沃川帶의 地質 및 鑛物資源에 關한 硏究

Studies on geology and mineral resources of the Okchŏn belts - geological structure of the areas between Pyŏngchang, Yŏngwŏl and Jechŏn -

The geological structures and some of the stratigraphy in the area studied are being thought to be ambiguous and controvertible. The present study intended to clarify these ambiguities by correct interpretation of the geological structures and lithostratigraphy of the area concerned. The so-called “Sambangsan formation”, which was designated as an unknown age by the Taebaksan Geological Investigation Corps (1962) and as the mid-Cambrian age by T. Kobayashi (1966) and I.S. Kim (1983), has been determined by the present study as the Hongjŏm series of Carbo-Permian age resting unconformably on the Cambro-Ordovician limestone formations. This determination was supported by conodont study concurrently carried out by I.S.Kim. The so-called “Daehari formation”, which was renamed by the later study group after the original “Sambangsan formation” distributed in the area from southwest of Sambangsan toward southwest to Juchŏn, possesses more or less the same lithlogy as “Sambangsan formation” of the old designation in the eastern of the area, but different lithology in the western localities where Sadong formation, the basal sandstone member of the Kobangsan formation and the green shale member of the Nokam formation are cropped out. The narrow belt of the complex mixture of the Pyŏngan group in-between limestone formations extending over 16km with a width of 500m to 1000m was formed by the faults: the northern boundary with the limestone formations is a fault contact all the way through entire area and the southern boundary is either fault contact in most of the area and unconformity in some other area. The Hongjŏm formation on the Mt. Sambangsan shows rather steeply dipping nearly isoclinal folds which plunges 10° to 20° southward. There are also field evidences that the limestone formations distributed in both north and south of the Hongjŏm formation (erstwhile “Sambangsan formation”) along the Sambangsan ridge are the same formations and show the same folding as the Hongjŏm formation. Therefore, these limestone formations should be rezoned in the light of the new structural interpretation although they were differently designated in the previous studies as Pyŏngchang and Yŏngwŏl-type of the Josŏn Group. The structures developed in the area mostly faults, which acted as one of the guides for the new interpretation of the geology and structure of the area are described and shown on the geologic map.