Genetic Environments of the Eunjeok Au–Ag Deposit in the Yeongam District: Implications for Cretaceous Epithermal Au–Ag Mineralization in South Korea
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Abstract:
Eunjeok Au–Ag deposits are situated in the Yeongam district, Cheollanamdo-province, South Korea. They are genetically related to the Bulgugsa magmatic event (ca. 110–60 Ma), caused by the transition in the subduction direction and style of the Izanagi Plate. Three gold- and silver-bearing hydrothermal veins filled the fractures of the Cretaceous rhyolitic tuff. The major ore minerals were arsenopyrite (31.47–32.20 at.% As), pyrite, chalcopyrite, sphalerite (8.58–10.71 FeS mole%) and galena with minor amounts of electrum (62.77–78.15 at.% Au), native silver, and argentite. Sericitization was dominant in the alteration zone. The various textures of quartz veins (i.e., breccia, crustiform, comb, and vuggy) may indicate the formation of an epithermal environment. The auriferous fluids with the H2O–NaCl system have homogenization temperatures and salinities of 204 °C to 314 °C, less than 10 wt.% equiv. NaCl, and experienced mixing (dilution and cooling) events during mineralization. Considering the characteristics of the geologic setting, major fault system, and host rock, the Eunjeok Au–Ag deposit within the Yeongam district tends to share the general geologic characteristics of Haenam–Jindo epithermal mineralization episodes. However, the age of gold–silver mineralization (86.0 Ma) is older than that of Haenam–Jindo epithermal mineralization episodes (<70.3 Ma), implying some differences exist in the genetic sequence of extensional characteristics caused by transcurrent Gwangju–Yeongdong faults.Keywords:
Breccia
Arsenopyrite
Arsenopyrite
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The primary coexisting mineral with galena is sphalerite. Hence, it is critical to selectively separate galena from sphalerite by flotation. In this work, thiourea and related derivatives as potential flotation collectors for separating galena from sphalerite were investigated. Thiourea and its related derivatives were found to be effective selective collectors in batch flotation studies of a single mineral, with 1,1-diphenylthiourea (11DTA) emerging as the best choice. Galena has superior floatability compared to sphalerite in the presence of 11DTA, and the recovery difference between the two minerals at pH 8 (where the 11DTA concentration is 5 × 10−6 mol/L) is around 38%. This was revealed in batch flotation studies using artificial mixed minerals. Moreover, the findings from the measurements of adsorption amount, FTIR, zeta potential and XPS revealed that 11DTA has a strong adsorption on galena yet a relatively weak adsorption on sphalerite. Additionally, DFT calculations demonstrated that sphalerite exhibits stronger hydrophilicity than galena, and 11DTA possessed a better affinity for galena.
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