• The Journal of the Petrological Society of Korea
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• v.15 no.4 s.46
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• pp.167-179
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• 2006

Division of granites in the Galmal-Yeonbug area, northern Gyeonggi, can be grey hornblende biotite granite (JHBG), biotite granite (JBG) and pink hornblende biotite granite (CHBG) by lithofacies. JHBG of small stock occurs as medium-grained with grey color and minute sphene. JBG occurs as medium-grained and light grey to grey in the north-east part of the area. The main study target CHBG covers in the north-southeast part of the area, and occurs medium-to coarse-grained with pink color. CHBG shows partly minute miaroles, and pegmatitic pocket with druse texture. From the mineral age data (K-Ar method). JHBG and JBG and CHBG are the igneous activity products of Daebo orogeny with different Jurassic and Bulgugsa disturbance of Cretaceous, respectively. And the age data also agree with geologic occurrences and interpretations of the granites in the field. CHBG consists of quartz, plagioclase, alkali-feldspar, biotite, hornblende, allanite, apatite, zircon, some calcite and opaques. Among them, alkalifeldspar and calcite occur characteristically in mostly perthitic othoclase and secondary filling of minutely miarolitic cavity, respectively. In modal analysis and QAP diagram, CHBG plots in granite field, and especially boundary of monzo-and syeno-granite fields. From the major oxide variations, molar A/CNK, $SiO_{2}\;vs\;K_{2}O$, AMF and so on, CHBG belongs to the acidic, peraluminous and high-K calc-alkaline, and was late differentiation product of single granitic magma. Barium and strontium have also dominantly differentiation trend, and in CaO vs Sr and $K_{2}O$ vs Sr, Sr was more participitated in the fractionation of plagioclase than that of alkali-feldspar. Normalized REE concentrations to chondrite value have parallel and gradual LREE enrichment and HREE depletion patterns, and weak Eu negative anomalies and narrow ranges of normalized Eu can suggest that plagioclase fractionations occurred mildly in the whole CHBG.

• Economic and Environmental Geology
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• v.3 no.1
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• pp.25-34
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• 1970

Very few articles are available on geologic structure and genesis of Sangdong scheelite-deposits in spite of the fact that the mine is one of the leading tungsten producer in the world. Sangdong scheelite deposits, embedded in Myobong slate of Cambrian age at the southem limb of the Hambaek syncline which strikes $N70{\sim}80^{\circ}W$ and dips $15{\sim}30^{\circ}$ northeast, comprise six parallel veins in coincide with the bedding plane of Myobong formation, namely four footwall veins, a main vein, and a hangingwall vein. Four footwall veins are discontinuous and diminish both directions in short distance and were worked at near surface in old time. Hangingwall vein is emplaced in brecciated zone in contact plane of Myobong slate and overlying Pungchon limestone bed of Cambrian age and has not been worked until recent. The main vein, presently working, continues more than 1,500 m in both strike and dip sides and has a thickness varying 3.5 to 5 m. Characteristic is the distinct zonal arrangement of the main vein along strike side which gives a clue to the genesis of the deposits. The zones symmetrically arranged in both sides from center are, in order of center to both margins, muscovite-biotite-quartz zone, biotite-hornblende-quartz zone and garnet-diopside zone. The zones grade into each other with no boundary, and minable part of the vein streches in the former two zones extending roughly 1,000 m in strike side and over 1,100 m in dip side to which mining is underway at present. The quartz in both muscovite-biotite-quartz and biotite-hornblende-quartz zones is not network type of later intrusion, but the primary constituent of the special type of rock that forms the main vein. The minable zone has been enriched several times by numerous quartz veins along post-mineral fractures in the vein which carry scheelite, molybdenite, bismuthinite, fluorite and other sulfide minerals. These quartz veins varying from few centimeter to few tens of centimeter in width are roughly parallel to the main vein although few of them are diagonal, and distributed in rich zones not beyond the vein into both walls and garnet-diopside zone. Ore grade ranges from 1.5~2.5% $WO_3$ in center zone to less than 0.5% in garnet-diopside zone at margin, biotite-hornblende-quartz zone being inbetween in garde. The grade is, in general, proportional to the content of primary quartz. Judging from regional structure in mid-central parts of South Korea, Hambaek syncline was formed by the disturbance at the end of Triassic period with which bedding thrust and accompanied feather cracks in footwall side were created in Myobong slate and brecciated zone in contact plane between Myobong slate and Pungchon limestone. These fractures acted as a pathway of hot solution from interior which was in turn differentiated in situ to form deposit of the main vein with zonal arrangement. The footwall veins were developed along feather cracks accompanied with the main thrust by intrusion of biotite-hornblende-quartz vein and the hangingwall vein in shear zone along contact plane by replacement. The main vein thus formed was enriched at later stage by hydrothermal solutions now represented by quartz veins. The main mineralization and subsequent hydrothermal enrichments had probably taken place in post-Triassic to pre-Cretaceous periods. The veins were slightly displaced by post-mineral faults which cross diagonally the vein. This hypothesis differs from those done by previous workers who postulated that the deposits were formed by pyrometasomatic to contact replacement of the intercalated thin limestone bed in Myobong slate at the end of Cretaceous period.

• The Journal of the Petrological Society of Korea
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• v.13 no.3
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• pp.142-151
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• 2004

The metamorphic rocks of Yongin-Anseong area in Gyeonggi massif are composed of high-grade gneisses and schists which are considered as Precambrian basement, and Jurassic granite which intruded the metamorphic rocks. In this paper, we discuss the geochemical characteristics of metamorphic rocks and granites in this area based on REE and Nd isotope geochemistry. And we also discuss the petrogenetic relationship between metamorphic rocks and granites in this area. Most of Nd model ages (T$\_$DM/$\^$Nd/) from the metamorphic rocks range ca. 2.6Ga～2.9Ga which are correspond to the main crustal formation stage in Gyeonggi massif by Lee et. al. (2003). And Nd model ages show that the source material of quartzofeldspathic gneiss is slightly older than that of biotite banded gneiss. In chondrite-normalized rare earth element pattern, the range of (La/Yb)$\_$N/ value from biotite banded gneiss is 37～136, which shows sharp gradient and suggests that biotite banded gneiss was originated from a strongly fractionated source material. However, that of amphibolite is 4.65～6.64, which shows nearly flattened pattern. Particularly, the chondrite normalized REE patterns from the high-grade metamorphic rocks show the REE geochemisoy of original source material before metamorphism. In addition, the values of (La/Yb)$\_$N/ and Nd model ages of granite are 32～40 and 1.69Ga～2.08Ga, respectively, which suggest that the source material of granite is different from that of Precambrian basement such as biotite banded gneiss and quartzofeldspthic gneiss in the area.

• The Journal of the Petrological Society of Korea
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• v.19 no.4
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• pp.283-292
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• 2010

The Suljeongri east three-story stone pagoda in Changnyeong (National Treasure No. 34) has been damaged mainly by lots of cracks. The stones used for this pagoda are medium-granied equigranular pinkish biotite granite. Measured magnetic susceptibility values are of from 2 to 9 (${\times}10^{-3}$ SI unit). From the ${\gamma}$-ray spectrometer mesurement K, eU, and eTh contents of the stones are 3 to 7%, 8 to 19 ppm, and 11 to 35 ppm, respectively. Comparing the petrographical and chemical characteristics between the stones of the pagoda and the country rocks near Suljeongri, it is suggested that the most similar rock could be equigranular biotite granite in the western slope of the Mt. Hwawangsan. Vertical, horizontal and diagonal cracks are intensely developed at the lower part of the stone pagoda. Biotite granite has intrinsic microcracks defined as rift and grain rock cleavages. Both rock cleavages are assumed to have led to the crack growth and consequent mechanical damage of the pagoda. It seems that vertical cracks have been grown parallel to the principal compressional stress, and that horizontal cracks to the reacting tensional stress. Diagonal cracks seems likely to have been resulted from conjugate rift and grain rock cleavages.

• Economic and Environmental Geology
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• v.42 no.3
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• pp.247-259
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• 2009

This study is focused on the relationship between whole rock boron contents and metamorphic P-T conditions of metasedimentary rocks from northeastern Yeongnam massif around Samcheok area, Korea. Metamorphic P-T conditions of sillimanite and garnet zones based on the Ti-biotite geothermometer is 553-687$^{\circ}C$ and 582-722$^{\circ}C$ at 4-6 kbar, respectively. In the metasedimentary rocks, boron contents in whole rock decrease with increasing metamorphic grade, from sillimanite zone (9.60-189 ppm B) to garnet zone (2.63-15.97 ppm B), except one sample (90.9 ppm B) from garnet zone containing graphites. Boron depletion in garnet zone has relation with mode of tourmaline which are broken down with increasing metamorphic temperature. Boron contents are indirectly proportional to major and trace elements such as $Al_2O_3$, MgO, $Fe_2O_3$, $K_2O$, Li, Ba, Sc, Co, Cr, Rb and Cs that are abundant in tourmalines. In conclustion, tourmalines and graphite are modulator of boron contents in metasedimentary rocks. In the biotite granitic gneisses, boron contents (2.62-12.2 ppm B) are similar or lower than those of metasedimentary rocks and have no relation with metamorphic P-T conditions.

• Economic and Environmental Geology
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• v.35 no.4
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• pp.347-353
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• 2002

Dominant rock types of stones used presently for cooking utensils in Korea are pyroxenite, breccia and biotite diorite. Pyroxenite and biotite diorite relatively abundant in mafic minerals have higher specific gravities of 3.0 than breccia of 2.5. Breccia shows the highest absorption (2.9%) among three stones used as cooking utensils and pH value of three stone types shows the alkaline range of 9.7 to 9.9. Among the studied stones used for cooking utensils, biotite diorite is the most durable against abrasion and has the highest strength and therefore, it is expected to be used effectively for the longest time except for other specific causes. Heavy metals such as Cu, Pb, Co, Cr and Ni were leached lower than their detection limit (0.1 ppm) regardless of reaction time and initial pH value of solution. But the leached contents of Fe are various with rock types and leaching conditions and those by acidic solution are generally 1.8 to 31 times higher than those by neutral solution. Breccia and biotite diorite show the highest leached content of Fe in cases of neutral and acidic solutions, respectively. Standard criteria of leached heavy metals and macrominerals should be studied thoroughly to utilize stones for cooking utensils of high quality which are harmless to the human body. Also it is required to examine mon detailed abiochemical properties of various stone types used for cooking utensils.

• Economic and Environmental Geology
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• v.35 no.1
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• pp.75-95
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• 2002

The Andong pluton in the Andong Batholith is composed of comagmatic plutonic rocks, in which the lithofacies comprise hornblende biotite tonalite in the central paft biotite granodiorite in the marginal paft and porphyritic biotite granite at the topside (noJthea~tern paft) of the pluton. The pluton is petrographically and petrochemically zoned, having more mafic center than margin and topside. Distribution pallern of the lithofacies represents a reverse zoning in the pluton. Modal and chemical data in the pluton show progressive and gradual compositional variations from the centrer via the margin to the topside. Quartz and K-teldspar increase toward the topside of the pluton, whereas hornblende, biotite and color index increase toward the center. The bulk composition in the pluton is also reversely zoned, with high $Si0_2$ and $K_{2}O$ in the topside facies, and high MnO, CaO, $Ti0_2$, $Fe_{2}O_{3}$t, MgO and $P_{2}O_{5}$ in the central facies. The reverse zoning is also evident in higher Cr. V, Ni, Sc and Sr of the more mafic tonalite in the interior. The reversely zoned pluton results from remobilization (resurgence) of the lower more mafic compositional zone into the upper more felsic zones of the pluton modified by thennogravitational diffusion and fractional crystallization. In the initial stages of evolution, the pluton was a petrochemical system that fonned chemical compositional zonation with mafic tonalitic magma in the lower. granodioritic one in the middle and granitic one in the upper paft of the magma chamber. Periodic influxes of more mafic magma from the ba~e resulted in mingling of liquids and redistribution of minerals, and may have triggered the remobilil.ation of the lower compositional zone into the upper more felsic zones.

• The Journal of the Petrological Society of Korea
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• v.23 no.4
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• pp.375-383
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• 2014

Precambrian granitic gneisses and Cambrian meta-sedimentary rocks are prevalently distributed in the eastern part of the Taebaegsan region, and biotite granitic batholith of the Jurassic period (?) is found in the southern part of Uljin-si. But small scale leucocratic granitic stocks which commonly found here and there have been rather neglected in the previous studies. The presence of leucocratic granites could be differentiated from the older granitic rocks and biotite granite through the outcrop characteristics, mineral species and geochemical compositions. For the effective comparison between the older granitic rocks and leucocratic ones, pale gray to gray coloured Hongjesa granitic gneiss with granular texture was selectively chosen. The Hongjesa granitic gneiss and biotite granite usually have rather plenty of coloured minerals such as biotite and chlorites. But the leucocratic granites often show sericitic alteration due to the albitization and greisenisation during the post-magmatic alteration, and shows rather bright appearance because of poor amount of coloured minerals. Since all of granitic rocks passed rather high degrees of magmatic differentiation, they belong to calc-alkalic and peraluminous in their characters. Among the alkali elements of the leucocratic rocks $K_2O$ shows higher increase than those of the other granitic rocks, and $Na_2O$ only represents slight decrease than those of the Hongjesa granitic gneiss and Uljin granite. On the other hand, CaO and total Fe content are clearly decreased than those of the Hongjesa granitic gneiss and Uljin granite.

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.37-52
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• 1998

The granites in the Jeomchon area can be divided into hornblende biotite granite (Hbgr), deformed biotite granite (Dbgr), deformed pinkish biotite granite(Dpbgr), biotite granite (Btgr), and granite porphyry(Gp). These granites show metaluminous, 1-type and calc-alkaine characteristics from their whole-rock chemistry. Hbgr and Dbgr belong to ilmenite-series granitoids, but Gp to magnetite-series. Dpbgr and Btgr show the intermediate nature between ilmenite- and magnetite-series. Tectonic discriminations indicate that Hbgr and Dbgr were formed in active continental margin environment, whereas Dpbgr, Btgr, and Gp in post-orogenic and/or anorogenic rift-related environment. From the Harker diagrams major oxide contents of Hbgr and Dbgr show a continuous variation with $SiO_2$, indicating that they are genetically correlated with each other. On the other hand, any correlation of major oxides variation cannot be recognized among Dpbgr, Btgr and Gp. It seems like that Hbgr and Dbgr were derived from a same parent granitic magma, judging from their occurrence of outcrop, mineral composition as well as whole-rock chemistry. Variation trends of major oxide contents between Hbgr and Baegnok granodiorite are very similar and continuous. If the two granites were derived from a cogenetic magma, there exists a possibility that the granitic bodies had been separated by Btgr and Gp of Cretaceous age. Three stages of the granitic intrusions are understood in the Jeomchon area. After the intrusion of Hbgr and Dbgr during middle to late Paleozoic time, Dpbgr emplaced into the area next, and finally Btgr and Gp intruded during Cretaceous time. Tectonic movement accompanying shear and/or thrust deformation seems likely to have occurred bewteen the intrusions of Dpbgr and Btgr.

• The Journal of the Petrological Society of Korea
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• v.13 no.2
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• pp.81-102
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• 2004

The plutonic rocks in Seonsan area are divided into dioritic-syenitic rock, gneissose granite, biotite granite and fine grained biotite granite. These rocks intruded into the Pre-cambrian metamorphic complex and are all covered by the Cretaceous Nakdong formation. According to modal minerals, dioritic-syenitic rock corresponds to quartz monzonite, granodiorite, tonalite fields, whereas all the other plutonic rocks fall in granite field. Petrochemically the dioritic-syenitic rock is lower in SiO$_2$ content, differentiation index and Larsen index than all the other plutonic rocks. About the zircon morphology, dioritic-syenitic rock shows (100) dominant type but other granitic rocks exhibit mixed types between (100) and (110) type. The dioritic-syenitic rock could be crystallized in higher temperature than the other plutonic rocks. The plutonic rocks correspond to calc-alkaline rock series, and belong to I-type granite and mostly magnetite-series in magmatic origin. In plutonic processes, the dioritic-syenitic rock with 5kb vapor pressure could intrude into the metamorphic batement at 17km deep below the surface. Later the gneissose granite with lower 3kb vapor pressure could intrude at 10km deep. Sequentially the biotite granite with 0.7kb could intrude at 2km deep. Finally the fine grained biotite granite with 3kb vapor pressure could intrude at 10km deep.