Minerals Report - International Seabed Authority

the three-dimensional shape of the mound is that of a lens composed
primarily of massive sulphides underlain by a stem-shaped feeder or
stockwork zone where the hot solutions are welling up and replacing the
normal volcanic rocks of the ocean crust (Figure 3) ( 7/ ). The drilling clearly
established two points:
1) Renewable resource: It has been contended that active seafloor
massive sulphides are renewable resources that will regenerate by
precipitation from hot springs almost as quickly as the sulphides are
removed. This may be true for individual active mineralised chimneys
that have been observed to regenerate within days to years after
removal. However, absolute dating of the ages of massive sulphides
inside the TAG active mound range between 2,500 and 37,000 years
old (Figure 3) indicating that it takes thousands to tens of thousands of
years to form a sizable massive sulphide deposit. Massive sulphide
deposits are not renewable resources.
2) The size, shape and composition of the TAG active mound is similar to
that of a class of ancient mineral deposits, Volcanogenic Massive
Sulphide (VMS) deposits, that have been mined on land for centuries
for iron, copper, zinc, silver and gold without understanding how they
were formed. The TAG active mound and other similar massive
sulphide mounds on the seafloor enable economic geologists to
observe VMS deposits in process of formation, which gives them
unparalleled insight to guide their exploration for and mining of
ancient counterparts on land.
Divergent plate boundaries with the potential for the occurrence of
massive sulphide deposits lie primarily in the international seabed area with
exceptions shown in Figure 2 and listed in Table 2 ( 8/ ). The largest number of
exceptions lies in the volcanic island chains of the western Pacific (Figure 2).
The volcanic island chains form at convergent plate boundaries where the
lithosphere bends down and descends into the Earth's interior where is
destroyed to counterbalance the creation of lithosphere at divergent plate
boundaries (Figure 4). The components of seafloor hydrothermal systems
consisting of hot rocks at depth beneath the seafloor as a heat source, seawater
as the circulating fluid, and permeable pathways through volcanic rocks that
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