Liquid-rich Fluid Inclusions Research Articles

The genesis of the Liancheng Cu–Mo deposit in the Lanping Basin of SW China: Constraints from geology, fluid inclusions, and Cu–S–H–O isotopes

Liancheng is an important Cu–Mo deposit hosted by red-beds in the Mesozoic to Cenozoic Lanping Basin located in the Sanjiang Tethyan Orogen of SW China. The deposit is fault controlled where it has been affected and enriched by four hydrothermal events indicated by four distinct sets of veins and their cross-cutting relationships.A detailed Cu–S–H–O isotopic study is reported here on the mineralization focusing on the source of the metals and fluid, and on the mineralizing processes. The first two hydrothermal events are characterised by CO2 and fluid-rich inclusions with homogenisation temperatures of 124–446 °C and salinities ranging from 0.4 to 24.6 wt% NaCl equiv. The next two hydrothermal events are characterised by liquid–rich fluid inclusions that homogenise at 145–256 °C, with salinities ranging from 1.4 to 22.9 wt% NaCl equiv. The H–O isotope values obtain from the fluid inclusions indicate that the first three hydrothermal events relate to mineralizing fluids derived from a metamorphic source, but the last event includes a mixed metamorphic and meteoric source. Chalcopyrite, tennantite, and bornite from the deposit have δ34S values between −11.5 and 3‰. The δ65Cu values for quartz-Cu sulfide mineralization associated with the second hydrothermal event range from −0.31 to 0.2‰, but carbonate-Cu sulfide mineralization associated with the third hydrothermal event ranges from −1.01 to −1.08‰. The combination of the Cu and S isotopic values and field observations indicate that the controlling factors include structures, the temperature of regional metamorphism, and the pH of the mineralizing fluid. The zation is, therefore, characteristic of an orogenic-type deposit.

Characterization of Fluid Inclusions Encaged in Quartz Veins of Parsoi Formation, Central India

ABSTRACT The study focuses on analysis of primary and secondary fluid inclusions present in quartz veins hosted in the phyllites to explore the stress and temperature conditions at the time of formation of metasediment sequences of the of Parsoi Formation, central India. The results reveal the two-phase liquid-rich fluid inclusions that indicate that the intrusions of quartz veins in phyllite may have taken place between the temperature from 168.8°C to 256.3°C with an average of 205.55°C from a magmatic moderately saline fluid (3.7 to 18.29 wt. % NaCl equiv.). The final ice-melting temperatures ranges from -14.6°C to -2.2°C which indicate that the aqueous fluids are mainly H2O-NaCl. The density distribution of fluid inclusions rich in liquid H2O only are unimodel and low in natures and appears to be entrapped between pressure 1.666 to 2.125 kbar at depth of 200m. The study supports epithermal nature of fluid inclusions. The characteristic of fluid inclusions along with lithological and structural peculiarities, nature of structural features may be helpful in exploring the future potential zone of gold mineralization in similar types of area.

Mineralogical, petrographic and fluid inclusion evidence for the link between boiling and epithermal Ag-Au mineralization in the La Luz area, Guanajuato Mining District, México

Theoretical, experimental and observation data provide strong evidence that boiling is the dominant depositional mechanism in many low to intermediate sulfidation epithermal precious metals deposits. Textural and petrographic features that are evidence for boiling in the epithermal environment include the presence of coexisting liquid-rich and vapor-rich fluid inclusions, assemblages consisting of only vapor-rich fluid inclusions, colloform quartz, adularia and bladed calcite. We have examined 213 samples collected from surface outcrops, underground workings and drill cores from the central part of the La Luz vein system in the Guanajuato mining district, Mexico. In each sample, the various features that are evidence of boiling have been recorded. These observations have been quantified using a Boiling Confidence Factor that provides a means of scoring and rating each sample or area relative to the likelihood that boiling occurred.Homogenization temperatures of liquid-rich fluid inclusions within assemblages of coexisting liquid-rich and vapor-rich fluid inclusions have been measured to estimate the depth of trapping of the inclusions, and these data have been used to estimate the depth to the 300°C isotherm along the La Luz vein system.Fluid inclusions and mineral textural features show strong evidence of boiling in the deepest levels sampled in the La Luz system. This observation suggests that the bottom of the boiling zone is at some depth beneath the deepest levels explored and opens the potential for additional resources at depth.

The Nadun Cu–Au mineralization, central Tibet: Root of a high sulfidation epithermal deposit

A new high sulfidation epithermal Cu–Au occurrence (Nadun) has been discovered adjacent to the Cretaceous Duolong porphyry Cu–Au deposit within the Bangong–Nujiang metallogenic belt, central Tibet. The Nadun Cu–Au mineralization is hosted in a tectonic–hydrothermal breccia with advanced argillic alteration, which occurs above sandstone, associated with quartz–pyrite veins. The granodiorite porphyry with strong argillic alteration yields a zircon U–Pb age of 119.1±1.3Ma, whereas the weakly argillic granodiorite porphyry intruded into the breccia has a younger age of 116.1±1.3 Ma. This indicates that Cu–Au epithermal mineralization likely occurred between ~116Ma and ~119Ma, consistent with the duration of magmatic–hydrothermal activity at Duolong (~115–118 Ma), and providing evidence that Nadun and Duolong were formed during the same event. Moreover, the Nadun and Duolong porphyries have similar Hf isotopic compositions (εHf(t) values ranging from −8.8 to 8.1; mean=5.0±1.1, n=32), likely indicating that the deposits are comagmatic. In addition, boiling assemblages in vapor-rich inclusions coexisting with brines occur in early stage quartz–pyrite veins, and likely record phase separation at a temperature of > 550–300 °C and pressure of 700–110 bars. Most liquid-rich fluid inclusions formed at the breccia stage show similar salinity (1.7–19.3 wt.% NaCl equiv) to vapor-rich inclusions from the underlying quartz–pyrite veins, likely indicating vapor contraction during cooling at elevated presssure. This suggests that quartz–pyrite veins may act as conduits for ore-forming fluid traveling from the porphyry to the epithermal hydrothermal system. O and H isotopic compositions (δ18Ofluid=0.42–9.71‰ and δD=−102 to −66‰) suggest that ore-forming fluids are dominantly from a magmatic source with a minor addition of meteoric water at a later stage. The S and Fe isotope compositions of sulfides (δ34S=−5.9 to 0.5‰ and δ57Fe=−2.15 to 0.17‰) decrease from the quartz–pyrite vein to breccia ore, indicating that ore-forming fluids gradually become SO42-enriched and relatively oxidized. This body of evidence suggests that the Nadun Cu–Au mineralization may represent the root of a high sulfidation epithermal deposit.

Origin and evolution of hydrothermal fluids in epithermal Pb-Zn-Cu ± Au ± Ag deposits at Koru and Tesbihdere mining districts, Çanakkale, Biga Peninsula, NW Turkey

The Koru and Tesbihdere mining districts in Biga Peninsula, Northwestern Turkey, consist of twelve deposits covering approximately 12km2. The epithermal Au-Ag enriched base metal veins and associated low-grade breccia and stockwork at Koru and Tesbihdere are hosted by Oligocene subaerial and calc-alkaline volcanic rocks including basaltic andesite lavas, dacitic lava-tuffs, rhyolitic lava-domes and tuffs. NW- to N-trending strike-slip faults and E- and NE-trending faults constitute the most important ore-controlling structures in the Koru and Tesbihdere districts respectively. In the Koru mining district, galena is the dominant ore mineral in barite-quartz veins containing sphalerite, chalcopyrite, pyrite, bornite, enargite and tennantite. According to base metal content, the Tesbihdere mining district can be subdivided into sphalerite-galena dominated Tesbihdere mineralization and chalcopyrite-pyrite dominated Bakır and Kuyu Zones mineralization. Gold is present in small quantities with maximum 3.14g/t Au values either as free grains in quartz or as micro inclusions in pyrite and galena. The most widespread silver minerals are polybasite, pearceite, argentite and native silver which commonly occur as replacements of galena, sphalerite and pyrite, and other sulfides, or as fillings of microfractures in sulfides and quartz.Microthermometric measurements of primary liquid-rich fluid inclusions in sphalerite, barite and quartz in Koru indicate that the veins were formed at temperatures between 407 and 146°C from fluids with salinities between 0.7 and 12.5wt.% equiv. NaCl. Barite from the Tahtalıkuyu, Kuyutaşı and 5th Viraj mineralization show the highest homogenization temperatures. Fluid inclusion data for ore-stage quartz and sphalerite from the Tesbihdere mining district, indicate that these minerals were deposited at temperatures between 387 and 232°C from more diluted fluids with moderate salinities between 0.2 and 10.6wt.% NaCl equiv. Tahtalıkuyu and 5th Viraj mineralization show only boiling trends while Kuyutaşı, Tesbihdere, Bakır and Kuyu Zones mineralization show both boiling and isothermal mixing trends. The O and H isotope compositions of ore fluids from the Tahtalıkuyu (δ18O=−1.40 to 0.25‰; δD=−72.49 to −52.68‰) and Kuyutaşı (δ18O=−2.29 to 3.59‰; δD=−90.70 to −70.93‰) mineralization indicate that there was a major contribution from a magmatic component to ore genesis. Based on 9 quartz samples associated with orebodies at the Tesbihdere mining district, the relatively higher δ18O and lower δD isotope compositions from hydrothermal fluids could be attributed to a relatively dilute fluid derived by the mixing with meteoric water. The Pb isotope compositions also reveal that most of the lead in both mining districts is derived from the Oligocene-Miocene magmatic rocks, possibly with smaller contributions from the Eocene magmatic rocks.

Fluid inclusion and H–O–S–Pb isotopic evidence for the Dongxiang Manto-type copper deposit, South China

The Dongxiang copper deposit is located in northeastern Jiangxi Province, South China. Ore bodies in the Zishan Formation of this province are primarily stratoid and lentiform and show a close spatial association with Jurassic intrusive rocks. The current debates generally concentrate on whether the Dongxiang copper deposit is a Carboniferous sedimentary deposit or, alternatively, a Jurassic porphyry–skarn deposit. Three stages of mineralization can be observed in this deposit: the pre-ore, main ore, and post-ore stages. The massive sulfide ore bodies are identified as the main ore stage, whereas the pyrite-quartz veins and barren quartz veins are identified as pre-ore and post-ore stages, respectively. Three fluid inclusion types were recognized: two-phase vapor-rich fluid inclusions (type 1), two-phase liquid-rich fluid inclusions (type 2), and halite-bearing fluid inclusions (type 3). All three of these types of inclusions are present in the main copper mineralization stage, but only type 2 inclusions occur in both the pre-ore and post-ore stages. Type 2 inclusions in the pre-ore stage display homogenization temperatures (Th) of 349–392°C, with salinities of 1.4–8.1wt.% NaCl equivalent. In the main ore stage, types 1 and 3 inclusions show similar Th at 289–346°C and 273–348°C but contrasting salinities of 0.4–4.5 and 29.4–41.9wt.% NaCl equivalent, respectively. In the post-ore stage, type 2 inclusions have Th of 144–228°C and salinities of 0.4–6.0wt.% NaCl equivalent. The coexisting types 1 and 3 inclusions in the main ore stage have similar Th ranges but contrasting salinities, which indicates that fluid boiling occurred. The determined hydrogen and oxygen isotopic values for these fluids (δD from −42‰ to −69‰; δ18OH2O 5.04‰ to 9.01‰), based on analysis of fluid inclusions and host quartz, imply that the inferred ore fluids were principally derived from magmatic water. The lead isotopic compositions of sulfides from the ores and plagioclases from the adjacent porphyry indicate that they share a common origin. The sulfides from the ores show δ34S values of 0.3–3.2‰, also suggests a magmatic source. As the fluid inclusions and isotopic compositions strongly suggest a magmatic origin, this argues against a SEDEX origin for this deposit. In addition, the presence of stratoid and lentiform ore bodies and the absence of skarn alteration minerals suggest that the Dongxiang copper deposit is best described as a Manto-type rather than a porphyry–skarn deposit.

Fluid inclusion and stable isotope study of the Khalyfehlou copper deposit, Southeast Zanjan, Iran

The Khalyfehlou deposit is one of volcanic-hosted vein-type Cu deposits located in the Tarom metallogenic zone, NW Iran. The host rocks are part of an Eocene volcano-sedimentary sequence formed into a NE–SW trending anticline with the Khalyfehlou deposit in its axis. The main ore minerals are chalcopyrite, bornite, chalcocite, and covellite and the gangue minerals are quartz, sericite, and calcite. This paper attempts to identify the source of the mineralizing fluids by using sulfur and oxygen isotope data and fluid inclusion studies. Two-phase liquid-rich fluid inclusions in the quartz gangue associated with the sulfide veins were studied and interpreted. Homogenization temperatures for these inclusions range from 159 to 293 °C and salinities are between 14 and 19.3 wt% NaCl equivalent. The sulfur isotope values for the chalcopyrite range from −2.0 to −5.3 ‰. Negative sulfur isotopes values and the occurrence of framboidal pyrite in the tuffaceous sandstone host rocks suggest a sedimentary origin for the sulfur. The oxygen isotope composition of quartz from the veins ranges from 12.3 to 14.3 ‰. The δ18Ofluid values calculated from the oxygen isotope data and the mean value of the homogenization temperatures range from 0.6 to 3.6 ‰. The constant fluid salinities at the whole range of temperature values and the H–O isotopic characteristics indicate that the ore-forming fluid for the Khalyfehlou deposit was relatively high salinity recirculating Ca–Na-rich meteoric-formational water. This study suggests that mineralization at the Khalyfehlou deposit is similar to cordilleran vein-type deposits. As such and based on the fluid inclusion data and other geological data, the cordilleran-type Khalyfehlou deposit would have been emplaced by a mesothermal system.

Genesis and Magmatic-Hydrothermal Evolution of the Yangla Skarn Cu Deposit, Southwest China

The Yangla skarn Cu deposit (150 Mt at 1.03% Cu) is located in the central segment of the Jinshajiang metallogenic belt within the Sanjiang (Three Rivers) region, southwest China. Skarn orebodies are mainly developed between different units of Devonian carbonate and quartz sandstone rocks with stratiform-like shapes, or within the contact zone between granitoids and marbles. Re-Os dating of molybdenite intergrowth with chalcopyrite yielded a well-constrained 187Re-187Os isochron age of 232.0 ± 1.5 Ma with a weighted average age of 231.8 ± 1.3 Ma, both coeval with the related intrusions (233.1 ± 1.4 and 231.0 ± 1.6 Ma at 2 σ by zircon U-Pb dating) from our previously published work. Field and textural relationships indicate three hydrothermal stages characterized by assemblages of prograde skarn (pre-ore stage), retrograde skarn and Cu-Fe-Mo-Bi sulfides (main ore stage), and Pb-Zn sulfides associated with calcite and quartz (late ore stage), as well as one supergene stage marked by secondary Cu mineralization (malachite and azurite). Skarns contain garnets with andraditic compositions (Ad96 Gr2~3Py0~1) and clinopyroxene (two series: Hd6Di94 and Hd86Di13Jo1) with low Mn/Fe ratios (<0.1), typical of Cu skarn deposits worldwide. Three stages of fluid evolution were observed by a detailed fluid inclusion study: (1) Early fluids were trapped under two-phase conditions, as evidenced by the coexistence of brine (homogenization temperatures = 560°–600°C, average salinity = 49.4 ± 1.7 wt % NaCl equiv, n = 33) and vapor-rich inclusions in pre-ore stage andradite and diopside (trapped at ~600 bars, or a depth of approximately 2 km assuming lithostatic pressure conditions). (2) Main ore stage fluid inclusions in quartz were also trapped under two-phase conditions (boiling), as identified by the coexistence of vapor- and liquid-rich fluid inclusions; liquid-rich inclusions homogenized between 312° and 389°C (average = 350° ± 24.7°C, n = 20), with salinities of 2.4 to 5.6 wt % NaCl equiv (average = 4.2 ± 0.9 wt % NaCl equiv, n = 13) and a depth of ~2 km (~200 bars, hydrostatic pressure conditions). (3) Late ore stage fluids are represented by inclusions in calcite, characterized by homogenization temperatures ranging from 220° to 290°C (average = 249° ± 27°C, n = 14) and salinities between 2.1 and 8.0 wt % NaCl equiv (average = 4.6 ± 1.5 wt % NaCl equiv, n = 11). Sulfur isotope compositions of sulfide minerals (pyrite, chalcopyrite, pyrrhotite, and molybdenite) from the main and late ore stage have a narrow range of δ 34S values from −1.9 to 2.6‰, consistent with a magmatic origin. Calcite in the late ore stage has δ 13C values ranging from −3.2 to −5.9‰ and δ 18O from 7.2 to 18.0‰, distinct from the host-rock marble compositions ( δ 13C = 1.2–4.3‰, δ 18O = 10.8–23.9‰). When corrected for temperature (250°C, estimated from fluid inclusion analysis in calcites), these calcite data correspond to ore fluid δ 13Cfluid values of −2.0 to −4.6‰ and δ 18Ofluid values of 0.5 to 11.2‰ (clustering at ~10‰), which are consistent with a magmatic origin. Lead isotope compositions of sulfides (206Pb/204Pb = 18.273–18.369, 207Pb/204Pb = 15.627–15.677, and 208Pb/204Pb = 38.445–39.611) are similar to those of the granitic intrusions and sedimentary wall rocks, but distinct from those of basalts (206Pb/204Pb = 18.282–19.133, 207Pb/204Pb = 15.564–15.665, and 208Pb/204Pb = 38.367–38.942) in the mining area. Taken together, these geologic, geochemical, and isotopic data confirm that Yangla is a typical Cu skarn deposit.

Fluid inclusion and mineralization of Dafulou tin deposit in Dachang metal district, Guangxi, south China

Based on the study of the petrology, mineralogy, structural geology and fluid inclusion of the Dafulou ore deposit in the Dachang ore field, the ore deposit geology and ore-forming fluids were analyzed. It shows that there are five main hydrothermal alteration types in the Dafulou ore district, namely the silicification, carbonate, sericite, pyrite and pyrrhotite. The mineralization types are composed of the stratiform type, interlayer type and stockwork type. The ore textures present as metasomatic texture, euhedral-subhedral granular texture and solid solution texture. The ore structure consists of massive structure, dissemination structure, fine veined structure, stockwork structure and brecciated structure. Four ore types are recognized, namely the disseminated ore, dense massive ore, veinlet ore and brecciated ore. Six types of fluid inclusions are determined, i.e. the single-phase gaseous fluid inclusions, single-phase salt solution fluid inclusions, two-phase vapour-rich fluid inclusions, two-phase liquid-rich fluid inclusions, three-phase CO2-rich fluid inclusions and solid(s)-bearing fluid inclusions, all of which form in three dominant temperature scopes, 120–150, 230–270, 350–460 °C. But, the majority of them form in the high temperature environment (350–460 °C). The tectonism plays an important role in the mineralization, which usually controls the scale, occurrence and shape of the Sn orebody. There are four types of hydrothermal fluid systems, H2O-NaCl-CaCl2, H2O-CaCl2, H2O-NaCl-MgCl2 and H2O-MgCl2. Similar to the other ore deposits in the Dachang ore field, there also exists the multiple source of ore-forming fluids. Overall, the Dafulou ore deposit should be the result of the crust-mantle interaction.

Constraints on the ore fluids in the Chah Zard breccia-hosted epithermal Au–Ag deposit, Iran: Fluid inclusions and stable isotope studies

The Chah Zard gold–silver deposit, in the central part of the Urumieh-Dokhtar Magmatic Arc (UDMA) of Iran, is a breccia-hosted low- to intermediate-sulfidation epithermal deposit with a resource of ~2.5Mt averaging 1.7g/t Au and 12.7g/t Ag. Gold and silver mineralization occurs in breccia and veins associated with a 6.2±0.2Ma volcanic complex. Microthermometric measurements on quartz- and sphalerite-hosted, two-phase liquid-rich fluid inclusions indicate that the mineralization may have taken place between 260 and 345°C, from a moderately saline hydrothermal fluid (8.4–13.7wt.% NaCl equiv.). First ice-melting temperatures between −37 and −53°C indicate that the aqueous fluids contained NaCl, CaCl2±MgCl2±FeCl2. Coexisting liquid-rich and vapor-rich fluid inclusions in quartz and sphalerite provide evidence for boiling in ore-stage breccia and veins. Additionally, the occurrence of adularia and bladed calcite in high-grade ore zones and the presence of hydrothermal breccias and chalcedonic quartz are consistent with boiling. Calculated δ18O values of water in equilibrium with quartz (+3.4 to +13.1‰) suggest that the fluid may have had a magmatic source, but was 18O-depleted by mixing with meteoric water. The average calculated δ34SH2S values are −0.2‰ for pyrite, +0.2‰ for chalcopyrite, −1.0‰ for sphalerite and −0.2‰ for galena. The δ34SH2S values are consistent with a magmatic source for sulfur. Gold deposition at Chah Zard is inferred to have been largely caused by boiling, although fluid mixing and/or wall rock reactions may also have occurred. After rising to a depth of between 970 and 440m, the fluid boiled, causing deposition of fine-grained quartz, and sealing of the hydrothermal conduit. Episodic boiling in response to alternating silica sealing and hydraulic brecciation was responsible for ore deposition. Gold and silver may have precipitated due to the destabilization of HS− complexes, caused by the boiling-off of H2S to vapor, whereas the dilution and/or cooling of hydrothermal fluids led to the precipitation of base metals.

Hydrothermal fluid evolution and ore genesis in the Arghash epithermal gold prospect, northeastern Iran

The Arghash epithermal gold prospect is located in the Sabzevar zone near the northern margin of the Central Iranian Microcontinent. The prospect includes six gold vein systems, hosted mostly by Lower-Middle Eocene intermediate to felsic volcanic and intrusive rocks with chemical compositions characteristic of continental arc magmas. Wall rocks are variably altered to clay minerals and subordinate carbonates, chlorite, and epidote, with intense alteration confined within 1–5m of the veins. Mineralization consists of fracture fillings with local occurrences of hydrothermal breccias, and disseminations and veinlets in the immediate wall rocks. The veins consist of quartz, carbonates, minor sulfides, and gold. Pyrite is the main sulfide mineral in the hypogene ore in all vein systems except Au-VI where abundant stibnite occurs intergrown with quartz and minor pyrite; base metal sulfides are rare. Four generations of pyrite were identified: (1) disseminated euhedral to anhedral pyrite (Py-I), with up to 430ppm Au; (2) framboidal pyrite (Py-II) with concentric As-poor and As-rich bands and up to 960ppm Au; (3) arsenian pyrite overgrowths (Py-III) occurring on euhedral to anhedral Py-I grains, with up to 1980ppm Au; and (4) fracture-filling, late-stage pyrite (Py-IV) that is anhedral and barren.Homogenization and ice-melting temperatures of fluid inclusions vary from 186 to 306°C and −0.1 to −3.2°C in quartz, and from 169 to 287°C and 0.0 to 2.3°C in calcite, respectively. Laser combustion analyses indicate a narrow range of δ34S values for Pyrites I–III, between −5.8‰ and +0.1‰, consistent with a magmatic source for sulfur. Pyrite IV is highly enriched in 34S (δ34S=+8.9‰ to +23.7‰), and may reflect a contribution from a source enriched in 34S, such as evaporites. The δ34S values for two stibnite samples from the stibnite-rich vein (−18.8‰ and −14.4‰) sharply contrast with those of the pyrite, suggesting a different sulfur, and possibly metal source, or strong fractionation. The δ13C values for calcite are near 1‰, which is typical of marine carbonates. The calculated δ18O values for the hydrothermal fluid in equilibrium with quartz range from +5.5‰ to +7.1‰, and the calculated δD values of the fluid in equilibrium with illite range from −48‰ to −57‰.The fluid inclusion and stable isotope data suggest that the fluids experienced a complex history of prolonged water/rock interaction, boiling, and mixing. Evidence for boiling is shown by quartz pseudomorphs after bladed calcite and coexisting vapor-rich and liquid-rich fluid inclusions. Water/rock interaction is supported by the occurrence of sulfides and anomalous concentrations of gold in the altered wall rocks adjacent to veins. The alteration and ore mineralogy, textures, fluid inclusion data, and calculated fluid isotopic composition are more consistent with the described characteristics of low-sulfidation epithermal deposits.

Geochemical Characteristics of the Fluid Inclusion of the Dafulou Deposits in Guangxi, China

Abstract In this paper, the fluid inclusions study was performed on quartz, sphalerite and calcite from the Sn–polymetallic orebodies of the Dafulou deposit. On the basis of optical observations and microthermometric data, six types of fluid inclusions have been recognized, such as single-phase gaseous fluid inclusions, single-phase salt solution fluid inclusions, two-phase vapour-rich fluid inclusions, two-phase liquid-rich fluid inclusions, three-phase CO2-rich fluid inclusions, solid(s)-bearing fluid inclusions, etc. And it showed that water is the main component, for example the water content of quartz more than 1700 μg/g, ranges from 1717 to 2320 μg/g. The sphalerite has lower content than quartz, only 978 μg/g. The calcite has lowest water content, i.e. 242 μg/g and 324 μg/g respectively. The gas component of inclusions mainly consists of CO2 and H2O. The main cationic consists of Ca2+, secondly Mg2+, K+ and Na+, only little Li+ and NH4+.

Geological setting, alteration, and fluid inclusion characteristics of Zaglic and Safikhanloo epithermal gold prospects, NW Iran

Abstract The Zaglic and Safikhanloo epithermal gold prospects are located in the Arasbaran zone, to the west of the Cenozoic Alborz-Azarbaijan magmatic belt in NW Iran. Mineralization is mainly restricted to quartz and quartz -carbonate veins and veinlets. Pyrite is the main sulphide, associated with subordinate chalcopyrite and bornite. Gold occurs as microscopic and submicroscopic grains in quartz and pyrite. The country rocks are Tertiary intermediate–mafic volcanic and volcaniclastic rocks of andesite to trachy-andesite composition intruded by a composite granitic to syenitic pluton. They are medium- to high-K, calc-alkaline and alkaline rocks and display fractionated REE (rare earth element) patterns, with light rare earth elements (LREE) significantly enriched relative to the heavy rare elements (HREE). On primitive mantle normalized plots, they display depletions in Nb, Ti and P, and enrichments in Pb, which are common characteristics of arc-related magmas worldwide. Hydrothermal alteration minerals developed in the wall rocks include quartz, calcite, pyrite, kaolinite, montmorillonite, illite, chlorite, and epidote. Minor alunite occurs in Safikhanloo. Gold is locally enriched in the altered rocks immediate to the veins. The ore-stage quartz from both prospects is dominated by liquid-rich fluid inclusions; vapour-rich inclusions are rare. The homogenization temperature varies between 170–230 and 170–330 °C and salinity varies between 1.4 to 9.5 and &lt;1 to 6.7 wt% NaCl equivalent, for Safikhanloo and Zaglic, respectively. The occurrence of hydrothermal breccias, bladed calcite, adularia, and rare coexisting vapour- and liquid-dominant inclusions suggest that boiling occurred in the course of the evolution of the ore fluids. The large variations in Th and the salinity values can be explained by boiling and/or mixing. Lack of sulphate minerals in the veins suggests that sulphides and gold precipitated from a reduced, H 2 S-dominant fluid. Calculated δ 34 S values for the ore fluid vary between −4.6 and −9.3‰. Sulphur could have been derived directly from magmatic sources, or leached from the volcanic and plutonic country rocks. Ore formation in Zaglic and Safikhanloo occurred in response to mixing, boiling, and interactions with wall rocks. Considering the intermediate-argillic alteration, the low contents of base metal sulphides, and the overall low salinities, the Zaglic and Safikhanloo can be classified as low-sulphidation epithermal systems.

Fluid inclusion study of the Tangjiaping Mo deposit, Dabie Shan, Henan Province: implications for the nature of the porphyry systems of post-collisional tectonic settings

The Tangjiaping porphyry Mo deposit in Shangcheng County is located in the Dabie continental collisional orogenic belt. The hydrothermal alteration and mineralization processes can be divided into three stages: K-feldspar + quartz + pyrite + magnetite + molybdenite in the early stage, quartz + pyrite + molybdenite ± chalcopyrite in the middle stage, and quartz + carbonate ± pyrite veins or carbonate veinlets in the late stage. The middle stage involved important Mo mineralization. Four compositional populations of fluid inclusions (FIs) occur in hydrothermal quartz formed in the early and middle stages, namely: pure CO2, CO2–H2O, daughter mineral-bearing, and NaCl–H2O. The late-stage quartz-carbonate ± pyrite veinlets contain only NaCl–H2O FIs. Homogenization temperatures of the early-stage FIs are mainly above 375°C, with salinities up to 62.10 wt.% NaCl equiv. Haematite daughter minerals, which probably represent an oxidizing environment, together with halite, sylvite, and chalcopyrite, are present in the FIs of this stage. Most of the middle-stage FIs homogenized between 235 and 335°C, with fluid salinities ranging from 1.06 to 45.87 wt.% NaCl equiv. In middle-stage quartz, besides halite and sylvite daughter minerals, abundant chalcopyrite and jamesonite are also present, reflecting a reducing environment. The daughter mineral-bearing FIs coexist with vapour- and liquid-rich FIs with contrasting salinities, and they homogenized in divergent ways at similar temperatures. This feature strongly suggests that fluid boiling occurred during the middle stage, which is well accepted as an important mechanism for the precipitation of ore-forming materials. FIs in late-stage minerals totally homogenized in the range 115–195°C, with low salinities ranging from 1.91 to 9.98 wt.% NaCl equiv. Combined with the published H–O isotope data, we propose that the initial ore fluids were magmatic in origin and were characterized by high temperature, high salinity, high oxygen fugacity, high levels of metallic elements, and high levels of CO2. In the middle stage, the fluids boiled and resulted in CO2 release, oxygen fugacity decrease, and rapid precipitation of ore-forming materials. The late-stage fluids, characterized by low temperatures, low salinities, and low contents of CO2, might have been sourced from meteoric water. Daughter mineral-bearing CO2–H2O FIs, especially multiple species daughter mineral-bearing FIs, are regarded as indicators of porphyry ore systems generated in continental collisional settings. This understanding is validated by recent studies of other porphyry ore systems in Chinese collision orogens.

Geochronology and Geochemistry of the MAX Porphyry Mo Deposit and its Relationship to Pb-Zn-Ag Mineralization, Kootenay Arc, Southeastern British Columbia, Canada

The MAX porphyry Mo deposit is located at the northern end of the Kootenay arc in southeastern British Columbia, Canada. Molybdenum mineralization is genetically related to the variably altered Trout Lake granodiorite stock, which has lithogeochemical affinities to the low fluorine, calc-alkaline, granodiorite-hosted porphyry Mo deposit type. Three molybdenite samples from early and late Mo-bearing veins yield Re-Os dates that overlap within analytical error, with a weighted average age of 80.3 ± 0.2 Ma. These dates are in close agreement with two 206Pb/238U weighted average zircon ages for phases of the Trout Lake stock at 80.3 ± 1.6 and 79.2 ± 1.0 Ma, indicating that crystallization of the stock and hydrothermal molybdenite formation were coeval and likely cogenetic. 40Ar/39Ar plateau ages for primary biotite in igneous dikes, secondary biotite in early potassic alteration, and muscovite in late phyllic alteration range from 80 to 76 Ma. The younger 40Ar/39Ar plateau ages may reflect unusually slow cooling of the magmatic-hydrothermal system or a late thermal disturbance. Pb-Zn-Ag vein deposits are common throughout the Kootenay arc and several such veins are located within and proximal to the MAX porphyry Mo deposit. The presence of rare molybdenite associated with sphalerite and argentiferous galena in some of these Pb-Zn-Ag veins suggests that they represent a late-stage event related to the MAX magmatic-hydrothermal system. Fluid inclusions in quartz from Mo and Pb-Zn-Ag veins are similar and can be divided into two compositional groups: type 1, aqueous liquid-rich fluid inclusions; and type 2, aqueous-carbonic liquid-rich fluid inclusions. Pressure-corrected (1.4–1.7 kbar) trapping temperatures of typical type 1 inclusions from Mo-bearing veins range from 430° to 460°C, and for Pb-Zn-Ag veins, from 335° to 365°C. The ranges of salinity (0–12 wt % NaCl equiv) in fluid inclusions from both vein types are almost identical, and type 2 inclusions from both vein types contain similar amounts of CO2 (avg XCO2 = 0.08) with traces of CH4. The similarity of chemistry in the two vein types suggests a genetic link between porphyry Mo mineralization and adjacent Pb-Zn-Ag deposits. However, muscovite from the alteration halo around a Pb-Zn-Ag vein within the MAX deposit yielded a 40Ar/39Ar plateau age of 72.2 ± 0.5 Ma. This date is significantly younger than the ~80 Ma age of porphyry magmatism and Mo mineralization, suggesting either that this event is in fact unrelated to porphyry Mo mineralization at 80 Ma, or that the K-Ar isotope system has been disturbed by a later thermal event.

Epithermal gold mineralization at Wadi Abu Khushayba, southwestern Jordan

The Wadi Abu Khushayba area in southwestern Jordan hosts an auriferous, quartz-veined shear zone with features of an epithermal low-sulfidation gold system. The quartz-lode and quartz-carbonate mineralization is characterized by open-space textures, typically with sharp-walled veins and multi-stage brecciation of the late Neoproterozoic (~ 560 Ma) rhyolitic and granophyric host rocks. Silicic alteration by cryptocrystalline quartz is abundant; potassic alteration is expressed by muscovite and K-feldspar blastesis, commonly with dispersed hematite laths. Sulfide content is low. Relict pyrite and chalcopyrite occur in comb and cockade quartz. Gold occurs disseminated in the volcanic and subvolcanic wall rocks and as late vein infill. The coexistence of vapor-rich and liquid-rich fluid inclusions in quartz, quartz textures, and the presence of adularia and calcite in the vein mineralogy suggest boiling concomitant with gold deposition in a structural setting favoring high fluid flow. Fluid inclusions in quartz define a temperature range of 350–380 °C and low salinity (~ 1.5–7 wt.% NaC1 equiv.) for the ore system. Pressure is estimated at 200–250 bars, indicating a maximum paleo-depth of 2500 m (hydrostatic). It appears likely that the Wadi Abu Khushayba system represents the near-surface epithermal expression of a larger unexposed mesothermal system. Such mesothermal systems are typical elsewhere in the Arabian–Nubian Shield, but are not exposed in southwestern Jordan where the present-day erosional level is close to the unconformity of the transgressive Early Cambrian platform sedimentation.

The Qiyugou gold-bearing breccia pipes, Xiong'ershan region, central China: fluid-inclusion and stable-isotope evidence for an origin from magmatic fluids

Gold ores of the Qiyugou deposit in the eastern part of the Xiong'ershan region are hosted in breccia pipes within a Mesozoic granitic porphyry. Three stages of hydrothermal alteration activity are recognized within the Qiyugou breccias. The first stage of hydrothermal metasomatism produced extensive K-feldspar alteration. The second stage is associated with deposition of gold and base metal sulphides. The third stage is defined by fine quartz–calcite ± pyrite veinlets containing minor gold. Four types of fluid inclusions are present in quartz and calcite within the breccia matrix and veins. Type I are solid(s)-bearing high-salinity fluid inclusions, with homogenization temperatures up to 420°C and high salinities of 31–47 wt% NaCl equivalent. Type II are two-phase, vapour-rich fluid inclusions that homogenized between 265 and 476°C, with low to moderate salinities (7.2–19.8 wt% NaCl equivalent). Homogenization of Type III two-phase, liquid-rich fluid inclusions takes place at temperatures between 109 and 253°C, with salinities of 3.9–14.3 wt% NaCl equivalent. Type IV two/three-phase carbonic fluid inclusions are only found in calcite–quartz veins cutting wall rocks in the upper parts of the pipes or in adjacent country rocks, with homogenization temperatures that range from 239 to 315°C and salinities between 9.2 and 12.2 wt% NaCl equivalent. The coexistence of Types I and II in the middle parts of the breccia pipes suggests that these fluid inclusions either resulted from trapping of boiling fluids or represented immiscible fluids, most likely derived from a granitic magma. The fluid history, reflected in the fluid-inclusion characteristics, was complex, involving variable amounts of boiling, cooling and mixing in the breccia pipe system. values ( − 101.7 to − 60.1‰) and values (0.3–7.5‰) calculated from inclusion water in quartz on the basis of mean-to-maximum fluid inclusion homogenization temperatures are intermediate between magmatic water and surface-derived fluids (meteoric water). Ranges for δ34S values of ore sulphides ( − 3.0 to 0.8‰) suggest that sulphur originated directly from a magmatic (mantle) source or indirectly from leaching/desulphidation of primary magmatic sulphide minerals. The combined fluid-inclusion and stable-isotope data support previous proposals for a genetic relationship between the Qiyugou ores and magmatic fluids.

Migration of geothermal fluids in extensional terrains: the ore deposits of the Boccheggiano-Montieri area (southern Tuscany, Italy)

An integrated study based on fluid inclusion, δ18O composition and structural analyses was carried out on a Pliocene fossil hydrothermal system, located to the South of the present active Larderello geothermal field, in the Boccheggiano-Montieri area. The study area is typified by mineralized cataclastic levels related to Late Oligocene–Early Miocene thrust surfaces, and to the following two generations of normal faults of Miocene and Pliocene ages, respectively. Within the damage zone of the Pliocene Boccheggiano fault, the mineralization is mainly made up of quartz and pyrite. Quartz + Pb–Zn sulfides, or quartz + Pb–Zn sulfides + fluorite + carbonates assemblages occur instead in the older cataclastic levels. Two generations of liquid-rich fluid inclusions were recognized in quartz and fluorite: the first one, with homogenization temperatures ranging between 172 and 331°C and salinity between 0.0 and 8.8 wt.% NaClequiv., records the early stage of hydrothermal activity. The second generation of fluid inclusions documents a later stage, with homogenization temperature from 124 to 288°C and salinity from 0.2 to 1.9 wt.% NaClequiv.. Fluid inclusions analyses also indicate that mixing of fluid with distinct salinities and/or temperatures was a widespread process during the early stage, and that fluid temperatures decreased moving from the Boccheggiano fault toward the more distal and older cataclastic levels. The δ18O values of water in equilibrium with hydrothermal quartz, which range from −5.7 to −0.1‰, are related to the circulation of meteoric water mixed with saline water that leached the evaporite level and enriched in δ18O through water–rock interaction, and/or with magmatically derived fluids. Results indicate that the damage zone of the Pliocene Boccheggiano fault represented the main channel for the flow of meteoric water, which was heated at depth, then mixed with high salinity fluids, and finally ascend to infiltrate along the older cataclastic levels. Our results, based on fluid inclusions, oxygen isotopic compositions and structural analyses indicate that a single fluid flow path run through the damage zone of the Boccheggiano fault and the older cataclasites, which were thus hydraulically connected.

New thermochronologic constraints on the evolution of the Zaldívar porphyry copper deposit, Northern Chile

Life spans and thermal evolution of hydrothermal systems are of fundamental metallogenic importance. We were able to establish the chronology and cooling history of the Zaldivar porphyry copper deposit (Northern Chile) by applying a combination of different isotopic dating methods in minerals with different closure temperatures, including 40Ar/39Ar geochronology and zircon fission track thermochronology, together with fluid inclusion thermometry and previous published U–Pb zircon geochronology. The hydrothermal mineralization in the Zaldivar deposit is genetically related to the Llamo Porphyry unit. Samples of igneous biotites from this intrusion yielded 40Ar/39Ar plateau ages between 35.5 ± 0.7 and 37.7 ± 0.4 Ma defining a weighted average of 36.6 ± 0.5 Ma (2σ). In contrast, one sample from the Zaldivar porphyry, one from the andesites, and two from the Llamo porphyry yielded considerably younger fission track ages of approximately 29 Ma with a weighted mean for all ages of 29.1 ± 1.7 Ma (2σ). Thermal and compositional constraints for the hydrothermal system in the Zaldivar deposit from fluid inclusions thermometry show that at least three fluid types broadly characterize two main hydrothermal episodes during the evolution of the deposit. The main mineralization and alteration event is characterized by high temperature (above 320°C) hypersaline fluids (salinity between 30 and 56 wt.% NaCl equivalents) coexisting with low-density gas-rich inclusions (salinity less than 17 wt.% NaCl equivalents) that homogenizing into the gas phase at temperatures above 350°C. The second episode corresponds to a low-temperature event which is characterized by liquid-rich fluid inclusions that homogenize into the liquid phase at temperatures ranging from 200°C to 300°C with salinities lower than 10 wt.% NaCl equivalents. The 40Ar/39Ar data (36.6 ± 0.5 Ma, weighted average) obtained from igneous biotites represent the minimum age for the last high-temperature (above 300°C) hydrothermal pulse. When compared with previously published U–Pb ages (38.7 ± 1.3 Ma) in zircons from the Llamo porphyry, a close temporal relationship between crystallization of the parental intrusion and the thermal collapse of the last high-temperature hydrothermal event is evident. Cooling took place from approximately 800°C (crystallization of the intrusive complex defined by zircon U–Pb ages) to below 300 ± 50°C (biotite 40Ar/39Ar closure temperature) within approximately 1.5 m.y. Because the thermal annealing of fission tracks in zircons occurs at temperatures of 240 ± 30°, the zircon fission track (ZFT) ages of 29.1 ± 1.7 Ma (2σ) mark the end of the thermal activity in the Zaldivar area, specifically the time when the whole area cooled below this temperature, well after the collapse of the main hydrothermal event in the Zaldivar porphyry copper deposit. This cooling age roughly coincides with the age defined for the emplacement of dacitic dikes at 31 ± 2.8 Ma (2σ) (published K–Ar whole rock), 5 km south of the Zaldivar deposit, in the Escondida area. This late magmatic pulse probably is responsible for high heat flow in the Zaldivar deposit as late as 29 Ma. There is no evidence that the low temperature hydrothermal pulse recognized by fluid inclusion studies is related to this thermal event. The zircon fission track cooling ages are interpreted to be related to the time lag required for complete relaxation of the perturbation of the isotherms in the geothermal field imposed by the intrusion of magmatic bodies, with or without any association with low temperature hydrothermal activity.

Hydrothermal Evolution of the Miduk Porphyry Copper System, Kerman, Iran: A Fluid Inclusion Investigation

The Miduk porphyry copper deposit is located in SSE central Iran in the elongated NW-trending median mountain range of Kerman Province (85 km northwest of the Sar-Cheshmeh porphyry copper deposit). It is associated with Miocene quartz-diorite to quartz-monzonite which intruded Eocene volcanosedimentary rocks. Copper mineralization was accompanied by both potassic and phyllic alteration. Field observations and petrographic studies demonstrate that emplacement of the Miduk pluton took place in several intrusive pulses, each with associated hydrothermal activity. Four main vein groups have been identified: (I) quartz + K-feldspar ± anhydrite ± molybdenite (0.002%), with sporadic pyrite, chalcopyrite, and bornite; (II) quartz + chalcopyrite + pyrite ± sporadic bornite; (III) quartz + pyrite + calcite + chalcopyrite ± anhydrite; and (IV) quartz, and/or calcite, and/or gypsum ± pyrite. Early hydrothermal alteration produced a potassic assemblage (orthoclase-biotite) in the central part of the stock, and propylitic alteration in its periphery. Later phyllic alteration overprinted these alteration zones. Early hydrothermal fluids are represented by high-temperatures (380 to 550°C), high-salinity (up to 60 wt% NaCl equiv.) liquid-rich fluid inclusions, and hightemperature (320 to 550°C), low-salinity, vapor-rich inclusions. These fluids are interpreted as orthomagmatic fluid that boiled episodically; the brines evidently caused potassic alteration, and deposition of Group I and II quartz veins containing chalcopyrite and very rare molybdenite. Propylitic alteration is attributed to a liquid-rich, lower temperature (200 to 350°C), Ca-rich, evolved meteoric fluid. Influx of meteoric water into the central part of the system, and mixing with magmatic fluid produced salinities ranging from 1 to 20 wt% NaCl equivalent in Group II and III veins. Phyllic alteration and copper leaching resulted from the inflow of oxidized, acidic meteoric waters during cooling of the system. Late boiling occurred in the upper part of the phyllic zone, and was associated with significant copper deposition.