Seiya UYEDA and the author recently expressed a hypothesis that the extensional regional stress environment is favorable to the kuroko or similar volcanogenic massive sulphide mineralization and the compressional stress environment to the porphyry type copper concentration (UYEDA and NISHIWAKI, 1980). The investigation for the tectonic control of the 23 porphyry copper mines and important prospects, with more than 3×10 ⁵ tons of copper metal contents (Fig. 1) in the Western Pacific island arc region (Fig. 2) was attempted and reported here. They are all young in age, 20 to 1.5 m.y. BP except 3 probable Eocene deposits. Possible application for prognosis and exploration was also considered.
The distribution of these porphyry coppers in the region is confined in the island arcs under the collisional tectonics in a broad sense, which includes;
(1) The mobile zone between two subduction zones, facing each other as a probable consequence of the polarity reversal, one subducts from the trench in the Pacific side and the other from the trench in the peripheral sea or back-arc side. Some amount of crustal shortning between two arcs is also observed (Examples: Philippines and Solomons, Figs. 2, 3, 4).
(2) Arc-arc collision (Example: Sabah, East Malaysia, Fig. 3).
(3) Continent-arc collision (Example: Papua New Guinea, Fig. 13).
Many other large island arcs like Kuril, Japan, Izu-Bonin, Mariana, Ryukyu, Sunda, Sumatra, et al. have no large concentration of copper of this type, so far inspite of the extensive exploration. Observing above-mentioned distributional pattern the author speculates that the compressional stress regime, common in collisional tectonic zone, might be the favorable tectonic environment. Consequently stress fields at the time and place of ore emplacement were investigated through studies of the direction of (1) elongation, alignment or protrusion of the mineralized intrusive stocks, (2) swarms of dykes including breccia or pebble dykes, (3) mineralized fissure systems, (4) elongated alteration zones, (5) faults, (6) certain geophysical anomalies and foldings of the host formations (Figs. 5, 6, 7, 9, 10, 11, 12, 14, 15).
As a result, 19 among 23 of them are found to be under compressional horizontal stress with its maximum direction being roughly orthogonal to the arc direction. Other 4 deposits are developed along the conspicuous transcurrent Philippine fault or its branch zones under the stress and shear caused by the coupling force of their eminent left lateral movement (Fig. 8). This coupling ultimately results in the compressional stress more or less parallel to the direction of the plate movement which is also roughly orthogonal or with an obtuse angle to the general arc direction.

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Tin-polymetallic veins in the Akenobe mine area comprise at least three major stages of Au-Ag, Cu-Zn and Cu-Sn mineralizations, in which the latter two mineralizations are superimposed. Recently discovered cross cutting relationship in the Chiemon vein group indicates that the earlier Cu-Zn vein is different from the later Cu-Sn vein in the metal ratio, particularly Zn/Sn ratio, and the sulfur isotopic ratio. Thus these veins are considered to have formed by independent ore solution originated in two different sources. A candidate for the Cu-Sn related igneous activity may be the Wadayama granite. This granite is leucocratic, ilmenite-series, biotite granite characterized by small pegmatite and granophyric texture. Similar granite was found in the middle of the Hikihara caldera to the west of the Akenobe mine. Centers of the Cu-Sn mineralization are aligned to the tie-line between the Wadayama and Hikihara granites. Thus unknown area between the western Akenobe mine claim and the eastern edge of the Hikihara caldera may have some value to be explored for hidden vein swarms.

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In the Kamioka silver-lead-zinc mining area, zonal arrangement of ore and skarn minerals is recognized in accordance with the distance from the rock mass called metabasite. Besides mineral assemblage data, Ag-Pb-Zn ratio in ore and decrepitation temperature of skarn minerals can be used to delineate the zoning pattern. Molybdenum mineralization with actinolite skarn occurs in some zones overlapping the silver-lead-zinc mineralization, and is likely to be related to the activity of granite porphyry.
There are four types of Ag-Pb-Zn ores in the mining area; "mokuji" type, "shiroji" type, dissemination type and gold-silver type. The mokuji type ore, which is most prevalent and appears to have the highest formative temperature in this mineralized sphere, is found, without exception, in contact with the Inishi-type migmatite.
Thus, it is thought that the silver-lead-zinc mineralization in this mining area has been genetically related to the metabasite and the Inishi-type migmatite. Distribution of these rocks, and therefore the indication of silver-lead-zinc mineralization, is confined to a specific tectonic unit of the Hida metamorphic belt, named the Central massif.
It has been suggested from the ore lead isotopic data that leads in this area came from more than a single source of material. There is also some indication that primary concentration of Ag-Pb-Zn in this area might have occurred prior to the formation of the migmatite and the metabasite.

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The main Pb-Zn deposits in this district are found to be confined in the specific horizons of Upper Jurassic and Lower Cretaceous sequences, which consist of reef limestone and calcarenite with dolomitic layers. The deposits are also clearly related to dome or anticlinorium structure. The stratigraphic and structural peculiarities of them are thus very similar to those of petroleum and natural gas deposits of Mexican Gulf oil field.
The mineralization is structurally controlled by longitudinal and cross faults and bedding planes of the country rock, resulting in three major forms; manto, chimenea and vein, which are occasionally gradational and mutually connected with each other. Depending on the alteration status of the host carbonate rocks, the deposits can be divided into three groups; no alteration or weak recrystallization group, normal recrystallization group with or without small amounts of skarn minerals and skarn group. The first group that includes such ore deposits as Dos Marias and Plomosas has a simple ore mineral paragenesis; pyrite-sphalerite-galena, and the second, represented by Ojuela, Potosi (Santa Eulalia) and Providencia (Avalos), shows a more complex mineral association; pyrite-sphalerite-galena-chalcopyrite-pyrrhotite-arsenopyrite-tetrahedrite with some Ag-minerals. The third group comprising the deposits such as Naica, San Antonio (Santa Eularia), La Encantada, San Martin, Charcas, La Paz, Fresnillo and Concepcion. del Oro, has various other minerals including magnetite, hematite, scheelite, molybdenite and some Bi-minerals, in addition to the above mentioned minerals. Fluorite, barite and gypsum or anhydrite are commonly present in all three groups of the deposits.
The main mineralization in this district has been dated as Late Eocene or Early Oligocene, correlated to the serorogenic phase of Laramide Orogeny, by both radiometric and stratigraphic analyses. The ore deposits are thus evidently of epigenetic type. While many authors consider the mineralization to be of magmatic origin, some favour a Mississippi Valley-type genesis. Although the detailed features of the deposits show much difference from the typical Mississippi Valley-type mineralization, it seems probable that highly saline brine commonly associated with the oil-bearing sedimentary sequences would have been involved in primary concentration of lead and zinc in this ore field.

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