from the Smelter Area, 1974 to 1982 Period

YearMetric tonsCu (%)As (%)Au (ppm)Ag (ppm)
197412,94725.15nana325
197513,68726.08nana180
19769,87622.93nana118
19775,54924.53nana104
19782,15025.288.652.40130
19793,81925.788.603.50130
198080324.388.294.63171
19815,75024.588.394.08116
19822,38132.6210. 095.41134
1974–198256,96225.228.944.08181
YearMetric tonsCu (%)As (%)Au (ppm)Ag (ppm)
197412,94725.15nana325
197513,68726.08nana180
19769,87622.93nana118
19775,54924.53nana104
19782,15025.288.652.40130
19793,81925.788.603.50130
198080324.388.294.63171
19815,75024.588.394.08116
19822,38132.6210. 095.41134
1974–198256,96225.228.944.08181

Notes: na = not available

Contents

GeoRef

References

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98
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494
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Perú
,
Instituto Nacional de Cultura de Pasco, Cerro de Pasco
,
449
p.
Petersen
,
U.
Vidal
,
C.E.
,
1996
,
Magmatic and tectonic controls on the nature and distribution of copper deposits in Peru
:
Society of Economic Geologists Special Publication
 
5
, p.
1
18
.
Rivera
,
N.
,
2002
,
Metalogenia del distrito mineral de Cerro de Pasco
:
Boletín de la Sociedad Geológica del Perú
 , v.
94
, p.
71
97
.
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,
R.
,
1983
,
Structural and geochemical evolution of a mineralized volcanic vent at Cerro de Pasco, Peru
:
Unpublished Ph.D. thesis
,
Tucson
,
University of Arizona
,
116
p.
Sáez
,
J.
,
2003
,
Estudio al microscopio de 20 muestras (14 secciones pulidas y 6 secciones delgadas) del proyecto Marcapunta, distrito minero de Colquijirca
 :
Lima
,
Sociedad Minera El Brocal S.A.A.
,
unpublished report
,
85
p.
Sempere
,
T.
Carlier
,
G.
Soler
,
P.
Fornari
,
M.
Carlotto
,
V.
Jacay
,
J.
Arispe
,
O.
Néraudeau
,
D.
Cárdenas
,
J.
Rosas
,
S.
Jiménez
,
N.
,
2002
,
Late Permian-Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics
:
Tectonophysics
 , v.
345
, p.
153
181
.
Silberman
,
M.L.
Noble
,
D.C.
,
1977
,
Age of igneous activity and mineralization, Cerro de Pasco, central Peru
:
Economic Geology
 , v.
72
, p.
925
930
.
Sillitoe
,
R.H.
,
1988
,
Gold and silver in porphyry systems
, in
Schafer
,
R.
Cooper
,
J.J.
Vikre
,
P.G.
, eds.,
Bulk mineable precious deposits of the western United States. Symposium Proceedings
 :
Reno
,
Geological Society of Nevada, Proceedings
, p.
233
258
.
Sillitoe
,
R.H.
1999
,
Styles of high-sulphidation gold, silver and copper mineralisation in porphyry and epithermal environments
:
Pacrim ’99 Conference, Bali, Indonesia, 1999
 ,
Melbourne
,
Australasian Institute of Mining and Metallurgy, Proceedings
, p.
29
44
.
Singer
,
D.A.
,
1995
,
World class base and precious metal deposits: A qualitative analysis
:
Economic Geology
 , v.
90
, p.
88
104
.
Stoffregen
,
R.
,
1987
,
Genesis of acid-sulfate alteration and Au-Cu-Ag mineralization at Summitville, Colorado
:
Economic Geology
 , v.
82
, p.
1575
1591
.
Vidal
,
C.E.
Cedillo
,
E.
,
1988
,
Los yacimientos de enargita-alunita en el Perú
:
Boletín de la Sociedad Geológica del Perú
 , v.
78
, p.
109
120
.
Vidal
,
C.E.
Mayta
,
O.
Noble
,
D.C.
McKee
,
E.H.
,
1984
,
Sobre la evolución de soluciones hidrotermales desde el centro volcánico Marcapunta, en Colquijirca, Pasco
:
Sociedad Geológica del Perú
 , Volumen Jubilar
600
Aniversario, Fascículo 10
, p.
1
14
.
Vidal
,
C.E.
Proaño
,
J.A.
Noble
,
D.C.
,
1997
,
Geología y distribución hidrotermal de menas con Au, Cu, Zn, Pb y Ag en el distrito minero Colquijirca, Pasco [ext. abs.]
:
Congreso Peruano de Geología, 9th, Lima, 1997, Sociedad Geológica del Perú, Resúmenes Extendidos
 , Volumen Especial
1
, p.
217
219
.

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