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A Model for the Intrusive Sequence and Skarn Formation
at the Antamina Deposit, Peru
S A Mrozek, Z Chang, and L D Meinert
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Introduction 1. Antamina geology
2. Intrusive sequence
3. Three-stage deposit model
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Antamina
Project Location
3
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A
A’
5 km
Antamina deposit
District Geology
A A’ 5000 m 4000 m 3000 m
Miocene
Cretaceous
Mgr - Granitic intrusion
Kcd - Celendin Fm. (limestone)
Kj - Jumasha Fm. (limestone)
Kpp - Pariatambo/Pariahuanca Fm. (limestone) Kcz - Carhuaz Fm. (sandstone And shale)
Kcu - Chimu Fm. (sandstone)
Kca - Chicama Fm. (sandy shale)
4
Kcd
Kj
Kj
Kj
Kcd
Kcd
Kcd
Mgr
Mgr
Kcu
Kj
Kpp
Kcz
Kcz
Kcz
Kca
Kcz Kcz Kca Kcu Kj Kcd Kj Kj Kpp Mgr
Modified after Goodman, 2012.
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Deposit Geology (2004)
Green garnet skarn
Brown garnet skarn
Limestone
Monzonite porphyry intrusion
Marble
N
1 km
Area of Interest
Modified after Redwood, 2004.
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Deposit Geology (2014)
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Antamina Mine
A A’
4275 m
4250
4000
3750
3500
Marble
Marble
P1a P2b Undifferentiated skarn P2a
A’
A
N
1 km
Modified after Redwood, 2004.
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P2b
P1a P1a endoskarn
Key Rock Types
P1a exoskarn Marble
P2a
P3a P3b
2 cm
7
Antamina Mine
A A’ 4275 masl
4250
4000
3750
3500
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Antamina Intrusive Sequence A B
C
D P2a cuts P1a endoskarn
P2a cuts P1a exoskarn
P2a xenolith in P2b
P2b chilled margin on P2a
2 cm 2 cm
2 cm
2 cm
P2a P2a P2a
P2a
P1a-endo
P1a-exo
P2b
P2b
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Antamina Deposit Model: Overview
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Stage 1
• P1a intrusion • P1a skarn formation
Stage 2
• P2a intrusion • P2a skarn formation
Stage 3
• Late intrusions (P2b, P3) • Erosion
Requirements for each stage:
• Favourable host rock marble/limestone (Ca-supply)
• Structural focusing anticline, faults,
contacts • Ample hydrothermal fluid multiple intrusions
• Continuous tectonic uplift
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10
0 km
1
2
3
4
5
Contact metamorphic aureole
P1a intrusion
Undifferentiated limestone
P1a porphyry veins
P1a endoskarn
P1a exoskarn
Deposit Model – Stage 1: P1a Intrusion – P1a Skarn Formation – Tectonic Uplift
P1a fluid release at favourable depth
2 cm
P1a-exoskarn
P1a-endoskarn
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11
0 km
1
2
3
4
5
Deposit Model – Stage 2: P2a Intrusion – P2a Skarn Formation – Tectonic Uplift
P1a intrusion
Undifferentiated limestone
P1a porphyry veins
P1a endoskarn
Exoskarn
Contact metamorphic aureole
P2a intrusion
P2a porphyry veins
P2a endoskarn
2 cm
A B
P1a fluid release at favourable depth
P2a fluid release at similar depth
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12
0 km
1
2
Deposit Model – Stage 3: Late Intrusions – Erosion
Endoskarn
Exoskarn
P2a
P1a
P2b intrusion
Retrograde alteration
Antamina Mine P2b
P1a-exo
P2b
P1a-exo
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N
1 km 13
Stacked Skarn & Nested Porphyry Hypothesis
P1a
P2a
P2b
P2b
9.9 ± 0.3 Ma
P1a: 10.9 ± 0.2 Ma
2 cm
A B
A: least-altered, B: endoskarn
P2a: 10.0 ± 0.2 Ma
A B
A: least-altered, B: endoskarn
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• Two major porphyry units (plus 6 minor porphyry units) comprise the Antamina intrusive sequence
• At least 2 skarn-forming events created a vertically extensive, coalesced system in favourable wall rocks
• Contemporaneous tectonic uplift (1-2 mm/year over ~0.5 Ma) may have increased the vertical extent of skarn
14
Summary & Closing Thoughts
Acknowledgements