우석광상 다금속 광화작용의 시공간적 특성변화

Spatio-Temporal Variation of Polymetallic Mineralization in the Wooseok Deposit

Abstract

제천시 청풍면에 위치한 우석광상은 옥천변성대 동북부 황강리광화대에 속한다. 지질은 조선누층군의 석회암이 넓게 분포하며, 광상 동측에 백악기 무암사화강암이 관입하였다. 광상은 스카른 및 맥상광체가 W-Mo-Fe 및 Cu-Pb-Zn 광화작용을 수반하며, 스카른은 하부갱에서만 발달한다. 광석광물은 스카른광물을 교대 및 절단하며, 자철석-적철석, 휘수연석-회중석-철망간중석, 자류철석-황동석-황철석-섬아연석-방연석 순으로 정출되었고 전반적으로 황화광물이 우세하다. 석류석의 조성은 $Ad_{65.9-97.8}Gr_{0.3-32.0}Pyr_{0.9-3.0}$으로 Fe가 부화된 안드라다이트 계열을 보이며, 휘석은 $Hd_{4.5-49.7}Di_{42.3-93.9}Jo_{0.5-7.9}$로서 투휘석 계열이 우세하여 스카른화 작용이 전체적으로 산화환경에서 진행되었음을 지시한다. 맥상광체에 수반된 섬아연석에 대한 FeS-MnS-CdS 삼각도에서 심부에서 천부로 가면서 FeS는 감소하고 MnS는 증가하는 경향을 보이는데 이는 심부의 W 광화작용과 천부의 Pb-Zn 광화작용과 관련된 것으로 보인다. 황화광물의 황안정동위원소 조성은 5.1-6.8 ‰로 마그마에서 기원된 황이 모암이 영향을 받은 것으로 여겨진다. 우석광상의 W-Mo 스카른 및 Pb-Zn 열수맥상 광화작용은 시공간적으로 심부에서 천부로 가면서 온도 및 산소분압의 감소와 함께 황분압이 증가하면서 진행된 것으로 보인다.

The Wooseok deposit in Jecheon belongs to the Hwanggangri Mineralized Distict of the northeastern Ogcheon Metamorphic Belt. Its geology consists mostly of limestone of the Choseon Supergroup and the Cretaceous Muamsa granite intruded at the eastern area of the deposit. The deposit shows vertical occurrence of skarn and hydrothermal vein ores with W-Mo-Fe and Cu-Pb-Zn mineralization and skarn is developed only at lower levels of the deposit. Skarn minerals are replaced or cut by ore minerals in paragenetic sequence of magnetite-hematite, molybdenite-scheelite-wollframite, and higher abundances of pyrrhotite-chalcopyrite-pyrite-sphalerite-galena. Garnet has chemical compositions of $Ad_{65.9-97.8}Gr_{0.3-32.0}Pyr_{0.9-3.0}$, corresponding to andradite series, and pyroxene compositions are $Hd_{4.5-49.7}Di_{42.3-93.9}Jo_{0.5-7.9}$, prevailing in diopside compositions, both of which suggest oxidized conditions of skarnization. On the FeS-MnS-CdS ternary diagram, FeS contents of sphalerite in vein ores decrease with increasing MnS contents from bottom to top levels, possibly relating to W mineralization in deep and Pb-Zn mineralization in shallow level. Sulfur isotope values of sulfide minerals range from 5.1 to 6.8‰, reflecting magmatic sulfur affected by host rocks. W-Mo skarn and Pb-Zn vein mineralization in the Wooseok deposit were established by spatio-temporal variation of decreasing temperature and oxygen fugacity with increasing sulfur fugacity from bottom to top levels.

Fig. 1. Regional geologic map of the Hwanggangri Mineralized District. J: Jecheon granite, M: Muamsa granite, S: Susan granite, W: Weolaksan granite, NM: Nangrim massif, PB: Pyeongnam basin, IB: Imjingang Belt, GM: Gyeonggi massif, OB: Okcheon belt, YM: Yeongnam massif, GB: Gyeongsang basin.

Fig. 2. Geologic map of the Wooseok deposit(Modified from Park and Park, 1979).

Fig. 3. Cross section of the Wooseok deposit(Modified from KORES, 1981).

Fig. 4. Rock slabs and microscopic images of skarn in the Wooseok deposit. (a) Pyroxene skarn in the No.3 adit, (b) Recrystallized limestone in the No.3 adit, (c, d) Pyroxene skarn replaced by sulfide minerals in the Main adit, (e, f) Garnet and pyroxene skarn cut by quartz and calcite vein in the Deajeol adit. (g) Pyroxene coexisting with quartz in the No.3 adit, (h) Recrystallized and/or altered calcite in the No.3 adit, (i, j) Pyroxene cut by ore vein in the Main adit, (k, l) Euhedral and zoned garnet replaced or cut by pyroxene, quartz and calcite in the Daejeol adit. Abbreviations: Cc: calcite, Cp: chalcopyrite, Fl: fluorite, Gt: garnet, Mb: molybdenite, Po: pyrrhotite, Py: pyrite, Px: pyroxene, Qtz: quartz.

Fig. 5. Representative images of polished sections from the South(a-c), No.3(d-f), Main(g-i) and Daejeol(j-l) adit in the Wooseok deposit. (a-c) Pyrrhotite coexisting with pyrite and replaced by sphalerite and chalcopyrite, (d) Galena and sphalerite in contact with subhedral pyrite, (e) Chalcopyrite disease showing dusting texture in sphalerite, (f) Molybdenite coexisting with pyrrhotite and chalcopyrite, (g) Pyrite and pyrrhotite replaced by galena, sphalerite and chalcopyrite, (h) Arsenopyrite replaced by pyrrhotite, chalcopryte and sphalerite, (i) Chalcopyrite, pyrrhotite and galena cut by late pyrite, (j) magnetite and hematite replaced by pyrite and chalcopyrite, (k) Molybdenite coexisting with scheelite and wolframite, (l) Pyrite and pyrrhotite replaced by sphalerite and galena. Abbreviations: Asp: arsenopyrite, Gn: galena, Ht: hematite, Mt: magnetie, Sch: scheelite, Sph: sphalerite, Wf: wolframite, Refer to Fig. 4 others.

Fig. 6. Paragenetic sequence of minerals in the Wooseok deposit.

Fig. 7. Ternary diagrams of chemical composition of garnet and pyroxene from the Wooseok deposit and representative ore deposits in the Hwangganri and Taebaeksan mineralized district (data from Chang and Park, 1988; Choi and Kim, 1989; Choi et al., 2007; Kim et al., 2012; Lim et al., 2013; Moon, 1983; Yun, 1979, 1983).

Fig. 8. Chemical compositions of sphalerite from the Wooseok deposit.

Fig. 9. Ternary diagram showing chemical compostions of sphalerite from the Wooseok deposit and representative Pb-Zn and W deposits in other areas: Dangdu(Lim et al., 2013), Subok(Shin et al., 2017), Eunch(Park et al., 1988), Samgwang(Yoo et al., 2002), Sangdong(Moon, 1983), Tungsten deposits in Japan(Shibue, 1988).

Fig. 10. Oxygen fugacity vs sulfur fugacity diagram showing depositional condition of oxide and sulfide phases at 1kb and 300℃(Modified from Pandit, 2015).

Table 5. Features of various metallic ore deposits in the Hwanggangri mineralized district

Table 1. Representative EPMA analyses of garnet from the Wooseok deposit

Table 2. Representative EPMA analyses of pyroxene from the Wooseok deposit

Table 3. Representative EPMA analyses of sphalerite from the Wooseok deposit

Table 4. Sulfur isotope compositions of sulfide minerals from the Wooseok deposit