P—T—t—deformation—fluid characteristics of lode gold deposits: evidence from alteration systematics

Phanerozoic continental growth and gold metallogeny of Asia

Tectonic implications from Re–Os dating of Mesozoic molybdenum deposits in the East Qinling–Dabie orogenic belt

A tectono-genetic model for porphyry-skarn-stratabound Cu-Au-Mo-Fe and magnetite-apatite deposits along the Middle-Lower Yangtze River Valley, Eastern China

Resolving mantle and crustal contributions to ancient hydrothermal fluids: HeAr isotopes in fluid inclusions from Dae Hwa WMo mineralisation, South Korea

The Mesozoic gold–silver deposits in South Korea are closely associated with the Mesozoic granitoids. The Jurassic gold–silver deposits can be distinguished from the Cretaceous ones in terms of occurrence, alteration style, gold fineness, associated mineral assemblage, fluid inclusion and stable isotopic compositions. The Jurassic deposits were formed in mesozonal environments related to deep-seated granitoids, whereas the Cretaceous ones were formed in epizonal environments related to shallow-level granitoids. The Jurassic auriferous deposits (about 165–145 Ma) show fluid characteristics typical of an orogenic-type gold deposit, and were probably generated in a compressional regime caused by an orthogonal convergence of the Izanagi oceanic plate into the Asiatic margin. However, strike-slip faults and caldera-related fractures, together with subvolcanic to volcanic activity, may have played an important role in the formation of Cretaceous gold–silver lode deposits (about 110–45 Ma) under a continental arc setting.

Origin of Mesozoic gold mineralization in South Korea

Jurassic (166 + or - 2 Ma) gold vein deposits of the Samhwanghak mine, Youngdong area, are examples of mesothermal gold deposits in the Republic of Korea. The deposits are composed of gold-bearing but relatively sulfide-poor massive quartz veins which occupy shear zones in graphite-bearing paragneiss of Precambrian age.Vein quartz was deposited mostly prior to deposition of sulfides and gold, and contains three main types of fluid inclusions: (I) CO 2 -CH 4 fluids, (II) low-salinity ( 2 kbars. Initial hydrothermal fluids were near their critical states at temperatures of 410 degrees to 480 degrees C and were homogeneous compositionally with X (sub CO 2 ) +CH 4 of 0.45 (X (sub CH 4 ) = 0.14) and salinity of [asymp] 9 wt percent NaCl. Type III inclusions appear to be secondary and represent later fluids which formed through extensive fluid unmixing of type II fluids with progressive decreases in temperature (below 370 degrees C) and pressure (down to [asymp] 1 kbar), but may also include deep circulating meteoric waters.Thermochemical calculations indicate the following evolution of hydrothermal fluids: fugacity of sulfur decreased progressively with decreasing temperature near the pyrite-pyrrhotite sulfidation curve; fugacity of oxygen was controlled largely through graphite-fluid interaction and evolved near the QFM buffer; pH was maintained near neutrality. Temperature versus f (sub O 2 ) relationships indicate that hydrothermal fluids were derived originally from a nearby S-type magma, the Middle Jurassic Kimcheon Granite. Gold occurs as gold-rich (avg 72 at. % Au) electrum intimately associated with sulfide minerals, and precipitated from later aqueous (type III) fluids at temperatures of 340 degrees to 240 degrees C, as a combined result of cooling and decrease of sulfur activity (by sulfide precipitation and/or H 2 S loss accompanying fluid unmixing).Calculated sulfur isotope compositions of hydrothermal fluids (delta 34 S (sub Sigma S) ) near 2 per mil indicate that ore sulfur was derived from an ilmenite series (S-type) granitic melt. Measured and calculated oxygen and hydrogen isotope compositions of ore fluids (delta 18 O water = 6.1-8.4ppm; delta D water = -62 to -72ppm) are consistent with derivation from and interaction with magmatic rocks. Mesothermal gold vein deposits of the Youngdong area were formed by extensive fracturing and veining during the Jurassic Daebo orogeny and developed from fluids that may have included an important component of magmatic fluids. Mineralogy and ore fluid chemistry of the deposits of the Youngdong area are similar to those of Archcan mesothermal gold vein deposits, possibly validating a more general application of a magmatic hydrothermal model for the formation of mesothermal gold vein deposits.

Jurassic Mesothermal gold mineralization of the Samhwanghak Mine, Youngdong Area, Republic of Korea : Constraints on hydrothermal fluid geochemistry

Regional geologic setting and metallogenesis of central Inner Mongolia, China: guides for exploration of mesothermal gold deposits

The Hwanggangri mineralized district within the Ogcheon metamorphic belt of the southern Korean peninsula contains more than 60 W-Mo- and Cu-Pb-Zn(-Au-Ag)-bearing metallic ore occurrences and lesser fluorite and talc occurrences related to intrusion of Late Cretaceous (83-90 Ma), I-type and magnetite series granites. Fissure-filling veins in the district differ in mineralogy with distance from the granites: W-Mo vein deposits are located within or near (<500 m) the granites, whereas Cu-Pb-Zn vein deposits occur up to 5 km from the granites. The Geumsil and Daehyun Au-Ag-Pb-Zn mines are unique and represent the most distal deposits in the district. They consist of quartz-carbonate veins which contain economic concentrations of gold (3 g/t) and silver (250 g/t) in addition to abundant base metal sulfides (6 wt % Pb + Zn). Study of these Au-Ag-enriched mines provides a key to understanding ore-forming processes in the outer portions of a very large, batholith-driven hydrothermal circulation system.Phase equilibria, fluid inclusions, and stable isotopes indicate that ore deposition was the result of interaction of progressively less evolved meteoric waters with earlier, highly evolved meteoric waters. Early Fe sulfide mineralization occurred at temperatures of 380 degrees to 310 degrees C from fluids (delta 18 O = 10-12ppm) whose chemistry was controlled dominantly by reactions with granite and carbonate-bearing host rocks. Main base metal-Au-Ag mineralization occurred at temperatures of 250 degrees to 210 degrees C from fluids (delta 18 O = 6-7ppm) whose chemistry changed rapidly as a result of fluid unmixing and cooling. Late, postore carbonates were deposited at temperatures of 250 degrees to 165 degrees C from fluids whose stable isotope compositions (delta 18 O = 1-4ppm; delta D = -89ppm) and salinities (<3 wt % NaCl) reflect increasing meteoric water dominance.The most intriguing result of our studies is that gold deposition occurred from fluids whose chemistries were controlled dominantly by granites (and wall rocks) at temperatures well below magmatic conditions (250 degrees C) at great distances from the intrusion. The occurrence of increased gold and silver grades in these distal areas bodes well for increased exploration for Au-Ag-Pb-Zn deposits at relatively great distance from granite batholiths.

Geochemistry and genesis of hydrothermal Au-Ag-Pb-Zn deposits in the Hwanggangri mineralized district, Republic of Korea

Mesothermal gold mineralization at the Samdong mine (5.5–13.5 g/ton Au), Youngdong mining district, is situated in massive quartz veins up to 1.2 m wide which fill fault fractures within upper amphibolite to epidote-amphibolite facies, Precambrian-banded biotite gneiss. The veins are mineralogically simple, consisting of iron- and base-metal sulfides and electrum, and are associated with weak hydrothermal alteration zones (<0.5 m wide) characterized by silicification and sericitization. Fluid inclusion data and equilibrium thermodynamic interpretation of mineral assemblages indicate that the quartz veins were formed at temperatures between 425 and 190°C from relatively dilute aqueous fluids (4.5–13.8 wt. % equiv NaCl) containing variable amounts of CO2 and CH4. Evidence of fluid unmixing (CO2 effervescence) during the early vein formation indicates approximate pressures of 1.3–1.9 kbars, corresponding to minimum depths of ≈ 5–7 km under a purely lithostatic pressure regime. Gold deposition occurred mainly at temperatures between 345 and 240 °C, likely due to decreases in sulfur activity accompanying fluid unmixing. The δ34S values of sulfide minerals (-3.0 to 5.3 ‰), and the measured and calculated O-H isotope compositions of ore fluids (δ18O = 5.7 to 7.6‰; δ = −74 to −80‰) indicate that mesothermal gold mineralization at the Samdong mine may have formed from dominantly magmatic hydrothermal fluids, possibly related to intrusion of the nearby ilmenite-series, ‘Kimcheon Granite’ of Late Jurassic age.

Chil Sup So

Papers

Origin of Mesozoic gold mineralization in South Korea

Jurassic Mesothermal gold mineralization of the Samhwanghak Mine, Youngdong Area, Republic of Korea : Constraints on hydrothermal fluid geochemistry

Regional geologic setting and metallogenesis of central Inner Mongolia, China: guides for exploration of mesothermal gold deposits

Geochemistry and genesis of hydrothermal Au-Ag-Pb-Zn deposits in the Hwanggangri mineralized district, Republic of Korea

Mesothermal gold vein mineralization of the Samdong mine, Youngdong mining district, Republic of Korea