Trapping Pressures Research Articles

Geology, Fluid Inclusion, and H–O–S–Pb Isotope Constraints on the Mineralization of the Xiejiagou Gold Deposit in the Jiaodong Peninsula

The Xiejiagou deposit is a representative medium-sized gold deposit in Jiaodong the Peninsula, which contains gold reserves of 37.5 t. The orebodies are hosted in the Linglong biotite granite with a zircon LA-ICP-MS U–Pb age of 160.5±1.3 Ma (N=15, MSWD=1.2) and are characterized by disseminated- or stockwork-style ores. Mineralization and alteration are structurally controlled by the NE-striking fault. Three stages of mineralization were identified with the early stage being represented by (K-feldspar) sericite quartz pyrite, the middle stage by quartz gold polymetallic sulfide, and the late stage by quartz carbonate. Ore minerals and gold mainly occurred in the middle stage. Three types of primary fluid inclusions were distinguished in the Xiejiagou deposit, including carbonic-aqueous, pure carbonic, and aqueous inclusions. The primary fluid inclusions of the three stages were mainly homogenized at temperatures of 262–386°C, 192–347°C, and 137–231°C, with salinities of 2.22–8.82, 1.02–11.60, and 1.22–7.72 wt% NaCl equivalent, respectively. These data indicate that the initial ore-forming fluids were a medium temperature, CO2-rich, and low-salinity H2O–CO2–NaCl homogeneous system, and the ore-forming system evolved from a CO2-rich mesothermal fluid into a CO2-poor fluid. Considering the fluid inclusion characteristics, H–O–S–Pb isotopes, and regional geological events, the ore-forming fluid reservoir was likely metamorphic in origin. Trapping pressures of the first two hydrothermal stages estimated from the carbonic aqueous inclusion assemblages were ~224–302 MPa and ~191–258 MPa, respectively. This suggests that the gold mineralization of the Xiejiagou gold deposit occurred at a lithostatic depth of ~7.2–9.7 km. Au(HS)2− was the most probable gold-transporting complex at the Xiejiagou deposit. Precipitation of gold was caused by a CO2 effervescence of initial auriferous fluids.

Ore Genesis at the Jinchang Gold–Copper Deposit in Heilongjiang Province, Northeastern China: Evidence from Geology, Fluid Inclusions, and H–O–S Isotopes

The Jinchang gold–copper deposit is located in Eastern Heilongjiang Province, Northeastern China. The orebody comprises primarily hydrothermal breccias, quartz veins, and disseminated ores within granite, diorite, and granodiorite. Three paragenetic stages are identified: early quartz–pyrite–arsenopyrite (Stage 1), quartz–pyrite–chalcopyrite (Stage 2), and late quartz–pyrite–galena–sphalerite (Stage 3). Gold was deposited during all three stages and Stage 1 was the major gold-producing stage. Copper is associated with the mineralization but has low economic value. Fluid inclusions (FIs) within the deposit are liquid-rich aqueous, vapor-rich aqueous, and daughter-mineral-bearing types. Microthermometric data for the FIs reveal decreasing homogenization temperatures (Th) and salinities of the ore-forming fluids over time. The Th for Stages 1–3 of the mineralization are 421–479, 363–408, and 296–347 °C, respectively. Stage 1 fluids in vapor-rich and daughter-mineral-bearing inclusions have salinities of 5.7–8.7 and 49.8–54.4 wt% NaCl equivalent, respectively. Stage 2 fluids in vapor-rich, liquid-rich, and daughter-mineral-bearing inclusions have salinities of 1.2–5.4, 9.5–16.0, and 43.3–48.3 wt% NaCl, respectively. Stage 3 fluids in liquid-rich and daughter-mineral-bearing inclusions have salinities of 7.9–12.6 and 38.3–42.0 wt% NaCl equivalent, respectively. The estimated trapping pressures are 160–220 bar, corresponding to an entrapment depth of 1.6–1.2 km in the paleo-water table. Oxygen and hydrogen isotope data (δ18OV-SMOW = 8.6‰ to 11.4‰; δDV-SMOW = −92.2‰ to −72.1‰) suggest that the ore-forming fluids were derived from magmatic fluids during the early stages of mineralization and subsequently incorporated meteoric water during the late stages. The sulfide minerals have δ34SVCDT values of 0.2‰–3.5‰, suggesting that the sulfur has a magmatic origin. The Jinchang deposit is a typical gold-rich gold–copper porphyry deposit.

Cosmic-ray propagation in the bi-stable interstellar medium

Context. Cosmic rays propagate through the galactic scales down to the smaller scales at which stars form. Cosmic rays are close to energy equipartition with the other components of the interstellar medium and can provide a support against gravity if pressure gradients develop. Aims. We study the propagation of cosmic rays within the turbulent and magnetised bi-stable interstellar gas. The conditions necessary for cosmic-ray trapping and cosmic-ray pressure gradient development are investigated. Methods. We derived an analytical value of the critical diffusion coefficient for cosmic-ray trapping within a turbulent medium, which follows the observed scaling relations. We then presented a numerical study using 3D simulations of the evolution of a mixture of interstellar gas and cosmic rays, in which turbulence is driven at varying scales by stochastic forcing within a box of 40 pc. We explored a large parameter space in which the cosmic-ray diffusion coefficient, the magnetisation, the driving scale, and the amplitude of the turbulence forcing, as well as the initial cosmic-ray energy density, vary. Results. We identify a clear transition in the interstellar dynamics for cosmic-ray diffusion coefficients below a critical value deduced from observed scaling relations. This critical diffusion depends on the characteristic length scale L of Dcrit ≃ 3.1 × 1023 cm2 s−1(L/1 pc)q+1, where the exponent q relates the turbulent velocity dispersion σ to the length scale as σ ~ Lq. Hence, in our simulations this transition occurs around Dcrit ≃ 1024–1025 cm2 s−1. The transition is recovered in all cases of our parameter study and is in very good agreement with our simple analytical estimate. In the trapped cosmic-ray regime, the induced cosmic-ray pressure gradients can modify the gas flow and provide a support against the thermal instability development. We discuss possible mechanisms that can significantly reduce the cosmic-ray diffusion coefficients within the interstellar medium. Conclusions. Cosmic-ray pressure gradients can develop and modify the evolution of thermally bi-stable gas for diffusion coefficients D0 ≤ 1025 cm2 s−1 or in regions where the cosmic-ray pressure exceeds the thermal one by more than a factor of ten. This study provides the basis for further works including more realistic cosmic-ray diffusion coefficients, as well as local cosmic-ray sources.

Insights into the genesis of orogenic gold deposits from the Zhengchong gold field, northeastern Hunan Province, China

The Zhengchong gold deposit is located in the central Jiangnan Orogen Belt, where gold ore occurs mainly as quartz veins, altered slates, and minor breccias hosted by shear zones in the Lengjiaxi Group. Based on its vein crosscutting relationships, mineral assemblages, and paragenetic sequences, mineralization in this deposit is divided into four stages: Stage 1: quartz(Q1)–pyrite stage, Stage 2: quartz(Q2)–pyrite–arsenopyrite stage, Stage 3: quartz(Q3)–pyrite–polymetallic sulfide mineral stage, and Stage 4: quartz(Q4)–carbonate stage. Two types of fluid inclusions have been recognized in the quartz grains: CO2-bearing fluid inclusions (C-type) and aqueous fluid inclusions (W-type). Fluid inclusions in hydrothermal quartz yield homogeneous temperatures and salinities of 312–406 °C and 4.65–9.21 wt% NaClequiv (Stage 1), 252–324 °C and 2.20–8.10 wt% NaClequiv (Stage 2), 193–296 °C and 2.24–14.04 wt% NaClequiv (Stage 3), and 127–209 °C and 2.57–6.59 wt% NaClequiv (Stage 4). The co-occurrence of these inclusion types despite their variable fluid salinities can be explained by fluid boiling during Stages 2 and 3 of mineralization, possibly as a result of episodic pressure decreases linked to fault-valve activity. Laser Raman spectroscopic analysis results reveal that small quantities of CH4 and N2 are present in the Stage 2–3 fluid inclusions. Fluid inclusion data and microthermometric results show that the ore fluids were low-salinity and CO2-rich, yielding both CO2 inclusions (C-type) and aqueous inclusions (W-type). The trapping pressures estimated from the C-type inclusions are 80–180 MPa for Stages 2 and 3, yielding gold mineralization depths of ∼7–8 km. The mineralizing fluids had calculated δ18OH2O values ranging from +3.7‰ to +8.2‰ and δD values from −75.2‰ to −61.8‰, indicating derivation mainly from metamorphic fluids. The sulfide minerals yield δ34S values of −8.9 to −0.1‰ and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 17.83–18.12, 15.67–15.76, and 38.03–38.62, respectively, which differ significantly from the isotopic composition of the granodiorite (δ34S = −2.4‰ to +1.0‰; 206Pb/204Pb = 18.57–19.28; 207Pb/204Pb = 15.69–15.76; 208Pb/204Pb = 38.97–40.34). However, the S–Pb isotopic compositions of the sulfide minerals are similar to those of slates of the Lengjiaxi Group in the study area. The Zhengchong gold deposit probably originated from a metamorphic fluid system characterized by low salinity, low density, and CO2 enrichment with limited admixture of magmatic fluids. Based on similarities to other orogenic gold deposits, we infer that the Zhengchong orebody represents an orogenic gold deposit formed during the Late Ordovician Jiangnan Orogeny caused by collision of the Yangtze and Cathaysia blocks.

Utility of inclusions for interpreting reservoir thresholds for tight sandstone gas accumulation in the Longfengshan and Dongling sags, Southeast China

To better understand the thresholds for hydrocarbon migration in tight sandstone, we studied the gas migration and accumulation processes in the Longfengshan and Dongling sags in the Songliao Basin by determining the ancient pore pressure evolution and gas fractionation. The trapping pressure of coeval aqueous inclusions can be used to identify systematic overpressure trends, which increase during gas charging. Early formation of overpressure and a maximum surplus pressure greater than 6 MPa in reservoirs adjacent to high-quality source rocks (total organic carbon > 1.2%) indicate that the formation of surplus pressure is related to the gas generation capacity. The gas-bearing inclusion distribution and systematic geochemical trends suggest that dynamic gas migration was accompanied by gas fractionation. The results indicate that dissolved gas mainly accumulated in reservoirs with a maximum surplus pressure greater than 6 MPa and that the free gas diffused toward reservoirs with maximum surplus pressures less than 6 MPa. The gas saturations were generally stable and greater than 50% in the high surplus pressure zone. However, in the low surplus pressure zone, the gas saturation was less than 25%, although this value was relatively higher in reservoirs where the maximum surplus pressure was less than 3 MPa. Our results demonstrate that the resistance thresholds for the migration of dissolved gas and free gas differ in tight sandstone reservoirs. The surplus pressures greater than 6 MPa are advantageous for dissolved gas accumulation. An obvious resistance threshold is not observed for free gas migration, although the migration of this gas was relatively inefficient and occurred mainly via diffusion in the direction of decreasing surplus pressure. The results of this study confirm the importance of considering the driving force for natural gas in different phases as a key factor when determining optimal exploration targets.

Characteristics of fluid inclusions and implications for the timing of hydrocarbon accumulation in the cretaceous reservoirs, Kelasu Thrust Belt, Tarim Basin, China

Abstract The Kelasu Thrust Belt is a key area for oil and gas exploration within the Tarim Basin of China, an area containing abundant oil and gas resources but where the processes that controlled hydrocarbon accumulation remain unclear. This study reconstructs the accumulation history of hydrocarbons within the Kelasu Thrust Belt by studying multiple sets of fluid inclusions from the Cretaceous reservoirs using laser Raman, infrared spectroscopy, fluorescence spectroscopy, total scanning fluorescence, and PTV simulation analyses. The resulting data yield the following results. (1) Three types of Cretaceous hydrocarbon-bearing fluid inclusions are present, and they record three periods of hydrocarbon accumulation. Period I involved low-maturity medium oil as recorded by the presence of yellow–green fluorescent oil inclusions, with this accumulation occurring between the Neogene Jidike and Kangcun stages (20–5 Ma). Period II involved high-maturity light oils (or condensates) that are recorded by the presence of blue–white fluorescent oil inclusions, with this accumulation occurring during the early Kuche stage (5–2.5 Ma). Period III involved the significant accumulation of gas, as recorded by non-fluorescent gas inclusions, during and after the late Kuche stage (2.5–0 Ma). (2) Inclusion PVT simulations indicate that the pressures during the trapping of oil inclusions within the west Kelasu reservoirs increase with increasing capture temperature, suggesting that west Kelasu Cretaceous oil reservoirs formed over a short period of time. In contrast, the trapping pressures of oil inclusions within the east Kelasu area are invariant with increasing trapping temperature, indicating that the formation of east Kelasu Cretaceous oil reservoirs was a relatively slow and gradual process. This most likely relates to the fact that the east Kelasu reservoirs are close to the hydrocarbon generation centre in an area with sufficient hydrocarbon supply, with hydrocarbon accumulation processes involving all of the stages of hydrocarbon generation recorded by the source rocks in this area. In comparison, the west Kelasu reservoirs are far from the hydrocarbon generation centre and as such record only one phase of oil filling. (3) Significant tectonism associated with the uplift of the South Tianshan Mountain during the late Kuche stage caused widespread changes to Cretaceous paleo-oil reservoirs in this area. This led to some Cretaceous paleo-oils being transported to shallower traps to form secondary oil reservoirs, whereas others were transported to the surface and were lost, with residual paleo-oils were also changed to condensate gas as a result of gas washing after the addition of large amounts of late-stage gas.

Origin of the intrusion-related Lang Vai gold-antimony district (Northeastern Vietnam): Constraints from fluid inclusions study and C[sbnd]O[sbnd]S[sbnd]Pb isotope systematics

The Lang Vai ore district, located in the central part of the Lo Gam domain in the Northeast Vietnam, contains at least three deposits: Khoun Puc, Lang Vai, and Lung Luong. The general paragenetic sequences for these deposits may be represented by the following mineral associations (from early to late): (i) arsenopyrite, pyrite, native gold, sphalerite; (ii) Bi-rich Pb-Sb sulfosalts; (iii) Bi-poor Pb-Sb sulfosalts; (iv) Sb sulfosalts; (v) Sb-rich minerals, native antimony; and (vi) Pb-rich Sb sulfosalts (as a distal mineral association). Three major types were recognized within the primary fluid inclusions based on the phases present at room temperature, including: V-type, vapor-rich inclusions; L-type, liquid-rich inclusions; and C-type, CO2-rich inclusions. The early Au-As stage quartz crystals contain the V- and L-type fluid inclusions. The results indicate that the initial ore-forming fluid belonged to a (CO2-CH4)–H2O–NaCl system characterized by high temperatures (290–352 °C) and variable to moderate salinities (3.16–13.89 wt% NaCl), which are analogous to reduced intrusion-related ore-forming fluids that exhibit high homogenization temperatures and moderate salinities. The quartz crystals from the Bi-Pb-Sb mineral paragenesis (occurred only at the Khoun Puc deposit) contain both V- and L-type fluid inclusions and characterized by high temperatures (mainly 304–340 °C) and moderate salinities (6.28–8.22 wt% NaCl equiv.). The quartz crystals from the middle hydrothermal stage contain the V- and L-type fluid inclusions that yield moderate homogenization temperatures (240–290 °C) and variable salinities (3.3–8.2 wt% NaCl equiv.). These features indicate that the fluid evolved into an (CO2 ± CH4)–H2O–NaCl system at moderate temperatures, lower CH4 concentrations, and variable salinities, thus indicating changing physicochemical conditions. In the last Sb stage (the Lang Vai deposit) and Pb-Sb stage (the Lung Luong deposit), the ore-forming fluid belongs to CO2–H2O–NaCl system, which is characterized by low temperature (180–240 °C), enrichment of CO2, and medium-low salinity (1.12–9.5 wt% NaCl equiv.), that corresponded to typical fluids which formed the Sb-, and distal AgPbZn veins of the IRGS deposits in the Tintina Gold Province of Alaska USA and Yukon Canada. The fluid inclusion studies and laser Raman spectroscopy suggest that the early fluids were dominated by CH4, whereas the late fluids, by CO2. Our study suggests that the fluid boiling and accompanying decrease in the solubility of gold-bisulfide complex played an important role in gold deposition at the Khoun Puc and Lang Vai deposits. The trapping pressures estimated from the boiling fluid inclusions were 123–343 MPa during the ore-forming process. This suggests an alternating lithostatic–hydrostatic fluid system controlled by a fault-valve activity at a depth of 12.9–15.2 km. The characteristics of the S isotopes and fluid inclusions suggest that the ore-forming fluids were of magmatic origin. During mineralization process, the fluid–rock interaction between the fluids and host rocks resulted in the increase of δ34S values of the fluids as reflected in the range of sulfur isotope from the different deposits. On a plumbotectonic diagram, the sulfides show correlations between 206Pb/204Pb and both 207Pb/204Pb and 208Pb/204Pb, which suggest a two-component mixing between a high radiogenic end-member and another low radiogenic end-member. The δ13CPDB vs. δ18OSMOW study clear show that C and O in the Khoun Puc ore-forming fluids were most likely to be derived from the magma with limited contribution from the carbonate host rocks (predominantly magmatic origin of hydrothermal fluids). Wherein, the calcite separates from the Lang Vai and Lung Luong deposits have δ18OSMOW values higher than those of the Khoun Puc, suggesting that the carbonate host rocks may have provided more C and O for ore-forming fluids in these deposits. The results, combined with existing data on the regional geology, ore geology, ore geochemistry, age of mineralization, and tectonic setting, indicate that the Lang Vai ore district is an intrusion-related gold system.

Ore‐forming Fluid and Mineral Source of the Hongshi Copper Deposit in the Kalatage Area, East Tianshan, Xinjiang, NW China

AbstractThe Hongshi copper deposit is located in the middle of the Kalatage ore district in the northern segment of the Dananhu‐Tousuquan island‐arc belt in East Tianshan, Xinjiang, NW China. This study analyses the fluid inclusions and H, O, and S stable isotopic compositions of the deposit. The fluid‐inclusion data indicate that aqueous fluid inclusions were trapped in chalcopyrite‐bearing quartz veins in the gangue minerals. The homogenization temperatures range from 108°C to 299°C, and the salinities range from 0.5% to 11.8%, indicating medium to low temperatures and salinities. The trapping pressures range from 34.5 MPa to 56.8 MPa. The δ18OH2O values and δD values of the fluid range from –6.94‰ to –5.33‰ and from –95.31‰ to –48.20‰, respectively. The H and O isotopic data indicate that the ore‐forming fluid derived from a mix of magmatic water and meteoric water and that meteoric water played a significant role. The S isotopic composition of pyrite ranges from 1.9‰ to 5.2‰, with an average value of 3.1‰, and the S isotopic composition of chalcopyrite ranges from –0.9‰ to 4‰, with an average value of 1.36‰, implying that the S in the ore‐forming materials was derived from the mantle. The introduction of meteoric water decreased the temperature, volatile content, and pressure, resulting in immiscibility. These factors may have been the major causes of the mineralization of the Hongshi copper deposit. Based on all the geologic and fluid characteristics, we conclude that the Hongshi copper deposit is an epithermal deposit.

Fluid Inclusions and Stable Isotopic Characteristics of the Yaoling Tungsten Deposit in South China: Metallogenetic Constraints

AbstractThe Yaoling tungsten deposit is a typical wolframite quartz vein‐type tungsten deposit in the South China metallogenic province. The wolframite‐bearing quartz veins mainly occur in Cambrian to Ordovician host rocks or in Mesozoic granitic rocks and are controlled by the west‐north‐west trending extensional faults. The ore mineralization mainly comprises wolframite and variable amounts of molybdenite, chalcopyrite, pyrite, fluorite, and tourmaline. Hydrothermal alteration is well developed at the Yaoling tungsten deposit, including greisenization, silicification, fluoritization, and tourmalinization. Three types of primary/pseudosecondary fluid inclusions have been identified in vein quartz, which is intimately intergrown with wolframite. These include two‐phase liquid‐rich aqueous inclusions (type I), two‐ or three‐phase CO2‐rich inclusions (type II), and type III daughter mineral‐bearing multiphase high‐salinity aqueous inclusions. Microthermometric measurements reveal consistent moderate homogenization temperatures (peak values from 200 to 280°C), and low to high salinities (1.3–39 wt % NaCl equiv.) for the type I, type II, and type III inclusions, where the CO2‐rich type II inclusions display trace amounts of CH4 and N2. The ore‐forming fluids are far more saline than those of other tungsten deposits reported in South China. The estimated maximum trapping pressure of the ore‐forming fluids is about 1230–1760 bar, corresponding to a lithostatic depth of 4.0–5.8 km. The δDH2O isotopic compositions of the inclusion fluid ranges from −66.7 to −47.8‰, with δ18OH2O values between 1.63 and 4.17‰, δ13C values of −6.5–0.8‰, and δ34S values between −1.98 and 1.92‰, with an average of −0.07‰. The stable isotope data imply that the ore‐forming fluids of the Yaoling tungsten deposit were mainly derived from crustal magmatic fluids with some involvement of meteoric water. Fluid immiscibility and fluid–rock interaction are thought to have been the main mechanisms for tungsten precipitation at Yaoling.

Tungsten mineralization in the Tien Shan Gold Belt: Geology, petrology, fluid inclusion, and stable isotope study of the Ingichke reduced tungsten skarn deposit, western Uzbekistan

The Ingichke reduced W skarn deposit (100Kt WO3, with the average grade of 0.58% WO3) is the largest one among W deposits known in the Tien Shan Gold Belt. It is associated with an Early Permian multiphase granitoid pluton that comprises ilmenite-series to ilmenite-titanite-bearing, medium- to high-K, metaluminous to peraluminous I-type granitoid (monzodiorite-granodiorite to granite-leucogranite) rocks. The pluton is related to crustal accretionary-type reservoirs of granitoid magma likely formed in response to an ascent of asthenospheric material at the post-collisional stage. It is part of the continuum of plutonic suites related to reduced W-Au-polymetallic deposits, with further links to reduced intrusion-related Au deposits. The deposit comprises abundant pyroxene (mainly hedenbergitic) skarn, and a minor garnet skarn (mostly grossular-rich garnet with elevated almandine and spessartine contents). Hydrosilicate (propylitic) alteration (amphibole-chlorite-calcite-quartz with abundant pyrrhotite and minor chalcopyrite) partially overprints skarn and is in turn overprinted by zones of phyllic alteration (quartz-sericite-Fe-carbonate, locally with albite, scheelite, and sulfides, Bi and Au minerals).Prograde and retrograde skarns were formed from aqueous, dominantly magnesian-sodic-chloride, moderately-saline (10–14 to 4–7 wt% NaCl-eq.) hot fluid, with its progressing enrichment in Ca. Hydrosilicate (propylitic) and phyllic alteration assemblages were formed from boiling low salinity, carbonic-aqueous, magnesium-sodic-calcic fluids at moderate (330–355 °C) to lower (250–265 °C) temperatures, respectively, with separation of carbonic (with varying CO2/CH4 ratio) and aqueous-chloride fluids. Trapping pressures ranged from ∼2000 to 1500 bars, indicating a lithostatic depth of some 6 to 8 km, i.e., a lower-intermediate level in an integrated model of reduced W skarn deposits. The stable isotope data indicate an influence of a sedimentary (limestone) source of oxygen and carbon at the retrograde skarn stage (δ18OH2O = +8.1 to +9.0%, δ13CCO2 = −2.5 to +0.3%), and a dominantly magmatic (mantle- to crustal-derived) source of water (δ18OH2O = +7.0 ± 0.5%) at the hydrosilicate (propylitic) and phyllic alteration stages and carbon (δ13CCO2 = −7.8 to −4.7%) at the hydrosilicate (propylitic) stage. At the phyllic alteration stage, a strong enrichment in the light carbon isotope (δ13CCO2 = −10.1 to −9.4%) indicates a possible influence of a reduced organic carbon source. A magmatic source of sulfur is envisioned for the hydrosilicate (propylitic) (δ34S = +2.0 ± 0.5%) and phyllic (δ34S = −1.0 ± 0.3%) alteration stages.

Charge history of CO2 in Lishui sag, East China Sea basin: Evidence from quantitative Raman analysis of CO2-bearing fluid inclusions

Abstract The accumulation of carbon dioxide in natural gas reservoirs is common, and CO2 gas fields have been widely discovered in the world. In the last decades, three CO2 pools were discovered in Lishui sag, East China Sea Basin. Geochemical proxies indicate that CO2 in these gas reservoirs is dominated by mantle-source volcano degassing. Although three volcanic events occurred in the formation of these reservoirs, the CO2 charging period is not clear. In this study, pure CO2, CO2-rich and H2O-rich fluid inclusions were found in healed micro-fractures and overgrowth zones of quartz in the reservoir of Lishui sag. The composition and density of two H2O-rich inclusions, two CO2-rich inclusions and twenty-three pure CO2 inclusions were determined by Raman quantitative analysis. The burial depth of CO2 fluid inclusion assemblages (FIA) can be determined by the trapping pressure constrained from Raman quantitative analysis and thermodynamic models. The combination of C-He isotope analyses, PT entrapment conditions of CO2-bearing inclusions, feature of fault activity and simulation of burial history permits to assign periods of CO2 fluid activity. The low-density (∼0.15 g cm−3) CO2 gas inclusions recorded an early-period of CO2 activity eruption to be related with the Late-Paleocene volcanic event. The mid-density (∼0.45 g cm−3) and high-density (∼0.75 g cm−3) CO2 inclusions were assigned to the Miocene volcanic event and to a later CO2 charging event during Pliocene.

Investigating responses to control: a comparison of common myna behaviour across areas of high and low trapping pressure

Harvesting of wildlife by humans is commonly known to impact target species’ demography, life history and behaviour. Yet in the context of invasive and pest species control, behavioural shifts have received very little attention. The introduced common myna, Acridotheres tristis, is undergoing intensive control efforts in some areas of its Australian distribution. In order to investigate whether myna populations respond to harvesting, we compared the behaviour of free-ranging common mynas in areas of high and low trapping pressure. Behavioural analyses revealed that mynas in high trapping risk areas stayed closer to refuges, tended to form smaller groups, and were overall less detectable. Behavioural differences between high and lowly trapped areas were not attributable to variation in population density. Overall, these results are consistent with the hypothesis that common mynas have the potential to adjust their behaviour in response to heightened anthropic risk in the environment. Behavioural shifts in invasive alien species could modify their ecological impact and may interfere not only with the effectiveness of control measures, but also with how their effectiveness is assessed. Future research should aim to isolate behavioural mechanisms underpinning compensatory responses to control so that any potential effects can be mitigated.

A new genetic mechanism of natural gas accumulation

Natural gas of organic origin is primarily biogenic or thermogenic; however, the formation of natural gas is occasionally attributed to hydrothermal activity. The Precambrian dolomite reservoir of the Anyue gas field is divided into three stages. Dolomite-quartz veins were precipitated after two earlier stages of dolomite deposition. Fluid inclusions in the dolomite and quartz are divided into pure methane (P-type), methane-bearing (M-type), aqueous (W-type), and solid bitumen-bearing (S-type) inclusions. The W-type inclusions within the quartz and buried dolomite homogenized between 107 °C and 223 °C. Furthermore, the trapping temperatures and pressures of the fluid (249 °C to 319 °C and 1619 bar to 2300 bar, respectively) are obtained from the intersections of the isochores of the P-type and the coeval W-type inclusions in the quartz. However, the burial history of the reservoir indicates that the maximum burial temperature did not exceed 230 °C. Thus, the generation of the natural gas was not caused solely by the burial of the dolomite reservoir. The results are also supported by the presence of paragenetic pyrobitumen and MVT lead-zinc ore. A coupled system of occasional invasion by hydrothermal fluids and burial of the reservoir may represent a new genetic model for natural gas accumulation in this gas field.

Genesis of the Bianbianshan Cu-polymetallic deposit of the Xilamulun Cu-Mo metallogenic belt, Inner Mongolia, China: A fluid inclusion and O–H–S–Pb isotope study

The Bianbianshan Cu-polymetallic deposit is located in the Xilamulun Cu-Mo belt of Inner Mongolia, NE China, and occurs within Late Jurassic andesite, rhyolite and tuff. Cu mineralization is observed in various types of hydrothermal disseminated veins exhibiting siliciification, sericitization and chloritization. The ore-forming process occurred in four stages: (1) chalcopyrite-pyrite-quartz, (2) pyrite-chalcopyrite-quartz-vein, (3) sphalerite-galena-quartz-vein, (4) and quartz-calcite-vein. Three types of fluid inclusions were identified in the deposit, including C-type (CO2-NaCl-H2O) as well as V- and L-type (NaCl-H2O) inclusions, where only L-type inclusions are observed in the fourth stage. Homogenization temperature of fluid inclusions in the four stages are 325–365 °C, 282–335 °C, 268–312 °C, and 195–259 °C, respectively, all of which exhibit salinities lower than ∼ 13 wt% NaCl equiv. Trapping pressure estimated from C, V- and L-fluid inclusions are between 550 and 900 bars, corresponding to minimum depths of 2.5–3.7 km. Hydrogen and oxygen isotopic compositions of quartz from different stages (δD = −109.7 ~ –107.6‰, δ18O = 7.6–9.6‰, V-SMOW) suggest that the mineralizing fluid gradually evolved from a magmatic to a meteoric origin. Sulfur (δ34SV-CDT = −0.7 to 0.4‰) and lead isotopes (208Pb/204Pb = 37.746–38.137‰; 208Pb/204Pb = 15.52–15.56%; 206Pb/204Pb = 17.75–18.36%) indicate that ore-forming materials were derived from mantle with minor additional participation of crustal reservoirs. Our data suggests the ore-forming fluids of the Bianbianshan Cu-polymetallic deposit are attributed to a moderate temperature, moderate-low salinity, and moderate density system, where decreases in pressure, phase separation and local mixing with meteoric water drove precipitation of metals.

Hydrothermal evolution and isotope studies of the Baghu intrusion-related gold deposit, Semnan province, north-central Iran

The middle Eocene intrusion-related Baghu gold deposit is located in the Torud-Chahshirin segment of the Neotethyan magmatic arc of north-central Iran, Semnan province, Iran. The wallrocks at the deposit include a volcano-sedimentary sequence of calc-alkaline andesitic to dacitic lavas, marls, tuffs, and sandstones, which are intruded by epizonal granodioritic stocks and mafic dikes. Zircon U-Pb secondary ion mass spectrometry dating of a number of the granodiorite and micro-granite bodies yields an age of ca. 43.4 ± 1.3 Ma. Mineralization is in the form of subparallel sheeted quartz veins that are up to ∼1 km long within extensional faults. The ore-forming process included early potassic alteration with quartz + adularia + biotite + pyrite + chalcopyrite + native gold veins (average 0.25 g/t), and late phyllic alteration with quartz + sericite + pyrite + chalcopyrite + bornite + sphalerite + native gold veins (average 1.5 g/t). Supergene kaolinitization is also extensive in the Baghu area and has locally replaced up to 50 percent of the hypogene sulfide minerals. Turquoise is a diagnostic supergene phase, and locally, the iron oxy-hydroxides replacing the sulfides contain up to 57 g/t Au. The current hypogene and supergene resource estimate for the Baghu Au-Cu deposit is approximately 3.5 million tonnes averaging 1.17 g/t Au.Fluid inclusions in quartz from phyllic stage vein samples include monophase aqueous (I), monophase gas-rich (II), aqueous liquid + vapor (III), mixed aqueous-carbonic (IV), and multi-solid (V) inclusion types. The average homogenization temperatures and salinities of fluid inclusion assemblages from type III and IV inclusions range from 180 to 382 °C, with a mode at about 330 °C, and 4.2–5.4 wt% NaCl equiv., respectively. The type IV inclusions showed clathrate melting temperatures between +3.1 and +8.5 °C, indicating salinities of 2.8–11.5 wt% NaCl equiv. The type V inclusions also show a Th range from 310 to 478 °C (average 440 °C) corresponding to high salinities of 33–45 wt% NaCl equiv. The trapping pressure of the fluid inclusions was estimated to be 94–132 MPa corresponding to depths of 2.5–3.9 km during late stage of mineralization. Sericite from the stage II veins yields an 40Ar/39Ar age of ca. 44 Ma, suggesting that the mineralization at Baghu overlap granite emplacement. The δ18O of the ore-forming fluid also indicates no significant meteoric water input, despite gold deposition in a relatively shallow epizonal environment (δ18Ofluid = +8.0 to +10.3 per mil). In addition, δ34S values in stage II pyrite and chalcopyrite sulfide minerals range from +1.5 to +3.1 per mil, which is consistent with fluid saturation from a reduced magmatic source of sulfur. Historic gold production from occurrences hosted by the Torud-Chahshirin volcano-plutonic complex has been minor compared to that from orogenic gold deposits in Iran. However, identification of intrusion-related gold deposits in the complex indicates that more thorough exploration in the Eocene arc of north-central Iran could be promising.

Analysis of the charging process of the lacustrine tight oil reservoir in the Triassic Chang 6 Member in the southwest Ordos Basin, China

With the success of Bakken tight oil (tight sandstone oil and shale oil) and Eagle Ford tight oil in North America, tight oil has become a research focus in petroleum geology. In China, tight oil reservoirs are predominantly distributed in lacustrine basins. The Triassic Chang 6 Member is the main production layer of tight oil in the Ordos Basin, in which the episodes, timing, and drive of tight oil charging have been analyzed through the petrography, fluorescence microspectrometry, microthermometry, and trapping pressure simulations of fluid inclusions in the reservoir beds. Several conclusions have been reached in this paper. First, aqueous inclusions with five peaks of homogenization temperatures and oil inclusions with three peaks of homogenization temperatures occurred in the Chang 6 reservoir beds. The oil inclusions are mostly distributed in fractures that cut across and occur within the quartz grains, in the quartz overgrowth and calcite cements, and the fractures that occur within the feldspar grains, with blue–green, green, and yellow–green fluorescence colours. Second, the peak wavelength, Q650/500, and QF535 of the fluorescence microspectrometry indicate three charging episodes of tight oil with different oil maturities. The charging timings (141–136, 126–118, and 112–103 Ma) have been ascertained by projecting the homogenization temperatures of aqueous inclusions onto the geological time axis. Third, excess-pressure differences up to 10 MPa between the Chang 7 source rocks and the Chang 6 reservoir beds were the main driving mechanism supporting the process of nonbuoyancy migration.

A lung model to demonstrate dynamic gas trapping and intrinsic positive end-expiratory pressure at realistic ventilation settings.

Intrinsic positive end-expiratory pressure (PEEP) and gas trapping are recognised hazards during ventilation of patients with airflow obstruction. Demonstration of these phenomena on conventional lung models using realistic ventilation settings is difficult. We describe an Intrinsic PEEP Model that is able to demonstrate dynamic gas trapping and intrinsic PEEP at realistic ventilation settings, and demonstrate its ability to develop intrinsic PEEP in a timeframe useful for teaching. The model uses a Heimlich valve to permit a lower resistance on inspiration than expiration. The model was tested using a series of typical ventilation settings which, when applied in a clinical setting on patients with airflow obstruction issues, would result in prolonged low expiratory flow and the development of intrinsic PEEP of 10 to 20 cmH₂O, and ultimately significant gas trapping. The IPM can be used to demonstrate this effect and the ventilator adjustments required to minimise these problems.

Quartz-Amethyst Hosted Hydrocarbon-Bearing Fluid Inclusions from the Green Ridge Breccia in the Snoqualmie Granite, North Cascades, WA, USA

The Green Ridge Breccia cuts the composite Miocene Snoqualmie Batholith in King County, WA, USA. The granite was emplaced at ~5 km depth between ~17 and 20 Ma and the crosscutting NW trending breccia contains large angular blocks of the host granite (<1 m in longest dimension). The brecciated granite blocks are cemented by quartz-amethyst euhedra (<10 cm in longest dimension) bearing vugs. A notable feature is the presence of centimetric scale amber coloured oil inclusions within the quartz-amethyst crystals. Fluid inclusion studies using Transmitted Light Petrography, UV Microscopy, Microthermometry, Laser Raman Microspectroscopy and Gas Chromatography-Mass Spectrometry record the presence and the fluid composition of three fluid inclusion types hosted by the euhedra: primary Type 1 (liquid rich two-phase (L + V) aqueous inclusions) and secondary Type 2 bituminous two-phase (S + L) inclusions and Type 3 amber coloured oil bearing two-phase immiscible liquid inclusions. The Green Ridge Breccia was the locus for convective hydrothermal fluid flow that formed the quartz-amethyst vugs formed at T~390 °C assuming a trapping pressure of ~1.65 kb. Later, hydrocarbon fluids migrated downwards from the roof source rock (e.g., the Guye Sedimentary Member) and were trapped in the euhedra. This was followed by unroofing of the batholith and exposure of the Green Ridge Breccia. This study highlights the potential for other oil migrations into the Snoqualmie Batholith in areas where it forms the basement capped by the Guye Sedimentary Member.

Reproductive characteristics of a coyote population before and during exploitation

ABSTRACTThe eastward expansion of coyotes (Canis latrans) has brought the species into ecosystems and landscapes different from those it historically occupied, yet little is known about the reproductive biology of coyotes in the southeastern United States or the effects of exploitation on reproduction in coyotes. Our objective was to quantify litter size, pregnancy rate, and fecundity in an essentially unexploited coyote population in South Carolina, USA and to evaluate the effect of exploitation on these parameters. We examined reproductive tracts from 235 female coyotes trapped during 2010–2012. Placental scars from coyotes trapped during 2010 indicated that prior to trapping (2009), pregnancy rates were zero for juveniles, 0.25 for yearlings, and 0.389 for adults. Litter size for adults during 2009 averaged 5.4 pups/female, resulting in fecundity of 2.1 pups/female. The number of coyotes trapped was similar among years, indicating that the population recovered following trapping each year, but it shifted toward a younger age structure during trapping. However, although pregnancy rate, litter size, and fecundity of adults all tended to increase from pre‐trapping (2009) through the last trapping period (2011–2012), differences were not significant for this or any other age class. Fecundity of the population did not significantly increase during the first year of trapping (2010) but was lower during the last trapping period (2011–2012; 0.56 ± 0.15 [95% CL]) than prior to trapping (0.90 ± 0.15 [95% CL]). Thus, we observed only weak evidence for compensatory reproduction in response to trapping pressure and conclude that the increase in the juvenile component of the population was attributable primarily to immigration from neighboring areas rather thanin situreproduction. This increased representation of juveniles in the population, which rarely bred, coupled with a concurrent decrease in adults, which accounted for 59.2% of breeding, explains the reduction in population fecundity. High immigration rates as indicated herein render coyote populations extremely difficult to control. © 2017 The Wildlife Society.

Fluid inclusion and isotope geochemistry of the Atebayue Sb deposit, South Tianshan Orogen, Kyrgyzstan

The Atebayue Sb deposit is hosted in the Silurian clastics in the South Tianshan Orogen in Kyrgyzstan. The Sb ores appear as veins/veinlets and disseminations, with stibnite being the main ore mineral. Gangue minerals comprise quartz, calcite, and clay minerals. The quartz at Atebayue only contains aqueous fluid inclusions with low homogenization temperature (215–336 °C) and salinity (3.4–6.9 wt.% NaCl equiv.), supporting an epizonogenic hydrothermal origin. The minimum trapping pressures estimated from the NaCl─H2O inclusions are 9–14 MPa, suggesting that the Sb mineralization mainly occurred at a depth of 0.9–1.4 km. Sulphur isotopes (δ34S = −0.4 to 6.2‰) suggest that the host rocks within the Silurian system to be a significant source of ore metals. The ores contain average 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.112, 15.547, and 38.064, respectively, and 2‐stage model ages of 337–381 Ma, indicating the ores were likely sourced from the Paleozoic strata. Integrating the data obtained from the studies including ore geology, fluid inclusion, and S─Pb isotope geochemistry, we conclude that that the Atebayue Sb deposit is best classified as epizonogenic type formed by the Tarim–Kazakhstan continent–continent collision.