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Metal Dispersion around Porphyry Cu-Mo-Au Deposits: Implications for Fluid Flow and Exploration

Metal Dispersion around Porphyry Cu-Mo-Au Deposits: Implications for Fluid Flow and Exploration

Cerro Casale porphyry Cu-Au deposit, Chile

J. Bruce Gemmell

AMIRA P765 (2004 – 2006)Transitions and Zoning in Porphyry - Epithermal Districts:

Indicators, Discriminators and Vectors7 industry sponsors

AMIRA P765 (2004 – 2006)Transitions and Zoning in Porphyry - Epithermal Districts:

Indicators, Discriminators and Vectors7 industry sponsors

AMIRA P765A (2008 – 2010)Geochemical and Geological Halos in Green Rocks and Lithocaps:

The explorer’s toolbox for porphyry and epithermal districts18 industry sponsors

AMIRA P765A (2008 – 2010)Geochemical and Geological Halos in Green Rocks and Lithocaps:

The explorer’s toolbox for porphyry and epithermal districts18 industry sponsors

AMIRA P1060 (2011 – 2014)Enhanced Geochemical Targeting in Magmatic-Hydrothermal Systems

21 industry sponsors

2

From Holliday and Cooke (2007), with inspiration from Sillitoe and Thompson (2006)

Epidote: basic field techniques

• Map epidote’s distribution– Largest deposits have the largest

propylitic halos

– Epidote veins are more abundant close to the deposit centre

– Larger deposits have intensely developed epidote stockworks

• Map mineral associations – Epidote + actinolite – higher

temperature (proximal)

– Epidote + chlorite – lower temperature (distal)

– Pyrite + epidote typically occurs close to mineralisation

• Watch for colour changes – Pink – high Mn epidote

– Orange – high Pb epidoteAlteration map of the Collahuasi district, Chile Modified after Ireland (2010)

Rosario

Ujina

Alteration

PotassicEpidote-Hematite

Epidote-(Chlorite)ChloriteSkarn

Monctezuma

La Grande

Sample Location

1 km1 km

3

SBD-145-66m 2 cm

Epidote ChemistryEpidote group minerals:

A2B3(SiO4)3(OH,F)

A - Ca, Ce, Pb, Sr, Y

B - Al, Fe, V, Mg, Mn

+ REE & other assorted “metals”

Solid solution: Ca2Al3Si3O12(OH) –clinozoisite to

Ca2Fe3+Al2Si3O12(OH) –epidote

LA-ICPMS facility

EpidoteMineral Chemistry

4

1

10

100

1000

10000

100000

1000000

10000000

0.68

74.

075

7.46

210

.85

14.2

37

17.6

25

21.0

12

24.3

99

27.7

87

31.1

75

34.5

62

37.9

49

41.3

37

44.7

24

48.1

12

51.4

99

54.8

86

58.2

74

61.6

62

65.0

49

68.4

36

71.8

24

75.2

11

78.5

99

81.9

86

85.3

74

88.7

61

92.1

49

95.5

36

98.9

24

Ca43

V51

Mn55

Fe57

Cu65

Zn66

Ga69

As75

Sr88

Y89

Zr90

Mo95

Sn118

Sb121

Te125

Ba137

La139

Ce140

Pr141

Nd146

Sm147

Eu153

Dy163

Yb172

Lu175

Au197

Tl205

Pb208

Bi209

Th232

SrSr

CaCaPb

AsAsSbSb

LaLa

ZnZn

VV

MnMn

FeFe

0 20 40 60 80 100

Time (seconds)

1

10

100

1,000

10,000

1 * E05

1 * E06

1 * E07

Co

un

ts p

er s

eco

nd

Epidote LA-ICP-MS Analysis

Luzon Central Cordillera, Philippines

Baguio District2.7 Mt Cu, 35 Moz AuBaguio District2.7 Mt Cu, 35 Moz Au

Mankyan District7.69 Mt Cu, 37 Moz AuMankyan District7.69 Mt Cu, 37 Moz Au

200 km

Cooke et al. (in review)

5

Baguio District, Philippines

Baguio District, Philippines

Cooke et al. (in review)

Black Mt Kennon: 47Mt @ ~ 0.38% Cu, 0.35g/t Au & 0.01% Mo.

Southeast: 15mt @ ~ 0.37% Cu & 0.26g/t Au.

Nugget Hill

Rock chip assays up to 1.17% Cu and 4.58g/t Au.

n(max) whole rock = 985n(max) epidote = 3,521

Whole rock – p. 25

Whole rock – p. 75

Whole rock – mean

Whole rock – median

Epidote – p. 25

Epidote – p. 75

Epidote – mean

Epidote – median

Legend

Co

nce

ntr

atio

n (

pp

m)

Na Mg K Ba Zr Cu Ce Nd La Yb Bi

0.1

1

10

100

1,000

10,000

Ti Zn Y Mo

Epidote Mineral Chemistry

Cooke et al. (in review)

6

n(max) whole rock = 985n(max) epidote = 3,521

Epidote is significantly enriched in As, Sb and Pb in the distal

halo to porphyry deposits

Whole rock – p. 25

Whole rock – p. 75

Whole rock – mean

Whole rock – median

Epidote – p. 25

Epidote – p. 75

Epidote – mean

Epidote – median

Legend

Co

nce

ntr

atio

n (

pp

m)

Al Fe Mn Sr V As Pb Sb Sn Eu Bi

0.1

1

10

100

1,000

10,000

100,000

Epidote Mineral Chemistry

Cooke et al. (in review)

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

Cooke et al.. (in review)

Pyrite halo

Potassic alteration

7

Au_ppm to 0.05Au_ppm to 0.04Au_ppm to 0.03Au_ppm to 0.02BDL

Au_ppm

Mo_ppm to 1.32Mo_ppm to 0.76Mo_ppm to 0.38Mo_ppm to 0.07BDL

Mo_ppm

Sn_ppm to 10.09

Sn_ppm to 5.94

Sn_ppm to 4.31

Sn_ppm to 1.36

Sn_ppm to 0.71

Sn_ppm to 0.41Sn_ppm

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

Cu_ppm to 27.97

Cu_ppm to 10.56

Cu_ppm to 4.00

Cu_ppm to 1.36

Cu_ppm to 0.60

Cu_ppm to 0.18

BDLCu_ppm

Cooke et al.. (in review)

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

Cooke et al.. (in review)

8

As_ppm to 137.54

As_ppm to 98.84

As_ppm to 45.59

As_ppm to 11.93

As_ppm to 5.63

As_ppm to 3.06As_ppm

Sb_ppm to 48.43

Sb_ppm to 22.46

Sb_ppm to 5.04

Sb_ppm to 2.06

Sb_ppm to 0.88

Sb_ppm to 0.20Sb_ppm

Pb_ppm to 102.10

Pb_ppm to 69.96

Pb_ppm to 32.87

Pb_ppm to 16.89

Pb_ppm to 4.67

Pb_ppm to 0.83Pb_ppm

Zn_ppm to 113.02

Zn_ppm to 38.53

Zn_ppm to 21.28

Zn_ppm to 12.88

Zn_ppm to 5.71

Zn_ppm to 1.42Zn_ppm

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

BM‐SE

BMNH

Mx

Tg

LLCMC

BR

Cooke et al.. (in review)

Mexico Black Mt Nugget Hill

Pyrite haloPyrite halo

Potassic alteration

0

5

10

15

20

25

30

0 500 1000 1500 2000 2500 3000 3500 4000

distance

pp

m

replacement epidote vein epidote skarn epidote whole rock

B'A C

Sn (ppm)

Mexico Creek transect Liw-Liw Creek transect

Cooke et al. (in review)

9

Mexico

As (ppm)

0

20

40

60

80

100

120

140

160

180

200

0 500 1000 1500 2000 2500 3000 3500 4000distance

ppm

B'A C

replacement epidote vein epidote skarn epidote whole rock

Black Mt Nugget Hill

Cooke et al., (in review)

Pyrite halo

Potassic alteration

Mexico Creek transect Liw-Liw Creek transect

Metal enrichment in epidote: lateral fluid migration and

depletion of H2S

Potassic zone(H2S, SO4

2- available)Potassic zone

(H2S, SO42- available)

High T (> 450°C):

• Deposition of Cu-sulfides and Au

• Most other metals too soluble to precipitate

• High aqueous sulfate contents causes Ca deposition as

anhydrite

• Epidote not stable

High T (> 450°C):

• Deposition of Cu-sulfides and Au

• Most other metals too soluble to precipitate

• High aqueous sulfate contents causes Ca deposition as

anhydrite

• Epidote not stable

Pyrite halo(H2S abundant)

Pyrite halo(H2S abundant)

Moderate T (<450°C):

• Deposition of pyrite, minor chalcopyrite

• As, Sb, Pb scavenged by pyrite

• Epidote enriched in Y and REEs

• Epidote also incorporates Zr, minor Sn, trace Cu, Mo

Moderate T (<450°C):

• Deposition of pyrite, minor chalcopyrite

• As, Sb, Pb scavenged by pyrite

• Epidote enriched in Y and REEs

• Epidote also incorporates Zr, minor Sn, trace Cu, Mo

Green rock halo(H2S exhausted)Green rock halo(H2S exhausted)

Moderate - low T (220 – 350°C)

• As, Sb and Pb substitute into epidote when sulfides are no longer being

deposited

• Mn substitutes into epidote due to the similar ionic radius to Fe3+

Moderate - low T (220 – 350°C)

• As, Sb and Pb substitute into epidote when sulfides are no longer being

deposited

• Mn substitutes into epidote due to the similar ionic radius to Fe3+

The most highly productive porphyries flux the most metals

The most highly productive porphyries flux the most metals

chalcopyrite

pyrite epidote Cooke et al. (in review)

10

Py halo

Lithocap

Strongly mineralisedporphyry (e.g., Nugget Hill)

Weakly mineralisedporphyry (e.g., Mexico)

Concealed porphyry

K-s

ilica

te h

alo

Rep

lace

men

t ep

ido

te o

nly

Vei

n +

rep

lace

men

t ep

ido

te

Rep

lace

men

t ep

ido

te o

nly

Coalescing epidote alteration halos

Epidote chemistry (inside pyrite halo of

productive porphyry):

Cu, Sn, Mo, Bi, Zn elevated

Epidote chemistry (outside pyrite halo of productive porphyry):

Pb, As, Sb, La, Y, Zr elevated

Cu, Zn, Sn, Mo depleted

Epidote chemistry (non-productive

porphyry):

Zn elevated

Sn, Pb, As, Y, La depleted

Cooke et al. (in review)

From Holliday and Cooke (2007), with inspiration from Sillitoe and Thompson (2006)

11

Alteration

N.C. White, unpublished

2) Introduction of metalliferous metals

rock saturatedwith groundwater

1) Acidic magmatic condensates cause AA alteration

magmatic liquids

ORE 1

2

Lithocap Mineralogy

Steven & Ratté, 1960

vuggy quartzvuggy quartz

alunite,and quartz

illite and smectite(montmorillonite)

propylitic(chlorite)

alunite, quartz and kaolinite

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AA Alteration Mineralogy

Quartz SiO2

Alunite KAl3(SO4)2(OH)6

Kaolinite Al2Si2O5(OH)4

Halloysite Al2Si2O5(OH)4

Dickite Al2Si2O5(OH)4

Pyrophyllite Al2Si4O10(OH)2

Diaspore AlO(OH)

Topaz Al2SiO4(F,OH)2

Zunyite Al13Si5O20(OH,F)18Cl

Dumortierite Al6.5-7BO3(SiO4)3(O,OH)3

Corundum Al2O3

Andalusite Al2SiO5

Cordierite Mg2Al4Si5O18

Cathedral Peal lithocap with quartz‐alunite “ledges”,Cerro Casale, Chile

Filter WR Geochemistry

• use samples with < 0.1% Cu,                      < 0.1ppm Au and contain alunite

Mineralization at a later stage

Vuggy quartz and alunite, MankayanChang et al. (2011)

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Alunite Mineral ChemistryKAl3(SO4)2(OH)6

Alunite, Mankayan

Variations in K, Na and trace element contents (e.g., Pb, La, etc.)

Al > Fe Fe > Al

alunite KAl3(SO4)2(OH)6 jarosite KFe3(SO4)2(OH)6

natroalunite NaAl3(SO4)2(OH)6 natrojarosite NaFe3(SO4)2(OH)6

minamiite (Na,K,Ca)2Al6(SO4)4(OH)12 hydronium jarosite (H3O)Fe3(SO4)2(OH)6

huangite Ca2Al6(SO4)4(OH)12 argentojarosite AgFe3(SO4)2(OH)6

walthierite BaAl6(SO4)4(OH)12 beaverite Pb(Fe,Cu)3Fe3(SO4)2(OH,H2O)6

ammonioalunite NH4Al3(SO4)2(OH)6 ammoniojarosite (NH4)Fe3(SO4)2(OH)6

schlossmacherite (H3O,Ca)Al3(SO4)2(OH)6 plumbojarosite PbFe6(SO4)4(OH)12

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1480 1482 1484 1486 1488 1490 1492 1494 1496 1498 1500

Na/

(Na+

K)

rati

o (

mo

le)

Mankayan

Baguio

Cocanes

Kuruga

Casale

89 samples554 microprobe analysesCorrelation coefficient = 0.84

Higher Na/(Na+K) ratio indicates higher formation temperature             (Stoffregen and Cygan, 1990)

Alunite 1480nm Spectral (SWIR) Feature

14

DG3(TO4)2(OH,H2O,F)6

K, Na, Ag, Tl, NH4, H3O, Ca, Ba, Pb, Hg, Sr, Zn, Cu, Rb, Ag,

Th, Bi, REE

Sn4+, Al, As3+, Fe3+, Cr3+, V3+,

Ga, Mg, Mn, Cu2+

S6+, As5+, Cr6+, Sb, P5+

Trace Elements in Alunite

Jambor, 1999

canmin.geoscienceworld.org

mineralatlas.com

Cr-rich Fe-Mn-rich

Zn-rich K-richCa-rich

2.2 to 1.8 Ma

Mankayan

Linked porphyry and lithocap parts of system; lithocap hosts HS ore

Lepanto HS: >0.9 Mt Cu & 102 t Au

Production

FSE porphyry: 650 Mt @ 0.65% Cu &

1.3 g/t Au resource

Victoria veins, 11 Mt @ 7.3 g/t Au +

Ag-Cu-Pb-Zn

Chang et al. (2011)

Cretaceous to Miocene

1.2 to 0.9 MaMineralisation 1.4 Ma

13 to 12 Ma

15

Porphyry, lithocap and HS mineralization

Genetic relationship between porphyry and lithocap established (lateral flow to NW): alteration, dating, fluid inclusion, isotope 

geochemistry study

Arribas et al. (1995), Mancano and Campbell (1995), Hedenquist et al. (1998)

Dickite ± kaolinite

Dickite ± kaolinite

Quartz-alunite

1 km

Chang et al. (2011)

Alunite absorption peak at ~1480 nm shifts to higher values closer to intrusive centre

Chang et al. (2011)

16

Alunite composition (LA-ICPMS) Sr

Chang et al. (2011)

Alunite composition (LA-ICPMS) Pb

Chang et al. (2011)

17

Increase: Alunite 1480 pk positionAlunite La, La/Pb, Sr, Sr/PbEnargite: Au, Te, Ba, Th, As/SbWhole-rock (alunite-bearing only):

La/Pb, Sr/Pb, Cu/Hg

Decrease: Alunite Pb, Ag/AuWhole-rock (alunite-bearing only): Pb, Ag, Ag/Au, Hg, Te, As/ZnAll whole rock: Te, As/Zn

4 km long Lithocap

Mankayan lithocap and ore deposits- schematic cross section

Mankayan lithocap and ore deposits- schematic cross section

Chang et al. (2011)

Bingham Canyon, Utah

Lithocaps

Fluid Flow: vapour vs brine transport into lithocap

Exploration: alunite 1480nm peak position, alunite geochemistry and filtered whole rock geochemistry vector to intrusion (heat source) and potential sites for HS/porphyry ore

Green Rock

Fluid Flow: metal dispersion related to H2S availability

Exploration: epidote geochemsitry can detect productive porphyry deposits several km beyond the limits of conventional lithogeochemical sampling (outside pyrite halo)

epidote texture and chemistry as vectoring tools

fertility assessment tool

Innovation and Exploration

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FootprintsFootprints

District, camp and deposit scale

Geological, mineralogical and geochemical

• VHMS

• SEDEX

• Sediment-hosted Cu

• Sediment-hosted Au (poster)

• Epithermal Au-Ag

• Porphyry Cu-Au-Mo

Gemmell (2007)