Pt 5 Breccias Workshop

Breccias

Breccias - definition

Broken rock sometimes associated with mineralisation Breccias include

– Sedimentary bx– Volcanic bx (often host rocks)– Magmatic bx (often pre-mineral mineralised magmatic

hydrothermal) – Tectonic bx (mineralised tectonic hydrothermal)

Relationships of breccia

types

Breccia terminology Descriptive terminology based upon the

appearance of the rock using features such as fragment type and rounding and relationship to matrix etc

Genetic terminology relates to the interpreted mechanism of breccia formation and uses conceptual geological models to provide a link between the breccia and mineralisation

Genetic Summary

Intrusion Breccias

Associated with emplacement of intrusions with no hydrothermal activity

Magmatic hydrothermal breccias Combination of intrusion and hydrothermal

activity generally at depth without venting to the surface

Alteration as early chlorite and later silica-sericite + pyrite

Common in:– Upper portions of porphyry Cu deposits (pebble dykes)

and – Breccia pipes in deeper level sub volcanic terrains – Breccia pipes in batholith terrains (Cu-Tourmaline

breccias)

Magmatic Hydrothermal Bx

Pebbledykes/breccias

Kidston NE Australia

Kidston map

Kidston

Mixed breccia

Kidston

Marginal breccias:

Metamorphic bxGranodiorite bx

Kidston

Felsic fragment breccia

Spherulitic rhyolite

Kidston Intrusion features

KidstonSheeted veins

Kidston map

Kidston setting

Kidston Interp

Tourmaline Bx – Model

Cu-Tourmaline breccias

Occur in batholith terrains probably at apophyses Cu>Au in association with tourmaline, pyrite,

chalcopyrite Initial collapse produced by venting of volatiles

promotes collapse and development of:– flat dipping sheeted fractures and associated shingle

breccias– Steep dipping ring fractures at pipe margin

Later mineralisation exploits plumbing system

Tourmaline Bx - rocks

Shingle bxMt Terrible

Shingle Bx - Mexico

Shingle breccias - Tooloom

Phreatomagmatic Bx

Phreatomagmatic breccias Formed by explosive activity involving magma

and water turned to vapour Of interest here associated with high level

typically felsic intrusons commonly in flow dome complexes

Rising intrusion becomes depressurised and may come in contact with groundwaters in same fault

Vent with tuff rings and endogenous domes Mineralisation later high and low sulphidation Characterised by clay-pyrite alteration

Milled matrix breccia

Acupan, Philippines Lihir, PNG

Cripple Creek, USA Veladero, Argentina

Bedded breccias –Tuff rings

Pascua, ChileNauti, Wau, PNG

Sumbawa, Indonesia

Surficial features

Wood Fragments,Lihir, PNG

Accretionary Lapilli, Lihir, PNG

Bedded, lapilli,Kelian, Indonesia

Juvenile intrusion fragments

UpperRidges, Wau, PNG

Veladero, Argentina Yanacocha, Peru

Mineral Hill, Australia Namie Breccia, Wau, PNG

Domes

Wau Diatreme, Papua New Guinea

Crumple breccia

Namie Breccia

Mineralisation

Mineralisation at pipe margin - Acupan

Mineralisation at pipe margin – Lepanto

Mineralisation outside pipes – Kelian

Mineralisation within pipes

Mt Leyshon, Australia

Yanacocha, Peru

Veladero, Argentina

Phreatomagmatic breccias

Fluidised injection breccias

Smaller scale emplacement of sulphides into fractured rocks

Characterised by significant transport of matrix and lesser transport of host rocks fragments

Matrix of sulphides and rock flour Characterised by dyke-like forms grading to more

marginal crackle breccias Common in high sulphidation and some quartz-

sulphide low sulphidation deposits

Injection Bx

Fluidised injection breccias

Rotational breccia

Fluidised brecciaKelian, Indonesia Lihir Is., Papua New Guinea

Crackle and fluidised crackle breccias

Bowdens, AustraliaLihir, PNG

Goonumbla, AustraliaLama Argentina

Phreatic or Eruption breccias

Explosions result from depressurising of hot water to form steam

Near surficial breccia pipes No magmatic component Common where circulating cells of

geothermal fluids Cap quartz veins and silicified breccias Fluid outflows for sinter deposits

Ebx

Champange Pool Champagne Pool

Eruption breccia

Fluid outflows

Pamukale sinter terrace Turkey

Lihir Is - Phreatic/eruption

brecciaIntrusion related

hydrothermal system

Silicified breccias

Twin Hills, Australia

Toka Tindung, Indonesia

Puhipuhi, New Zealand

McLaughlin crack seal

breccia-sinter

Twin Hills – breccias

Twin Hills dismembered dyke

Ebx

Tectonic-hydrothermal brecciasincluding dilational (open space)

breccias

Form in open space faults Common infill of hydrothermal minerals Common sub surface sedimentary structures Local milled, floating clast breccias, many

with bonanza ores

Dilational Bx

Dilational /open space / expansion breccias

Mt Kare

Mosaic breccias

Kidston, Australia

Porgera, Papua New Guinea

Floating clast breccias

Hishikari

Viento El Indio DistrictTwin Hills Australia

Milled floating clast breccias

Subsurface sedimentary structures in open space faults

Mineralised Fault

Breccia

Tectonic-hydrothermal

breccias

Vera Nancy, rucked up vein fragment led to discovery

Rucked up fragments

Bilimoia, pebble dyke with rucked up shale fragments

Fault Breccia

Exploration significanceBreccias

Importance of descriptive classifications in the field Analysis of field data to produce genetic

classification which allow the application of prospects to geological models

Breccia types vary with deposit type and display distinct relationships to mineralisation

Barren eruption breccias overly sheeted and fissure vein systems while ore may occur marginal to, or at depth within, phreatomagmatic breccia pipes.

Lepanto rucked up

breccia fragment

Breccia matrix