Abstract The borehole electrical imaging log offers general visual borehole wall, leaving no doubt that the conductivity contrast is sufficient to obtain a qualitative gain-size distribution of rocks. In this study, an automatic grain-size classification method is proposed using gray values of borehole electrical images from Baikouquan Formation in Mahu Depression. The first stage is comparing electrical images with cores. Gravels, sands, silts and clays are all discovered in the cores. The gravels are “mottled” in electrical images, and the bigger the spots, the coarser the gravels. The images of sands are homogeneous bright colored, and the coarser the sandy grains, the brighter the images. The electrical images of silts and clays are homogeneous brown and dark-brown colored. The second stage is auto-discriminating four categories of grain sizes roughly using averages and variances of gray values. The variances of gray values of gravels are high, whereas those of sands are medium. The gray averages of silts are between 160 and 220, whereas those of clays are larger than 200. The third stage is auto-classifying three kinds of gravels or sands finely using frequency distribution of gray values. The gray values of frequency peaks of cobbles are less than 50 and frequencies are larger than 15%, whereas those of pebbles are less than 50 or larger than 200 and frequencies are between 10% and 20%; almost gray frequencies of granules are less than 10%. The dominated gray values of coarse sandstones, medium sandstones and fine sandstones are less than 50, between 50 and 160 and ranged from 160 to 240, respectively. The proposed method is demonstrated to be useful and fast to auto-classify grain size of various rocks in conglomeratic environments.
Distributive fluvial systems (DFS) are widespread in drylands in the northwestern China. Analyzing differences in fluvial morphology in drylands is beneficial for studying ancient rock records and the extra-terrestrial surface environment. The remote sensing image, characterized by real-time and possibility of repeated observations, is a vital tool for recording and comparing fluvial systems in drylands. Satellite remote sensing technology is a method of investigating fluvial morphologies. Due to the limited accuracy of satellite imagery, there are few reports on the detailed description of the fluvial system in drylands of NW China. We analyze the pattern of fluvial morphology changes in the Golmud distributive fluvial system (DFS) in the Qaidam Basin, northwestern China, using satellite remote sensing and unmanned aerial vehicles (UAV). Firstly, we use Google Earth real-time image data, historical image data, and radar digital elevation data to extract geomorphological information; then the UAV remote sensing image data were used to interpret fluvial network information; finally, we use the gray-scale differential vector method to describe the fluvial morphologies. Three zones have been identified in the Golmud DFS: the proximal, the medial, and the distal, by comparing the differences in topographic and geomorphic characteristics, fluvial morphologies, and sedimentary characteristics of the Golmud DFS. The proximal slope is higher than the other two zones, and the geomorphic features are mainly gravel gobi. The proximal fluvial morphologies are mainly large braided rivers, and sediments are more gravelly and less sandy. The medial slope is relatively small, and the geomorphic features are mostly oasis plains. The medial fluvial morphologies are mainly meandering rivers associating with braided rivers, and sediments are more sandy and less gravelly. The distal slope is the lowest, and the geomorphic features are mostly oasis plains, lakes, and marsh plains. The distal fluvial morphologies are mainly meandering rivers, and sediments are sandy and muddy. Comparison of the DFS from proximal to medial to distal in Golmud confirmed the potential of remote sensing image technology in identifying the fluvial morphologies and sedimentary facies distribution in dryland.
Abstract Based on large amounts of cores, open-hole conventional logs and mineral components analysis, abnormal natural gamma ray (GR) log showing high values in conglomerates and low values in fine-grained sediments, are described and explained in Baikouquan Formation of Xiazijie Fan-delta, Mahu Depression, Junggar Basin. After observing cores, normalizing the GR log and correcting depth errors between both, the GR log values of individual grain-sized lithology are extracted and counted. When grain-size decreases, the average GR values of different sized grains increase generally. The GR values of conglomerates are mostly between 50 and 80 API, while the values of fine-grains are mainly between 70 and 100 API. However, abnormal GR log features exist in the cores and wells of Baikouquan Formation prevalently. A great deal of high radioactive intermediate-acid volcanic minerals, such as volcanic tuff, felsite, andesite, granite, rhyolite, et al ., distribute widely in the conglomerates, which results in abnormal high GR values in conglomeratic intervals. Low radioactive quartz components exit widely in high percentage in mudstones, which is the primary mineral explanation for the abnormal low GR values in reddish-brown siltstones and sandstones intervals.
The use of either analytical or numerical models of groundwater inflow into a tunnel, ignoring the excavation process, will result in inaccurate prediction. More researchers have begun to study prediction methods with temporal and spatial variables, in accompaniment with the tunnel excavation progress. The hydrogeological parameters significantly affect tunnel inflow prediction; thus, it is always worthy to carry out an inversion analysis when the inflow rate observation is available for the excavated part of a tunnel. Based on a transient analytical model and the Trust Region Reflection (TRR) algorithm, this paper proposes a Dynamic Parameter Calibration (DPC) method to sequentially optimize parameters for a tunnel that is divided into several sectors. The results of two case studies indicate that the fitting effects by DPC are significantly improved compared with the empirical trial-and-error method, indicating good optimizations. The proposed scheme can conduct calibration simultaneously for multiple tunnel sectors and also several optimizations for the same sector. The parameter optimization results reflect the lithologic heterogeneity of different strata. Parameter sensitivity analysis proves that the hydraulic conductivity K has a greater influence on water inflow calculation than the specific storage coefficient S.
The Zaozigou Au-Sb deposit has been controversial in its genesis and remains one of the most difficult ore systems to fully understand in West Qinling. The mineralization shows a broad spatial association with Triassic dikes and sills, which were previously thought to be genetically related to mineralization. Our U-Pb zircon dating in this contribution indicates that the ore-hosting porphyritic dacites were formed at 246.1 ± 5.2 Ma and 248.1 ± 3.8 Ma. The magmatic zircons yield εHf(t) values ranging from −12.5 to −8.9, with corresponding two-stage model ages of 2.08 to 1.83 Ga. The magma therefore could be derived from partial melting of Paleoproterozoic crustal materials. The ore-hosting porphyritic dacites have low oxygen fugacity, with ΔFMQ ranging from −4.61 to −2.56, indicating that magmas could have been sulfide-saturated during evolution in deep chambers and precluding the possibility that metals were released from the melt. Zaozigou exhibits characteristics widespread volcanics, massive sulfide mineralization, rare reduced mineral assemblage and discrete alteration zones which are not typical of reduced intrusion-related or porphyry gold systems. We propose that the spatially-related Triassic porphyritic dacite and dike swarm is not genetically related to the ore formation of Zaozigou Au-Sb deposit.
Determining absolute ages of orogenic faults is critical to understanding the deformation process in the upper crust, but obtaining age remains a problem due to the lack of readily available techniques. Carbonates occur as veins in faults in a range of geological settings, and thus it is a suitable mineral for U-Pb geochronology. Here, we apply the new approach of U-Pb dating on syn-tectonic dolomite veins from the Gelouang gold deposit in the western Qinling Orogen to unravel the absolute timing of the fault formation shedding new light on the regional upper crustal deformation archive. In situ LA-ICP-MS U-Pb dating of dolomite yielding a successful age of 115–112 Ma demonstrates that the dolomite precipitated coeval with tectonic events ascribed to the post-orogenic deformation phase in the Qinling Orogen. This event is possibly correlated with broader intracontinental processes and might be an inevitable response to the extensional deformation of the Qinling Orogen. The presented LA-ICP-MS dolomite U-Pb age successfully represents the age of a specific structure that encompasses the intracontinental process in the Qinling Orogen. Moreover, it demonstrates the utility of the method to decipher a response to complex deformation histories on a regional scale.
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