• The Journal of the Petrological Society of Korea
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• v.9 no.4
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• pp.238-253
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• 2000

In the eastern part of the Euiseong Basin acidic~intermediate volcanic rocks widely distribute on the Cretaceous sedimentary basement. Coeval granitic rocks and dyke rocks intruded into the volcanic rocks. Volcanic stratigraphy of study area are andesite lava, dacitic lapilli tuff, dacitic flow-banded lava, rhyolitic bedded tuff, rhyolitic massive tuff, dacitic massive lava, rhyolitlc welded tuff occur from the lower to the upper strata. $SiO_2$ content of the volcanic rocks range from 51 to 74 wt.%. With the increase of $SiO_2$, the contents of $TiO_2$, $Al_2$$O_3$, MgO, FeOT MnO, CaO, $P_2$$O_{5}$ decrease but those of $K_2$O increase. The contents of $Na_2$O show dispersive variation. This trend is quite sim-ilar to the major oxide variation in the volcanic rocks from the Yucheon sub-basin. The geochemical natures indicate that the volcanic rocks in the study area are discriminated to the island-arc type high K to medium K calc-alkaline rocks. The compositional variation of the volcanic rocks can be explained by the plagioclase fractionation of the volcanic magmas originated from similar source materials. The volcanic stratigraphy seems to have formed by at least two eruptive sequences of andesitic to rhyolitic and dacitic to rhyolitic magmas which underwent crystallization differentiation.

• Economic and Environmental Geology
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• v.48 no.1
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• pp.1-13
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• 2015

The geology of the Seungryung Zn deposit, located in the Muzu basin, consists of Precambrian leucocratic granitic gneiss, Cretaceous clastic rocks, pyroclastic rocks, and intrusive rocks. The deposit shows a weakly skarnized hydrothermal replacement ore developed along limestone bed in the gneiss. The mineralization can be divided into three stages: the early skarnization producing garnet and pyroxene, the main mineralization in the middle stage precipitating most metallic minerals such as magnetite, sphalerite, chalcopyrite, pyrrhotite, Pb-Ag-Bi-S system minerals, and the late stage for altered or low temperature minerals such as chlorite and marcasite. Pb-Ag-Bi-S system minerals include heyrovskite-eskimoite solid solution, lillianite-gustavite solid solution, and vikingite. Chalcopyrite diseases are quite common in sphalerite showing bead chains and dusting textures. The ${\delta}^{34}S$ values of sulfides minerals are concentrated within the narrow range of 3.4~4.1‰ for pyrite, 3.3~4.3‰ for sphalerite, 4.0~4.3‰ for chalcopyrite, and 2.8‰ for galena, suggesting that most sulfur is of igneous origin. Sulfur isotope geothermometry is calculated to be $346{\sim}431^{\circ}C$, implying that the mineralization occurred at relatively high temperature. FeS contents of sphalerite are relatively high in the range of 6.58~20.16 mole% (avg. 16.58 mole%) with the enrichment of Mn compared to Cd, similarly to representative skarn Pb-Zn deposits in South Korea. On the contrary, sphalerite from Au-Ag deposits in the Seolcheon mineralized zone around the Seungryung deposit is enriched in Cd, showing similar feature like representative epithermal Au-Ag deposits. This suggests that around the related igneous rocks, magnetite and sphalerite were produced at high temperature in the Seungryung deposit, and with decreasing temperature and compositional change of mineralizing fluids, Au-Ag mineralization proceeded in the Seolcheon mineralized zone.

• Economic and Environmental Geology
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• v.43 no.4
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• pp.417-427
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• 2010

The Lankawi archipelago is located in 30 km western offshore near the Thailand-Malaysia border in west coast of the Malay Peninsula and consists of 99 (+5) tropical islands, covering an area of about $479km^2$. Together with biodiversity in flora and fauna, the Lankawi archipelago displays also geodiversity that includes rock diversity, landform diversity, and fossil diversity. These biodiversity and geodiversity have led to the Lankawi islands as a newly emerging hub for ecotourism in Southeast Asia. As a result, the Lankawi islands have been designated the first Global Geopark in Southeast Asia by UNESCO since July 1st, 2007. The geodiversity of Lankawi Geopark today is a result of a very long depositional history under the various sedimentological regimes and paleoenvironments during the Paleozoic, followed by tectonic and magmatic activities until the early Mesozoic, and finally by surface processes that etched to the present beautiful landscape. Paleozoic strata exposed in the Lankawi Geopark are subdivided into four formations that include the Machinchang (Cambrian), Setul (Ordovician to Early Devonian), Singa (Late Devonian to Carboniferous), and Chuping (Permian) formations in ascending order. These strata are younging to the east, but they are truncated by the Kisap Thrust in the eastern part of the islands. Top-to-the-westward transportation of the Kisap Thrust has brought the older Setul Formation (and possibly Machinchang Formation) from the east to overlay the younger Chuping and Singa formations in the central axis of the Lankawi islands. Triassic Gunung Raya Granite intruded into these sedimentary strata, and turned them partially into various types of contact metamorphic rocks that locally contain tin mineral deposits. Since Triassic, not much geologic records are known for the Lankawi islands. Tropical weathering upon rocks of the Lankawi islands might have taken place since the Early Jurassic and continues until the present. This weathering process played a very important role in producing beautiful landscapes of the Lankawi islands today.

• Economic and Environmental Geology
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• v.36 no.4
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• pp.257-268
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• 2003

The Cretaceous magmatism in the Gyeongsang Basin, Korea, led to the formation of two contrasting metallogenic provinces: the Haman-Gunbug-Goseong(-Changwon) (HGGC) and the Euiseong (EU). The mineralization in the HGGC metallogenic province represents copper, gold and iron of porphyry-related deposits that display close relationships in time and space with subvolcanic granitoids. Much of copper-gold-forming events in this province are consistently constrained to the period between ca. 89 and 81 Ma. The hydrothermal systems of copper-gold vein deposits in the HGGC province are associated with ore-forming fluids of high to intermediate temperature (300∼50$0^{\circ}C$) with high salinity (20∼55 equiv. wt. % NaCl). The ore-forming fluids become progressively more diluted by the incorporation of decreased quantities of magmatic water further from the nearby intrusion, suggesting significant input and fluid mixing of a meteoric water component to the magmatic fluids during the late stage of geothermal systems. In contrast, the EU metallogenic province is characterized by polymetallic vein deposits that are consistently constrained to a period of 78∼60 Ma. The geothermal systems of polymetallic vein deposits in the EU province are derived from a narrow range of intermediate temperature (200∼40$0^{\circ}C$) with relatively low salinity(1∼7 equiv. wt.% NaCl). It may represent a mixed fluid of magmatic and meteoric waters. The base-metal mineralization in the Gyeongsang Basin shows a close spatial and temporal distinction between the proximal environment derived from shallow-level granitoids in the southwestern HGGC province and the distal condition derived from volcanic environments in the northwestern EU province.

• Economic and Environmental Geology
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• v.50 no.5
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• pp.375-387
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• 2017

Amphibolite-hosted Fe-Ti mineralization at the Soyeonpyeong Island, located in central western part of the Korean Peninsula is a typical orthomagmatic Fe-Ti oxide deposit in South Korea. The amphibolite intruded into NW-SE trending Precambrian metasedimentary rocks. Lower amphibolite is characterized by igneous layering, consisting of feldspar-dominant and amphibole-Fe-Ti oxide-dominant layers. The igneous layering shows complicated and/or sharp contact. In contrast, upper amphibolite has a more complicated lithofacies (garnet-bearing, coarser, and schistose), and massive Fe-Ti oxide ore alternates with schistose amphibolite. NS- and EW-trending fault systems lead to redistribute upper amphibolite-hosted Fe-Ti orebody and igneous layering of lower amphibolite, respectively. The whole-rock compositions of amphibolite and Fe-Ti oxide ore reflect their constituent minerals. Amphibolite shows significantly positive Eu anomalies whereas Fe-Ti oxide ore has weak negative Eu anomalies. Plagioclase (Andesine to oligoclase) and Fe-Ti oxide minerals have constant composition regardless of their distribution. Amphibole has a compositionally variable but it doesn't reflect the chemical evolution. Mineral compositions within individual layers and successive layers are relatively constant not showing any stratigraphic evolution. This suggests that there are no successive injections of Fe-rich magma or assimilation with Fe-rich country rocks. Contrasting Eu anomalies between amphibolite and Fe-Ti oxide ore also suggest that extensive plagioclase fractionation during early crystallization stage cause increase in $Fe_2O_3/FeO$ ratio and overall Fe contents in the residual magma. Thus, Fe-rich residual liquids may migrate at the upper amphibolite by filter pressing mechanism and then produce sheeted massive Fe-Ti mineralization during late fractional crystallization.

• Economic and Environmental Geology
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• v.35 no.3
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• pp.211-220
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• 2002

The Xiaoxinancha Cu-Au deposit in the Jilin province, located in NNE 800 km of Beijing, is hosted by diorite. The ore mineralization of Xiaoxinancha Cu-Au deposit show a stockwork occurrence that is concentrated on the potassic and phyllic alteration zones. The Xiaoxinancha Cu-Au deposit in the south is being mined with its reserves grading 0.8% Cu, 3.64 g/t Au and 16.8 g/t Ag and in the north, grading 0.63% Cu, 3.80 g/t Au and 6.8 glt Ag. The alteration assemblage occurs as a supergene blanket over deposit. Hydrothermal alteration at the Xiaoxinancha Cu-Au deposit is centered about the stock and was extensively related to the emplacement of the stock. Early hydrothermal alteration was dominantly potassic and followed by propylitic alteration. Chalcocite, often associated with hematite, account for the ore-grade copper, while chalcopyrite, bornite, quartz, epidote, chlorite and calcite constitute the typical gangue assemblage. Other minor opaque phases include pyrite, marcasite, native gold, electrum, hessite, hedleyite, volynskite, galenobismutite, covellite and goethite. Fluid inclusion data indicate that the formation of this porphyry copper deposit is thought to be a result of cooling followed by mixing with dilute and cooler meteoric water with time. In stage II vein, early boiling occurred at 497$^{\circ}$C was succeeded by the occurrence of halite-bearing type III fluid inclusion with homogenization temperature as much as 100$^{\circ}$C lower. The salinities of type 1II fluid inclusion in stage II vein are 54.3 to 66.9 wt.% NaCI + KCI equiv. at 383$^{\circ}$ to 495$^{\circ}$C, indicating the formation depth less than 1 km. Type I cupriferous fluids in stage III vein have the homogenization temperatures and salinity of 168$^{\circ}$ to 365$^{\circ}$C and 1.1 to 9.0 wt.% NaCI equiv. These fluid inclusions in stage III veins were trapped in quartz veins containing highly fractured breccia, indicating the predominance of boiling evidence. This corresponds to hydrostatic pressure of 50 to 80 bars. The $\delta$$^{34}S$ value of sulfide minerals increase slightly with paragenetic time and yield calculated $\delta$$^{34}S_{H2S}$ values of 0.8 to 3.7$\textperthousand$. There is no mineralogical evidence that fugacity of oxygen decreased, and it is thought that the oxygen fugacity of the mineralizing fluids have been buffered through reaction with magnetite. We interpreted the range of the calculated $\delta$$^{34}S_{H2S}$ values for sulfides to represent the incorporation of sulfur from two sources into the Xiaoxinancha Cu-Au hydrothermal fluids: (1) an isotopically light source with a $\delta$$^{34}S$ value of I to 2$\textperthousand$, probably a Mesozoic granitoid related to the ore mineralization. We can infer from the fact that diorite as the host rock in the Xiaoxinancha Cu-Au deposit area intruded plagiogranite; (2) an isotopically heavier source with a $\delta$$^{34}S$ value of > 4.0$\textperthousand$, probably the local porphyry.