EXPLORATION METHODS
Regional geological survey should be carried
on for the determination of the Kuroko horizon
and for discarding unfavourable areas where
the ore horizon may have been eroded or uneconomically
deeply seated.
" Observation of old mine site and collecting
of antique information are also important
work, because Kuroko type deposits would
be distributed in regular way related to
the tectonic setting on that time and have
a tendency coming together in rectangle area
called Cluster."
" Modern and practical exploration methods
such as Element variation, Magnetic susceptibility
and Clay mineral assemblage have been devised
by means of footwall rocks because of following
reasons; "
(1) The footwall rocks were emplaced there
before Kuroko mineralization that the rocks
must be affected by alteration effect.
(2) The footwall unit is distributed the
whole area of all Kuroko cluster therefore
the method is expected to be applicable to
all Kuroko region.
"(3) Hence the footwall unit is relatively
uniform and homogeneous composition, the
variation of elements or minerals would be
comparative between altered and unaltered
area. "
" In case of Fukazawa deposit in the
central Hokuroku district, Low magnetic susceptibility
anomaly is the most extensive distribution
as extended as 3Km in long and 1.5Km in width
compaired to the other modern exploration
methds mentioned above. The anomaly is resulted
from substitution of Pyrite after Magnetite
affected by the high sulfur condition during
Kuroko mineralization. "
" Low Na2O anomaly defined by the content
less than 0.4% is the most effective, because
the boundary is very clear and abruptly changes
to the un-altered rock contained 3 to 5%
Na2O. The anomaly is considered to be generated
by the decay of Na rich plagioclase. "
Clay mineral assemblage is also useful and
easy to detect by naked eye. There are two
trends of zonation; One is lateral change
in the footwall unit from Sericite-Chlorite
zone in central part to mixed layered clay
mineral assemblage in the peripheral part.
Anther is vertically changing from mixed
layered clay mineral zone in the ore horizon
to smectite zone in the hanging wall unit.
"In consequence of argilization and
pyritization, Geophysical anomaly such as
low registivity and high conductivity anomaly
could be detected as a inverted 'V' form
by means of surface exploration. "
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