Dongbok Shin

Skarn zonation and rock physical properties of the Wondong Fe-Pb-Zn polymetallic deposit, Korea

The Wondong Fe-Pb-Zn polymetallic skarn deposit is located in the Taebaeksan Basin, South Korea. This deposit is associated with the Paleocene quartz porphyry and characterized by abundant exoskarn and subordinate endoskarn. A general zonation pattern is developed comprising a proximal reddish-brown garnet-rich zone, a distal greenish garnet ± pyroxene zone, and a wollastonite-rich zone at the marble front. The mineralization is characterized by Fe in the proximal garnet-rich zone and Pb-Zn within and beyond the garnet ± pyroxene zone. In general, skarn deposits show complex geophysical signatures in their rock properties in relation to metasomatism. Garnet-rich and garnet ± pyroxene skarns accompanying Fe-oxides and sulfides are significantly denser (3.3–3.4 g/cm3) than the other rocks (2.5–3.0 g/cm3) such as quartz porphyry, wollastonite-rich skarn, and silicic hornfels. Reactions related to creating garnet may increase porosity, which promotes further infiltration and reaction to produce garnet growth. The porosity of skarn rocks (1.8–8.4%) has a broad range and is generally higher than the other rocks (0.8–3.3%). In contrast, most skarn rocks show a remarkably low electrical resistivity (mostly 211–848 Ωm) than the other rocks (1,815–8,601 Ωm). Magnetic susceptibilities of skarn rocks (15–140 × 10–5 SI) are higher than quartz porphyry and siliceous hornfels (<25 × 10–5 SI). P wave velocities in the garnet ± pyroxene zone at the skarn front show lower values (1,487–3,674 m/s) than the other rocks (2,902–5,590 m/s), which is likely related to the porosity of the rocks. Thus, in general, the physical properties of rocks as exampled above from the skarn environment reflect their mineral assemblages and can be used for mineral exploration of skarn deposits.

Regional variations of sulfur isotope compositions for metallic deposits in the Taebaeksan Mineralized District, South Korea

Metallic ore deposits of various genetic types are distributed in the Taebaeksan mineralized district in South Korea. The different basements or host rocks for these deposits vary across the northern and southern regions of the district with the Baegunsan Syncline as its center. Previous and newly analyzed sulfur isotope data of 374 sulfide minerals collected from 45 ore deposits were reviewed to compare the genetic characteristics of the two regions. Metallic deposits in the study area were classified into skarn, hydrothermal replacement, and hydrothermal vein based on genetic types and W-Mo, Fe-Cu(-Mo-Pb-Zn), Pb-Zn(-Cu-Au- Ag), and Au-Ag(-Cu-Pb-Zn) deposits with regard to ore species. For each genetic type, average sulfur isotope values were found to be 6.8‰, 7.7‰, and 6.3‰ in the northern region, and 2.3‰, 3.6‰, and 3.5‰ in the southern region, respectively. Average sulfur isotope values for each of the ore species were 11.3‰, 2.6‰, 6.6‰, and 6.9‰ in the northern region, and 1.3‰,–0.2‰, 4.2‰, and 3.3‰ in the southern region, respectively. The results indicate that sulfur isotope compositions for both genetic types and ore species are distinctly higher in the northern region than in the southern region. These differences could be ascribed to different sulfur isotope compositions of basement and host rocks that provided sulfur to ore minerals during the evolution of hydrothermal fluids, though the mineralizing fluids were originated from magmatic source. In the northern region, higher δ34S values of ore sulfurs could be attributed to high δ34S values of sulfate and sulfide in carbonate rocks formed in seawater. On the contrary, lower δ34S values of sulfide minerals in the southern region seem to be attributed to metasedimentary rocks that have lower δ34S values as a result of bacterial sulfate reduction.

PGE distribution in the metalliferous black slates of the Okcheon Metamorphic Belt, South Korea

Chinese Ni-Mo sulfide ores. Chondrite-normalized PGE pattern for the coaly slates displays a strong positive Ru anomaly and slightly negative Pt anomaly. The Zn-rich shale of Czech and the black shale of South China show similar patterns to the coaly slates except its slightly enriched Au and positive Pt anomaly, respectively. Positive correlations of organic carbon and the redox-sensitive trace elements such as U, V and Mo with PGEs concentrations in the coaly slates suggest that the PGEs were most likely introduced by submarine hydrothermal activity and precipitated with organic matters under anoxic environment. In general, the metalliferous black slates in the OMB seem to be metamorphosed analogue of the Early Cambrian black shales of the South China Block in the former continental back-arc basin setting, which host metalliferous Ni-Mo-PGE sulfide ores.