NaCl Equiv Research Articles

Mineralogy, fluid inclusions and S-Pb-H-O isotopes of the Erdaokan Ag-Pb-Zn deposit, Duobaoshan metallogenic belt, NE China: Implications for ore genesis

The recently discovered Erdaokan Ag-Pb-Zn deposit is located in the Duobaoshan gold-copper metallogenic belt in the eastern part of the Central Asian Orogenic Belt. The ore-bodies occur mainly as veins hosted in the breccia. Three stages of mineralization, including early magnetite-quartz-pyrite, middle silver-sulfide-bitumen-quartz and late carbonate stages, were recognized. Here we report results from electron microprobe analysis (EPMA), S-Pb-H-O isotopes and fluid inclusions studies to gain insights into the salient characteristics of the ore mineralization and mechanism of silver precipitation. The silver occurs mainly as argentite, pyrargyrite and invisible silver in the tetrahedrite grains, in which Ag, Fe and As isomorphically substituted Cu, Zn and Sb, respectively. The homogenization temperatures of fluid inclusions in the early, middle and late stage mineralisation range from 96 to 179 °C, 78 to 178 °C, and 98 to 191 °C, respectively. The fluid salinities vary from 0.35 to 5.54 wt.%NaCl equiv. The δ34S values of the pyrite and galena show a range from −0.97‰ to +9.31‰. 206Pb/204Pb vary from 18.0125 to 18.1864, 207Pb/204Pb, from 15.561 to 15.081, and 208Pb/204Pb, from 38.0445 to 37.6979, with a mean of 18.0298, 15.5125 and 37.7281 respectively. The δD and δ18Owater values of the quartz from the ore body range from −119.1‰ to −109.7‰ and −4.64‰ to 1.98‰, respectively. Based on these results, we argue that the ore-forming fluids were derived from a magmatic source, with fluid mixing as the dominant mechanism for silver precipitation, involving hydrocarbon fluid interaction as inferred from the presence of bitumen in the ore.

Overprinting by episodic mineralization in the Dongyaozhuang gold deposit, Wutai Mountain, China: Constraints from geology, mineralogy, and fluid inclusions

The Archean volcanic‐sedimentary rocks (greenstones) hosting the Dongyaozhuang (DYZ) gold deposit are situated in the Wutai Mountain, north‐central China. Field geology and mineral assemblages show at least two episodes of mineralization. The first episode features deformed quartz‐pyrite veins filling in the regional foliation (MI, Paleoproterozoic) and can be divided into two stages (MIa and MIb) based on whether the mineralization is accompanied by tourmalinization. The mineral assemblages are mainly quartz + carbonate + pyrite + chalcopyrite (+ tourmaline for MIb); both are cut by deformed barren quartz veins, which represent the final stage of MI. The second episode features undeformed stockworks/veinlets with a mineral assemblage of quartz + carbonate + pyrite + chalcopyrite + arsenopyrite ± native gold (MIIa), crosscutting MI; these ore bodies are also cut through by undeformed barren carbonate and/or quartz veins (MIIb), which represent the end of metallogeny. By integrating the crustal evolution history with ore geology, we suggest that the DYZ gold deposit is a product by overprinting of episodic mineralization rather than a single metallogenic event. For further understanding and evidence in support of this speculation, fluid inclusions and hydrothermal chlorite and biotite were studied to reveal the physicochemical conditions of fluids from various stages, and C‐H‐O isotopes were used to trace the source(s) of fluids. Temperatures recorded in chlorite from various stages C1 (from the MIa), C2 (MIb), and C3 (MIIa) generally agrees with the homogenization temperatures of aqueous type fluid inclusions (FIs) of corresponding stages. Components of FIs from each stage are dominated by water with low salinities (0–12.6 wt% NaCl equiv). The Ib‐1, Ib‐2, and Ib‐s type CO2‐H2O FIs observed from the same deformed quartz vein of the MIb can be attributed to overprinting of hydrothermal fluids. The primary Ib‐1 and Ib‐2 FIs (209–404°C) were trapped at pressures of approximately 2.2–3.7 kbar, representing the formation pressure of the MI stage, whereas the secondary Ib‐s FIs (240–349°C) were trapped at pressures of approximately 0.8–1.5 kbar, which indicates overprinting induced by MII. The C‐H‐O isotope compositions of quartz and carbonates from MIa, MIb, and MIIa can be interpreted to indicate that the fluids were derived from the same source with multistage evolution or to reflect a homogeneous signature induced with overprinting mineralization. According to the geology, mineral assemblages, component of fluid inclusions, and C‐H‐O isotopes, the DYZ gold deposit is likely to be a product of overprinting of an orogenic gold deposit.

Geology, geochronology, and fluid evolution of the Pingshun skarn iron deposit, southern Taihang Mountains

The Pingshun skarn iron deposit is located in the southern Handan–Xingtai iron district of the southern Taihang Mountains, North China Craton. Skarns and ore bodies occur as lamina, lenses, and veins along the contact between a dioritic pluton and carbonates of the Middle Ordovician Majiagou Formation. The paragenetic sequence is albite followed by diopside, then garnet, magnetite, and finally calcite. Diorite and olivine-bearing hornblende gabbro in the Pingshun area contain zircon grains with SHRIMP U–Pb ages of 123.4 ± 1.7 and 125.5 ± 2.3 Ma, respectively. Based on the close spatial association between diorite and mineralization, we suggest that both magma activities and iron mineralization in the Pingshun area took place at 125–123 Ma. Three types of fluid inclusions identified in minerals from the Pingshun deposit include three-phase (type 1), two-phase (type 2), and pure liquid (type 3) inclusions. The ore-forming fluid evolved from high temperature (515–679 °C) with high salinity (39.8–77.6 wt% NaCl equiv.) in diopside, to medium–high temperature (365–496 °C) with moderate–low salinity (11.8–17.6 wt% NaCl equiv.) in garnet, and to low temperature (162–295 °C) with moderate–low salinity (6.7–35.5 wt% NaCl equiv.) in calcite. The presence of hematite, halite, and gypsum daughter minerals in type 1 fluid inclusions and the occurrence of andradite in skarns indicate that the pre-ore–forming fluid was oxidized. The δ34S values of pyrite separated from ores vary from 12.5 to 17.4‰, with 206Pb/204Pb = 17.26–19.03, 207Pb/204Pb = 15.42–15.69, and 208Pb/204Pb = 37.29–39.76, suggesting the ore-forming fluid was originated from a magmatic source and with additional crustal material during the mineralization process. This is consistent with H–O isotope data (δ18Odiopside-H2O = 10.8‰, δ18Ogarnet-H2O = 9.5–10.8‰, δ18Omagnetite-H2O = 9.8–13.4 ‰, δDgarnet varying from − 106 to − 86‰, δDdiopside = − 90‰). The microthermometry of fluid inclusions and isotope data reveal that the addition of gypsolyte and salt-bearing marlstone into the ore-forming fluid increases Na, Ca, and Cl and that it significantly increases the ability to transport Fe and enhances the capacity of Fe in the ore-forming fluid. Fluid boiling and additional meteoric water involved are two major key factors controlling the ore precipitation. Mantle materials involved in magma and high oxygen fugacity are considered to be crucial roles in the formation of numerous iron deposits in the Handan–Xingtai iron district.

Mineralization and Alteration of a Modern Seafloor Massive Sulfide Deposit Hosted in Mafic Volcaniclastic Rocks

Abstract Tinakula is the first seafloor massive sulfide deposit described in the Jean Charcot troughs and is the first such deposit described in the Solomon Islands—on land or the seabed. The deposit is hosted by mafic (basaltic-andesitic) volcaniclastic rocks within a series of cinder cones along a single eruptive fissure. Extensive mapping and sampling by remotely operated vehicle, together with shallow drilling, provide insights into deposit geology and especially hydrothermal processes operating in the shallow subsurface. On the seafloor, mostly inactive chimneys and mounds cover an area of ~77,000 m2 and are partially buried by volcaniclastic sand. Mineralization is characterized by abundant barite- and sulfide-rich chimneys that formed by low-temperature (<250°C) venting over ~5,600 years. Barite-rich samples have high SiO2, Pb, and Hg contents; the sulfide chimneys are dominated by low-Fe sphalerite and are high in Cd, Ge, Sb, and Ag. Few high-temperature chimneys, including zoned chalcopyrite-sphalerite samples and rare massive chalcopyrite, are rich in As, Mo, In, and Au (up to 9.26 ppm), locally as visible gold. Below the seafloor, the mineralization includes buried intervals of sulfide-rich talus with disseminated sulfides in volcaniclastic rocks consisting mainly of lapillistone with minor tuffaceous beds and autobreccias. The volcaniclastic rocks are intensely altered and variably cemented by anhydrite with crosscutting sulfate (± minor sulfide) veins. Fluid inclusions in anhydrite and sphalerite from the footwall (to 19.3 m below seafloor; m b.s.f.) have trapping temperatures of up to 298°C with salinities close to, but slightly higher than, that of seawater (2.8–4.5 wt % NaCl equiv). These temperatures are 10° to 20°C lower than the minimum temperature of boiling at this depth (1,070–1,204 m below sea level; m b.s.l.), suggesting that the highest-temperature fluids boiled below the seafloor. The alteration is distributed in broadly conformable zones, expressed in order of increasing depth and temperature as (1) montmorillonite/nontronite, (2) nontronite + corrensite, (3) illite/smectite + pyrite, (4) illite/smectite + chamosite, and (5) chamosite + corrensite. Zones of argillic alteration are distinguished from chloritic alteration by large positive mass changes in K2O (enriched in illite/smectite), MgO (enriched in chamosite and corrensite), and Fe2O3 (enriched in pyrite associated with illite/smectite alteration). The δ18O and δD values of clay minerals confirm increasing temperature with depth, from 124° to 256°C, and interaction with seawater-dominated hydrothermal fluids at high water/rock ratios. Leaching of the volcanic host rocks and thermochemical reduction of seawater sulfate are the primary sources of sulfur, with δ34S values of sulfides, from –0.8 to 3.4‰, and those of sulfate minerals close to seawater sulfate, from 19.3 to 22.5‰. The mineralization and alteration at Tinakula are typical of a class of ancient massive sulfide deposits hosted mainly by permeable volcaniclastic rocks with broad, semiconformable alteration zones. Processes by which these deposits form have never been documented in modern seafloor massive sulfide systems, because they mostly develop below the seafloor. Our study shows how hydrothermal fluids can become focused within permeable rocks by progressive, low-temperature fluid circulation, leading to a large area (>150,000 m2) of alteration with reduced permeability close to the seafloor. In our model, overpressuring and fracturing of the sulfate- and clay-cemented volcaniclastic rocks produced the pathways for higher-temperature fluids to reach the seafloor, present now as sulfate-sulfide veins within the footwall. In the geologic record, the sulfate (anhydrite) is not preserved, leaving a broad zone of intense alteration with disseminated and stringer sulfides typical of this class of deposits.

Geological structure and conditions of formation of Strizhkovskoe barite-polymetallic deposit (Ore Altai)

Strizhkovskoe barite-polymetallic deposit is a typical medium-low-temperature hydrothermal-metasomatic deposit.It’s located within north-west part of Zmeinogorsk-Bystrushinskiy downfold; host rocks are volcano-terrigenous Devonian rocks. Ore bodies are related to sublatitudinal and submeridional faults intercrossing.Wallrock quartz-chlorite-sericite metasomatites formed prior to ores formation. Ore mineralization process began in Middle Devonian. Main ore minerals are sphalerite, galena, and chalcopyrite. Also there are gold and silver occurring as electrum, acanthite; silver is present in fahlores as an isomorphous admixture. Formation of the deposit subdivides into two main stages and five phases; according to obtained results of isotope study of the sulfides, it’s possible to conclude that there was a mixed source of ore matter (mantle source replacing with crust source). The temperature of main ore formation stage varied form 230 to 180 degrees. Solutions salinity varied from 9 to 15 % wt of NaCl equiv. According to fluid inclusions study results, the solutions consisted of water and following compounds CO2, NH3, SO2, HCO3.

Fluid evolution of the Wushan skarn-dominant copper deposit in the Middle-Lower Yangtze River metallogenic belt, Eastern China

The Wushan copper skarn deposit (1.37 Mt at 1.17% Cu) is located in the Middle-Lower Yangtze River polymetallic belt. Skarn orebodies mainly occur in the Carboniferous and Permian carbonates adjacent to Early Cretaceous granodiorite porphyries (148–138 Ma). Ore deposition underwent two episodes of metallogenic events, involving hydrothermal evolution followed by skarn formation and porphyry-related mineralization. The skarn episode formed massive, disseminated, veinlet- and breccia-style mineralization at the contact zone, whereas porphyry mineralization is characterized as disseminated and veinlet-style only. Various types of fluid inclusions (daughter mineral-bearing, CO2-bearing, vapor and aqueous–vapor) are classified based on their fluid composition and phase assemblages.The hydrothermal fluids are mainly derived from a magmatic origin, which exsolves during the melt-fluid differentiation. Primary fluid in endoskarn is interpreted as representing two immiscible phases evolving from a low-salinity initial fluid. The initial supersaturated fluid has a relative low salinity and the wide range of Th values (433–626 °C) implies heterogeneous trapping, corresponding to pressures of 371–646 bars and hydrostatic depth of 3.7–6.5 km. Primary fluid inclusions trapped in syn-ore quartz show the coexistence of S-type inclusions (~30.0 wt% NaCl equiv) with vapor-rich and liquid-rich inclusions, indicating fluid immiscibility and phase separation from heterogeneous trapping. The homogenization temperatures (347–434 °C) of primary vapor-rich inclusions represent the trapping temperatures, corresponding the trapped pressures range from 152 to 374 bars and a hydrostatic depth of 1.5–3.7 km. Copper mineralization in episode porphyry occurs on a very small scale and have a clear trend of decreasing temperatures and salinities during fluid evolution. A similar scenario occurred during the porphyry episode in which fluid immiscibility led to copper mineralization.Significant trends of decreasing temperatures and salinities for both mineralization episodes reflect the change from a magmatic fluid-dominated system to a mixed source fluid that incorporated formation water from the country rocks and/or meteoric water. Controlled by the chemical transition of the fluid, this mixing process produced a relatively cool fluid system with lower salinities, which enhanced the precipitation of Cu–Fe sulfides. H–O–C isotope signatures further indicate that both the fluid and metal are predominantly derived from magmatic sources, and that multiple fluid pulses contributed to form skarn minerals and sulfides in the Wushan deposit.

Fluid inclusion and isotopic (C, H, O, S and Pb) constraints on the origin of late Mesozoic vein-type W mineralization in northern Guangdong, South China

Northern Guangdong of South China occurs many large tungsten deposits, including Shirenzhang, Meiziwo and Yaoling quartz-vein type wolframite deposits. In this study, we carried out a detailed study on fluid inclusions and C-H-O-S-Pb isotopic analyses of mineral separates for these three deposits, in order to resolve the origin and evolution of ore-forming fluids and the ore deposition mechanism. The ore veins in these deposits present a similar mineral paragenesis that could be divided into three stages: (I) pre-ore stage, (II) syn-ore stage, and (III) post-ore stage. The pre-ore stage is the magmatic-hydrothermal transition stage, which is marked by fluid exsolution from the highly fractionated granites, accompanied with potassic alteration and greisenization. The syn-ore stage can be further divided into two stages: silicate-oxide stage (stage II-1) that is characterized by significant tin-tungsten mineral deposition, and sulfide stage (stage II-2) that is characterized by abundant sulfide minerals deposition. The post-ore stage is dominated by quartz and fluorite. The three deposits show similar temperature and salinity variations for syn-ore and post-ore stages. In the Shirenzhang deposit, the fluid temperature and salinity range from 239 to 301 °C and 1.4 to 8.7 wt% NaCl equiv in stage II-1, from 206 to 256 °C and 1.4 to 7.0 wt% NaCl equiv in stage II-2, and from 186 to 236 °C and 1.4 to 8.6 wt% NaCl equiv in stage III. In the Meiziwo deposit, the fluid temperature and salinity range from 242 to 310 °C and 1.1 to 8.6 wt% NaCl equiv in stage II-1, from 196 to 252 °C and 1.4 to 8.1 wt% NaCl equiv in stage II-2, and from 188 to 234 °C and 1.2 to 7.3 wt% NaCl equiv in stage III. In the Yaoling deposit, the fluid temperature and salinity range from 230 to 304 °C and 1.2 to 9.0 wt% NaCl equiv in stage II-1, from 203 to 258 °C and 1.4 to 6.5 wt% NaCl equiv in stage II-2, and from 184 to 231 °C and 1.6 to 8.3 wt% NaCl equiv in stage III. The ore-forming fluids in the three deposits belong to a medium temperature, low-salinity H2O-NaCl system, with trace amounts of volatile components including CO2, CH4 and N2. The C-H-O isotope data (δ13CCO2 = −18.9 to −6.7‰; δ18Owater = +1.1 to +6.3‰; δDH2O = −78 to −55‰) indicate that the ore-forming fluids were mainly magmatic water, which might be modified by fluid-rock interaction and mixing with meteoric water. Sulfur (δ34S = −7.0 to +0.3‰) and Pb isotope data (206Pb/204Pb = 18.531–18.693, 207Pb/204Pb = 15.728–15.753, 208Pb/204Pb = 38.902–39.081) suggest that the ore metal and sulfur are of magmatic origin. The involvement of both organic matter in metasedimentary rocks during fluid-rock interaction and oxidized meteoric water may have been responsible for the negative δ34S and δ13C values. Fluid boiling, fluid-rock interaction and minor input of meteoric water might have been effective factors for the precipitation of wolframite, cassiterite and scheelite. The sulfide precipitation may have resulted from cooling and dilution of magmatic fluids by mixing with meteoric water.

The geology and mineralogy of the Stypsi porphyry Cu-Mo-Au-Re prospect, Lesvos Island, Aegean Sea, Greece

The Stypsi Cu-Mo-Au-Re prospect, Lesvos island, is a shallow porphyry-epithermal system hosted within a middle Miocene microgranite porphyry, which was emplaced along NNE-, NW- and NE-trending structures, within trachyandesites to trachydacites and felsic pyroclastics of the Stypsi caldera. The mineralization comprises three stages: Stage I is characterized by magnetite-actinolite ± quartz in transitional and banded quartz veins mostly developed within the microgranite and the surrounding lavas related to calcic-potassic and propylitic alteration of the host rocks. In the banded veins, quartz is botryoidal, suggesting crystallization from a gel. Abundant vapor-rich inclusions in the bands produce a dark grey to black color. Within the veins, magnetite, chalcopyrite, bornite and native gold were followed in time by pyrite, hematite, sphalerite and galena. Stage I mineralization was synchronous and also postdates quartz formation in the veins, since it crosscuts and/or fills vugs in the center of the veins. Sulfides are associated with various combinations of K-feldspar, actinolite, epidote, chlorite, and calcite gangue minerals. Pyrite-molybdenite-chalcopyrite (Stage II) and late intermediate sulfidation epithermal veins (Stage III) overprint earlier mineralization and alteration, and are associated with sericite-calcite and sericite-kaolinite alteration of the porphyry system and spatially associated lavas, respectively. Molybdenite is widespread in the first two mineralization stages, with Re content ranging from about 0.3 wt% in Stage I to 1.96 wt% in Stage II. A barren silicic and advanced argillic (alunite-kaolinite) lithocap, is exposed on top of the porphyry-style mineralization and is crosscut by non-mineralized high-sulfidation epithermal chalcedony-barite veins. Bulk ore analyses of surface samples from the Stypsi prospect yielded values of up to 276 ppm Mo, 978 ppm Cu, up to 0.5 g/t Au, up to 3 g/t Ag, and up to 70 ppb Pd and Re.Fluid inclusion data indicate that the Stage I transitional and banded quartz veins were deposited at 420 °C–530 °C and at pressures up to 450 bars, from boiling hydrothermal fluids. The fluid in the veins consists of a brine (40–61 wt% NaCl equiv) that coexists with a lower salinity (6–14 wt% NaCl equiv) liquid phase and a low-density vapor-rich fluid. Fluid inclusions in quartz of the Stage III intermediate-sulfidation epithermal veins are characterized by relatively low homogenization temperatures (231 °C–288 °C) and salinities (up to 1.9 wt% NaCl equiv), which was the result of subsequent dilution of the moderately saline fluids by circulating meteoric water. This study verifies earlier works suggesting that Au-enriched felsic magmas are able to crystallize Re-rich molybdenite, and that Re may also be redistributed and enriched in later stages during the deposition of porphyry-style mineralization. The Stypsi prospect ressembles in many respects (e.g., Au grades, Cu/Mo ratios, the Re content of molybdenite and the presence of ore-grade calcic-potassic alteration), other porphyry Cu-Mo-Re-Au systems hosted in calc-alkaline rocks in northeastern Aegean, Greece.

Physicochemical conditions governing the formation of gold deposits along the southern margin of the North China Craton: A case study from the Chen'er deposit

The Chen'er gold deposit hosted in the Precambrian Taihua Supergroup metamorphic rocks is one of the typical gold deposits in the Xiaoqinling region along the southern margin of the North China Craton. The metallic mineral assemblage in this deposit includes sulfides, tellurides, native gold, electrum, and native bismuth. The telluride minerals are composed of calaverite, petzite, hessite, altaite, joseite; except for hessite and matildite, the other tellurides and native bismuth are first reported in this study. Fluid inclusion studies in the auriferous quartz reveal three types: aqueous, aqueous–carbonic, and carbonic inclusions. The homogenization temperatures range from 184 to 364°C, and salinities are in the range of 1.74‐ to 11.47‐wt.% NaCl equiv. At temperatures of 275°C, the logfTe2 and logfS2 of the fluid are estimated as −16.13 to −8.19 and −12.74 to −4.80, respectively, and at temperatures of 305°C, the pH and logfO2 of the fluid are estimated as 3.61 to 5.69 and −34.31 to −27.81, respectively. It is inferred that Au(HS)2− and Au(HS)0 are the predominant gold‐bearing complexes, and tellurium was transported as Te22−. Based on thermodynamic models of logfO2(g) versus pH, we suggest that the precipitations of native gold and electrum in the early and main mineralization stages are different, with the oxygen and hydrogen isotope values of auriferous quartz suggesting mixing of magmatic water with meteoric water.

Fluid inclusion and stable isotope study of the Lubin-Zardeh epithermal Cu-Au deposit in Zanjan Province, NW Iran: Implications for ore genesis

The Lubin-Zardeh deposit is located in the Western Alborz Magmatic belt, 45 km NE of Zanjan, Iran. This deposit contains polymetallic (Cu, Au, Pb, Zn) mineralization which is hosted by the Cenozoic volcanic-intrusive rocks of mainly intermediate and acidic composition. Pyrite, chalcopyrite, galena, sphalerite, bornite and tennantite-tetrahedrite, with native gold and silver are present in the ores. Quartz, adularia and clay minerals (illite-montmorillonite) with minor calcite are the most abundant gangue minerals and generally occur as fine-grained assemblages; some are, however, medium- and coarse-grained assemblages. The ore minerals show disseminated, vein-veinlet, replacement, and brecciated textures while the gangue minerals represent replacement, cockade, crustiform, colloform, comb, vein-veinlet and plumose textures. Alteration haloes along the main vein are silicic, argillic (illite-montmorillonite), sericitic and pyritic. Gold contents of the quartz-chalcopyrite-gold veins range from 0.002 to 10 ppm with an average of 0.52 ppm. The average values for total reserve of 0.5 Mt of Lubin-Zardeh deposit has been determined 1.3%, 0.7% and 0.4% for Cu, Pb and Zn, respectively. Most of fluid inclusions in the quartz-gold-sulfide veins consist of two vapor and liquid phases at room temperature. The primary fluid inclusions have a low to intermediate homogenization temperature between 127 and 327 °C and salinity between 4.07 and 13.98 wt% NaCl equivalent. Stable isotope and fluid inclusion studies indicate that mineralization occurred in two stages at Lubin Zardeh deposit i.e. stage I; along which base metal deposited and stage II which is associated with copper and gold mineralization. The δ18Oquartz values from stage I and stage II range from 9.56 to 12.77‰ and from 7.23 to 9.24‰, respectively while their δ34S values of sulfide minerals range from −0.9‰ to +6.2‰ and form −6.6‰ to −1.9‰. The isotopic and microthermometric data indicate that the hydrothermal solution evolved through mixing of magmatic fluids with meteoric waters. Boiling of magmatic fluid and mixing with meteoric waters were the main mechanisms of ore deposition in the Lubin-Zardeh low sulfidation epithermal deposit.

Characterization of ore-forming fluids in the Tamusu sandstone-type uranium deposit, Bayingobi Basin, China: Constraints from trace elements, fluid inclusions and C–O–S isotopes

The Tamusu deposit is a large sandstone-type uranium deposit discovered in recent years in the Bayingobi basin, Inner Mongolia. Hydrothermal activity was recorded by veins in this deposit, but its relationship with uranium mineralization has not been clarified. In this study, petrographic observations, chemical composition of U minerals, whole rock geochemistry, fluid inclusions and C–O–S stable isotope studies of sandstone and veins were integrated to characterize the mineralizing fluids and mineralization conditions. We found uranium minerals generally co-exist with pyrite occurring in interstitial pores or on detrital grains in sandstone. The main ore mineral is pitchblende, and minor ore minerals include brannerite and coffinite. Pitchblende coexists with subhedral pyrite, whereas brannerite and coffinite coexist with cubic pyrite and calcite. Calcite also occurs in veins together with gypsum. Fluid inclusions from calcite and gypsum in the veins have homogenization temperatures ranging from 124 °C to 326 °C, with salinities of 5.7–17.2 wt% NaCl equivalent. The C–O and S isotopes of the vein minerals suggest that the hydrothermal fluids were derived from circulated formation water. Trace element analysis shows that the U-bearing sandstone is commonly enriched in V, Re and Mo, while the high-grade uranium ores are further enriched in Zn, Co, Ni and Cu. The REE patterns and δEu values in the high-grade U-bearing sandstone are similar to those in the veins, which are characterized by high LREE and low δEu, suggesting that the high-grade U-bearing sandstone is related to hydrothermal activity. The mineral assemblages, temperatures, trace elements and isotopes indicate that the Tamusu deposit was affected by two distinct types of fluids: supergene diagenetic alkaline oxidizing fluids and acidic reducing hydrothermal fluids. The oxidizing fluids started to be involved after the deposition of the ore-hosting upper Bayingobi Formation, forming a large amount of low-grade U-bearing ores. The hydrothermal fluids occurred in association with the eruption of basalt in the overlying Suhongtu Formation. The involvement of hydrothermal fluids changed the pH and Eh conditions, superimposed and reformed the low-grade uranium ores, forming high-grade uranium ores, and finally fixed the position of the uranium orebodies. Therefore, the Tamusu deposit experienced four main stages: (i) sedimentary and early diagenetic uranium concentration, (ii) oxidation and ore-forming stage, (iii) hydrothermal alteration and superimposed mineralization, and (iv) post-ore stage.

Fluid Evolution and Ore Genesis of the Qibaoshan Polymetallic Ore Field, Shandong Province, China: Constraints from Fluid Inclusions and H–O–S Isotopic Compositions

The Qibaoshan polymetallic ore field is located in the Wulian area, Shandong Province, China. Four ore deposits occur in this ore field: the Jinxiantou Au–Cu, Changgou Cu–Pb–Zn, Xingshanyu Pb–Zn, and Hongshigang Pb–Zn deposits. In the Jinxiantou deposit, three paragenetic stages were identified: quartz–pyrite–specularite–gold (Stage 1), quartz–pyrite–chalcopyrite (Stage 2), and quartz–calcite–pyrite (Stage 3). Liquid-rich aqueous (LV type), vapor-rich aqueous (V type), and halite-bearing (S type) fluid inclusions (FIs) are present in the quartz from stages 1–3. Microthermometry indicates that the initial ore-forming fluids had temperatures of 351–397 °C and salinities of 42.9–45.8 mas. % NaCl equivalent. The measured hydrogen and calculated oxygen isotopic data for fluid inclusion water (δ18OFI = 11.1 to 12.3‰; δDFI = −106.3 to −88.6‰) indicates that the ore-forming fluids were derived from magmatic water; then, they were mixed with meteoric water. In the Changgou deposit, three paragenetic stages were identified: quartz–pyrite–specularite (Stage 1), quartz–pyrite–chalcopyrite (Stage 2), and quartz–galena–sphalerite (Stage 3). LV, V, and S-type FIs are present in the quartz from stages 1–3. Microthermometry indicates that the initial ore-forming fluids had temperatures of 286–328 °C and salinities of 36.7–40.2 mas. % NaCl equivalent. The measured hydrogen and calculated oxygen isotopic data for fluid inclusion water (δDFI = −115.6 to −101.2‰; δ18OFI = 12.2 to 13.4‰) indicates that the ore-forming fluids were derived from magmatic water mixed with meteoric water. The characteristics of the Xingshanyu and Hongshigang deposits are similar. Two paragenetic stages were identified in these two deposits: quartz–galena–sphalerite (Stage 1) and quartz–calcite–poor sulfide (Stage 2). Only LV-type FIs are present in the quartz in stages 1–2. The ore-forming fluids had temperatures of 155–289 °C and salinities of 5.6–10.5 mas. % NaCl equivalent. The measured hydrogen and calculated oxygen isotopic data for fluid inclusion water (δDFI = −109.8 to −100.2‰; δ18OFI = 10.2 to 12.1‰) indicates that the ore-forming fluids were derived from circulating meteoric waters. The sulfur isotopes (δ34Ssulfide = 0.6 to 4.3‰) of the four deposits are similar, indicating a magmatic source for the sulfur with minor contributions from the wall rocks. The ore field underwent at least two phases of mineralization according to the chronology results of previous studies. Based on the mineral assemblage and fluid characteristics, we suggest that the late Pb–Zn mineralization was superimposed on the early Cu (–Au) mineralizaton in the Changgou deposit.

The sources of mineralizing fluids of orogenic gold deposits of the Baikal-Patom and Muya areas, Siberia: Constraints from the C and N stable isotope compositions of fluid inclusions

The compositions of fluid inclusions in quartz and sphalerite from five gold deposits of the Baikal-Patom (Sukhoi Log, Verninsk and Dogaldyn) and Baikal-Muya (Uryakh and Irokinda) foldbelts in the northern margin of the Central Asian Orogenic Belt, along its boundary with the Siberian craton, indicate that the gold mineralization was formed predominantly from heterogeneous CO2-H2O orogenic fluid. All deposits are structurally controlled and composed of veinlet-disseminated and vein to stockwork types of ores that are hosted by rocks that underwent regional metamorphism to the greenschist facies in Baikal-Patom and up to the granulite facies in Baikal-Muya. The gold-quartz veins of all the Baikal-Patom deposits and the Uryakh were formed by fluids of similar composition with salinity of 1.4–9.5 wt% NaCl equiv. and CO2 content of 1.4–8.6 mol/kg of solution, under comparable physical conditions, at temperatures of 128–385 °C and pressures of 570–3290 bar. Fluids of the granulate-hosted Irokinda deposit are distinguished for the highest temperatures and pressures and involve relics of medium- to high-temperature (179–453 °C) brines with salinity of 4.6–46.3 wt% NaCl equiv. The temperature and pressure of the mineralizing fluid increase roughly from north to south, which correlates with the increase in the metamorphic grade of the host rocks. The increase is accompanied by the simultaneous systematic shift in the C isotope composition of CO2 (released from the quartz by the chrush-leach method) from −1.9 to −5.5‰ δ13CCO2 in the Baikal-Patom and Uryakh from −0.6 to +0.7‰ δ13CCO2 at Irokinda. The C and N isotope compositions of CO2 suggest that Irokinda fluids were partly derived from decarbonated marine limestone, whereas the orogenic gold-bearing fluids of the other deposits are interpreted to have been composed mostly of fluid from a crustal magmatic (granitic?) source.

Geology and ore-forming fluids of the Dayingezhuang gold deposit, Jiaodong Peninsula, eastern China: Implications for mineral exploration

The Dayingezhuang deposit is a representative large gold deposit within the Zhao-Ping fault zone in Jiaodong Peninsula, eastern China, and contains gold reserves of 170 t with an average grade of 3.10 g/t. The orebodies are hosted in the Late Jurassic Linglong granite intrusion and are Jiaojia-type (disseminated- or stockwork-style) ores. Mineralization and alteration are structurally controlled by the NE- to NNE-striking Linglong detachment fault located near the central section of the regional Zhao-Ping fault zone. Mineralization can be divided into primary and supergene periods. The primary period can be further divided into four hydrothermal stages: I) pyrite–(K-feldspar)–sericite–quartz; II) auriferous quartz–pyrite; III) quartz–gold–polymetallic sulfides; and IV) quartz–carbonate. Gold was mainly deposited in the second and third stages. Three types of fluid inclusion were observed (in decreasing order of abundance): AC-type (aqueous–carbonic), A-type (aqueous), and PC-type (pure carbonic). Based on petrographic, microthermometric, and laser Raman spectroscopic analyses of these fluid inclusions, three types of fluid inclusion assemblage (FIA) were identified in the quartz grains: FIA1 (AC- and PC-type), FIA2 (AC-, PC- and A-type), and FIA3 (A-type). First stage quartz grains contain mainly FIA1-type inclusions, with trapping temperatures of 305–388 °C and salinities of 4.28–8.51 wt% NaCl equivalent. Quartz grains that formed in the second and third mineralization stages contain all three types of FIA. Second stage inclusions homogenize completely at temperatures of 219–317 °C and have salinities of 1.56–11.12 wt% NaCl equivalent, while third stage inclusions homogenize completely at temperatures of 195–319 °C and have salinities of 2.73–13.33 wt% NaCl equivalent. In contrast, quartz grains that formed during the last mineralization stage contain mainly FIA3-type inclusions that yield homogenization temperatures of 126–233 °C and salinities of 0.48–6.72 wt% NaCl equivalent. The microthermometric data indicate that the ore-forming system evolved from a CO2-rich mesothermal fluid into a CO2-poor fluid. The existence and microthermometric characteristics of AC-, PC-, and A-type inclusion assemblages (FIA2) within a single thin section of grains that formed during the second and third stages show that ore fluids underwent unmixing during the syn-ore mineralization stages, due to pressure and temperature fluctuations. The microstructural deformation of auriferous samples indicates that both ductile and brittle deformation occurred during the syn-ore mineralization. Based on the inference that fluids were immiscible in FIA2, trapping pressures during ore formation are estimated at 127–276 MPa. Assuming a fluid pressure regime controlled by fault-valve activity, these pressures are equivalent to a mineralization depth of 9.2–14.0 km. The depth to which erosion occurred in the study area has been calculated as ~10.3 km since the formation of the deposit at 130 Ma, which suggests good prospecting potential for gold at depth in Dayingezhuang.

Contribution to Understanding of Ore Fluids in the Zletovo Mine Based on Fluid Inclusion Data

Abstract The Zletovo is lead–zinc (Pb–Zn) deposit, adjacent to the Plavica volcanic centre (R. Macedonia) with high-sulphidation and porphyry mineralisation. The analysis of fluid inclusions showed homogenisation temperatures in the range 335–145°C, which reflects phases of pulsation of hydrothermal solutions and defined into four groups from the lowest to the highest temperatures. The frequency of the homogenisation temperatures ranged from 265 to 125°C and with the most dominant from 245 to 225°C, from 225 to 205°C and from 145 to 125°C. Also, it was confirmed that hydrothermal ore-bearing solutions were defined as NaCl-type with range from 4.4 to 8.6 wt% NaCl equivalent. The latest stage salinities ranged from 3 to 12 wt% NaCl equivalent, where those from 10 to 12 wt% and from 6 to 8 wt% NaCl equivalent, prevailed. This suggests that hydrothermal solutions within analysed quartz grains were at final mineralizing phase. Density of fluid inclusions ranged from 0.7 to 0.95g/cm3. Calculated pressures and paleo-depths of mineralisation ranged from 14 to 130 bar and from 0.6 to 0.8 km.

Microthermometric evidence for the formation of Permian VHMS deposits in Tasik Chini area, Central Belt of Peninsular Malaysia

The VHMS deposits of Tasik Chini area are located in the Pahang State of Central Belt, Peninsular Malaysia. The deposits occur in a package of Permian volcanics within mixed volcano-sedimentary sequence, and have been exploited from the Bukit Botol and Bukit Ketaya deposits. They have many similarities with Kuroko-style massive sulfide deposits. The host rocks at both deposits are felsic volcanic rocks of rhyolitic to rhyodacitic composition. Mineralization occurs as distinct ore zonation forming a stringer to massive sulfide zone at the footwall followed by barite lenses and exhalite layers (Fe + Mn ± Si ore) at the stratigraphic top. The sulfide phases are characterized by pyrite as the major sulfide mineral, with subordinate chalcopyrite, sphalerite and rare galena; traces of gold, silver- and Sn-bearing minerals occur in the massive sulfide and barite ores. Primary fluid inclusions within quartz and barite occur as two types: (1) type I: two phase, liquid-vapour inclusions without daughter minerals, and (2) type II: three phase, liquid CO2-bearing carbonic inclusions. These three phase inclusions include liquid H2O, liquid CO2 and vapour CO2, with variable CO2 content, and often decrepitate before complete homogenization. Microthermometric measurements of the type I inclusions show that the temperature of homogenization (Th) varies between 180 °C and 310 °C with salinities ranging from 1.0 to 15.0 wt% NaCl equivalent in the quartz samples. Homogenization temperatures (Th) of 190 °C to 300 °C and salinities between 1.0 and 13.0 wt% NaCl equivalent are recorded from the barite samples. Type II inclusions have an initial melting temperature range of −57.1 °C to −57.5 °C, clathrate melting temperature (Tmclathrate) of 7.4 °C to 8.0 °C and CO2 homogenization temperature (ThCO2) between 30.1 °C and 30.3 °C, and salinity ranging from 4.0 to 5.1 wt% NaCl equivalent. Densities, pressure and depth of ore forming fluids range from 0.711 to 0.970 g/cm3, 12 to 93 bars, and ∼1500 m depth of seawater. Laser Raman spectroscopic analysis shows the presence of CO2 in the carbonic inclusions. The fluid inclusion results suggest that the main ore fluid during the formation of the Tasik Chini VHMS deposit is a seawater-dominated fluid, but contribution from a modified seawater or possibly magmatic origin is also indicated by higher salinities relative to seawater (3.2 wt% NaCl) and the presence of CO2. Taking into account the regional geodynamic evolution, it is also concluded that the formation of VHMS deposits in the Tasik Chini area occurred in a back-arc geotectonic setting.

Alteration mineralogy, fluid inclusions and stable isotope studies from Chigargunta and Bisanatham gold deposits, South Kolar Greenstone Belt, Dharwar Craton, India: Implications on genesis of gold mineralization

There are many Neoarchaean orogenic gold hosting greenstone belts in the Dharwar Craton (DC), India; among them the southern extension of the Kolar greenstone belt (SKGB) contain promising gold deposits such as Chigargunta and Bisanatham. Auriferous laminated quartz-calcite veins are hosted mainly within the sheared and altered Champion gneiss and amphibolite in Chigargunta and Bisanatham respectively. The hydrothermal alteration mineral assemblages show three main alteration zones at Chigargunta. However, only two alteration zones were identified at Bisanatham. The hydrothermal mineral assemblage at Chigargunta and Bisanatham indicate a similar mineralogy that consists of tourmaline, muscovite, biotite, chlorite, epidote, sericite, calcite and quartz along with sulfide and gold. Sulfides associated with ore are predominantly pyrrhotite, pyrite, arsenopyrite, chalcopyrite, ±molybdenite in both the places. Native gold is mainly associated with pyrrhotite in the inner and proximal zone of both the deposits. Fluid inclusion petrography and microthermometry from quartz-calcite veins within the mineralized zone at Chigargunta reveal a low to medium salinity (0.5 to 13.3 wt% NaCl equiv.) H2O-NaCl-CO2-CH4 ± N2 bearing fluid. However, at Bisanatham only H2O-NaCl fluid with low salinity (1.56 to 6.44 wt% NaCl equiv.) was observed. P-T conditions of the gold mineralization at the Chigargunta and Bisanatham deposits range between 1.7 and 3.5 kbar pressure/285 °C to 378 °C temperature and 0.8 to 1.2 kbar pressure/365 °C to 405 °C temperature respectively. Alteration mineralogy, ore mineral assemblages, fluid compositions and P-T conditions from the SKGB confirm that the near neutral to slightly alkaline mineralizing fluid transported gold as Au(HS)2− complexes with low ƒO2 conditions. The observed drastic pressure and temperature fluctuation suggests that fault-valve mechanism/pressure cycling occurred at the time of gold precipitation.Carbon (δ13CCO2) isotopic composition of ore fluid deduced from calcite varies from −2.4 to +3.3‰ (average: −0.3‰) and −2.1 to +1.4‰ (average: −0. 8‰) for Chigargunta and Bisanatham respectively. Oxygen isotopic (δ18OH2O) values for both the deposits vary from +7.2 to +14.6‰ (average: +9.3) and +7.3 to +8.9‰ (average: +8.3‰) respectively. Ore-forming fluid could have possibly been derived from the decarbonation of marine carbonates during the metamorphic devolatilization of greenstones. The slight intra-deposit variation of the carbon isotopic value implies the Rayleigh fractionation with progressive consumption of the CO2 as a result of interaction between hydrothermal fluid and wall rock as well as immiscibility of CH4 and CO2 fluid. Ore fluid sulfur (δ34SH2S) isotopic composition, derived from δ34S values of sulfides, varies from −0.42 to +2.43‰ and +0.25 to +2.34‰ for Chigargunta and Bisanatham respectively. Both the sulfur and carbon isotopic values, from these deposits are comparable with other orogenic gold deposits in the DC and elsewhere in the world. Although carbon isotopic values possibly indicate the metamorphic fluid source, the sulfur isotopes signify average crustal sulfur composition that is from crustally derived/modified fluid. Based on the field-geological, mineralogical, fluid, and isotopic compositions, the possible fluid source could be from the metamorphic devolatilization process of the thick greenstone sequence in the SKGB. However, a magmatic source could be further tested with geochronological studies on intrusives in the area.

Genesis of the Xiaolonghe quartz vein type Sn deposit, SW China: Insights from cathodoluminescence textures and trace elements of quartz, fluid inclusions, and oxygen isotopes

Quartz textures revealed by scanning electron microscope cathodoluminescence (SEM–CL) images suggest that quartz in the Xiaolonghe Sn deposit formed in at least three fluid episodes. Quartz (Q1) in the pre-ore silicification zone has homogeneous texture, high CL intensity and high Ti content (19–53 ppm). Fluid inclusions hosted in Q1 are vapor-rich (V1-type) and homogenized as supercritical fluid at ∼570 °C. Quartz (Q2) in the syn-ore topaz-cassiterite-quartz veins has lower CL intensity and is characterized by euhedral growth zones with lower Ti content (1.3–12 ppm). Fluid inclusions hosted in Q2, topaz and cassiterite are liquid-rich fluid inclusions of moderate salinity (∼15 wt% NaCl equiv) (L1-type) which homogenized at ∼423 °C. The post-ore quartz (Q3) closely associated with sericitization of topaz generally crosscuts Q2, and has dark CL intensity and much lower Ti concentration (<1.5 ppm). In Q3, the vapor-rich (V2-type) fluid inclusions coexist with the halite-bearing (S-type) fluid inclusions, which homogenized at ∼269 °C, 0.05 kbars.The upper limits of T–P conditions of pre-ore and syn-ore stage are constrained by the intersection of NaCl–H2O fluid inclusion isochores and Ti-in-quartz isopleths, and the lower limits are based on microthermometry results of fluid inclusions. Combined with the δ18Ofluid value (8.3‰) of Q1, it indicates that the pre-ore supercritical fluid was directly exsolved from a granitic magma at T = 570–600 °C and P = 0.70–0.77 kbars, corresponding to a maximum depth of 2.8 km under lithostatic pressure. The syn-ore subcritical fluid (8.0‰ > δ18Ofluid > 6.3‰) mixed with some meteoric water was under 423–450 °C, 0.32–0.45 kbars. The transition from the pre-ore supercritical fluid to the syn-ore subcritical fluid indicates boiling condition (probably at 512 °C, 0.62 kbars), which was likely caused by hydraulic fracturing under high pressure. Both the fluid boiling and fluid mixing contribute to the cassiterite precipitation in Xiaolonghe Sn deposit. In the post-ore stage, the coexisting S-type and V2-type fluid inclusions in Q3 indicates a second fluid boiling at 269 °C, 0.05 kbars, which was probably caused by decompression due to rapid denudation of the overlain strata. The low salinity (5.5 wt% NaCl equiv) L2-type fluid inclusions hosted in fluorite homogenized at 199 °C and <0.02 kbars, indicating that fluorite veins probably formed in open fractures. The δ18Ofluid results from sericite (5.1–5.0‰), quartz (−1.3 to −2.0‰), and chlorite (−7.9‰) suggest that increasing meteoric water was involved after second fluid boiling.

Formation and evolution of snowball quartz phenocrysts in the Dongping porphyritic granite, Hebei Province, China: Insights from fluid inclusions, cathodoluminescence, trace elements, and crystal size distribution study

Quartz phenocrysts are common in many granites, volcanic rocks, metamorphic rocks and hydrothermal deposits. The Dongping porphyritic granite contains large amounts of rounded to sub-rounded quartz phenocrysts. Minerals in this porphyritic granite show weak but distinct orientation. Dense clusters of fluid inclusions and albite crystals exist in the quartz, showing snowball texture. Two types of snowball quartz are recognized: (1) large snowball quartz phenocrysts containing large albite grains distributed in the core and small albite grains distributed in the mantle, and (2) small snowball quartz crystals containing small albite grains. The granite is characterized by high SiO2 (7.15–73.44 wt%), K2O (4.70–5.10 wt%) and Na2O (4.93–5.21 wt%) contents, low CaO (0.41–0.71 wt%), MgO (0.03–0.05 wt%), Fe2O3 (0.87–0.94 wt%), TiO2 (0.02–0.03 wt%) and ΣREE (7.10–9.80 ppm) contents. The granite has similar mineral and chemical composition with the aplite in the area, and they were derived from the residual melt of the Shuiquangou magma that suffered assimilation fractional crystallization process. Fluid inclusions in the quartz phenocrysts have homogenization temperatures of 260–380 °C and salinities of 1.4–12.4 wt% NaCl equiv. for liquid + vapor type inclusions and 34.1–44.3 wt% NaCl equiv. for brine ones. The quartz phenocrysts exhibit homogeneous cathodoluminescence without growth bands or zoning. The trace element contents in the quartz phenocrysts are extremely low (Ti 3.4–5.1 ppm, Al 13–118 ppm, Li < 0.1 ppm, Ge < 0.5 ppm) compared to published data of igneous quartz, which may result from the crystallizing conditions of quartz and chemical compositions of the magma. Crystal size distributions (CSD) of albite in quartz show that the snowball quartz formed in two stages, whereby an increase in nucleation and growth rates resulted in the core-mantle texture of quartz phenocrysts. The co-existence of low-, high-salinity and melt inclusions indicates that the quartz phenocrysts crystallized rapidly in a fluid-enriched magma. Magmatic flow led to mineral rotation and resulted in the rounded and sub-rounded shapes of the quartz phenocrysts. Fluid exsolved from the magma raised nucleation and growth rates and resulted in the two types of snowball quartz.

Fluid inclusion and stable isotope constraints on ore genesis of the Zajkan epithermal base metal deposit, Tarom–Hashtjin metallogenic belt, NW Iran

In the Zajkan Pb–Zn–Cu (Au–Ag) deposit of the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran, mineralization occurs as quartz-base metal sulfide veins hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Four stages of ore formation are identified at Zajkan: (1) quartz-chalcopyrite-pyrite veins, (2) quartz-galena-sphalerite ± chalcopyrite ± pyrite veins and breccias, (3) quartz-hematite veins and breccias, and (4) barren quartz-carbonate veinlets. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, galena, and trace amounts of hematite; gangue minerals are mainly quartz, sericite, chlorite, and calcite. The main wall-rock alteration is silicification, and intermediate argillic, and propylitic alteration. The coexistence of different types of fluid inclusions (LV, VL, and V) in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping. Excluding the heterogeneously entrapped fluid inclusions, the microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 °C from fluids with salinities between 1.7 and 6.4 wt% NaCl equiv. The oxygen isotopic compositions (δ18Owater-VSMOW of +3.7 to +1.1‰) indicate that the ore-forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore-stages. Sulfur isotopic values of sulfide minerals vary over a narrow range from −5.0 to −0.9‰VCDT (averaging −2.2‰VCDT), suggesting that sulfur was derived from a homogeneous magmatic source. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Zajkan. Our data suggest that the Zajkan deposit is an intermediate-sulfidation style epithermal mineralization. The estimated ore formation depth of Zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the THMB.