Two-phase Liquid-rich Fluid Inclusions Research Articles

Multi-stage magmatic fluid recharge and fluid mixing developed the Gongdongchong intermediate-sulfidation type epithermal Pb-Zn deposit, North Huaiyang, China: Constraints from petrography, fluid inclusion and in situ geochemistry studies of sphalerite

The Gongdongchong (GDC) lead and zinc deposit is located in the North Huaiyang (NHY) metallogenic belt, northern part of the Dabie orogen. Its Pb-Zn orebodies are predominately in the breccia pipe hosted by the Early Paleozic Foziling Group. Three stages of mineralization could be divided according to replacement relationships and petrography, and the ore and gangue mineral assemblages at the main base metal stage were recognized as combination of Fe-poor sphalerite + galena + pyrite + chalcopyrite + tetrahedrite with quartz and calcite. Three successive generations of sphalerite were distinguished through detailed petrographic observation on crystal-scale, namely Spc (core), Spm (mantle), and Spr (rim). Fluid inclusion petrography result shows that two-phase liquid-rich fluid inclusions are the dominant type in sphalerite. Microthermometric results show the homogenization temperatures and salinities of Spc ranged from 233 °C to 268 °C and 6.6 to 10.4 wt% NaCl equiv. While fluid inclusions in the Spm display homogenization temperatures of 241 °C to 284 °C, with salinities of 8.7 to 11.3 wt% NaCl equiv. This increasing trend may imply a magmatic fluid recharging from core to mantle. However, fluid inclusions in the Spr have homogenization temperatures of 231–254 °C, with salinities of 6.3–9.1 wt% NaCl equiv. A trend of mixing with meteoric water is manifested by the decrease of temperatures with decreasing salinities from mantle to rim. It suggests the combination of the magmatic fluid recharging and mixing of meteoric water should be the key mechanism responsible for the sphalerite precipitation at the GDC deposit. Meanwhile, the GDC deposit shows a similar range of homogenization temperatures and salinities with typical intermediate-sulfidation epithermal deposits, and these homogenization temperatures also correspond well with the geological thermometer results acquired by trace element concentrations of sphalerite. In addition, the sphalerite geochemical results obtained from trace elements as Mn, Co, In and Ge illustrate that the GDC Pb-Zn deposit shares a good consistence with epithermal Pb-Zn deposit.Based on the evidences presented above, combined with the geological and geochemical features, the GDC deposit can be classified as an intermediate-sulfidation epithermal deposit. Intermediate-sulfidation epithermal deposits usually share spatial and genetic relationships with porphyry deposits. This may provide new implication for the mineral exploration of porphyry deposits at depth in the NHY metallogenic belt.

Sulfide melts in ore deposits from low-grade metamorphic settings: Insights from fluid and Tl-rich sulfosalt microinclusions from the Monte Arsiccio mine (Apuan Alps, Tuscany, Italy)

Sulfide melting is increasingly recognized as an efficient ore remobilization process in several ore bodies deformed and metamorphosed under amphibolite to granulite facies conditions. Actually, sulfide melts may also occur at lower metamorphic conditions, provided the abundance of the so-called Low-Melting point Chalcophile Elements (LMCE). The Monte Arsiccio ore body (Apuan Alps, northern Tuscany, Italy) is strongly enriched in several LMCE, i.e., Ag, As, Hg, Pb, Sb, and Tl, and experienced greenschist facies metamorphism (T = 350–450 °C; P = 0.3–0.4 GPa) during the Alpine orogeny. Trails of polyphase sulfosalt inclusions (up to five phases), coexisting with fluid inclusions, were observed within quartz and baryte crystals found in late-stage veins. Sulfosalt assemblages are formed by LMCE-rich phases, the main being ferdowsiite, Ag8As3Sb5S16, chabournéite, Tl2Pb(Sb,As)10S17, and intermediate members of the arsiccioite/routhierite isotypic pair, (Ag1−xCux)Hg2TlAs2S6, along with minor realgar. Sulfosalt inclusions range between 200 nm and more than 100 µm in size, whereas larger inclusions, likely formed through the coalescence of smaller melt droplets, are up to 500 µm. Sulfosalt inclusions are associated with primary two-phase liquid-rich fluid inclusions (Type 1a), containing CO2 and N2, as revealed by microthermometric investigations and micro-Raman spectroscopy. Secondary two-phase liquid-rich fluid inclusions (Type 1b) were also identified. Microthermometric measurements carried out on Type 1a fluid inclusions gave homogenization temperatures (Th) in the range 265–296 °C, whereas Type 1b fluid inclusions showed lower Th, between 222 and 246 °C. As microthermometric heating experiments on sulfosalt inclusions revealed homogenization temperatures around 270 °C, it is very likely that sulfosalt inclusions were in the liquid state during their entrapment, in agreement with many Tl-bearing systems. These results are fully consistent with the occurrence of LMCE-rich sulfide melt during the formation of the sulfosalt assemblages observed at the Monte Arsiccio mine. In addition, the polyphase nature of most of the observed sulfosalt inclusions may be related to the unquenchable nature of sulfide melts. The formation of LMCE-rich sulfosalt assemblages could be related to the release of these elements from pyrite during its metamorphic recrystallization. Consequently, pyrite ores may produce sulfide melts, with potential implications in the change of speciation of LMCE, from trace to major elements.

Fluid inclusions, H-O, S, Pb, and noble gas isotope studies of the Baiyun gold deposit in the Qingchengzi orefield, NE China

The Baiyun gold deposit is located in the Qingchengzi orefield, NE China. The gold mineralization occurs mainly as auriferous quartz veins and auriferous altered rock. Wall-rock alteration includes silicification and potassic alteration along with minor sericitization, carbonatization, and chloritization. Three stages of mineralization are recognized: an early quartz and coarse-grained pyrite stage (Stage I), a middle quartz–gold and fine-grained pyrite–polymetallic sulfide stage (Stage II), and a late quartz–carbonate stage (Stage III). Four types of inclusions are recognized in the quartz veins: two-phase liquid-rich fluid inclusions (Type I), CO2 three-phase aqueous fluid inclusions (Type II), two-phase vapor-rich fluid inclusions (Type III), and pure liquid fluid inclusions (Type IV). The early stage quartz contains Type I–III fluid inclusions that yield low–medium homogenization temperatures (162 °C–350 °C), low salinities (1.57–10.33 wt% NaClequiv.), and belong to a NaCl–H2O–CH4–CO2 ± H2S hydrothermal fluid system. The middle-stage quartz also contains Type I–III fluid inclusions that yield low–moderate homogenization temperatures (148 °C–290 °C), variable salinities (1.02–16.43 wt% NaClequiv.), and belong to a NaCl–H2O–CO2–H2S ± N2 system. The late-stage quartz contains Type I, II, and IV fluid inclusions that yield homogenization temperatures and salinities of 150 °C–183 °C and 6.30–13.29 wt% NaClequiv, respectively, and belong to a NaCl–H2O–CO2 ± N2 system. Therefore, the ore-forming fluids of the Baiyun gold deposit are generally characterized by low–moderate homogenization temperatures and low–medium salinities, and belong to a NaCl–H2O–CO2–H2S ± N2 system. The coexisting Type I and II inclusions of the early and middle stages have similar Th ranges but weakly contrasting salinities, indicating that fluid boiling occurred.The H-O isotopic values (δ18OH2O = −0.7‰ to 5.6‰; δD = −108.3‰ to −74.0‰) and composition of the fluids suggest that the ore-forming fluids consisted mainly of magmatic water with a small amount of meteoric water and metamorphic fluids. Fluid inclusions in hydrothermal pyrite yield 3He/4He ratios of 0.43–0.52 Ra and 40Ar/36Ar ratios of 4648.7–7685.9, indicating the mixing of fluids with mantle and crustal components, which were mainly crust-derived. The δ34SV-CDT values of pyrite are between −12.5‰ and 1.9‰ (average −5.0‰), while δ34SV-CDT values of wall-rocks are between 7.0‰ and 18.7‰ (average 12.6‰). The 206Pb/204Pb, 207Pb/204Pb, and 207Pb/204Pb values of the pyrites are 17.416–18.908, 15.511–15.714, and 35.541–40.032, respectively, indicating that the ore-forming metals may came from Triassic magma and Gaixian Formation. Based on geological, fluid inclusion, and isotopic data, as well as data from previous studies, we propose that the Baiyun gold deposit is a magmatic–hydrothermal ore deposit.

Characterization of fluid inclusions encaged in quartz veins of Parsoi Formation, central India

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 H 2 O-NaCl. The density distribution of fluid inclusions rich in liquid H 2 O 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.

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.

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.

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+.