Download Seafloor massive sulfide - International Seabed Authority

Seafloor massive sulfide (SMS)
potential within and beyond
national jurisdiction in
the Asia-Pacific region
Raymond Binns
CSIRO Earth Science and Resource
Engineering, Sydney
Research School of Earth Sciences
Australian National University, Canberra
Acknowledgements: Nautilus Minerals Inc.
ISA: INTERNATIONAL WORKSHOP ON ENVIRONMENTAL MANAGEMENT NEEDS
FOR EXPLORATION AND EXPLOITATION OF DEEP SEABED MINERALS
November 2011
“SMS” are bodies of metallic sulfides
precipitated at and near the sea floor when
submarine volcanic hot-spring fluids (250-350ºC)
mix with cold seawater, typically at depths of 10003000m. High pressure inhibits boiling.
The process is inefficient, creating buoyant
“smoke” laced with fine mineral particles.
The structures formed on the seafloor have been
called “chimneys” despite often complex shapes!
Close-up of
“smoking”
chimneys,
30-50 cm
high
3m-high
“chimney”
SMS deposits occur mainly at the margins of
tectonic plates, with two main settings
plate margin
Convergent plate margin
Divergent plate margin
(subduction zones)
(spreading axes)
Ultramafic
exhumation
Red Sea
oozes
SMS History
• 1965 Metal enrichments noted in
………... sediments on East Pacific Rise
• 1977 First SMS (inactive) discovered
……….…in Galapagos Rift, east Pacific
• 1979 First “black smoker” SMS
………….East Pacific Rise at 21ºN
• 1986 First SMS in a subduction
…………setting (Manus Basin PNG)
• 2005 First commercial SMS
…………survey (Manus Basin, PNG)
The “National Geographic”
black smoker chimney
• 2600 m water depth
• 350°C hot, metal-rich fluids
• 2013? First SMS mine (Nautilus, PNG)
Young Chimneys
• actively venting fields
• individual chimneys short-lived
• “smoke” helps find them
• chemosynthetic microbes quickly
populate surfaces, providing food
for remarkable macrofauna
Chimney grew 60 cm in
2 days over a drill hole
Old Chimneys
(extinct fields)
• Environmentally-favoured
targets for mining?
• Harder to find (no “smoke”)
• Will valuable metals be
preserved when “weathered”?
Why consider mining SMS?
Solwara-1 chimney, Eastern Manus Basin PNG
Cu 25.7%
Au
58 g/ton
Zn
Ag
97 g/ton
0.2%
$US 5,800 per ton
or $US 19,000 per cubic metre
2.5 metres tall
What lies below the chimneys?
“Roman Ruins” field, Manus Basin PNG
3 metre high
composite
chimney
2. Deeper subseafloor mineralisation
1. Mound of
fallen chimneys
3. Footwall stockwork
Solwara-1 (PNG) profile (based on drilling)
Chimneys
high Cu, Au
upper semimassive
sulfides: high Cu, Au
2008 Resource
(Nautilus Minerals)
fallen
chimneys
... .
.
.
... . ..
lithified tephra
(some sulfides)
deeper massive
sulfides:
moderate Cu, Au
2.2 million tonnes
sulfide veins
(‘stockwork’)
7.2% copper
6.2 g/ton gold
= US$ 950 per ton
footwall
(altered volcanics)
most is sub-seafloor
Production cost
US$150/ton?
RAB 11/2011
NOT TO SCALE
Solwara 7
151º41‘
E
Clustered SMS chimney fields at PACMANUS,
ManusHydrothermal
Basin PNG Field
PACMANUS
Rogers
Ruins
Roman Ruins
Satanic Mills
Snowcap
Fenway
Tsukushi
Solwara 8
Metres below sea level
2100
Solwara 6
2000
1900
1800
1700
Chimneys
1650
Alteration
N
Regional-scale clusters of SMS deposits
100 km
Manus Basin, Bismarck Sea, PNG
(Nautilus Minerals)
Contrasted SMS genesis at the two main
plate-tectonic settings
plate margin
Convergent plate margin
Divergent plate margin
(subduction zones)
(spreading axes)
MID-OCEAN
SPREADING
AXIS
Next slide
(divergent or “constructive”
plate boundary)
OCEAN
BASALT
CRUST
MAGMA
MANTLE
Molten MAGMA forms
when plates spread apart
and pressure drops in hot
(1200ºC) mantle.
It then rises and solidifies
to form new basaltic crust.
MID-OCEAN SPREADING AXES
Hydrothermal systems
MAGMA
• Magma body is a heat engine driving fluid circulation. “Dry” reduced magmas.
• Seawater becomes reduced & acidic by reaction with crustal rocks (sulfate
sulfide)
• Metals leached from traversed crustal rocks, especially in “high-T reaction zone”
• Fe (pyrite) dominates sulfides deposited at seafloor vents, Zn minor and Cu less so.
SUBDUCTION ZONES
(convergent plate boundaries)
TRENCH
MANTLE
MANTLE
Magma forms when aqueous fluids from the down-going slab flux melting
in the hot mantle, and magma rises to build a Volcanic Arc. Some erupts in
the Backarc Basin. Resultant lavas are relatively oxidised, hydrous, and
siliceous compared to mid-ocean magmas.
SUBDUCTION ZONES
Arc and Back-Arc
hydrothermal systems
• Water-rich oxidised magmas erupted as more siliceous lavas (andesite, dacite)
• Magmatic fluids yield a higher input of Cu and Au, less Fe. Seawater also entrained.
• Prominent hydrous alteration permits more sub-seafloor mineralisation?
Back-arc basins may
contain small “spreading
axes” as well as conventional
arc-like submarine volcanoes
(cones, ridges)
2
1
Oblique convergence between the Pacific
and Australian plates causes NW-SE
extension in the Manus Basin. This is
accommodated between major faults by
.......
1 distributed extensional rifting and arcstyle volcanism in the far east, and.........
........focussed
spreading with basaltic infill
2
in the central basin
Hydrothermal venting and SMS
deposits occur in both settings.
Arc-style volcanism produces
the richest SMS deposits
Hannington et al 2011
USGS
Ring of Fire
Arcs, SMS, and
EEZs
Subaerial
Seismicity,
bathymetry
volcanoes
USGS
Arcs, SMS,
and EEZs
Seismicity,
bathymetry
Japan
Arcs, SMS,
and EEZs
Seismicity,
bathymetry
Okinawa Trough and Izu-Bonin Arc, Japan
Sea of
Japan
Pacific
Plate
Myojin Knoll
(Sunrise)
Okinawa
Trough
Izu-Bonin
Rise
Philippine
Sea Plate
Volcanoes
Mariana
Trough
Subaerial
Submarine
Suiyo
Seamount
Myojin Knoll
Frontal arc volcano with a large
summit caldera and a postcaldera resurgent dome.
Sunrise field estimated at 9
million tons from topography,
not confirmed by drilling
SUNRISE DEPOSIT
1 km
Cu
Zn
%
%
Sunrise
6
Suiyo Smt 12
20
15
Pb Au
• extends from caldera floor to
lower talus slope (1360-1210
mbsl)
Ag
%
g/t
g/t
2
2
18 1210
28 190
• mound 400 m across, 30 m
high
• maximum vent T 278ºC
• 9 million tons?
Okinawa Trough
Kagoshima
Kagoshima
• “Backarc” rift on continental crust
• No active arc associated with trench!
• Explosive, siliceous volcanism in rift
Minami-Ensei
Ihena North
CLAM
Jade-Izena
Okinawa
Philippine
Sea Plate
200 km
Cu
%
Jade 3
Ihena 3
Jade
Ihena
Zn Pb Au Ag
% % g/t g/t
25 12 3.3 1150
31 14 1.2 465
Jade estimated
at 7 Mt,at$2,300
Jade estimated
7 Mt / ton
Marianas
Arcs, SMS,
and EEZs
Seismicity,
bathymetry
J
NM
Remnant arc
G
FSM
PNG
Arcs, SMS,
and EEZs
Seismicity,
bathymetry
PNG EEZ
Solomons,
Vanuatu
Arcs, SMS,
and EEZs
Seismicity,
bathymetry
Ontong
Java
Plateau
PNG
Triple
Junction
JCT
Australian
Plate
PNG
FJ
THE AREA
AUS
Active subduction
Inactive trench
Spreading axis
N Fiji
S.R.
CT
FJ
MH
Hunter Ridge
The “Triple Junction”, NW Solomon Islands
Ghizo Ridge
Simbo
Ridge
Kana Keoki Smt
Plume
anomaly
96SO6 Smt
PNG
Coleman Smt
SOL
Eastern Solomon
Islands and Vanuatu
Hydrothermal Indications
SOL
Vate Trough
VAN
Erromango
Erromanga
Trough
Trough
Futuna Trough
Fiji
Tonga
NZ
Arcs, SMS,
and EEZs
Seismicity,
bathymetry
North Fiji
Basin
South Fiji
Basin
North Fiji Basin
• Unusually large area of ”backarc
TUV
TA
oceanic” crust
• Greatest length of spreading
ridges per area of ocean floor
SOL
• Orientation of some ridges difficult
to explain
FJ
TA
• Perhaps initiated in the forearc of
the Vitiaz subduction zone
VAN
• Still propagating southwards (into
the Hunter Ridge)
• 4 chimney fields within 4 km near
junction of 3 spreading ridges
Cu Zn Au Ag
% % g/t g/t
.
White Lady
8.0 4.7
Pere Lachaise 17.9 5.9 4.1 216
Sonne-99
0.6 12.8 3.6 309
FJ
MH
North Fiji
Basin
21º 30’ S
22º 00’ S
Fiji EEZ
22º 30’ S
Matthew Hunter Is. EEZ
173º 00’ E
174º 00’ E
Is the Hunter Ridge a “look-alike” of the Manus Basin?
Lau Basin – Havre Trough
Back-arc to the Tonga-Kermadec Arc
Tonga
Tonga
Trench
New
Zealand
KA
Island
volcano
Submarine
volcano
NZ
Sulfides
(arc)
Lau Basin
Kings 3 Jn
Tonga
Cu Zn Au Ag
.
%
Kings 3 Jn
%
5.6 28.2
g/t
Central
Lau SR
g/t
18
East Lau SR
Valu Fa Ridge
White Church
0.4
Vai Lili
5.3 26.9 3.3 124
Hine Hina
6.5 2.6 83
1.6 11.0 1.4 405
Valu Fa
Ridge
1887 Proclamation
Environmental
Issues
The Geologist’s Perspective
• Resilient fauna survives natural hazards
• dispersed particulates, toxic chemistry
•
tectonic disturbances (earthquakes)
• turbidity currents, explosive volcanism
• Biota ultimately doomed (systems short-lived)
What about the long-term future?
• Geophysics will find buried deposits?
• More overburden sediment
• Robotic mining?
• Large-scale “opencast” mining
• Future sub-seafloor (equivalent of
…underground mining on land)?
• Could open up the older arcs for
...exploitation (“submerged PNGs”)?
• Start learning from experience
• Careful observations and relevant
…experiments during initial mining
…activities
A missing deposit type in today’s oceans
(sediment hosted massive sulfides in rifts lacking volcanism)
“Exhalative sulfides”
(“SEDEX” deposit)
Seawater (modern) or…
Cover Sequence (ancient)
Rift-filling
sediments
Basement
Basinal
brines
“Growth Fault”
Hotter, deeper
crust
Known in ancient sequences, e.g. Red Dog Alaska: >85M tons of 18.2% Zn, 4.6% Pb