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The Quiruvilca Cu-Pb-Zn district is located in the District of Quiruvilca, Province of Santiago de Chuco, Department of La Libertad, in northwestern Peru, ~76 km east of the city of Trujillo. Elevations in the immediate mine area range from 3450 to 4075 m asl (#Location: 8° 0' 43"S, 78° 19' 20"W).
Mining at Quiruvilca was first documented in 1789, with early activity on a small scale and principally for silver. From 1895, argentiferous copper became an important product. During the early 20th century, the mines in the area were consolidated into the Sociedad Minera Quiruvilca. In 1919, the copper-rich central part of the district was optioned to the newly formed Northern Peru Mining and Smelting Company, which took formal control of the district in 1924. The district has been in almost continuous production from 1924, except for the period 1931 to 1940. Between 1940 and 1981, ~8.1 @ 1.27 g/t Au, 140 g/t Ag, and 2.97%. Cu. Prior to 1967, only Cu, Ag and Au were produced. At that time, the emphasis shifted from the copper-rich central portion to the complex Cu-Pb-Zn ores in the outer silver-rich portion of the district. In 1980, ~0.3 Mt @ 1.3 g/t Au, 175 g/t Ag, 1.38% Cu, 1.36% Pb, 4.06% Zn were milled (Bartos, 1984; NB. these figures are metricated and original tons assumed to be short tons).
The Quiruvilca mine extends over an area that is 4 km east-west by 3 km north-south and from an RL of 4050 m at the top of the mountain down to the 340 m RL (an elevation difference of ~3537 m. More than 130 narrow polymetallic veins are known in this area, at least 75% of which have been in production. Access to the current mine has been from seven adits driven into the side of the mountain at elevations ranging from 3925 to 3650m.
For details of the regional setting, see the separate Peruvian Andes Cu-Au Province record.
The Quiruvilca deposit is located within the eastern margin of a major sequence of volcanic rocks, interpreted be part of the Mid-Miocene Calipuy Volcanic complex (Bartos, 1984). This sequence has a thickness of ~2000 m, and consists of andesite flows and flow breccias inter-layered with thin basalt flows and occasional tuffaceous lacustrine sediments.
Although narrow, the veins at Quiruvilca tend to have an extensive lateral and vertical continuity with abundant splits, cymoid loops, pinch and swell structures. In some places, the veins show some thick ore shoots connected to thinner diagonal sub-economic to non-economic zones. The width varies up to two metres in the central zone to stringers in the Zinc-Lead Zone (as defined below). The average width of veins currently being mined is 0.65 metres. The average dip of the veins is 70 degrees, but range from vertical to 40 degrees.
Mineralisation is hosted by tension gash veins produced as a result of sinsitral strike-slip faulting cutting the central facies of a Miocene andesitic stratovolcanic complex. Over 130 veins are known, of which 75% have been mined. Although narrow, the veins at Quiruvilca tend to have an extensive lateral and vertical continuity with abundant splits, cymoid loops, pinch and swell structures. In some places, the veins show some thick ore shoots connected to thinner diagonal sub-economic to non-economic zones. The width of the veins average ~0.3 m in thickness, but may be as thick as 2.5 m in the central zone to stringers in the 'lead-zinc zone' (see below). The average width of veins being mined in 2003 was 0.65 metres, with an average dip of 70°, ranging from vertical to 40°. These veins are typically coarse grained but are extensive and have persistant mineralisation and grades, although in detail they may comprise thick shoots connected by thin sub-ore necks.
There are four broadly concentric mineralogic zones from the centre to the periphery of the district of:
i). the central copper-rich 'energite zone' zone, which covers an area of ~700 x 2800 m, predominately consists of enargite-pyrite, with lesser chalcopyrite, tennantite, tetrahedrite, sphalerite and galena,
ii). the 'transitional zone', which is relatively narrow, characterised by tennantite, tetrahedrite, sphalerite and galena, but no enargite,
iii). 'lead-zinc zone', with predominately sphalerite and galena and base metal carbonates, which extends some 500 m beyond the Transition Zone. In recent years some 70% of the Quiruvilca mine's production has come from the Zinc-Lead Zone.
iv). 'outer zone' with stibnite, arsenopyrite and pyrites and lesser lead and zinc.
Irrespective of their position in these zones, all have the same gross paragenesis stages of pyrite → base metals → sulphosalts → carbonate. The volume of each paragenetic stage varies across the district, with veins closest to the centre contain relatively greater proportions of the earlier paragenetic
stage assemblages. Individual veins are commonly zoned about major structural intersections. Typically there is an Ag-rich pyritic core with distal sphalerite-galena or carbonate-dominant fringes. The principal development of pervasive alteration was contemporaneously with the pyrite stage of mineralisation. Ore deposition was principally in the base metal stage, such that, ore formation in the veins largely part postdated the formation of the alteration selvages about the veins. Wall rock alteration proceeds outwards from the vein margins from intense sericite, to strong sericite, to moderate sericite, to strong argillic, to weak argillic and to propylitic (Bartos, 1984).
Based on mineral stabilities and thermodynamic data, ore deposition occurred from >320 to 230°C, decreasing with time. The sulphidation state and activity of hydrogen ion decreased both with time and laterally away from the district centre (Bartos, 1984).
Historic reserve grades are quoted as 2.85% Cu, 1.97% Pb, 5.78% Zn, 225 g/t Ag (Bartos, 1987).
Remaining ore reserves and mineral resources at 31 December 2002 were (Pan American Silver Corporation, 2002) were:
Proved + probable reserves - 2.1091 Mt @ 186 g/t Ag, 4.39% Zn, 1.59% Pb, 0.47% Cu.
Measured + indicated resources - 1.4820 Mt @ 179 g/t Ag, 3.69% Zn, 1.37% Pb, 1.61% Cu;
Inferred resources - 2.0441 Mt @ 170 g/t Ag, 4.45% Zn, 1.64% Pb, 0.43% Cu.
Note: reserves are additional to resources.
For detail see the reference(s) listed below. Information is also taken from "Annual Information Form by Pan American Silver Corp, Report Year Ended December, 31, 2002, to Securities and Exchange Commission, Washington DC.". Information in that report and this record is based largely on "Bartos, P.J., 1984 - Mineralization, alteration, and zoning of the Cu-Pb-Zn-Ag lodes at Quiruvilca, Peru; MSc thesis submitted to the Department of Applied Sciences, Stanford University, 219p."
The most recent source geological information used to prepare this summary was dated: 2002.
Record last updated: 26/9/2016
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
References to this deposit in the PGC Literature Collection:
Bartos P J 1987 - Quiruvilca, Peru: mineral zoning and timing of wall-rock alteration relative to Cu-Pb-Zn-Ag vein-fill deposition: in Econ. Geol. v82 pp 1431-1452|
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