• Journal of the Mineralogical Society of Korea
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• v.6 no.2
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• pp.122-144
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• 1993

The Kimhae napseok clay deposit was studied to characterize its mineralogy and genesis. Geology of the deposit is composed of Tertiary volcanic rocks and granodiorite. Tertiary volcanic rocks consist of andesitic tuff with minor interstratified tuffaceous shale, and rhyodacitic tuff. The main ore body of 2.4 to 4 m in thickness developed parallel to the bedding of andesitic tuff bed. Its strike and dip are $N70^{\circ}E-N85^{\circ}E$ and $16^{\circ}NW-32^{\circ}NW$, respectively. Two alteration zones; the propylitic zone of albite-epidote-chlorite-quartz assemblage and advanced argillic zone of pyrophyllite-dickite-alunite-diaspore assemblage are developed. Correlation of $SiO_2$ to $Al_2O_3$ shows no relation in propylitic zone, while a negative linear relation in advanced argillic zone. Chemical variation shows that $SiO_2$, $Al_2O_3$, MgO, CaO, $Na_2O$ and $K_2O$ were leached out during hydrothermal alteration. Pyrophyllite, the most abundant mineral in advanced argillic zone, occurs as low temperature 2M polytype. It is closely associated with dickite, diaspore and alunite. The Hinckley index of dickite is 0.83 showing moderate crystallinity. Na content is increasing in the M site with the increasing content of cations in the R-site. the mole percent of Na replacing K in alunite ranges from 53.2 to 71.6. It is also found that pyrophyllite grows in the dissolution site of diaspore. Plagioclase was albitized. Lowering of pH caused mainly by sulfide and sulfate decomposition resulted in preferential leaching of Si. It is inferred that aluminum released from plagioclase in the volcanic rocks as well as from the tuffaceous shale intercalated in andesitic tuff were the main sources of aluminum required for the formation of clay deposit. pH in hydrothermal fluid decreased from propylitic zone to advanced argillic zone with increasing degree of alteration. Based on experimental data reported in the literature and mineral assemblages, the formation temperature of the deposit ranges 270 to $320^{\circ}C$.

• Journal of the Mineralogical Society of Korea
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• v.28 no.3
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• pp.265-277
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• 2015

Hydrothermal alteration patterns and environment are studied by mineral assemblages and chemical analyses of surface and core samples from Miryang pyrophyllite deposit. The alteration zones of this deposit can be divided into three zones on the basis of mineral assemblage; advanced argillic, phyllic, and propylitic zone. Advanced argillic zone mainly consists of pyrophyllite-dickite (-quartz) and corresponds to principal mining ore. The common mineral assemblage of phyllic zone and propylitic zone are sericite-quartz-dickite and chlorite-quartz, respectively. Horizontal and vertical alteration patterns and major element geochemistry indicate that pyrophyllite ores have been formed several times by hydrothermal alteration. And it also suggests that the huge ore bodies may be extended from the deeper part of recent quarries to the south-southeastern direction. The paragenesis of ore minerals and polytype (2M) suggest that ore deposit was formed at about $300-350^{\circ}C$.

• Economic and Environmental Geology
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• v.44 no.6
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• pp.463-474
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• 2011

The Haenam epithermal mineralized zone is located in the southwestern part of South Korea, and hosts low sulfidation epithermal Au-Ag deposit (Eunsan-Moisan) and clay quarries (Okmaesan, Seongsan, and Chunsan). Epithermal deposits and accompanying hydrothermal alteration related to Cretaceous volcanism caused large zoned assemblages of hydrothermal alteration minerals. Advanced argillic-altered rocks with mineral assemblages of alunite-quartz, alunite-dickite-quartz, and dickite-kaolinite-quartz exposed on the Okmaesan, Seongsan, and Chunsan area. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), with three visible and near infrared bands, six shortwave infrared bands, and five thermal infrared bands, was used to identify advanced argillic-altered rocks within the Haenam epithermal mineralized zone. The distinct spectral features of hydrothermal minerals allow discrimination of advanced argillic-altered rocks from non-altered rocks within the study area. Because alunite, dickite, and kaolinite, consisting of advanced argillic-altered rocks within the study area are characterized by Al-O-H-bearing minerals, these acid hydrothermal minerals have a strong absorption feature at $2.20{\mu}m$. The band combination and band ratio transformation cause increasing differences of DN values between advanced argillic-altered rock and non-altered rock. The alunite and dickite-kaolinite of advanced argillic-altered rocks from the Okmaesan, Seongsan, and Chunsan have average DN values of 1.523 and 1.737, respectively. These values are much higher than those (1.211 and 1.308, respectively) of non-altered area. ASTER images can remotely provide the distribution of hydrothermal minerals on the surface. In this way good relation between ASTER spectra analysis and field data suggests that ASTER spectral analysis can be useful tool in the initial steps of mineral exploration.

• Journal of the Mineralogical Society of Korea
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• v.15 no.3
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• pp.205-220
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• 2002

The gold-silver deposits in the Casado district were formed in the sheeted and stockwork quartz veins which fill the fault fractures in volcanic rocks. K-Ar dating of alteration sericite (about 70 Ma) indicates a Late Cretaceous age for ore mineralization. These veins are composed of quartz, adularia, carbonate, and minor of pyrite, sphalerite, chalcopyrite, galena, Ag-sulfosalts (argentite, pearceite, Ag-As-Sb-S system), and electrum. These veins are characterized by chalcedonic, comb, crustiform and feathery textures. Based on the hydrothermally altered mineral assemblages, regional alteration zoning associated with mineralization in the Gasado district is defined as four zones; advanced argillic (kaolin mineral-alunite-quartz), argillic (kaolin mineral-quartz), phyllic (quartz-sericite-pyrite) and propylitic (chlorite-carbonate-quartz-feldspar-pyroxene) zone. Phyllic and propylitic zones is distributed over the study area. However, advanced argillic zone is restricted to the shallow surface of the Lighthouse vein. Compositions of electrum ranges from 14.6 to 53.7 atomic % Au, and the depositional condition for mineralization are estimated in terms of both temperature and sulfur fugacity: T=245。$~285^{\circ}C$, logf $s_2$=$10^{-10}$ ~ $10^{-12}$ Fluid inclusion and stable isotope data show that the auriferous fluids were mixed with cool and dilute (158。~253$^{\circ}C$ and 0.9~3.4 equiv. wt. % NaCl) meteoric water ($\delta^{18}$ $O_{water}$=-10.1~8.0$\textperthousand$, $\delta$D=-68~64$\textperthousand$). These results harmonize with the hot-spring type of the low-sulfidation epithermal deposit model, and strongly suggest that Au-Ag mineralization in the Gasado district was formed in low-sulfidation alteration type environment at near paleo-surface.

• 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.23 no.3
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• pp.287-308
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• 1990

The Ogmae alunite-kaolinite deposit occurs in acidic tuff, the Hwangsan Tuff, of upper Crataceous age in the Haenam volcanic field, SW Jeonnam. This deposit characterized by advanced argillic alteration formed $71.8{\pm}2.8{\sim}73.9{\pm}2.8$ Ma ago in very shallow depth environment with acid-sulfate solution. Wallrock alteration can be classified into four zones from the center to the margin of the deposit: alunite, kaolinite, illite, and silicified zone. The mineral assemblage in the alunite zone, ore zone, is alunite-quartz-pyritekaolinite. Consideration of stability relation of these minerals suggests that the maximum alteration temperature is estimated at about $250^{\circ}C$ with solution pH of 3 or below assuming that pressure does not exceed 0.3 Kb. Alunite occurs as two different types; replacement and vein-type deposit. The former one consists of fine grained alunite and the later one coarse grained and relatively pure alunite that formed by open space filling. Isomorphous substitution of Na for K in these two types of alunites range 0 to 40 %, indicating that Na/K ratio in the solution is spontaneously changed during the alteration process. Alunite which has higher Na substitution probably formed in an earlier stage while the solution sustain high Na/K ratio. K-Ar age of alunites indicate that the replacement alunite formed earlier($73.9{\pm}2.8Ma$) than the vein-type alunite($71.8{\pm}2.8Ma$). The ${\delta}^{34}S$ value of pyrite and alunite indicate that those minerals formed at isotopically nonequillibrium state. The ${\delta}^{16}O$ and ${\delta}D$ values, of kaolintics 5.0 to 9.0‰ and -54 to -99‰, respectively, indicate that those are formed by hydrothermal solution having magmatic origin which have been diluted by low ${\delta}D$ meteoric water.

• Economic and Environmental Geology
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• v.50 no.1
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• pp.15-26
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• 2017

Advanced argillic, argillic, and phyllic zones are the most important alteration patterns to predict the hidden ore body during exploration of hydrothermal deposits. We examined the quantitative relationship between the spectral absorption characteristics and the mineral content of the synthetic mixtures such as alunite-kaolinite and illite-kaolinite using short wavelength infrared (SWIR) spectroscopy. In the alunite-kaolinite mixtures, the spectral absorption characteristics of the alunite was highly correlated with the Hull quotient reflectance(0.99) and the kaolinite had the highest correlation with the Gaussian peak(0.92). Illite-kaolinite mixtures are essential for Gaussian deconvolution because of the overlap of absorption region. Illite and kaolinite mixtures indicate the high correlation of 0.93 and 0.98, respectively. The error ranges in the alunite-kaolinite(8%) and illite-kaolinite mixtures(5%) derived from SWIR were smaller than the ones(29% and 26%) obtained from X-ray diffraction(Rietveld) analysis. These results show that SWIR spectroscopic analysis is more reliable than XRD Rietveld analysis in terms of quantification of allowed minerals.