Freeport Epithermal and porphyry exploration under lithocaps.pdf

Freeport presentation on porphyry and high sulfidation exploration beneath lithocaps in the philippines.

1. www.fcx.com
EXPANDING RESOURCES

Exploring for Porphyry and
High Sulfidation Epithermal Cu-Au
Deposits Beneath Lithocaps in the
Philippines



Ingemar Arellano
Leonardo Subang

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Presentation Outline
2

A. What are Lithocaps?
B. Why Explore in Areas of Lithocap Cover?
C. Where do they occur?
D. Exploration Methodology – The Philippine experience
E. Results and Insights

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A. What are Lithocaps?

Sillitoe, 1995

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May exceed 20km
2
in original areal extent and 1km in
thickness

 Mankayan: ~30km
2

 Tampakan: >90 km
2

 Bantug: ~50km
2



A. What are Lithocaps?

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Porous silica
Propylitic Alteration
Phyllic Alteration
Potassic Alteration
Volcanic pile
Subvolcanic basement
Porphyritic stock
Massive Sulphide
Breccia hosted
HS mineralisation

Lithocap
chl-epi chl-epi se
se
se-py-di
se-py-di-alu
di-alu di-alu
alu
alu
alu
chl-se
chl-se
se
se
bi-kf
- Bn (bornite)
- Cp (chalcopyrite)
- Dg (digenite)
- Cv (covellite)
- En (enargite)
- Lz (luzonite)
Modified from Sillitoe, 1999
alu alu
A. What are lithocaps?
(Alteration and Cu mineralization zoning)

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A. What are lithocaps?
(Telescoping)
Sillitoe, 2010

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Rohrlach, 2002
HS: ~3.23-3.34Ma (Rohrlach, 2002)
Porphyry:~4.24-4.76Ma (Rohrlach 2002)

A. What are lithocaps?
(Telescoping)

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B. Why explore in areas of lithocap cover?

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1. Already very mature

2. Remaining prospects with potential are hidden by young volcanic
rocks or lithocaps

3. Biggest and richest Cu-Au systems found in the Philippines are partly
to completely hidden by lithocaps (i.e. FSE-Lepanto, Tampakan)

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C. Where do they occur?


Tectonic Setting of Porphyry-HS Systems w/ associated
Lithocaps


1. In arc regions influenced by tectonic perturbations
2. Regions with high uplift and degradation that cause telescoping

A. Regions influenced by ophiolite obduction (Diwata Range, East
Mindanao)

B. Regions influenced by ridge subduction (Luzon Central Cordillera)

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Mankayan
Baguio
Tampakan
Dobdob
Malangsa
Batong Buhay
Minlawi
Sagay
Bantug
Marian
Nagtipunan
Runruno
Polillo
Lobo
Del Gallego
Nalesbitan
Ragay
Mt Uwak
Pan de Azucar
Ayungon
Amlan
Sibutad
Tiong
Tantingon
Dipore Masara

LEGEND

FMI Project/Prospect
Lithocap
C. Where do they occur?
(Known Lithocaps in the Philippines)

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D. Exploration Methodology - Reconnaissance

1. Initial Reconnaissance Phase

a. Establish that it is a “true” lithocap


magmatic-water dominated (lithocap environment)
(>150°C up to 450°C) (Sinclair, Knight & Merz, 2000)

versus

meteoric water-dominated (steam-heated acid sulphate
environment)(<150°C ) (Sinclair, Knight & Merz, 2000)

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Magmatic steam
environment
Magma
150°C
A)
600°C
250°C
O
2
O
2
H
2
S
H
2
S
Steam heated acid
sulfate environment
150°C
400°C
600°C
400°C
`
250°C
SO
2±H
2S
Water table
Water table
Vapour plume with
H
2
S+SO
2
Magmatic hydrothermal
acid sulfate environment
Steam heated acid
sulphate environment
Silica sinter
Ore zone
Boiling
200°C
300°C
250°C
Magma
B)
lithocap
environment
Lithocap Clays

High Temperature:
~350°C-450°C
Andalusite, corundum,
woodhouseite, diaspore
(Hemley, 1980; Reyes, 1990;
Khashgerel, 2006)

Moderate Temperature:
~250°C-350°C
Pyrophyllite, diaspore,
zunyite, topaz, ±dickite,
±alunite (Hemley, 1980;
Reyes, 1990; Khashgerel,
2006)

Low Temperature:
>150°C-250°C
Alunite, dickite, kaolinite
(Hemley, 1980; Reyes, 1990;
Khashgerel, 2006)

D. Exploration Methodology - Reconnaissance

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Malangsa Lithocap, Panaon Island
Southern Leyte, Philippines
Alunite-dickite
pyrophyllite-diaspore
covellite
PIMA
TerraSpec

D. Exploration Methodology - Reconnaissance

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b. Establish fertility

- Cu-Au mineralization associated with lithocap

10.74ppm Au, 240ppm Cu, 420ppm As, 2309ppm Mo,
Spanish Workings, Lepanto Mine
KTC Vein, Tampakan,
Southern Mindanao
Subang, 2004
Type locality of luzonite
D. Exploration Methodology - Reconnaissance

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c. Establish evidence of possible telescoping

- AA overprinted porphyry quartz veining within
lithocap




Buaki Porphryy, Lepanto Mine

D. Exploration Methodology - Reconnaissance

Hedenquist, 2010
Minlawi Project Batong Buhay – MCB Project

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2. Prospect target definition
a. Geological Mapping

1. Clay geothermometry - low/high temperature AA clays


 pyrophyllite+diaspore±dickite

 Na-Alunite vs K-Alunite

D. Exploration Methodology - Prospect

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2. Prospect target definition
a. Geological Mapping
2. “ghost” porphyry quartz veining in lithocap and/or in
clasts in hydrothermal/diatreme breccias

altered hydrobrecciated
basalt
altered hydrobrecciated basalt
Recent dacite pyroclastics Recent dacite pyroclastics
HBx
Dark Tonalite Clast with P1 Quartz Veinlets
0.29% Cu, 1.84ppm Au
D. Exploration Methodology - Prospect

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2. Prospect target definition
a. Geological Mapping
3. zones of Py-Bn-Cv/En-Lz mineralization
HS-1 Cu
2600ppm Cu, 132ppm Mo, 63ppm As, 106ppm
Sb, 4.60ppm Au
8800ppm Cu, 15ppm Mo, 7070ppm As,
700ppm Sb, 2.74ppm Au
Pyrite-bornite-chalcopyrite fills with alunite ± dickite ± pyrophyllite in vuggy quartz cut by
drussy chalcedony veinlets.
Pyrite-enargite fills in vuggy quartz.

D. Exploration Methodology - Prospect

Batong Buhay – MCB Project HS-2 Cu

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2. Prospect target definition
a. Geological Mapping
4. zones of “gusano” texture
TMPD 103 74m-76m: 1.50% Cu, 0.50ppm Au,
50ppm As, 122ppm Mo, 6ppm Zn

D. Exploration Methodology - Prospect

Bantug Project
Tampakan deposit Subang, 2004
Patchy /“Gusano” texture of AA clays in andesite

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2. Prospect target definition
a. Geological Mapping
5. zones of vuggy quartz

Pyrite+bornite+covellite fills in vuggy residual quartz
TMPD 119 108m: 0.81% Cu, 0.18ppm Au
En+Bn±Py vug fill + drusy quartz
Tampakan deposit
Bantug Project

D. Exploration Methodology - Prospect

Subang, 2004

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2. Prospect target definition
b. Grid Soil Geochemistry
1. zones of coincident high Mo-Cu-Au

D. Exploration Methodology - Prospect

Bantug Project

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2. Prospect target definition
b. Grid Soil Geochemistry
2. zones of coincident high As-Pb-Zn

D. Exploration Methodology - Prospect

Bantug Project

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2. Prospect target definition
c. Geophysics
1. zones of coincident high chargeability and
high resistivity
Chargeability - 800m RL Resistivity - 800m RL

D. Exploration Methodology - Prospect

Bantug Project

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2. Prospect target definition
c. Geophysics
2. zones of coincident low magnetics and high
chargeability
Ground Mag - RTEq Chargeability - 800m RL

D. Exploration Methodology - Prospect

Bantug Project

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E. Results and Insights

Sagay Project


a. HS Cu-Au mineralization

b. moderate to high temperature AA clays

c. coincident high Mo-Cu-Au in soil

d. coincident zones of low magnetics and high chargeability

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Sagay Project



E. Results and Insights

SGY-006
580.50m:
0.33% Cu,
0.05 g/t Au
SGY-007
653.00m:
0.49% Cu,
0.16 g/t Au
SGY-006
937.20m:
0.40% Cu,
0.06 g/t Au
SGY-007
820.70m:
1.11% Cu,
0.37 g/t Au

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E. Results and Insights

Feature Bantug Sagay Minlawi
Po Veining within lithocap
Po Veining in clast in hydrothermal breccia
HS Cu-Au mineralization in lithocap
Moderate to high temp AA clays (pyrophyllite+diaspore±dickite±alunite)
Soil Geochemistry (coincident Mo-Cu-Au)
Coincident high chargeability and high resistivity
Coincident low magnetics and high chargeability

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Summary


Exploring for Cu-Au fertile heat centers within lithocaps:


1. Alteration: Pyrophyllite+diaspore (~250°C-350°C)±dickite±alunite

2. Mineralization: (HS-2 Cu) Pyrite
+bornite+covellite±enargite±molybdenite
3. Soil and Rock Geochemistry: Cu-Au-Mo

4. Geophysics: Magnetic low + Chargeability high + Resistivity high

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