• Economic and Environmental Geology
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• v.20 no.2
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• pp.85-95
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• 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
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• v.9 no.1
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• pp.43-53
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• 1996

The detailed crystal chemistry of ilmenite from the Hadong massif was studied by the EPMA, M ssbauer spectroscopy, and Rietveld structural refinement using X-ray powder diffraction data. The ilmenite-bearing anorthosite shows complicated mineral assemblage which consists of plagioclase, clinopyroxene, hornblende, biotite, chlorite, apatite, allanite, and zircon. Anorthite is andesine in composition (Ab 28-57), and clinopyroxene drops in ferro-hypersthene (Fs 62-70). Ilmenite is trigonal symmetry with R space group, whose structure shows the alternation of Fe2+ (M1 site) octahedral layer and Ti (M2 site) layer along c axis. M ssbauer spectroscopy indicates that there are three doubles which assigned to couple of Fe2+($\delta$=0.812, 0.890mm/sec) and one Fe3+($\delta$=0.303mm/sec) in octahedral sites. Their Fe3+/$\Sigma$Fe is 0.065 and chemical formula is established as Fe2+0.94Fe3+0.07Ti0.97O3 using both EPMA and M ssbauer analysis. Rietveld structural refinement reveals that site occupancies of Fe in M1 and Ti in M2 are 91.2% and 89.4%, respectively. This implies that Ti and Fe2+ are alternatively occupy M1 and M2 sites. In addition, smaller M2 site is more preferable to Fe3+ occupancy over M1.

• Economic and Environmental Geology
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• v.31 no.5
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• pp.447-458
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• 1998

The spinel Ihelzolite of ultramafic xenoliths are found in the alkali basalt from eastern part of the Cheju island, Korea. The xenolith is are mainly composed of olivine, orthopyroxene, clinopyroxene and spinel. Based on the chemical compositions of the constituent minerals, the ultramafic xenolith belong to upper mantle peridotite. Each minerals have a protogranular texture. Olivine with kink band texture partly shows undulatory extinction. Some clinopyroxenes have spongy textured rims. Brown spinels occur in the interstices between olivine and pyroxene grains. Olivine is mostly forsterite $(Fo_{89-90})$. Orthopyroxene is enstatite $(Wo_{1.3}En_{88.4}Fs_{10.3})$ with 3.87~5.25 wt% $Al_{2}O_{3}$. Clinopyroxene is diopside $(Wo_{48.0}En_{46.2}Fs_{5.8})$ with 6.75~5.03 wt% $Al_{2}O_{3}$. Spinel has the Mg value of 75.9 and its Cr-number is 10.2. According to the PoT estimations for the mantle xenoliths, equilibrium temperatures of the xenoliths range from 1023 to $1038^{\circ}C$ and pressure is 18 kbar. Spinellhelzolite from this area, which is characterized by lower Cr-number (10.2) and homogeneous chemical compositions, supports that these ultramafic xenoliths are derived from the upper mantle.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2001.06a
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• pp.75-75
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• 2001

We report Sr, Nd and Pb isotope data of clinopyroxene separates from ultramafic xenoliths and their host basaltic rocks in Jeju Island, Baekryeong Island, Boeun and Ganseong, Korea. The isotopic data of the xenoliths and host basalts are distinctly different from those of Korean basement rocks. Except for two xenoliths from Ganseong, all samples in this study have isotopic ratios within the combined range of MORB-OIB data. All basaltic rocks have Nd-Sr-Pb isotope compositions different from those of xenoliths, indicating that the host basaltic magma did not derive from the lithospheric mantle where the xenoliths originated. The range of isotopic composition of xenoliths is much greater than that observed in host basalts, which reflects small-scale heterogeneity of the lithospheric mantle. The greater isotopic heterogeneity of the lithospheric mantle probably reflects its long-term stability. The spinel peridotite xenolith data of Jeju Island, Baekryeong Island and Boeun display mixing hyperbolas between DMM and EM II end members. Since Jeju basalts have EM II-like isotopic signature, the mixing relationship shown by the isotopic data of the Jeju xenoliths can be interpreted as the result of infiltration of metasomatic fluid or melt derived from basaltic magma into DMM-like lithospheric mantle. In contrast to other xenolith sites, the Ganseong xenoliths are dominantly clinopyroxene megacryst and pyroxenite. Clinopyroxene megacrysts have different isotopic ratios from their host basalt, reflecting its exotic origin. Two Ganseong xenoliths (wherlite and clinopyroxenite) have much enriched Sr and Nd isotopic ratios and Nd model ages of 2.5-2.9 Ga, and plot in an array away from the MORB-OIB field. The mantle xenoliths from Korean Peninsula have similar $\^$87/Sr/$\^$86/Sr,$\^$143/Nd/$\^$144/Nd and $\^$207/Pb/$\^$204/Pb ratios to, but higher $\^$208/Pb/$\^$204/Pb ratios than, those from eastern China, indicating that Korean xenoliths are derived from the lithospheric mantle with higher Th/U ratio compared with Chinese ones. The isotopic data of xenolith-bearing basalts of Baekryeong Island and Ganseong, along with Ulreung and Dok Islands, show a mixing trend betlveen DMM and EM I in Sr-Nd-Pb isotopic correlation diagrams, which is also observed in tile northeastern Chinese basalts. However, the Jeju volcanic rocks show an EM II signature that is observed in southeastern Chinese basalts. The isotopic variations in volcanic rocks from the northern and southern portions of the East Asia reflect a large-scale isotopic heterogeneity in their source mantle.

• Journal of the Mineralogical Society of Korea
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• v.29 no.3
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• pp.141-153
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• 2016

The Manjang deposit is emplaced in Hwajeonri formation comprising limestone that is interbeded with slate and phyllite in the central Okcheon Group. It consists of the Main and the Central orebody of Cu-bearing hydrothermal vein deposit and the Western orebody of iron skarn deposit. Based on coexisting mineral assemblage the skarnization can be divided into prograde skarnization (stage I : clinopyroxene ${\pm}$ magnetite ${\pm}$ quartz, stage II : garnet + clinopyroxene ${\pm}$ magnetite ${\pm}$ quartz) and retrograde hydrothermal alteration (stage III: magnetite + amphibole + quartz ${\pm}$ garnet ${\pm}$ clinopyroxene ${\pm}$ chlorite ${\pm}$ epidote ${\pm}$ fluorite ${\pm}$ calcite, stage IV: fluorite ${\pm}$ pyrrhotite ${\pm}$ chalcopyrite ${\pm}$ amphibole ${\pm}$ quartz ${\pm}$ calcite). Diopside is abundant in stage I, and hedenbergite was produced in stage II and III. Garnet compositions change from grandite to andradite, which suggests a redox transition from relatively reduced to oxidized condition during the skarn formation. Magnetite in stage I and II has relatively constant Fe contents, while in the stage III it has increased Si and Ca concentrations. This variation could indicate that magnetite was more strongly affected by host rocks during the retrograde stage. Sulfur isotope compositions of pyrrhotite and chalcopyrite produced in stage IV are within the range of + 5.9~6.9 ‰, corresponding to igneous origin, but slightly high sulfur isotope values could be attributed to an interaction with host rocks, limestone.

• The Journal of the Petrological Society of Korea
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• v.16 no.2 s.48
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• pp.59-72
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• 2007

Kilauea volcano located in the southern part of Hawaii island chains has been formed by continuous and sporadic eruption activities from 16 century to September of 1982. Kilauea volcano was investigated from collecting the samples of basalt to identify the geochemical characteristics of the lavas. Olivine, clinopyroxene, plagioclase, and opaque minerals with glass groundmass are observed. Clinopyroxene formed glomerophopyritic texture with plagioclase and zoning texture was observed in some of plagioclase phenocrysts. Major elements such as $K_2O$, $P_2O_5$, $TiO_2$ increased with respect to MgO. $Al_2O_3$ and CaO show the kink on Marker diagram due to the crystal fractionation of plagioclase and clinopyroxene with plagioclase respectively. Olivine has a wide range of Fo% ranging from 60 to 90, and MnO and FeO in the olivine are decreased with increasing Fo% oppositely increased $SiO_2$, MgO, and NiO. Ni in the whole rock is controlled not only by the mode of olivine but also by the Ni abondance in the olivine.

• Journal of the Korean earth science society
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• v.23 no.1
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• pp.38-51
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• 2002

Mantle xenoliths in alkali basalt at Boun, the Gansung area and Baegryung Island in South Korea are spinel lherzolites composed of olivine, orthopyroxene, clinopyroxene, and spinel. Minerals show homogeneous compositions. Olivine compositions have Fo$_{89.0}$ to Fo$_{90.2}$, low CaO (0.03 to 0.12 wt%), and NiO of 0.34 to 0.40 wt%; the orthopyroxene is enstatite with En$_{89.0}$ to En$_{90.0}$ and Al$_{2}$O$_{3}$ of 4 to 5 wt%; the clinopyroxene is diopside with En$_{47.2}$ to En$_{49.1}$ and Al$_{2}$O$_{3}$ of 7.42 to 7.64 wt% from Boun and 4.70 to 4.91 wt% from Baegryung. Spinel chemistry shows a distinct negative trend, with increaeing Al corresponding with decreasing Cr, and Mg$^{#}$ (100Mg/Mg+Fe) and Cr$^{#}$ (100Cr/Cr+Al) of 75.1 to 81.9 and 8.5 to 12.6, respectively. The equilibrium temperatures of these xenoliths, taken as the average obtained from those of Mercier (1980) and Sachtleben and Seck (1981), lie between 970 and 1020$^{\circ}$C, and equilibrium pressures derived from Mercier (1980) fall within the range of 12 to 19 kbar (i.e., 42 to 63 km). These temperatures and pressures are reinforced by considerations of the Al-isopleths in the MAS system (Lane and Ganguly, 1980), as adjusted for the Fe effect on Al solubility in orthopyroxene (Lee and Ganguly, 1988). The equilibrium temperatures and pressures of xenoliths, as considered in P/T space, belong to the oceanic geotherm, based upon the various mantle geotherms presented by Mercier (1980). This geotherm is completely different from continental geotherms, e.g., from South Africa (Lesotho) and southern India. Mineral compositions of spinel-lherzolites in South Korea and eastern China are primitive; paleo-geotherms of both are quite similar, but degrees of depletion of the upper mantle could vary locally. This is demonstrated by eastern China, which has various depleted xenoliths caused by different degrees of partial melting.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2000.05a
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• pp.19-19
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• 2000

;Ultramafic xenoliths found in alkali basalts from Jeju-do, Korea are mostly spinel Iherzolites composed of olivine, orthopyroxene, clinopyroxene and spinel. A subordinate amount of spinel harzburgites and pyroxenites are also found. Temperatures for these xenoliths were estimated from the compositions of coexisting pyroxenes (Wood '||'&'||' Banno 1973; Wells 1977; Bertrand '||'&'||' Mercier 1985; Brey '||'&'||' Kohler 1990), the AI-solubility in orthopyroxene coexisting with olivine and spinel (Sachtleben '||'&'||' Seck 1981; Webb '||'&'||' Wood 1986), and from Fe/Mg partitioning between olivine and spinel (Ballhaus et al. 1991). Temperature estimates from the thermometers by Wells (1977) and Brey and Kohler (1990) are compatible. Average equilibrium temperatures by these two methods for spinel peridotites range from 890 to 1030$^{\circ}$C. Pressures for spinel peridotites were estimated from the geobarometer by Kohler and Brey (1991) derived from the equilibrium Ca content of olivine coexisting with clinopyroxene, and fall within the range of 12.9 to 26.3 kbar. The combination of the thermometer by Brey and Kohler (1990) and the geobarometer by Kohler and Brey (1991) yields P- T estimates for Jeju-do spinel peridotites that fall in experimentally determined spinel lherzolite field in CFMASCr system (O'Neill 1981). These P-T data sets have been used to construct the Quaternary Jeju-do geotherm, which is significantly different from the conventional conductive geotherm. The xenolith-derived geotherm has a higher T gradient at low P (13 kbar) than at high P, which may be due to perturbation of the conductive heat flow by magma underplating or overplating at the crust-mantle boundary. Temperature estimates and statistics on the xenoliths indicate that the crust/mantle boundary in Jeju-do lies at about 11 kbar (~39 km). Spinellherzolite is inferred as a main constituent rock of the uppermost lithospheric mantle beneath Jeju-do. Pyroxenites were intercalated in peridotites in similar depth and temperature as re-equilibrated veins or lens.

• Journal of the Mineralogical Society of Korea
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• v.18 no.1
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• pp.61-72
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• 2005

Modal and chemical compositions of clinopyroxnes in spinel peridotites from the Baegryeong Island and the Boeun, enclosed in Miocene alkali basalt, are important for understanding the pre-eruptive temperature condition and chemical processes such as mantle depletion and enrichment. All spinel peridotites show transitional texture between protogranular and porphyroclastic textures. Temperature ranges of spinel peridotites from the Baegryeong Island and the Boeun at 15 kb are 773∼1188℃ and 705∼1106℃, respectively. The spinel peridotites from the Baegryeong Island and the Boeun have undergone the 1∼10% and 1∼4% fractional melting, which were determined by using primitive mantle-normalized Y and Yb of clinopyroxenes. LREE enrichment patterns of clinopyroxene indicate that these rocks from both areas have undergone cryptic mantle metasomatism without new minerals.

• The Journal of the Petrological Society of Korea
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• v.21 no.3
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• pp.309-333
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• 2012

Basalt having lots of feldspar phenocryst occurred at the northern and southern slope of the Mt. Halla, Jejudo. Among them, the Sioreum trachybasalt in southern slope consists of abundant phenocrysts of plagioclase in aphanitic groundmass. And the number of plagioclase grains are about 20 per $10cm^2$, and based on 667 grains the sizes are 13~0.7 mm (average 4.23 mm) in length and 8.6~0.5 mm (average 2.3 mm) in width. In according to modal analyses, Sioreum basaltic rock consists mainly of plagioclase (16~28%), olivine, clinopyroxene (1.5~6%) and opaque minerals (~0.1%) of magnetite and ilmenite as phenocryst and microphenocryst and groundmass (60~82%). The compositions of plagioclase, olivine and clinopyroxene are bytownite~andesine, chrysolite~hyalosiderite, augite respectively. Plagioclase phenocrysts show different type of zoning, namely, normal, reversal, patchy, oscillatory type. The An contents of zoned plagioclase mainly increase from core to rim. Those of oscillatory type from core to rim show variations of increase following decrease or decrease following increase, being more enriched in rim or almost same to core. Under the microscope, some plagioclase phenocrysts are especially melted in core part or marginal part, or found as only the remnant remain which resulted from reaction with melt. Some clinopyroxene are also corroded in margin part or found as irregular shape resulted from melting. The characteristics of petrography and compositional variation from core to rim of plagioclase and clinopyroxene, indicate that they are disequilibrium with melt and has been undergone geological environmental changes in magma batch during crystallization including magma mixing with replenishment of more mafic and high temperature melt.