2019 Vol. 30, No. 4
The Binh Do Pb-Zn deposit in the Phu Luong region (Thai Nguyen Province, northern Vietnam) is located on the southern margin of the South China Block. The fault-controlled Pb-Zn orebodies are mainly hosted in Upper Paleozoic carbonate formations. In order to reveal the mineralization type and metallogenesis of this deposit, multi-isotopic (S, Pb, H and O) analyses on typical ore and gangue minerals were conducted. The average ore sulfide δ34S∑S value is 4.3‰, suggestive of magmatic sulfur. The ore sulfide Pb isotope compositions are homogeneous, with the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 18.501 to 18.673, 15.707 to 15.798, and 38.911 to 39.428, respectively. Lead isotope model ages of the ore sulfides (240-220 Ma) are consistent with the timing of regional Triassic S-type granite emplacement (250-220 Ma), suggesting that the metals may have been granite-derived. The quartz δDV-SMOW (-82.4‰ to -70.5‰) and δ18OH2O (-0.4‰ to +6.4‰) values suggest that the ore-forming fluids were composed of mixed magmatic and meteoric waters. Combined with the geological features of the Pb-Zn deposit in the region, we propose that the Pb-Zn deposits belong to magmatic-hydrothermal type, rather than MVT-type as previously suggested. The Triassic granites may have contributed the ore-forming material and heat that drove the hydrothermal system. The ore-forming fluids may have migrated into interlayer faults and fractures of the carbonate strata, diluted by subsurface meteoric water and deposited successively the vein-type and stratiform-type Pb-Zn ores.
New zircon U-Pb dates obtained by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), whole-rock geochemical data and Sm-Nd and Rb-Sr isotopic data are presented for miarolitic alkaline granites, porphyritic syenite and rhyolites of the Nianzishan A-type granitoid complex (NAGC) in the Great Xing'an Range-Songliao Basin in Northeast (NE) China. New crystallization ages of 112.95±0.93 and 114.1±1.71 Ma for granite and 118.6±0.51 Ma for porphyritic syenite were determined by high-precision LA-ICP-MS. The εNd(t) of the rocks range from +1.85 to +2.06, with Nd model ages (TDM1) from 671 to 821 Ma, indicating that the NAGC originated from juvenile source rocks and exhibits geochemical characteristics of A1-and AA-type granite which formed in an extensional setting. We attribute the magmatism to regional extension and lithospheric thinning caused by the subduction of the western Pacific Plate about 120 to 100 Ma.
Strategic emerging minerals such as lithium, beryllium, niobium and tantalum are the most important rare metals currently, especially with the increasing demand of emerging industries on rare metals in China. The Jiajika deposit with a complete Li-Be-Nb-Ta metallogenic series is the largest pegmatite type rare metal deposit in China at present. In this paper, systematic researches of geochronology and petrogeochemistry were carried out to understand the genetic relationships between mineralization and magma evolution in the Jiajika deposit, which might be helpful to further rare-element prospecting in Songpan-Garze area. Zircon LA-ICP-MS U-Pb dating yields a concordia age of 217±1.1 Ma and a weighted mean 206Pb/238U age of 217±0.84 Ma for the aplite from the No. 308 pegmatite. Cassiterite LA-MC-ICPMS dating yields concordant ages of 211±4.6 Ma for the No. 308 pegmatite vein and 198±4.4 Ma for the No. 133 pegmatite vein, indicating that the rare metal mineralization mainly occurred in the Late Indosinian Period, further suggesting that the granites, aplites and pegmatites in Jiajika formed during a relatively stable stage after the intense orogeny of the Indosinian cycle. The rare metal-bearing granitic rocks and pegmatites show a clear linear relationship between A/CNK and A/NK and are enriched in total alkalis and depleted in CaO, FeO, MnO, MgO, Ba and Sr. All barren rocks and mineralized rocks feature similar rare earth element and trace element geochemical patterns. Thus, these characteristics indicate that the aplites and pegmatites represent the highly differentiated products of the two-mica granite (MaG) in this area, which is the most likely parent magma. During the evolution of magma, strong alkali metasomatism occurred between the melt phase and the volatile-rich fluid phase; as a result, large-scale rare metal mineralization occurred in certain structural zones of the pegmatite veins in the Jiajika deposit.
Beach rock, which forms at the intertidal zone, is a natural barrier to protect beach and island from wave erosion. The formation mechanism of beach rocks is significant in the study of surface carbonate diagenesis and protection of island. Beach rocks in Qilian Islets and Cays were formed about 500-700 a BP, neither its composition nor sedimentary structure experienced intense post-reformation. Beach rocks in Qilian Islets and Cays are mainly composed of reef-building skeletal fragments and bioclasts without terrigenous sediments. This study focused on the types and morphologies of cements in beach rocks of Qilian Islets and Cays, and its cementation mechanisms and influencing factors. Biological activities, such as micritization caused by microbial activities and algae binding action, play an important role in the initial stage of bioclast transformation and promote the subsequent early marine and early meteoric cementation. Acicular aragonite induced by early marine cementation is well developed in beach rocks, especially in those samples from Medium Islet. Early meteoric cementation is not common as marine cementation, generally presenting granular and meniscus cements. The main factors affecting the formation and development of beach rocks in Qilian Islets and Cays include sediment source, hydrodynamic condition, climate, sea level change and anthropogenic impacts.
Compositionally and texturally zoned diabase dykes and sills occur in the outer zone of the Emeishan large igneous province (ELIP) in the southern Guizhou Province, Southwest China. Based on the detailed petrology, whole rock geochemistry, zircon U-Pb geochronology and Hf isotopes and clinopyroxene mineral compositions studies, we investigate a representative diabase sill in the Luodian region with a view to understanding its petrogenesis and tectonic implications. Formed as composite zoned sub-volcanic intrusion, the diabase sill is characterized by gabbros and diabases in the inner zone and amygdaloidal diabases sporadically in the chilled zone within the upper sill margin. The diabasic and gabbroic rocks are composed of quartz-free and quartz-bearing groups. The quartz-free group rocks have low SiO2 (45.7 wt.%-49.5 wt.%), moderate MgO (5.66 wt.%-7.88 wt.%), high TiO2 (2.54 wt.%-3.65 wt.%), and Ti/Y values (536-747), corresponding to high-Ti type rocks. The quartz-bearing group rocks have higher SiO2 (49.8 wt.%-51.7 wt.%) and lower MgO (4.23 wt.%-4.74 wt.%), higher TiO2 (3.16 wt.%-3.63 wt.%), but lower Ti/Y values (399-419) than the quartz-free group ones, and thus belong to the low-Ti type. Both groups of rocks are enriched in LREE and LILE with negative Nb-Ta anomalies, and show broad tholeiitic affinity. The precursor magma of the high-Ti rocks might have originated from a source composed of mantle plume and subcontinental lithosphere mantle components, with minor crustal contamination during ascending. The magma of the low-Ti rocks was produced by mingling of the high-Ti diabasic rocks with minor injected intermediate-acidic magma plugs or blebs, suggesting magma mingling as one of the effective ways to change the high-Ti to low-Ti rocks of the ELIP. The diabasic sill underwent a rapid cooling event probably in response to a rapid tectonic uplift event, which probably occurred in the waning stage of ELIP during transition between the Middle and Late Permian after the domal uplift induced by the mantle-plume or in the Late Jurassic.
Two kinds of basalts with different chemical compositions were obtained in the Sanshui Basin, they share the same eruption period. Although they have significant differences in major and trace element concentrations, their isotopic ratios suggest a similar magma source. Based on mineral geochemical analysis, orthopyroxene with reaction rim and zoned clinopyroxene are observed in Zidong (ZD) basalts, but not found in Wangjiegang (WJG) basalts. Linear scanning of these minerals suggests compositional variation between within-plate tholeiite and within-plate alkali-basalt. Presence of a double-layer magma chamber under the Sanshui Basin, and occurrence of magma mixing between upper and lower chambers is proposed. This magma mixing leads to different chemical composition and mineral constitution of two kinds of basalts, as well as reaction rim and compositional variation of minerals in ZD basalts.
The 150-km-long Feather River ultramafic belt (FRB) of the northern Sierra Nevada, California, consists of serpentinized ultramafic rocks, gabbroic rocks, with lesser amounts of amphibolitic rocks. The gabbroic rocks contain metagabbro and dikes within it. Based on the electron microprobe analyses, the metagabbro consists of typical igneous composition for clinopyroxene and early hornblende, indicating that they bear low grade metamorphism. The gabbroic rocks show Nb and Ta depletion in primitive-mantle normalized plots that is similar to typical island arc rocks. We present that the metagabbro within the ultramafic rocks is forming in the suprasubduction zone setting. Tectonic models are presented for the metagabbro and amphibolitic rocks in FRB. The low P burial metamorphism of the upper plate metagabbro and the high grade amphibolitic rocks are typical of relationships of upper plate ophiolites to metamorphic soles. The amphibolitic rocks record as metamorphic sole forming during subduction initiation beneath the ultramafic rocks and metagabbro. The unusual and protracted tectonic history of the FRB is similar to other ophiolite belts of the Cordillera of California but differs in the lack of crustal rocks.
The Chezhen depression, located in the south of Bohai Bay Basin, is an oil-producing basin in China. The third and fourth members of the Shahejie Formation (Es3 and Es4) are the main source rock series in the Chezhen depression. Widespread overpressures occurred in the Es3 and Es4 from the depths of approximately 2 000 to 4 600 m, with the maximum pressure coefficient of 1.98 from drillstem tests (DST). Among the sonic, resistivity and density logs, sonic-log is the only reliable pressure indicator and can be used to predict the pore pressure with Eaton's method. All the overpressured mudstones in the source rock series have higher acoustic traveltimes compared with normally pressured mudstones at a given depth. The overpressured mudstones in the Es3 and Es4 units are characterized by a normal geothermal gradient, high average density values up to 2.5 g/cm3, strong present-day hydrocarbon generation capability, abundant mature organic matter and high contents of residual hydrocarbons estimated by the Rock-Eval S1 values and chloroform-soluble bitumen "A" values. All suggest that the dominant mechanism for overpressure in the mudstones of source rock series in the Chezhen depression is hydrocarbon generation. A comparison between the matrix porosity of the normally pressured sandstones and overpressured sandstones, the quantitative evaluation of porosity loss caused by compaction and the conventional thin section inspection demonstrate that the sandstones in the Chezhen depression were normally compacted. The high contents of hydrocarbons in the overpressured reservoirs prove that the overpressure in the sandstones of the source rock series was caused by pressure transmission from the source rocks.
This paper studied seismic imaging of the sedimentary system of the Nenjiang Formation in the Northern Songliao Basin based on seismic sedimentology. An accurate and detailed depiction and explanation is provided for underground geological bodies within a relative geological period using the stratal slice technology, based on three-order sequence correlations of well logging and seismic data for the purpose of obtaining high-resolution pictures of the sedimentary system. Research results have revealed that the sedimentary system of the Upper Cretaceous Nenjiang Formation in the Northern Songliao Basin includes meandering streams, anastomosing streams, lake deltas, and sediment gravity flow channels. Based on seismic imaging analysis, the genesis and seismic geomorphology of the sedimentary system of the Nenjiang Formation are explored in order to understand the spatial distribution of typical sedimentary bodies and the evolution of streams in the Nenjiang Formation. According to the research results, the sedimentation of the Nenjiang Formation was subject to the delta system in the east and northeast of the formation. The provenance in the northeastern part played a dominant role during the deposition of the Nenjiang Formation for some time; after the earlier maximum flooding in the second and third members of the Nenjiang Formation, the northeastern system began to decline and was gradually replaced by the eastern system. Stratal slices have revealed that a well-developed gravity flow channel system was developed in the first member of the Nenjiang Formation, and massive slip blocks occurred in the second and third members of the formation. The research results indicated that the large gravity flow channel system in the first member of the Nenjiang Formation was formed by streams that emptied directly into the lake; and the slip blocks in the second and third members were the results of gravity sliding of sediments along steep slopes at the delta front.
To describe the distribution of sandstone reservoirs between wells finely, this paper takes the sandstone reservoir of Layer Nm Ⅱ -4 in Qinhuangdao 32-6 Oilfield for example, and uses the seismic forward simulation and well loggings to study the channel sandstone reservoir. Under the guidance of the modern rivers and outcrops sandstone distribution pattern, the predicting limitations of the seismic forward simulation about channel sandstone boundaries such as mudstone interlayer between channel sandstone and elevation distance between adjacent channel sandstone are clear. The research shows that the mudstone interlayer can be described by seismic forward simulation seismic when the mudstone interlayer is thicker than 2 m and the channel sandstone is thicker than 10 m because of the appearance of the seismic peak when the main frequency of seismic data is nearly 60 Hz. And the elevation distance between adjacent channel sandstone can be described by the seismic forward simulation when elevation distance is longer than 6 m and the channel sandstone is thicker than 10 m because of the appearance of the seismic peak. And the seismic waveform features of single channel sandstone boundaries such as elevation distance between channels, overbank sandstone and abandoned channels. Under the study mentioned above, the single channel boundaries are described in Layer Nm Ⅱ -4 of Qinhuangdao 32-6 Oilfield, and the predicting boundaries are confirmed by the chemical tracers. The results show that the channel sandstone reservoir architecture characterization can be improved by the seismic forward simulation.
The convergence of the multi-layered continental lithospheres with variable and complex thermal and rheological properties results in various modes of continental collision with distinct deformation behavior of the lithospheric mantle. Using high-resolution thermo-mechanical numerical models, we systematically investigated the effects of crustal rheological strength and the convergence rate on the continental subduction mode. The model results reveal three basic modes of continental subduction, including slab break-off, steep subduction and continental flat-slab subduction. Whether lithospheric mantle of the overriding plate retreats or not during convergence enables the division of the first two modes into two sub-types, which are dominated by the crustal rheological strength. The mode of slab break-off develops under the conditions of low/moderate rheological strength of the continental crust and low convergence rate. In contrast, continental flat-slab subduction favors the strong crust and the high convergence rate. Otherwise, continental steep subduction occurs. The numerical results provide further implications for Geodynamics conditions and physical processes of different modes of continental collision that occur in nature.
Due to heterogeneous pore distributions within shales, petrophysical properties of shales determined by scanning electron microscopy (SEM) and X-ray computed tomography (CT) methods strongly depend on the observed domain size (analysis scale). In this paper, the influence of the analysis scale on areal and bulk porosities and pore size distribution (PSD) for lacustrine shales from the Dongying sag of Bohai Bay Basin, China were investigated using broad ion beam (BIB)-SEM and X-ray CT methods. The BIB-SEM cross-sections with high imaging resolution (10 nm/pixel) and a large field of view (>1 mm2) mainly describe the 2D nanoscale pore system in the two shales (samples F41#-2 and Y556#-1), while CT-based 3D reconstructions with resolutions of 0.42 (F41#-1) and 0.5 μm/pixel (H172#-1) reflect the 3D sub-micron pore system. The results indicate that the areal (bulk) porosity exhibits a multiple power-law distribution with increasing analysis area (volume), which can be used to extrapolate the porosity of a given area (volume). Based on SEM and CT investigations, the sizes of the minimum representative elementary areas (REAs) and volumes (REVs) were determined respectively, which are closely associated with the heterogeneousness of the pore system. Minimum REAs are proposed to be 2.93×104 (F41#-2) and 0.91×104 μm2 (Y556#-1), and minimum REVs are 0.016 (F41#-1) and 0.027 mm3 (H172#-1). As the analyzed areas (volumes) are larger than the minimum REA (REV), obtained 2D (3D) PSDs are comparable to each other and can be considered to reflect the shale PSD. These results provide insights into the porosity and PSD characterization of shales by SEM and X-ray CT methods.
The effect of operating conditions on the time-dependent X-ray intensity variation is of great importance for the optimal EPMA conditions for accurate determinations of various elements in carbonate minerals. Beam diameters of 0, 1, 2, 5, 10, 15, and 20 μm, and beam currents of 3, 5, 10, 20, and 50 nA were tested. Ca, Mg, Zn, and Sr were found to be more sensitive to electron beam irradiation as compared to other elements, and small currents and large beam diameters minimized the timedependent X-ray intensity variations. We determined the optimal EPMA operating conditions for elements in carbonate:10 μm and 5 nA for calcite; 10 μm and 10 nA for dolomite; 5 μm and 10 nA or 10 μm and 20 nA for strontianite; and 20 nA and 5 μm for other carbonate. Elements sensitive to electron beam irradiation should be determined first. In addition, silicate minerals are preferred as standards rather than carbonate minerals.
This paper describes parallel simulation of the memory/computation-intensive acoustic wave equation with CPU template buffer optimization. Considering the 8-core CPU shared storage platform as an example, we obtain a one-time speed-up ratio of 6.7×compared with the serial program by using a coarse-grained OpenMP parallel scheme. Then, data is vectorized on the template buffer using the single instruction-multiple data (SIMD) technique to further exploit the computing potential of the CPUs. We apply an 8-channel parallel vector to simulate seismic wavefields with the 256-bit advanced vector extensions (AVX) instruction set. This increases the computing bandwidth, thus eliminating a significant volume of the computing instructions and obtaining a secondary speed-up ratio of 3-7×. In addition, we use 32-byte data alignment, shortest data direction vectorization, and loop tiling optimization algorithm to achieve faster program execution. Finally, we analyze the factors affecting the secondary speed-up of AVX through three-dimensional modeling experiments with the salt model. The results indicate that the memory, cache, and register can better cooperate with each other and the speed-up is increased by optimizing the AVX algorithm.
Semblance, a measure of multi-trace coherence, has been used extensively in seismic data processing and interpretation such as velocity analysis and fault detection. The traditional algorithm has a difficulty at zero-crossings of seismic recordings. This problem is alleviated by applying a smoothing window at the cost of losing vertical resolutions. In this paper, we improve the algorithm by computing semblance from complex traces. Our initial results show that the complex semblance is smooth at zero-crossings. Because the smoothing time window becomes unnecessary, the higher vertical resolution can be achieved by using small windows or none. Some geological features, like faults and unconformities, appear clearer and easier to identify with the complex semblance. As the advantages are obvious and the implementation is straight-forward with the Hilbert transform, this new algorithm may replace the traditional one in future applications.
Fault identification in vegetated area (e.g., grassland) is a major challenge compared to that in outcrop areas. To identify concealed faults in a grassland covered area, a hybrid method combining the temperature vegetation dryness index (TVDI) and the singularity index was proposed in this paper to extract TVDI anomalies associated with concealed fractures in the Sonid Left Banner Grassland, Inner Mongolia, North China. In the triangle space of LST/NDVI (land surface temperature/normalized difference vegetation index), scattered points were concentrated in the areas of partial and full cover, while few data points were in the areas of bare soil with low values of NDVI and high values of LST; this result is consistent with the semiarid grassland landscape of the study area. Although TVDI imaging shows an obvious linear pattern with an NE-NNE trend, which indicates the existence of concealed faults, the surrounding background weakened and reduced the significance of the anomalies. To better delineate the concealed faults, the singularity index was employed to remove the influence of the background and enhance the TVDI anomalies associated with the concealed faults. The TVDI imaging and singularity index mapping showed NNE and NE orientations; this finding is consistent with the regional tectonic framework. Geological mapping footprints showed that the hybrid method is useful to identify concealed faults in covered areas of grassland.
The ligand-stabilized soluble Mn(Ⅲ) recognized as active intermediate can potentially mediate the attenuation of contaminants. In this study, the abiotic degradation behaviors of methyl parathion in the ligand stabilized Mn(Ⅲ)-sulfite system were investigated. The results showed that the yield of soluble Mn(Ⅲ) produced from the redox reaction of MnO2 and oxalic acid was dependent linearly on the dosage of MnO2 and caused the decomposition of methyl parathion up to 50.1% in Mn(Ⅲ)-sulfite system after 30 minutes. The fitted pseudo-first-order reaction constants of methyl parathion degradation increased with the increasing of the amount of produced Mn(Ⅲ) but was not effected linearly by the addition of sulfite. Other ligands, including pyrophosphate and oxalic acid, acted as effective complexing agents to stabilize soluble Mn(Ⅲ), and exhibited competitive effect on methyl parathion degradation with sulfite. The formation of Mn(Ⅲ)-sulfite complexes is the critical step in the system to produce abundant reactive oxygen species identified as SO3-· to facilitate methyl parathion degradation. The hydrolysis and oxidation of methyl parathion were acknowledged as two primary transformation mechanisms in Mn(Ⅲ)-sulfite system. These findings indicate that naturally ligands-stabilized soluble Mn(Ⅲ) can be generated and could oxidatively decompose organophosphate pesticides such as methyl parathion.
The exploitation of thermal water and the mix of cold water changed the properties of geofluid in shallow reservoir, which altered the concentration of the chemical constitutes and continuously built new water-rock reaction. This paper deduced reservoir pressure and temperature variation tendency from 2004 to 2013, analyzed the change of some components in the shallow reservoir water, and finally obtained the evolution of the shallow geothermal water with hydrogeochemical model. The results show the reservoir pressure decreased significantly compared with the slight decline of reservoir temperature, and much cold groundwater infiltrated into the shallow reservoir, which affected the solubility of SiO2 and led to precipitation, the increased CO2 in shallow reservoir promoted the dissolution of aluminosilicate. Calcite and kaolinite precipitation zone has extended to the north in the field, which influenced the porosity of the reservoir rock.