• The Journal of the Petrological Society of Korea
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• v.12 no.2
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• pp.79-99
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• 2003

Muscovite and biotite from 52 metasediments and 5 granites in the Hwasan area, the southwest of the Okcheon metamorphic belt and the Miwon-Jeungpyeong area, central Okcheon metamorphic belt were dated by the K-Ar and $^{40}$ Ar/$^{39}$ Ar methods. Muscovite and biotite ages from metapelitic and psammitic rocks (metasediments) of the Boeun and Pibanryeong units in the Hwasan area are concentrated in the mid-Jurassic (149-180 Ma). K-Ar and $^{40}$ Ar/$^{39}$ Ar ages for metapelitic and psammitic rocks of the Boeun and Pibanryeong units in the Miwon-Jeungpyeong area show complicated age distribution. Muscovite and biotite ages are classified by three groups, 142-194 Ma, 216-234 Ma, and 241-277 Ma. Younger (Cretaceous) ages occur only in metasediments close to Cretaceous granitic rocks in the southeastern region and the older ages of 216-277 Ma are restricted to the middle Part of the Jeungpyeong area. Most ages in the other area of the central Okcheon metamorphic belt fall between 142-194 Ma (Jurassic). K-Ar and $^{40}$ Ar/$^{39}$ Ar ages for granite from the northern part in the both the southwest and central Okcheon metamorphic belt also gave middle Jurassic ages (156-168 Ma). The similar ages from both metasediments and granites in the study areas indicate simultaneous cooling of both rocks to 300-350$^{\circ}C$ during the middle Jurassic. The state of graphitization of carbonaceous material of all metasediments in the study areas Indicates fully ordered graphite falling within a small range, from 3.353 to 3.359 ${\AA}$, which indicate amphibolite facies regional metamorphism. In the southern sector of the Boeun unit from the Hwasan area, metamorphic grade indicated by mineral paragenesis during regional intermediate-P/T metamorphism is greenschist facies. Whereas, the $d_{002}$ values for carbonaceous materials in the same sector show fully ordered graphite (ca. 500$^{\circ}C$) indicating amphibolite facies. This result with the concentration of mica ages of metasediments into the middle Jurassic, the presence of low-P/T thermal metamorphic zone (>500$^{\circ}C$) in the metasediments close to the Jurassic granite and the regional intrusion of Jurassic granites and their middle Jurassic intrusion and cooling ages may indicate the low-P/T regional thermal event during the early(\ulcorner)-middle Jurassic after main intermediate-P/T metamorphism which formed main mineral assemblage regionally in the study area. The regional thermal event failed, however, to reset the mineral assemblage of regional intermediate-P/T metamorphism except for narrow aureole (1-2 km) around Jurassic granite because e duration of thermal effect was relatively short by repid cooling of the Jurassic granite. In the middle part of the Jeungpyeong area, central Ogcheon metamorphic belt, muscovite and biotite K-Ar ages from 5 samples are 263-277 Ma and 241-249 Ma, respectively. An intermediate-P/T metamorphism is currently accepted to have occurred between 280 and 300 Ma. Therefore, the muscovite and biotite ages can be interpreted as cooling ages after Ml metamorphism indicating rapid cooling to ca 350$^{\circ}C$ between 280-300 Ma and 263-271 Ma, and biotite ages indicate slower cooling to ca. 300$^{\circ}C$ between 263-277 Ma and 241-249 Ma. However, more detail study is needed to confirm why the Permian to Triassic ages occur only in the middle Part of the Jeungpyeong area.a.

• Economic and Environmental Geology
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• v.12 no.3
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• pp.147-176
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• 1979

The Yeonhwa II zinc-lead mine is characterized by a dozen of moderately dipping tabular orebodies of skarn and zinc-lead sulfides, developed in accordance with the ENE-trending bedding thrusts and bedding planes of the Pungchon Limestone and underlying Myobong Formation, mostly along the contacts of a ENE-trending sill and a NW-trending dike of quartz mononite porphyry. The orebodies occur in three groups: (1) the footwall Wolgok orebodies with respect to the sill, (2) the hangingwall Wolgok orebodies, and (3) the Seongok orebodies extended from dike contacts into carbonate beds. Mineral compositions of these orebodies are dominated by calc-silicates (skarn) associated with ore minerals of sphalerite, galena, and chalcopyrite, as well as sulfide gangue of pyrrhotite. A pair of exo- and endo-skerns in the Wolgok footwall contact aureole between the Pungchon Limestone and quartz monzonite porphyry on the -120 level represents a well-developed symmetrical pattern of mineral zoning: a garnet/quartz zone in the center of exoskarn, two zones of pyroxene with ore minerals on both sides of the garnet/quartz zone, further outwards-an epidote/chlorite-bearing hornfelsic zone in the Myobong slate beyond a zone of unaffected limestone, and an epidote-dominated zone of endo skarn on the opposite side toward fresh quartz monzonite porphyry. These features indicate a combination of two effects on the skarn formation: (1) differences in composition of the host rocks(sedimentary and ignous), and (2) progressive outward migration of inner zones on outer zones on the course of metasomatic replacement of the pre-existing minerals. Microprobe analyses of garnet, pyroxene, pyroxenoids, epidote, and chlorite for nine major elements on a total of 23 mineral grains revealed that: the pyroxenes are hedenbergitic, in most zones, with a gradual decrease of Fe- and Mn-contents toward the central zone, whereas the garnets are andraditic in outer zones, but are grossularitic in the central zone. This indicates a reverse relationship of Fe-contents between pyroxene and garnet across the exoskarn zones. Pyroxenoids are lacking in wollastonite but are dominated by pyroxmangite, rhodonite and bustamite, indicating a Mn-rich nature in bulk chemistry. Pseudomorphic fluorite after garnet occurs abundantly reflecting a fluorine-enhanced evidence of the skarn-forming fluids. Epidote contains 0.19-0.25mole fraction of pistacite, and chlorite is Mn-rich but is Mg-poor. Sulfide mineralization took place with the most Fe-rich pyroxene rather than with garnet as indicated by the fact that the highest value of hedenbergite mole fraction occurs in the ore-bearing pyroxene zone. The Yeonhwa II ores are characterized by high zinc and low lead in metal grade, with minor quantity of copper content in almost constant grade. The hangingwall Wolgok and Seongok orebodies, that formed in a more open environment with respect to their local configurations of geologic setting, are more variable in metal grades and ratios, than are the footwall Wolgok orebodies formed in a more closed condition in a narrow interval of sedimentary beds.

• Journal of Biosystems Engineering
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• v.6 no.2
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• pp.20-32
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• 1982

This survey was conducted to investigate the present status of farm tractor utilization for obtaining a basic reference to the establishment of the government's agricultural mechanization strategies. Thirty two counties from the eight provinces except Jeju were covered in this study. From these selected areas, 433 sample farms having farm tractor were taken to obtain the general informations by the enquete, and 93 sample farms among them to investigate the status of daily tractor use in the year of 1980. The analyzed results are summarized as follows: 1. Farm tractors owned by the rice-oriented farms holds 71.5 percent of the total number of tractors the livestock-oriented farms 17.0 percent, and the orchard-oriented farms 7.0 percent. Among the farm tractors 64.3 percent was a large size (46ps) and 35.7 percent a small size(19~23ps). 2. Most of the tractors surveyed were equipped with the essential attachments such as plow and rotavator. About 18 percent of the tractor owners had no trailer, which seemed too high considering the large percentage of tractor use for transportation. The availability of other attachments was very low except a grader on the rice-oriented farms and a hay harvester and a front loader on the livestock-oriented farms. 3. The average size of farm was 3.9 hectare for the rice-oriented farms, 13.9 hectare for the livestock-oriented farms and 7.4 hectare for the orchard-oriented farms. It was obious that the average farm size of was too small compared to the theoretical machine capacity of the tractors. 4. About 70 percent of the tractor operators were in the age of twenties and thirties. About 90 percent of them had an educational level of middle school graduate or above even though their technical level was very low. 5. Any particular problem in tractor use was not found in this survey. From the farmer's preference for purchasing a new tractor, however, it is estimated the demand on a 20-30ps tractor will be more increased. 6. The average annual use of tractor was of about 100 days or 400 hours. It appeared that the rice-oriented farms used most with 412.4 hours per year, and followed by the livestock-oriented farms with 403.6 hours, the orchard oriented farms with 377.7 hours. 7. Among the total hours of tractor use, 47.3 percent was for transportation, and 41.6 percent was for plowing and rotary tillage. The largest portion of the annual tractor use was taken by transportation on the livestock-oriented farms, by land preperation on the rice-oriented farms, and by loading and chemical spraying on the orchard-oriented farms. 8. The hours of tractor use had a peak in May. The hours of use for own farm was remarkably different among the different farm oriented, but there was no considerable difference between the too different sizes of tractor. 9. The hours of tractor use decreased as the age of the operator or the educational level increased. The reason might be that the operators who had a high educational level or were older had a tendency of disliking custom works. 10. The average custom use of tractor was 171.3 hours per year, and the ratio of custom work was 63.7 percent on the rice-oriented farms, 31.7 percent on the livestock-oriented farms and 22.4 percent on the orchard-oriented farms. Among the custom works, the most popular one was the grader leveling. 11. The charge on custom work was about 40,000 Won per hectare for plowing and rotary tillage, and it was the most expensive in the southeastern region, and next followed by the southwestern region. 12. The average plowing capacity of the small tractor was 7.8 hours per hectare in the paddy field, and that of the large tractors was 4.3 hours per hectare. The average rotary-tilling capacities of the small and the large tractors were 6.5 and 4.3 hours per hectare, in the paddy field respectively.