Fluid inclusion and isotopic constraints on the origin of ore‐forming fluid of the Jinman–Liancheng vein Cu deposit in the Lanping Basin,western Yunnan,China

Extensive quartz–carbonate–Cu sulfide veins occur in clastic rocks and are spatially related to Paleocene granites in the western border of the Lanping Basin, western Yunnan, China. Abundant aqueous‐carbonic fluid inclusions occur in these veins but their origin is debated. In the Jinman–Liancheng deposit, individual primary inclusion groups contain either exclusively liquid‐rich inclusions (Gl), or coexisting liquid‐rich and vapor‐rich inclusions (Glv). Microthermometry and estimate of CO₂ content indicate that type Gl inclusions either have homogenization temperatures (Th) 238–263°C and contain c. 3.9–5.5 mole % CO₂, or have Th 178–222°C and contain c. 1.6–3.2 mole % CO₂. Type Glv inclusions are thought to represent samples of fluid unmixing that occurred at 183–218°C. At that time, the liquid phase in the unmixing fluid may contain c. 2.0–3.3 mole % CO₂. As such, the correlation of CO₂ content with Th for type Gl inclusions is thought to be caused by fluid unmixing with decreasing temperature and subsequent CO₂ escape. δ¹⁸O and δD values of the parent water mainly fall in the field below that of primary magmatic water, indicative of fluid derivation from degassed (in open system) magmatic water, with no contributions from basinal or meteoric water. Initial Sr isotopic compositions of hydrothermal carbonates suggest that the fluid was magmatic, probably derived from the Paleogene granites. δ¹³C_PDB values (?4‰ to ?7‰) of the hydrothermal carbonates and δ³⁴S_V‐CDT values of sulfides (mainly ?11‰ to +5‰) indicate that the carbon and sulfur can be derived from (degassed) magma and/or nonmagmatic sources. The CO₂‐rich and magmatic‐water‐derived fluid at Jinman–Liancheng differs from the CO₂‐poor and basinally derived fluid in sediment‐hosted stratiform Cu (SSC) deposits, which suggests that there are no genetic linkages between the vein Cu and SSC deposits in the Lanping Basin.     

Density and isothermal compressibility of supercritical H2O–NaCl fluid: molecular dynamics study from 673 to 2000 K, 0.2 to 2 GPa,and 0 to 22 wt% NaCl concentrations

We report on molecular dynamics (MD) simulations for predicting the density and isothermal compressibility of an H₂O–NaCl fluid as a function of temperature (673–2000 K), pressure (0.2–2.0 GPa), and salt concentration (0.0–21.9 wt%). The atomistic behavior was analyzed via the hydration number of ions and number of ion pairs. Hydration numbers of Na⁺ and Cl^? increased with increasing pressure and decreasing temperature. Conversely, the fraction of Na–Cl ion pairs increased with decreasing pressure and increasing temperature. This hydration and association behavior is consistent with the low dielectric constant of H₂O under these conditions. The presence of polynuclear clusters of Na–Cl was confirmed at high temperatures, low pressures, and high salt concentrations. We propose a purely empirical equation of state (EoS) for H₂O–NaCl fluids under high temperatures and pressures that should be useful for estimating the fluid distribution in Earth's crust and upper mantle in relation to effects on earthquakes and volcanic eruptions.     

From deep to shallow fluid reservoirs: evolution of fluid sources during exhumation of the Sierra Almagrera,Betic Cordillera,Spain

The combination of structural, geochemical and palaeotopographic data proves to be an efficient tool to understand fluid transfers in the crust. This study discriminates shallow and deep fluid reservoirs on both sides of the brittle–ductile transition under an extensional regime and points out the role of major transcurrent fault activity in this palaeohydrogeological setting. Palaeofluids trapped in quartz and siderite–barite veins record the transfer of fluids and metal solute species during the Neogene exhumation of the Sierra Almagrera metamorphic belt. Ductile then brittle–ductile extensional quartz veins formed from a deep fluid reservoir, trapping metamorphic secondary brines containing low‐density volatile phases derived from the dissolution of Triassic evaporites. During exhumation, low‐salinity fluids percolated within the brittle domain, as shown by transgranular fluid inclusion planes affecting previous veins. These observations indicate the opening of the system during Serravalian to early Tortonian times and provide evidence for the penetration of surficial fluids of meteoric or basinal origin into the upper part of the brittle–ductile transition. During exhumation, synsedimentary transcurrent tectonic processes occurred from late Tortonian times onwards, while marine conditions prevailed at the Earth's surface. At depth in the brittle domain, quartz veins associated with haematite record a return to high‐salinity fluid circulation suggesting an upward transfer fed from a lower reservoir. During the Messinian, ongoing activity of the trans‐Alboran tectono‐volcanic trend led to the formation of ore deposits. Reducing fluids caused the formation of siderite and pyrite ores. The subsequent formation of galena and barite may be related to an increase of temperature. The high salinity and Cl/Br ratio of the fluids suggest another source of secondary brine derived from dissolved Messinian evaporites, as corroborated by the δ³⁴S signature of barite. These evaporites preceded the main sea‐level drop related to the peak of the salinity crisis (5.60–5.46 Ma).     

Geometry‐coupled reactive fluid transport at the fracture scale: application to CO2 geologic storage

Water acidification follows CO₂ injection and leads to reactive fluid transport through pores and rock fractures, with potential implications to reservoirs and wells in CO₂ geologic storage and enhanced oil recovery. Kinetic rate laws for dissolution reactions in calcite and anorthite are combined with the Navier‐Stokes law and advection–diffusion transport to perform geometry‐coupled numerical simulations in order to study the evolution of chemical reactions, species concentration, and fracture morphology. Results are summarized as a function of two dimensionless parameters: the Damköhler number Da which is the ratio between advection and reaction times, and the transverse Peclet number Pe defined as the ratio between the time for diffusion across the fracture and the time for advection along the fracture. Reactant species are readily consumed near the inlet in a carbonate reservoir when the flow velocity is low (low transverse Peclet number and Da > 10^?1). At high flow velocities, diffusion fails to homogenize the concentration field across the fracture (high transverse Peclet number Pe > 10^?1). When the reaction rate is low as in anorthite reservoirs (Da < 10^?1), reactant species are more readily transported toward the outlet. At a given Peclet number, a lower Damköhler number causes the flow channel to experience a more uniform aperture enlargement along the length of the fracture. When the length‐to‐aperture ratio is sufficiently large, say l/d > 30, the system response resembles the solution for 1D reactive fluid transport. A decreased length‐to‐aperture ratio slows the diffusive transport of reactant species to the mineral fracture surface, and analyses of fracture networks must take into consideration both the length and slenderness of individual fractures in addition to Pe and Da numbers.     

Pyrophyllite formation in the thermal aureole of a hydrothermal system in the Lower Saxony Basin,Germany

A combined clay mineralogical, fluid inclusion, and K‐Ar study of Upper Jurassic metasediments at the Gehn (Lower Saxony Basin, Germany) provides evidence for a transient hydrothermal event during Upper Cretaceous basin inversion centered on a prominent gravimetric anomaly. Kaolinite and smectite in Oxfordian pelitic parent rocks that cap a deltaic sandstone unit were locally transformed into pyrophyllite, 2M₁ illite, R3 illite–smectite, chlorite, and berthierine at the Ueffeln quarry. The pyrophyllite‐bearing metapelites lack bedding‐parallel preferred orientation of sheet silicates and experienced peak temperatures of about 260–270°C consistent with microthermometric data on quartz veins in the underlying silicified sandstones. The presence of expandable layers in illite–smectite and high Kübler Index values indicate that the thermal event was rather short‐lived. K‐Ar dating of the <0.2 μm fraction of the pyrophyllite‐bearing Ueffeln metapelite yields a maximum illitization age of 117 ± 2 Ma. Lower trapping temperatures of aqueous fluid inclusions in quartz veins and the absence of pyrophyllite in metapelites of the Frettberg quarry in a distance of about 2.5 km from the Ueffeln quarry infer maximum paleotemperatures of only 220°C. The highly localized thermal anomaly at Ueffeln suggests fault‐controlled fluid migration and heat transfer that provided a thermal aureole for pyrophyllite formation in the metapelites rather than metamorphism due to deep burial. A pH neutral hydrothermal fluid that formed by devolatilization reactions or less likely by mixing of meteoric and marine waters that interacted at depth with shales is indicated by the low salinity (3–5 wt. % NaCl equiv.) of aqueous inclusions, their coexistence with methane–carbon dioxide‐dominated gas inclusions as well as carbon, hydrogen, and oxygen isotope data. The upwelling zone of hydrothermal fluids and the thermal maximum is centered on a gravimetric anomaly interpreted as an igneous intrusion (‘Bramsche Massif’) providing the heat source for the intrabasinal hydrothermal system.     

Cyclic loading of an idealized clay‐filled fault: comparing hydraulic flow in two clay gouges

The flow of water along discontinuities, such as fractures or faults, is of paramount importance in understanding the hydrogeology of many geological settings. An experimental study was undertaken comprising two experiments on a 30° slip‐plane filled with kaolinite or Ball Clay gouge using a bespoke Angled Shear Rig (ASR). The gouge was initially loaded in equal step changes in vertical stress, followed by unloading of the sample in similar equal steps. This was followed by reloading to a new maximum stress, followed by unloading; the test history was therefore load‐unload‐reload‐unload (LURU). The transmissivity of the kaolinite and Ball Clay gouge showed a power‐law relationship with vertical stress. The LURU history showed considerable hysteresis, with flow effectively unchanged during unloading, even when vertical stress was close to zero. Reloading resulted in flow similar to that seen during unloading suggesting that the unloading‐reloading path is similar to the rebound‐reconsolidation line in classic soil mechanics. These observations show the importance of stress history on fracture flow; consideration of just the current stress acting upon a fracture may result in inaccuracies of predicted hydraulic flow. Once a new stress maximum was achieved the transmissivity of the fracture continued to reduce. No significant variation was seen in the flow response of kaolinite and Ball Clay gouge suggesting that the inclusion of illite and quartz did not have a significant influence on the form of the relationship between stress and flow, i.e. both described by a power‐law.     

Large‐scale chemical stratification of fluids in the crust: hydraulic and chemical data from the geothermal research site Urach,Germany

The Urach 3 research borehole in SW Germany has been drilled through a sedimentary cover sequence and reached gneisses of the Variscan crystalline basement at 1604 m below surface. An additional 2840 m has been drilled through fractured basement rocks. The borehole has been used for hydraulic tests in the context of a ‘hot dry rock’ (HDR) project. The sedimentary cover ranges from the Carboniferous to the Middle Jurassic (Dogger) in age and comprises mostly clastic sediments in the Paleozoic and limestone and shale in the Mesozoic. Water composition data from 10 different depths include samples from all major lithological units. The total dissolved solids (TDS) increases from the surface to about 650 m where it reaches 4.1 g l^?1 in Triassic limestone. In lower Triassic sandstones, TDS increases very sharply to 28.5 g l^?1 and the water is saturated with pure CO₂ gas. With increasing depth, TDS does not change much in the clastic sediments of the Permian and Carboniferous. The crystalline basement is marked by a very sharp increase in TDS to 55.5 g l^?1 at about 1770 m depth. TDS increases within the basement to more than 78.5 g l^?1 at about 3500 m depth. The data suggest that there is limited vertical chemical communication over long periods of time. The CO₂ gas cap in the lower Triassic sandstones requires a gastight cover. The chemical stratification of the fluids relates to the permeability structure of the crust at the Urach site and fits well with hydraulic and thermal data from the site.     

A fluid inclusion record of magmatic/hydrothermal pulses in acid Salar Ignorado gypsum,northern Chile

Salar Ignorado is a shallow acid saline lake hosted by a small intervolcanic basin high in the Andes Mountains of northern Chile. Modern surface waters have 3.3–4.1 pH, 0.5–3% total dissolved solids (TDS) and are actively precipitating gypsum crystals. The gypsum crystals trap the acid saline water as fluid inclusions, providing a record of recent surface water characteristics. Salar Ignorado gypsum contains three distinct types of primary fluid inclusions, which result from growth of the gypsum from surface waters. Petrography and microthermometry were performed on 27 gypsum crystals from Salar Ignorado to gain an understanding of recent water chemistry of the salar. One 18.3‐cm‐long gypsum crystal, hosting primary fluid inclusions along 28 successive growth bands, was the focus for fluid inclusion studies and allowed a record of high‐resolution chemical trends. This crystal showed a change in parent fluids during growth, from low salinity, to high salinity, back to low salinity. At the bottom of the crystal, the lowest six fluid inclusion assemblages have salinities of 1.7–5.1 eq. wt. % NaCl. The next nine fluid inclusion assemblages have significantly higher salinity (18.6–27.4 eq. wt. % NaCl) inclusions. The twelve fluid inclusion assemblages near the top of the crystal have low salinity (0.9–8.3 eq. wt. % NaCl) like those at the bottom of the crystal. The high‐salinity fluid inclusions in the middle of this gypsum crystal are interpreted to have formed during a pulse of magmatic/hydrothermal fluids to the surface, perhaps during local active volcanism. Secondary evidence of a magmatic influence on surface waters includes hydrogen sulfide and high molecular weight solid hydrocarbons within some fluid inclusions. This study is among the first detailed fluid inclusion studies of gypsum and suggests that fluid inclusions in gypsum can be paleo‐hydrogeologic proxies.     

中国春运人口流动网络的富人俱乐部现象与不平衡性分析

基于“百度地图春节人口迁徙大数据”,利用加权网络的富人俱乐部系数和归一化不平衡系数方法,对2015年中国春运期间人口流动网络的富人俱乐部现象和不平衡性进行分析。研究结果表明：中国春运人口流动网络中存在明显的富人俱乐部现象,富人俱乐部城市包括北京、上海、广州、苏州、深圳和东莞,这些城市主导了超过77.66%中国城市的省际人口流动,且与这些城市之间的人口流动多属于不平衡关系,同时俱乐部城市之间、俱乐部城市与一小部分城市之间则属于平衡关系,这种流动格局很容易造成各城市在人口流动网络中的地位分化,严重影响了人口流动网络的公平性和安全性。     

中国入境后旅游流的空间分布研究

入境旅游是中国旅游业发展的重要组成部分。海外旅游者入境后,在空间上呈现出一定的流动特征及分布规律。本文根据中国旅游统计年鉴资料和项目组旅游调查资料,将全国旅游流划分为5大基本旅游流区,为加强各分区间的联合促销及客流、信息共享提供参考依据和技术支撑。