In this study, petrographic, microthermometric, and synchrotron radiation X-ray fluorescence (SRXRF) analyses of fluid inclusions were conducted to shed light on the mineralization mechanism of the Dongtongyu deposit and provide some evidence of the relationship among CO 2 , Au, and other ore elements (e.g., Cu, Fe, Zn, and Pb) in ore-forming fluids. The ore-forming fluid is characterized as the H 2 O–CO 2 –NaCl system with medium–high temperatures and low salinities. Four structural mineralization stages are distinguished: Pyrite-quartz (Stage 1), gold-quartz-pyrite (Stage 2), gold-quartz-polymetallic sulfide (Stage 3), and quartz-calcite (Stage 4). Fluid inclusions in Stages 1–3 are dominated by the H 2 O–CO 2 type, and most of them contain liquid H 2 O and liquid CO 2 at room temperature. The melting temperatures (T m-CO2 = −82.1°C to −57.5°C) of solid CO 2 in Stage 1 are relatively low. The values of T m-CO2 in Stages 2–3 are quite close, with ranges of −60.5°C to −56.5°C and −59.2°C to −58.6°C, respectively. The melting temperatures of clathrate in Stages 1–3 are −2.7°C to +7.8°C, −5.5°C to +7.8°C, and +3.7°C to +7.2°C. The homogenization temperatures of the CO 2 phase in the H 2 O–CO 2 inclusions of the three stages are measured as −7.5°C to +31.7°C, −7.5°C to +29.3°C, and 7.1°C to +24.1°C. The total homogenization temperatures in Stages 1–3 are 180°C–394°C, 202°C–305°C, and 224°C–271°C, with salinities of 4.3 wt.%–18.2 wt% NaCl, 4.3 wt.%–20.0 wt% NaCl, and 5.3 wt.%–11.0 wt% NaCl, respectively. The laser Raman spectroscopy results show that the CO 2 –H 2 O inclusions in the quartz veins contain abundant CO 2 and CH 4 . The SRXFR results show that most of the elements, especially As, Te, and Cu, are more enriched in liquid CO 2 than in liquid H 2 O. The elements of Au, Fe, Ni, Cu, and Pb have higher concentrations in H 2 O–CO 2 -type fluid inclusions in Stage 2 than other fluid inclusions in Stages 1–2, suggesting that gold mineralization is closely related to CO 2 -rich fluids. During the fluid evolution process, fluid immiscibility is an important mineralization mechanism of gold. The increase in CO 2 and CH 4 and the decrease in the fluid temperature might promote fluid immiscibility.
As the effective stress in coal-bearing reservoirs changes, the elastic wave velocities, stress sensitivity, and anisotropic characteristics of coal rocks exhibit certain variations. Therefore, this study selected samples from the same area (sandstone, mudstone, and anthracite) and conducted experiments on their transverse wave velocities (Vs) and longitudinal wave velocities (Vp) and wave velocity ratios in three directions (one perpendicular and two parallel to the layering), using the RTR-2000 testing system under loading pressure conditions. The results indicate that the longitudinal and transverse wave velocities of the coal rock samples show a phase-wise increase with rising pressure. The wave velocities and wave velocity ratios of sandstone, mudstone, and anthracite demonstrate certain anisotropic characteristics, with an overall trend of decreasing anisotropy strength that stabilizes over time. The anisotropic characteristics of the longitudinal wave velocities in sandstone and mudstone are stronger than those of the transverse wave velocities, whereas in anthracite, the anisotropic characteristics of the transverse wave velocities are stronger than those of the longitudinal wave velocities. Thus, it can be concluded that Vp is a sensitive parameter for detecting the anisotropic characteristics of sandstone and mudstone, while Vs serves as a sensitive parameter for detecting the anisotropic characteristics of anthracite.
Abstract The preexisting structures that developed in the basement and subsalt strata play a key role in the salt structural deformation in the Kuqa Depression, Tarim Basin. The characteristics of preexisting structures and their controls on the salt structure are investigated via the latest three‐dimensional seismic data and numerical modelling. The results show that the preexisting structures that developed in the Kuqa Depression mainly consist of basement faults, palaeouplifts, subsalt slopes and early passive salt diapirs. Basement faults are mainly distributed in the Kelasu and Qiulitag structural belts and control the position of development and deformation style of the Miocene compressive salt structure. The differences in styles and reactivation degrees of basement faults lead to great diversity in the salt structure. The palaeouplifts mainly include the Wensu, western Qiulitag, Xinhe and Yaha‐Luntai palaeouplifts. The original sedimentary range and later deformation space of the salt layer are limited by the palaeouplift, resulting in strong salt thrusting in the Awate sag in the western part of the Kuqa Depression. The heterogeneous spatial distribution of the palaeouplift promoted the development of regional strike‐slip transform belts. Subsalt slopes are located mainly on the northern edge of the western Qiulitag low uplift and block the southward flow of the salt, causing the salt to form salt domes; the size of these domes is closely related to the subsalt slope. Early passive salt diapirs mainly developed in the Quele and Bozidun areas of the western Kuqa Depression, and they were preferentially active during the compression period, inducing the formation of a piercement salt nappe. Numerical modelling revealed that the preexisting structure strongly controlled the stress–strain distribution during the deformation of the salt structure. The spatial distribution heterogeneity of the basement structure is an important factor in the structural zonation along the north–south strike and segmentation along the west–east strike in the Kuqa Depression, as well as an important inducer of the piercement salt structure.
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