A Model for the Intrusive Sequence and Skarn Formation
at the Antamina Deposit, Peru
S A Mrozek, Z Chang, and L D Meinert
Introduction 1. Antamina geology
2. Intrusive sequence
3. Three-stage deposit model
2
Antamina
Project Location
3
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.
Deposit Geology (2004)
Green garnet skarn
Brown garnet skarn
Limestone
Monzonite porphyry intrusion
Marble
N
1 km
Area of Interest
Modified after Redwood, 2004.
5
Deposit Geology (2014)
6
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.
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
8
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
Antamina Deposit Model: Overview
9
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
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
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
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
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
• 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