Relative age of Cordilleran base metal lode and replacement deposits, and high sulfidation Au?(Ag) epithermal mineralization in the Colquijirca mining district, central Peru

Abstract

At Colquijirca, central Peru, a predominantly dacitic Miocene diatreme-dome complex of 12.4 to 12.7 Ma ( 40 Ar/ 39 Ar biotite ages), is spatially related to two distinct mineralization types. Disseminated Au-(Ag) associated with advanced argillic alteration and local vuggy silica typical of high-sulfidation epithermal ores are hosted exclusively within the volcanic center at Marcapunta. A second economically more important mineralization type is characterized as ''Cordilleran base metal lode and replacement deposits.'' These ores are hosted in Mesozoic and Cenozoic carbonate rocks surrounding the diatreme-dome complex and are zoned outward from pyrite-enargite-quartz-alunite to pyritechalcopyrite-dickite-kaolinite to pyrite-sphalerite-galena-kaolinite-siderite. Alunite samples related to the Au-(Ag) epithermal ores have been dated by the 40 Ar/ 39 Ar method at 11.3-11.6 Ma and those from the Cordilleran base metal ores in the northern part of the district (Smelter and Colquijirca) at 10.6-10.8 Ma. The significant time gap ($0.5 My) between the ages of the two mineralization types in the Colquijirca district indicates they were formed by different hydrothermal events within the same magmatic cycle. The estimated time interval between the younger mineralization event (base metal mineralization) at $10.6 Ma and the ages of $12.5 Ma obtained on biotites from unmineralized dacitic domes flanking the vicinity of the diatreme vent, suggest a minimum duration of the magmatic-hydrothermal cycle of around 2 Ma. This study on the Colquijirca district offers for the first time precise absolute ages indicating that the Cordilleran base metal lode and replacement deposits were formed by a late hydrothermal event in an intrusive-related district, in this case post Au-(Ag) high-sulfidation epithermal mineralization.

Mineral Zoning and Geochemistry of Epithermal Polymetallic Zn-Pb-Ag-Cu-Bi Mineralization at Cerro de Pasco, Peru

“…In the Middle Miocene, magmatic activity affected the region (Silberman and Noble, 1977;Bendezú et al, 2003;Baumgartner, 2007;Bendezú, 2007) Hunt (1985), Dick et al (1994) First and second stage are referred to early and late Mineral abbreviations: asp = arsenopyrite; bn = bornite; cc = chalcocite; cp = chalcopyrite; cst = cassiterite, cv = covellite; dg = digenite; enr = enargite; fm = famatinite; gn = galena; lz = luzonite; mt = magnetite; mo = molybdenite; nk = nukundamite; po = pyrrhotite; pyrg = pyrargyrite; py = pyrite; sl = sphalerite; tn = tennantite; tt = tetrahedrite; wf = wolframite Rogers (1983) and Huanqui (1994, unpub. report dacitic diatreme breccia (known locally as Rumiallana Agglomerate), and sparse external volcanic deposits (only recognized southeast of the diatreme, in the Santa Rosa area; Fig.…”

“…A number of such base metal deposits are superimposed on porphyry copper deposits (e.g., Butte, Morococha), whereas others have no known link to mineralized porphyry deposits (Einaudi et al, 2003). In the porphyry environment, epithermal high-sulfidation Au-(Ag) deposits also may be overprinted by such base metal deposits (e.g., Bendezú et al, 2003).…”

“…The term Cordilleran base metal veins and/or deposits was subsequently used by Einaudi (1982), Gilbert and Park (1986), Bartos (1987), Macfarlane and Petersen (1990), Hemley and Hunt (1992), Bendezú and Fontboté (2002), and Bendezú et al (2003Bendezú et al ( , 2008. Cordilleran deposits have also been termed as Butte-type vein deposits (Meyer et al, 1968), polymetallic veins, and recently zoned base metal veins (Einaudi et al, 2003).…”

Cordilleran Epithermal Cu-Zn-Pb-(Au-Ag) Mineralization in the Colquijirca District, Central Peru: Deposit-Scale Mineralogical Patterns

“…1). These are the high-sulfidation Au-(Ag) ores emplaced within the Marcapunta diatreme-dome complex (Vidal et al, 1997;Bendezú et al, 2003), and the economically more important Cordilleran Cu-Zn-Pb-(Au-Ag) deposits hosted largely in carbonate sequences (Lindgren, 1935;McKinstry, 1936;Vidal et al, 1984;Bendezú et al, 2003Bendezú et al, , 2008Bendezú, 2007). The Cordilleran deposits include Colquijirca and Smelter or Marcapunta Norte (north of the Marcapunta volcanic complex), Marcapunta Oeste (west of Marcapunta), and San Gregorio, one of the largest undeveloped Zn-Pb deposits worldwide (south of Marcapunta, Fig.…”

“…Based on 40 Ar/ 39 Ar dating (Bendezú et al, 2003, the Cordilleran ores of Smelter and Colquijirca formed during the late hydrothermal history of the Colquijirca district at 10.8 and 10.6 Ma and postdated the episode of high-sulfidation epithermal Au-(Ag) mineralization in the Marcapunta volcanic complex, which formed at ~11.1 to 11.9 Ma in the center of the district, on the southern margin of the Colquijirca and Smelter deposits.…”