Seafloor Massive Sulfides (SMS)

Transcription

1 SPC-EU EDF Deep Sea Minerals Workshop, Nadi, Fiji, June 2011 Seafloor s (SMS) Global characteristics, distribution, and regional Pacific potential Sven Petersen (IFM-GEOMAR)

2 How do they form? influx of cold seawater (recharge) Discharge H 2 O = H + + OH - Mg 2+ + OH - = Mg(OH) 2 precipitation excess H + ph drop to ~ 4-5 heating of seawater to > 400 C leaching of Cu, Zn, Fe, Au, S etc. from the surrounding rock formation of hydrothermal precipitates due to mixing of hot fluid with seawater >30% water 150 C <1% water 375 C Reaction Zone Magma Recharge Extrusives Dike Section Gabbro fluid is hot, buoyant, weakly acid, reduced & metal+sulfur-rich source: Comou et al., 2008

3 Hydrothermal sites in the South Atlantic

4 Where do they form? latest discoveries: Cayman Trough Wallis & Futuna Northern Matas Piterskoe distribution of seafloor hydrothermal systems in the world ocean

5 massive sulfides as a resource? Nautilus mining liscence Russian exploration claim area Manafe & DFI mining liscence Chinese exploration claim area distribution of seafloor hydrothermal systems in the world ocean

6 Basic Facts >350 known sites of hydrothermal activity 270 sites of polymetallic sulfide deposits 180 sites of high-temperature hydrothermal activity (black smokers) 57% at mid-ocean ridges (64,000 km) 28% in back-arc environments 15% on submarine volcanic arcs (combined 25,000 km) <1% on intraplate volcanoes

7 Basic Facts Examples are known in very different tectonic settings: mid-ocean ridges (superfast, fast, intermediate, slow, ultraslow spreading centers) off-axis volcanoes intracontinental rifts & rifted margins intraoceanic back-arc basins intracontinental back-arc basins volcanic island arcs (Hannington et al., 2005)

8 massive sulfides as a resource? how many? grade? tonnage? other factors: water depth, distance to land, EEZ?

9 How many black smokers are there? Modern Seafloor 1.8 x W of heat flux at young crust (Mottl, 2003) 10% at black smoker temperatures; the rest is diffuse 2 to 5 MW for a single black smoker (Converse et al, 1984) 50,000 to 100,000 black smokers (at least 1 every km of ridge axis) 200 to 500 MW for a large field (500 to 1,000 fields) ~ 15% of the hydrothermal fields are currently known

10 NOAA >80 % look like this! Source: SOEST (Hawaii)

11 massive sulfides at mid-ocean ridges at fast-spreading ridges short lived hydrothermal activity cyclic volcanic and hydrothermal activity quick burial by extrusives 90% of the metals lost to the plume

12 massive sulfides at mid-ocean ridges average geochemistry of MORBhosted massive sulfides mainly pyrite with 5 % Cu 9 % Zn 0.3 ppm Au (strong bias due to sampling of chimneys) 1 cm pyrite - chalcopyrite - sphalerite isocubanite - pyrrhotite - wurtzite 1 cm

13 massive sulfides at mid-ocean ridges systems at slow-spreading ridges tend to be larger! commonly located off-axis deep penetrating faults allow long-lasting fluid flow some sites associated with mantle rocks

14 Logatchev hydrothermal field 2 hydrothermally active fields largest field 800x300 m Logatchev mantle rocks basaltic lava floor N km

15 Logatchev hydrothermal field hosted in mantle rocks water depth 3000m very high Cu and Au grades! 23 % Cu 4 % Zn 11 ppm Au Is it possible to utilize this? 1 cm 64ROV-11D

16 massive sulfides as a resource? waste Cu-rich chimney

17 massive sulfides in back arc basins Hydrothermal sites in Papua New Guinea

18 PACMANUS hydrothermal field host rocks: volcanic suite from basalt to rhyolithe water depth: 1650m Yeats (CSIRO) PacManus samples 10.3 % Cu 22.6 % Zn 0.5 % Pb 205 ppm Ag 14 ppm Au

19 altered dacite 58-GTVA

20 massive sulfides as a resource? 2010 PacManus Susu Knolls = 1. mine site? exploring companies: exploring countries: Nautilus South Korea Bluewater, and others Russia China (France/Germany)

21 massive sulfides at island arc volcanoes NOAA

22 massive sulfides as a resource? mid-ocean ridges island/back arcs basalt exposed mantle interm. - felsic Fe, Cu, Zn Cu, Fe Cu, Zn, Pb, Ba Co Au, Co, Ni, Sn As, Hg, Sb, Au, Ag ~1 ppm Au 3-10 ppm Au 5 30 ppm Au! deep water deep water shallow water source: geochemical differences in the rocks themselves + additional factors (magmatic input, biology, zone refining,... )

23 massive sulfides as a resource? Middle Valley Suiyo Manus 13 N, EPR TAG Krasnov Semyenov Logatchev Atlantis II Kairei high grade (Cu±Au±Zn) or large deposits

24 massive sulfides as a resource? Will these deposits by of commercial interest?

25 massive sulfides as a resource? Gay (>380 Mio t) compared to those on land? Uchaly + Novo Uchaly (>220 Mio t)

26 (C) National Geographic 1992 Modern Seafloor massive sulfides as a resource? Kelley et al., 2001 NOAA MARUM

27 massive sulfides as a resource? typical EPR chimneys 0.x Mio t Atlantis II Deep (Red Sea) 94 Mio t drilled ore mud from brine pool Middle Valley (JFR) 8-10 Mio t drilled large sulfide lenses in sediments (Fe dominated) 13 N Seamount (EPR) 5-10 Mio t? Krasnov, Semyenov ~ 15 Mio t? large pyrite mounds (Fe dominated) TAG (MAR) 4 Mio t drilled (low grade in interior) Suzu Knolls; Manus Basin >2 Mio t drilled (indicated + inferred)

28 massive sulfides as a resource? Middle Valley X Fe-only X too small Suiyo size? Manus size? 13 N, EPR TAG X too deep? low grade? Krasnov Semyenov Logatchev too small Atlantis II too deep? X Kairei high grade or large deposits

29 massive sulfides as a resource? Mining seafloor massive sulfides needs: 2 mio tonnes of ore /year (~ 200x200x20m) life-time of 10 years (= 20 mio t of ore!) (may be contained in several orebodies!) Currently not known! Will mining of seafloor massive sulfides replace land mining?

30 massive sulfides as a resource? Alaska, Brooks Range 33 Mt 2. Finlayson, Yukon 20 Mt 3. Windy Craggy 300 Mt 4. Northern Cordillera 100 Mt 5. Myra Falls 30 Mt 6. Shasta, Klammath 35 Mt 7. Jerome, Arizona 40 Mt 8. Central Mexico 120 Mt 9. Tambo Grande 200 Mt 10. Slave Mt 11. Ruttan, Manitoba 70 Mt 12. Flin Flon -Snow Lk 150 Mt 13. Geco -Manitouwadge 60 Mt 14. Sturgeon Lake 35 Mt 15. Ladysmith -Rhineland 80 Mt 16. Abitibi 600 Mt 18. Bathurst 250 Mt 19. Central Nfld. 75 Mt 20. Iberian Pyrite Belt 1000 Mt 21. Avoca 37 Mt 22. Tondheim Norway >100 Mt 23. Skellefte Sweden 70 Mt 24. Outokumpu -Pyhslm 90 Mt 25. Bergslagen -Orijarvi 110 Mt 27. Troodos Cyprus 35 Mt 28. Turkey, Black Sea 200 Mt 29. Saudi Arabia 70 Mt 30. S Oman 30 Mt 31. Southern Urals >400 Mt 32. Central Urals >100 Mt 33. Rudny Altai >100 Mt China >500 Mt 35. Bawdwin -Laochang >40 Mt 38. Hokuroku Japan 80 Mt 39. Besshi Japan 230 Mt 40. Philippines 65 Mt WA >75 Mt 43. Central Queensland 44. Lachlan Fold Belt 45. Mt. Read Tasmania 150 Mt worldwide VMS Districts (>> 6 billion tonnes) 50 % in only 50 deposits of >50 mio t GSC

31 massive sulfides as a resource? Why is the geologic record so well endowed? a snapshot in time At most the modern oceans contain only 175 million years worth of metal! Current exploration is considering only young crust! One giant deposit every 200 mio years!

32 Most seafloor sites: massive sulfides as a resource? are too small are of low grade occur too deep are too far from land occur in the Area (politics) or are active and too hot but: mining of few sites might be economically feasible

33 regional Pacific potential

34 regional Pacific potential

35 regional Pacific potential Opportunities: There is still a large potential for new discoveries using regional surveys!

36 regional Pacific potential Back-arc spreading centers still have large potential to discover new sites! By far most of those will be small. Intra-plate volcanoes are underexplored but have limited potential for sulfide deposits. Island-arc volcanoes have large potential, but frequent eruptions and shallow water depth may limit sulfide potential near the seafloor. Where are the large deposits in the Pacific region?

37 Challenges Current research and exploration is mainly related to active deposits at or near spreading axis. seafloor hydrothermal systems many deposits are buried underneath sediments or lava. Systematic surveys for hidden deposits are lacking. Regional geological and geophysical exploration using towed systems or AUV s is necessary to define resource potential.

38 IFM-GEOMAR s AUV ABYSS 6000m depth rating, 4Kn max. speed 24 h station time turbidity sensor (ECO), Eh-sensor (NIST Japan), CTD, 120/410 khz side-scan sonar (Edgetech), ADCP 3 konfigurations 200/400 khz multibeam (RESON 7125D) or sub-bottom profiler or b/w digital camera + flash underwater navigation: transponder (LBL, USBL) inertial navigation (Kearfott)

39 AUV-based bathymetry Reson Seabat khz central part = 65 km²!

40 AUV-based bathymetry

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42 Thank You!