Transitions and Zoning in Porphyry-Epithermal Districts: Indicators, Discriminators, and Vectors AMIRA Project Proposal - P765 El Teniente - Peripheral veins and argillic alteration
Porphyry-Epithermal Districts These districts host diverse styles of ore deposits and metal associations porphyry (Cu-Mo-Au) epithermal (Au-Ag) skarn (Cu-Au) carbonate replacement (Zn-Pb-Ag) sediment-hosted (Au) Adapted from Sillitoe (1989)
Porphyry-Epithermal Districts 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 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 Volcan Irruputuncu West Fissure/Quehuita Fm Landsat 741 /Spot merge Rosario Deposit Collahuasi Fm
Example: Collahuasi 26 Mt fine Cu - Rosario PCD LS Vein - Monctezuma HS Vein - Cerro La Grande
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 nonproductive 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 domain 2. Transitional environments 3. Carbonate environments 4. 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 Modified from Sillitoe (1995) 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?
Module 2: The transitional environment 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)? Cadia Ridgeway: Late cp-epi-py veins with broad orthoclase alteration selvages Kelian: sphaleritegalena-carbonatecemented auriferous breccia
Module 3: The carbonate environment Bingham Canyon 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 LS alkalic epithermal e.g. Ladolam, Porgera, Emperor Alkalic porphyries are poorly understood relative to calc-alkalic systems alteration zonation? carbonate zonation? peripheral deposits? lack of HS systems? porphyry Au-Cu e.g. Ridgeway, CFE, Mount Polley proximal Cu-Au- Fe skarn e.g. Big Cadia 1 km
Potential Study Areas We need to target districts with known and well-constrained porphyries and peripheral systems Bingham Oyu Tolgoi Palinpinon Lepanto FSE Collahuasi Batu Hijau Farrallon Negro, El Teniente Under Cover Exploration Cadia Module 1 Module 4 Module 2 Barren System Module 3
Cadia District, NSW, Australia 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 highlevel alteration zones are exposed at surface, and also by mining and exploration drilling. Cadia Quarry: pegmatitic or-qtzbio-py-mo-cp cemented breccia with sericite-altered QMP clasts Cadia Far East: albite-chlorite alteration overprinting bio-cp
Cadia District, NSW, Australia After Tedder et al. (2001) 21,000 mn 22,000 mn Silurian cover Cadia Far East Little Cadia Jensen & Barton (2000) Galore Creek 5,500 mrl 23,000 mn 5,000 mrl Legend - Alteration Goonumbla Regional Propylitic (chl-carb-epi-hm) 4,500 mrl CB Fault Zone 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) 500 m P2 Fault P1 Fault Inner Propylitic (ab-chl-act-epi-qz-cp-lm-pr-mt-hm) Outer Calc-Potassic (ab-chl-act-epi-kf-bn-mt-hm-cp) Inner Calc-Potassic (ab-bi-kf-act-qz-mt-bn)
Palinpinon geothermal field, Philippines 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 argillic propylitic (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 Alteration zonation & overprinting relationships - Palinpinon (Rae, 2002)
Other Suitable Districts High base level knowledge Batu Hijau Collahuasi El Teniente Lepanto - Far South East Farellon Negro Tintaya / Antapaccay From Hedenquist et al. (1996)
Research Objectives Our objectives can be grouped into three themes: Indicators Discriminators Vectors These will be based on fundamental geological documentation of the selected districts Grasberg: quartz-magnetite stockwork
Indicators 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 Steam-heated advanced argillic alteration, El Indio Pascua district, Chile
Discriminators Certain 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 Alunite REE (normalized to host rock composition) 1 0.1 MH alunite (WR alteration) Syn-Au MH alunite Steam heated alunite 0.01 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Data from El Indio-Pascua Belt (Deyell, 2001)
Mineral Discriminators: Module 2 Example: Epidote 1000 Cu/Eu 100 10 1 PCD s HS El Teniente Collahuasi Rio Blanco N Chile volcanics Basalt standard 0.1 0.01 Volcanics 0.001 0.01 0.1 1.0 Y/Sr Data from Chile PCDs (Cooke, 2001)
Vectors We will develop geological and whole rock and mineral geochemical 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 Deposits Ba/Sr increases Tl, Sb increase Limit of Tl halo Increase of Eu* in Fe-Si cherts Mn content of carbonate increase V V V V V δ34s decreases V δ18o decreases limit of Na depletion S/Na 2 O increases V CCPI increases Alt index increases V V V V Hangingwall volcanic facies Ore equivalent facies Massive Zn-Pb-Cu sulfide Footwall volcanic facies ALTERATION 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)
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 Team Project Leaders David Cooke Bruce Gemmell Chief Investigators Cari Deyell Robina Sharpe Noel White Potential Collaborators Jeff Hedenquist Dick Tosdal Brian Townley Peter Hollings Cadia Hill Monzonite with qz-epi-bn-cc vein, Cadia Hill
Timetable
Milestones Year 1 Literature review complete First year mapping & logging results Pilot studies on selected minerals completed Initial GIS compilation complete Year 2 Bulk of geochemical analyses complete Palinpinonstudy complete Preliminary geochronology & fission track Petrographic study of textural discriminators complete Year 3 Final synthesis of all field and analytical data Final district-scale analysis Comparative study complete Final development and testing of geochemical vectors Goonumbla: Apatite inclusions in anhydrite phenocryst
Deliverables 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
Budget 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
Sponsorship We are seeking $25K AUD (~$14K US) per annum from each sponsor for 3 years Preferred sponsorship - nine companies + ARC (full budget) = 2-3 case studies + barren system Minimum sponsorship - four companies + ARC (= 1 district + barren system)