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
Pebble
dykes/breccias
Kidston NE Australia
Kidston map
Kidston
Mixed breccia
Kidston
Marginal breccias:
Metamorphic bx
Granodiorite bx
Kidston
Felsic fragment breccia
Spherulitic rhyolite
Kidston
Intrusion features
Kidston
Sheeted
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 bx
Mt 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
Lihir, PNG
Acupan, Philippines
Cripple Creek, USA
Veladero, Argentina
Bedded breccias
Tuff rings
Sumbawa, Indonesia
Nauti, Wau, PNG
Pascua, Chile
Surficial features
Accretionary Lapilli, Lihir, PNG
Bedded, lapilli,
Kelian, Indonesia
Wood Fragments,
Lihir, PNG
Juvenile intrusion fragments
Mineral Hill, Australia
Namie Breccia, Wau, PNG
UpperRidges, Wau, PNG
Veladero, Argentina
Yanacocha, Peru
Domes
Wau Diatreme,
Papua New Guinea
Namie Breccia
Crumple 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 quartzsulphide low sulphidation deposits
Injection Bx
Fluidised injection
breccias
Rotational breccia
Fluidised breccia
Kelian, Indonesia
Lihir Is., Papua New Guinea
Crackle and fluidised crackle breccias
Lama Argentina
Lihir, PNG
Goonumbla, Australia
Bowdens, Australia
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
breccia
Intrusion related
hydrothermal system
Silicified breccias
Toka Tindung, Indonesia
Twin Hills, Australia
Puhipuhi, New Zealand
McLaughlin
crack seal
breccia-sinter
Twin Hills breccias
Twin Hills dismembered dyke
Ebx
Tectonic-hydrothermal breccias
including 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
Mosaic breccias
Kidston, Australia
Mt Kare
Porgera, Papua New Guinea
Floating clast
breccias
Hishikari
Twin Hills Australia
Viento El Indio District
Milled floating
clast breccias
Subsurface sedimentary structures in
open space faults
Mineralised
Fault
Breccia
Tectonichydrothermal
breccias
Rucked up fragments
Vera Nancy, rucked up
vein fragment led to
discovery
Bilimoia, pebble
dyke with rucked up
shale fragments
Fault
Breccia
Exploration significance
Breccias
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
