Exploration Challenges of the 21 st Century. 12 October 2011

Transcription

1 Exploration Challenges of the 21 st Century 12 October 2011

2 Big challenges Discovery especially better grade, world-class deposits Copper/gold average deposit/mining grade declining Increasing capital, operating, energy, water intensity Development license to operate, power and water, people Timelines extending discovery to mine: 10+ years? Complexity increasing no short-cuts Technology Improvements but no game changers Opportunities drilling, technology, data and interpretation Copper porphyry deposits Review current understanding Challenges 2

3 Global distribution of major porphyry copper deposits 65% of annual production 35% from Chile Mature continental and island arcs Preserved arc terranes Deposits dominantly Mesozoic and Tertiary 2 10 Mt Contained CuEq Mt Contained CuEq >31 Mt Contained CuEq 3

4 Porphyry model Magmatic fluids from crystallization of arc magmas Form at convergent plate margins because: Subduction generates volatile-rich magmas Arcs provide structural settings for high-level magma emplacement, fluid flow and deposition Variations include the metal suite, composition of intrusions, depth of formation (<1 to 8km), evolution of magmatic fluids/vapours, structural and lithological controls, and role of external fluids From Tosdal and Richards, 2004

5 Regional controls area selection Regional framework Tectonics Magmatic events Timing Ocean plate and arc structure Overprints 5

6 Regional controls modern arcs 30o 40o EQ <300km EQ >600km 55o >70o 65o 6 From Garwin, 2003

7 Porphyry deposits in BC Galore Creek Dease Lake Lorraine Mapped Terranes Stikine Quesnel Porphyry Occurrences Alkalic Calc-alkalic Mt Milligan Prince George Roads Towns/Cities Bella Coola Mount Polley Arc terrane deposits Post-accretion deposits Wrangelia Highland Valley Iron Mask (Afton, Ajax) Kamloops Copper Mountain From Chamberlain, 2010

8 Regional exploration E E COPAQUIRI QB E E N N N N 4 ROSARIO N UJINA Structure Intrusions magma chemistry Clusters Remote sensing colour anomalies Geophysics magnetics, gravity, EM Geochemistry streams, minerals El COLORADO N N N N

9 Magma series and deposits Na 2 O + K 2 O (wt%) silica-undersaturated alkalic Cu-Au Cu-Au silica-saturated alkalic high-k calcalkalic Cu-Au (-Mo) Cu-Au SiO 2 (wt%) Cu-Mo low- to medium-k calc-alkalic 9 Modified from Lang et al. 1995

10 Magmas and minerals Composition magma suites Mixing role of mafic magmas Fractionation hornblende, rare earth elements Oxidation state Fe (III)/(II); Zircon Ce(IV)/Ce(III) Mineralogy heavy mineral concentrates: PIM: apatite, rutile, garnet and titanite Contribution to exploration? 10

11 Target definition Geophysics IP +/- Magnetics, EM Geochemistry soils, talus Geology characteristics and zoning Veins (rare in alkalic systems) Metals Alteration Mineralogy Mineral chemistry 11

12 Vein types Vein controls: - temperature - Ductile to brittle fracturing - equilibrium D Veins O C O C O C A Vein O C O C Unidirectional solidification textures (UST) EDM Vein B Vein

13 Metal zoning Bingham Canyon, Utah Cu-Mo (Au) Cu-Mo-Au Pb-Zn 8 Km Au-As Cu-Au (Babcock et al., 1995; Cunningham et al., 2004) Py (+/- Pb-Zn-Ag-Au) Au (As-Sb-Hg-Tl)

14 Batu Hijau: Designer porphyry % Cu & 0.40 g/t Au

15 Batu Hijau Vain and alteration zoning: propylitic to intermediate argillic to advanced argillic

16 Alteration depth-time relationships Shallow Advanced argillic 1-4 km Intermediate argillic Sericitic Deep Early Ma Late

17 El Salvador lithocap zoning 18 Watanabe and Hedenquist, 2001

18 Watanabe and Hedenquist, 2001

19 20

20 Porphyry model Empirical and genetic models understood Dramatic features Scale large systems Strong zoning From Sillitoe and Hedenquist,

21 Porphyry copper deposits Disseminated Cu+/-Mo, Au, Ag mineralization spatially associated with porphyritic intrusions defines regional metallogeny Size: 100 to >5000 million tonnes; 0.5 to 1.5% Cu; vertical cylinder ~500 x 500 x 1000m Cluster of intrusions and deposits 10 x 20 km areas Concentric alteration zones 2->5 times the size of the deposit; vertical zoning ~ m Should be easy!

22 Exploration challenges Complexity and variability Depth of emplacement and erosion Geometry Intrusive system Structure Host rock form/composition Big targets with internal complexity Post-mineral intrusions and breccias Non/less-reactive wallrocks Lithocaps Structural modification and disruption 23

23 Shallow (<2km), volcanic-hosted porphyry deposit Marte, Chile Arc - fold and thrust belt porphyry Cu-Mo/Au - Granodiorite - Alteration/mineralization controlled by reactive rocks Deep (>2km), carbonate-hosted porphyry-skarn deposit Antamina, Peru Clastic sediments Skarn/manto Pure limestone Endoskarn Exoskarn Marble front K silicate/phyllic

24 Moderate depth, mixed clasticlimestone-hosted porphyry deposit Bingham Canyon, USA Alkaline porphyry system Cadia, Australia

25 26 BC deposits variability

26 Scale target testing 2 km Understanding the system Think big Escondida Escondida, Chile ~10% of gobal produciton 27

27 Escondida discovery Big system Leached cap interpretation Discovery: Hole 6 5 km 28 Sillitoe, 1995 Behn et al, 2001

28 Deformation and disruption Faulting and rotation Arizona/Sonora Ajo, Arizona Hagstrum et al 1987 San Manuel - Kalamazoo, Arizona Lowell and Guilbert,

29 Deformed porphyrys Treaty Glacier, Iskut Aitik, Sweden Deformation style Heterogeneous deformation Large intrusions buttress Alteration influence Resulting geometry 30

30 Cover challenge Central BC Quesnelia Complex cover Pre-/syn-mineral units/intrusions Younger volcanics Glacial till and sediments The Gap! 31

31 Development challenge Porphyry deposits - large mines Scale 30,000 to >200,000 tpd throughput is critical Blasting, crushing and grinding fractures and hardness Recovery and saleable concentrate Copper mineralogy As, F Geometallurgy 32

32 Conclusions Porphyry systems Scale, clusters, variability, complexity Understanding the geology is critical Cover Geophysical tools and inversion modeling Geochemistry selective/partial leach/interpretation Developments Drilling Downhole and core measurements Geometallurgy 34