The principal metallogenic epochs in the Inner Zone of southwestern Ja
pan are classified by considering mainly radiometric and microfossil a
ge data, as follows-(1) Early Cambrian Epoch: Characterized by podifor
m-type chromite deposits hosted in ophiolite complexes; these are the
earliest-formed mineral deposits in the Japanese Islands, and probably
formed in the shallow mantle of island-are settings; (2) Carboniferou
s to Permian Epoch: Characterized by Besshi-type base metal sulfide de
posits mainly associated with submarine lavas and tuffs of basaltic co
mposition including their metamorphosed equivalents, and by bedded cup
riferous pyrite deposits associated with submarine acidic tuffs. Both
types of deposits would have been formed in a back-are basin environme
nt, geochemically influenced by an island-are; (3) Middle Triassic to
Jurassic Epoch: Characterized by most of the bedded manganese deposits
associated with bedded cherts, including their metamorphosed equivale
nts, which would have formed by hot spring activity in an ocean basin
environment with a limited current circulation. The manganese deposits
and their host rocks are the result of seafloor accretion; (4) Late C
retaceous to Paleogene Epoch: Characterized by extensive continental-a
re magmatism (volcanic and plutonic), resulting in formation of variou
s mineral deposit types, related mainly to ilmenite series (Late Creta
ceous) or magnetite series (Paleogene) granitic rocks. Related to the
former are polymetallic skarns and veins containing Cu, Sn and W; also
related to this metallogenic activity are stratabound hydrothermal cl
ay deposits of kaolin, pyrophyllite, and sericite associated with pre-
ilmenite series granitoids subaerial felsic pyroclastic rocks. Molybde
nite-bearing veins and replacement-type sericite deposits are characte
ristics of the magnetite series terranes, with local skarns and vein o
ccurrences. As with ilmenite - series,granitoids occurring in southwes
tern Japan, eastward younging is also recognized in these mineral depo
sits, regardless of ore type; (5) Neogene Epoch: Characterized by inte
nse submarine volcanism of acidic composition and associated Kuroko de
posits in the Green Tuff region, a major tectonic division and a major
metallogenic province of the Neogene Tertiary of Japan. These mineral
deposits would be related to Japan Sea opening. In the 'Non-Green Tuf
f region,' important mineralization events are represented by sediment
ary uranium deposits, and veins characterized by Au, Sb or Hg occurren
ces; (6) Plio-Pleistocene Epoch: Characterized by epithermal Au-Ag and
Au-Ag-Cu veins associated with subaerial andesitic to dacitic volcani
c rocks of Plio-Pleistocene age. Volcanism of this and following epoch
s is characteristic of an island-are setting; and (7) Quaternary Epoch
: Characterized by volcanic sulfur deposits and minor iron sand deposi
ts. (C) 1998 Elsevier Science B.V. All rights reserved.