The Hishikari gold deposit was discovered by the Metal Mining Agency of Japan in 1981. Subsequent exploration and development by Sumitomo Metal Mining Co., Ltd.(SMM), the property owner, have proved Hishikari to be one of the outstanding gold deposits in the Japanese mining history.
The main obstacle to development was a large amount of hot water with a temperature of 60-65°C within the veins, of which original static water level was 100m above the upper limit of vein systems. A carefully arranged program which included a series of grout to fractures, a set of special valves and gates for unexpected outflow of hot water under pressure and a considerable modification to scale free dewatering operation Inade it possible to access the ore body at 100MLin July, 1985 when the mine started production at the rate of 200 t/d.
Other problem was a shortage of skilled underground workers because SMM had closed all domestic mines by 1979. In cooperation with subsidiary companies who kept mining people after the mine closure, OJT (on-thejob training) to local young and unexperienced workers was a key factor for successful development and initial stage of operation, by which the initial capital investment was paid back within two years from the start of production on simple calculation.
Recent economic circumstances, especially declining gold price by the exchange rate of yen to dollar, forced Hishikari to expand its production rate and improve operation process. The discovery of two new ore bodies in the adjacent area and the improvement of operation process enabled to expand its production rate to 150, 000t/y (555t/d) at the end of September, 1992.
Although these improvement will contribute to effective mine operation for the time being, new challenge and continuous efforts will be essential for future operation.

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The Mitsubishi Process for continuous copper smelting has various advantages over the conventional process. Since the start up of the first commercial plant at Naoshima in 1974, following development works have been carried out to improve the productivity and process efficiency.
.-intensive operation by increasing the degree of oxygen enrichment for higher productivity
-detailed study of impurities distribution
-test works for secondary materials treatment
-campaign life elongation by improving operation and furnace construction
Under these technical achievements Mitsubishi Materials Corporation decided to construct one new large scale Mitsubishi furnaces line and replace existing two lines, a reverberatory furnace line and a small Mitsubishi furnaces line, for achievement of substantial cost reduction. Construction started in March, 1990 and the new plant was put into operation in May, 1991. As a result, much improvement of productivity and cost reduction were accomplished. This paper presents development works for the large scale Mitsubishi furnaces and outline of the new smelter.

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The effects of agitation intensity and amount of bridging liquid on agglomerate formation in agglomeration in liquid were experimentally investigated. An increase in agitation intensity advanced the compaction of agglomerates, reduced the porosity and changed the saturation degree which is the ratio by volume of the bridging liquid to the pores of an agglomerate. It was observed that the process of agglomerate growth depended on the changes in porosity. Based on this observation, the effects of agitation intensity on the process of compaction and changes in porosity were quantitatively elucidated and a scale-up equation was formulated. In addition, model agglomerates of the zirconia powder were cold isostatically pressed to investigate the influence of green agglomerate porosity on the density of sintered agglomerates. The results showed that the agglomerates produced by agglomeration in liquid must have porosities less than 0.51 in order to achieve high density and strength after sintering. To achieve this objective, the formulated scale-up equation was utilized to design a batch-type horizontal agglomerator that can provide the agitation energy required to produce agglomerates with porosities below 0.51. The newly designed agglomerator was successfully tested in the production of highly dense microspherical agglomerates of zirconia.

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A principle was established to estimate the equilibrium distribution ratio of the impurity element X between NaO_0.5-CO₂-XOv/₂ slag (v: the valence of X) and molten copper defined by {(mass% of X in slag)/[mass% of X in metal]}, over a wide range of the slag composition as a function of partial pressures of CO₂ and oxygen. Based on the principle, the following measurements on NaO_0.5-CO₂-AsO_2.5 slag were conducted to estimate the distribution ratio of arsenic.
(1) Activity measurement of NaO_0.5; Activities of NaO_0.5 in the slag were determined by the EMF method using β″-alumina as a solid electrolyte over the composition range of 1>N>0.8{N=ⁿNaO_0.5/(ⁿNaO_0.5+ⁿAsO_2.5), n: the number of moles} under the partial pressures of CO₂ of 0.001-0.08 MPa at 1, 423-1, 523 K.
(2) Activity measurement of AsO_2.5; Activities of AsO_2.5 could be calculated from the activities of NaO_0.5 by integrating the Gibbs-Duhem relation. Activities of AsO_2.5 as the initial values of the integration were determined by the distribution equilibrium measurements of arsenic between the slag and molten copper.
From the obtained results, together with the solubility data of CO₂ in the slag reported in the previous study, the equilibrium distribution ratio of arsenic was successfully calculated over the composition range of 1>N>0.8 as a function of partial pressures of CO₂ and oxygen at the temperatures of 1, 423 and 1, 523 K.
The calculated distribution ratio of arsenic has a considerably large value and increases with increasing the value of N. The higher oxygen partial pressure and the lower CO₂ partial pressure and the lower temperature are more preferable for the removal of arsenic from molten copper.

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Experimental condition to make fine copper powder by disproportionation reaction and the physical properties of powders obtained were studied.
A 3 l-reactor to produce large amount of samples, similar to the 1 l-reactor described previously, was used. Fine copper powder (1-2μm) which was similar in shape and diameter to that with the 1 l-reactor was obtained.
By use of the 3 l-reactor, the formation of larger copper powders more than 10μm which were surrounded with flat crystal surface planes could be achieved.
Mixed powder, which consists 70% of large powder and 30% of small powder, showed the maximum tap density of 5.1g/cm³. Densely sintered product was obtained when mixed powders were sintered for 2.5 hours at 1, 000°C. Some results in thermomechanical analysis and SEM micrographs of sintered products are included.

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The DLVO theory has been used successfully to describe the stability of synthetic rutile suspensions in NaCl solutions of 2×10^-3 M and below. At higher NaCl concentrations, the suspension is more stable than predicted by the theory. At concentrations above 1 M, the suspension is peptized even at its i. e. p.It is believed that the additional stability is due to the structural force not considered in the DLVO theory. The structural force can be described by a double exponential function, the parameters of which have been determined on the basis of turbidity measurement. It has been also tried to explain the additional stability of rutile suspensions at NaC1 concentrations 2×10^-1 to 2×10^-2 M by modifying the electrostatic interactions of the DLVO theory. However, the modification requires the irregular shift of shear plane position with pH and an unacceptable assumption that particles will not coagulate at the deep secondary minimum of potential energy curve. The additional stability of rutile suspensions can be reasonably explained by the structural force, but not by the electrostatic interactions.

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Non-ferrous slags are becoming widely used in these days, the usage is however far from satisfactory level. In order to resolve the problem, it is important to develop new processes or to produce new materials which have higher values added from the slags.
In the present study, the effect of the cooling condition of copper slag melts on retained glass and crystalline phases was investigated. Simultaneously, the dissolution test decided by the Ministry of Environment was carried out for the samples.
The critical cooling rate for glass forming determined from the CCT diagram was 100°C/sec. The crystalline phase detected by X-ray diffraction was only fayalite as far as heat treatment was conducted in the H₂: CO₂ 1: 1 atmosphere in which wustite was stable. Magnesia formed the solid solution with fayalite, and lime and alumina were rich in glassy matrix which was consisted with low iron and high silica.
Dissolved concentrations of all metallic components from the water-granulated slags were under the standard of drinking water, and these from heat-treated slags were same except for iron. Iron dissolution from slags increased with decreasing cooling rate, and it may be attributed to the fayalite formation. Dissolved concentration of iron from furnace-cooled slag, however, was under the standard of waste water. After all, the dissolution of metallic components from copper slags was less than the regulation level, so the slags would not contaminate the environment.

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In order to evaluate three-dimensional anisotropy in fracture toughness of rocks, a chevron-notched round compact tension (C-RCT) test has been developed. By adding it to the present ISRM Suggested Methods for Determining the Fracture Toughness of Rock, fracture toughnesses in three perpendicular orientations can be determined with a single boring core. A 3-D boundary element analysis has been carried out first for the C-RCT specimen and evaluation formulae on the stress intensity factor and the compliance of CMOD have been presented. Then after verifying the evaluation formulae by comparing a K-resistance curve of a granite between SR tests and C-RCT tests, three-dimensional anisotropy in the K-resistance curve has been evaluated for two rocks by using three specimen types of CB, SR and C-RCT.

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Taiheiyo Coal Mining Co., Ltd. Kushiro Colliery has used steel arch sets as roadway supports.However rock bolting system widely used in Australia has been introduced to stabilise roadways and increase drivage rate corresponding to deeper mining. Therefore, in order to investigate the effect of rock bolting on the roadway maintenance, measurement of roadway displacement with extensometer was conducted at bolted and unbolted in-seam roadways in three longwall panels with drivage and longwall retreat.
The main results are as follows:
(1) The roadway deformation generally occurs just after drivage and tends to stability with face advance, however increase again with the approaching of the longwall face.
(2) The roadway is exposed to the deformation process by the increase of the ground pressure, and the major part of deformation is caused by the occurrence of discontinuity planes and the extension by the interlayer separation.
(3) Rock bolting restrain the occurrence of discontinuity planes and the enlargement of relieved zone, and core samples suggest the position and the occurrence of discontinuity planes.
(4) Rock bolting makes the displacement of the roadways less than half of that of unbolted sites in drivage, and also restrain the deformation in longwall retreat.

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Pressure loss expression in coal ash pneumatic conveyance system has been formed from slug flow model, which is established from the view point of Bingham fluid conveying in long distance pipeline.
This slug flow model is built up by dividing one slug into front part, main part and tail part. The pressure loss at the front part is obtained from momentum loss caused by accelerating liquid layer to the slug velocity. The loss at the main part is obtained from friction resistances caused by viscousity and normal stress. The loss at the tail part can be neglected because current gravity occurs at this part.
The motivation behind this study is to convey effectively coal ash discharged from power plants to land reclamation. Pneumatic conveyance system conveys effectively coal ash because mixed air decreases friction between coal ash slug and a pipe. However, the pressure loss expression with high accuracy has not been formed. In previous studies of air-liquid two-phase flow, low viscous liquid in short distance pipeline has been mainly studied. Applying the previous slug model to the Bingham fluid slug-air two-phase flow, pressure loss can not be estimated accurately because it is expressed only by friction resistance between a slug and pipe.
Pressure loss produced at conveying coal ash in the 100m length, 120mm diameter pipeline was measured. As results, the pressure loss obtained from this slug flow model is reasonably agreement with the experimental result.

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Using a modified household microwave oven, the carbothermic reduction of several metal oxides as well as carbonates was experimentally examined. The main results obtained are as follows:
(1) The temperature change of coal char layer placed in a ceramic crucible was determined under microwave radiation. It was found that the temperature elevation of the coal char layer is extremely fast, but it is necessary to give much attention to prevent a radiant heat for obtaining a high temperature.
(2) The addition of limestone was found to be effective to enhance the carbothermic reduction of both hematite and mill scale. Mill scale giving a slightly higher reduction than hematite was more sensitive to microwave radiation. However, the reduction differences between these iron oxides were actually not significant because the overall reduction rates might be controlled by the existence of coal char.
(3) Carbothermic reductions for metal oxides such as nickel and cobalt oxides also proceeded completely by the microwave radiation for 10 minutes. The addition of limestone to the reduction medium was essentilly unnecessary for the reductions of metal carbonates.
(4) Metal oxides of lower oxide states were formed in the carbothermic reductions of manganese oxide, titanum oxide of anatase type and manganese carbonate.

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