GoldGold andand CopperCopper DisseminationDisseminationin in thethe IgneousIgneous--VolcanicVolcanic

SaldaSaldaa a FormationFormation, Colombia, Colombiaandand ExtensionExtension ofof thethe Mineral Mineral ProvinceProvince

in in thethe AndeanAndean CordilleraCordillera

Prepared by:Prepared by:Alberto LoboAlberto Lobo--Guerrero S.Guerrero S.GeologistGeologist, , M.ScM.Sc., ., MinExMinEx

EconomicEconomic GeologyGeology ResearchResearch InstituteInstituteUniversityUniversity ofof thethe WitwatersrandWitwatersrand

JohannesburgJohannesburg, , SouthSouth AfricaAfrica, , JuneJune, 2003, 2003

CONTENTS

Introduction Saldaa Formation

LocationDescriptionLithologyPetrographyExtensionEnvironment of EmplacementStructural Geology

MineralizationTypes KnownPotentialProspects

Extension of ProvinceIn Colombian AndesPerij ChainIn Andean CordilleraInto Mexico

INTRODUCTION-1

Saldaa region constitutes

one of the best exploration targets

for large-tonnage Au + Cu disseminationsin Colombian Andes, South America

Saldaa Formation =Jurassic hypabissal + volcanic rocks

INTRODUCTION-2

Aulacogen extends throughout the Andes

from Venezuela into Argentina

Mineralization known all along

conformscontinent-wide metallogenic province

INTRODUCTION

SALDAA FORMATION-1

Natagaima region =isolated stretch of Colombian Central Cordillera

complex vulcano-sedimentarysequence of faulted blocks

Saldaa Formation composed by:

tuffs, agglomerates, lava flows,continental + shallow marine sedimentary rocks

+ small subvolcanic porphyritic bodies

GENERALIZED LITHOLOGIC UNITS, NATAGAIMA, COLOMBIA

UNIT NAME AGE LITHOLOGY/ENVIRONMENT

RELATEDINTRUSIVES

MINERALIZATION

Volcaniclasticdeposits

Q Continental clastic andvolcanic deposits

Not exposed Au placers, exotic Cu

HondaFormation

TContinental shales,siltstones, sandstones,mudflows and volcanic ash

T porphyriticstocks

Gypsum veinlets, exotic Cu

Cretaceous toTertiary

sedimentarysequence

K-T

Marine to continentalsiliciclastics:conglomerates,sandstones, shales,limestones

None known

Au placers, Paleoplacers(Gualanday Fm.)Exotic Cu

SaldaaFormation

JContinental volcanic rocks,sediments, shallow marinedeposits, lava flows

J stocks,batholiths, dikes

+ sills

Low+high sulf. Epithermal Au veins;low sulfidation Au diss. in stkwks;Au+Cu porph., Fe oxide-Cu-Au,Sediment-hosted Au, gypsumveins, Mo-Cu porph.

PayandFormation J-TR

Limestones, sandstonesand shales

None known Sediment-hosted Au; Cu skarnAu veins + skarn, Replacementdeposits

LuisaFormation

TRContinental red beds:conglomerates,sandstones and shales,(evaporites)

Mafic smallbodies

Sediment hosted Au, Manto typePb-Zn, evaporites, Sediment-hosted Cu, Sabkhas

TierradentroGneiss &Granulites

pEHigh grade metamorphicrocks (granulites andgneisses)

Pz stocksShear zones with Au,Mesothermal Au

LOCATION

INTRODUCTION

LOCATION

Isolatedwedge ofColombianCentralCordillera

SALDAA FORMATION-2

size of andesitic-daciticporphyritic bodies seldom >4km2

Most outcrops of intrusive rocks =apophysis of larger bodies

too small to map at 1:100,000 scale

porphyritic bodies composed bywell-formed plagioclase phenocrystals

up to a few centimeters longthat occur in gray-green aphanitic matrix

SALDAA FORMATION-3

PETROGRAPHY

composition varies from tonalite togranodiorite and quartzmonzonite

some rocks grade into diorite + basaltfew = syenitic

Numerous augite phenocrystals + abundantamygdules filled by chalcedony, calcite, chlorite, epidote, zeolites and native Cu are evident in the matrix

GeneralizedGeologicalMap

GeneralizedGeologicalMap

SALDAA FORMATION-4

In t/ region of study, extends for 1200 km2

evidence of fertile intrusive rocks, hydrothermalalteration and mineralization occur throughout

15,400 hectares within region have high potentialto host disseminated Au associated with the upperportion of Cu-Au porphyry systems

study area = approx.1/3 of total known Saldaa outcrops in Colombian Andes

= 1/10 of similar age/composition rocks in country

SALDAA FORMATION-5

ENVIRONMENT OF EMPLACEMENT

deposited in aborted rift basin

overlying Triassic continental red beds andcarbonate platform

Jurassic subductionproduced magmatism + vulcanism

Unconformably overlain by thick pile of Cretaceous+ Tertiary sediments

INTRODUCTION

SALDAA FORMATION-6

Mineral deposits = result of Jurassic, porphyriticforced intrusions emplaced along weak zones oftuffs and other Saldaa units

Repetitive intrusion == overprinting of hydrothermalalteration + mineralization

Extensional faults run parallel to main branches ofaulacogen = offered sites for fluid migration + mineral deposition

circular structures are not uncommon

INTRODUCTION

MINERALIZATION-1

Several types of mineralization are knownin region

world-class Au placersabundant sub-vertical high and low

sulphidation Au- & Cu-rich qtz veinsAg, Cu, barite, fluorite, Sb, Fe +

gypsum deposits exploited at smallscale since pre-Columbian times

MINERALIZATION-2

Au + Cu diss. mineralization detected in:

-stockworks-breccioid qtz veins-individual porphyritic bodies-hydrothermal bxs along contact

between intrusive + volcanic rocks

MINERALIZATION-3

Region has significant potential forexploration of various mineral deposit types

-high and low sulfidation epithermal Au-Au porphyry-Cu porphyry-sediment-hosted Au

(so-called Carlin type)-Fe Oxide-Cu-Au-REE-exotic Cu accumulations

INTRODUCTION

MINERALIZATION-4

Primary Cu mineralization generally associated w/ local intense sericitization and silicification

large portion of Saldaa Formation = covered by secondary Cu minerals + epidote

Numerous gossans with high contents of free Auhave been mapped

>22 zones of interest with potential large-tonnageAu + Cu mineralization identified to date

Zooming in on amineralized

stockwork

Intense argillizationoverprints mineralizedstockwork

MINERALIZATION-5

Few prospects have been studied in detail, mapped or explored under moderntechniques.

Old, small-scale Au miners only workedrock deposits >6gAu/tplacers >5gAu/m3

No disseminated deposits were sampledbefore 1990s

EXTENSION INTOCOLOMBIAN ANDES

Geological environment and associated Auand Cu mineralization of Saldaa Formation

extends thoughout Colombian Andes

from Guajira to Putumayo

INTRODUCTION

EXTENSION INTOANDEAN CORDILLERA

Saldaa Formation equivalentsextend furthermore

along Andean Cordillera

from Venezuela to Argentina

Venezuela:Perij and Mrida

Argentina: Patagonia

WORLD-CLASS DEPOSITS

occur in correlatives of Saldaa Formation

and fall within similar age spanin continent-wide metallogenic province

WORLD-CLASS DEPOSITS

COLOMBIAEl Silencio, Antioquia ~1500 ton AuAngostura, Santander >700 ton AuSerrana de San Lucas, Bolvar >>500 tonAu

ECUADORNambija, Serrana del Cndor >300 ton AuSan Carlos, Sna del Cndor >~5x10^6 ton Cu

ARGENTINACerro Vanguardia, Patagonia ~500 ton Au

EXTENSION INTOANDEAN CORDILLERA

Serrana de Perij(stretches between

Colombia + Venezuela)

contains numerous,under-explored Au + Cu depositsassociated to Saldaa-typeJurassic events

EXTENSION INTOOTHER REGIONS

Part of this provinceextends into Mexico

Guerrero and Oaxaca terranes

GoldGold andand CopperCopper DisseminationDisseminationin in thethe IgneousIgneous--VolcanicVolcanic

SaldaSaldaa a FormationFormation, Colombia, Colombiaandand ExtensionExtension ofof thethe Mineral Mineral ProvinceProvince

in in thethe AndeanAndean CordilleraCordillera

Prepared by:Prepared by:Alberto LoboAlberto Lobo--Guerrero S.Guerrero S.GeologistGeologist, , M.ScM.Sc., ., MinExMinEx

EconomicEconomic GeologyGeology ResearchResearch InstituteInstituteUniversityUniversity ofof thethe WitwatersrandWitwatersrand

JohannesburgJohannesburg, , SouthSouth AfricaAfrica, , JuneJune, 2003, 2003