Conduits For Fluid Flow Research Articles

Geochronology and geochemistry of the Dianfang gold deposit, western Henan Province, central China: Implications for mineral exploration

The Dianfang gold deposit, located in the Xiong’ershan–Waifangshan region within the southern margin of the North China Craton, consists of eastern and western ore blocks, which are hosted in the Dianfang breccia pipe and Paleoproterozoic volcanic rocks, respectively. The eastern ore block, which occurs within the southern and hanging wall margins of the Dianfang breccia pipe and in fractures in the rhyolites of the Jidanping Formation, consists of rhyolite-hosted and breccia-hosted disseminated gold mineralization structurally controlled by ENE-striking faults. The western ore block contains gold-bearing quartz-sulfide veins and minor disseminated rhyolite-hosted gold mineralization that occurs in the annular fractures around the Hougou breccia pipe. The two ore blocks have long been researched and prospected as two different genetic types. Detailed fieldwork and microscopic observations reveal that the eastern and western ore blocks contain the same hydrothermal alteration and mineral assemblages, which include K-feldspar, quartz, sericite, chlorite, epidote, carbonate, pyrite, galena, sphalerite, marcasite and chalcopyrite, as well as minor magnetite, anatase, cervelleite, matildite, and bismuthinite. Gold occurs as electrum inclusions in pyrite or along microfractures in sulfides and quartz. Zircon U–Pb geochronology of the granite porphyry around the Hougou breccia pipe constrains the timing of breccia pipe formation to 145.9 Ma which is consistent with the formation age of the Dianfang breccia pipe (145.8 Ma), indicating that the two breccia pipes formed coevally at the end of the late Jurassic, rather than during the Paleoproterozoic, as was suggested by previous studies. The hydrothermal sulfides from the main orebody yield a Rb–Sr isochron age of 119.5 ± 1.8 Ma, suggesting that the eastern and western ore blocks formed coevally at the end of the early Cretaceous. In situ mineral trace element data, as well as sulfur and lead isotope data suggest that the eastern and western ore blocks were formed by a common ore-forming fluid that evolved from a magmatic-hydrothermal system that was genetically related to a hidden late Mesozoic granite. Pre-existing fractures and breccia then served as ideal conduits for fluid flow, accumulation, and gold deposition. Consequently, we propose that the ENE-striking faults developed in and around the breccia pipes and the annular brittle faults around the breccia pipes are good targets for future gold exploration at the Dianfang gold deposit. Based on these results and data from other gold deposits of similar ages around the margins of the North China Craton, we argue that the gold deposits in Xiong’ershan region formed under conditions of lithospheric extension from the late Jurassic to the early Cretaceous, which resulted from lithospheric thinning due to the westward subduction of the Pacific Plate.

Linking natural fractures to karst cave development: a case study combining drone imagery, a natural cave network and numerical modelling

In carbonate rocks, channelized fluid flow through fracture conduits can result in the development of large and connected karst networks. These cavity systems have been found in multiple hydrocarbon and geothermal reservoirs, and are often associated with high-permeability zones, but also pose significant challenges in drilling and reservoir management. Here, we expand on the observed interplay between fractures, fluid flow and large cave systems, using outcrop analysis, drone imagery and fluid-flow modelling. The studied carbonate rocks are heavily fractured and are part of the Salitre Formation (750–650 Ma), located in central Bahia (NE Brazil). Firstly, the fracture and cave network data show a similar geometry, and both systems depict three main orientations, namely; NNE–SSW, NW–SE and ESE–WNW. Moreover, the two datasets are dominated by the longer NNE–SSW features. These observed similarities suggest that the fractures and caves are related. The presented numerical results further acknowledge this observed correlation. These results show that open fractures act as the main fluid-flow conduits, with the aperture model defining the fracture-controlled flow contribution. Furthermore, the performed modelling highlights that geometrical features such as length, orientation and connectivity play an important role in the preferred flow orientations. Thematic collection: This article is part of the Naturally Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/naturally-fractured-reservoirs

Physiology of the Arterial Wall

Arterial, venous, and lymphatic vessel walls are organized in three concentric layers that are composed of specialized cells and matrix components, allowing a vessel to function both as a conduit for fluid flow and regulate tone, control passage of cells and molecules to the interstitium and have the capacity to remodel after injury. The arrangement and proportions of these components vary depending on the location of a particular vessel within the circulation; variations allow specialization to accommodate pulsatile flow, regulate peripheral resistance, facilitate immune surveillance, or transport nutrients and metabolic waste. In addition to understanding the biology of the vessel wall and its role in pathology, a knowledge of the development of the vascular system and the various consequences of deviation from normal development will aid in identifying and treating a diverse range of vascular diseases. This review contains 5 figures, 1 table, and 44 references. keywords: artery, adventitia, angiogenesis, arteriogenesis, arteriole, intima, media, physiology, vasculogenesis

Aeromagnetic Investigation of Geologic Structures Associated with Gold Mineralization along Danja, Northwestern Nigeria

The study area falls within the basement complex of northwestern Nigeria and covers four adjacent quarter degree sheets of Funtua, Malumfashi, Masks and Zaria. Gold occurrence in the area was not reported until the recent discovery by artisanal miners. Previous works have shown that primary gold mineralization within the Nigerian basement complex is controlled by geologic structures where they act as conduits for fluids flow and as loci for mineralization. This paper is aimed at characterizing the major structural controls of gold mineralization in the study area. This was achieved by determining depth to basement, producing a magnetization map showing magnetic susceptibility range across the entire study area, and a model of the shape, location and depth of structures in the study area. The anomalies on the aeromagnetic map were defined by fitting a first order polynomial to the total fields, by the method of least squares to obtain the residual field data. First vertical derivative and analytic signal computed, defined distinct pattern of the magnetic signatures. Depths to the surface of the geologic structures (which appears as lineaments on aeromagnetic maps) were obtained from Euler deconvolution solutions which gives an average depths range of 200.2 m to 2229.1 m, with very few solutions having depths less than 300 m. The most prominent lineament and all major subtle lineaments have a depth range of 200 m to 600 m which shows that the structures are deep seated. The magnetic susceptibility values obtained from the magnetization map ranges from 0.000666 to 0.000996 SI. The lineament expected to be the major conduit for possible fluid flow that emplaced the Gold mineralization in the area is suspected to be the continuation of Kalangai fault which trends NE-SW along Malumfashi in the study area.

Rock Fracture Sorptivity as Related to Aperture Width and Surface Roughness

Core Ideas Spontaneous imbibition was measured in rock fractures using neutron radiography. Early‐time uptake of water displacing air showed a square root of time dependency. Fracture sorptivity was quantified from the slope of the early‐time uptake data. Fracture sorptivity increased with increasing fracture aperture width. Fracture sorptivity decreased with increasing fracture surface roughness. Fractures in low‐porosity rocks can provide conduits for fluid flow. Numerous researchers have investigated fluid flow through fractures under saturated conditions. However, relatively little information exists on spontaneous imbibition in fractures, whereby a wetting fluid displaces a non‐wetting fluid by capillarity. We investigated spontaneous imbibition of water displacing air in a suite of fractured low‐porosity sedimentary and igneous rock cores (5.08‐cm length by 2.54‐cm diameter). Mode I fractures were induced in the cores by compression between opposing parallel flat plates. The following physical properties were measured: bulk density, ρb; solid‐phase density, ρs; porosity, ϕ; contact angle, θe; fracture aperture width, xgeo; and fracture surface roughness, Wr. The wetting front in each fracture was imaged using dynamic neutron radiography. Early‐time uptake exhibited a square root of time dependency, and was quantified by linear regression, with the slope equal to the fracture sorptivity, Sf. Estimates of Sf ranged from 10.1 to 40.5 mm s−0.5, with a median value of 25.0 mm s−0.5. There was a statistically significant effect of rock type on Sf, with igneous rocks generally having lower mean values than sedimentary rocks. Differences in ρb, ρs, ϕ, and θe between the rock types did not contribute significantly to the variation in Sf. However, xgeo and Wr were significantly correlated with Sf. These correlations indicated that Sf increases with increasing xgeo, as predicted by early‐time capillary theory, and decreases with increasing Wr, analogous to the decrease in fracture permeability with increasing surface roughness observed under saturated flow conditions.

Seismic stratigraphy and sedimentary facies analysis of the pre- and syn- Messinain salinity crisis sequences, onshore Nile Delta, Egypt: Implications for reservoir quality prediction

Abstract This study provides the first high-resolution outlines of the Messinian sequence in the Nile Delta based on an integrated sedimentological, petrophysical and seismic stratigraphic approach. The distribution, pattern and architecture of the Messinian facies deposited before, during and after the Messinian salinity crisis (MSC) have been investigated. In seismic, the pre-MSC Qawasim Formation constitutes parallel oblique seismic facies interpreted as deltaic system prograding northward from prodelta, distal sand bars into subaqueous distributary channels and mouthbars and subaerial delta-plain distributary channels. The MSC Abu Madi Formation consists of three seismic-stratigraphic units infilling the Eonile canyon. A seismically chaotic lower unit paving the canyon-floor is overlain by the continuous, high-amplitude reflectors of the middle unit which is capped by semi-chaotic, low-amplitude facies of the upper unit. The lower unit corresponds to the subaerial gravity-flow deposits synchronously accumulated during the Eonile incision; whereas the middle unit comprises the aggradational-progradational fluvial facies, and the upper unit constitutes the retrogradational estuarine facies. The superimposed diagenetic alterations on these various depositional facies produced complex reservoir heterogeneity. Fluid flow conduits are restricted to the coarse-grained delta distributary channels and fluvial facies with limited marine influence and minimal depositional clay content and traces of diagenetic kaolinite and chlorite. On the other hand, flow baffles and barriers are common in the fine-grained marine-influenced facies with pervasive depositional clays, diagenetic calcite and glauconite.

Geochemical footprint of the Millennium unconformity-type uranium deposit, Canada: implications for vectoring new targets

The Millennium deposit, a c. 650-m deep monomineralic uranium deposit, is located in the southeastern Athabasca Basin, Saskatchewan, a region containing numerous high-grade unconformity-type U deposits. 3D modelling of the whole-rock lithogeochemistry of sandstones above the deposit reveals a distinct footprint with select major and trace elements showing increased concentrations towards mineralization. Molar Mg/K ratios increase from background levels 10 km north of the deposit, along the B1 conductive trend, whereas Mo, Co, Rb, and Ga exhibit elevated concentrations immediately above the deposit, extending vertically from the unconformity to surface. Lead, Ag, Bi, Sb, REE, and Y exhibit elevated concentrations up to 650 m above the main mineralized body. Increasing Mg/K values indicate the transition from diagenetic to hydrothermal alteration with shifts from illitic (K-dominant) to chloritic and dravitic (Mg-dominant) alteration, with the latter increasing more proximal to mineralization. Trace element enrichment patterns highlight that fractures and faults were conduits for fluid flow from the basement into the basin, both during ore formation and through tectonically driven post-depositional remobilization. Key indicators such as molar element ratios (Mg-K-Al) and trace elements related to redox reactions provide scalable vectors at the Millennium deposit that are likely applicable to similar unconformity-type U deposits elsewhere.

Faults and associated karst collapse suggest conduits for fluid flow that influence hydraulic fracturing-induced seismicity

During December 2011, a swarm of moderate-magnitude earthquakes was induced by hydraulic fracturing (HF) near Cardston, Alberta. Despite seismological associations linking these two processes, the hydrological and tectonic mechanisms involved remain unclear. In this study, we interpret a 3D reflection-seismic survey to delve into the geological factors related to these earthquakes. First, we document a basement-rooted fault on which the earthquake rupture occurred that extends above the targeted reservoir. Second, at the reservoir's stratigraphic level, anomalous subcircular features are recognized along the fault and are interpreted as resulting from fault-associated karst processes. These observations have implications for HF-induced seismicity, as they suggest hydraulic communication over a large (vertical) distance, reconciling the discrepancy between the culprit well trajectory and earthquake hypocenters. We speculate on how these newly identified geological factors could drive the sporadic appearance of induced seismicity and thus be utilized to avoid earthquake hazards.

Temporal Variations of Near‐Surface Anisotropy Induced by Hydraulic Fracturing at a Shale Play Site in Southwest China

AbstractKnowledge of the geometric properties of fractures and cracks in a petroleum reservoir is important to reservoir exploitation. When aligned and partially connected, fractures and cracks can act as conduits for fluid flow and thus can significantly increase the permeability of the reservoir. The aligned fractures and cracks, on the other hand, are an effective means to generate seismic anisotropy. In this study, we utilize the seismic data recorded by a vertical array installed in a shallow borehole at a shale play site in southwest China. By applying seismic interferometry to the ambient noise data recorded by 12 three‐component geophones, we extractPandSwaves propagating vertically along the borehole. TheSwaves show up to 20% velocity variations with respect to their polarization directions. Such largeSwave anisotropy can be explained by the horizontal transverse isotropic model and is likely caused by natural fractures that are widely present in the area and align approximately in the NE‐SW direction. During the 13‐day period of hydraulic fracking treatment, we also observe large and systematic temporal variations inSwave velocity, degree ofSwave polarization anisotropy, and fast polarization direction. By comparing our observations with normal strain changes calculated with a half‐space elastic model, we speculate that strain changes induced by hydraulic injection and fracturing are likely to be responsible for the observed temporal variations in seismic anisotropy. As such, seismic interferometry with shallow borehole acquisition might provide an alternative means to monitor hydraulic fracturing and wastewater injection in the future.

Preparation and performance of catalytic MOFs in microreactor

Abstract Reactions within the confined spaces of a microreactor often yield higher conversion and better selectivity as a result of enhanced transport processes. Traditional microfluidic reactors often constrain the fluid flow within fabricated microchannels leading to a large pressure gradient. This work employs the network of interconnecting channels defined by the strands of glass fibers in a glass fiber membrane as conduits for fluid flow, with the glass fibers as support for the MOF catalysts. Thus, a microreactor with a low pressure drop was obtained despite the narrow width of the flow channels (

Carbonic springs as distal manifestations of geothermal systems, highlighting the importance of fault pathways and hydrochemical mixing: Example from the Jemez Mountains, New Mexico

We examine a series of carbonic warm and hot springs in northern New Mexico, USA: 1) Tierra Amarilla springs 2) Penasco Springs and 3) Soda Dam, Jemez and Indian hot springs. Spring geochemistry is compared to waters from the Valles Caldera geothermal system and to groundwater in nearby sedimentary aquifers. Multiple hydrochemical tracers are applied to quantitatively evaluate flow paths and mixing at varying distances from the caldera. We test three hypotheses for source and transport of waters to Tierra Amarilla and Penasco Springs: San Juan basin origin, meteoric flow from the Nacimiento Mountains, and/or influence from the Valles Caldera geothermal system. Geochemically, carbonic spring groups are distinct from meteoric and sedimentary aquifer waters. Based on isotopes of He and Sr, and concentrations of Cl, SO4, Li and B, we interpret these carbonic springs to be distal manifestations of fluid circulation along faults with a mixture of Valles Caldera geothermal waters, local meteoric and Paleozoic aquifer waters, with the potential for small contributions from the San Juan Basin aquifers. Semi-confined fault conduits, the Jemez fault and Nacimiento fault systems, provide connectivity and help explain geochemical similarities and mixing trends within carbonic spring systems, and between these systems and the distal Valles Caldera. In addition, Penasco Springs are interpreted to reflect a component of outflow from the geothermal system that crosses the Nacimiento Mountain basement block along NE-trending faults. Input of deeply sourced waters can degrade water quality by contributing significant salinity and trace metals to groundwater at distances of >50 km from geothermal systems, with faults acting as conduits for subsurface fluid flow.

3‐D Seismic Investigation of a Gas Hydrate and Fluid Flow System on an Active Mid‐Ocean Ridge; Svyatogor Ridge, Fram Strait

AbstractTectonic settings play a large role in the development of fluid flow pathways for gas migrating through sedimentary strata. Gas hydrate systems worldwide are located on either the slopes of passive continental margins, often in large contourite deposits, or in accretionary wedges on subduction margins. The Svyatogor Ridge, however, located at the northwestern flank of the Knipovich Ridge and south of the Molloy Transform Fault (Fram Strait), is a gas hydrate system which is located on an actively spreading margin. Svyatogor Ridge has evidence of shallow gas accumulations; a strong BSR indicating a gas hydrate and underlying free gas system, and fluid flow pathways to the seafloor culminating in pockmarks. Using a high‐resolution P‐Cable 3‐D seismic survey, we investigate how tectonic and sedimentary regimes have influenced the formation of this well‐developed gas hydrate system. Large‐scale basement faults identified in the seismic data are interpreted as detachment faults, which have exhumed relatively young ultramafic rocks. These detachment faults act as conduits for fluid flow, and are responsible for the formation of folds in the overlying sediments that are breached by faults. We propose a model for fluid flow within this system whereby as sedimentary faults breach upward through the sedimentary strata, fluid is able to migrate further upward. We find that the tectonic regime on Svyatogor Ridge is the dominant driver of fluid migration and episodic release at the seafloor.

Fracture pattern of the Lower Paleozoic sedimentary cover in the Lublin Basin of southeastern Poland derived from seismic attribute analysis and structural restoration

We have characterized Late Devonian fracture systems in the northeastern part of the Lublin Basin in Poland using two independent approaches: (1) seismic data conditioning and volumetric attribute analysis and (2) structural restoration, geomechanical modeling, and fracture modeling. The study area was subjected to reverse faulting in the basement and fault-related folding at the end of Devonian. These late Devonian structures were not overprinted by later deformation events. We have applied a set of structurally oriented filters and seismic attributes aimed at highlighting discontinuities to reduce the seismic noise and improved the fracture visibility on structural steering volume. The main faults cutting intra-Neoproterozoic and intra-Ordovician horizons are principal east–west-striking reverse faults and minor northwest–southeast-oriented normal faults. Based on analysis of the seismic-scale faults, we have carried out fracture modeling for strike-slip and compressional stress fields, with a northwest–southeast-oriented axis of maximum compression. We have correlated tentative strikes for tensile, shear, and closing-mode fractures for both stress regimes, with fault-likelihood attribute maps. The observed fracture system can have developed in the strike-slip stress regime, although cracks generated due to gas overpressure, or of pre-Devonian age, are not excluded. The final fracture model may be extrapolated into Silurian strata, but the results should be perceived as a general approximation of structural trends due to significant differences in mechanical properties of Silurian shales and underlying Ordovician carbonates. Improved model calibration could be achieved after inspection of scanner image logs. We believe that understanding the fracture distribution within the gas-bearing Silurian strata may contribute to effective planning and performing of hydraulic fracturing because part of these fracture planes may be reopened and provide new conduits for fluid flow.

Subsurface fluid flow at an active cold seep area in the Qiongdongnan Basin, northern South China Sea

The active Haima cold seep sites were discovered by the remotely operated vehicle on the western part of the northern slope of South China Sea in 2015 and 2016. However, the subsurface structures in the seep area are not well studied, which prevents the further understanding of the evolution of fluid venting system in the active cold seep area. In 2017, a high-resolution 2D seismic line transecting the two main seep sites was acquired and processed. In this study, the subsurface structures were well resolved on the seismic profile. The new observations include the widespread subsurface fluid flow features (i.e., chimney structures and pockmarks) and the pervasively distributed magmatic activities. Seismic indicators for hydrothermal vents were also observed on the seismic section. This new discovery confirms the contribution of magmatic activities to the evolution of subsurface fluid flow in the study area. Minor faults under the recognizable resolution of seismic profile, which can act as conduits for the subsurface fluid flow, were also identified in the fine-grained sediment sequences. Overall, these results provide new insights into the evolution of subsurface fluid flow in the study area.

Modelling of hydrothermal fluid flow and structural architecture in an extensional basin, Ngakuru Graben, Taupo Rift, New Zealand

Present-day geothermal activity on the margins of the Ngakuru graben and evidence of fossil hydrothermal activity in the central graben suggest that a graben-wide system of permeable intersecting faults acts as the principal conduit for fluid flow to the surface. We have developed numerical models of fluid and heat flow in a regional-scale 2-D cross-section of the Ngakuru Graben. The models incorporate simplified representations of two ‘end-member’ fault architectures (one symmetric at depth, the other highly asymmetric) which are consistent with the surface locations and dips of the Ngakuru graben faults. The models are used to explore controls on buoyancy-driven convective fluid flow which could explain the differences between the past and present hydrothermal systems associated with these faults.The models show that the surface flows from the faults are strongly controlled by the fault permeability, the fault system architecture and the location of the heat source with respect to the faults in the graben. In particular, fault intersections at depth allow exchange of fluid between faults, and the location of the heat source on the footwall of normal faults can facilitate upflow along those faults. These controls give rise to two distinct fluid flow regimes in the fault network. The first, a regular flow regime, is characterised by a nearly unchanging pattern of fluid flow vectors within the fault network as the fault permeability evolves. In the second, complex flow regime, the surface flows depend strongly on fault permeability, and can fluctuate in an erratic manner. The direction of flow within faults can reverse in both regimes as fault permeability changes.Both flow regimes provide insights into the differences between the present-day and fossil geothermal systems in the Ngakuru graben. Hydrothermal upflow along the Paeroa fault seems to have occurred, possibly continuously, for tens of thousands of years, while upflow in other faults in the graben has switched on and off during the same period. An asymmetric graben architecture with the Paeroa being the major boundary fault will facilitate the predominant upflow along this fault. Upflow on the axial faults is more difficult to explain with this modelling. It occurs most easily with an asymmetric graben architecture and heat sources close to the graben axis (which could be associated with remnant heat from recent eruptions from Okataina Volcanic Centre). Temporal changes in upflow can also be associated with acceleration and deceleration of fault activity if this is considered a proxy for fault permeability. Other explanations for temporal variations in hydrothermal activity not explored here are different permeability on different faults, and different permeability along fault strike.

Implications of meso- to micro-scale deformation for fault sealing capacity: Insights from the Lenghu5 fold-and-thrust belt, Qaidam Basin, NE Tibetan Plateau

As faults can be barriers to or conduits for fluid flow, it is critical to understand fault seal processes and their effects on the sealing capacity of a fault zone. Apart from the stratigraphic juxtaposition between the hanging wall and footwall, the development of fault rocks is of great importance in changing the sealing capacity of a fault zone. Therefore, field-based structural analysis has been employed to identify the meso-scale and micro-scale deformation features and to understand their effects on modifying the porosity of fault rocks. In this study, the Lenghu5 fold-and-thrust belt (northern Qaidam Basin, NE Tibetan Plateau), with well-exposed outcrops, was selected as an example for meso-scale outcrop mapping and SEM (Scanning Electron Microscope) micro-scale structural analysis. The detailed outcrop maps enabled us to link the samples with meso-scale fault architecture. The representative rock samples, collected in both the fault zones and the undeformed hanging walls/footwalls, were studied by SEM micro-structural analysis to identify the deformation features at the micro-scale and evaluate their influences on the fluid flow properties of the fault rocks. Based on the multi-scale structural analyses, the deformation mechanisms accounting for porosity reduction in the fault rocks have been identified, which are clay smearing, phyllosilicate-framework networking and cataclasis. The sealing capacity is highly dependent on the clay content: high concentrations of clay minerals in fault rocks are likely to form continuous clay smears or micro- clay smears between framework silicates, which can significantly decrease the porosity of the fault rocks. However, there is no direct link between the fault rocks and host rocks. Similar stratigraphic juxtapositions can generate fault rocks with very different magnitudes of porosity reduction. The resultant fault rocks can only be predicted only when the fault throw is smaller than the thickness of a faulted bed, in which scenario self-juxtaposition forms between the hanging wall and footwall.

Effect of brine-CO2 fracture flow on velocity and electrical resistivity of naturally fractured tight sandstones

Fracture networks inside geologic [Formula: see text] storage reservoirs can serve as the primary fluid flow conduit, particularly in low-permeability formations. Although some experiments focus on the geophysical properties of brine- and [Formula: see text]-saturated rocks during matrix flow, geophysical monitoring of fracture flow when [Formula: see text] displaces brine inside the fracture seems to be overlooked. We have conducted laboratory geophysical monitoring of fluid flow in a naturally fractured tight sandstone during brine and liquid [Formula: see text] injection. For the experiment, the low-porosity, low-permeability, naturally fractured core sample from the Triassic De Geerdalen Formation was acquired from the Longyearbyen [Formula: see text] storage pilot at Svalbard, Norway. Stress dependence, hysteresis, and the influence of fluid-rock interactions on fracture permeability were investigated. The results suggest that in addition to stress level and pore pressure, mobility and fluid type can affect fracture permeability during loading and unloading cycles. Moreover, the fluid-rock interaction may impact volumetric strain and consequently fracture permeability through swelling and dry out during water and [Formula: see text] injection, respectively. Acoustic velocity and electrical resistivity were measured continuously in the axial direction and three radial levels. Geophysical monitoring of fracture flow revealed that the axial P-wave velocity and axial electrical resistivity are more sensitive to saturation change than the axial S-wave, radial P-wave, and radial resistivity measurements when [Formula: see text] was displacing brine, and the matrix flow was negligible. The marginal decreases of acoustic velocity (maximum 1.6% for axial [Formula: see text]) compared with the 11% increase in axial electrical resistivity suggest that in the case of dominant fracture flow within the fractured tight reservoirs, the use of electrical resistivity methods have a clear advantage compared with seismic methods to monitor [Formula: see text] plume. The knowledge learned from such experiments can be useful for monitoring geologic [Formula: see text] storage in which the primary fluid flow conduit is the fracture network.

Basin-scale structure control of Carlin-style gold deposits in central Southwestern Guizhou, China: Insights from seismic reflection profiles and gravity data

Carlin-style gold deposits are widely distributed in Southwestern Guizhou, China. Research has dominantly focused on deposit-scale geology and structural control of mineralization. The relationship between the gold deposits and regional structures, in particular their control on the formation and distribution of those deposits is less well understood. Here we use seismic survey and gravity data to reveal the basin-scale structure control of the gold deposits in central Southwestern Guizhou. The seismic reflection profiles show strong reflection horizons including Upper Permian coal measures, and Dongwu and Guangxi unconformities. The seismic data provide important evidence of the basinal structural style and the relationship between fault-related folding and the Carlin-style gold deposits. Regional gravity data also revealed several paleo-uplifts, which appear to control the distribution of Carlin-style gold deposits.The Carlin-style gold deposits are spatially and temporally associated with fault-related folds. Based on their location, we classify the gold deposits into two types, (1) low-angle thrust-controlled deposits; and (2) high-angle reverse fault-related deposits. In the low-angle thrust-controlled deposits, main thrusts are listric, strike NW-SE and dip southwest. These thrusts detach into coal measures, tuffs and volcanic rocks and are bedding-parallel in the vicinity of the Dongwu unconformity. Gold ore bodies are found in the thrusts and characterized by cutting-layer veins near the surface and bedding-parallel veins at depth. The high-angle reverse fault-related deposits are located in the hinge of northeast-southwest-striking fault-related folds, with high-angle reverse faults near the hinge of folds crosscutting the Upper Permian coal measures, volcanic rocks and Dongwu unconformity, and then into the limestone of Middle Permian Maokou Formation. Ore bodies are bedding-parallel in anticline culminations where interlayer fracture zones in Upper Permian coal measures and volcanic rocks are generated by high-angle reverse faulting.We consider that the formation of the gold deposits is part of the tectonic evolution in the area. The two sets of NW-SE- and NE-SW-striking fault-related folds were successively formed during the closure of eastern Tethys Ocean in Late Triassic, and major gold deposits formed in the fault-related folds. The Dongwu unconformity and faults provided conduits for ore fluid flow, and the coal measures and the tuffs of Dachang Member acted as detachment layers and hosts for ore deposition.

Pyrite-walled tube structures in a Mesoproterozoic sediment-hosted metal sulfide deposit

Unusual decimeter-scale structures occur in the sediment-hosted Black Butte Copper Mine Project deposit within lower Mesoproterozoic strata of the Belt Supergroup, Montana. These low domal and stratiform lenses are made up of millimeter-scale, hollow or mineral-filled tubes bounded by pyrite walls. X-ray micro−computed tomography (micro-CT) shows that the tube structures are similar to the porous fabric of modern diffuse hydrothermal vents, and they do not resemble textures associated with the mineralization of known microbial communities. We determined the sulfur isotopic composition of sulfide minerals with in situ secondary ion mass spectrometry (SIMS) and of texture-specific sulfate phases with multicollector−inductively coupled plasma−mass spectrometry (MC-ICP-MS). The sedimentological setting, ore paragenesis, sulfur isotope systematics, and porosity structure of these porous precipitates constrain the site of their formation to above the sediment-water interface where metalliferous hydrothermal fluids vented into the overlying water column. These data constrain the geochemistry of the Mesoproterozoic sediment-water interface and the site of deposition for copper-cobalt-silver mineralization. Metals in the hydrothermal fluids titrated sulfide in seawater to create tortuous fluid-flow conduits. Pyrite that precipitated at the vent sites exhibits large sulfur isotope fractionation (>50‰), which indicates a close association between the vents and sulfate-reducing microbiota. In the subsurface, base metal sulfides precipitated from sulfide formed during the reduction of early diagenetic barite, also ultimately derived from seawater. This model suggests dynamic bottom-water redox conditions at the vent site driven by the interplay between sulfate-reducing organisms and metalliferous fluid effluence.

Element mobility during regional metamorphism in crustal and subduction zone environments with a focus on the rare earth elements (REE)

This paper explores bulk-rock geochemical data for a wide array of metamorphosed mafic, quartzo-feldspathic, pelitic, and metacarbonate rocks using a quantitative mass-balance approach to assess fluid-driven element mobility—particularly of the rare earth elements (REE)—in regional metamorphic and some high-pressure subduction zone environments (40 examples; over 240 individual analyses). Most examples are from focused fluid flow settings, such as veins and lithologic contacts, where fluxes are large and metasomatic signals are thus strong. A variety of REE behaviors are observed, including little or no REE mobility (roughly a third of the data set); light REE (LREE), mid-REE (MREE), and/or heavy (HREE) mobility; europium “anomalies”; overall REE losses; and local REE redistribution. The REE are typically fractionated by mass transfer, with the exception of several examples that underwent fairly uniform overall losses of REE. The fractionation reflects strong mineralogical controls on REE uptake/loss by a comparatively small number of phases. Examples include: HREE mass changes associated with garnet, xenotime, and sphene; LREE and MREE changes associated with apatite, monazite, and allanite; and Eu changes associated with plagioclase and lawsonite. As mineralogy is a dominant control, the nature of the metasomatism is not strongly correlated with metamorphic grade, other than obvious mineralogical differences between settings (e.g., plagioclase in Barrovian metamorphism, lawsonite in subduction zones). Extensive mobilization of non-REE major and trace elements can happen without significant open-system transport of the REE. If REE mobility occurs, it is always accompanied by mobilization of other non-REE. When mobile, neighboring REE (e.g., Sm and Nd) typically have strongly correlated mass changes indicating that both were mobilized to about the same degree. Although individual examples of metasomatism can show correlations between patterns of mass transfer for the REE and the non-REE, little such correlation is evident across the entire data set, with the exception of P. Once again, this highlights the importance of individual minerals in controlling REE systematics. Broad correlations of REE and P mobility suggest REE transport by P complexes, or REE and P transport together by some other complexing agent. Mass changes for REE and Y are more strongly coupled, reflecting the geochemical similarity of these elements and perhaps indicating a role for Y complexing as well. The REE are the most mobile of the high field strength elements (HFSE). On a percentage mass basis, the amount of HFSE mobility decreases roughly in the order: REE > U > Nb > Ti > Th ~ Zr. Th mobility is rare but when present is positively correlated with U and REE mobility. The mobility of the more refractory HFSE is low in aqueous fluids, but is a larger concern in more extreme environments such as magmatic/magmatic-hydrothermal systems, charnockite metamorphism, and supercritical fluids in high-pressure/ultrahigh-pressure settings. The mobility of certain HFSE (e.g., Nb) can be large enough to affect rock plotting positions on petrotectonic discrimination diagrams. Potassium and related (Rb, Ba, Cs) large-ion lithophile elements (LILE) are typically lost in association with mica breakdown. As the data set focuses on high fluid flow environments, LILE changes will likely be smaller for rocks that undergo less fluid-rock interaction. Gains of K and related LILE are coupled to volatile gain and Na loss, consistent with fluid flow down temperature gradients, or infiltration from K-rich sources (e.g., pegmatites). In Barrovian settings, two other mass transfer trends are evident in addition to K mass transfer. First, silica loss is coupled to volatile loss, illustrating the dependence of silica mass transfer on devolatilization. Most of the silica loss reflects local mass transfer into adjacent vein fluid flow conduits were additional silica is precipitated; indeed, wallrock inclusions in veins can be highly silicified. Second, Na and Ca mass gains and losses are well correlated in the Barrovian examples, reflecting control of plagioclase growth or destruction. Strontium and Pb behaviors also appear to be largely related to plagioclase behavior (in subduction settings, this role can be played by phases such as lawsonite or epidote group minerals). Carbon dioxide mass transfer by conventional devolatilization as well as near-stoichiometric CaCO 3 dissolution or precipitation is represented in the data set. Determining the relative roles of these processes as functions of metamorphic grade, intensity of fluid-rock interaction, and tectonic setting will be an important challenge for future research.