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MRD-06 Granitic magmatism and related mineralizations

Fluid evolution and polymetallic mineralization in the Shinyemi skarn deposits, South Korea

Jieun Seo, Korea University (Republic of Korea)
Seon-Gyu Choi, Korea University (Republic of Korea)
Sang Joon Pak, Korea University (Republic of Korea)
Se-Jung Chi, Korea Institute of Geoscience and Mineral Resources (Republic of Korea)
Chang Seong Kim, Korea University (Republic of Korea)
In Kol Yoo, Korea Resources Corporation (Republic of Korea)
Tae Hyeong Kim, Korea Resources Corporation (Republic of Korea)
 

The Shinyemi deposits are characterized by Fe-Mo-Zn skarn and Zn-Cu replacement deposits along the contact between the Cretaceous granitoid and the Cambro-Ordovician carbonate sequence (the Choseon Supergroup). This granitoid is mainly composed of fine-grained biotite granite, quartz porphyry, aplite and rhyolitic breccia, implying shallow emplacement. The geochemical signatures idicate highly fractionated intrusions, based on REE patterns (La_n/Yb_n=3.4-11.7), Rb/Sr ratios (1.6-3.3) and K/Rb ratios (20.8-32.3). The Shinyemi ore body shows two main skarn stages: the early, stage I (magnesian) skarn associated with Fe mineralization, and the late, stage II (calcic) skarn with Mo and Zn mineralization. Prograde skarn mineral assemblages in stage I show Mg-rich minerals such as olivine (Fo_89-99) + diopside (Di_90-93), and retrograde skarn display serpentine + talc + clinohumite + phlogopite + Mg-rich chlorite. Stage II is characterized by contrasting mineral assemblages; prograde skarn is recognized Fe-rich minerals such like hedenbergite + garnet + wollastonite, and retrograde skarn is consist of epidote + amphibole + calcite + prehnite + Fe-rich chlorite. In particular, the clinopyroxene in vein skarn of stage II shows enriched Mn contents. The prograde skarns in all stages were formed at relatively higher temperatures (about 400° to 550°C) under low CO₂ fugacity (X_CO2 0.1), whereas the retrograde skarns were formed at lower temperatures (about 300° to 400°C). Calculated δ¹⁸O (10.7 ∼ 12.6‰) values of ore-forming fluid suggest a magmatic origin, whereas depleted δD (-103 ∼ -84‰) values indicate degassing in subsurface environment.