A Model for the Intrusive Sequence and Skarn Formation at ... · A Model for the Intrusive Sequence and Skarn Formation at the Antamina Deposit, Peru S A Mrozek, Z Chang, and L D

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