A model for the intrusive sequence and Cu-Zn skarn formation at the Antamina deposit, Peru

Mrozek, S.A., Chang, Z., and Meinert, L.D. (2015) A model for the intrusive sequence and Cu-Zn skarn formation at the Antamina deposit, Peru. In: Proceedings of PACRIM 2015. pp. 423-429. From: PACRIM 2015 Congress, 18-21 March 2015, Hong Kong, China.

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Abstract

Antamina, Peru is the largest Cu-Zn skarn deposit in the world. Skarn mineralisation is focused around a multiphase Miocene intrusive complex comprising at least eight distinct phases identified by cross-cutting relationships, including truncated veins, xenoliths and chilled margins. Skarn alteration and mineralisation, as observed in drill core, remain open at depths exceeding 2.2 vertical kilometres. Porphyry intrusions occur as four major phases with subphases (from oldest to youngest): P1 (a, b), P2 (a, b), P3 (a, b) and two dykes of uncertain timing named Oscarina-1 and Oscarina-2. Pla is a hornblende-biotite quartz diorite porphyry with pervasive K-alteration, local endoskarn and 30-40 per cent sheeted quartz veins, all of which obscure original igneous textures. P1b dacite porphyry is a minor unit with <10 per cent phenocrysts and <3 per cent quartz veins. Plb cuts Pla; P2 dykes cut both units. P2a porphyritic biotite quartz monzonite contains K-feldspar megacrysts up to 4 em long, local K-alteration and 2-80 per cent quartz stockwork veins. P2b biotite monzonite porphyry contains approximately 50 per cent phenocrysts and typically <10 per cent quartz veins. P3a (brown groundmass porphyry) and P3b (coarse phenocryst porphyry) are minor in volume and extent, and both cut P2 bodies. Oscarina dykes comprise two separate but parallel bodies. Oscarina-1 is a feldspar-phyric rhyolite porphyry, while Oscarina-2 is an intensely chloritised andesite porphyry. Oscarina-l has a U-Pb (laser ablation inductively coupled mass spectrometry (LA-ICP-MS)) age of 10.1 ± 0.1 Ma, whereas P2 U-Pb zircon ages (LA-ICP-MS) range from 10.0 ± 0.2 Ma to 9.9 ± 0.3 Ma. All the intrusive phases contain quartz veins, with Pla and P2a having the most intensive K-alteration and most abundant quartz veins ± endoskarns. Each phase may have contributed to mineralisation at the right depths and within favourable wall rocks (ie marble) during uplift of the Antamina structural block. Therefore, a model of multiple intrusions during continuous uplift explains the vertically extensive (>2.2 km) skarn and mineralisation at Antamina.

Item ID: 38254
Item Type: Conference Item (Research - E1)
ISBN: 978-1-925100-25-9
Date Deposited: 16 Jun 2015 04:03
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840102 Copper Ore Exploration @ 70%
84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840108 Zinc Ore Exploration @ 30%
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