Hi, my name is Mark Hannington.
I am an economic geologist in the Marine Mineral
Resources Group and I’m going to be talking
about the potential of marine minerals from
the deep sea as a supply of future raw materials.
So why are we interested in marine minerals
from the deep ocean?
The world’s population today is about 7
billion people, by 2050 the population will
be in excess of 9.7 billion people.
And with that growth comes an enormous demand
for raw materials, the materials that are
required to build the infrastructure for cities,
for transportation networks, for energy distribution.
But also the materials that are required for
the increasingly intensive use of metals in
electronics, in high technology, and especially
in green technology.
And this demand is encouraging an increasing
interest in alternative supplies of metals,
including metals potentially from the deep
sea.
A major question however is the extent to
which ocean resources might contribute to
this demand for metal supply.
What metals can we get from the deep sea?
The deep sea is mainly, deep sea mining is
mainly concerned with three types of mineral
resources.
They include manganese nodules, cobalt-rich
manganese crusts and sea floor massive sulfide
deposits.
Crusts and nodules are potential resources
of a variety of metals including cobalt, copper
and nickel and manganese and some important
trace elements like the platinum group elements
and the so-called rare earth elements.
The massive sulfide deposits on the other
hand are potential sources of potentially
much more valuable elements such as copper,
zinc, silver and gold.
But by far the greatest interest for deep
sea mining in the near term at least is manganese
nodules.
And manganese nodules are essentially solid
concretions of iron and manganese oxides that
form about the size of a small potato and
cover large parts of the deep ocean floor.
They grow from the metals that are dissolved
in ordinary sea water and by a phenomenon
which referred to as hydrogenetic growth,
if the metals are coming out of sea water
and also from metals dissolved in pore waters
in sediments below the sea floor.
And that’s referred to as diagenetic growth.
Manganese nodules were originally discovered
during a very early research exposition of...expedition
of the H.M.S. Challenger, in about 1872.
But now we know that they are widely distributed
in the oceans, in the deep ocean basins.
And they’re found at water depths anywhere
from 4,000 meters to about 6,000 meters which
makes them hard to get to, in areas particularly
where the rate of sedimentation is very low.
Typically less than 1 centimeter of sediment
deposition per thousand years.
This low sedimentation rate is required to
prevent the burial of the manganese nodules
because they get their metals from sea water
and they have to be...they have to be continually
exposed in order to grow.
And in some parts of the oceans such as in
the central Pacific and in the Indian Ocean,
the nodules cover more than 50% of the sea
floor.
So if you could walk on the sea floor, you
could barely take a step without stepping
on a nodule, over huge areas of the oceans.
The other resource that people are interested
in are in manganese crusts, which are very
similar to nodules because they are also composed
of mainly manganese oxides and iron oxides.
The minerals of interest, or the elements
of interest are absorbed into the manganese
and iron oxides at relatively small concentrations.
Unlike nodules the crusts actually grow on
a rocky substrate and they can accumulate
to...in black layers up to 30 centimeters
or more in thickness.
The crusts are also found throughout the world’s
oceans, but they tend to be found only on
the tops of very large seamounts.
And this is an important location because
the tops of large seamounts are swept clean
of the sediments that we have to prevent accumulating
on the crusts.
If they’re buried they can’t grow from
the...from the elements dissolved in sea water.
Also the crusts, because they grow on tops
of seamounts they occur at a much larger range
of water depths.
Nodules are at 4,000 meters to 6,000 meters,
whereas crusts are forming as shallow as 500
meters, which does make them more accessible.
So where do the metals come from?
There’s a very small amount of iron in manganese
dissolved in ordinary sea water and under
the right conditions it will form invisible,
small particles, submicroscopic particles
and we call them nano-particles that are attracted
electrostatically to each other and to exposed
surfaces like rock surfaces or a small sand
grain on the sea floor.
The manganese oxide particles, they have a
negative surface charge.
So the surface of the manganese oxide is electrostatically
negative.
And it will attract positively charged ions
dissolved in sea water such as cobalt and
nickel and copper that are also present in
sea water at very low concentrations.
The iron oxides which are actually equally
abundant in the manganese crusts, they have
a posi....
They have a positive surface charge, so they
attract elements that are dissolved in sea
water as negative ions.
For example, hydroxy...oxyanions of elements
like molybdenum, vanadium, arsenic and the
rare earth elements.
So together the manganese oxides and the iron
oxides absorb a large quantity of these very
rare elements dissolved in sea water.
And that’s the resource of interest.
Over time these particles accumulate as the
nodules and crusts commonly nucleated on a
small object, a sand grain, a shell, or in
the case of crusts on exposed rock surfaces.
But because the surfaces of the nodules and
the crusts must be continually exposed, there’s
been a great deal of debate about how this
happens.
In the deep ocean this can happen because
we have naturally low sedimentation rates
in some parts of the world’s ocean.
On the seamounts it happens because they’re
swept clean.
Some observers have suggested that marine
organisms, benthic organisms actually turn
the nodules continuously and bring them continuously
to the sea floor where they can be exposed.
This is an idea, but nobody’s actually every
seen it happen.
How long do they take to form?
The concentrations of metals and nodules are
many millions of times enriched compared to
background sea water.
And achieving this level of enrichment takes
a huge amount of time, a very long amount
of time.
Nodules grow at rates of only a few millimeters
per year, maybe a centimeter per million years.
So a nodule the size of a small potato could
be hundreds of thousands and even millions
of years old.
What’s fascinating is that this process
is taking place on such a large-scale throughout
the ocean basins that it’s actually modified
and had a measurable impact on the chemistry
of the oceans themselves.
So those are two resources that people are
interested in.
The others of course are the so-called black
smoker deposits.
These are the deposits of metallic sulfides
that form by hydrothermal fluids emitted from
active submarine volcanoes.
Most people have heard of black smokers or
the tube worm colonies that live around such
hydrothermal vents.
And certainly the discovery of the first black
smokers in the 1980s, early 1980s and especially
their link to chemosynthetic life was one
of the most compelling and significant scientific
advances in the last century.
Now more than 30 or 40 years later, we recognize
that there are at least 500 of these sites
of hydrothermal activity on the sea floor
where sulfide minerals, metallic sulfide minerals
are precipitating from these hydrothermal
vents.
That sounds like a big number, but in fact
we have only explored a very small number
of the submarine, active submarine volcanoes.
And many more remain to be explored.
About two-thirds of the black smoker deposits
that we know about occur on the mid-ocean
ridges.
This is the 60,000 kilometer long break in
the earth’s crust where new oceanic crust
is forming.
And it’s the loss of heat from that crust
that is responsible for the hydrothermal activity
that occurs along the ridges.
So at the plate boundaries where...where the
hydrothermal activity is occurring the magma
wells up from the earth’s interior and new
ocean crust is being produced at an astonishing
rate of about 20 to 30 cubic kilometers per
year.
And as that hot crust moves away from the
mid-ocean ridges, it cools, in part by the
conduction of heat through the lithosphere
but also by hydrothermal convection.
That is to say, sea water that leaks into
the crust to depths of as much a two or three
kilometers below the sea floor and literally
mines the heat from the new oceanic crust.
This process is responsible for an enormous
exchange of mass and energy with tens of thousands
and maybe even hundreds of thousands of black
smokers continually drawing heat from the
earth’s interior.
Just one of these black smoker complexes can
generate a 100 megawatts of thermal power
which is enough to energize a small city.
So where do those metals however, where do
the metals that occur in black smokers come
from?
When the cold water leaks into the crust,
along fractures and fissures it’s heated
to temperatures of as much as 400 degrees.
And at these very high temperatures the fluids
become buoyant and then rise very rapidly
to the sea floor.
But because sea water contains about three
and a half weight percent of dissolved salts,
at 400 degrees, it also becomes highly corrosive.
And it literally leaches or strips metals
from the rock, in particular, iron and copper
and zinc and also silver and gold that become
part of the black smoker chimneys and the
deposits that form on the sea floor.
These fluids also leach sulfur in the form
of dissolved hydrogen sulfide which is the
essential part of the food chain for the organisms,
the chemosynthetic life that live around the
hydrothermal vents.
So the same sulfur that the tube worms and
the bacteria are living on is also combining
with the metals to produce the mineral deposits
on the sea floor.
And yet, all of that is toxic to us, even
in small quantities.
The metals accumulate in the chimneys that
form around the vents, in part by the precipitation
of what’s referred to as black smoke, a
black smoker with billowing plumes of particles
of metallic sulfides.
This is what we normally see at high temperature,
hydrothermal vents where the high temperature
fluids mix very quickly and quench in contact
with cold sea water to produce tiny particles
of metallic sulfides that we call smoke.
The chimney-like structures that form around
the vents and here you can see the vent whole
from a chimney, also form from the same minerals.
The metals iron sulfides, the copper sulfides
and the zinc sulfides that contain the important
commodities that sea floor miners are actually
interested in.
The big difference between a black smoker
deposit and a nodule in terms of how they
form is that these can form in a fraction
of the time that it takes a million year-old
nodule to accumulate.
So this process, both processes are geologically
very important in terms of the history of
the earth.
In fact both nodules and black smoker deposits
are part of a very large geochemical flywheel
that buffers ocean chemistry.
So about 34% of the crustal heat is removed
by hydrothermal convection, at black smoker
vents.
This equates to a global hydrothermal flux
which is large enough to circulate the entire
volume of the world’s oceans through the
mid-ocean ridges about every ten million years.
That sounds like a long time, but the earth
is about four billion years old, so every
ten million years is a huge amount of hydrothermal
circulation.
This process has been going on for a very
long time.
In fact, it’s one of the oldest geological
processes on earth after sea floor volcanism.
In fact black smoker vents are a kind of living
fossil because identical chimneys in ancient
oceans, millions and millions of years ago,
were also producing large and valuable mineral
deposits that we mine on land today.
In fact some of the oldest mineral deposits
that are mined on land are as old as three
and a half billion years old.
Fossils of ancient vent organisms such as
tube worms that we see in modern vents have
also been found in such deposits.
And they’re beautifully preserved for example
in ancient mass of sulfide deposits in the
Urals mountains where geologists have found
fossil tube worms that are as much as four
hundred million years old.
So how much metal can we actually get from
black smoker deposits?
This is a very large question.
Unfortunately we still have only a very limited
understanding of the global resource potential
of these deposits.
Current estimates of the amount of massive
sulfide deposited in black smokers are on
the order of 500 million tons to more than
5,000 million tons.
These are big numbers, but we really don’t
know whether the black smoker deposits could
contribute significantly to global metal supply.
On the planet today we’re consuming about
16 million tons of copper metal a year.
And the black smoker deposits that we know
about could satisfy that demand for maybe
a few years.
Vast areas of the ocean floor however still
remain to be explored for these resources
and the proper resource assessment to know
whether or not they could contribute significantly
to long-term metal supply simply hasn’t
been done.
In contrast to black smoker deposits we know
that manganese nodules are enormously abundant.
And they are formed from these tiny particles,
these nanoparticles in sea water over very,
very long periods of time to produce a global
abundance of manganese nodules on the order
of trillions of tons.
These are truly astronomical numbers.
And just in the areas of the central Pacific
that are currently claimed for manganese nodule
exploration, they cover nearly a third of
the area of continental Europe.
Vast areas, tens of thousands of kilometers
covered by manganese nodules.
That’s enough manganese and nickel and copper
and cobalt to supply the planet with those
metals for decades.
And in the case of manganese, maybe even for
centuries.
Much of the technology for the recovery of
manganese nodules is already built.
And some of the exploration licenses that
were granted 13 years ago are set to expire
within the next two years.
And the expectation is that those exploration
licenses will become exploitation licenses.
But the question arises, do we need these
resources now and if not now, when do we need
those resources?
So with this basic understanding of the potential
of metallic mineral resources as nodules,
crusts or massive sulfides, we can begin to
address this basic question, is sea floor
mining a solution for the raw material needs
of the future?
The technology to achieve it is not a barrier
but the possibility of mining nodules and
sea floor massive sulfides is stirring considerable
debate about the sustainable use of this new
resource and whether commercial development
is actually worth the risk.
