• Journal of the Mineralogical Society of Korea
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• v.15 no.1
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• pp.69-77
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• 2002

Margarite, which occurs in the Unkyori Formation of Miwon area, Chungcheongbukdo, South Korea, was investigated using the petrographic microscope, back-scattered electron images (BSEI), and electron probe microanalyzer (EPMA) to characterize the alteration textures and mineral chemistries. Most margarite crystals are inhomogeneous, and chlorite was commonly observed to occur at the boundaries parallel to the rim of margarite. Cracks occur across the basal plane of the margarite, and margarite is partly replaced by chlorite along the cracks. In additon, muscovite and biotite are intergrown in margarite and chlorite crystals, suggesting that margarite was partially altered to chlorite as well as to muscovite and biotite. Chemical analysis data show that paragonite solid solution in the margarite is approximately 19.6 mol%, but clintonite solid solution is negligible. Margarite crystals in the Unkyori Formation cut or penetrate other metamorphic minerals In the same thin sections and are oriented randomly without any relationship with the foliation of host rocks, indicating that formed as a secondary mineral after peak metamorphism. Furthermore, it seems that hydrothermal fluids associated with the Mesozoic intrusions developed near the sample are closely related to the margarite formation.

• Journal of the Mineralogical Society of Korea
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• v.15 no.3
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• pp.221-230
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• 2002

Weathering of biotite shows a biotite-vermiculite-kaolinite sequence at the early stage, but presents biotite-kaolinite sequence without a significant intermediate phase (vermiculite) at the late stage from the weathering profile of the granitic gneiss. Secondary 1:1 phyllosilicates are kaolinite and halloysite which show different weathering textures originated by a different formation mechanism. Kaolinitization began from the edges of biotite and propagated toward the interior of grain along a multilayered front. $10 \AA$ layers of biotite are interleaving with $7\AA$ layers of kaolinite and c-axis of two phases is consistent. Kaolinite pseudomorph of biotite is isovolumetric, compared to the biotite boundary and includes many band-like porosities parallel to the cleavage. Platy kaolinite formed by 1:1 layer fur layer replacement of biotite. Halloysitization proceeded outward from the grain edges which were foliated as fine flakes and bent at the right angle for cleavage Halloysites were extensively fanning out and greatly increased the volume of grain. This indicated that halloysite tubes were formed by epitaxial overgrowth on the surface of biotite with import of Si and Al from the external solution by dissolution of plagioclase. These halloysites have abnormally high Fe content ( ~11%).

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

• Economic and Environmental Geology
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• v.42 no.3
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• pp.177-193
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• 2009

The Samgwang deposit consists of eight massive mesothermal quartz veins that filled NE and NW-striking fractures along fault zones in Precambrian granitic gneiss of the Gyeonggi massif. The mineralogy and paragenesis of the veins allow two separate discrete mineralization episodes(stage I=quartz and calcite stage, stage II-calcite stage) to be recognized, temporally separated by a major faulting event. The ore minerals are contained within quartz and calcite associated with fracturing and healing of veins that occurred during both mineralization episodes. The hydrothermal alteration of stage I is sericitization, chloritization, carbonitization, pyritization, silicification and argillization. Sericitic zone occurs near and at quartz vein and include mainly sericite, quartz, and minor illite, carbonates and chlorite. Chloritic zone occurs far from quartz vein and is composed of mainly chlorite, quartz and minor sericite, carbonates and epidote. Fe/(Fe+Mg) ratios of sericite and chlorite range 0.45 to 0.50(0.48$\pm$0.02) and 0.74 to 0.81(0.77$\pm$0.03), and belong to muscovite-petzite series and brunsvigite, respectiveIy. Calculated $Al_{IV}$-FE/(FE+Mg) diagrams of sericite and chlorite suggest that this can be a reliable indicator of alteration temperature in Au-Ag deposits. Calculated activities of chlorite end member are $a3(Fe_5Al_2Si_3O_{10}(OH)_6$=0.0275${\sim}$0.0413, $a2(Mg_5Al_2Si_3O_{10}(OH)_6$=1.18E-10${\sim}$7.79E-7, $a1(Mg_6Si_4O_{10}(OH)_6$=4.92E-10${\sim}$9.29E-7. It suggest that chlorite from the Samgwang deposit is iron-rich chlorite formed due to decreasing temperature from high temperature(T>450$^{\circ}C$). Calculated ${\alpha}Na^+$, ${\alpha}K^+$, ${\alpha}Ca^{2+}$, ${\alpha}Mg^{2+}$ and pH values during wallrock alteration are 0.0476($400^{\circ}C$), 0.0863($350^{\circ}C$), 0.0154($400^{\circ}C$), 0.0231($350^{\circ}C$), 2.42E-11($400^{\circ}C$), 7.07E-10($350^{\circ}C$), 1.59E-12($400^{\circ}C$), 1.77E-11($350^{\circ}C$), 5.4${\sim}$6.4($400^{\circ}C$), 5.3${\sim}$5.7($350^{\circ}C$)respectively. Gain elements(enrichment elements) during wallrock alteration are $TiO_2$, $Fe_2O_3(T)$,CaO, MnO, MgO, As, Ag, Cu, Zn, Ni, Co, W, V, Br, Cs, Rb, Sc, Bi, Nb, Sb, Se, Sn and Lu. Elements(Ag, As, Zn, Sc, Sb, Rb, S, $CO_2$) represents a potential tools for exploration in mesothermal and epithermal gold-silver deposits.

• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.259-270
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• 2002

A small granodiorite-quartz monzonitic stock containing sericitic and propylitic alteration assemblages hosts a Cu-W breccia-pipe deposit in the southeastern Cyeongsang basin. The mineralized breccia-pipe contains angular to subangular brecciated fragments of granitic rocks showing clast-supported textures. An assemblage of quartz, tourmalines, sulfide minerals (mainly chalcopyrite, arsenopyrite and pyrrhotite) and calcite was precipitated as a hydrothermal cement between the brecciated fragments. A tourmaline aureole surrounds the breccia pipe. Extensive tourmalinization of the granitic rocks near and within the pipe and no tourmalinization in the sedimentary and volcanic rocks. The tourmalines are marked by Fe-rich, black charcoal-like schorl (80 mol% schorl relative) nearer the schorl-dravite solid solution. The chemical changes in the hydrothermal fluid are reflected by variations in compositional Boning from cores to rims. They generally contain cores with low values of Fe/(Fe+Mg) and high values of Na/(Na+ca) relative to rims. This is because of an increase Fe and Ca contents toward rims. The main trend of these variations is a combination of the exchange vectors Ca(Fe, Mg) $(NaAl)_{- }$ $_1$ and $Fe^{3}^{+}$ $Al_{[-10]}$ $_1$ It is thought that boiling causes the loss of $H_2$ into the vapor phase resulting in the oxidation of Fe in the aqueous phase. pH of the melt would be one of important controlling factors for the tourmaline stability. The tourmalines could be precipitated when the system evolved to the acidic hydrothermal regime as most hydrothermal brines and acidic gases exsolved from the magma. The Ilgwang tourmaline crystallization is products of hypogene orthomagmatic hydrothermal processes that were strongly pipe-controlled.

• Korean Journal of Mineralogy and Petrology
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• v.35 no.2
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• pp.83-100
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• 2022

The Zhenzigou Pb-Zn deposit, which is one of the largest Pb-Zn deposit in the northeast of China, is located at the Qingchengzi mineral field in Jiao Liao Ji belt. The geology of this deposit consists of Archean granulite, Paleoproterozoinc migmatitic granite, Paleo-Mesoproterozoic sodic granite, Paleoproterozoic Liaohe group, Mesozoic diorite and Mesozoic monzoritic granite. The Zhenzigou deposit which is a strata bound SEDEX or SEDEX type deposit occurs as layer ore and vein ore in Langzishan formation and Dashiqiao formation of the Paleoproterozoic Liaohe group. White mica from this deposit are occured only in layer ore and are classified four type (Type I : weak alteration (clastic dolomitic marble), Type II : strong alteration (dolomitic clastic rock), Type III : layer ore (dolomitic clastic rock), Type IV : layer ore (clastic dolomitic marble)). Type I white mica in weak alteration zone is associated with dolomite that is formed by dolomitization of hydrothermal metasomatism. Type II white mica in strong alteration zone is associated with dolomite, ankerite, quartz and alteration of K-feldspar by hydrothermal metasomatism. Type III white mica in layer ore is associated with dolomite, ankerite, calcite, quartz and alteration of K-feldspar by hydrothermal metasomatism. And type IV white mica in layer ore is associated with dolomite, quartz and alteration of K-feldspar by hydrothermal metasomatism. The structural formulars of white micas are determined to be (K_0.92-0.80Na_0.01-0.00Ca_0.02-0.01Ba_0.00Sr_0.01-0.00)_0.95-0.83(Al_1.72-1.57Mg_0.33-0.20Fe_0.01-0.00Mn_0.00Ti_0.02-0.00Cr_0.01-0.00V_0.00Sb_0.02-0.00Ni_0.00Co_0.02-0.00)_1.99-1.90(Si_3.40-3.29Al_0.71-0.60)_4.00O₁₀(OH_2.00-1.83F_0.17-0.00)_2.00, (K_1.03-0.84Na_0.03-0.00Ca_0.08-0.00Ba_0.00Sr_0.01-0.00)_1.08-0.85(Al_1.85-1.65Mg_0.20-0.06Fe_0.10-0.03Mn_0.00Ti_0.05-0.00Cr_0.03-0.00V_0.01-0.00Sb_0.02-0.00Ni_0.00Co_0.03-0.00)_1.99-1.93(Si_3.28-2.99Al_1.01-0.72)_4.00O₁₀(OH_1.96-1.90F_0.10-0.04)_2.00, (K_1.06-0.90Na_0.01-0.00Ca_0.01-0.00Ba_0.00Sr_0.02-0.01)_1.10-0.93(Al_1.93-1.64Mg_0.19-0.00Fe_0.12-0.01Mn_0.00Ti_0.01-0.00Cr_0.01-0.00V_0.00Sb_0.00Ni_0.00Co_0.05-0.01)_2.01-1.94(Si_3.32-2.96Al_1.04-0.68)_4.00O₁₀(OH_2.00-1.91F_0.09-0.00)_2.00 and (K_0.91-0.83Na_0.02-0.01Ca_0.02-0.00Ba_0.01-0.00Sr_0.00)_0.93-0.83(Al_1.84-1.67Mg_0.15-0.08Fe_0.07-0.02Mn_0.00Ti_0.04-0.00Cr_0.06-0.00V_0.02-0.00Sb_0.02-0.01Ni_0.00Co_0.00)_2.00-1.92(Si_3.27-3.16Al_0.84-0.73)_4.00O₁₀(OH_1.97-1.88F_0.12-0.03)_2.00, respectively. It indicated that white mica of from the Zhenzigou deposit has less K, Na and Ca, and more Si than theoretical dioctahedral mica. Compositional variations in white mica from the Zhenzigou deposit are caused by phengitic or Tschermark substitution [(Al³⁺)^VI+(Al³⁺)^IV <-> (Fe²⁺ or Mg²⁺)^VI+(Si⁴⁺)^IV] substitution. It means that the Fe in white mica exists as Fe²⁺ and Fe³⁺, but mainly as Fe²⁺. Therefore, white mica from layer ore of the Zhenzigou deposit was formed in the process of remelting and re-precipitation of pre-existed minerals by hydrothermal metasomatism origined metamorphism (greenschist facies) associated with Paleoproterozoic intrusion. And compositional variations in white mica from the Zhenzigou deposit are caused by phengitic or Tschermark substitution [(Al³⁺)^VI+(Al³⁺)^IV <-> (Fe²⁺ or Mg²⁺)^VI+(Si⁴⁺)^IV] substitution during hydrothermal metasomatism depending on wallrock type, alteration degree and ore/gangue mineral occurrence frequency.

• Economic and Environmental Geology
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• v.50 no.1
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• pp.1-14
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• 2017

The analytical conditions including surface state, moisture effect, and device condition were investigated for applying Short Wave Infrared(SWIR) spectroscopy to the field survey. Among the three surface state of samples (exposed surface, cutting face and powder), both spectra from the exposed surface and cutting face are almost identical whereas spectral variation was detected in powder sample. Over 24-hours-dryring of the wet sample at room temperature, the samples show a similar spectrum with that of dry condition. The result suggests that outcrop samples mighty be dried for 24 ~ 48 hours depending on the wetness of outcrop. The bright minerals could produce stable spectra with 10 times measurements as default value of the device under SWIR spectroscopy but the dark minerals would require about 10 seconds, which corresponds to 100 times measurements to get the reliable spectra. The position and shape 2,160 ~ 2,330 nm and/or other spectral features of hydrothermal alteration minerals by SWIR spectroscopy could be used for a classification of hydrothermal alteration zone in the field. Absorption peaks in 2,160 ~ 2180 nm are useful for identifying (advanced) argillic zone by spectral characteristics of kaoline, dickite, pyrophyllite, and alunite. Absorption peaks in 2,180 ~ 2,230 nm are able to define muscovite, sericite, and smectite, which are key alteration minerals in phyllic zone. Absorption peaks in 2,230 ~ 2,270 nm can be used to recognize prophylitic zone where chlorite and epidote occur. Absorption peaks of other principle minerals such as talc, serpentine, amphibole, and carbonate group are mainly detected within the wave length of 2,270 ~ 2,330 nm. This result indicates that the spectra of these minerals need to be carefully interpreted.

• Economic and Environmental Geology
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• v.25 no.3
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• pp.259-273
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• 1992

The Seongsan mine is one of the largest dickite deposits in the southwestern part of the Korean Peninsula. The main constithent minerals of the ore are dickite and quartz with accessory alunite, kaolinite and sericite. The geology around the Seongsan mine consists mainly of the late Cretaceous felsic volcanic rocks. In the studied area, these rocks make a synclinal structure with an axis of E-W direction plunging to the east. Most of the felsic volcanic rocks have undergone extensive hydrothermal alteration. The hydrothermally altered rocks can be classified into the following zones: Dickite, Dickite-Quartz, Quartz, Sericite, Albite and Chlorite zones, from the center to the margin of the alteration mass. Such zonal arrangement of altered rocks suggests that the country rocks, most of which are upper part of the rhyolite and welded tuff, were altered by strongly acid hydrothermal solutions. It is reasonable to consider that initial gas and solution containing $H_2S$ and other compounds were oxidized near the surface, and formed hydrothermal sulfuric acid solutions. The mineralogical and chemical changes of the altered rocks were investigated using various methods, and chemical composition of fifty-six samples of the altered rocks were obtained by wet chemical analysis and X.R.F. methods. On the basis of these analyses, it was found that some components such as $SiO_2$, $Al_2O_3$, $Fe_2O_3$, CaO, MgO, $K_2O$, $Na_2O$ and $TiO_2$ were mobilized considerably from the original rocks. The formation temperature of the deposits was estimated as higher than $200^{\circ}C$ from fluid inclusion study of samples taken from the Quartz zone. On the basis of the chemical composition data on rocks and minerals and estimated temperatures, the hydrothermal solutions responsible for the formation of the Seongsan dickite deposits were estimated to have the composition: $m_{K^+}=0.003$, $m_{Na^+}=0.097$, $m_{SiO_2(aq.)}=0.008$ and pH=5.0, here "m" represents the molality (mole/kg $H_2O$).

• Economic and Environmental Geology
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• v.46 no.3
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• pp.267-278
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• 2013

The East African Rift System(EARS) is known to be hosted epithermal Au-Ag deposits, and the best-known example is Main Ethiopian Rift Valley(MER) related to Quaternary bimodal volcanism. Large horst-graben system during rifting provides open space for emplacement of bimodal magmas and flow channel of geothermal fluids. In recent, large hydrothermally altered zones(Shala, Langano, and Allalobeda) and hot spring related to deeply circulating geothermal water have been increasing their importance due to new discoveries in MER and Danakil depression. The hot springs in Shala and Allalobeda occur as boiling pool and geyser on the surface, whereas some areas didn't observe them due to decreasing ground water table. The host rocks are altered to quartz, kaolinite, illite, smectite, and chlorite due to interaction with rising geothermal water. The hot springs in MER are neutral to slightly alkaline pH(7.88~8.83) and mostly classified into $HCO_3{^-}$ type geothermal water. They are strongly depleted in Au, and Ag, but show a higher Se concentration of up to 26.7 ppm. In contrast, siliceous altered rocks around hot springs are strongly enriched in Pb(up to 33 ppm, Shala), Zn(up to 313 ppm, Shala), Cu(up to 53.1 ppm, Demaegona), and Mn(up to 0.18 wt%t, Shala). In conclusion, anomalous Se in hot spring water, Pb, Zn, Cu, and Mn in siliceous altered rocks, and new discoveries in MER have been increasing potential for epithermal gold mineralization.

• Korean Journal of Mineralogy and Petrology
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• v.36 no.4
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• pp.273-288
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• 2023

The Gubong Au-Ag deposit, which has been one of the largest deposits (Unsan, Daeyudong, Kwangyang) in Korea, consists of eight lens-shaped quartz veins (a mix of orogenic-type and intrusion-related types) that filled fractures along fault zones within Precambrian metasedimentary rock. Korea Mining Promotion Corporation found a quartz vein (referred to as the No. 6 vein with a grade of 27.9 g/t Au and a width of 0.9 m) at a depth of -728 ML by drilling (No. 90-12) conducted in 1989. Korea Mining Promotion Corporation conducted drilling (No. 04-1) in 2004 to investigate the redevelopment's possibility of the No. 6 vein. The author studied the occurrence and chemical composition of chlorite and white mica using wallrock, wallrock alteration and quartz vein samples collected from the No. 04-1 drilling core in 2004. The alteration of studied samples occurs chloritization, sericitization, silicification and pyritization. Chlorite and white mica from mineralized zone at a depth of -275 ML occur with quartz, K-feldspar, calcite, rutile and pyrite in wallrock alteration zone and quartz vein. Chlorite and white mica from ore vein (No. 6 vein) at a depth of -779 ML occur with quartz, calcite, apatite, zircon, rutile, ilmenite, pyrrhotite and pyrite in wallrock alteration zone and quartz vein. Chlorite from a depth of -779 ML has a higher content of Al and Mg elements and a lower content of Si and Fe elements than chlorite from a depth of -275 ML. Also, Chlorites from a depth of -275 ML and -779 ML have higher content of Si element than theoretical chlorite. Compositional variation in chlorite from a depth of -275 ML was mainly caused by phengitic or Tschermark substitution [Al^{3+,VI + Al3+,IV} <-> (Fe²⁺ or Mg²⁺)^VI + (Si⁴⁺)^IV], but compositional variation from a depth of -779 ML was mainly caused by octahedral Fe²⁺ <-> Mg²⁺ (Mn²⁺) substitution. The interlayer cation site occupancy (K+Na+Ca+Ba+Sr = 0.76~0.82 apfu, 0.72~0.91 apfu) of white mica from a depth of -275 ML and -779 ML have lower contents than theoretical dioctahedral micas, but octahedral site occupancy (Fe+Mg+Mn+Ti+Cr+V+Ni = 2.09~2.13 apfu, 2.06~2.14 apfu) have higher contents than theoretical dioctahedral micas. Compositional variation in white mica from a depth of -275 ML was caused by phengitic or Tschermark substitution [(Al³⁺)^VI + (Al³⁺)^IV <-> (Fe²⁺ or Mg²⁺)^VI + (Si⁴⁺)^IV], illitic substitution and direct (Fe³⁺)^VI <-> (Al³⁺)^VI substitution. But, compositional variation in white mica from a depth of -779 ML was caused by phengitic or Tschermark substitution [(Al³⁺)^VI + (Al³⁺)^IV <-> (Fe²⁺ or Mg²⁺)^VI + (Si⁴⁺)^IV] and direct (Fe³⁺)^VI <-> (Al³⁺)^VI substitution.