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Timing of porphyry (Cu-Mo) and base metal (Zn-Pb-Ag-Cu) mineralisation in a magmatic-hydrothermal system—Morococha district, Peru

Stein, Holly
Published in Mineralium Deposita. 2015, vol. 50, p. 895-922.
Abstract The Morococha district in central Peru is characterised by economically important Cordilleran polymetallic (Zn-Pb-Ag-Cu) vein and replacement bodies and the large Toromocho porphyry Cu-Mo deposit in its centre. U-Pb, Re-Os, and 40Ar/39Ar geochronology data for various porphyry-related hydrothermal mineralisation styles record a 3.5-Ma multi-stage history of magmatichydrothermal activity in the district. In the lateMiocene, three individual magmatic-hydrothermal centres were active: the Codiciada, Toromocho, and Ticlio centres, each separated in time and space. The Codiciada centre is the oldest magmatichydrothermal system in the district and consists of a composite porphyry stock associated with anhydrous skarn and quartz-molybdenite veins. The hydrothermal events are recorded by a titanite U-Pb age at 9.3±0.2 Ma and a molybdenite Re-Os age at 9.26 ± 0.03 Ma. These ages are indistinguishable from zircon U-Pb ages for porphyry intrusions of the composite stock and indicate a time span of 0.2 Ma for magmatic-hydrothermal activity. The small Ticlio magmatic-hydrothermal centre in the west of the district has a maximum duration of 0.3 Ma, ranging from porphyry emplacement to porphyry mineralisation at 8.04±0.14 Ma (40Ar/39Ar muscovite cooling age). The Toromocho magmatic-hydrothermal centre has a minimum of five recorded porphyry intrusions that span a total of 1.3 Ma and is responsible for the formation of the giant Toromocho Cu- Mo deposit. At least two hydrothermal pulses are identified. Post-dating a first pulse of molybdenite mineralisation, widespread hydrous skarn covers an area of over 6 km2 and is recorded by five 40Ar/39Ar cooling ages at 7.2–6.8 Ma. These ages mark the end of the slowly cooling and long-lived Toromocho magmatic-hydrothermal centre soon after last magmatic activity at 7.26±0.02 Ma. District-wide (50 km2) Cordilleran base metal vein and replacement bodies post-date the youngest recorded porphyry mineralisation event at Toromocho by more than 0.5 Ma. Polymetallic veins (5.78± 0.10 and 5.72±0.18 Ma; 40Ar/39Ar ages) and the Manto Italia polymetallic replacement bodies (6.23±0.12 and 6.0±0.2Ma; 40Ar/39Ar ages) are interpreted to have been formed by a single hydrothermal pulse. Hydrothermal activity ceased after the formation of the base metal vein and replacement bodies. Overlapping monazite U-Pb (8.26±0.18 Ma) and muscovite 40Ar/39Ar ages (8.1±0.5 Ma) from the early base metal stage of one Cordilleran vein sample in the Sulfurosa area provide evidence that a discrete hydrothermal pulse was responsible for polymetallic vein formation 2.6 Ma prior to the districtwide polymetallic veins. These ages pre-date those of Toromocho porphyry Cu-Mo formation and show that Zn- Pb-Ag-Cu mineralisation formed during several discrete magmatic-hydrothermal pulses in the same district.
Keywords GeochronologyZn-Pb-Ag-CuMorocochaPorphyryToromochoCordilleran polymetallic
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Other version: http://link.springer.com/10.1007/s00126-014-0564-x
Research group Mineral Resources and Geofluids
FNS: SNF20020-108026
(ISO format)
CATCHPOLE, Honza et al. Timing of porphyry (Cu-Mo) and base metal (Zn-Pb-Ag-Cu) mineralisation in a magmatic-hydrothermal system—Morococha district, Peru. In: Mineralium Deposita, 2015, vol. 50, p. 895-922. doi: 10.1007/s00126-014-0564-x https://archive-ouverte.unige.ch/unige:46836

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Deposited on : 2015-02-18

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