Minerals Report - International Seabed Authority

The deep-water ore body more closely resembles the accreted
gravel barrier complex in broad terms due to the highly variable physical
character, rather than the narrow linear beaches that are characterised by
rugged fixed bedrock trap site morphology. Repeated regression(s) and
transgression(s) across the middle to outer continental shelf has presented
the high-energy shore face with numerous opportunities to erode, truncate
and plane the Cretaceous and tertiary sequences preserved there within an
“active erosive zone” spanning about 20 m depth at any one time (pers.
comm. H Swart, 1986). Gravel deposits presented to the high-energy
shore face conditions are comprehensively reworked under these
conditions to produce a complex, super-condensed, coarse gravel lag
containing large intraclasts (metres in diameter) of shelf sedimentary rocks
plus quartzite-dominated terrigeneous cobble gravels supplied principally
by the Orange River.
Although fixed footwall trap sites do occur, they are probably
more rapidly destroyed by shore face reworking during regression(s) than
the more competent features eroded in the late Proterozoic bedrock of the
inner shelf. Diamond distribution and concentration is therefore likely to
be more controlled by sedimentary processes than fixed trap sites in this
environment. Hence the deeper-water deposits are generally less patchy
and exhibit greater continuity compared to the onshore linear and pocket
beach environments, but they are characterised by lower grades. These
observations have proved to have important implications for exploration
and mineral resource management.
3. Deep-water mineral resource management
Given that the deep-water offshore mining industry is
comparatively new, and the ore body is both remote, complex and highly
variable in character, the development of the approach to mineral resource
management forms part of a continuous learning process that guides
many aspects of De Beers Marine’s (DBM’s) applied research and
development aimed at delivering an appropriate level of mineral resource
knowledge to support all of the associated activities required to: -
� Sustain immediate production requirements;
� Develop DBM’s long-term future;
� Effectively mitigate both technical and financial risk.
INTERNATIONAL SEABED AUTHORITY 580