• The Journal of the Petrological Society of Korea
• /
• v.14 no.2 s.40
• /
• pp.108-115
• /
• 2005

Gyeonggi metamorphic complex in the Gwangju area include banded biotite gneiss and quartzofeldspathic gneiss. Detailed structural analysis suggests that structural elements in the study area were formed by at least five phase of deformations. Penetrative compositional foliations(S1) formed in the banded gneiss during the first metamorphism and deformation (D1). After intrusion of plutonic rocks, the second deformation (D2) produced S2 foliations in the banded gneiss and quartzofeldspathic gneiss during the second metamorphism. D3 structures are represented by isoclinal folds (F3) whose axial surfaces are parallel to S3 foliations. The N-S oriented shortening (D4) was accommodated by closed upright F4 fold with about 100m of axial surface separation. F4 fold is refolded by regional F5 folding resulting in different orientation and fold style of F4 fold according to the position of F5 fold. The F4 fold with tight interlimb angle is subparallel to the axial surface (north-south) of F5 fold in the core of the F5 fold. In contrast the F4 fold trends northeast in the western limb and northwest in the eastern limb of F5 fold. The interlimb angle is larger in the limbs than that in the core of F5 fold. The trace of foliations is constrained by mainly F4 and F5 folds. Joint fanning around fold is developed in the limbs of F5 fold and bc joints are dominant in the hinge area of F5 fold. A strike-slip fault had developed in tile central part of the study area after F5 folding. The orientation of joint and foliation is rotated anticlockwise about $15^{\circ}$ by the landslide occurred during the Quaternary.

• Journal of the Mineralogical Society of Korea
• /
• v.32 no.2
• /
• pp.127-143
• /
• 2019

The geology of the Chulmasan area consists of Precambrain Sogeunri formation, granitic gneiss, foliated biotite granite, foliated mica granite, basic dyke and acidic dyke. REE mineralization in the area occurs at granitic gneiss and foliated mica granite. Minerals with minor amounts of REE and Th from granitic gneiss and foliated mica granite are zircon ($Y_2O_3$ 0.00~1.18 wt.%, $Gd_2O_3$ 0.00~0.59 wt.%, $Er_2O_3$ 0.00~0.22 wt.%, $Yb_2O_3$ 0.00~0.34 wt.%, $Lu_2O_3$ 0.00~0.48 wt.%, $ThO_2$ 0.00~0.33 wt.%), thorianite ($Nd_2O_3$ 0.00~0.24 wt.%, $Lu_2O_3$ 0.00~0.26 wt.%), berthierine ($La_2O_3$ 0.04~0.26 wt.%, $Nd_2O_3$ 0.00~0.20 wt.%, $Tb_2O_3$ 0.04~0.12 wt.%, $Dy_2O_3$ 0.17~0.26 wt.%, $Er_2O_3$ 0.33~0.44 wt.%, $Lu_2O_3$ 0.00~0.19 wt.%, $ThO_2$ 0.61~0.93 wt.%), chlorite ($La_2O_3$ 0.44~0.68 wt.%, $Ce_2O_3$ 0.12~0.13 wt.%, $Nd_2O_3$ 0.31~0.44 wt.%, $Eu_2O_3$ 0.03~0.08 wt.%, $Dy_2O_3$ 0.09~0.21 wt.%, $Ho_2O_3$ 0.04~0.14 wt.%, $Er_2O_3$ 0.18~0.32 wt.%, $Lu_2O_3$ 0.07~0.21 wt.%, $ThO_2$ 0.00~0.97 wt.%), biotite ($Nd_2O_3$ 0.02~0.08 wt.%, $Gd_2O_3$ 0.07~0.08 wt.%, $Tb_2O_3$ 0.02~0.07 wt.%, $Dy_2O_3$ 0.35~0.43 wt.%, $Ho_2O_3$ 0.15~0.26 wt.%, $Er_2O_3$ 0.24~0.28 wt.%, $Yb_2O_3$ 0.06~0.18 wt.%, $ThO_2$ 0.00~0.12 wt.%), orthoclase ($Dy_2O_3$ 0.05~0.12 wt.%, $Ho_2O_3$ 0.05~0.06 wt.%, $Er_2O_3$ 0.28 wt.%, $Yb_2O_3$ 0.06~0.12 wt.%) and plagioclase ($Ho_2O_3$ 0.01~0.03 wt.%, $Er_2O_3$ 0.10~0.27 wt.%, $ThO_2$ 0.11~0.13 wt.%). REE minerals (bastnaesite and fergusonite) were sealed fractures in mainly fledspar, mica, zircon, apatite and ilmenite. Therefore, bastnaesite and fergusonite from the Chulmasan area were formed from redissolution/reconcentration of REE-and Th-bearing minerals from granitic gneiss and foliated mica granite at late stage by several igneous activies and metamorphism.

• The Journal of the Petrological Society of Korea
• /
• v.16 no.3
• /
• pp.162-179
• /
• 2007

Macheon Layered Intrusion (MLI) which intruded into Precambrian gneiss complex of the northern Jirisan area, southeastern part of Youngnam (or Sobaeksan) Massif, is a layered mafic-ultramafic complex of Triassic age (ca. 223 Ma). The MLI is divided into Layered Series and Laminated Series. Layered Series is subdivided into Central Zone (Lower Zone) consisting of olivine gabbros and Peripheral Zone (Middle or Upper Zone) consisting of hornblende gabbros based on the type of cumulus texture and the main mafic phase. The Central Zone of Layered Series comprises thinly laminated olivine gabbros and uniform or thickly laminated coarse olivine gabbros which consist of mela-gabbro, troctolite, leuco-troctolite, and anorthositic rocks. Laminated Series is also subdivided into quartz-bearing biotite-pyroxene gabbros and homblende diorite and both have variable amount of interstitial quartz and microcline. Laminated series display moderately to slightly developed igneous lamination which is defined by the planar alignment of lath-shape plagioclases. Chilled margin of quartz-bearing biotite-pyroxene gabbro with surrounding Precambrian gneisses insists shallower intrusion of more felsic cognate magma evolved in the deep a little later. Rocks of Layered Series have orthocumulus to adcumulus olivine, adcumulus to intercumulus plagioclase, and intercumulus to heteradcumulus pyroxene and hornblende. Magmatic modally grading, folding, and cross-lamination are not rarely occurred in thinly layered rocks. These textural characteristics define main mechanisms of the formation of layered and laminated structure in mafic-ultramafic rocks of Macheon Layered Intrusion are gravity settling and in-situ crystallization associated with slumping and density current.

• The Journal of the Petrological Society of Korea
• /
• v.27 no.2
• /
• pp.85-96
• /
• 2018

The Neoproterozoic Gyemyeongsan Formation and the Mesozoic igneous rocks are distributed in the Eoraesan area, Chungju which is located in the northwestern part of Ogcheon metamorphic zone, Korea, and the rare earth element (REE) mineralized zone has been reported in the Gyemyeongsan Formation. We drew up the detailed geological map by the lithofacies classification, and measured the radioactivity values of the constituent rocks to understand the distribution and characteristics of the source rocks of REE ore body in this paper. It indicates that the Neoproterozoic Gyemyeongsan Formation is mainly composed of metapelitic rock, granitic gneiss, iron-bearing quartzite, metaplutonic acidic rock (banded type, fine-grained type, basic-bearing type, coarse-grained type), metavolcanic acidic rock, and the Mesozoic igneous rocks, which intruded it, are divided into pegmatite, biotite granite, gabbro, diorite, basic dyke. The constituent rocks of Gyemyeongsan Formation show a zonal distribution of mainly ENE trend, and the distribution of basic-bearing type of metaplutonic acidic rock (MPAR-B) is very similar to that of the previous researcher's REE ore body. The Mesozoic biotite granite is regionally distributed unlike the result of previous research. The radioactive value of MPAR-B, which has a range of 852~1217 cps (average 1039 cps), shows a maximum value among the constituent rocks. The maximum-density distribution of radioactive value also agrees with the distribution of MPAR-B. It suggests that the MPAR-B could be a source rock of the REE ore body.

• Journal of the Mineralogical Society of Korea
• /
• v.17 no.3
• /
• pp.221-233
• /
• 2004

Mineralogical characteristics and genesis of phlogopite in the talc deposits of the chungnam area were studied. Mica is one of the major impurity of talc ores in the study area. Talc-related micas show typical phlogopite composition, whereas talc-unrelated micas show wide compositional variations between biotite and phlogopite. Phlogopite mainly occurs in the black-wall type zone, especially in the nodular talc ores near the outer part of talc ore bodies. Interleaving textures of phlogopite and chlorite are easily observed under the optical microscope and back-scattered electron images. Interleaving textures of phlogopite and talc are observed also. Examination of the phlogopite by transmission electron microscope reveals that 14 $\AA$ layers of chlorite are randomly interlayered within the 10 $\AA$ layers of phlogopite, which suggests that the genesis of phlogopite is closely related to chlorite. Considering the occurrence and mineralogical characteristics of phlogopite, and the possible origin of K for the formation of phlogopite, phlogopite of the study area was formed by interaction between talc ore body and hydrothermal solution containing sufficient K at the late stage of talc formation. K might be introduced from the granitic gneiss at the contact zone between the talc ore body and the granitic gneiss under favorable structural condition for the potash metasomatism.

• Journal of the Korean earth science society
• /
• v.25 no.4
• /
• pp.251-264
• /
• 2004

The Charnockite in Sancheong region is quarzofeldspathic rock containing orthopyroxene and garnet with a color dark than common granitic rocks. The Chamockite are mostly massive and medium to coarse-grained with K-feldspar phenocryst, but reveal weak foliation. The rock consist mainly of quartz, K-feldspar, plagioclase and orhopyroxene, with biotite, garnet, and anthophyllite. In petrochemistry, the Chamockite has 61-65% $SiO_2$ contents, varying gradually into the margin contacted with orthogneiss, which have compositions of felsic igneous rocks. Major element show almost systematical variation with those of the marginal orthogneisses, except the hornblende gneiss and anorthosite. The Charnockite and orthogneisses show the tholeiitic differentiational trend. Trace and rare earth element abundance patterns in the Charnockite show remarkable negative Sr and Eu anomalies similar to orthogneisses, but different from the hornblende gneiss and anorthosite. Eu contents of the Charnockite are richer than that of orthogneisses. The metamorphic condition of the Charnockite were tested by an orthopyroxene-garnet geotherrnorneter and a plagioclase-garnet geobarometer. Estimated P-T conditions are about $761^{\circ}C$ and 7 kbar at peak metamorphism, but $653^{\circ}C$ and 6.4 kbar at retrograde metamorphism. This suggests that the Charnockite have from an early stage of high-grade metamorphism to represent the granulite facies and then to a late stage medium-grade metamorphism belonging to the amphibolite facies.

• Journal of the Mineralogical Society of Korea
• /
• v.28 no.3
• /
• pp.221-231
• /
• 2015

Precambrian Jirisan gneiss complex suffered retrograde metamorphism ranging from granulite facies to the amphibolite facies and/or greenschist facies. Intrusive anorthositic rocks in gneiss complex are influenced by late metamorphism. Mafic mineral in anorthositic rock composed mainly of amphiboles, which can anticipate the information about metamorphic conditions and metamorphic facies. Amphiboles from anorthositic rock show subhedral to anhedral in shape and mostly blueish green and/or green in colour in plane polarized light. Some of brownish amphiboles show zonal texture with brownish to blueish green in color from core to rim. Reaction parts in clinopyroxene which exchange with amphibole. It suggests retrograde metamorphism and/or alteration. Amphiboles composing anorthositic rocks can be classified into two types depending on the size and occurrence of amphibole. The first type is microcrystalline amphibole occurring matrix [Group I: ferrohornblende]. The second type is amphibole with 1 mm or larger in size, which is usually occurred in the boundary between opaque mineral and plagioclase [Group II: ferropargasite]. Electron microscopic analyses base on the $Al^{vi}$ composition in amphiboles suggest that the metamorphic pressure of anorthositic rock was low with 5 kbar or less. Ti compositional range in amphibole and representing hornblende+ plagioclase+garnet+biotite+chlorite mineral assemblage suggest that metamorphic facies of anorthositic rock is in amphibolite facies.

• Journal of the Mineralogical Society of Korea
• /
• v.25 no.4
• /
• pp.221-231
• /
• 2012

Uljin cassiterite deposit had been known to be a pegmatitic origin derived from the Wangpiri (Buncheon) granitic gneiss of Precambrian period. Lithium ore also shows the same origin and its lithium bearing mineral was ascertained to be a taeniolite. But the presence of leucocratic granites which played the role of host rocks haven't been clearly designated yet in these provinces. Even though Bonghwa and Youngweol sericite deposits situated in the vicinities of Hambaeg syncline had been known to have their host rocks as Hongjesa Granites of Precambrian period and Pegmatitic migmatite of unknown age respectively. But younger leucocratic granites are characterized by more amounts of albite and sericite (muscovite-3T type) than those of the older granitic rocks which contain plenty of biotite and chlorites. Although the younger granites show rather higher contents of alkalies such as $Na_2O$ (0.13~8.03 wt%) and $K_2O$ (1.71~6.38 wt%), but CaO (0.05~1.21 wt%) is very deficient due to the albitization and greisenization. Manisan granite, which is assumed to be Daebo granite which intruded the Gyunggi Gneiss Complex was again intruded by leucocratic granite whose microclinized part changed into kaolins. Taebaegsan region shows a wide distribution of carbonate rocks which are especially favorable to the ore depositions. And the presence of alkali granites which formed in the later magmatic evolution are well known to be worthwhile to the prospections of various rare metals and REEs resources.

• The Journal of the Petrological Society of Korea
• /
• v.9 no.1
• /
• pp.40-50
• /
• 2000

This study is aimed at elucidating the source rocks of the Hayang strata in the northeastern part of the Gyeongsang Basin. Zircon morphology was analyzed for sandstones from the Iljig, Hupyeongdong, and Jeomgog formations of the Hayang Group and Precambrian gneisses and Jurassic granites. Generally, the composite zircon crystals extracted from the basement rocks and the Hayang Group sandstones show short prismatic to middle prismatic shapes. {110)={100) prism type is dominant and (101) pyramid is the average of the zircon morphology data. Zircon index@) and the shape trend characteristics clearly show that the zircon crystal forms of the Iljig and Hupyeongdong sandstones are dominantly similar to those of the biotite banded gneiss and granite gneiss of Precambrian age. Zircon morphology of the Jeomgog sandstones is dominantly similar to those of the Jurassic granites. Referring to the reported paleocurrent result, the source rocks of the Iljig and Hupyeongdong formations are mainly the Precambrian gneisses distributed in the southeastern and northeastern parts, respectively. And Jeomgog sandstones were mainly derived from Cheongsong granite at Cheongsong uplift region in the eastern part. At the time of completion of the Hupyeongdong sedimentation, the Precambrian basement rocks were severely eroded and formed low topography. During the Jeomgog period, the Jurassic granites which intruded the Precambrian basement began to crop out on the surface. The basin widely extended toward the east and the exposed Jurassic granite of Cheongsong uplift region actively supplied the sediments to the basin.

• The Journal of Engineering Geology
• /
• v.14 no.1
• /
• pp.61-69
• /
• 2004

Building stones are used mainly as a material for making decoration and sculpture, and consequently they must have predominant physical properties extensively. Among various physical properties, the coefficient of pore dominates the usefulness of building stones, so the plans were made for establishing the quality classification of building stones with respect to the nature of pore. For this study, bore-hole core samples according to the depth of the biotite granites and the granitic gneiss were applicated. From the related chart between porosity and absorption ratio, Mungyeong granitic gneiss($Gn_1$) shows the widest phase of distribution in the range of measurement values, and the values decrease in the order of Pocheon granite($Gr_2$) and Mungyeong granite($Gr_1$) in the range. The strength of each rock mass varies with the degree of alteration. Also in correlation between compressive strength and tensile strength, the range of measurement values decrease in the order of $Gn_1$, $Gr_2$and $Gr_1$. Porosity is adopted as a representative physical property for establishing the quality classification of building stones, and then relative evaluation was made with regard to various physical properties. From the related chart between porosity(n)-specific gravity(G), absorption ratio(Ab), compressive strength(${\sigma}_{c}$), tensile strength(${\sigma}_{t}$), shore hardness(Hs) and Young's modulus($E_{t}$), standard of each grade is established.