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Structural control of mineral deposits

Profile image of Young-Seog KimYoung-Seog Kim
https://doi.org/10.1007/S00126-012-0443-2
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Abstract

The Seongsan district in the Jindo-Haenam basin of southwest Korea comprises Precambrian gneissic basement, overlain and intruded by Cretaceous volcanic (98-71 Ma) and plutonic (86-68 Ma) rocks, respectively. Haenam Formation volcanic and volcaniclastic rocks are the dominant rock type exposed in the district and are the main host to high-sulphidation (82-77 Ma) and low-sulphidation (79-73 Ma) epithermal deposits. The Eunsan and Moisan low-sulphidation epithermal deposits have similar vein mineralogy, zoned hydrothermal alteration mineral assemblages, structural framework and interpreted deformation events. These similarities suggest that they formed by district-scale hydrothermal fluid flow at about 77.5 Ma. At this time, ore fluid movement along subvertical WNWtrending faults was particularly focussed in dilatant fault bends, jogs, and at intersections with N-trending splays. At Eunsan, Au-Ag ore shoots coincide with these areas of structural complexity, whereas at Moisan, narrower ore zones correspond with several parallel, poorly connected veins. A secondary control on the location of ore zones is the intersection between mineralised WNW-striking structures and rocks of the Haenam Formation. The higher permeability and porosity of these rocks, in comparison with mudstones and siltstones of the underlying Uhangri Formation, resulted in the more efficient lateral migration of ore fluids away from subvertical faults and into wall rocks. The intersection between subvertical WNW-striking faults and the gently dipping Haenam Formation imparts a low angle SW plunge to both ore bodies. WNW-striking postmineralisation faults displace ore zones up to 100 m and complicate the along-strike exploration and mining of WNW-trending ore zones. Future exploration strategies in the district involve the systematic testing of WNW-trending mineralised structures along strike from known deposits, with a particular emphasis on identifying structurally complex areas that experienced local dilation during the mineralisation event. Poorly exposed regions have historically been under-explored. However, based on the proposed exploration model for the Eunsan and Moisan deposits, these areas of poor outcrop are now considered important target areas for hidden ore bodies using ground-based geophysical exploration tools, such as seismic surveys.

FAQs

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What structural controls influence Au-Ag mineralisation in the Seongsan district?add

The study identifies WNW-striking, subvertical faults as primary controls for Au-Ag mineralisation, with dilational jogs enhancing fluid concentration. Both Eunsan and Moisan deposits exhibit varying vein geometries, reflecting distinct structural influences.

How does hydrothermal alteration vary between Eunsan and Moisan deposits?add

Alteration zones at Eunsan are characterized by thicker proximal areas of potassic alteration compared to the Moisan deposit. Distinct hydrothermal assemblages, such as advanced argillic alteration at Moisan, highlight geochemical differences.

What significance do the 77.5 Ma dates hold for mineralisation timing?add

The 40Ar/39Ar adularia ages indicate that Au-Ag mineralisation at both Eunsan and Moisan occurred around 77.5 Ma, contemporaneous with hydrothermal activity linked to volcanic processes. This timing suggests an association with subduction-related geological events.

How do fault systems impact ore body geometries at these deposits?add

Faults at Eunsan displace ore bodies vertically by up to 100 m and impact the overall shape and continuity of Au-Ag deposits. In contrast, fault systems at Moisan allow for more discrete ore bodies that lack significant plunge.

What exploration strategies are suggested for finding new deposits in this region?add

The study recommends using geophysical methods like seismic surveys to explore less exposed structural corridors and intersections identified during this research. Focusing on the WNW-trending faults and associated splay zones is emphasized for future exploration.

Figures (15)
Fig. 1 The Seongsan district is located in the Haenam—Jindo basin, in the south-western part of the Korean peninsula. Cretaceous rocks are indicated in the figure by different colours while all other rocks are represented by shades of grey
Fig. 1 The Seongsan district is located in the Haenam—Jindo basin, in the south-western part of the Korean peninsula. Cretaceous rocks are indicated in the figure by different colours while all other rocks are represented by shades of grey
The Eunsan and Moisan low-sulphidation epithermal deposits are located in nam—Jindo province ( 1 km apart, are hosted the Seongsan district of the Hae- Fig. 2). These deposits are about by similar rock types, display com- parable hydrothermal alteration patterns and formed at about 77.5 Ma (Bowden 2007). These similarities suggest that the deposits are the produc of the same district-scale mineral- isation event. Accordingly, the aims of this study are to (1) compare the structural development of the deposits, (2) identify similarities and differences in ore fluid pathways and focussing mechanisms at the two deposits, and (3) use this information to devise improved exploration strategies for the district. The present study benefits from severa existing studies in the documents stratigraphic ation relationships in the district and relates the formation o low- and high-sulphidat tion and alteration events in the district. Choi et al. (2005 examine vein paragenesis, hydrothermal alteration minera Seongsan district. Bowden (2007 , Structural and hydrothermal alter- ion epithermal deposits to deforma- assemblages and the physicochemical properties of the ore
The Eunsan and Moisan low-sulphidation epithermal deposits are located in nam—Jindo province ( 1 km apart, are hosted the Seongsan district of the Hae- Fig. 2). These deposits are about by similar rock types, display com- parable hydrothermal alteration patterns and formed at about 77.5 Ma (Bowden 2007). These similarities suggest that the deposits are the produc of the same district-scale mineral- isation event. Accordingly, the aims of this study are to (1) compare the structural development of the deposits, (2) identify similarities and differences in ore fluid pathways and focussing mechanisms at the two deposits, and (3) use this information to devise improved exploration strategies for the district. The present study benefits from severa existing studies in the documents stratigraphic ation relationships in the district and relates the formation o low- and high-sulphidat tion and alteration events in the district. Choi et al. (2005 examine vein paragenesis, hydrothermal alteration minera Seongsan district. Bowden (2007 , Structural and hydrothermal alter- ion epithermal deposits to deforma- assemblages and the physicochemical properties of the ore
occurs as discontinuous lenses throughout the Seongsan district (Fig. 3). “°K/*°Ar whole-rock dating of basalt from the Hwawon Formation indicates a crystallisation age of 103.442.5 Ma (Kim and Nagao 1992; Moon et al. 1990). The Hwawon Formation is unconformably overlain by 250— 450 m of black shale, laminated siltstone and mudstone, tuffaceous sandstone, chert and calcareous siltstone and minor intercalated volcanogenic units of the Uhangri For- mation (Kim 1991; Koh 1996). The formation locally con- tains plant fossils (Chun and Chough 1995) as well as trace fossils of dinosaurs, pterosaurs, birds and arthropods (Hwang et al. 2002). 40K Ar whole-rock dating of andes- ite from the Uhangri Formation indicates a crystallisation age of 95.4+2.9 Ma (Kim and Nagao 1992). The Haenam Formation unconformably overlies the Uhangri Formation and includes four dacitic to rhyolitic tuff members: from oldest to youngest, the Hwangsan, Haenam, Seoho and Yongdang members (Koh 1996). The Hwangsan Tuff of the Haenam Formation is the principal unit exposed in the Seongsan district and is the main host to epithermal depos- its (Park et al. 1997). The Haenam Formation is locally
occurs as discontinuous lenses throughout the Seongsan district (Fig. 3). “°K/*°Ar whole-rock dating of basalt from the Hwawon Formation indicates a crystallisation age of 103.442.5 Ma (Kim and Nagao 1992; Moon et al. 1990). The Hwawon Formation is unconformably overlain by 250— 450 m of black shale, laminated siltstone and mudstone, tuffaceous sandstone, chert and calcareous siltstone and minor intercalated volcanogenic units of the Uhangri For- mation (Kim 1991; Koh 1996). The formation locally con- tains plant fossils (Chun and Chough 1995) as well as trace fossils of dinosaurs, pterosaurs, birds and arthropods (Hwang et al. 2002). 40K Ar whole-rock dating of andes- ite from the Uhangri Formation indicates a crystallisation age of 95.4+2.9 Ma (Kim and Nagao 1992). The Haenam Formation unconformably overlies the Uhangri Formation and includes four dacitic to rhyolitic tuff members: from oldest to youngest, the Hwangsan, Haenam, Seoho and Yongdang members (Koh 1996). The Hwangsan Tuff of the Haenam Formation is the principal unit exposed in the Seongsan district and is the main host to epithermal depos- its (Park et al. 1997). The Haenam Formation is locally
during basin development and associated sub-volcanic and volcanic activity during the Cretaceous (Choi et al. 2003). The onset of high-sul pre-dates that of low-su phidation epithermal mineralisation phidation systems (81—70 and 78— 70 Ma, respectively). Both forms of epithermal mineralisa- tion temporally overlap 98-71 Ma) and plutoni suggesting that minera felsic to intermediate volcanism (ca. sm (ca. 86-68 Ma) in the district, isation coincided with prolonged subduction-related plutonic and volcanic activity (Bowden 2007). Oxygen, H, and district suggest that met S isotope data for the Seongsan eoric-derived fluids were important for transporting metals in low-sulphidation epithermal sys- tems, whereas magmatic fluids were involved in high- sulphidation systems (Bowden 2007).
during basin development and associated sub-volcanic and volcanic activity during the Cretaceous (Choi et al. 2003). The onset of high-sul pre-dates that of low-su phidation epithermal mineralisation phidation systems (81—70 and 78— 70 Ma, respectively). Both forms of epithermal mineralisa- tion temporally overlap 98-71 Ma) and plutoni suggesting that minera felsic to intermediate volcanism (ca. sm (ca. 86-68 Ma) in the district, isation coincided with prolonged subduction-related plutonic and volcanic activity (Bowden 2007). Oxygen, H, and district suggest that met S isotope data for the Seongsan eoric-derived fluids were important for transporting metals in low-sulphidation epithermal sys- tems, whereas magmatic fluids were involved in high- sulphidation systems (Bowden 2007).
The Eunsan deposit was mined from 2002 to 2009 as two open pits, followed by underground workings. The inferred All rock types are cut by 0.5—100-cm thick, Au—Ag-bearing quartz veins that strike WNW and dip steeply to the NE (e.g. 300°/75° NE) (Figs. 5 and 8a). The veins mostly consist of quartz, with minor adularia, pyrite, sphalerite, chalcopyrite, galena, electrum, native silver, proustite, argentite, aguilarite,
The Eunsan deposit was mined from 2002 to 2009 as two open pits, followed by underground workings. The inferred All rock types are cut by 0.5—100-cm thick, Au—Ag-bearing quartz veins that strike WNW and dip steeply to the NE (e.g. 300°/75° NE) (Figs. 5 and 8a). The veins mostly consist of quartz, with minor adularia, pyrite, sphalerite, chalcopyrite, galena, electrum, native silver, proustite, argentite, aguilarite,
generated by Ivanhoe Mines Ltd.). d, e The WNW-ESE long sections show contoured Au and Ag values, lithological contacts and faults that are interpreted from drill hole intersections. Steeply dipping F, faults offset strata, V; veins and Au—Ag ore zones. mRL refers to distance relative to sea level Fig. 6 Geological sections for Eunsan: a-c The SW-NE cross- sections demonstrate the spatial and timing relationships between Au-Ag-bearing V, veins and subparallel F, faults. The SW-dipping strata and near-vertical V, veins are displaced vertically about 100 m by normal-sinistral F, faults (modified after unpublished sections
generated by Ivanhoe Mines Ltd.). d, e The WNW-ESE long sections show contoured Au and Ag values, lithological contacts and faults that are interpreted from drill hole intersections. Steeply dipping F, faults offset strata, V; veins and Au—Ag ore zones. mRL refers to distance relative to sea level Fig. 6 Geological sections for Eunsan: a-c The SW-NE cross- sections demonstrate the spatial and timing relationships between Au-Ag-bearing V, veins and subparallel F, faults. The SW-dipping strata and near-vertical V, veins are displaced vertically about 100 m by normal-sinistral F, faults (modified after unpublished sections
movement. Vertical displacements of shallowly dipping strata are up to | m, whereas lateral displacements are less than a metre. These structures are interpreted to be the product of the third deformation event at the Eunsan deposit (Dg3). 45° to vein margins. They are interpreted to represent subsid- iary R fractures to the main WNW-striking D fractures in a dextral transtensional wrench system (cf. Riedel 1929). Based on these vein geometries, the interpreted movement sense for veins is dextral-SSW side up, with undetermined displace- ment magnitudes. These structures are interpreted to be the product of the earliest deformation event at the Eunsan deposit (Drz}).
movement. Vertical displacements of shallowly dipping strata are up to | m, whereas lateral displacements are less than a metre. These structures are interpreted to be the product of the third deformation event at the Eunsan deposit (Dg3). 45° to vein margins. They are interpreted to represent subsid- iary R fractures to the main WNW-striking D fractures in a dextral transtensional wrench system (cf. Riedel 1929). Based on these vein geometries, the interpreted movement sense for veins is dextral-SSW side up, with undetermined displace- ment magnitudes. These structures are interpreted to be the product of the earliest deformation event at the Eunsan deposit (Drz}).
Fig. 8 Photographs showing structural relationships at Eunsan: a Heterolithic coarse tuff and overlying volcanogenic sandstone in the western wall of the Eunsan pit are cut by subvertical WSW-striking V, veins with a SW-side-up-dextral displacement. The strata and V, veins are in turn displaced by a subvertical, WSW-striking F2 fault with a SW-side-down (and minor sinistral) displacement of about 100 m. b Plan view of a quartz-carbonate V, vein that cuts volcanogenic sand- stone beds in the north wall of the Eunsan pit. The vein strikes WNW (295°) and dips 80° to the SW. A subordinate horsetail splay strikes NNW (352°) and dips 86° to the E, suggesting a dextral shear compo- nent to the SW-side-up vertical displacement of the V, veins. ¢ Sub- sidiary V, veins in the west wall of the pit demonstrate a SW-side-up movement component to the veins. d A <1 m-wide, subvertical, WNW-striking F, fault cuts shallowly SW-dipping bedding in mud- stone and V vein breccias in the west-facing wall of an underground drive (i.e. in the -80 mRL level). The fault zone is filled with friable, fine-grained, granular fault gouge containing minor fragments of quartz-altered mudstone wallrock. e Steeply SE-dipping, NE-striking, F; faults cut volcanogenic sandstone in the south wall of the pit. Striations on the fault plane pitch 60° to the NE. Fault splays to the main F; fault plane indicate SE-side-up and dextral displacement. f A <5 cm-wide, bedding-parallel normal F, fault offsets a V, vein in volcanogenic sandstone in the west wall of the pit
Fig. 8 Photographs showing structural relationships at Eunsan: a Heterolithic coarse tuff and overlying volcanogenic sandstone in the western wall of the Eunsan pit are cut by subvertical WSW-striking V, veins with a SW-side-up-dextral displacement. The strata and V, veins are in turn displaced by a subvertical, WSW-striking F2 fault with a SW-side-down (and minor sinistral) displacement of about 100 m. b Plan view of a quartz-carbonate V, vein that cuts volcanogenic sand- stone beds in the north wall of the Eunsan pit. The vein strikes WNW (295°) and dips 80° to the SW. A subordinate horsetail splay strikes NNW (352°) and dips 86° to the E, suggesting a dextral shear compo- nent to the SW-side-up vertical displacement of the V, veins. ¢ Sub- sidiary V, veins in the west wall of the pit demonstrate a SW-side-up movement component to the veins. d A <1 m-wide, subvertical, WNW-striking F, fault cuts shallowly SW-dipping bedding in mud- stone and V vein breccias in the west-facing wall of an underground drive (i.e. in the -80 mRL level). The fault zone is filled with friable, fine-grained, granular fault gouge containing minor fragments of quartz-altered mudstone wallrock. e Steeply SE-dipping, NE-striking, F; faults cut volcanogenic sandstone in the south wall of the pit. Striations on the fault plane pitch 60° to the NE. Fault splays to the main F; fault plane indicate SE-side-up and dextral displacement. f A <5 cm-wide, bedding-parallel normal F, fault offsets a V, vein in volcanogenic sandstone in the west wall of the pit
Fig. 10 The simplified map of underground workings situated about 30 m below sea level illustrates the local occurrence of horsetail jog geometries associated with normal-dextral, Au-Ag-bearing V,veins and their offset by normal-sinistral F, faults (modified after an unpub- lished plan generated by Ivanhoe Mines Ltd.) Au—Ag ore zones are widest in volcaniclastic units of the Haenam Formation, which have a higher primary porosity and permeability than the underlying, mudstone and silt- stone beds of the Uhangri Formation. The gentle SW plunge of the Eunsan ore body is interpreted to reflect the intersec- tion of the V; veins and rocks of the Haenam Formation (Fig. 6d and e). The maximum vertical extent of the Eunsan ore body is probably largely controlled by the lower limit of fluid boiling zones, but could also reflect the position of the basal contact of the Haenam Formation with the underlying Uhangri Formation.
Fig. 10 The simplified map of underground workings situated about 30 m below sea level illustrates the local occurrence of horsetail jog geometries associated with normal-dextral, Au-Ag-bearing V,veins and their offset by normal-sinistral F, faults (modified after an unpub- lished plan generated by Ivanhoe Mines Ltd.) Au—Ag ore zones are widest in volcaniclastic units of the Haenam Formation, which have a higher primary porosity and permeability than the underlying, mudstone and silt- stone beds of the Uhangri Formation. The gentle SW plunge of the Eunsan ore body is interpreted to reflect the intersec- tion of the V; veins and rocks of the Haenam Formation (Fig. 6d and e). The maximum vertical extent of the Eunsan ore body is probably largely controlled by the lower limit of fluid boiling zones, but could also reflect the position of the basal contact of the Haenam Formation with the underlying Uhangri Formation.
WNW-striking F, faults spaced about 50 m apart segment the Eunsan ore body, offsetting Au-Ag zones by up to 100 m vertically (Fig. 9). On some levels in the underground mine, SW-block-down movement along F, faults duplicated V, veins and associated ore zones and significantly increased the total width of the ore body (Fig. 10). By contrast, F; and Fy, faults displace the ore body by <I m and have negligible influence on the geometry of Au—Ag ore shoots.
WNW-striking F, faults spaced about 50 m apart segment the Eunsan ore body, offsetting Au-Ag zones by up to 100 m vertically (Fig. 9). On some levels in the underground mine, SW-block-down movement along F, faults duplicated V, veins and associated ore zones and significantly increased the total width of the ore body (Fig. 10). By contrast, F; and Fy, faults displace the ore body by <I m and have negligible influence on the geometry of Au—Ag ore shoots.
bearing V, veins cut the subhorizontal strata and are surrounded by zoned hydrothermal wall-rock alteration Fig. 11 Geological section for Moisan showing the distribution of rock types, hydrothermal alteration, structures and Au mineralisation (modified after Bowden 2007). Subvertical, WNW-striking, Au-Ag- The Moisan mine stratigraphy is similar to the Eunsan deposit and consists of mudstone and siltstone beds of the Uhangri Formation that are overlain by volcanic and volca- niclastic rocks of the Haenam Formation (Fig. 11). The latter sequence of rocks includes (1) coarse-grained Hwangsan tuff, (2) heterolithic lapilli tuff (Fig. 12a, b) interbedded with
bearing V, veins cut the subhorizontal strata and are surrounded by zoned hydrothermal wall-rock alteration Fig. 11 Geological section for Moisan showing the distribution of rock types, hydrothermal alteration, structures and Au mineralisation (modified after Bowden 2007). Subvertical, WNW-striking, Au-Ag- The Moisan mine stratigraphy is similar to the Eunsan deposit and consists of mudstone and siltstone beds of the Uhangri Formation that are overlain by volcanic and volca- niclastic rocks of the Haenam Formation (Fig. 11). The latter sequence of rocks includes (1) coarse-grained Hwangsan tuff, (2) heterolithic lapilli tuff (Fig. 12a, b) interbedded with
Fig. 12 Photographs of representative rock types in the Moisan de- posit: a coarse-grained, lithic-fragment-rich lapillistone that is matrix- supported and contains <5 vol% plagioclase crystals. Pyrite and chlo- rite replace primary volcanic vesicles, resulting in pyrite-filled amyg- dales with chlorite rims. b A fine tuff comprises mainly ash, with up to 5 vol%, 1 mm-diameter plagioclase crystals, and rare spherical and concentrically layered lapilli. e A green, well-sorted, crystal- and lithic fragment-poor tuff that is moderately hydrothermally chlorite-pyrite- altered. d The coarse tuff is moderately sorted and comprises angular, subhedral plagioclase and amphibole crystals, lithic fragments, and a matrix of plagioclase, quartz and ash. Amphibole is preferentially replaced by pyrite. All photographs are of core from diamond drill hole MS08-03, with the exception of photograph (b), which is from drill hole MS08-02
Fig. 12 Photographs of representative rock types in the Moisan de- posit: a coarse-grained, lithic-fragment-rich lapillistone that is matrix- supported and contains <5 vol% plagioclase crystals. Pyrite and chlo- rite replace primary volcanic vesicles, resulting in pyrite-filled amyg- dales with chlorite rims. b A fine tuff comprises mainly ash, with up to 5 vol%, 1 mm-diameter plagioclase crystals, and rare spherical and concentrically layered lapilli. e A green, well-sorted, crystal- and lithic fragment-poor tuff that is moderately hydrothermally chlorite-pyrite- altered. d The coarse tuff is moderately sorted and comprises angular, subhedral plagioclase and amphibole crystals, lithic fragments, and a matrix of plagioclase, quartz and ash. Amphibole is preferentially replaced by pyrite. All photographs are of core from diamond drill hole MS08-03, with the exception of photograph (b), which is from drill hole MS08-02
Fig. 13 Outcrop map and horizontal sections for Moisan. a The simplified outcrop map shows the distribution of major rock types and structures. The lower-hemisphere, equal-area stereographic projec- tions display bedding, vein and fault orientations. b-e The series of horizontal slices through the deposit demonstrate the geometry and position of ore zones that spatially coincide with WNW-trending, sheeted V, veins
Fig. 13 Outcrop map and horizontal sections for Moisan. a The simplified outcrop map shows the distribution of major rock types and structures. The lower-hemisphere, equal-area stereographic projec- tions display bedding, vein and fault orientations. b-e The series of horizontal slices through the deposit demonstrate the geometry and position of ore zones that spatially coincide with WNW-trending, sheeted V, veins
Table 1 A comparison of deformation events for the Eunsan and Moisan deposits adularia from proximal hydrothermal alteration zones at Chunsan has a *°Ar/??Ar crystallisation age of 78.1+0.3 Ma (Bowden 2007), which overlaps the timing of Au-Ag miner- alisation at Eunsan and Moisan. Bowden (2007) interprets the Chunsan low-sulphidation veins and hydrothermal alteration zones to have replaced an earlier, high-sulphidation-related clay alteration in the rocks. Hydrothermal ore fluids associated with low-sulphidation epithermal mineralisation exploited these zones of enhanced secondary permeability in the volca- niclastic rocks (Bowden 2007). of <1 m, but with unconstrained lateral displacements. a disp disp high resu men These faults formed as a result of approximately ENE- SSW-directed shortening (Fig. 14c). Only observed at Eunsan, shallow-dipping, bedding-parallel normal F4 faults ace V, veins with <1 m offsets and indicates a fourth deformation event involving NE-SW-directed extension (Fig. 14d). Although post-Dz event structures generally ay minor displacements, they clearly cut V, veins at angles and have the potential to displace ore shoots, ting in complexity in regard to underground develop- and exploration.
Table 1 A comparison of deformation events for the Eunsan and Moisan deposits adularia from proximal hydrothermal alteration zones at Chunsan has a *°Ar/??Ar crystallisation age of 78.1+0.3 Ma (Bowden 2007), which overlaps the timing of Au-Ag miner- alisation at Eunsan and Moisan. Bowden (2007) interprets the Chunsan low-sulphidation veins and hydrothermal alteration zones to have replaced an earlier, high-sulphidation-related clay alteration in the rocks. Hydrothermal ore fluids associated with low-sulphidation epithermal mineralisation exploited these zones of enhanced secondary permeability in the volca- niclastic rocks (Bowden 2007). of <1 m, but with unconstrained lateral displacements. a disp disp high resu men These faults formed as a result of approximately ENE- SSW-directed shortening (Fig. 14c). Only observed at Eunsan, shallow-dipping, bedding-parallel normal F4 faults ace V, veins with <1 m offsets and indicates a fourth deformation event involving NE-SW-directed extension (Fig. 14d). Although post-Dz event structures generally ay minor displacements, they clearly cut V, veins at angles and have the potential to displace ore shoots, ting in complexity in regard to underground develop- and exploration.

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Igor M Villa

Ore Geology Reviews, 2017

The Sangdong scheelite-molybdenite deposit in northeast South Korea consists of strata-bound orebodies in intercalated carbonate-rich layers in the Cambrian Myobong slate formation. Among them, the M1 layer hosts the main orebody below which lie layers of F1-F4 host footwall orebodies. Each layer was first skarnized with the formation of a wollastonite + garnet + pyroxene assemblage hosting minor disseminated scheelite. The central parts of the layers were subsequently crosscut by two series of quartz veining events hosting minor scheelite and major scheelite-molybdenite ores, respectively. The former veins associate amphibole-magnetite (amphibole) alteration, whereas the latter veins host quartz-biotite-muscovite (mica) alteration. Deep quartz veins with molybdenite mineralization are hosted in the Cambrian Jangsan quartzite formation beneath the Myobong formation. In the Sunbawi area, which is in close proximity to the Sangdong deposit, quartz veins with scheelite mineralization are hosted in Precambrian metamorphic basement. Three muscovite 39 Ar-40 Ar ages between 86.6 ± 0.2 and 87.2 ± 0.3 Ma were obtained from M1 and F2 orebodies from the Sangdong deposit and Sunbawi quartz veins. The Upper Cretaceous age of the orebodies is concordant with the literature age of the hidden Sangdong granite, 87.5 ± 4.5 Ma. This strongly suggests that the intrusion is causative for the Sangdong W-Mo ores and Sunbawi veins. Fluid inclusions in the quartz veins from the M1 and F2 orebodies, the deep quartzmolybdenite veins, and the Sunbawi veins are commonly liquid-rich aqueous inclusions having bubble sizes of 10-30 vol.%, apparent salinities of 2-8 wt% NaCl eqv., and homogenization temperatures of 180-350 °C. The densities of the aqueous inclusions are 0.70-0.94 g/cm 3. No indication of fluid phase separation was observed in the vein. To constrain the formation depth in the Sangdong deposit, fluid isochores are combined with Ti-in-quartz geothermometry, which suggests that the M1 and F2 orebodies were formed at depths of 1-3 km and 5-6 km below the paleosurface, respectively. The similarity of the Cs concentrations and Rb/Sr ratios in the fluid inclusions of the respective orebodies indicate an origin from source magmas having similar degrees of fractionation and enrichment of incompatible elements such as W and Mo. High S concentrations in the fluids and possibly organic C in the sedimentary source likely promoted molybdenite precipitation in the Sangdong orebodies, whereas the scheelite deposition in the deep quartz-molybdenite veins hosted in the quartzite is limited by a lack of Ca and Fe in the hydrothermal fluids. The molybdenite deposition in the Sunbawi quartz-molybdenite veins hosted in the Precambrian metamorphic basement rocks was possibly limited by a lack of reducing agents such as organic C.

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Mesothermal Gold Vein Mineralization of the Seolhwa Mine, Asan Mining District, Korea
Gold Heo

Resource Geology, 2009

Gold mineralization of the Seolhwa mine occurs in a single stage of massive quartz veins which filled the north-east-trending fault shear zones in the Jurassic granitoid of 161 Ma within the Gyeonggi Massif. The vein quartz contains three main types of fluid inclusions at 25°C: (i) aqueous type I inclusions (0–15 wt.% NaCl) containing small amounts of CO2; (ii) gas-rich (more than 70 vol. %), vapor-homogenizing, aqueous type II inclusions; and (iii) low-salinity (less than 5 wt.% NaCl), liquid CO2-bearing, type III inclusions. The H2O-CO2-CH4-N2-NaCl inclusions represent immiscible fluids trapped earlier along the solvus curve in the temperature range 250–430°C at pressures of ∼1 kb. Detailed fluid inclusion chronologies suggest a progressive decrease in pressure during the mineralization. Aqueous inclusion fluids represent either later fluids evolved through extensive fluid unmixing from a homogeneous H2O-CO2-CH4-N2-NaCl fluid due to decreases in temperature and pressure, or the influence of deep circulated meteoric waters. Initial fluids were homogeneous H2O-CO2-CH4-N2-NaCl fluids as follows: 250° to 430°C, 16–62 mol% CO2, 5–14 mol% CH4, 0.06–0.31 mol% N2 and salinities of 0.4–4.9 wt.% NaCl. The T-X data for the Seolhwa mine suggest that the hydrothermal system has been probably located nearer to the granitic melt, which facilitated the CH4 formation and resulted in a reduced fluid state indicated by the predominance of pyrrhotite. Measured and calculated isotopic compositions of the hydrothermal fluids [δ18O = 5.3–6.5‰; δD =−69 to −84‰] provide evidence of the CH4-H2O equilibria and further indicate that the auriferous fluids were magmatically derived. Both the dominance of δ34S values of sulfides close to the meteoric reference (−0.6–1.4‰; δ34SΣS values of 0.3–1.1‰) and the available δ13C data (−4‰) are consistent with their deep igneous source. The Seolhwa mine was probably formed by extensive fracturing and veining due to the thermal expansion of water derived from the Jurassic granitoid melt.

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Preliminary metallogenic belt and mineral deposit maps for northeast Asia
Ariunbileg Sodov

Open-File Report, 2003

Podiform chromite Serpentinite-hosted asbestos C. Deposits associated with anorthosite complexes Anorthosite apatite-Ti-Fe-P D. Deposits associated with kimberlite Diamond-bearing kimberlite II. Deposits related to intermediate and felsic intrusions A. Pegmatite Muscovite pegmatite REE-Li pegmatite B. Greisen and quartz vein Fluorite greisen Sn-W greisen, stockwork, and quartz vein W-Mo-Be greisen, stockwork, and quartz vein C. Alkaline metasomatite Ta-Nb-REE alkaline metasomatite D. Skarn (contact metasomatic) Au skarn Boron (datolite) skarn Carbonate-hosted asbestos Co skarn Cu (±Fe, Au, Ag, Mo) skarn Fe skarn Fe-Zn skarn Sn skarn Sn-B (Fe) skarn (ludwigite) W±Mo±Be skarn Zn-Pb (±Ag, Cu) skarn E. Porphyry and granitoid pluton-hosted deposit Cassiterite-sulfide-silicate vein and stockwork Felsic plutonic U-REE Granitoid-related Au vein Polymetallic Pb-Zn ± Cu (±Ag, Au) vein and stockwork Porphyry Au Porphyry Cu (±Au) Porphyry Cu-Mo (±Au, Ag) Porphyry Mo (±W, Bi) Porphyry Sn III. Deposits related to alkaline intrusions A. Carbonatite-related deposits Apatite carbonatite Fe-REE carbonatite Fe-Ti (±Ta, Nb, Fe,Cu, apatite) carbonatite Phlogopite carbonatite REE (±Ta, Nb, Fe) carbonatite B. Alkaline-silisic intrusions related deposits Alkaline complex-hosted Au Peralkaline granitoid-related Nb-Zr-REE Albite syenite-related REE Ta-Li ongonite C. Alkaline-gabbroic intrusion-related deposits Charoite metasomatite Magmatic and metasomatic apatite Magmatic graphite Magmatic nepheline Deposits related to extrusive rocks IV. Deposits related to marine extrusive rocks A. Massive sulfide deposits Besshi Cu-Zn-Ag massive sulfide Cyprus Cu-Zn massive sulfide Korean Pb-Zn massive sulfide Volcanogenic Cu-Zn massive sulfide (Urals type) Volcanogenic Zn-Pb-Cu massive sulfide (Kuroko, Altai types) B. Volcanogenic-sedimentary deposits Volcanogenic-hydrothermal-sedimentary massive sulfide Pb-Zn (±Cu) Volcanogenic-sedimentary Fe Volcanogenic-sedimentary Mn V. Deposits related to subaerial extrusive rocks A. Deposits associated with mafic extrusive rocks and dike complexes Ag-Sb vein Basaltic native Cu (Lake Superior type) Hg-Sb-W vein and stockwork Hydrothermal Iceland spar Ni-Co arsenide vein Silica-carbonate (listvenite) Hg Trap related Fe skarn (Angara-Ilim type) B. Deposits associated with felsic to intermediate extrusive rocks Au-Ag epithermal vein Ag-Pb epithermal vein Au potassium metasomatite (Kuranakh type) Barite vein Be tuff Carbonate-hosted As-Au metasomatite Carbonate-hosted fluorspar Carbonate-hosted Hg-Sb Clastic sediment-hosted Hg±Sb Epithermal quartz-alunite Fluorspar vein Hydrothermal-sedimentary fluorite Limonite from spring water Mn vein Polymetallic (Pb, Zn±Cu, Ba, Ag, Au) volcanic-hosted metasomatite Polymetallic (Pb, Zn, Ag) carbonate-hosted metasomatite Rhyolite-hosted Sn Sulfur-sulfide (S, FeS 2) Volcanic-hosted Au-base-metal metasomatite Volcanic-hosted Hg Volcanic-hosted U Volcanic-hosted zeolite Deposits related to hydrothermal-sedimentary sedimentary processes VI. Stratiform and stratabound deposits Bedded barite Carbonate-hosted Pb-Zn (Mississippi valley type) Sediment-hosted Cu Sedimentary exhalative Pb-Zn (SEDEX) VII. Sedimentary rock-hosted deposits Chemical-sedimentary Fe-Mn Evaporate halite Evaporate sedimentary gypsum Sedimentary bauxite Sedimentary celestite Sedimentary phosphate Sedimentary Fe-V Sedimentary siderite Fe Stratiform Zr (Algama Type) VIII. Polygenic carbonate-hosted deposits Polygenic REE-Fe-Nb deposits (Bayan-Obo type) Deposits related to metamorphic processes IX. Sedimentary-metamorphic deposits Banded iron formation (BIF, Algoma Fe) Banded iron formation (BIF, Superior Fe) Homestake Au Sedimentary-metamorphic borate Sedimentary-metamorphic magnesite X. Deposits related to regionally metamorphosed rocks Au in black shale Au in shear zone and quartz vein Clastic-sediment-hosted Sb-Au Cu-Ag vein Piezoquartz Rhodusite asbestos Talc (magnesite) replacement Metamorphic graphite Metamorphic sillimanite Phlogopite skarn Deposits related to surficial proceses XI. Residual deposts Bauxite (karst type) Laterite Ni Weathering crust Mn (±Fe) Weathering crust and karst phosphate Weathering crust carbonatite REE-Zr-Nb-Li XII.

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Integrated 3D Geological Modeling to Gain Insight in the Effects of Hydrothermal Alteration on Post-Ore Deformation Style and Strain Localization in the Flin Flon Volcanogenic Massive Sulfide Ore System
Ernst Schetselaar

Minerals

3D geological modeling of lithogeochemical and geological data provides insight into the role of the sulfide ore horizon and associated footwall hydrothermal alteration in localizing shear strain in the Flin Flon volcanogenic massive sulfide deposits, Canada, as deformation evolved from brittle-ductile to ductile regimes during collisional stages of the 1.9-1.8 Ga Trans-Hudson orogeny. 3D spatial characterization of hydrothermal alteration based on the Ishikawa index (AI) and normative corundum percentages outline sericite + chlorite-rich high strain zones, consisting of Al-enriched and Na-depleted felsic and mafic volcanic rocks in the footwall of the sulfide ore horizon. The hydrothermal vent complex, from which these sheared alteration zones originated, was stacked together with the ore horizon by W-vergent thrust faults during an early collisional deformation regime, imbricating molasse-type clastic sediments with the ore-hosting volcanic and volcaniclastic rocks of the Flin Flon arc assemblage. Chlorite-rich planar zones marked by high values of the Carbonate-chlorite-pyrite index (CCPI) are laterally more extensive and outline a later system of ductile shear zones, in which phyllosilicates, quartz and chalcopyrite in stringer zones localized shear strain and enhanced transposition of the hydrothermal vent stockwork. The contrasting deformation styles of these two thrusting events and their localization within the ore horizon and hydrothermal vent stockwork have important implications for vectoring towards undiscovered ore in this mature mining camp that are possibly also relevant to other strongly deformed VMS ore systems.

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Ore Geology Reviews
tebogo kelepile

Khoemacau Mining (KCM) Cu-Ag deposits in the Ghanzi-Chobe Belt (GBC) portion of the Kalahari Cu Belt are hosted in the Neoproterozoic sedimentary succession of the Ghanzi Group. These deposits are characterized by two styles of mineralization including disseminated and structurally-controlled mineralization. A detailed study that combined whole rocks and sulfides Pb isotope characteristics, carbonate rare earth element (REE) analysis, and fluid inclusion examination was carried out in order to constrain the source(s) of Cu amd Ag, characterize the mineralizing fluids and then unravel the processes that converged and led to the genesis of the Khoemacau sediment-hosted Cu-Ag deposits. The Pb isotope compositions of both the sulfides and whole rocks overlap and display a heterogeneous character. Whereas, sulfides yielded (206 Pb/ 204 Pb) t of 17.204-67.717, (207 Pb/ 204 Pb) t ranging from 15.576 to 19.025 and (208 Pb/ 204 Pb) t between 37.026 and 45.911, whole rocks are characterized by (206 Pb/ 204 Pb) 0 = 16.284-20.897, (207 Pb/ 204 Pb) 0 = 15.273-15.869 and (208 Pb/ 204 Pb) 0 = 36.128-42.537. Previous studies regarded the underlying basalts of the Kgwebe Formation as the main metal source; however, our results rule out the possibility of the rhyolites of the Kgwebe Formation as the source of the metals. On the other hand, clastic rocks of the Ngwako Pan Formation (red beds) that underlie the mineralized unit and their precursor felsic basement rocks are likely the main Cu-Ag source rocks for the KCM deposits, with a possible minor contribution from the dolerite of the Kgwebe Formation. Furthermore, the carbonates from the KCM Cu-Ag deposits are characterized by significant variation in their ƩREE contents (26.4-328.5 ppm) and extreme diversity in REE patterns. These results indicate that both the metals of interest (Cu and Ag) and fluids were sourced from multiple sources, and multi-stage hydrothermal activities were involved in the genesis of the KCM Cu-Ag deposits. The negative Eu anomalies (0.28-0.88) of hydrothermal calcite associated with Cu-Ag mineralization are also consistent with the involvement of reduced hot (at temperatures above 200°C) hydrothermal mineralizing fluids. These fluids are characterized by a wide range of salinities (4.0-23.5 wt% NaCl + CaCl 2 equiv.) and homogenization temperatures (T h) (ca. 94-396°C), thus suggesting that the fluids involved in the mineralization processes of the KCM Cu-Ag deposits are both basinal brines, possibly mixed with seawater and meteoric water, as well as metamorphic fluids. The bimodal distribution (vapor-rich and liquid-rich) of fluid inclusions at room temperature is attributed to the boiling of fluids during entrapment. Meanwhile, the occurrence of both high temperature-high salinity and low temperature-moderate salinity fluids, as well as fluid inclusions characterized by a wide range of salinities but similar T h reflects fluid mixing. A decrease of T h in the fluid inclusions but with very similar salinities also indicates a simple cooling process during the evolution of the ore-forming fluids.

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The Silidor Deposit, Rouyn-Noranda District, Abitibi Belt:Geology, Structural Evolution, and Paleostress Modeling of an Au QuartzVein-Type Deposit in an Archean Trondhjemite
Michel Jebrak

Economic Geology, 2000

Late orogenic gold-bearing quartz vein deposits within the Rouyn-Noranda mining district occur mainly within Archean tonalitic plutons of the Blake River Group (southern Abitibi belt). The Silidor deposit is a representative example of a pluton-hosted lode gold deposit. The Silidor mine contained 2.95 million tons (Mt; mined and estimated reserves), grading 5.1 g/t Au (~15 t Au). The mineralized zone is 900 m in length and has a vertical extent of 900 m, an average thickness of 3.5 m, and trends northwest-southeast with a dip of 50°to 70°NE. Its alteration envelope consists of a red hematite-altered trondhjemite. Measured δ 18 O values for quartz veins (7.7-10.9‰) and δ 34 S values for pyrite (-6.1 to-9.4‰) imply oxidizing conditions during gold deposition. The mineralized zone comprises: vein quartz (white, gray, and smoky varieties), beige mineralized trondhjemite, and green carbonate-sericite-fuchsite breccia, which resulted from shearing and metasomatism of an early northwest-southeast dioritic dike. A quantitative microtectonic study (>400 measurements) was carried out on the Powell tonalitic sill in the Silidor mine area to reconstruct the deformation before, during, and after the mineralizing events. The reduced stress tensors display large variations in σ1 orientation, trending successively northwest-southeast, northeast-southwest, and finally north-south. The Silidor deposit is the result of several vein-filling events, which occurred during evolution from strike-slip faulting to reverse faulting regimes, with σ1 remaining northeastsouthwest but with exchange of orientation of σ2 and σ3. Such variations may reflect an oblique collision and processes of stress permutation. Paleostress mapping of Archean terranes can be used as a targeting tool for mesothermal lode gold deposits. Reduced stress tensors were used for the computation of paleostress maps, using a distinct element model. The Silidor Au quartz mineralization appears on these paleostress maps in an area characterized by low mean stress throughout the deformation history of the area near the Horne Creek fault. This study emphasizes the role of second-order faulting in the location of low-and high-pressure zones in the Archean crust and the possible role of a tectonic indentor in the location of Au mineralization.

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Geochemical studies of the Gyeongchang W-Mo Mine, Republic of Korea; progressive meteoric water inundation of a magmatic hydrothermal system
S.-t. Yun

Economic Geology, 1991

The Gyeongchang W-Mo mine is located within the Cretaceous Gyeongsang basin along the southeastern margin of the Korean peninsula. The major ore minerals, wolframite and molybdenite, together with galena, sphalerite, scheelite, and minor Ag and Bi sulfosalts, occur in fissure-filling quartz veins contained within a micrographic biotite granite. Radiometric dates of 83.7 _ 2.2 Ma for the granite and 82.4 __+ 1.4 Ma for vein alteration muscovite indicate a Late Cretaceous age for granite emplacement and associated W-Mo mineralization. The ore mineral paragenesis can be divided into four distinct stages: W-Mo, Fe oxide, Pb-Zn, and carbonate. The shifts in mineralogy reflect decreases in the temperature and fugacity of sulfur with a concomitant increase in the fugacity of oxygen. Fluid inclusion data indicate progressive decreases in temperature and salinity within each stage with increasing paragenetic time. During the W-Mo stage, high-temperature (>450øC), high-salinity fluids (30-33 wt % NaC1 equiv) formed by condensation during decompression of a magmatic vapor phase at pressures between 300 and 500 bars. In the waning portion of the W-Mo stage, the hightemperature, high-salinity fluids gave way to progressively cooler, more dilute fluids of the Fe oxide (380ø-270øC, 23-5 wt % NaCI equiv) and Pb-Zn (270ø-200øC, 11-1 wt % NaC1 equiv) stages. These trends are interpreted to indicate progressive mixing of high-salinity, magmatic hydrothermal fluids with cooler, less acidic, more oxidizing meteoric waters. There is a systematic decrease in calculated $•SOwater values with decreasing temperature in the Gyeongchang hydrothermal system, from values of •7 per mil for W-Mo stage mineralization, to 2.8 per mil for the Fe oxide stage, to-0.6 to-2.2 per mil for the Pb-Zn stage. The $D values of inclusion waters also decrease with paragenetic time: W-Mo stage,-50 to-57 per mil; Fe oxide stage,-68 per mil; Pb-Zn stage,-69 to-71 per mil. These trends are interpreted to indicate progressive meteoric water inundation of an early magmatic W-Mo hydrothermal system. We suggest that without significant introduction of meteoric waters into the Gyeongchang hydrothermal system, its deposits would be simple quartz-wolframite-molybdenite veins rather than a complex sequence of W-Mo, Fe oxide, Pb-Zn, and precious metal mineralization. o JOO KM ß i FIG. 1. Simplified geologic map of the Republic of Korea showing the location of the Gyeongchang W-Mo mine and other W-(Mo) mines. during W-Mo concentration and later involvement of meteoric waters (So et al., 1983a; Shelton et al., 1987). Deposits of the Gyeongchang W-Mo mine contain a complex sequence of W-Mo, Fe oxide, Pb-Zn, and precious metal mineralization. This study documents the mineralogy, geochemistry, and fluid interactions which were a result of progressive meteoric water inundation of a magmatic hydrothermal system. Geology The Gyeongchang W-Mo mine is located approximately 420 km southeast of Seoul along the southeastern margin of the Gyeongsang basin (Fig. 1). Rocks in the mining area consist of the sedimentary Upper Cretaceous Icheonri Formation of the Silla subbasin and younger calc-alkaline igneous rocks (Fig. 2). W-Mo-bearing hydrothermal quartz veins crosscut the igneous rocks. The Icheonri Formation strikes N 15 ø to 45 ø W, dips 8 ø to 20 ø NE, and is composed mainly of dark gray to black shale interlayered with minor, finegrained sandstone and thin limestone beds. Sandstone and shale are strongly altered to quartzite and hornfels, respectively, near contacts with intrusive rocks. Upper Cretaceous volcanic rocks intruding and conformably covering the Icheonri Formation are predominantly andesitc and rhyolitic tuff (>200 m thick). Andesitc (locally latite) is composed of plagioclase phenocrysts (<0.5 mm) in a matrix of feldspars, hornblende, quartz, sphene, and iron oxides. It is altered locally to hornfels at contacts with granitic rocks. Rhyolitic tuff conformably overlies andesitc and is composed of lapilli and welded tuff. Lapilli tuff contains fragments (<2 cm) of rhyolite and chert and is overlain by welded tuff containing glassy shards and feldspar phenocrysts. Late Cretaceous granitic rocks occur as small stocks in the mining area and are composed of Bulgugsa Series granites and masanites. The Bulgugsa Series granites in Korea consist of plutonit rocks varying in composition from tonalitc and granodiorite through adamellite to granite porphyry. Biotite-and hornblende-bearing adamellites are the most common rock types. Masanites (the Masan granites), the youngest members of the Bulgugsa Series, are restricted to the southeastern portion of the Gyeongsang basin, are highly differentiated, and display a trend from tonalitc through adamellite and micrographic granite to granite porphyry. The masanites are finer grained, have higher quartz and potassium feldspar contents and lower biotite contents than the Bulgugsa granites. Detailed mineral norms and compositions were reported by Son et al. (1978). Bulgugsa granites vary in composition from biotite granite to granodiorite. Medium-grained biotite granite in the mining area consists mainly of orthoclase, quartz, microcline, and plagioclase with minor ohiorite, sphene, muscovite, zircon, apatite, and iron oxides. It grades into hornblende granite outside the mining area. A small granodiorite stock displaying micrographic texture occurs in the northeastern portion of the mining area.

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Structural Geology , Tectonics and Geodynamics
Ngom Papa Malick

We present major and trace element analyses combined with U-Pb zircon crystallization ages from an intermediate to granitic intrusion sequence within the Dur Kan Complex, in the Iranian North Makran. The sampled granites-diorites-trondhjemites-plagiogranites and basaltic to andesitic lavas have tholeiitic and calc-alkaline chemical features. Field observations, petrographic relationships, trace element compositions and isotope chemistry indicate three different melt sources for granites, granitoids and the volcanic rocks. Granites yield 170-175Ma ages and represent the last crystallized melt of a continentally derived magma. The fractional crystallization dominated diorite-trondhjemite-plagiogranite sequence was crystallizing over 12Ma (165-153Ma) from the same source which has a mantle and minor continental component. East-west trending mafic dykes intruded the granitoids, which were eroded before being covered by lavas and their Cretaceous (Valangian) sedimentary cover. The source of dykes and lavas is mantle derived. Temporal correlation with plutonites from the Sanandaj-Sirjan Zone suggests a narrow northwest-southeast striking belt of Jurassic granitoid intrusions that extends over nearly 2000km. Different than previous studies in the Sanandaj-Sirjan Zone, that interpreted these rocks as a magmatic arc and proof for Jurassic subduction of the Neotethys, we suggest extension, that separated the Sanandaj-Sirjan Zone and Central Iran. The increasing mantle inf luence in the magma source is explained by continuous thinning of continental crust and related mantle up-welling. This extensional phase resulted in the formation of the North Makran Ophiolites.

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References (15)

  1. Bowden CD (2007) Epithermal systems of the Seongsan district, South Korea: an investigation on the geological setting and spatial and temporal relationships between high and low sulfidation systems. PhD, James Cook University of North Queensland Choi Y-S (1995) Structural evolution of the Cretaceous Eumseong Basin, Korea. PhD, Seoul National University Choi S-G, Ryu I-C, Wee S-M, Kim CS, Pak S-J (2003) Overview of epithermal gold-silver mineralization, Korea: tectonic and genetic implication. In: Program with abstracts: the origin of granites and related rocks. The 5th Hutton Symposium, Toyohashi, Japan, Geological Survey of Japan, p 23
  2. Choi S-G, Ryu I-C, Pak S-J, Wee S-M, Kim C-S, Park M-E (2005) Cretaceous epithermal gold-silver mineralization and geody- namic environment, Korea. Ore Geol Rev 26:115-135
  3. Chough S-K, Kwon S-T, Ree J-H, Cho D-K (2000) Tectonic and sedimentary evolution of the Korean peninsula: a review and new view. Earth Sci Rev 52:175-235
  4. Chun S-S, Chough S-K (1995) The cretaceous Uhangri formation, SW Korea, lacustrine margin facies. Sedimentology 42:293-322
  5. Hwang K-G, Huh M, Lockley MG, Unwin DM, Wright JL (2002) New pterosaur tracks (Pteraichnidae) from the Late Creta- ceous Uhangri Formation, southwestern Korea. Geol Mag 139:421-435
  6. Kim I-J (1991) Geochemistry of hydrothermal alteration and clay deposits in the Haenam area, southwest Korea. PhD, University of Tokyo
  7. Kim C-S, Choi S-G (2009) Potassium-argon ages of the epithermal gold-silver mineralisation in the Haenam-Jindo area, southwest- ern Korea. Resour Geol 59(4):415-421
  8. Kim I-J, Nagao K (1992) K-Ar ages of the hydrothermal clay deposits and the surrounding igneous rocks in southwest Korea. J Petrol Soc Korea 1:58-70
  9. Koh S-M (1996) Geochemical characteristics of the Cretaceous volcanic rocks and Bukok hydrothermal deposits in the Hae- nam volcanic field, Chollanamdo, Korea. PhD, Seoul Nation- al University
  10. Lee D-W, Paik K-H (1990) Evolution of strike-slip fault-controlled cretaceous Yongdong basin, South Korea: signs of strike-slip tectonic during infilling. J Geol Soc Korea 26:257-276
  11. Moon H-S, Kim Y-H, Kim J-H, You J-H (1990) K-Ar ages of alunite and sericite in altered rocks, and volcanic rocks around the Hae- nam area, southwest Korea. J Korean Inst Min Geol 23:135-141
  12. Park K-H, Choi H-I, Reedman AJ (1997) Late Cretaceous volcanic mega-breccia in the Haenam area of southwest Korea. KIGAM Bulletin, vol 1
  13. Riedel W (1929) Zur Mechanik geologischer Brucherscheinungen. Zentralbl Miner Geol Paläo 1929B:354-368
  14. Simmons SF, White NC, John DA (2005) Geological characteristics of epithermal precious and base metal deposits. Econ Geol 100:485- 522
  15. Yang S-Y (1992) Stratigraphic distribution and taxonomic problems of the Mesozoic non-marine mollusks in Korea. In: Choi D-K, Lee J- D, Yun H (eds) Biostratigraphy, bioprovincialism and bioevents in the Far East. Paleontological Society of Korea, pp 194-196 (Spe- cial Publication)

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Mineralization Characteristics and Structural Controls of Hydrothermal Deposits in the Gyeongsang Basin, South Korea
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Hydrothermal deposits in the Gyeongsang Basin show the genetic relationship with igneous activity from Late Cretaceous to Early Tertiary in the spatial and temporal viewpoints. Many hydrothermal Au-Ag-Cu-Pb-Zn and clay deposits are dominantly distributed within the Gyeongsang Basin. The Gyeongsang Basin is divided into seven metallogenic provinces by spatial distribution. The age ranges of igneous activity and mineralization are 140~40 Ma and 100~40 Ma, respectively, and the most dominant age ranges of the both activities are from 90 Ma (Coniacian) to 50 Ma (Eocene). The age consistency between igneous activity and mineralization suggests that this age range is the climactic period of the hydrothermal activity of the Gyeongsang Basin. The metallogenic epochs in the Gyeongsang Basin are divided into three epochs of 100~80 Ma (western part of the Gyeongsang Basin), 80~60 Ma (central part of the Gyeongsang Basin), and 60~40 Ma (eastern part of the Gyeongsang Basin). The mineralization and igneous activity tend to become young eastward in the Gyeongsang Basin. NNW-SSE mineralized veins from 100 to 80 Ma in the western part of the Gyeongsang Basin are interpreted as the control of the parallel tensional fissures caused by NNW-SSE compressional stress. NW-SE mineralized veins from 80 to 60 Ma in the central part of the Gyeongsang Basin seem to have been formed under the same stress as that of the Gaeum and Yangsan Fault Systems. Namely, NW-SE tensional stress is associated with a conjugate set of fracturing of the WNW-ESE Gaeum Fault System and NNE-SSW Yangsan Fault System. Also NE-SW mineralized veins from 60 to 40 Ma in the eastern part of the Gyeongsang Basin seem to be controlled by the NE-SW fractures. The fractures are related with NE-SW compressional stress and are developed as secondary fractures within the dextral strike slip Yangsan Fault System.

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saisai li

Resource Geology, 2019

Many types of hydrothermal deposits (e.g. W, Bi, Pb, Zn, Ag) are confined by faults and hidden granodiorite in the Luowei Orefield in Xidamingshan, Guangxi, China. The orebodies in the Luowei W-Bi deposit are predominantly layered and distributed along bedding in sandstones of the Cambrian Xiaoneichong Formation. The orebodies in the Lujing Pb-Zn deposit are controlled mainly by west-southwest (WSW)-trending faults, and those in the Fenghuangshan Ag deposit are controlled mainly by west-northwest (WNW)-trending faults, which were reverse faults during mineralization and were later reactivated as sinistral strike-slip faults. The Luowei fault was formed postmineralization and resulted in sinistral displacement of the subsurface granodiorite and the Cambrian strata. A tectonomagmatic mineralization model of the Luowei Orefield is proposed, and the following conclusions were made. (i) Under a regional N-S compressive stress regime, WSW-and WNW-trending reverse faults and N-S-trending tensional fractures were formed. (ii) Magma intruded along the tensional fractures. Under the force of magmatic thermodynamics, mineralizing fluid migrated along bedding planes in sandstones and formed W-Bi orebodies at favorable sites. Some fluid migrated along WSW-and WNW-trending faults to sites farther from the magma source, forming vein-type Pb-Zn and Ag orebodies. (iii) After mineralization, under E-W compression, a NW-trending left-lateral slip fault was formed, cutting the subsurface granodiorite and orebodies. Concurrently, sinistral shear slip occurred on WNW-trending ore-controlling faults. However, the small displacement on these faults did not change the overall distributions of the rock mass and orebodies.

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A classification of mineral systems, overviews of plate tectonic margins and examples of ore deposits associated with convergent margins
Franco Pirajno

Gondwana Research, 2015

In this contribution I presents definitions of mineral systems, followed by a proposed classification of mineral deposits. The concept of mineral systems has been tackled by various authors within the framework of genetic models with the aim of improving the targeting of new deposits in green field areas. A mineral system has to be considered taking into account, by and large, space-time patterns or trends of mineralisation at the regional scale, their tectonic controls and related metallogenic belts. This leads to a suggested classification of mineral systems, together with a summary of previous ideas on what is, without doubt, a kind of "mine field", because if a classification is based on genetic processes, these can be extremely complex due to the fact that ore genesis usually involves a number of interactive processes. The classification presented is based on magmatic, magmatichydrothermal, sedimentary-hydrothermal, non-magmatic, and mechanical-residual processes. An overview of plate tectonics (convergent and divergent margins) is discussed next. Convergent plate margins are characterised by a tectonic plate subducting beneath a lower density plate. Convergent plate margins have landward of a deep trench, a subduction-accretion complex, a magmatic arc and a foreland thrust belt. An important feature is the subduction angle: a steep angle of descent, is exemplified by the Mariana, or Tonga-Kermadec subduction systems, conducive to porphyry-high-sulphidation epithermal systems, whereas in an intra-arc rift systems with spreading centres is conducive to the generation of massive sulphide deposits of kuroko affinity. A shallower subduction zone is the domain of large porphyry Cu-Mo and epithermal deposits. The implications of this difference in terms of metallogenesis are extremely important. Continent-continent, arc-continent, arcarc, amalgamation of drifting microcontinents, and oceanic collision events are considered to be a major factor in uplift, the inception of fold-and-thrust belts and high P metamorphism. Examples are the Alpine-Himalayan orogenic belt formed by the closure of the Tethys oceanic basins and the great Central Asian Orogenic Belt (CAOB), a giant accretionary collage of island arcs and continental fragments. The closing of oceanic basins, and the accretion of allochthonous terranes, result in the emplacement of ophiolites by the obduction process. Divergent plates include mid-ocean ridges, passive margins and various forms of continental rifting. At midocean spreading centres, magma chambers are just below the spreading centre. Once the oceanic crust moves away from the ridge it is either consumed in a subduction zone, or it may be accreted to continental margins, or island arcs. Spreading centres also form in back arc marginal basins. Transform settings include transtensional with a component of tension due to oblique divergence, transform or strike-slip sensu stricto and transpressive with a component of compression due to oblique convergence. Strike-slip faults that form during extensional processes lead to the formation of pull-apart basins. Mineral systems that form at convergent margins, the topic of this special issue, are succinctly introduced in Tables 1 to 7, as follows: principal geological features of selected mineral systems at convergent plate margins and back-arcs (Table 1); their recognition criteria (Table 2); principal geological features of selected ore deposits of back-arc basins and post-subduction rifting (Table 3) and of subduction-related magmatic arcs (Table 4), their respective recognition criteria (Table 5); accretionary and collisional tectonics and associated mineral systems (Table 6); principal geological features and associated mineral systems of transform faults (Table 7).

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Active Fault and Shear Processes and Their Implications for Mineral Deposit Formation and Discovery
steven micklethwaite

Journal of Structural Geology, 2010

Mineralisation associated with fault, vein and shear zone systems can be related to processes that operated when those systems were active. Despite the complexity of processes that operate in faults, veins and shear zones, there are typically systematic patterns in geometry (e.g. segmentation and stepovers) and scaling, which are the cumulative result of multiple slip events. In turn, there are systematic patterns in individual slip events (e.g. earthquake-aftershock sequences, shear zone creep transients,earthquake swarms) with implications for permeability enhancement and mineral deposit formation. This review identifies three avenues for future research: (1) a need to improve constraints on the scaling characteristics of faults, shear zones and veins specifically related to mineralisation. (2) The integration of stress change and damage concepts with 3-D lithological observations and reactive transport modelling. (3) Understanding the impact of multiphase fluids (e.g. H2O–CO2–NaCl fluids) on fault mechanics and permeability. Static stress change modelling, damage mechanics modelling and fault/vein scaling concepts have promising predictive capabilities for the future discovery of mineral deposits. The review mostly refers to epithermal, mesothermal, and carlin-type gold deposits, but the principles could extend to any hydrothermal mineral deposit formed during faulting, fracturing and shearing.

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