Minerals Report - International Seabed Authority

describing the active sulphide mound in the TAG hydrothermal field, the
surface expression is only the "tip of the iceberg" (Figure 3). Drilling is
required to directly determine the third dimension including grade and
tonnage of a massive sulphide deposit on the seafloor just as for such as
deposit on land. For massive sulphide bodies on land hundreds of holes
each tens to hundreds of meters long spaced meters apart may be drilled
to recover almost continuous cores of the material penetrated. These cores
are used to determine the shape, grade and tonnage of the massive
sulphide mound and underlying feeder/stockwork zone (Figure 3).
Present capability to drill a massive sulphide body at a water depth of
several kilometres in the deep ocean is far more limited. For example, the
active sulphide mound in the TAG hydrothermal field is one of only two
such mounds that have been drilled to date by the Ocean Drilling Program
(ODP). ODP Leg 158 spent two months at sea in 1994 and with
formidable technical difficulty drilled 17 holes up to 125 meters long with
overall core recovery of 12 percent ( 7/ ). Drilling methods for massive
sulphide deposits and associated volcanic rocks in the deep ocean are
being improved, but will fall far short of land standards for the foreseeable
future.
6. Environmental Considerations
Marine organisms are associated with marine mineral deposits and
must be considered with reference to exploration and mining activities. Some
observations of biodiversity of these organisms in the context of seafloor
settings exclusive of and associated with deep ocean hot springs are, as
follows:
1) Deep ocean exclusive of hot springs:
• Marine species diversity in the deep ocean is comparable to
that in tropical rainforests ( 20/ ).
• The species diversity of marine life is so high that an
investigation found new species in every square meter of
seafloor sediment sampled ( 21/ ).
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