Download Drilling Survey at the Suiyo Seamount in the Izu-Ogasawara

Proceedillgs of The FOllrth (2001) Oceall Millillg Symposillm
Szczecin, Poland, September 23-27, 200 I
Copyright © 200 J by The JllteTllatiollal Society of Offshore alld Polar Ellgilleers
ISBN 1-880653-56-7
Drilling Survey at the Suiyo Seamount
in the Izu-Ogasawara Arc, Japan
Nobuyasu NISHIKAWA
Metal Mining Agency of Japan
Tokyo, Japan
Abstract
Since 1975, Metal Mining Agency of Japan
(MMAJ) has been surveyed of mineral resources on
deep-sea floor: manganese nodules (1975-1996),
submarine hydrothermal deposits (1985- ) and
cobalt-rich manganese crust deposit (1987- ).
In 1999, the MMAJ has been conducting drilling
surveys at the Suiyo seamount in the IzuOgasawara Are, Japan using the Deep-sea Boring
Mashine System (BMS) which was developed by the
MMAJ. The seamount is located about 24 km
northwest of Chichi Island and is characterized by
submarine
hydrothermal
polymetallic
mineralization of the back-arc basin type. Three of
five drill holes intersected polymetallic mineralized
parts enriched in Cu and Zn and characterized by
pyrite, chalcopyrite and zincblende, making it the
first recovery of a modern hydrothermal deposit.
This paper describes the outline of the current
activities
on the exploration
of submarine
hydrothermal deposits in the Suiyo seamount.
Keywords
submarine hydrothermal deposits, drilling machine,
Suiyo seamount
Introduction
The Metal Mining Agency of Japan (MMAJ) has
been
conducting
surveys
of
submarine
hydrothermal deposits since 1985. The exploration
of submarine hydrothermal deposits must define
the distribution of potential mineral resources in
the vertical section and the grades of the deposits.
To meet such a demand, in 1996, the MMAJ
developed the Boring Mashine System (BMS) for
deep-sea exploration which has a capacity of 20m
core drilling at a depth of 6000m as shown in Fig.1
(Matsumoto and Sarata,1996; Sarata et al., 1999).
During the period of twenty days from December
8 to 27, 1999, using the BMS, an exploration of
submarine hydrothermal deposit was conducted at
the Suiyo seamount in the Izu-Ogasawara Arc. The
Suiyo seamount is a submarine volcano on the
volcanic front of Izu-Ogasawara
Arc and a
submarine hydrothermal deposit is being currently
formed at the summit crater of the seamount.
As the result, three of five drill holes intersected
polymetallic mineralized parts enriched in Cu and
Zn and characterized by pyrite, chalcopyrite and
zincblende, making it the first recovery of a modern
hydrothermal deposit at an oceanic island-arc
(Sarata and Matsumoto,2000).
Geological setting' at the Izu-Og'asawara Arc
The Izu-Ogasawara Arc extends -1,100 kID from
north to south and lies at the boundary of the
Pacific and Filipino Sea plates. The Izu-Ogaswara
Arc is divided in two by the Sofugan Tectonic Line
(Fig.2). The physiography of the northern sector of
the arc is quite different from that of the southern
sector. Volcanic rocks from the northern sector are
more acidic than those from the southern sector.
Evidence
for
submarine
hydrothermal
mineralization has been observed at four seamounts
along the Izu-Ogasawara
Arc (Myojin Knoll,
Myojinsho, Suiyo Seamount and Kaikata Caldera),
and submarine hydrothermal activity is evident at
another three seamounts along the arc (Kurose Hole,
Mokuyo Seamount, and Doyo Seamount).