Porphyry indicator minerals (PIMS) and porphyry vectoring and fertility tools (PVFTS)

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1 Porphyry indicator minerals (PIMS) and porphyry vectoring and fertility tools (PVFTS) Epidote albite alteration in McLeod Hill quartz monzodiorite, Yerington, Nevada Indicators of mineralization styles and recorders of hypogene geochemical dispersion halos Pete Hollings, David R Cooke, Paul Agnew, Michael Baker, Zhaoshan Chang, Jamie J. Wilkinson, Noel C. White, Lejun Zhang, Jennifer Thompson, Ayesha Ahmed, J. Bruce Gemmell, Nathan Fox, Huayong Chen, Clara Wilkinson

2 Giant geochemical anomalies Porphyry ore deposit geology 1 km 3 km 3 = 9 billion tonnes of ore 65 million tonnes of Cu >110 million tonnes of S Chuquicamata, Eocene-Oligocene porphyry belt, Northern Chile (Courtesy of CODELCO)

3 Porphyry districts Hydrous, multiphase, oxidised intrusive complex Peripheral styles of mineralisation (epithermal, skarn) Huge 3D volumes of hydrothermal alteration Distinctive alteration and magmatic mineral chemistry After Holliday and Cooke (2007); Cooke et al. (2014, 2017)

4 Definitions Porphyry indicator minerals (PIMS): Minerals that can be used to potentially help to identify the presence of, or potential for, porphyry and other styles of mineralisation (fingerprints) Porphyry vectoring and fertility tools (PVFTS): Minerals that can be used to predict the likely direction and distance to mineralized centres, and the potential metal endowment of a district (footprints) Cerro Casale district, Chile

5 Enabling technologies Unlocking the exploration potential of mineral chemistry LA ICP MS SWIR Method for rapid acquisition of multi element mineral chemistry data Significantly lower detection limits than electron microprobe and other techniques New developments in automated data reduction and quality control are about to facilitate more efficient and consistent data processing Rapid, reliable clay mineral identification technique Revolutionized alteration mapping in lithocaps and high sulfidation epithermal environments

6 Porphyry indicator minerals (PIMS) Geochemical fingerprints of porphyry deposits PIMS have distinctive trace element compositions Distinct from local country rocks (e.g., zircon) Distinctive of particular mineralization styles and/or alteration zones (e.g., magnetite) Ideally, PIMS should be resistate, so that they can be preserved in stream sediments, till, etc. Zircon, magnetite, apatite, tourmaline, garnet, epidote, pyrite, andradite, gold Some PIMS require bedrock sampling to be used in exploration Plagioclase, (chlorite)

7 Figure from Dilles et al. (2015) Zircon geochemistry Geochronology, petrogenesis, fertility Zircon is the most robust high temperature geochronometer available for magmatic rocks Isotopic and trace element analyses can provide profound insights into magma petrogenesis Key information gained from trace elements in zircons include: i. Magmatic oxidation states from Ce and Eu anomalies (oxidised magmas form porphyry mineralisation) ii. iii. Temperature of zircon crystallization from Ti content Evolution of magma compositions from variations in Zr/Hf, U, Th and REE patterns

8 (Water content) Fertile 10000*(Eu/Eu*)/Y Barren (Oxidation state of magma) Batu Hijau porphyry Cu Au Tampakan porphyry Cu Au Dexing porphyry Cu Mo Au Jiama porphyry skarn Cu Mo Au Sar Chesmeh porphyry Cu Mo Au Zircon A porphyry indicator mineral Magmatic oxidation state, water content, degree of fractionation Degree of hornblende (Ce/Nd)/Y fractionation Nannihu porphyry Mo W Yuchiling porphyry Mo Sungun porphyry Cu Mo Qulong porphyry Cu Mo Fertile Lu et al. (2016) Barren Ce 4+ /Ce 3+ Yellowstone rhyolite Bandelier rhyolite Hawkin S type dacite Kadoona ( type dacite Bishop Tuff Lucerne reduced granite Shen et al. (2015) Cu (Mt) Larger Paleozoic porphyry deposits of the Central Asian orogenic belt have zircons with high Ce 4+ /Ce 3+ (Shen et al., 2015) Barren Paleozoic granitoids in the Lachlan Fold belt, Australia, have low Ce 4+ /Ce 3+ ratios (Belousova et al., 2006)

9 Zircon Eu/Eu* and Ce 4+ /Ce 3+ anomalies a product of titanite fractionation? (Loader et al., 2017) Loader et al. (2017) showed that small amounts of titanite crystallisation can produce zircon Eu/Eu* and Ce 4+ /Ce 3+ anomalies melt/chondrite 10 1 Titanite fractionation will deplete REE from the melt MREE are more depleted than LREE or HREE during this process Sm and Gd more depleted than Eu 0,1 % titanite crystallisation La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu This process could produce false positives for porphyry explorers applying zircon as a PIM in regional exploration Loader et al. (2017)

10 Hornblende geochemistry petrogenesis and fertility Hollings et al. (2013) high Si, low Al, Ca and alkalis group in intermediate felsic rocks shallow crystallization high alkali, Al and Ca, low Si group in intermediate mafic rocks crystallising at deeper crustal levels. Cao et al. (2018) Zoning suggests mixing of the two magmas Presence of both groups in a single sample indicates interaction and phenocryst exchange between the two parental magmas

11 Porphyry indicator minerals Plagioclase (Williamson et al. 2016) An % Excess Al B B A A An % Excess Al Anorthite % Plagioclase from fertile porphyry systems contains excess Al related to high melt water contents It may record injections of hydrous fluid or fluidrich melts into the sub porphyry magma chamber Excess Al may exclude copper from plagioclase, enriching the remaining melts in Cu Sr/Y Cu in plagioclase (ppm) Excess Al Sr/Y in plagioclase Cu (ppm) Williamson et al. (2016) A Position along the LA ICP MS point traverse B

12 Porphyry indicator minerals Magnetite Magmatic Hydrothermal Al/Ti 1.0 Ilmenite exsolution lamellae in magnetite, Grasberg 50 µm Magnetite is resistive and easily separated, making it an attractive PIM candidate Two decades of research have shown that major and trace element ratios can effectively discriminate magmatic and hydrothermal magnetite from a diversity of ore deposit types Fine exsolution lamellae can affect magnetite LA ICP MS analyses Magnetite is prone to diffusional resetting by post crystallization hydrothermal fluids care must be taken in data interpretation Cross (2000) V/Ti Dare et al. (2014)

13 Discrimination of porphyry magnetite Existing deposit type discrimination does not work for porphyries with new data Porphyry results plot from Fe Ti V deposits across into Kiruna and IOCG fields Diagram: Dupuis and Beaudoin (2011); Data from Sievwright (2017) Sievwright (2017) Recrystallised hydrothermal magnetite vein

14 Magnetite alteration association Colour Alteration Argillic-intermediate Phyllic Potassic Potassic-Phyllic Potassic-Propylitic Propylitic Unaltered Weak Propylitic Hydrothermal magnetite derived from different porphyry alteration domains can be discriminated DP1 is mainly controlled by Co+ Mg and Al DP2 is mainly controlled by V+ Co and Mg Sievwright (2017) Magnetite in chalcopyrite

15 Porphyry indicator minerals Apatite Bouzari et al. (2016) Bouzari et al. (2016) Apatite chemistry and luminescence discriminates magmatic and hydrothermal apatites from different porphyry alteration zones (Bouzari et al., 2016; Loader, 2017)

16 Discrimination of porphyry related apatite Discriminant projection analyses can distinguish apatite from magmatic and a variety of hydrothermal environments, including porphyries (Mao et al., 2016) Porphyry apatite Low Mg, Dy, Pb, U High Mn, Y, Ce, Eu, Yb, Th DP2 3 1 = logmg logmn logy logce logeu logdy logyb logpb logth logu DP2 3 2 = logmg logmn logy logce logeu logdy logyb logpb logth logu Mao et al. (2016)

17 Igneous apatite potential Miles et al. (2012) Low fo 2 Cu-Mo/Au Oxidised Cu-Mo(-Au) Redox sensitivity of apatite chemistry (Mn & V) No fertility discrimination but broad separation of porphyry types Does not take into account complex apatite paragenesis Alkalic Cu-Au Rukhlov et al. (2017)

18 Geochemical footprints of porphyry deposits Porphyry fertility and vectoring tools (PFVTS) Subtle, low level hypogene geochemical signals are preserved in hydrothermal alteration minerals distal to porphyry deposits Analysis of these alteration minerals can potentially provide explorers with both fertility and vectoring information They allow the presence, location and significance of porphyry and epithermal deposits to be assessed during the early stages of exploration This can potentially be achieved with remarkably low density sampling and very low cost relative to most other available search technologies

19 Propylitic alteration: a distal indicator of porphyry Cu deposits 2-6km 2-6 km Slide courtesy of Paul Agnew Modified after Holliday and Cooke (2007)

20 AMIRA International s footprints research program ( ) P765 ( ) Transitions and zoning in porphyry epithermal districts: Indicators, Discriminators and Vectors P765A ( ) Three major questions being addressed: 1. Fertility: Can we detect the presence of well endowed systems how large? 2. Vectoring: How far to the ore zone? 3. Vectoring: In what direction? Geochemical and geological halos in green rocks and lithocaps: The explorer s toolbox for porphyry and epithermal districts P1060 ( ) Enhanced geochemical targeting in magmatic hydrothermal systems P1153 ( ) Applying the explorers toolbox to discover porphyry and epithermal Cu, Au and Mo deposits P1202 ( ) Far field and near mine footprints: finding and defining the next generation of Tier 1 ore deposits

21 Porphyry footprints Arsenic in epidote Fertility indicator Baguio district, Philippines (Cooke et al., 2014) A B B C As (ppm) Mexico skarn prospect Geochemical anomaly A Pyrite halo Green rocks Black Mt Small porphyry Cu Au Pyrite halo Potassic zone Pyrite halo B' Green rocks Nugget Hill Large porphyry Cu Au Pyrite halo Potassic zone C ,000 1,500 2,000 2,500 3,000 3,500 4,000 Distance (m) replacement epidote vein epidote skarn epidote whole rock

22 Porphyry footprints Ti/Sr in chlorite Vectoring tool Batu Hijau, Indonesia (Wilkinson et al., 2015) Sr in chlorite (sample mean values) SW traverse (original) SW traverse traverse south Whole rock 2009 traverse north W traverse Bambu Ti/Sr 10.0 Size of symbols proportional to ppm; Maximum symbol size = 84 ppm No Sr depletion Base map modified from Garwin (2000) 1000 m Chlorite trace element ratios provide vectors to the mineralized centre of Batu Hijau within 2.5 km (potentially up to 5 km for some trace elements) Distance = ln {[Ti/Sr]/3x10 6 } Batu Hijau Distance to centre (m) Trace element substitution into the chlorite crystal lattice is strongly controlled by temperature

23 Green rock vectoring Example from Resolution, Arizona, USA Provided as green rock blind test site to P765A by Rio Tinto Porphyry Cu Mo deposit with total inferred resource of Gt at 1.47% Cu and 0.037% Mo Data from Resolution Copper and Rio Tinto websites

24 Reproduced from Hehnke et al. (2012)

25 Rio Tinto blind site plan view N Projection onto N S cross section 2 km S 500 m

26 South Pseudo cross section: view west North km

27 Green Rock Tools Validation from Blind Sites X = ln [ Ti / Sr] S N cross section; colours are Ti/Sr bins B 300 A Elevation (m) Northing Northing Elevation 1000m Distances calculated using Batu Hijau Ti/Sr proximitor

28 A Rio Tinto s Response B Resolution, Arizona Excellent results from 12 samples on a 2 km long section that passed through the deposit Resolution Porphyry Cu Mo Deposit

29 Porphyry footprints combining epidote and chlorite Taldy Bulak, Kyrgyzstan Southern Tien Shan Paleozoic Fold Belt Northern and middle Tien Shan Paleozoic Arc Porphyry Copper Major orogenic gold deposits Russia After image from Ivanhoe Mines Website, 2003 Uzbekistan Daugystau 6 Moz Muruntau > 110 Moz. Zarmitan 6 Moz Kazakhstan Tashkent Jilau 3 Moz Taldy Bulak Bishkek Almaty China Tuwu Kumtor (10 Moz) Kyrgyzstan Tajikistan China Almalyk (>2 0.4% Cu 0.4g/t Au; 80 Moz Au) Mongolia Kharmagtai (> 5 Moz) Ulaanbatar Oyu Tolgoi (50 Moz) Beijing km A blind test site provided to AMIRA P765A by Andrew Wurst (Gold Fields)

30 Taldy Bulak, Kyrgyzstan Vectoring tools combining epidote and chlorite data Barkol Au Cu prospect Prospect ( Younger Devonian Cover ( Taldybulak Bulak Au Cu Porphyry porphyry Andash Andash Au Cu Au Cu skarns Skarns and and Porphyry Porphyry Tokhtonasai Au Cu skarns Skarns ( ( (( ( ( ( ( N Devonian Cover Au Cu Porphyry 250 m Ordovician Arc Host Rocks Ordovician Arc Host Rocks 10 km Ordovician arc host rocks Model Mt Au (g/t) Cu (%) Au (Moz) Cu (Mlb) May 08 (indicated) May 08 (inferred) A blind test site provided to AMIRA P765A by Andrew Wurst (Gold Fields)

31 Porphyry footprints combining epidote and chlorite Vectoring tools TaldyBulak, Kyrgystan Grid sampling of 4 x 1.5 km area (27 samples) One outlier collected 4 km away with distinctive features TGR 25 this sample does not contain pyrite the epidote has anomalous Pb, low As and Sb Metamorphic epidote in Devonian cover unrelated to Ordovician porphyry deposit 27 samples with porphyry related epidote chlorite alteration 1 km TGR 11 Weak chlorite epidote replacement of diorite porphyry TGR 22 Epidote chlorite (calcite) cemented breccia with sandstone clasts

32 Porphyry footprints combining epidote and chlorite Vectoring tools TaldyBulak, Kyrgystan Taldy Bulak, Kyrgyzstan Contouring of epidote and chlorite LA ICPMS data 2D grid sampling allowed for contouring of results Epidote Chlorite No epidote or chlorite 200 m 600 pm Cu in soil anomaly Epidote Chlorite m 500 m

33 Porphyry vectoring and fertility tools Lithocaps SWIR, whole rock and mineral geochemistry Cathedral Peak lithocap, Cerro Casale, Chile

34 Lithocap exploration alunite SWIR peak shifts Mankayan lithocap Philippines Higher Na/(Na+K) ratio indicates higher formation temperature (Stoffregen and Cygan, 1990) Wavelength position (nm) In the Mankayan lithocap, alunite absorption peak at ~1480 nm shifts to higher position closer to intrusive centre Wavelength position of the alunite absorption feature at 1480 nm Chang et al. (2011)

35 Lithocap exploration whole rock geochemistry data (filtered) Alunite crystals PIXE images Samples distal to FSE Proximal Pb Pb Sr Mankayan lithocap Philippines ~ 7,000 ppm Pb ~ 4,000 ppm Pb ~ 950 ppm Sr In the Mankayan lithocap, quartz alunite altered rocks show spatial variations in Sr/Pb ratios that vector towards the FSE porphyry deposits Also La/Pb increases; Hg, Ag, Ag/Au, Te, As/Zn decrease Only plotting alunite bearing samples with < 0.1% Cu, Au < 0.1 ppm Au Chang et al. (2011)

36 Conclusions There are several magmatic and hydrothermal minerals that show considerable potential as PIMS and/or PVFTS Contribution to a major porphyry discovery would help to validate these approaches and to facilitate their widespread acceptance as geochemical exploration techniques We predict that some of these are likely to become routine tools used by explorers over the next decade New and emerging technologies need to be embraced by industry if geochemistry is to maintain a critical role in the discovery of new resources over the next decade Access to LA ICP MS technology is mostly through university laboratories this needs to change for widespread uptake Epidote crystals image source: www. gemselect.com/other info/ epidote unakite.php