transitions and zoning in porphyry epithermal districts€¦ · transitions and zoning in...
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Transitions and Zoning Transitions and Zoning in Porphyryin Porphyry--Epithermal Epithermal
Districts:Districts:
Indicators, Discriminators, Indicators, Discriminators, and Vectorsand Vectors
AMIRA Project Proposal AMIRA Project Proposal -- P765P765
El Teniente - Peripheral veins and argillic alteration
Porphyry-Epithermal Districts
Adapted from Sillitoe (1989)
• porphyry (Cu-Mo-Au) • epithermal (Au-Ag) • skarn (Cu-Au) • carbonate replacement
(Zn-Pb-Ag) • sediment-hosted (Au)
These districts host diverse styles of ore deposits and metal associations
Discrete mineralized zones in these districts(PCD, HS, LS, IS) are typically separated by barren gaps• We do not see continuity between deposit styles
• Hybrid mineralization styles are rare
Porphyry-Epithermal Districts
How can we identify productive ore zones within these large magmatic-hydrothermal systems?
Can we use peripheral deposits ± alteration systems to point us towards major deposits?
Rhodochrosite cement, phreatic breccia, Kelian, Indonesia
Example: Collahuasi, Chile
Landsat 741 /Spot merge
Volcan Irruputuncu
West Fissure/Quehuita Fm
Rosario DepositCollahuasi Fm
HS Vein - Cerro La GrandeLS Vein - Monctezuma
Example: Collahuasi
26 Mt fine Cu - Rosario PCD
Project Goals
We aim to help improve exploration success in porphyry-epithermal districts
Our goal is to develop and test criteria that will help explorers:• indicate prospective environments
• discriminate between mineralization styles and between productive and non-productive districts
• vector towards ore zones
qz-cp-cc stockwork, qz-fspr porphyry, Spence, N. Chile
Scope of Project
Four discrete research modules have been designed to address significant technical challenges within a given mineral district.
1. Lithocap domain2. Transitional environments3. Carbonate environments4. Alkalic systems
The modules that will be included will depend on sponsor interest and access to suitable sites
Volcanic Fumarole, White Island, New Zealand
Module 1: The lithocap domain
Challenges for exploration:• diversity of possible
origins• difficulties assessing
location of and depth to mineralized zones
• deposits may be laterally offset from alteration domains
• Can we systematically track alteration, metals, ± physical properties as a pathfinder to ore?Modified from Sillitoe
(1995)
Module 2: The transitional environment
Cadia Ridgeway: Late cp-epi-py veins with broad orthoclase alteration selvages
Kelian: sphalerite-galena-carbonate-
cemented auriferous breccia
The significance of green rocks:• When does the presence of
chlorite or epidote indicate proximity to a large hydrothermal system?
• Can we discriminate between green rocks on the margins of a porphyry centre from those around epithermal veins?
• Can we discriminate background alteration (diagenesis, metamorphism)?
Bingham Canyon
Module 3: The carbonate environment
• What happens to metals and fluids as they migrate through sedimentary rocks away from porphyry intrusions?
• What is the nature and extent of alteration in these environments?
• What is the nature and significance of zonation around carbonate-hosted-HS systems?
Barney’s Canyon: laminated
dolomitic siltstone
Module 4: Alkalic Systems
1 km
LS alkalic epithermale.g. Ladolam, Porgera, Emperor
porphyry Au-Cue.g. Ridgeway, CFE, Mount Polley
proximal Cu-Au-Fe skarne.g. Big Cadia
Alkalic porphyries are poorly understood relative to calc-alkalic systems
• alteration zonation?• carbonate zonation?• peripheral deposits?• lack of HS systems?
Potential Study AreasWe need to target districts with known and well-constrained
porphyries and peripheral systems
Collahuasi
Farrallon Negro, El Teniente
Lepanto FSE
Module 1
Batu Hijau
Module 2
Bingham
Cadia
Module 3
Oyu Tolgoi
Module 4
Palinpinon
Barren System
Under Cover Exploration
The Cadia district of Australia is one the largest known alkalic porphyry Au-Cu districts
It contains four known porphyry mineral centres (two of which have preserved tops),
Peripheral skarns and barren high-level alteration zones are exposed at surface, and also by mining and exploration drilling.
Cadia Quarry: pegmatitic or-qtz-bio-py-mo-cp cemented breccia with sericite-altered QMP clasts
Cadia Far East: albite-chlorite alteration overprinting bio-cp
Cadia District, NSW, Australia
Cadia District, NSW, Australia
Jensen & Barton (2000)
Galore Creek
Goonumbla
Silurian cover
Cadia Far East Little Cadia
500 m
21,000 mN 22,000 mN
5,500 mRL
5,000 mRL
23,000 mN
P1Fault
P2Fault
CB
FaultZ one
Regional Propylitic (chl-carb-epi-hm)
Skarn (py-hm-mt-chl-carb-gt)
Skarn Propylitic (epi-py)
Albite-Sericite (ab-qz-ser-py-tm)
Sodic (ab-qz-hm)
Calc-Sodic (ab-act-qz-carb-py)
Inner Propylitic (ab-chl-act-epi-qz-cp-lm-pr-mt-hm)
Legend - Alteration
Outer Calc-Potassic (ab-chl-act-epi-Kf-bn-mt-hm-cp)
Inner Calc-Potassic (ab-bi-Kf-act-qz-mt-bn)
4,500 mRL
After Tedder et al. (2001)
Palinpinon is a barren, porphyry-related system exposed over a 3 km vertical interval.
Alteration assemblages:K-silicate (biotite, magnetite)calc-silicate (garnet, clinopyroxene)hypogene advanced argillic (andalusite, zunyite)Steam-heated advanced argillicpropylitic (tremolite-actinolite, epidote) illitic (smectite, illite)
There are fossil (0.9 Ma) PCD-HS mineral assemblages, and recent PCD-LS assemblages
Bladed alunite, Palinpinon geothermal field, Philippines
Palinpinon geothermal field, Philippines
Palinpinon geothermal field, Philippines
Alteration zonation & overprinting relationships - Palinpinon (Rae, 2002)
Other Suitable Districts
High base level knowledge
Batu HijauCollahuasiEl TenienteLepanto - Far South EastFarellon NegroTintaya / Antapaccay
From Hedenquist et al. (1996)
Our objectives can be grouped into three themes:
Research Objectives
Grasberg:quartz-magnetite stockwork
• Indicators
• Discriminators
• Vectors
These will be based on fundamental geological documentation of the selected districts
• What makes a given mineral district prospective for porphyry/epithermal mineralization?
• Many factors need to be considered, involving processes that operate at a variety of scales.
• We aim to define the diagnostic geological, geochemical and geophysical charactersitics of prospective districts
Indicators
Steam-heated advanced argillic alteration, El Indio – Pascua district, Chile
DiscriminatorsCertain minerals can be used to discriminate effectively between deposit styles and/or alteration zones (e.g., garnet, amphibole, pyroxene, alunite)
We will test the potential of other minerals to better discriminate between the various hydrothermal environments, e.g.:
• Sphalerite • Kaolinite / illite• Pyrite • Epidote / chlorite• Enargite • Carbonates• Apatite • Biotite
These tools may be able to help assess the depth of erosion, and thereby help to evaluate the potential for shallow and/or deeper-level ore deposits
Collahuasi: Late-stage massive sulfide veins
Mineral Discriminators: Module 1
Example: Alunite REE fractionation
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu0.01
0.1
1
MH alunite (WR alteration)Syn-Au MH aluniteSteam heated alunite
Alun
ite R
EE
(nor
mal
ized
to h
ost r
ock
com
posi
tion)
Data from El Indio-Pascua Belt (Deyell, 2001)
Mineral Discriminators: Module 2
Example: Epidote
0.01
0.1
1
10
100
1000
0.001 0.01 0.1 1.0
Y/Sr
Cu/E
u
El TenienteCollahuasiRio BlancoN ChilevolcanicsBasalt standard
PCD’s
Volcanics
HS
Data from Chile PCDs (Cooke, 2001)
Vectors
We will develop geological and whole rock and mineralgeochemical vectors that can be used to help identify the mineralised centres
These will be based on the characteristics and geochemistry of vein arrays and alteration zones
Low sulfidation epithermal Au-Ag veins, Serijan Pit, Mt Muro, Indonesia
Zn-rich Polymetallic VHMS DepositsZn-rich Polymetallic VHMS Deposits
VV
VV
VV
VV
V
V
Increase of Eu*in Fe-Si cherts
δ34S decreasesδ18O decreases
limit of Na depletionCCPI increases
Alt index increases
S/Na2O increases
Mn content ofcarbonate increase
Limit of Tl haloBa/Srincreases Tl, Sb
increase
Hangingwall volcanic facies
Ore equivalent facies
Massive Zn-Pb-Cu sulfide
Footwall volcanic faciesV
Silica zone (qtz-chl-ser-py)
Chlorite zone (chl-ser-py)
Carbonate zone (carb-chl-ser-py)
Sericite zone (ser-carb-chl-py)
Albite zone (alb-qtz)
ALTERATION
Methodology
Starting point: well-constrained geology & geochronology
Modules 1 & 4: mineralogy & mineral chemistry, petrography, stable isotopic and exploration geochemistry & geophysics
Modules 2 & 3: also require fluid inclusions for depth constraints
We will carefully assess features that have the potential to offer simple, field-based criteria for determining where we are in the system
Spence, N Chile: biotite altered andesite; qz-cp veins cut by qz-py-chl vein with sericite alteration halo
Research TeamProject Leaders
David CookeBruce Gemmell
Chief InvestigatorsCari DeyellRobina SharpeNoel White
Cadia Hill Monzonite with qz-epi-bn-cc vein, Cadia Hill
Potential Collaborators
Jeff HedenquistDick TosdalBrian TownleyPeter Hollings
Timetable
Year 1• Literature review complete• First year mapping & logging results• Pilot studies on selected minerals completed• Initial GIS compilation completeYear 2• Bulk of geochemical analyses complete• Palinpinon study complete• Preliminary geochronology & fission track• Petrographic study of textural discriminators
completeYear 3• Final synthesis of all field and analytical data• Final district-scale analysis• Comparative study complete• Final development and testing of geochemical
vectors
Milestones
Goonumbla: Apatite inclusions in anhydrite phenocryst
DeliverablesDeliverables
Geological and geochemical vectors to identify the
location and likely distance to high-grade ore zones
Deliverables
• New mineral discriminators for different hydrothermal environments
• Criteria for evaluating a district’s potential
• A database of geochemical, geological, and geophysical data for the selected mineral districts
Electrum, tellurides & base metal sulfides, Acupan, Phillipines
Key Items• Salaries (Deyell, Sharpe)• Analytical• Travel• Reporting
Summary• AMIRA Funding - $225K p.a. • ARC Linkage - $225K p.a.• In-kind (CODES) ~$100K p.a.• Additional funding streams also being
pursued (e.g., NSERC)• Industry Leverage ~ 22 : 1
Budget
SponsorshipWe are seeking $25K AUD (~$14K US) per annum from each sponsor for 3 years
Preferred sponsorship -nine companies + ARC
(full budget) = 2-3case studies +barren system
Minimum sponsorship -four companies + ARC (= 1 district + barren system)