The Journal of the Geological Society of Japan

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The present report contains the following articles, in which is described what the writer has studied on the geology and ore deposits of a part of the Unsan mine, north Korea, under the gui-dance of Pvof., Dr., Takeo KATO., Introduction-The mine was developed by James R., MORSE in 1895, and had been managed by the Oriental Consolidated Mining Company till it was bought by the Nippon Mining Company in 1939., Its mining claim is about 800km² broad and as in many other mines in that district is rich in numerous quartz veins of which some contain gold, The main gold veins are Tarakol, Tabowie, Tong-kol, Sambong, Candlesticks, Kuksan-ong, Maibong and Chittabalbie, of which the first two are directly mined by the company and the others with many minor ones by dredgers Tokutais who are subcontract miners, characteristic of that land., Placer gold is also mined by dredgers in the R., Kuyongan ( ?? ?? ?? )., The area where the study has been carried out is about 100km² broad, occupying the eastern corner of the claim., Geology-In the area we find metamorphic rocks, granites, dikes and the Quaternary sediments., The metamorphic rock complex, comprising the metamorphosed sedimentaries and the gray gneisses of the pre-Cambrian system, consists of mica-schist, mica-quartz-schist, granulite, mica-gneiss, granite-gneiss., metamorphosed pegmatite, amphibolite, biotite-amphibole-gneiss and injection-gneiss., The granites, which are classified into two-mica-, Kodang( ?? ?? )-porphyritic, muscovite-, biotite-, schistose biotite-, Kututong( ?? ?? ?? )-porphyritic, and migmatitic varieties, occur as a composite batholith and sheets intruding the metamorphic rocks., Of the granites the first three are considered to be of the Bukkokuzi series, Mesozoic, but the last four are of unknown age, though the latter are intruded by the former., The rocks of dikes are porphyrite, pegmatite, aplite, quartz vein, and melanocratic rocks., Three major faults are observed in the area, along one of which hot springs issue., Ore Deposits-In the area in question some of the pegmatites and quartz veins, and the river deposit of the Kuyongan are auriferous, as is usual in the gold-fields of north Korea., The gold veins are tabular to lenticular in form, simple and massive in structure, as observed in outcrops, occur in almost all kinds of the rocks of the area, both the metamorphic rocks and granites, which are slightly altered in general., From the modes of occurence and mineral composition they are classifled into 6 types-galena-quartz, pyrite-quartz, pyrite-quartz, pegmatitic, muscovite-quartz, and simplequartz veins, each forming a peculiar vein are., In north Korea and south Manchuria most veins belong to hypo-to mesothermal gold-quartz veins, related to intrusions of granites, and it is doubtless that those of the area under consideration are of the same type., But it is not easy to point out the ore-bringer among various granites., When we examine types of veins and vein areas, we see zonal arrangement of ores around the Bukkokuzi granite, as an igneous centre., Therefore, it is most probable to conclude that thisgranite is the ore-bringer., From the microscopic as well as field examinations it is concluded that the veins were forme by the following process: (1) formation of vein fissures, (2) deposition of barren pegmatites and quartz veins, accompanying carbonates and muscovite, (3) reopening of fissures in barren veins, (4) deposition of muscovite, chlorites, carbonates and sulphides., Of the sulphides, pyrrhotite deposited abundantly at the beginning and galena at the end., Gold was accompanied chiefly by galena.,

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