1) Results of the geoscientific researches except for the MIU Project

Concerning geology and geological structure in and around the Shobasama site, existing data include surveys on the Tsukiyoshi uranium deposits^20),21), the RHS Project¹⁵⁾, the Shaft Excavation Effect Experiment, investigations in the Tono Mine and the literature survey. Following are the overviews.

(1) Lineament interpretation¹⁵⁾

Lineament refers to linear topography reflecting discontinuous structure such as fault and photogeologically traceable features using aerial or satellite photographs²³⁾.

In the RHS Project, we used photographs (1/200,000 scale) of Thematic Mapper (TM : multiple spectrum scanning radiometer with ground level resolution of 30m) of LANDSAT for an area of 50km square. As are shown in Fig.4.1.(1), 1,276 lineaments are identified including active faults¹⁴⁾ such as Adera Fault, Ako Fault, Hanadate Fault, Shirakawa Fault, Byobusan Fault, Kasahara Fault, Enasan Fault and Sanageyama-Kita Fault.

The area shows development of grid-like pattern consisting of blocks divided by active faults. Resultant trends of strike of lineaments in each fault-bounded block are compared. It becomes clear that, as is shown in Fig.4.1.(1), there are differences in distribution patterns in lineament strikes among the blocks. This may suggest that, if we assume the lineament is a reflection of discontinuities such as fault, there are regional differences in stress conditions among the blocks. Also, each block can be treated as independent evolution unit with development histories of geological structure²⁴⁾.

In the RHS Project, more detailed lineament interpretation is carried out in the area where Tono mine and the Shobasama site are located (an area surrounded by Ako fault, Byobusan fault, Hanadate fault and Shirakawa fault in Fig.4.1.(1)). Because different results are expected to be obtained from photographs with different scales or availability of stereoscopic view, following three kinds of photographs are used.
(a) above-mentioned TM photographs of LANDSAT (1/200,000)
(b) photographs of HRV (High Resolution Visible Imaging System) with ground resolution of 20m by multiple spectrum scanning radiometer from French SPOT satellite (1/100,000)
(c) aerial photographs (1/40,000)
The results are compiled separately. As a result, in this area many large and small lineaments are recognized including lineaments corresponding to the active faults such as Byobusan Fault, Kasahara Fault and Ako Fault. Over ten lineaments longer than 3km²³⁾ are recognized in and around Tono Mine. These are thought to correspond to faults. In addition, NW-SE, NS and NNE-SSW trending ones are prominent. Some of them correspond to known faults²⁰⁾ such as Yamada Fault Zone and Shizuki Fault.

As a result, ten blocks are recognized with unique distribution patterns in lineament characteristics. Discontinuous structures such as faults and joints are formed by stress accompanying structural movement. Therefore, each of ten blocks is regarded as having been subjected to each unique stress condition. Those ten blocks are shown in Fig.4.1.(2)²⁵⁾. The Shobasama site is located in the 'f' block in Fig.4.1.(2).

(2) Ground geological surveys

Ground geological survey is aimed to gather most basic data of geology and geological structures by walking on the ground surface and observing rocks with unaided eyes with the purpose of drawing geological map.

The Shobasama site and its neighboring area have geological map^15),26) made in the RHS Project, which aims at understanding the lithological variety and internal structure (faults and fractures) of the Toki Granite. Besides, some existing geological maps are available^13),20),21).

i) Geology

The basement composed of Paleozoic, Mesozoic formations and granites. The basement is overlain by Neogene to Quaternary sediments (Fig.2.3(a)) in the vicinity of the Shobasama site. Mizunami Group unconformably overlies the basement granites. The Mizunami Group is overlain by the Seto Group with a distinct unconformity.

Basement rocks
In the Shobasama site, the Toki Granite is predominant. The Toki Granite adjoins sedimentary rocks of the Mino Belt on its south, west and north sides. On its northeast and southeast, it adjoins the Nohi Rhyolite and the Ryoke Granite (the Sumikawa Granite), respectively. The contacts of the Toki Granite with sedimentary rocks of the Mino Belt and the Nohi Rhyolite are confirmed on the ground surface, and the nature of the contacts are well known. On the other hand, the contact with the Sumikawa Granite is not confirmed on the ground surface because both show little lithological difference.

Toki Granite is divided into three facies lithologically (grain-size and texture) : coarse-grained, medium-grained and fine-grained biotite granite. The center of the granite (Hiyoshi district of Mizunami City to Jorinji district of Toki City) is occupied by fine-medium-grained biotite granite. It is surrounded by coarse-grained biotite granite. Near the contact with the sedimentary rocks of the Mino Belt, especially at the contact, the Toki Granite tends to be fine-grained. This is confirmed at Takodo district of Mizunami City where a transition from coarse- to medium- to fine-grained is observed.

Sedimentary rocks
Sedimentary rocks in the vicinity of the Shobasama site consist of the Mizunami Group and the Seto Group. The Mizunami Group is divided into the Toki Lignite-bearing Formation, Akeyo Formation and Oidawara Formation in ascending order.

a) Mizunami Group
The group consists mainly of pyroclastic materials and granitic clastics, occasionally yielding silicified wood and organic remains (large fossils of molluscs and plants). It generally decreases in grain-size upward, composed of silty rocks in the uppermost part. While the Toki Lignite-bearing Formation consists of arkosic sandstone and conglomerate containing granite cobble to boulder, the Akeyo Formation is composed mainly of medium-grained tuffaceous sandstone. The Oidawara Formation is composed mainly of fine-grained tuffaceous sandstone and siltstone.

b) Seto Group
The Seto Group unconformably overlies the Mizunami Group. It is composed mainly of conglemerate containing granule to cobble, with a few layers (13m thick) of clay and sandy clay intercalated in the lower part. Constituent gravels of the conglomerate are granite, chert, rhyolite, mudstone and volcanic rocks, while the matrix is white-colored tuffaceous or arkosic.

ii) Geological structure

Faults
The Tsukiyoshi Fault is recognized east and west on the ground surface in the vicinity of the Shobasama site. It is a reverse fault with a strike of N80W, a dip of 70 and an estimated throw of about 30m in a gallery of the Tono Mine. Fault gouge (scores of centimeters thick) is recognized in the gallery of the Tono Mine, which seems to act as a impermeable layer.

Fractures in granite
Fracture investigations in the RHS Project include sketching and photographing of the outcrops with fractures as well as measurements of various parameters of the fractures as are shown in Tab.4.1¹⁵⁾.

It becomes clear that two trends (NNW-SSE and NE-SW) of fractures are dominant in the Toki Granite. Small faults are recognized at the outcrops, but large-scale ones except for Tsukiyoshi Fault are not found.

On the other hand, quartz porphyry dikes (roughly vertical, several tens of meters wide) are found in the central (Kawai district, Toki City) and southern parts (Dachi district, Toki City) of the Toki Granite. The strikes of those dikes are mostly NS to NNW-SSE. Small-scale dikes are observed as quartz veins (less than 10cm wide) at the periphery of the granite with the strike of NNW-SSE. The strikes of those dikes tend to be N-S to NNW-SSE, suggesting they are extensional fractures. However, some dikes with the same strikes are clearly shear fractures. Therefore, the dikes represent mixed origins.

To see relationships between lineaments and fractures, strike of fractures at each outcrop is compared with that of seemingly corresponding lineament. The results show that both strikes are well-matched. Each of the ten blocks (See Chapters 4.1.2 1) (1), Fig.4.1.(2)) proves to have different prevailing fracture trend as is shown in Tab.4.2. It shows that the prevailing fracture trend is consistent with lineament trend in each block.

It implies that it is possible to guess dominant fracture trend using trend of the linearments in the block.

(3) Ground geophysical survey

Regarding ground geophysical survey, the results of ground electromagnetic survey in the RHS Project is available. It is carried out to estimate the depth of conformity between sedimentary rocks and granite and structures in the granite. Furthermore, the results of reflection/refraction seismic survey, carried out to understand the geology and geological structure in the RHS Project and Shaft Excavation Effect Experiment are also available. Details of those surveys are shown in Tabs.4.3 and 4.4. Dynamite as well as small-size hydraulic impactors are used as the seismic source.

^*:1count��4,096points�~3stacks

Table 4.4 Details of reflection / refraction seismic survey

Reflection seismic survey (See Fig.4.4)	Line-R-1 (1,700m)	Seismic source : dynamite Seismic source interval : 70160m Receiver interval : 10m
	Line-R-2 (1,900m)	Seismic source : dynamite Seismic source interval : ca.100m Receiver interval : 10m
Refraction seismic survey (See Fig.4.4)	Line-2-1�i500m�j Line-2-2�i500m�j Line-2-3�i500m�j	Seismic source : dynamite Seismic source interval : 5m Sampling rate : 1ms Data length (Recording time): 1s
	Line-1�i650m�j	Seismic source : Impactor Seismic source interval : 4m Sampling rate : 1ms Data length (Recording time): 1s

Size Length, Width , Height	Weight	Impact energy	Rod weight	Baseplate weight	Impact frequency	Maximum tilt angle
2.5m,1.0m,2.2m	1.2t	2000J	65kg	65kg	10sec	30

i) Ground electromagnetic surveys (MT method / CSMT method)^15),27)

MT (Magneto-Telluric) method is a way to estimate underground resistivity distribution using natural or artificially induced electromagnetic signal (geomagnetism). In this survey, both natural and artificially induced signals are utilized for MT and CSMT methods, respectively. Data stations number 144, and two components for both electric and magnetic fields are measured. For each point, single dimentional analysis assuming horizontal multi-layered structure is performed. 2-D analysis is carried out for five survey lines as is shown in Fig.4.2.

A horizontal resistivity distribution map of single dimension analysis at an elevation of 200m (Fig.4.3) reveals extended low resistivity areas around the Mizunami sedimentary basin. These are towards Tono Mine to the west, and towards Shirakura, Hosokute and Shukubora to the north. Another low resistivity area is found in the NW part of study area, from Misano to Tsubashi. According to the results of resistivity logging, it is estimated that resistivity area lower than 80m corresponds to sedimentary rock of Seto and Mizunami Groups, while area higher than 80m corresponds to granite and other basement rocks. Therefore, above-mentioned low resistivity areas may correspond to ancient river channel structure on the surface of the granite.

Fig.4.3 shows that low resistivity areas corresponding to the sedimentary rocks do not extend to deeper than 0m in elevation. It is estimated that the area deeper than 0m in elevation is occupied by high resistivity basement rocks. This is consistent with the results obtained by borehole investigations. Also it indicates that the depth distribution of unconformity between granite and sedimentary rocks can be estimated using the result of this survey.

ii) Refraction seismic survey^15),28)

Refraction seismic survey uses differences in arrival times of seismic wave at different measurement points. Using these data, estimate seismic wave velocity structure and thickness of each layer can be estimated. This method has been widely used to determine geological structure and rock condition in the study fields of resource exploration and civil engineering.

The length of the survey line is set taking the thickness (up to ca.150m) of Neogene strata into consideration (Tab.4.4, Fig.4.4). Receiver interval is 10m, and source interval is 70160m.

As is shown in Fig.4.5 (Survey Line-R-1), the Neogene strata are divided into horizontal three units based on seismic wave velocity. Also, depth and shape of unconformity between Neogene strata and granite are estimated. The results are consistent with the data obtained from the boreholes near the survey line. The seismic wave velocity of the granite is 4km/sec in the valleys, while it is 56km/sec in hills on both sides of the valley. It implies that the fractures have developed more in the granite in the valley than in the hills.

The fracture zone accompanying Tsukiyoshi Fault may correspond to low velocity zone (1.2km/sec) at 519568m on the survey line. The width of the fracture zone is estimated to be about 50m, much wider than the width of the clay observed along the fault in sedimentary rocks. Also, two following low velocity zones are recognized :
NE of Tsukiyoshi Fault, 271350m on the survey line : (velocity : 1.7km/sec)
SW of Tsukiyoshi Fault, 1,3331,362m on the survey line : (velocity : 0.6km/sec)
This implies existence of faults or subordinate fault of the Tsukiyoshi Fault.

iii) Reflection seismic survey³⁸⁾

This survey gives higher resolution than the other geophysical surveys. Also, it can be used to know geological structure in two dimensions. For these reasons, it is widely used in many kinds of study area.

As is shown in Fig.4.6, geological structure down to 200m in depth is estimated^15),29). In this cross section, Tsukiyoshi Fault is represented as discontinuities of reflections within Neogene strata. The result also shows unknown subordinate faults.

One of the results of reflection seismic survey carried out in the Shaft Excavation Effect Experiment is shown in Fig.4.7. Also in Fig.4.7, the results (cross section) of the same kind of survey carried out for Tsukiyoshi Uranium deposit is shown. Nine reflection plains recognized by this survey roughly coincide with the geological strata : the top of the Akeyo Formation, a bedding plane in the Akeyo Formation, the top of the Upper Toki Lignite-bearing Formation, the top of the Lower Toki Lignite-bearing Formation, two bedding planes in the Lower Toki Lignite-bearing formation and the top of the basement granite.

(4) Borehole investigations

Borehole investigations are mainly carried out aiming at sedimentary rocks. For example, surveys for the Tsukiyoshi uranium deposit^20),21) and the Shaft Excavation Effects Experiment (12 TH-series boreholes²²⁾, 8 AN-series boreholes, 6 SN-series boreholes and 1 HN-series borehole)³⁰⁾ (Fig.4.8). The borehole investigations confirm the validity of geological stratigraphy estimated by the ground geological surveys.

Contour maps^{20), 21), 31)} of the basement rock in the Tono area compiled through borehole investigations and other surveys on the Tsukiyoshi uranium deposit, indicate that the basement granite has channel structures.

Borehole investigations carried out for the Shaft Excavation Effects Experiment reveals a correlation between the lithofacies (e.g. grain-size) of sedimentary rocks and their apparent resistivity/permeability obtained by electrical logging. These surveys also reveal a high permeability of conglomerate layers in the Lower Toki Lignite-bearing Formation and a low permeability of the Oidawara and Upper Toki Lignite-bearing Formations^{32), 33)}.

Drilling of the AN-1 and the AN-3, core descriptions³⁴⁾, geophysical loggings and BTV investigations are carried out in the Shobasama site to develop methodologies and techniques for the rock mass evaluation (Tab.4.6). The results of borehole investigations in the AN-1 indicate that the granite could be divided into three segments according to shapes of fractures, the varieties/characteristics of fracture fillings, and the fracture density³⁵⁾. These three segments are Segment I: Ground surface Ground level (henceforth "GL")-300m; Segment II: GL-300m GL-420m; Segment III: GL-420m ). The results of application tests of radar instruments carried out in the AN-1 and AN-3 indicate that there is a zone characterized by a high decay rate of electromagnetic wave amplitude between the ground surface and about 150m in depth³⁶⁾. However, there is no more information on the continuity of these segments and the high decay rate zone. Thus it is not clear whether or not this division is applicable to the surrounding rock mass as the representative data of the Shobasama site.

Table 4.6 Details of borehole investigations (AN-1, AN-3)

	AN-1	AN-3
Depth (m)	1,000	408
Diameter	HQ (ca.100mm)	HQ (ca.100mm)
Drilling fluid	Fresh water	Fresh water
Geophysical logging*
BTV investigations
In-hole hydraulic test	(33 points)	(24 points)
Laboratory tests using rock specimen	Apparent density (20 points) Effective porosity (20 points) Water ratio (20 points) Seismic wave velocity (20 points) Uniaxial compression test(20 points) Brazilian test (40 points)	-
Hydraulic fracturing test	(20 points)	-

^* : Electrical, Micro resistivity, Density, Neutron, Gamma-ray, Acoustic, Temperature, Caliper and Deviation

2) Results of the Phase I-a

Reflection seismic survey and borehole investigations (MIU-13) are carried out in the Shobasama site in the Phase I-a. On the basis of the result of these investigations, geological model is constructed. Details of the investigations are as follows.

An electric survey is carried out in the Shobasama site (survey line : N-S, 200m, Tab.3.1), however, accurate result is not obtained because of the existence of a low-resistivity zone in a shallow part of the site. Also, application test of remote-reference method in magnetoelectric survey (MT method) is carried out aiming at understanding the geological structure in deep part of the Shobasama site. However, significant data is not obtained because noise is not negligible. Thus the results of these surveys are omitted in this report.

(1) Reflection seismic survey^37),38)

Reflection seismic survey is carried out to aim at obtaining data concerning geological structure, dinsontinuity and the shape of unconformity. Survey lines run N-S and E-W as are shown in Figs.4.4 and 4.9. These data are used to construct geological model. Details of the reflection seismic survey are shown in Tab.4.7.

Some continuous reflection planes are detected above an elevation of 100m throughout the both survey lines. They are consistent with the shape of unconformity between the sedimentary rocks and the basement granite and the internal structures of the sedimentary rocks (Fig.4.10). While partial discontinuities (SF-13 in Fig.4.10) are recognized in the reflection planes, it is not confirmed yet whether or not they represent faults.

Insufficient lengths of the survey lines and strong reflections in the sedimentary rocks and at the upper part of the granite might reduce the reliability of the result below an elevation of 200m.

(2) Borehole investigations^{39), 40), 41)}

Borehole investigations are one of the most important methods to investigate the underground geology and geological structure. It allows collecting core samples and measuring properties of the rock mass and groundwater using various instruments in the borehole.

In the Phase I-a, core descriptions, geophysical loggings and BTV investigations are carried out in three 1,000m-class boreholes (MIU-13). Furthermore, petrological and mineralogical studies are carried out using collected core samples from these boreholes.

The core descriptions include recordings of drilling depth, lithofacies, rocks' name, texture, grain-size, mafic mineral ratio, color, weathering, alteration, rock mass grade, RQD, core recovery rate, fracture shape, fracture type and fillings of fractures. As for geophysical logging, electrical logging, micro-resistivity logging, density logging, neutron logging, gamma-ray logging, acoustic logging, temperature logging, caliper logging and deviation logging are carried out. The BTV investigations record depth, dip, strike, shape, filling, and alteration of discontinuities such as fractures. As for petrological and mineralogical studies, modal and chemical composition analyses are carried out.

The results of above-mentioned investigations (core descriptions, geophysical loggings, BTV investigations and petrological and mineralogical studies) in the MIU-13 are described below. Besides, the overviews of the results in these boreholes are shown in Appendix 13.

i) Lithofacies of granite

Based on the results of core descriptions in the MIU-13, the granite in the Shobasama site is classified into 'Biotite granite' and 'Felsic granite'. Furthermore, the Biotite granite is subdivided into coarse-grained, medium-grained, and fine-grained ones.

According to the modal composition analysis of the granites found in the MIU-13, all of the granite come under the classification of granite by IUGS (1973) (Fig.4.11).
According to the chemical composition analysis, chemical compositions of the Biotite granite and Felsic granite are plotted on two different lines on the oxide content-depth diagrams (Fig.4.12).

ii) Characteristics of fracture distribution in the granite

In the MIU-13, sedimentary rocks occur from the ground surface down to GL-88m-89m, underlain by the Biotite granite. The uppermost part of the granite is occupied by ca.10�`15m-thick weathered granite.

Fig.4.13 shows changes in density, cumulative frequency, and direction of fractures with the depth in the MIU-2. Fig.4.14 shows frequency histograms of fracture density. According to the trend of fracture density, the granite is divided into following three structural part : "Upper fracture zone", "Moderately fracture zone" and "Fractured zone along the fault" in descending order. Each zone's characteristics are as follows.

"Upper fracture zone"
This zone ranges from the weathered granite down to GL-300-370m in the three boreholes, where the fracture density varies from 35 per meter (Tab.4.8). This zone is characterized by the prevailing fractures with a low inclination (Fig.4.15, Tab.4.8).

"Moderately fracture zone"
This zone occurs between the "Upper fractured zone" and undermentioned "Fracture zone along the fault", ranging from 13 per meter in fracture density in the three boreholes (Tab.4.8). Like the underlying "Fracture zone along the fault", this zone is dominated by low-inclination, high-inclination (strike : E-W, dip : S) (strike : NE-SW, dip : SE), and medium-inclination (strike : E-W, dip : N) (Fig.4.15, Tab.4.8).

"Fracture zone along the fault"
This zone is characterized by the concentration of fractures developed along the Tsukiyoshi Fault, ranging from 36 per meter in fracture density in the three boreholes (Tab.4.8). As for fracture characteristics, this zone is dominated by low-inclination, high-inclination (strike : EW, dip : S) and medium-inclination (strike : NNE-SSW, dip : WNW) fractures (Fig.4.15, Tab.4.8). Particularly, the strike and dip of most dominant ones (high-inclination, EW-strike and S-dip) are almost coincident with those of the Tsukiyoshi Fault.

In general, the "Upper fracture zone" and the "Fracture zone along the fault" are characterized by high permeability, whereas the "Moderately fracture zone" by low permeability (Fig.4.16).

Differences in characteristics of fractures (e.g. shapes and fillings) in the three fractured zones are left to be examined.

Table 4.8 Densities and prevailing directions of fracture of each fracture zone

	"Upper fracture zone"	"Moderately fracture zone"	"Fracture zone along the fault"
Average fracture density*	3�`5 /m	1�`3 /m	3�`6 /m
Prevailing inclination, strike and dip	Low	Low High, EW, S Medium, EW, N High, NE-SW, E	Low High, EW, S Medium, NNE-SSW, WNW

^* : Number of fracture obtained BTV investigations

iii) Physical properties obtained by geophysical loggings in the granite

In the MIU-13 are carried out electrical logging, micro-resistivity logging, density logging, neutron logging, gamma-ray logging, acoustic logging, temperature logging, caliper logging and deviation logging. Fig.4.17 shows the results of apparent resistivity (short-normal and long-normal) obtained from electrical loggings, porosity obtained from neutron logging, P-wave velocity obtained from acoustic logging. All of these are thought to be closely related to the permeability of the rock mass.

The results of comparison of porosity, apparent resistivity and P-wave velocity among the three zones of the granite are as follows.

Porosity
The average of the porosity of "Upper fracture zone", "Moderately fracture zone" and "Fracture zone along the fault" are 47%, 35% and 48%, respectively. When encountered by the Tsukiyoshi Fault, porosity averages ca.8% and ca.14% in the MIU-2 and MIU-3, respectively.

Apparent resistivity
The average of the apparent resistivity is smallest in "Fracture zone along the fault" and largest in "Moderately fracture zone". These averages are (SN(short-normal) : 8002,000m; LN(long-normal) : 1,8002,800m), (SN: 1,5002,500m; LN: 2,8003,500m) and (SN: 4001,500m, LN: 7001,600m) for "Upper fracture zone", "Moderately fracture zone" and "Fracture zone along the fault", respectively.

Local depressions of apparent resistivity appear at shorter intervals in the '"Upper fracture zone" than in the "Moderately fracture zone". When encountered by the Tsukiyoshi Fault, apparent resistivity averages are (SN: 400m; LN: 300m) and (SN: 100m; LN: 200m) in the MIU-2 and MIU-3, respectively.

P-wave velocity
The average of the P-wave velocity is smallest in "Fracture zone along the fault" and largest in "Moderately fracture zone". The averages are 4.85.1km/sec., 5.25.3km/sec. and 4.64.8km/sec. for "Upper fracture zone", "Moderately fracture zone" and "Fracture zone along the fault", respectively.

Local depressions of P-wave velocity (<5.0km/sec.) appear at shorter intervals in the "Upper fracture zone" than in the "Moderately fracture zone". When encountered by the Tsukiyoshi Fault, P-wave velocity averages lower than ca.4km/sec. in the MIU-2 and MIU-3.

iv) Characteristics of faults in the granite

The Tsukiyoshi Fault is recognized at GL-890-915m in the MIU-2 and at GL-693-719m in depth in the MIU-3. Both are composed of ca.1020m-wide cataclasite zone, around which ca.100m-wide fractured zones develop. Particularly, "Fractured zone along the fault" in the MIU-2 is much more permeable than the "Moderately fracture zone" (Fig.4.16).