The lnakuraishi mine of the Tekkosha Co. Ltd. has been producing manganese ore since 1929. The ore deposit is the fissure filling veins in volcanic and pyroclastic rocks of the Miocene epoch. As a result of the active exploration and the persistent rationalization of the operation, the mine has produced 1, 300, 000 tons of manganese ore during the past 38 years. The following improvements have been recently carried out to promote the efficiency in the production of ore.
1) Study of the structural control of veins make the exploration efficient and as the result ore reserves has increased.
2) Since 1966, the dry magnetic separation has been applied to the low grade manganese ore instead of the heavy media separation. A high power couplepolar magnetic separator has been successful. in the separation.

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As the mining method of shallow deposit, the vertical open-cut mining by means of open-column has been tried, and it can be said that although there are some technical problems, universality as mining method has been acknowledged.
The merits of the vertical open-cut mining compared with traditional bench-cut mining are as follows
(1) As the surface area required for development is very small, the range of adaptability has been greatly increased.
(2) The amount of theearth to be carried off has been decreased, therefore it has many economical factors such as the shortening of the time for development, the problem of spoil-bank.
(3) It dose not need particular facilities for development, and there arenot so many problems of repayment and diversion of facilities.
(4) As riged sheeting of earth is established before excauation, there is little danger of destruction of slope surface, therefore safety maintanance is carried at a small outlay and we canexprct safety in operation.

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It is impracticable to extract a coal seam without having an effect on the surface area, and it should be borne in mind that extraction under those area that are heavily populated causes extensive surface damage to the structures and results in many social problems. The recent development of the theory of “surface movement due to mining” has produced a new mining method. This new method, called “harmonic extraction method” enables us to extract the wnole of a seam, say, unaer a town wrtnout causing anywhere near as much damage as the conventional method.
The author has been testing the theory for ten years in the collieries ofthe Chikuhd district and has found them practical. Results obtained have indicated that extraction is possible even in area that has not been worked for many years because of various complex surface conditions of the district and fear of minig damage. However, with a thorough precaiculation of the mining damage, based on the theory of harmonic extraction and, if necessary, data of test mining, theseam can be extracted.

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The molten salts of sodium fluoride-calcium fluoride-barium fluoride-aluminum fluoride quaternary system, are known as “Hurter's bath” and “Sumitomo's bath” forelectrolytic refining of aluminum.
1) The densities of the molten salts of sodium fluoride-calcium fluoride-aluminum fluoride ternarysystem were determined in a wide range of composition. The densities changed in a range from 2.0 to 2.3g/cc at 950°C, and increased with the increase in thecontent of calcium fluoride.
2) In this ternary system, the compound NaCaAIF₆ is assumed to have been formed according to the following reaction;
NaAlF₄+ CaF₂=NaCaAlF₆
3) When the content of calcium fluoride is kept in constant, the maximum density is observed at the composition that the mol ratio of sodium fluoride and aluminum fluoride corresponds to 3:1 (Na₃AIF₆) after the displacement reaction has occurred.
4) The densities of the molten salts of thequaternary system at 950°C changed in a range 2.3 to 3.2g/cc.
The density change has the same tendency as that of the molten salts of the above-mentioned ternary system.
5) In this quaternary system, it has been assumed that the formation of the compound NaBaAIF₆ has priority to the formation of NaCaAIF6.
6) Calculated densities, assuming the additivity of the density of each salt and theformation of compound NaCaAIF₆ and NaBaAIF₆, accord well with measured ones in ternary and quaternary systems respectively.
7) Isothermal liquidus line diagram of this quaternary system has a likeness to that of NaF-BaF₂-AIF₃ ternary system when the content of calcium fluoride is kept constant, but the melting temperatures are lower than the latter on the whole. And the melting temperatures of two composition ranges are about 750°C.
8) We think that we can use some other compositions of this quaternary moltensalts besides Hurter's or Sumitomo's bath as an electrolyte of aluminum refining.

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