Richard Tosdal

discovery through researchdiscovery through researchMineralMineral Deposit Research UnitDeposit Research Unit

Fluid pathways around carbonate hosted polymetallic deposits

Tracking Fluid Exhaust from Polymetallic Carbonate Rock-Hosted Ore Deposits: Examples from Central Per

A joint project between the Mineral Deposit Research Unit, Anglo American Peru, BHP Billiton, Cia. Minera Antamina;

Cia. Minas de Buenaventura, Falconbridge(Noranda), Phelps Dodge Peru, and Teck ComincoAdditional support from Natural Science

and Engineering Research Council of Canada

Richard Tosdal, Thomas Bissig, Abraham Escalante, Greg Dipple, Shane Ebert, Julio Jurado - MDRU

Manuel Pacheco, Eric Manuel Pacheco, Eric LiptenLipten, , JhonJhon Espinoza Espinoza -- Minera AntaminaMinera Antamina

Angel Angel SabastizagalSabastizagal -- Minas BuenaventuraMinas Buenaventura GervasioGervasio Rodriguez Rodriguez -- Minera CoronaMinera Corona

Gracias a Minera Corona y Volcan CompaniaGracias a Minera Corona y Volcan Compania



Predictable halos surround skarn, vein, and carbonate replacement deposits that reflect the composition of the host rock as well as the depth of formation and deposit type.

Visual

Mineralogic

Geochemical



Cretaceous

JurassicPaleozoic and Precambrian

Paleocene to Oligocene volcanic rocks

Miocene volcanic and sedimentary rocks

Coastal Batholith(Late Cretaceous to ~Eocene)

Major Miocene Intrusions

IquitosPiura

LimaIca

Arequipa

Trujillo

SimplifiedSimplified geologygeology of Central Perof Central Per

Cerro de Pasco

Tarma

Huancayo

La Oroya

Producing mine

Antamina

Uchucchacua

Yauricocha

Colquijirca



Visual mineral zoningDeeper deposits have thermal aureoles and distal Ag-veins

Bleaching of host rocks and conversion to marble nearest the intrusions

Predictable set of veins dispersed laterally and vertically

All deposit surrounded by geochemical halo

Minerals and alteration around deposits dependant on depth of formation and host rocks

.

Antamina



Cu-Zn skarn core through Marble-hornfels aureole tolimestone

The dominant fluid escape structures are sedimentarylayering and early-stagequartz feldspar porphyrydikes

Skarn environment

Antamina



T-16 T-17

West Wall

Bleaching of limestone at depth near stock



Cachi Cachi

Mina Central

Cordilleran base metal lode (deep)

Yauricocha DistrictRegionally and locally defined 3 broad

alteration zones surrounding the sulfide deposits

Zone A: Inner and adjacent to stock -

Cachi Cachi --Bleached marble

Mina Central -- Mn-flooding of marble

Zone B: Intermediate

Cachi Cachi -- Bedding controlled bleaching

Mina Central - Grey marble with carbonate veins

Zone C: Fresh limestone with some areas of bleached limestone



Mina Central Zone A - Bleached marble with Mn

Mn in veins and pervasive in rock

Zone A

Zone B



Zoning around deeper carbonate rock hosted systems



NW SE

Upper Jumasha Fm.

Marker horizon

Middle Jumasha Fm.

Lower Jumasha Fm.

Ros

a Ve

in

Ro s

a Ve

in

Ros

a 2

Vein

Ros

a 3

Vei n

4180m

4360m

4450m

4725m

4940m

4400m

4500m

4600m

4700m

4800m

4900m

5000m

4300m

4200m

4100m

Vein, faultAg ore zone

0 100Meters

Surface

4450 m level

Rosa vein

Shallow veins

Uchuccachua



3 Visual Alteration Zones Inner Dolomitized Limestone Intermediate White Marble fresh Pucara Limestone

Jasperoid Bodies within dolomitized zoneSulfide-bearing carbonate veins in fresh limestone

Cordilleran base metal lode (shallow)



Mineral zoningShallow or very distal in marls characterized by dolomite halos and jasperoid

Colquijirca - dark jasperoid with dolomite halo Cerro de Pasco - Irregular jasperoid in dolomitized limestone about 500 m from

ore body; fresh limestone is behind the dark jasperoid body



Vein zoningVeins surrounding skarn and deeper CRD - characterized by calc-silicate, Mn-oxide, and orange brown carbonate with the latter having the greatest lateral and vertical extent.

Orange brown carbonate veins Mn-oxide rich veins



Vein typesType 1 - Calc-silicate

a. Garnetb. Wollastonitec. Calc-silicate

Type 1a: Garnet pods

Type 1b: Wollastonite network

High-temperature veins near to

magmatic source

Cachi Cachi, Yauricocha



Vein typesa. Orange-brown carbonate

calcitequartzpyrite

b. Orange-brown carbonatecalcitequartzpyriteMnoxides

400 m from Mina Central, Yauicocha

500 m above and lateral from Antamina



Vein types

a. Mn-oxideorange-browncarbonatecalcitequartzpyrite

b. Pervasive Mn-oxide-orange-brown carbonate

c. Mn-oxidequartzpyrite

Concentrated close to cordillera base metal lode

Mina Central, Yauicocha



NW SE

Upper Jumasha Fm.

Marker horizon

Middle Jumasha Fm.

Lower Jumasha Fm.

Ros

a Ve

in

Ro s

a Ve

in

Ros

a 2

Vein

Ros

a 3

Vei n

4180m

4360m

4450m

4725m

4940m

4400m

4500m

4600m

4700m

4800m

4900m

5000m

4300m

4200m

4100m

Vein, faultAg ore zone

0 100Meters

Surface

4450 m level

Rosa vein

Shallow veins

Uchuccachua



Shallow barren calcite veins

Uchucchacua

White comb calcite cut by Mn-oxide cemented veins and breccia, Rosa

Vein



Recrystallization of limestone, Cerro de Pasco

Introduction of silica (creamy distal and darker with presence of increase

sulfide)

Colquijirca

Cordilleran base metal lodes (shallow)



UV FluorescenceWhite, yellow, green, blue, and red-orange fluorescence with UV light associated with distinct elements in calcite.

Red-orange fluorescence associated with Mnand Ag, and is spatially associated with sulfide deposits

Seen up to 1-km from Antamina



Ag

Surface 4725m

0.001

0.01

0.1

1

10

100

0 30 60 90 120 150

openA

g

(

p

p

m

)

4180 Level

0.001

0.01

0.1

1

10

100

0 30 60 90 120 150

A

g

(

p

p

m

)

A

s

(

p

p

m

)

As

Surface 4725m

1

10

100

1000

0 30 60 90 120 150

open

Brecciated limestone

Gray limestonesAilcocha limestones

Limit of geochemical haloThreshold

Distance from the vein (m)Distance from the vein (m)

Trace elemental changes with depth

Uchucchacua (Escalante unpublished)



Cachi Cachi(Jurado, 2006)

Element distribution

As increases in rocks and veins away from bleached marble and the intrusion.

As enriched in marble over limestone

As enriched in orange-brown carbonate and Mn-rich veins over high T calc-silicate veins

Lateral elemental dispersion

Similar patterns for Sb



Geochemical halosElements distributed in regular arrangements both vertically and laterally.

Forms 1-km scale halo

High temperature elements found closer to thermal source

Low temperature elements found farther away.

Elemental distribution is vertical and lateral.

Distribution dependant on the permeability structure.

Uchucchacua

Fortuna

Antamina



Sr removal accompanied recrystallization of host limestone to dolomitic limestone

Sr depletion potential to discriminate hydrothermal dolomite from diagenetic dolomite

Shallow Cordilleran base metal lodes

Cerro de Pasco (Bissig et al, unpublished)



Jasperoid in shallow cordilleran base metal

lodes

Jasperoid - replaces dolomitized limestone accompanied by As, Sb, Hg, Tl and maybe Cs

Can distinguish hydrothermal from diagenetic silica replacement



Distal Alteration Synopsis

Vertical and lateral zonation dependant on host rocks and permeability structure

Halos can extend to 1000m along fluid pathways. Much shorter across permeability.

Key is to recognize the pathway



Predictable halos surround skarn, vein, and carbonate replacement deposits that reflect the composition of the host rock as well as the depth of formation and deposit type.

Visual

Mineralogic

Geochemical



Geochemical guias Fluid escape structures are sedimentary layering, intrusive contacts, faults, cleavage

and fracture mesh. High T elements (Cu, Bi and Mo) form large halos close to the skarn Moderate to low T elements (Mn, Hg and Tl) define halos at higher levels around

veins. Sr depletion accompanies shallow cordilleran base metal lodes

As, Sb, Hg, Tl and maybe Csdistinguishes hydrothermal jasperoid from diagenetic replacementOrange-red UV fluorescence (high Mn) up to 1 km awayPeripheral veins have characteristic colors, chemistry, and spatial distribution around deposits; up to 1 km but mostly

Richard Tosdal

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