Hydrothermal solution scenario and uplift-erosion scenario are important for high level nuclear waste disposal in Japan.The study on the rare earth elements behavior in the hydrothermal alteration in the Kuroko deposits suggests light rare earth elements did not release during the hydrothermal alteration of volcanic glass which could be a chemical analogue of Am and Cm derived from high level nuclear waste glass.
The study on the weathering of soils (andosol, red-yellow soil) indicates that the secondary minerals (iron hydroxides, manganese oxide, clay minerals) retard the migration of rare earth elements by the adsorption and ion exchange reaction. This suggests that radioactive elements (e.g., Am, Cm) in shallow geologic environments are retarded by these mechanisms.

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Paleohydrogeological study is a method to clarify the state of hydrogeological and geological environments from the past to the present.
In the Tono uranium deposit, most of the uranium has been preserved in the deposit since formation, even though the deposit has been subjected to the effects of several cycles of uplift, erosion and subsidence since its formation about 10 million years ago. Such long-term uranium fixation results from the preservation of a favorable geological environment. At present, redox, pH and PC02 are estimated to control the uranium solubility and groundwater-rock-microbe interactions are important to the redox buffer system.
In order to enhance confidence in the demonstration of long-term safety of a geological disposal system for high-level radioactive waste in a geologically active area such as the Japanese Islands, it is necessary to understand how geological phenomena such as uplift and erosion have affected deep geological environments and how such multiple phenomena have influenced the hydrogeological and geological systems. To contribute the studies of the Tono uranium deposit to paleohydrogeology, it is important to determine any long-term changes and to evaluate the stability of the geological environments. Because the deep geological environment is affected by many factors such as groundwater flow, microbes, water-rock interaction and so on, a paleohydrogeological approach is essential to know the state of ancient, deep geological environments which might influence the preservation or mobilization of uranium.

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Slaking is a specific property of sedimentary rocks. Slaking causal factors are the ionic concentration and cationic valence of in-site groundwater, dehydration of pore water and solution chemistry to contact with the rock after dehydration. Opaliuns clay (Switzerland), coarse sandstone (Kushiro coal mine, Japan) and fine sandstone (Ikeshima coal mine, Japan) are used to investigate the slaking property. The pore water of these rocks consists of high sodium chloride like seawater.
Under the brackish water environment, the interlayer cation in smectite is occupied by sodium ion. The univalent cation rich smectite normally has one water molecule layer under the low humidity environment. The divalent cation rich smctite has two water molecule layers. Sedimentary rocks including univalent cation rich smectite are more shrinkable than the divalent cation rich smectite including sedimentary rock. Strongly rapid slaking rocks are generally contained more than 1.5wt% sodium rich smectite.
The dehydrated sedimentary rocks sampled at the brackish groundwater environment easily disintegrate to contact with the low ionic concentration solution like fresh water. The other side, these rocks don t disintegrate to contact with high ionic concentration solution like seawater. Zeta potential of rock particles obviously involves in slaking properties. In the case of the underground disposal of radioactive nuclear waste in sedimentary rocks, an unsaturated zone is possibly formed around the waste pit due to ventilation and additional heat from waste. To keep the waste pit wall, further investigations is needed with special attention to rapid slaking properties by using a deep underground sedimentary rock site.

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One of the important methods for the safety assessment of the geological disposal of HLW (high-level radioactive waste) is a performance assessment based on a numerical model of groundwater flow. Thus, improvement of groundwater flow model is crucial for the reliability of the safety assessment. To improve the groundwater flow model, it is useful to use the groundwater monitoring data for its validation and updating. For this purpose, water level, pore pressure and chemical composition of groundwater in wells are often monitored, while systematic geophysical monitoring is not widely used. In this paper, we reviewed the case studies of the geophysical exploration method used for the groundwater monitoring and proposed its feasibility to the monitoring program for geological disposal of HLW especially for gravity, resistivity, self potential, and micro-seismicity. Monitoring of these data should be started from early stage of the site selection survey for capturing the baseline characteristics before the groundwater perturbation caused by construction of the shafts and drifts. With these monitoring data, computer codes called "post-processor" is often used to calculate geophysical parameters using groundwater flow model for the parameter matching. It is emphasized that progress of modeling technology including the development and validation of these codes is important as well as the progress of monitoring technology.

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The purpose of this paper is to point out the effectiveness of strainer well observation to obtain information on water quality of different groundwater units. A 30 m deep well drilled through Tertiary sedimentary rock and Cretaceous granite in Kanamaru area was observed to draw water quality profiles under various hydrological conditions. In dry season stepwise change of well-water quality, that is, increase of pH and electric conductivity, and decrease of dissolved oxygen and Eh with increasing depth, is observed. On the other hand, in wet season especially in snow melting season all of well-water column has characteristics of near surface water down to the bottom.
The difference of vertical distribution of well-water quality depending on seasons can be explained as follows. In dry season all of the groundwater units have similar hydraulic heads bringing little intra-well vertical flow, which makes similar water quality distribution in intra-well water column to that in surrounding bedrocks. In wet season hydraulic head of the shallower unit exceeds that in the deeper ones bringing downwards intra-well flow, which makes most well-water column replacing to the near surface water.
It is generally thought to be very difficult to obtain reliable information of each water quality for several different groundwater units from a simple strainer well. The reason is that different hydraulic heads possibly kept by each groundwater unit cause vertical infra-well flow that brings severe disturbance of water quality distribution in well-water column.
As long as obtaining water quality profiles logged under several different hydrological conditions combined with reasonable hydrogeological model, it can be possible to get much more reliable information on water quality of independent groundwater units.

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Several borehole logging methods were tested in a 103m deep hole drilled in Inada Granite, Ibaraki, Japan to detect permeable fractures. Borehole camera logging is essential to judge whether a fracture is open. Water quality logging is effective to detect permeable fractures from which groundwater inflows. Hydrophone VSP logging is effective to detect a permeable fracture on condition that the fracture plane and wave direction make near right angle. Sonic logging seems to be effective to detect permeable fractures. Flow meter logging using heat pulse method was tested but not to be proven effective because of too low speed of vertical flow in the hole.
Double-packered permeable tests were performed on three representative depth sections (26, 85 and 100m deep) each of which is thought to have permeable fracture(s). All the three sections have permeability greatly larger than those of intact bedrocks. Groundwater samples were successfully collected from all the sections which proved effectiveness of this multiple application of borehole logging methods to detect permeable fractures. Water quality of all the samples from the three depth sections were measured to show neutral to weak alkaline Ca>Na-HCO₃ type with almost no dissolved oxygen and electric conductivity three times as high as local surface waters. It is somewhat strange that even the shallowest groundwater has the same water quality as the deepest water has. This was probably because of the higher water head distribution with increasing depth. Under that condition the deepest groundwater flows into the shallowest section prior to sampling, which can make water quality of the shallowest section changed towards that of the deepest one.

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Around the Izu-Bonin back-arc rift, JOGMEC had conducted surveys targeting for deep-sea hydrothermal mineral deposits from 2000 to 2003 as a part of the deep-sea mineral exploration program supported by the Ministry of Economy, Trade and Industry (METI). As a result, a huge hydrothermal sulfide deposit(Hakurei ore deposit)was discovered in the Bayonnaise knoll caldera during the April 2003's survey cruise. It was the first discovery of Kuroko-type ore deposit in the Izu-Bonin back-arc rift. There are many inactive sulfide chimneys inside the caldera wall of Bayonnaise knoll. The water depth of Hakurei ore deposit is about 700-800 m, which is the shallowest sea-floor hydrothermal deposit known in the world. These sulfide chimneys mainly consist of sphalerite associated with chalcopyrite, galena, pyrite and barite. The maximum metal contents of four chimneys from Bayonnaise knoll caldera are 37.1 g/t Au, 1, 275 g/t Ag, 1.36 % Cu, 5.57 % Pb and 51.56 % Zn. The horizontal dimension of sulfide deposit is 700×500m, and is almost equal to that of the Sunrise ore deposit in the Myojin knoll caldera, one of the largest submarine hydrothermal deposits in the Izu-Bonin island arc, situated in the volcanic front. The potential of Kuroko-type ore deposit in the Izu-Bonin back-arc rift seems to be as high as that in the Izu-Bonin volcanic front. The survey results gave not only new knowledge about the potential of Kuroko-type ore deposit in the Izu-Bonin back-arc rift but also an useful guide for how to explore submarine Kuroko-type ore deposits.

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Based on the latest research and newly obtained bulk chemical data of rare earth element (REE) for ores and intrusive rocks, we describe a summary of geology, mineralogy, and ore refining process of the Mountain Pass REE deposit, California, USA and briefly assess their potential and future issue. The Mountain Pass deposit is associated with carbonatite and alkaline intrusive rocks and has a tonnage of over 20Mt of 8.9% REO; which is represented by elevated LREE (La to Eu) contents such as La, Ce, and Nd owing to high bastnasite content. In addition to the Mountain Pass deposit, LREE-rich deposits such as Bayan Obo Fe-Nb-REE deposit, China, which occupied about 50% of global REO production in 2004, are also enriched in LREE. The bulk chemical data are revealed that ores from the Mountain Pass deposit record total HREE (Gd to Lu) contents ranging from 252 ppm to 1, 028 ppm with a maximum 2, 427 ppm for bastnasite concentrate, which indicates that LREE-rich deposits have potentially a significant economic contribution to HREE as well as LREE. For high-tech-nology industries with particular consumption of HREE resources, 1) a harmless and effective refining process extracting HREE from giant LREE-rich deposits even with a low-grade HREE (ex. Mountain Pass and Bayan Obo deposits) should be developed for the short-term demand, 2) an exploration for REE deposits which are primarily concentrated in HREE would be necessary for the approaching long-term shortage of HREE.

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Devonian peralkaline igneous rocks of the Kola Alkaline Carbonatite Province (KACP), occur mostly in the Kola Peninsula (Russia) and parts of northeastern Finland of the northern Baltic Shield. KACP consists mainly of nepheline syenites, evolved alkaline syenites and ijolite accompanied with ultramafic to mafic cumulates, and small amount of carbonatites dyke and neck intruded at a late stage. Lithological zonation by multiphase intrusions and fractional crystallization are observed in the representiative phases of the Khibina and Lovozero plutons. Rare earth minerals of apatite, loparite and eudialyte are cumulate phases of the fractionated peralkaline syenitic magmas. Based on whole-rock Sr and Nd isotopic compositions of plutonic bodies, the peralkaline magmas of KACP are considered generated from isotopically heterogeneous mantle. Mineral compositions of apatite and loparite and homogeneous isotopic compositions in each plutonic body suggest that fractional crystallization is main process of magmatic evolution and lithological layering in each plutonic body.
The peralkaline syenites of KACP contain abundant rare earth minerals, and loparite, eudialyte and apatite would be economically important. The Khibina body is well known for the large apatite deposits and loparite from the Lovozero body is mined for rare earth resources in Russia. Heavy rare earth contents of eudialyte (Y=400-900ppm) from the Lovozero body are often higher than those contents of apatite (Y=140-700ppm) and loparite (Y<150ppm). Rare earth minerals from peralkaline syenites of KACP would have a high potentiality for rare earth resources.

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