Taiheiyo coal mine, eastern Hokkaido, produces the annual production of 2, 450, 000 tons of clean coal base mined under sea field.
Since 1939, the geological survey have been carried out above the offshore area by the methods adopted.dredg-ings, diving observation, seismic refrection and drillings. It is very difficult, however, to survey the southwest district due to large water depth and thickness of Quaternary deposits. Accordingly, we try to make an investigation in this district by the development of underground gallarys before starting the coal mining project.
The gallary named Jyoso Nisi Ichi-oroshi was developed to survey the offshore area in 1973 and performed in 1980. It is advanced 2, 600 m from the starting point of the main level gallary. The survey revealed the following circumstances of the coal seams:
(1) No. 5 coal seam (Honso: main seam) is wider and thicker than our expection.
(2) No. 6 coal seam (Kaso: under main seam) gets gradually thickness southwestward.
Concequentaly, the coal reserves has increased by about 100 million tons.

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A fine-grained, compact kuroko ore regarded as one of the most primitive kuroko deposits, occurs in the Shakanai Mine of Hokuroku district, Japan. From this type of ore, fossil foraminifera replaced by sphalerite have been found in an uncovered, doubly-polished thin section. Because of observation only in sectional forms of the foraminifera, it is difficult to decide the species names for most of the specimens, but some well-preserved ones can be identified with regard to the genus level. They include the genera of planktonic and calcareous foraminifera such as Globorotalia, Globoquadrina and Globigerina (or Globigerinoides). Among them an important Miocene index fossil, Globorotalia cf. peripheroronda, has been recognized.
The fossil foraminifera replaced by sphalerite exist in fine-grained matrix of yellow ore mainly composed of chalcopyrite. In the fossils, two types of sphalerite can be recognized under a microscope; one is transparent, colorless sphalerite replacing the test part of the fossils, and another is opaque one filling their chambers. Electron probe X-ray microanalyses have revealed that the opaque nature of the chamber sphalerite can be attributed to small inclusions of chalcopyrite of some six weight percent.
The fossil-bearing kuroko deposit is stratiform and intercalated between altered dacite pyroclastics and mudstones. It shows many features characteristic of slumping and sliding, such as fragmentation of ores and intraformational soft-rock-deformation. It is assumed that the fossil foraminifera which were first replaced by sphalerite after their settling down onto the bottom of the ore-depositing basin, would have been physically mixed with the chalcopyrite-rich ore in an unconsolidated condition by slumping or sliding.

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To evaluate an exploration system, the prize-penalty function,
GmΣk=1 ψkNk{1+γk nkΣi=1 nkΣj=1 jkijφkij}
has been proposed, where G is a gain in the system, (Ψ_k), (N_k), (γ_k), (η_kij), and (φ_kij) are matrixes of prize, sample number, penalty coefficient, identification probability and penalty, respectively, m is number of kinds of information, and n_k is number of groups in the kind of information denoted by k. The sufixes i and j indicate that the sample belonging to the group i is seemed to belong to the group j. The diagonal elements of matrixes (η_ij)k and (φ_ij)k correspond to correct identification, while the other elements to wrong identification. If the matrix (η_ij)k is diagonal, then the iden-tification is perfect. All of the diagonal elements of the matrix (φ_ij)k are zero, while others are negative-The larger absolute value of a element of the matrix corresponds to the more serious mistake. The values of prize, penalty coefficeint and penalty matrixes are given in accordance with the purpose of the exploration, which is represented especially by the penalty matrix.

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