• Economic and Environmental Geology
• /
• v.43 no.5
• /
• pp.491-503
• /
• 2010

Geochemical characteristics of the Moisan epithermal gold-silver deposit with total 140 samples in Haenam area, Jeollanamdo were studied by using multivariate statistical analysis (correlation analysis, factor analysis and cluster analysis). The correlation analysis reveals that Ag, Cu, Bi, Te are highly correlated with Au in the both non-mineralized and mineralized zone. It is resulted from the presence of Au-Ag bearing minerals (electrum, sylvanite, calaverite and stuezite) and non Au-Ag containing minerals (chalcopyrite, tellurobismuthite and bismuthinite). Mo shows relatively much higher correlation at the mineralized zone (0.615) than non-mineralized zone (0.269) which implies Mo content is strongly affected by Au-mineralization. While Mn, Cs, Fe, Se correlated with Au at the nonmineralized zone, they have negative correlation at the mineralized zone. Therefore, they seem to be eluviated elements from the host rock during gold mineralization. Sb is enriched during the gold mineralization showing high correlation at the mineralized zone and negative correlation at the non-mineralized zone. According to the factor analysis, Se, Ag, Cs, Te are the indicators of gold mineralization presence due to the strong affection of gold content in the non-mineralized zone. In the mineralized zone, on the other hand, Mo, Te and Sb, Cu are the indicators of gold and silver mineralization, respectively. While the cluster analysis reveals that Cd-Zn-Pb-S, Bi-Fe-Cu-Mn, Se-Te-Au-Cs-Ag, As-Sb-Ba are the similar behavior elements groups in the non-mineralized zone, Cd-Zn-Mn-Pb, Fe-S-Se, As-Bi-Cs, Ag-Sb-Cu, Au-Te-Mo are the similar behavior elements groups in the mineralized zone. Using multivariate statistical analysis as mentioned above makes it possible to compare the behavior of presented minerals and difference of geochemical characteristics between mineralized and non-mineralized zone. Therefore, it will be expected a useful tool on the similar type of mining exploration.

• Economic and Environmental Geology
• /
• v.22 no.3
• /
• pp.221-235
• /
• 1989

Gold-silver mineralization of the Goryeong-Waegwan area was deposited in three stages of quartz and calcite veins which fill fissures in Cretaceous sedimentary rocks of the Sindong Group. Radiometric dating indicates that mineralization is Late Cretaceous age(98 Ma) likely associated genetically with intrusion of a small biotite granite stock. Fluid inclusion and stable isotope data indicate that Au-Ag ore was deposited at temperatures between $280^{\circ}C$ and $230^{\circ}C$ from fluids with salinities between 1.7 and 8.7 equiv.wt.% NaCl. Evidence of boiling indicates pressures of <100 bars, corresponding to depths of 425 and 1,150m, respectively, assuming lithostatic and hydrostatic loads. Within ore stage I there is an apparent decrease in ${\delta}^{34}S$ values of $H_2S$ with paragenetic time, from +1.4 to -2.5 per mil. This pattern was likely achieved through progressive increases in pH and activity of oxygen accompanying boiling. Measured and calculated hydrogen and oxygen isotope values of ore-forming fluids(${\delta}D$ = -90 to -100 per mil; ${\delta}^{18}O$ = +3.9 to -11.4 per mil) indicate meteoric water dominance, approaching unex-changed meteoric water values. Au-Ag deposition is thought to be the result of cooling and dilution of a boiling fluid through mixing with less evolved meteoric waters.

• Economic and Environmental Geology
• /
• v.26 no.4
• /
• pp.433-444
• /
• 1993

Electrum (32~73 atom. % Ag)-sulfide mineralization of the Bodeok mine in the Boseong area was deposited in two stages of mineralogically simple, massive quartz veins that fill the fractures along fault shear zones in Precambrian gneiss. Radiometric dating indicates that mineralization is Late Jurassic age ($155.9{\pm}2.3$ Ma). Fluid inclusion data show that ore mineralization was formed from $H_2O-CO_2$ fluids with variable $CO_2$ contents ($X_{CO_2}=0.0$ to 0.7) and low salinities (0.0 to 7.4 wt. % eq. NaCl) at temperatures between $200^{\circ}$ and $370^{\circ}C$. Evidence of fluid unmixing ($CO_2$ effervescence) indicates pressures up to 1 kbar. Gold-silver deposition occurred later than base-metal sulfide deposition, at temperatures near $250^{\circ}C$ and was probably a result of cooling and decreasing sulfur activity caused by sulfide precipitation and/or $H_2S$ loss (through fluid unmixing). Calculated sulfur isotope compositions of ore fluids (${\delta}^{34}S_{{\Sigma}S}=1.7$ to 3.3‰) indicate an igneous source of sulfur in hydrothermal fluids. Measured and calculated O and H isotope compositions of ore fluids (${\delta}^{18}O_{water}=4.8$ to 7.2‰, ${\delta}D_{water}=-73$ to -76‰) indicate that mesothermal auriferous fluids at Bodeok were likely mixtures of $H_2O-rich$, isotopically evolved meteoric waters and magmatic $H_2O-CO_2$ fluids.

• Economic and Environmental Geology
• /
• v.41 no.5
• /
• pp.563-575
• /
• 2008

The ore depositional and geochemical exploration on Bougouni area in Mali, central-western Africa covering $2,000\;Km^2$ was conducted for determining the detailed survey area. According to the results of this exploration, the highly potential area for the zinc-tin-gold-silver mineralization was found in Kolani and Riarako areas. The contents of zinc in heavy sand collected in the stream sediments range from 14 to 8,600 ppm, while the mean values of zinc in this area are 543 ppm with threshold($x+2{\sigma}$) of zinc anomalies being 1,000 ppm in Bougouni area. Generally zinc anomalies are associated with the tin and molybdenum anomalies and hence the anomalous area was selected for the detailed survey area for tracing the primary zinc and precious ore deposits related to these anomalies in following project.

• Economic and Environmental Geology
• /
• v.39 no.5 s.180
• /
• pp.567-581
• /
• 2006

The Au-Ag lode deposits in South Korea are closely associated with the Mesozoic granitoids. Namely, the Jurassic deposits formed in mesozonal environments related to deep-seated granitoids, whereas the Cretaceous ones were developed in porphyry-related environments related to subvolcanic granitoids. The time-space relationships of the Au-Ag lode deposits in South Korea are closely related to the changing plate motions during the Mesozoic. Most of the Jurassic auriferous deposits (about $165{\sim}145$ Ma) show fluid characteristics typical of an orogenic-type gold deposits, and were probably generated in a compressional to transpressional regime caused by an orthogonal to oblique convergence of the Izanagi Plate into the East Asian continental margin. On the other hand, strike-slip faults and caldera-related fractures together with subvolcanic activity are associated with major strike-slip faults reactivated by a northward (oblique) to northwestward (orthogonal) convergence, and probably have played an important role in the formation of the Cretaceous Au-Ag lode deposits (about $110{\sim}45$ Ma) under a continental arc setting. The temporal and spatial distinctions between the two typical Mesozoic deposit styles in South Korea probably reflect a different thermal episodes (i.e., late orogenic and post-orogenic) and ore-forming fluids related to different depths of emplacement of magma due to regional changes in tectonic environment.

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

• Economic and Environmental Geology
• /
• v.35 no.4
• /
• pp.299-316
• /
• 2002

The Samkwang gold-silver deposits consist of gold-silver-bearing hydrothermal massive quartz veins which filled the fractures along fault shear (NE, NW) zones within Precambrian banded or granitic gneiss of Gyeonggi massif. Ore mineralization of this deposits occurred within a single stage of quartz vein which was formed by multiple episodes of fracturing and healing. Based on vein mineralogy and paragenesis, massive quartz veins are divided into two main paragenetic stages which are separated by a major faulting event. Main ore mineralization occurred at stage I. Wall-rock alteration from this deposits occur as mainly sericitization, chloritization, silicification and minor amounts of pyritization, carbonitization, propylitization and argillitization. Ore minerals are composed mainly of arsenopyrite (29.21-32.24 As atomic %), pyrite, sphalerite (6.45-13.82 FeS mole %), chalcopyrite, galena with minor amounts of pyrrhotite, marcasite, electmm (39.98-66.82 Au atomic %) and argentite. Systematic studies of fluid inclusions in early quartz veins and microcracks indicate two contrasting physical-chemical conditions: 1). temperature (215-345$^{\circ}$C) and pressure (1296-2022 bar) event with $H_{2}O-CO_{2}-CH_{4}-NaCl$fluids (0.8-6.3 wt. %) related to the early sulfide deposition, 2). temperature (203-441$^{\circ}$C) and pressure (320 bar) event with $H2_{O}$-NaCI $\pm$ $CO_{2}$ fluids (5.7-8.8 wt. %) related to the late sulfide and electrum assemblage. The H20-NaCI $\pm$ $CO_{2}$ fluids represent fluids evolved through fluid unmixing of an $H_{2}O-CO_{2}-CH_{4}-NaCl$fluids due to decreases in fluid pressure and influenced of deepcirculated meteoric waters possibly related to uplift and unloading of the mineralizing suites. Calculated sulfur isotope compositions (${\delta}^{34}S_{fluid}$) of hydrothermal fluids (1.8-4.9$\textperthousand$) indicate that ore sulfur was derived from an igneous source. Measured and calculated oxygen and hydrogen isotope compositions (${\delta}^{18}O_{I120}$, ${\delta}D$) of ore fluids (-5.9~10.9$\textperthousand$, -102~-87$\textperthousand$) indicate that mesothermal auriferous fluids at Samkwang gold-silver deposits were likely mixtures of $H_{2}O$-rich, isotopically less evolved meteoric water and magmatic fluids.

• Economic and Environmental Geology
• /
• v.34 no.1
• /
• pp.25-38
• /
• 2001

Contrasts in the style of the gold-silver mineralization in geologic and tectonic settings in Korea, together with radiometric age data, reflect the genetically different nature of hydrothermal activities, coinciding with the emplacement age and depth of Mesozoic magmatic activities. It represents a clear distinction between the plutonic settings of the Jurassic Daebo orogeny and the subvolcanic environments of the Cretaceous Bulgugsa igneous activities. During the Daebo igneous activities (about 200-130 Ma) coincident with orogenic time, gold mineralization took place between 197 and 127 Ma. The Jurassic deposits commonly show several characteristics: prominent association with pegmatites, low Ag/Au ratios in the ore-concentrating parts, massive vein morphology and a distinctively simple mineralogy including Fe-rich sphalerite, galena, chalcopyrite, Au-rich eIectrum. pyrrhotite and/or pyrite. During the Bulgugsa igneous activities (120-60 Ma), the precious-metal deposits are generally characterized by such features as complex vein morphology, medium to high AgiAu ratios in the ore concentrates, and abundance of ore minerals including base-metal sulfides, Ag sulfides, native silver, Ag sulfosalts and Ag tellurides. Vein morphology, mineralogical, fluid inclusion and stable isotope results indicate the diverse genetic natures of hydrothermal systems. The Jurassic Au-dominant deposits were formed at the relatively high temperature (about 300 to 450$^{\circ}$C) and deep-crustal level (>3.0 kb) from the hydrothermal fluids containing more amounts of magmatic waters (3180; 5-10 %0). It can be explained by the dominant ore-depositing mechanisms as CO2 boiling and sulfidation, suggestive of hypo/mesothermal environments. In contrast, mineralization of the Cretaceous Au-Ag type (108-71 Ma) and Agdominant type (98-71 Ma) occurred at relatively low temperature (about 200 to 350$^{\circ}$C) and shallow-crustal level «1.0 kb) from the ore-fonning fluids containing more amounts of less-evolved meteoric waters (15180; -10-5%0). These characteristics of the Cretaceous precious-metal deposits can be attributed to the complexities in the ore-precipitating mechanisms (mixing, boiling, cooling), suggestive of epilmesothermal environments. Therefore, the differences of the emplacement depth between the Daebo and the Bulgugsa igneous activities directly influence the unique temporal and spatial association of the deposit type.

• Economic and Environmental Geology
• /
• v.44 no.5
• /
• pp.413-431
• /
• 2011

An Epithemal Au-Ag mineralized zone is developed in the Moisan area of Hwangsan-myeon, Haenam-gun, Jeol-lanam-do, Korea, which is located in the southwestern part of the Ogcheon metamorphic zone. It is hosted in the Hwangsan volcaniclastics of the Haenam Formation of the Late Cretaceous Yucheon Group. This research investigated the characteristics of bedding arrangement, fold, fault, fracture system, quartz vein and the time-relationship of the fracture system to understand the geological structure related to the formation of the mineralized zone. On the basis of this result, the tectonic environment at the time of the mineralization was considered. Beds mainly trend east-northeast and gently dip into north-northwest or south-southeast. Their poles have been rearranged by subhorizontal-upright open fold of (east)-northeast trend as well as dip-slip fault. Fracture system was formed through at least 6~7 different deformation events. D1 event; formation phase of the main fracture set of EW (D1-1) and NS (D1-2) trends with a good extensity, D2 event; that of the extension fracture of NW trend, and conjugate shear fracturing of the EW (dextral) and NS (sinistral) trends, D3 event; that of the extension fracture of NE trend, and conjugate shear refracturing of the EW (sinistral) and NS (dextral) trends, D4 event; that of the extension fracture of NS trend showing a poor extensity, D5 event; that of the extension fracture of NW trend, and conjugate shear refracturing of the EW (dextral) and NS (sinistral) trends, D6 event; that of the extension fracture of EW trend showing a poor extensity. Frequency distribution of fracture sets of each deformation event is D1-1 (19.73 %)> D1-2 (16.44 %)> D3=D5 (14.79 %)> D2 (13.70 %)> D4 (12.33 %)> D6 (8.22 %) in descending order. The average number of fracture sets within 1 meter at each deformation event is D6 (5.00)> D5 = D4 (4.67)> D2 (4.60)> D3 (4.13)> D1-1 (3.33)> D1-2 (2.83) in descending order. The average density of all fractures shows 4.20 fractures/1 m, that is, the average spacing of all fractures is more than 23.8 cm. The frequency distribution of quartz veins at each orientation is as follows: EW (52 %)> NW (28 %)> NS (12 %)> NE (8 %) trends in descending order. The average density of all quartz veins shows 4.14 veins/1 m, that is, the average spacing of all quartz veins is more than 24.2 cm. Microstructural data on the quartz veins indicate that the epithermal Au-Ag mineralization (ca. 77.9~73.1 Ma) in the Moisan area seems to occur mainly along the existing D1 fracture sets of EW and NS trends with a good extensity not under tectonic stress but non-deformational environment directly after epithermal rupture fracturing. The D1 fracturing is considered to occur under the unstable tectonic environment which alternates compression and tension of NS trend due to the oblique northward subduction of the Izanagi plate resulting in the igneous activity and deformation of the Yucheon Group and the Bulguksa igneous rocks during Late Cretaceous time.

• Economic and Environmental Geology
• /
• v.26 no.2
• /
• pp.117-127
• /
• 1993

Ag-Au vein ores from the Weolyu mine, Youngdong district, contain significant germanium (up to 145g/t, average 34.9g/t), in the form of argyrodite ($Ag_8GeS_6$). Mineral chemistries of argyrodite and its associated minerals were determined by electron probe microanalysis. Twenty eight elements in thirteen ore samples were analyzed using an ICP mass spectrometer. Argyrodite occurs in the paragenetically later mineral assemblage consisting of carbonates+quartz+native silver+argentite+Ag-sulfosalts, indicating that the germanium mineralization represents the culmination of a complex mineral sequence which includes early gold and late silver deposition. The mean formula of the argyrodite is $Ag_{7.90}\;(Ge_{0.76}Sn_{0.04})S_6$, with minor amounts of Cu, Fe, Sb, As, Sn, and Zn. The Weolyu argyrodite shows systematic substitutions of Ag by Cu, and of Ge by Sb. Chemical analyses of vein ores indicate that metals were precipitated in the order of $Fe{\rightarrow}Pb$, $Zn{\rightarrow}Cu{\rightarrow}Ag$, Sb, As, Ge. Germanium has a strong geochemical affmity with As and Sb, and Cu, Pb, Zn, Mo, and Sr show weak positive correlations with Ge. Germanium deposition at Weolyu was mainly a result of cooling of hydrothermal fluids (down to $175^{\circ}C{\sim}210^{\circ}C$, due to increasing involvement of cooler meteoric waters in the epithermal system.