• Economic and Environmental Geology
• /
• v.47 no.2
• /
• pp.107-119
• /
• 2014

NMC Moland mine, which is classified as a contact replacement or skarn deposit, has been interpreted to have been formed by Daebo igneous activity which intruded into the Joseon Supergroup, because it is quite closely located to Jecheon granite. However, an alternative interpretation was recently suggested that the mine could be related with the hydrothermal fluid originated from Cretaceous granitic rocks, bringing about skarnization and Mo mineralization. Here we present an interpretation on the source granite of the mine based on the gravity exploration: the gravity anomaly, unlike the surface geology, shows that the Muamsa granite could be the related granite of the mine, because its hidden subsurface structure is expected to be more widely extended to surrounding area of the mine and deeper than the Jecheon granite.

• Economic and Environmental Geology
• /
• v.23 no.2
• /
• pp.245-259
• /
• 1990

Petrochemical analyses of granitic rocks including trace element, REE and oxygen isotope were carried out to understand petrogenesis of plutonic rocks from the Chungju, Wolaksan and Jecheon granite batholiths, which might be related with tungsten-base metal-fluorite mineralization in the Hwanggangri metallogenic province. Different geochemical characteristics such as major and trace elements were found between Jurassic Daebo granitic rocks (Chungju, Jecheon, Wonju, and Boeun granitic rocks) and Cretaceous Bulgugsa granitic rocks (Wolaksan, Muamsa and Sokrisan granitic rocks). Cretaceous granitoids are characterized by high $SiO_2$and $K_2O$ contents and low $TiO_2$, $Al_2O_3$, MgO and CaO contents. They also have relatively high contents of trace elements(Zn, V, Co, Cr, Sr, and Ba) in comparison with the Jurassic granitoids. (Eu)/($Eu^*$) and $(La/Lu)_{CN}$ ratios of Jurassic plutons vary from 0.78 to 1.13 and from 26.02 to 30.5, respectively, while the ratios of Cretaceous ones range from 0.22 to 0.28 and from 4.42 to 14.2, respectively. The REE patterns of the Cretaceous and Jurassic granitic rocks have quite different Eu anomalies: large negative Eu anomaly in the former, and mild or absent Eu anomaly in the latter. The large Eu negative of Cretaceous granitic rocks are interpreted as a differentiated product of fractional crystallization of granitic magma deduced by Rayleigh fractionation model(Tsusue et al., 1987). Oxygen isotopic compositions of quartz for Daebo and Bulgugsa granitic rocks range from 9.98 to 10.51‰ and from 8.26 to 9.56‰, respectively. The Daebo granitic rocks enriched in $^{18}0$ suggest that the magma be undergone different partial melting processes from the Bulgugsa ones. Of the Bulgugsa granitoids, Wolaksan and Sokrisan mass have different contents of trace elements and ${\delta}\;^{18}0$ values of the silicate minerals, which indicate that they are not from the identical source of magma. Many mineral deposits are distributed in and/or near the Wolaksan and Muamsa granitic rocks, but a few mineral deposits are found in and near the Chungju and Jecheon granite batholiths. It might be depend on geochemisty of the related igneous rocks which have low contents of Ba, Sr, Co, V, Cr, Ni, Zn and high contents of Nb and Y, and on lithology of country rocks such as cabonate and noncarbonate rocks.

• Economic and Environmental Geology
• /
• v.19 no.spc
• /
• pp.3-17
• /
• 1986

Hundred mineral deposits including W-Mo, Pb-Zn-Cu, fluorite and talc occur in the Cambre-Ordovician limestone contacting with the Cretaceous Muamsa and Wolak granitoids in the Susanri-Hwanggangri mineralized zone. In most mineral deposits characterized by metasomatic replacement, skarn and hydrothermal vein types, two distinct tendencies were found as W-Mo mineralization in or/and near granitoid batholith and ($Pb-Zn-Cu(CaF_2)$) mineralization which is gradually increased toward the batholith. W-Mo veins of extensive vein system occupy northly striking fractures whilst $Pb-Zn-Cu-CaF_2$ veins strike northeast or northwest. In this work, three representative lead-zinc-copper deposits choosing the Dangdu, Useog and Eoksu mines were dealt with in detail. Skarn ore bodies in the Dangdu mine were grouped into early diopside rich clinopyoxene-garnet, barren skarn and ore bearing late hedenbergite rich clinopyroxene-garnet skarn. Temperature and $X_{CO_2}$, obtained from hedenbergite-andradite-calcite-quartz mineral equilibria in the Dangdu ore deposits were $580{\sim}650^{\circ}C$ and 0.15~0.3, respectively. Fluid inclusien evidence in the Useog mine indicates that main stage mineralization temperature ranges from 224 to $389^{\circ}C$ with a salinity of 2~17 equivalent wt. percent NaCl. Sphalerites from the Dangdu and Useog mines have 16~17.7 mole percent in FeS which is relatively consistent to those of some other lend-zinc ore deposits in South Korea. Filling tcmjCerature of fluid inclusion frem the Eoksu mine shows deposition of ore within the temperature ranges from 237 to $347^{\circ}C$ and within the salinity ranges from 2.6 to 10.77 equivalent wt. percent NaCl.

• The Journal of the Petrological Society of Korea
• /
• v.4 no.2
• /
• pp.153-167
• /
• 1995

Emplacement ages for the granite plutons of the Jurassic and the Cretaceous times in the central Ogcheom Fold Belt were determined by Rb-Sr whole rock and mineral isocheon methods. In addition mineral ages for the plutons were determined by K-Ar and fission track methods. In turn, thermal histories and uplifting rates of the granitic bodies are elucidated from the isotopic ages. The Jecheon(~203 Ma) and Mungyeong(at lest~200 Ma) granites of the Jurassic and the Muamsa, Wolagsan and Daeyasan granites(~110 Ma) of the Cretaceous show high strontium initial ratios [$(^{87}Sr/^{86}Sr)_1$0.7100],suggesting that the granitic magmas have been generated by partial melting of crustal materials (S-type), or by mixing of mantle and crustal materials. Only mineral ages of the Sogrisan and Hyeongjebong granites (~90 Ma) were determined by K-Ar method, and petrogenesis of them were not defined yet. The two Jurassic granite plutons were cooled rapidly down to $300^{\circ}C$, right after the plutons were slowly cooled down since then, due to their deep emplacment. During the Middle Cretaceous period, the Jurassic Mungyeong granitic pluton was intruded and thermally affected much by the surrounding Wolagsan and Daeyasan granites. Accordingly the Rb-Sr mineral age, K-Ar hornblende and biotite ages of the Mungyeong granite appear to be reduced or reset due to the thermal effects above their blocking temperatures. All the cretaceous granites have been cooled much ore simply and rapidly down than the Jurassic ones below $300^{\circ}C$, owing to their shallow emplacement.

• The Journal of the Petrological Society of Korea
• /
• v.28 no.2
• /
• pp.143-156
• /
• 2019

We carried out the sensitive high resolution ion microprobe zircon U-Pb age dating and whole rock geochemical analysis of granites in the Gudambong and Sainam geosites, Danyang Geopark. The granites crop out in the western and southern parts of Danyang County, and intruded sedimentary successions of the Yeongweol and Taebaek Groups, respectively. The U-Pb isotopic compositions of zircon from the Gudambong and Sainam granite samples yielded the Cretaceous intrusion ages of $90.4{\pm}0.5Ma(t{\sigma})$ and $90.0{\pm}1.5Ma(t{\sigma})$, respectively. The major and trace elements compositions of the samples showed an affinity of typical A-type granite, indicating their petrogenesis during the late stage of the Bulguksa orogeny or a tectonic dormancy. The geochronologic and geochemical results are identical to those of granites previously reported from the Cretaceous Muamsa and Wolaksan suites.

• Economic and Environmental Geology
• /
• v.30 no.6
• /
• pp.505-517
• /
• 1997

Lead and zinc mineralization of the Kwangsin mine was formed in quartz and carbonate veins that filled fault-related fractures in the limestone-rich Samtaesan Formation of the Chosun Supergroup and the phyllite-rich Suchangni Formation of unknown age. A K-Ar date of alteration sericite indicates that the Pb-Zn mineralization took place during Late Cretaceous (83.5 Ma), genetically in relation to the cooling of the nearby Muamsa Granite (83~87 Ma). Mineral paragenesis can be divided into three stages (I, II, III): (I) the deposition of barren massive white quartz, (II) the main Pb-Zn mineralization with deposition of white crystalline quartz and/or carbonates (rhodochrosite and dolomite), and (III) the deposition of post-ore barren calcite. Mineralogic and fluid inclusion data indicate that lead-zinc minerals in middle stage II (IIb) were deposited at temperatures between $182^{\circ}$ and $276^{\circ}C$ from fluids with salinities of 2.7 to 5.4 wt. % equiv. NaCl and with log $fs_2$ values of -15.5 to -11.8 atm. The relationship between homogenization temperature and salinity data indicates that lead-zinc deposition was a result of fluid boiling and later meteoric water mixing. Ore mineralization occurred at depths of about 600 to 700 m. Sulfur isotope compositions of sulfide minerals (${\delta}^{34}S_{CDT}=9.0{\sim}14.5$ ‰) indicate a relatively high ${\delta}^{34}S_{{\Sigma}S}$ value of ore fluids (up to 14 ‰), likely indicating an igneous source of sulfur largely mixed with an isotopically heavier sulfur source (possibly sulfates in surrounding sedimentary rocks). There is a remarkable decrease of calculated ${\delta}^{18}O$ value of water in hydrothermal fluids with increasing paragenetic time: stage I, 14.6~10.1 ‰; stage IIa, 5.8~2.2 ‰; stage IIb, 0.8~2.0 ‰; stage IIc, -6.1~-6.8 ‰, This indicates a progressive increase of meteoric water influx in the hydrothermal system at Kwangsin. Measured and calculated hydrogen and oxygen isotope values indicate that the Kwangsin hydrothermal fluids was formed from a circulating (due to intrusion of the Muamsa Granite) meteoric waters which evolved through interaction mainly with the Samtaesan Formation (${\delta}^{18}O=20.1$ to 24.9 ‰) under low water/rock ratios.

• Economic and Environmental Geology
• /
• v.51 no.6
• /
• pp.493-507
• /
• 2018

The Wooseok deposit in Jecheon belongs to the Hwanggangri Mineralized Distict of the northeastern Ogcheon Metamorphic Belt. Its geology consists mostly of limestone of the Choseon Supergroup and the Cretaceous Muamsa granite intruded at the eastern area of the deposit. The deposit shows vertical occurrence of skarn and hydrothermal vein ores with W-Mo-Fe and Cu-Pb-Zn mineralization and skarn is developed only at lower levels of the deposit. Skarn minerals are replaced or cut by ore minerals in paragenetic sequence of magnetite-hematite, molybdenite-scheelite-wollframite, and higher abundances of pyrrhotite-chalcopyrite-pyrite-sphalerite-galena. Garnet has chemical compositions of $Ad_{65.9-97.8}Gr_{0.3-32.0}Pyr_{0.9-3.0}$, corresponding to andradite series, and pyroxene compositions are $Hd_{4.5-49.7}Di_{42.3-93.9}Jo_{0.5-7.9}$, prevailing in diopside compositions, both of which suggest oxidized conditions of skarnization. On the FeS-MnS-CdS ternary diagram, FeS contents of sphalerite in vein ores decrease with increasing MnS contents from bottom to top levels, possibly relating to W mineralization in deep and Pb-Zn mineralization in shallow level. Sulfur isotope values of sulfide minerals range from 5.1 to 6.8‰, reflecting magmatic sulfur affected by host rocks. W-Mo skarn and Pb-Zn vein mineralization in the Wooseok deposit were established by spatio-temporal variation of decreasing temperature and oxygen fugacity with increasing sulfur fugacity from bottom to top levels.