porphyry and epithermal systems science driven exploration successes l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Porphyry and Epithermal Systems - Science-driven Exploration Successes PowerPoint Presentation
Download Presentation
Porphyry and Epithermal Systems - Science-driven Exploration Successes

Loading in 2 Seconds...

play fullscreen
1 / 19

Porphyry and Epithermal Systems - Science-driven Exploration Successes - PowerPoint PPT Presentation


  • 996 Views
  • Uploaded on

Porphyry and Epithermal Systems - Science-driven Exploration Successes. Richard Sillitoe. Porphyry and epithermal deposits. Porphyry copper-molybdenum and copper-gold deposits are centred on shallow-level porphyry intrusions. Grasberg, Indonesia. Epithermal gold and silver

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Porphyry and Epithermal Systems - Science-driven Exploration Successes' - paul


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
porphyry and epithermal deposits
Porphyry and epithermal deposits

Porphyry copper-molybdenum and copper-gold deposits are centred on shallow-level porphyry intrusions

Grasberg, Indonesia

Epithermal gold and silver

deposits are typically

hosted by volcanic rocks

Round Mountain, Nevada

porphyry and epithermal systems the state of play at end of 1960s 1
Porphyry and epithermal systems – the state of play at end of 1960s (1)
  • Epithermal-hot spring linkage proposed (D.White), but relationship uncertain
  • Types of epithermal deposits not appreciated (forgetting F.L.Ransome and W.Lindgren)
  • Porphyry-epithermal connection unknown
  • Porphyry intrusion-volcano connection unknown
  • Plate tectonic setting and relationship of porphyry copper deposits to subduction unrecognised (plate tectonics in its infancy)
porphyry and epithermal systems the state of play at end of 1960s 2
Porphyry and epithermal systems – the state of play at end of 1960s (2)
  • Ages of copper and gold belts and provinces poorly defined (isotopic dating in its infancy)
  • Zoning patterns of hydrothermal alteration in porphyry and epithermal deposits poorly appreciated
  • Porphyry gold and gold-rich porphyry copper deposits undefined (notwithstanding Panguna)
  • Bulk-tonnage epithermal gold deposits undefined (reflecting low gold price)
the favourite buzz words for today s press releases on porphyry and epithermal projects
The favourite buzz words for today’s press releases on porphyry and epithermal projects

HOT-SPRING SINTER

STEAM-HEATED ENVIRONMENT

PALEO-WATER TABLE

HIGH-SULPHIDATION SYSTEM

VUGGY QUARTZ

LOW-SULPHIDATION SYSTEM

POTASSIC ALTERATION

DIATREME-HOSTED

HYPOGENE COPPER ENRICHMENT

ADVANCED ARGILLIC LITHOCAP

Unknown to the exploration

community at the end of 1960s

Active hot-spring sinter terrace,

Champagne Pool, New Zealand

porphyry epithermal relationships
Porphyry-epithermal relationships

Linkages between porphyry, high- and intermediate-sulphidation epithermal, skarn, carbonate-replacement, and Carlin-like environments now widely appreciated

The necessary information was supplied by worldwide exploration activities

high sulphidation porphyry transition
High-sulphidation - porphyry transition
  • 1.5 – 2 km vertical interval represented from paleo-surface to porphyry deposit
  • Vuggy quartz → quartz-alunite → quartz-pyrophyllite → quartz-sericite from top downwards
  • Au-dominated → Cu-dominated from top downwards
shallow epithermal features
Shallow epithermal features
  • High- and intermediate sulphidation deposits with andesitic-dacitic arc volcanism
  • Low-sulphidation deposits with compositionally bimodal (basalt-rhyolite) volcanism in extensional (rift) settings
  • Steam-heated environment, hot-spring sinter and paleo-water table silicification recognised above Au-Ag mineralization

- Again exploration supplied the data

deposit scale features
Deposit-scale features

Alteration zoning — recognising importance of potassic alteration for copper introduction in porphyry copper deposits

Los Pelambres, Chile

Discovered 1969, United Nations

3,300 Mt @ 0.63% Cu, 0.016% Mo

Bajo de la Alumbrera, Argentina

Discovered 1971, United Nations

700 Mt @ 0.51% Cu, 0.66 g/t Au

Potassic alteration

(beneath weathering zone)

Potassic alteration

(weathered at surface)

deposit scale features10
Deposit-scale features

Alteration zoning — recognising significance of alteration types in

high-, intermediate- and low-sulphidation epithermal systems

La Coipa HS deposit, Chile

Discovered 1983, Amax

8.46 Moz Au Eq

Vuggy quartz in discovery outcrop: residue

after leaching by highly acidic fluid

Pascua-Lama HS deposit, Chile-Argentina

Discovered 1989, Lac Minerals,

then Barrick Gold

Barren steam-heated alteration above

16 Moz gold and >600 Moz silver

tops of porphyry copper deposits
Tops of porphyry copper deposits

Guinaoang porphyry copper-gold system, Philippines

Discovered 1983, RGC Exploration

>500 Mt @ 0.4% Cu, 0.4 g/t Au

Deposit concealed beneath advanced argillic lithocap containing high-sulphidation mineralization

tops of low and intermediate sulphidation epithermal deposits
Tops of low- and intermediate-sulphidation epithermal deposits

El Peñón, Chile

Blind vein discoveries 1998-2007, Meridian Gold

8.4 Mt @ 14 g/t Au, 234 g/t Ag

Fence drilling to intersect predicted favourable stratigraphic interval

Quebrada Colorada

Esquel, Argentina

Discovered 2000, Minera El Desquite (Brancote)

3.8 Moz Au, 7 Moz Ag

Recognition that two-thirds of deposit is concealed beneath pre-mineral cover

Fruta del Norte, Ecuador

Discovered 2006, Aurelian

13.7 Moz Au, 22.4 Moz Ag

Drilling deep beneath a linear silicified zone containing anomalous arsenic and antimony

recognition of new mineralization styles
Recognition of new mineralization styles

Montana Tunnels, Montana, USA

Discovered 1983, Centennial Minerals

61 mt @ 0.96 g/t Au, 12 g/t Ag, 0.67% Zn, 0.28% Pb

Disseminated mineralization in phreatomagmatic diatreme breccia

Marte porphyry gold deposit, Chile

Discovered 1982,

Anglo American-Cominco j.v.

Soon led to discovery of nearby Lobo porphyry gold deposit by same j.v.

Combined: 5.5 Moz Au

Wafi, Papua new Guinea

Discovered 1990, CRA Exploration

Hypogene copper enrichment due to high-sulphidation copper sulphides at base of lithocap overprinting porphyry copper-gold deposit

district scale porphyry copper alignments and clusters trendology
District-scale porphyry copper alignments and clusters (“trendology”)
  • Comparable brownfield discoveries in Los Bronces alignment (Sulfatos, Anglo American) and Escondida cluster (Pampa Escondida, MEL), Chile

Detailed geology and scout RC drilling beneath alluvial cover

Chuquicamata district, Chile

Orogen-parallel alignment

New discoveries 2000-2006, Codelco

Oyu Tolgoi district, Mongolia

Arc-transverse alignment

New discovery 2007, Ivanhoe Mines

(supplied by I.Kavalieris)

Deep IP survey – on trend

definition of porphyry copper belts and epochs
Definition of porphyry copper belts and epochs

Isotopic dating has defined regional-scale belts and corresponding epochs in most porphyry copper provinces

Examples:

  • Gaby (Gabriela Mistral): 540Mt @ 0.52% Cu Ox – prioritised during initial exploration because of 43 Ma age
  • Other prospects – discarded because of 290-200 Ma ages

Isotopic dating now routine selection tool

in Andean copper province and elsewhere

definition of epithermal belts and provinces
Definition of epithermal belts and provinces

Regional-scale belts and provinces become focus of exploration for specific epithermal deposit type

Examples:

  • Northern Nevada rift: 16-14 Ma
  • Patagonia: 160-150 Ma

After Riley et al. (2001)

After John et al. (2000)

origin of metallogenic provinces
Origin of metallogenic provinces

Tectono-magmatic processes or predisposition?

  • Clustering of 10 Moz Au belts and isolated deposits of different types and ages
  • Suggestive of predisposition – metal preconcentration or other chemical parameter (e.g. redox state)
  • Focus exploration on endowed arc segments, but usually well explored (exception Colombian Andes)
  • Or define unrecognised gold-rich arc segments – but how?
key role of geology in porphyry and epithermal exploration
Key role of geology in porphyry and epithermal exploration

68

s

6

t

i

s

16

o

67

p

e

15

66

24

47

31

d

4

f

o

36

23

46

65

14

30

r

e

59

b

64

53

35

39

50

13

19

22

45

29

9

2

m

u

58

61

72

74

77

79

63

70

18

38

49

12

52

55

21

26

28

34

42

44

2

8

4

N

10

11

17

20

32

33

37

40

41

43

48

51

54

56

57

60

62

69

71

73

75

76

78

7

25

27

80

81

5

6

3

1

Geological work

1970

2000

1980

1990

6

Discovery Year

4

2

2000

1980

1990

1970

Geochemistry

6

4

2

2000

1980

1990

1970

Geophysics

6

4

2

2000

1980

1990

1970

Serendipity

6

Drilling

4

2

2000

1980

1990

1970

Circum-Pacific Region

Parameters

  • 37–year history
  • 81 deposits
  • Mainly porphyry, epithermal, & sediment-hosted gold (minor VMS & orogenic gold)

Main conclusions

  • Notwithstanding exploration changes, little overall evolution in discovery methodology (but see next slide)
  • Geologic fieldwork: 90% of discoveries
    • routine observation, mapping, & interpretation
    • familiarity with deposit models (since 1980s)
  • Geochemistry: 70% of discoveries
    • stream sediment, soil, & rock chip
  • Geophysics: 15% of discoveries (only 50% of programs)
    • Ground IP & EM
  • Drilling & serendipity: 12% of discoveries
  • Remote sensing (satellite imagery, airborne scanners: 0%)
the future of porphyry and epithermal exploration
The future of porphyry and epithermal exploration

We need:

  • New geological concepts
  • Characterisation of distal manifestations of concealed and potentially deep orebodies
  • New technological break-throughs
  • Properly qualified and motivated personnel to do the job

Rio Tinto, 2008

Last 40 years have brought great advances in the porphyry-epithermal environment; next 20 years must bring even greater advances if we are to satisfy growing demand for copper, gold and silver and societal expectations in general – all within increasingly stringent environmental and community constraints