In Jules Verne’s 20,000 Leagues Under the Sea*, the iconic
Captain Nemo announced that “in the depths of the ocean, there are mines
of zinc, iron, silver and gold that would be quite easy to exploit”
while predicting that the abundance of marine resources could satisfy
human need. If the pace of development for deep-sea mining projects and
the estimated value of deep-sea ores is any indicator, it seems as
though our misanthropic mariner was wrong on both counts.
In The abundance of seafloor massive sulfide deposits,
an international team of geologists attempts to quantify the total
available copper and zinc contained in deep-sea massive sulfide mounds.
Seafloor massive sulfide mounds are a byproduct of the processes that
create deep-sea hydrothermal vents. As super-heated sea water emerges
from the vent, it deposits heavy metals and other elements and minerals
along the walls of the vent. Over thousands of years, an active vent
field can build up a huge mound of metal and mineral rich ore – a
massive sulfide mound. In addition to copper and zinc, these mounds can
contain gold and silver. Generally, the ore is of much higher quality
than its terrestrial counterpart. Over the last few decades, many
exploration companies were eyeing these deposits, but it’s
only recently that technological developments and economic incentives
have aligned to permit potentially profitable deep-sea mining.
Not all hydrothermal vent systems
produce massive sulfide mounds, and not all massive sulfide mounds are
rich in heavy metals and valuable ore. To determine how much ore really
is available in the deep sea, Hannington and his team examined 32
control sites of approximately equal size that broadly represent the
geologic conditions of the global seafloor. They discovered 106 ore
deposits great than 100 square meters, with many concentrated around
neo-volcanic regions (areas of volcanic activity where most hydrothermal
vents are found). Based on these samples, they estimated that there are
approximately 900 neo-volcanic massive sulfide deposits, but that
number could be as low as 500 or as high as 5000.
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