An exploration program conducted by Akenobe Mining Co., Ltd. has resulted in a discovery and development of the Chiemon copper-zinc-tin vein swarm localized at the southwestern part of the Akenobe vein-type deposit. The Chiemon vein swarm has salient characteristics as follows: (1) it is far from known veins in the Akenobe deposit; (2) it has many ore shoots in the lower part; (3) it consists of many branchs or parallel veins; (4) it is essentially blind.
A history of the development of the Chiemon vein swarm to date is summarized below:
(1) In 1955, a crosscut at -2 level (340 m above sea level) was undertaken first in the Chiemon area, but his program was stopped in 1959 because of its poor mineralization.
(2) In 1969, a crosscut was again opened at -4 level (280 m above sea level), and the remarkable mineralization was found at the lower elevation. During the period from 1969 to 1972, active exploration works including underground geological survey, crosscutting, drifting, raising and diamond drilling were operated mainly between -4 and -8 levels.
(3) Based on the results of this exploration, during the period from 1973 to 1980, the exploration and development works were carried out between -9 and -14 levels. It realized that the Chiemon vein swarm was predominant mainly below -10 level.
(4) Since 1981, a trackless system has been introduced to prospect and develop for the levels deeper than -14 level (the present bottom is -17 level) in the Chiemon area.
Our exploration philosophy for the Chiemon vein swarm is summarized as follows.
(1) Based on the analysis of the post-ore movement caused by major faults, an exploration target of the Chiemon area is extended to -20 level.
(2) Assay maps indicate that ore shoots generally pitch toward south. This fact suggests that ore shoots were situated in deeper levles in the Chiemon area.
(3) It is neccessary for the exploration to pay special attention to two remakable mineralizations distinguished in the Chiemon vein swarm, an earlier chalcopyrite-sphalerite stage and a later cassiterite-ferberite-quartz stage.
(4) Vein fractures and ore shoots of the Chiemon vein swarm are developed mainly in the basic lava of brittle nature (the upper Permian Maizuru Group).
(5) Chiemon No. 4 vein, a champion of the swarm, is considered to have been a channel way of ascending ore solution. Most or other veins are localized around this champion vein as branchs or parallel veins.
(6) For the complicated vein system, systematic short hole (less than 50 m) and shallow hole (100-200 m) drilling operations many useful indications to the exploration program.
Current ore reserves of the Chiemon vein swarm have totalled about 2, 000, 000 metric tons of minable ore, averaging 1.78% of copper, 6.25% of zinc and 0.42% tin. Based on geology of the ore deposit, it is highly expected that ore reserves of the Chiemon vein swarm (including the Monju vein swarm) will be increased more than 1, 000, 000 metric tons by future exploration and development works.

View full abstract

Pyrometasomatic lead and zinc deposits of the Nakatatsu mine are embedded in skarn zones replacing the Fujikuradani formation of Paleozoic age. Known were Nakayama, Hitokata and Senno deposits occurring from east to west.
Systematic exploration has been carried out in Kurotodo area, the western side of the Nakatatsu mine, on the basis of studies of geological structure, assemblage and distributions of skarn minerals, and characteristics of mineralization. The exploration has resulted in discovery of the Kurotodo ore deposit that consists of numerous massive orebodies in a hedenbergite and garnet skarn zone embedded between limestone and sandstone-slate strata.
Another systematic exploration has been carried out in deeper levels of the Nakayama deposit as well by applying the study of geological structure, skarn mineral zoning and characteristics of mineralization. As the result of exploration, many massive and bedded orebodies have been discovered in hedenbergite and garnet skarn zones, especially in hedenbergite skarn zones, embedded concordantly with general structure of the Paleozoic strata.
A total ore reserve obtained recently at the Kurotodo deposit and deeper levels of the Nakayama deposit has amounted to 1.15 million tonnes (grade Ag 43 g/t, Pb 1.20%, Zn 6.7%) and it contributes greatly to stable operation of the Nakatatsu mine.

View full abstract

The trace elements, such as Ba, Sr, and Rb, were systematically used to decipher the differentiation process of the Jurassic and Cretaceous granitic rocks of South Korea.
From Ba, Sr, and Rb relationships of the Cretaceous granitic rocks in both Kyongsang basin and Ogcheon zone, it is suggested that the Cretaceous granitic rocks were mainly formed by fractional crystallization of parental magmas.
Quartz diorite (Jindong granite) in the Kyongsang basin has the chemistry of crystallized melts, as opposed to cumulate-like chemistry. While, granodiorite, adamellite, and granite (Bulgugsa granite, masanite, hypersolvus granite, and Cretaceous granitic rocks in the Ogcheon zone) have the chemistry between crystallized melts and cumulus crystals. This fact suggests that perfect separation of cumulus crystals from intermediate and felsic melts is unlikely, and some trapped intercumulus melt may be anticipated.

View full abstract

Stability of braunite and associated phases in parts of the system Mn-Fe-Si-O is experimentally deter-mined using synthetic bixbyite and quartz as starting material by Tuttle-type bomb and piston-cylinder apparatus under Mn₂O₃-Mn ₃O₄ and Mn ₃O₄-MnO buffers. Some phase boundaries have been bracketed by reverse runs. Mixture 1 with bixbyite and quartz in 5:1 molecular proportion produces braunite+jacobsite at 675°C, 1 kb under Mn₂O₃-Mn ₃O₄ buffer and at 600°C, 1 kb under Mn ₃O₄-MnO buffer. Mixture 2 bixbyite and quartz (3.5:1) produces braunite+hematite+quartz under Mn₂O₃-Mn ₃O₄ buffer and braunite+magnetite+quartz under Mn ₃O₄-MnO buffer at 550°C, 1 kb. The former assemblage breaks down to jacobsite+pyroxmangite at 675°C, 1 kb while the latter to jacobsite (2 ph)*1+tephroite+quartz at 650°C, 1 kb under the respective buffers. In mixture 3 composition (bixbyite: quartz=2.5:1), braunite+jacobsite+quartz assemblage is stabilized under both buffers at 550°C, but breaks down to tephroite+jacobsite (2 ph) (±quartz) at 750°C and 1 kb under Mn ₃O₄-MnO buffer. All the phase boundaries are rather insensitive to pressure upto 7 kb.
The important conclusions of this study are: (a) stability of tephroite is restricted to Mn ₃O₄-MnO buffer even under suitable bulk composition, but this phase can appear in the so far unreported non-carbonatic situations, (b) upper stability of braunite is extended to higher temperatures at higher fO ₂ and the lower stability is extended to lower fO ₂ as compared to the Fe free system, (c) stability of bixbyite is reduced in low silica bulk composition with the lowering of fO ₂, (d) the assemblage jacobsite+pyroxmangite and jacobsite (2 ph)+tephroite are restricted to a narrow range of bulk composition and fO ₂.
Chemical composition of the synthetic phases reveals that the Fe content of braunite varies depending on the bulk composition and temperature of equilibration, but that of silica is restricted to a narrow range. In coexisting braunite and jacobsite, Fe is preferentially partitioned to braunite with increasing temperature, while Mn is partitioned to jacobsite. Jacobsite equilibrating with pyroxmangite has the highest Fe/Mn ratio, while when equilibrating with tephroite+quartz, it has the lowest Fe/Mn ratio.

View full abstract

The partial pressure of sulfur is an important factor in the equilibria of metal sulfide systems, the genesis of ore deposits, and in the preparation of sulfide semiconductors. Thermoelectric power, which is one of the semiconducting properties, can easily be measured by using particulate mineral samples. Therefore, an Eh-pH diagram, in which semiconducting properties could be predicted on the stable region for the metal sulfide, would be very useful. Such a diagram was constructed for the Pb-S-H₂O system at 200°C (473 K) by introducing isobaric curves of the partial pressure of sulfur obtained from the vapour pressure of elemental sulfur, and by extrapolating reported data for preparation of semiconducting PbS at high temperatures to 200°C. It was shown that the stable region for undoped PbS on the diagram involved two regions for p- and n-type PbS. Measured values of thermoelectric power for particulate galena samples were briefly described. It was shown that galena samples from the kuroko-type ore deposits were p-type semiconductors, whereas those from the other vein-and skarn-type ore deposits were n-type.

View full abstract