• Journal of the Mineralogical Society of Korea
• /
• v.20 no.2 s.52
• /
• pp.103-114
• /
• 2007

Gabbroic xenoliths in poikilitic and equigrnular textures and plagioclase megacrysts, up to 15 cm in size, are trapped in alkaline basalts from Sinsanri and Sangeumburi, Jeju island. Gabbroic xenoliths are gabbro norite in composition. Plagioclase is the most dominantly present $(42{\sim}94vol%)$, while olivine crystals are absent. Pokilitic xenoliths, interpreted as cumulates, include euhedral opx+cpx in oikocryst plagioclase. Equigranular xenoliths include subhedral to anhedral opx+cpx+pl. Based on the textural and geochemical natures, occurrence mode at the outcrops, poikiltic and equigranular xenoliths and plagioclase megacrysts were from rigid zone, mushy zone and crystal-suspended zone of the magma chamber, respectively. The gabbroic xenoliths in alkaline basalts of the Juju island represent crystallization products of relatively evolved basaltic magma at the Jeju magma reservoir beneath the Jeju Island. They are gabbro fragments that represent crystallization-isolation-capture processes associated with magma batches temporarily occupying reservoirs.

• Economic and Environmental Geology
• /
• v.33 no.2
• /
• pp.147-163
• /
• 2000

The Buseok pluton in the Yeongju Batholith is a comagmatic plutonic rocks which haveconcentrically compositional zoning. The lithofacies of the Buseok pluton comprise hornblende biotite tonalite in the southern part of the pluton, porphyritic and equigranular biotite granodiorite in the northern part and biotite granite in the north-central part. The compositional variations change gradually with continuity both within and between the lithofacies. The concentrically zoned pattern is relatively mafic rocks composed of high-temperature mineral assemblages in margin of the southern part, passing inward and northward gradually to more felsic rock in core of the north-central part. Changes in the textures and microstructures, as well as in the mineral content, take place between rock types of the plutons. Darker colored, generally coarse-grained, well foliated tonalite pass inward to light colored, coarse-grained, poorly foliated granodiorite, and finally give way to lighter colored, medium-grained, nearly nonfoliated granite. The foliation are best developed in the marginal part of the tonalite. Here, the regional myolitic foliation in the tonalite is steep northward and parallels to its southeastern contact with the country rock, but the magmatic foliation from disc-shaped mafic microgranitoid enclaves is subvertical and parallels the contacts with the country rock. As the tonalite approaches biotite granite in composition, the foliation is indistinct. Modal and chemical data for the pluton show quantitative compositional variation from the margin of the southern part to the core of the north-central part. Quartz and K-feldspar increase toward the core of the pluton, whereas hornblende, biotite and color index decrease. /Abundances of $SiO_2$and $K_2O$$_2$O increase toward the core according to the variation in quartz and K-feldspar, whereas those of MnO, CaO, $TiO_2$, $Fe_2O_3$, MgO and $P_2O_5$ decrease corresponding to the variation in mafic and accessaries. The compositional zonation resulted from fractional crystallization involving downward settling of earlier crystals, accompanied by upward movement of melt and volatiles, and followed by accessary marginal accretion of crystalline material in the magma to the marginal part. Although a little crustal contamination by the wall rock is recognized from the isotope data, the contamination is not only dominated over but also appropriate for forming the compositional variation in the pluton.

• Economic and Environmental Geology
• /
• v.32 no.6
• /
• pp.669-688
• /
• 1999

The Yeongju granitoid batholith is a plutonic complex of huge area (1180km2) intruding the metamorphic rocks of the Yeongnam massif. The batholith, which is divided into fivelithofacies, consists of three separate plutons. The oldest Buseok pluton comprises four lithofacies: hornblende biotite tonalite, porphyrotoc biotite granodiorite, equigranular biotite grandiorite and biotite granite. The middle Chunyang pluton has been called as Chunyang granite that ranges in compostion from granodiorite to granite. The youngest Jangsu pluton is intrusions that has lithofacies of two mica granite. The contact between Buseok pluton and the rest two plutons shows obvious intrusive relations, but relation between the Chunyang and the Jangsu pluton is far away, so gives no indication of relative ages. Changes in nextures and micristructures, as well as in the mineral contents, take place between rock types og the plutons. only the Buseok pluton shows faliations of two type: magmatic foliation and regional mylonal foliation. K-Ar age deteminations fall into 171.7$\pm$3.2~162.3$\pm$3.1 Ma in the Buseok pluton, 153.9$\pm$2.9 Ma in the Chunyang pluton and 145.3$\pm$2.7 Ma in the jangsu Pluton. The batholith presents three separate intrusive phases which range in composition from tonalite to granite to granite. Each intrusive phase apperars to have been intruded in a pulse from an underlying, differentiating magma. The petrochemical data showthat three plutons are within the diagnostic range for continental arc orogenic tectonic setting, whereas Jangsu pluton approaches postorogenic setting. The data suggest that three plutons are calc-aclkalline series, and that temporal compositional variations change progerssively from tonalite through grandiorite to granite between the intrusive phases. so we consider that the magmas for all the phases were probably derived from a differentiation by fractional crystallization of a parental magma. The tonalite magma of the Buseok phase was tapped was tapped from a chamber deep in the crust, and then would have to rise at a rapid rate to its final level of emplacement. The tonalite magma in the chamber was gradually enolved through granodiorite magma into granite magma by fractional crystallization. The magmas of the younger phases were respectively tapped with temporal interval from a evolved magma of the chamber that rose into a shallower lever in the crust, and rose to their present level of emplacement.

• The Journal of the Petrological Society of Korea
• /
• v.9 no.3
• /
• pp.142-168
• /
• 2000

The granites distributed in the Kyongsang basin contain the rocks which are different from the host rocks, and they are known as magic microgranular enclaves. The genesis of the magic micro-granular enclaves can be divided into four types: (1) rock fragments from country rocks; (2) cumulation of the early crystals in host magma or disruption of early chilled borders; (3) magma mingling; and (4) restite. These enclaves can be easily found in the granites around Mt. Wonhyo, Yangsan city. They are ellipsoidal in shape, and have phenocrysts might be originated from the host rocks and sharp contacts with the granites. Under the microscope, textures such as oscillation zoning, horn-blende-mantled quartz, rapakivi texture, and acicular apatite are observed, and these indicate that the enclaves were originated from magma and then produced by chilling. The evidences showing that the enclaves were formed by magma mingling are: (1) petrographical characteristics; (2) similarity of the compositions between the rim of plagioclase in the enclave and plagioclase in the granite; (3) linear trends of the major elements; (4) total REE content of the enclaves; and (5) Textural and compositional variations from rim to core in zoned enclaves. The magic end member of the enclave is regarded as the aphyric basaltic andesite in Mt. Sinbul-Youngchui area. The granites around Mt. Wonhyo experienced the magma mingling process which was produced by the injection of mafic magma at about 70 Ma, during the crystal differentiation, and then continued the crystallization. The equigranular granites and the micrographic granites in the study area are considered as the results after the magma mingling process.

• The Journal of the Petrological Society of Korea
• /
• v.13 no.1
• /
• pp.1-15
• /
• 2004

In this study we propose that the ‘enclaves’ which occur in the granites should be translated into ‘Po-yu-am’in Korean. Also we suggest some criteria to discriminate the mafic microgranular enclaves (MME) of igneous origin from the xenoliths, which possibly come from the plutonic, volcanic and sedimentary country rocks. The color of the MME is gray green∼dark gray and the mineral grains are fine and equigranular. The MME are generally of ellipsoidal shape and can be easily found within the granites. They do not show any evidence of contact metamorphism by granite host. On the other hand. the xenoliths are generally of angular shape and are of the same mineral assemblage and texture as the country rocks around the granites. The distribution of the xenoliths is mostly concentrated along the intruding plane of the granites near the country rocks. The xenoliths were partly metamorphosed by the granite intrusion. The xenoliths from the plutonic rocks are easily distinguished from the MME in terms of their angular shape and coarser grain size, but they do not have any metamorphic mineral assemblage and texture. The xenoliths from the tuffaceous rocks show angular shape and porphyritic and pyroclastic textures. Large size xenoliths from the sedimentary rocks specifically preserve bedding structure which are indicative of the sedimentary strata. However, the sedimentary xenoliths of small size are often difficult to distinguish from the MME. Metamorphic minerals and texture are a useful key to discriminate the small-sized sedimentary xenoliths from the MME. In summary the xenoliths in the granites can be megascopic ally distinguished from the MME by comparing their color, shape, grain size and remnant original structure like bedding. Additionally the metamorphic mineral assemblage and texture are microscopic discriminators between the xenoliths and the MME in the granites.

• Journal of the Mineralogical Society of Korea
• /
• v.22 no.2
• /
• pp.163-176
• /
• 2009

The pyrophyllite deposits located in Jinhae area have been studied through field observations and laboratory works including the X-ray diffraction (XRD), X-ray fluorescence (XRF), Electron probe microanalyzer (EPMA) and Inductively Coupled Plasma (ICP). The pyrophyllite deposits consist of mainly illite, dickite, pyrophyllite, diaspore, chlorite, pyrite and copiapite. According to the mineral assemblages, geological occurrences and alteration modes, the altered rocks can be classified into four types: Type A; quartz with silicifictaion, Type B; quartz + illite with illitization, Type C; quartz + dickite + illite with kaolin alteration, Type D; pyrophyllite + illite + dickite + diaspore with pyrophyllite alteraion. Rocks in Type A, which is generated by silicifictaion, have high $SiO_2$ contents more than 90 wt% and distinctive equigranular textures with microcrtstalline quartz. The pyrophyllites from the study area belong to 2M polytype. The host rocks of the pyrophyllite ore in this mine are rhyolitic rock, andecitic tuff and volcanic breccia. The alteration products seem to be controlled by the different lithology of the host rocks. The hydrothermal solution formed the deposits would be inferred to the acidic and have relatively high ionic activity of hydrogen and silica judging from alteration mineral assemblage. Pyrophyllite alteraion zone is generated by highest temperature condition of all alteration zone.

• Economic and Environmental Geology
• /
• v.20 no.2
• /
• pp.85-95
• /
• 1987

The host rocks of titaniferous magnetite deposits in Gonamsan are alkaline gabbros, which are typical of undersaturated alkaline rocks in terms of the lack of normative quartz. According to field occurrences and petrographic features, these alkaline gabbros are divided into 3 rock types: coarse-grained and pegmatitic rock, medium-grained rock with equigranular texture, and layered cumulate rock. All these rocks mainly contain clinopyroxene(salite), plagioclase(An 43-66), pargasite, and ilmenite. The accessory minerals are apatite, sphene, quartz, and sometimes titaniferous magnetite. Pargasite, sphene, and quartz are considered to be secondary minerals formed by the reaction among clinopyroxene, plagioclase and Fe-Ti oxide at deuteric stage. Fe-Ti oxides generally occur as ilmenite in the alkaline rocks, and titaniferous magnetite in the ore deposits. Layered cumulate rocks are characterized by a recurrence of discontinuous thin mesolayer of clinopyroxene-pargasite within leucolayer mainly composed of plagioclase. Clinopyroxene is cumulus mineral whereas plagioclase, ilmenite and apatite occur as intercumulus minerals. According to the variation diagrams of oxide and trace element contents against the differentiation index, incompatible elements, such as Na, Ba and Sr, show positive correlations whereas compatible elements, such as Mg and Cr, show negative correlations. However some compatible elements, such as Co, Ni and V show irregular variations, reflecting relative cumulate status of cumulus and intercumulus minerals. On the de la Roche multicationic diagram, these alkaline gabbros are distributed along the differentiation curve of undersaturated alkaline series from alkaline basaltic composition through basanitic composition to tephritic composition. Layered cumulate rocks, which are distributed between basanitic composition and tephritic composition, reflect their cumulate character, slightly scattering away from the curve. The medium-grained rock shows higher contents in Ba, Sr and light rare earch elements than the coarse-grained and pegmatitic rock. The former shows two times higher contents of total rare earth elements than the latter, $while(La/Lu)_{cn}$ ratios maintain fairly constant values of 5.08~5.06 in these two rocks. This means that coarse-grained and pegmatitic rock, as compared with the medium-grained rock, was formed by the earlier differentiated magma but rare-earth element distribution pattern remained almost parallel during differentiation. From the data the above mentioned, these alkaline gabbros are considered to be comagmatic and to be formed by intrusions of differentiated magmas in its reservoir.

• Journal of the Mineralogical Society of Korea
• /
• v.18 no.3 s.45
• /
• pp.165-181
• /
• 2005

The granitic rocks distributed in the southern part of the Yangsan Fault are classified into five distinct rock facies based on the field relation, petrography and geochemical characteristics. These five different rock facies can be grouped into two considering their origins. Group I, which reveals various evidences of magma mixing, includes three rock facies of granodiorite, enclave-rich porphyritic granite, and enclave-poor porphyritic granite. Group H intruding Croup I includes equigranular granite and micrographic granite with no evidence of magma mixing. It is suggested that the distinctively different trace element and isotopic chemistries between group I and II, support evolution from the different parental magma. It is suggested that the three rock facies in group I were generated by different degrees of magma mixing in addition to fractionation of plagioclase. MMEs experienced fractionation of biotite. The two facies in group H seem to have been generated from different parent magma from group I and evolved by fractionation of K-feldspar. The Rb-Sr whole-rock ages of the group I rocks yield $59.2\~58.9Ma$, and those of the group II rocks give 53. $3\~51.7Ma$, regardless of their distribution whether they occur in the eastern or western parts of the Yangsan Fault. Based on Sm-Nd isotope compositions, depleted mantle model ages $(T_2DM)$ of the group I range $0.8\~0.9Ga$, while those of the group II$0.6\~0.7Ga$.

• Journal of the Mineralogical Society of Korea
• /
• v.17 no.4
• /
• pp.365-383
• /
• 2004

Granitic rocks in the southeastern Gyeongsang Basin can be classified into three groups. The group I contains various mafic microgranular enclave (MME) and/or mafic clot which implies magma mixing or mingling. The group II show the feature of shallow depth emplacement at low pressure, and the group III is characterized by A-type granite implying extensional tectonic environment. Mineralogical characteristics of the granitic rocks have showed systematic variations in perthite exsolution temperatures and biotite compositions according to their rock facies, although they do not show any distinctively different trend in geography and textures or rock facies. Amphiboles from Group I are calcic-amphibole and they were formed at 0.4 ～ 2.8 kb in pressure based on the amphibole geobarometry. Amphiboles from group ill are riebeckite, whileas amphiboles were not observed in Group II. The chemical composition of biotite defined in clusters showing a continuous spectrum between group I to ferric-annite of group ill. The composition of plagioclase generally plotted in albite, oligoclase, and andesine area without any distinctive differences among their geography or rock facies. The exsolution temperatures by perthite geothermometry are calculated as $300～400^{\circ}C$ in Group I, and 500～$600^{\circ}C$ in equigranular granite of group II and alkali-feldspar granite of group III.

• Journal of the Mineralogical Society of Korea
• /
• v.20 no.2 s.52
• /
• pp.71-81
• /
• 2007

The marble-type dolomite from the Jasung Mine, which was farmed by duplicated affects of contact metamorphism and subsequent hydrothermal alteration, corresponds to a high-purity dolomite ranging up to above 98wt.% in dolomite contents. The dolomite contain minor impurities such as quartz, muscovite, and pyrite. It is characteristic that the dolomite is fairy Fe-rich corresponding to 0.4 wt.% due to the presence of pyrite of possible hydrothermal origin. The dolomite is nearly white-colored and constituting with subhedral crystals ranging $0.35{\sim}0.46mm$M in size, forming equigranular texture. Compared to the typical high-Ca limestone from the Pungchon Formation, the powder characteristics of dolomite is rather superior in milling efficiency, yields of fine particles, and size distribution. In addition, except for iron contents, the dolomite powder is no less superior than the limestone in quality and characteristics as fillers with respects to not only whiteness, oil absorption, and specific surface area but also shape characters such as elongation ratio, aspect ratio, and sphericity. This good characteristics of dolomite powder seem to be originated basically from comparatively higher grade and crystallinity of dolomite. Higher iron contents and the presence of sulfides prevents the dolomite from application for uses by thermal treatment, except for metallic manufacture. However, if proper ore separation procedure is available, the dolomite can be sufficiently utilized as substitutes for high-Ca limestone in most fields of filler industries.