Ohe Mine, situated in the south-western part of Hokkaido, have experienced ups and downs many times since opening.
At that time when our Hokushin Mining Co.succeeded management of the mine, in October 1953, it was very dull state due to ruin of mine, waste of installation and inactive market.
In order to restore and enlarge the mine production, we made untiring effort actively in general measurement and improvement of engineering-such as prospecting, mining and beneficiation.
The principal improvements are given as follows.
1) Precise surveying of geology and are deposits established clear theory that the are deposits were echelon-arrangement-composite vein repeating fissure forming and mineralization contained various sulfide ores and manganese ores.
2) We adopted the following prospecting method to confirm the whole feature of-thn deposits.
At first, prospecting gallery was drifted in the foot-wall, then cross-cut or boring holl were cut toward the hanging wall.
Thus, we could discover large quantity of are reserves during short time, and could find occurence of vein containing many various are minerals.
3) The concentration of stoping faces were performed, and shrinkage method was replaced with sand filllng stoping methgd, then, stoplng efficency was remarkably increased.
4) In the beneficiation, the concentrates of useful minerals such as gold and silver bearing galena, sphaierite, pyrite and rhodochrosite were effectively separated by adoption of sulfide flotation with soap flotation.
Then, the commercial are reserves increased remarkably, and it made able to enlarge the production scale.
5) To improve the quality of manganese concentrates, investigation of roasting method of the concentrates was successfuly carried out.
Since March 1958, roasting and sintering process by use of rotary kiln were operated, and grade of manganese concentrates advanced from 33% to 47% of Mn, then, economical value of the are rised evidently.
As the result, we have accomplished the stabilized production of present scale, 5, 000 tons of crude ore per month.Nowadays, we are planning the production-increase up to 10, 000 tons per month.

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The thermodynamical investigations on the thermal decomposition and the oxidation reaction of arsenic-bearing copper concentrates were executed. It was found consequently that the thermal decomposition of enargite occured at the temperatures above 600°C approximately, and that, furthermore, the roasting in the atmosphere containing rich SO₂ and poor O₂, as well as in CO₂, was exceedingly effective for dearsenising Kinkaseki are which contained enargite.
Based on these fundamental experiments, the author carried out the dearsenising roasting tests of Kinkaseki are by pilot fluidised bed roaster in the atmosphere above-mentioned and clarified the conditions required for commercialisation of this method. Moreover in 1956, the author designed to put this method into practice and undertook the construction of the dearsenising roasting plant, whose daily capacity was 40 tons, in Saganoseki Smelter, Nippon Mining Co. Ltd.
This plant started on commercial scale in January, 1959 and has been in operation satisfactorily and smoothly up to the present with the dearsenising efficiency of more than 80%.

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We can see many times the galleries buried with the debris to almost all section. in a considerable length after the occurence of outbursts of gas and coal. These practical situations appear very important, to us in order to throw light on the mechanism of outbursts which was almostly unknown up to date.
In this report, that is to say, in 1st report of.this subject the authors looked over many memoirs concerning the outbursts of the past to generalize them typically into four groups.
As a result of this consideration, it was recognized that almost all of outbursts on a large scale had brought a buried situation of gallery.
On the other hand, the authors investigated a buried situation of outbursts occured recently in the “A” Coal-Mine in Hokkaido District (an outburst size-about 800 tons broken), and there sampled the debris in some points. After several calibrations and experimental data of the samples of debris, the authors could comprehend somethings as follow:
(1) The outbursts of “A” Coal-Mine was a typical case in relation to the buried situation of gallery too.
(2) The internal gas pressure near the outlet of gas and coal was comparatively low and changeable at that in duration of projection.
(3) The debris projected was almost broken through attrition.

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With the object of investigating the motion of pulp and bubbles in the Agitair cell and finding out the correlation between their motion and intensity of agitation at the bottom of the cell, the authors have made experiments on a small batch cell of the Agitair type. The results obtained are as follows:-
1. It was ascertained that the core beneath the impeller was different from those that had been reported in the past literatures.We attemped to reveal the relationship between the intensity of suction force into the core and the various mechanical factors of the cell by means of a formula obtained by introducing a “coefficient of clippage”.
2. It was demonstrated that the impeller had an optimum height to keep the flow of pulp in good condition, and its opimum height decreased with increase of numbers of its slits and its circumferential velocity and, on the other hand, with decrease of specific gravity, size and quantity of particles.
3. Intensity of agitation at the bottom of the cell increases in proportion as the numbers of slit and the circumferential velocity of the impeller increase. It, however, decreases with increases of fhe air quantity introduced in the cell and the height of the impeller from the bottom.
4. In order to make the agitation effective, it is necessary to settle the impeller at such a position as to keep the coefficient of slippage in maximum value.

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Fundamental studies concerning the mutual dissolution between matte and slag in equilibrium with solid iron were previously carried out by the authors. In order to investigate the behaviours of magnetite in the principal system of copper smelting, the equilibrium between matte and gas was at first studied in the current work. Synthetic matte prepared was melted in an alumina crucible, and then, the system was kept in equilibrium with a mixture of CO, CO₂ and SO₂ gases for a certain period of time. The desired partial pressures of oxygen and sulfur which are closely related to the expectant activities of FeO and Fe₃O₄ were obtained by controlling the composition of leading gas (CO-CO₂-SO₂) to the system. In this work, series of experiments concerning the effects of gas composition, temperature and matte composition on the oxygen content in matte were performed and discussed in terms of FeO and Fe₃O₄ activities. The results obtained clearly show that the content of oxygen in matte increases with increasing activities of FeO and Fe₃O₄.

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With the presence of Co⁺⁺ in the electrolyte ranging from 0.5 to 50 mg/l, the corrosion of pure and silver-containing lead anodes was investigated by measuring the anode potential, the amount of anode slime, the distribution of lead in cathode zinc and the mean lead content of zinc deposit. The formation of lead peroxide on the anode surface was reduced markedly by increasing the concentration of Co⁺⁺ present in the electrolyte, thus the anode potential, the amount of anode slime and the lead content of cathode were decreased. The distribution of lead in cathode zinc at each anode is almost uniform when the. cobaltus ion concentration exceeds 5mg/l.

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