A method for recovering paleohydrodynamic conditions of a sedimentary basin

Abstract

The present application belongs to the technical field of sedimentary basin uranium exploration, and particularly relates to a method for restoring paleo-hydrodynamic conditions of a sedimentary basin. The present application comprises the following steps: Step 1: determining the tectonic evolution process and uranium mineralization period of a study area; Step 2: extracting drilling data; Step 3: drawing maps; Step 4: restoring paleo-hydrodynamic conditions. Based on the research on the relationship between tectonic evolution and uranium mineralization age, the present application draws paleo-topographic maps, paleo-geological maps, lithology distribution maps and the like of the last uranium mineralization period through a drilling database.

Description

Technical Field

[0001] This invention belongs to the field of uranium exploration technology in sedimentary basins, specifically relating to a method for restoring paleohydrodynamic conditions in sedimentary basins. Background Technology

[0002] The study of paleohydrodynamic conditions in sedimentary basins is of great significance for the exploration of sandstone-type uranium deposits. This is because sandstone-type uranium deposits are sedimentary uranium deposits, and groundwater, as the carrier of uranium migration, controls the migration direction, velocity, and distance of oxygen- and uranium-bearing water, oil- and gas-bearing water, and other fluids. Therefore, the distribution and evolution characteristics of the paleohydrodynamic field of groundwater play a crucial role in the formation and distribution of sandstone-type uranium deposits. Reconstructing the paleohydrothermal conditions of the basin can provide guidance for the exploration of sandstone-type uranium deposits.

[0003] There are many methods for reconstructing paleohydrodynamic conditions. Paleohydrodynamic conditions during the depositional period can be roughly reconstructed based on factors such as bedding type, sediment grain size variations, and stratigraphic thickness variations. Paleohydrodynamic conditions after the depositional period are mainly reconstructed based on changes in fluid potential. The concept of fluid potential was first proposed by Hubbert (1954), and later Toth (1962) proposed the concept of "hydrodynamic field" and established a new theory on the relationship between gravity transstrata flow and hydrocarbon migration and accumulation, combining the distribution and evolution of the basin's hydrodynamic field with fluid migration and accumulation. With the recent development of quantitative basin analysis and basin simulation technology, basin hydrodynamic numerical simulation has become the main means of studying hydrodynamic conditions (Wang Zhenliang, 2007). The paleohydrodynamic conditions reconstructed by the above methods have certain guiding significance for the exploration of sandstone-type uranium deposits, but they are still insufficient for reconstructing the paleohydrodynamic conditions of the main mineralization period of uranium deposits and cannot indicate the comprehensive replenishment-drainage conditions of regional stratigraphy. Sandstone-type uranium deposits are characterized by staged, episodic mineralization. The primary influencing factor is tectonic activity, with uranium mineralization typically occurring within several million years following intense tectonic uplift. Each uplift alters or reactivates the hydrodynamic conditions of groundwater, allowing uranium mineralization to develop. Based on the relationship between uranium mineralization ages and tectonic activity in existing sedimentary basins in China, it can be concluded that most basins did not experience large-scale tectonic activity after the last stage of uranium mineralization. This suggests that the paleogeography and paleohydraulic conditions of the period of the last mineralization stage have been largely inherited by modern geological processes. Therefore, identifying the paleotopography, stratigraphic distribution, and lithological distribution during the last stage of uranium mineralization can directly reconstruct the flow direction of surface and groundwater, the groundwater recharge and discharge areas of the ore-bearing strata, and the groundwater watershed, and can also roughly predict the distribution of ancient rivers and catchment areas. Summary of the Invention

[0004] The technical problem solved by this invention is based on the laws of groundwater dynamics. This invention provides a method for restoring the paleohydrodynamic conditions of sedimentary basins. Based on the study of the relationship between tectonic evolution and uranium mineralization age, it compiles paleotopographic maps, paleogeological maps, and lithological distribution maps for the last period of uranium mineralization through borehole database.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for reconstructing paleohydraulic conditions in a sedimentary basin includes the following steps:

[0007] Step 1: Determine the tectonic evolution process and uranium mineralization stages of the study area; Step 2: Extract borehole data; Step 3: Draw maps; Step 4: Reconstruct paleohydrodynamic conditions.

[0008] Step 1 specifically includes

[0009] Step 1.1: Determine the tectonic evolution process of the study area; Step 1.2: Determine the uranium mineralization period; Step 1.3: Determine the stratigraphic age t of the last uranium mineralization period.

[0010] Step 1.1 specifically includes

[0011] Within the study area, existing rock apatite fission track dating data were collected. When the data was insufficient, additional rock samples were collected for apatite fission track dating. The main tectonic evolution stages of the study area were determined by combining the above data with the regional tectonic evolution history.

[0012] Step 1.2 specifically includes

[0013] For uranium deposits in the study area, existing uranium-lead isotope data of uranium ore were collected. When the data was insufficient, additional uranium ore samples were collected for uranium-lead isotope analysis. Using the above data, the isochron ages of the uranium deposits were uniformly calculated and fitted to determine the main mineralization periods of the uranium deposits.

[0014] Step 1.3 specifically includes

[0015] By comparing the tectonic evolution stages obtained from step 1.1 with the uranium mineralization periods calculated from step 1.2, the relationship between tectonic evolution and uranium mineralization periods in the study area is analyzed. Each large-scale tectonic uplift activity will cause sedimentary discontinuities in the regional strata. If the last large-scale tectonic activity coincides with the last large-scale uranium mineralization period, it is considered that the last large-scale tectonic activity led to uranium mineralization in the study area at time t. Based on the regional stratigraphic timescale, the sedimentary discontinuity period and overlying strata at the last uranium mineralization period t are determined.

[0016] Step 2 specifically includes

[0017] Collect and organize geological logging data from various boreholes in the study area. Using the sedimentary discontinuity period where the last uranium mineralization period t determined in step 1.3 is located as the boundary point, remove all the overlying strata data determined in step 1.3. Extract the uppermost strata, uppermost lithology, and uppermost strata elevation data of each borehole after removing the overlying strata data.

[0018] Step 3 specifically includes

[0019] Based on the underlying strata, underlying lithology, and elevation data of the top surface of the underlying strata extracted in step 2 for each borehole at geological time t, a stratigraphic distribution map, a lithological distribution map, and a topographic map for geological time t are drawn respectively.

[0020] Step 4 specifically includes

[0021] Based on the stratigraphic distribution map, lithological distribution map, and topographic map drawn in step 3, and taking into account the stratigraphic, lithological distribution, and surface undulation, a paleohydrodynamic environment map is compiled using a map containing elements such as stratigraphy, structure, and topography as the base map. The flow direction and watershed of surface water and groundwater are roughly drawn; ancient rivers and lakes are inferred and drawn; secondary hydrodynamic units are delineated; and the recharge and discharge areas of the target mineral strata are delineated to reconstruct the paleohydrodynamic environment at that time.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) This invention provides a method for restoring paleohydrodynamic conditions in sedimentary basins. Based on borehole data, this method restores the paleohydrodynamic environment at the time by compiling topographic maps, geological maps, and surface lithology distribution maps of the last mineralization period. It can indicate the groundwater recharge-drainage conditions during the mineralization period, provide support for the study of mineralization mechanisms and mineralization models, guide the direction of mineral exploration, improve mineral exploration efficiency, and significantly reduce exploration costs. Attached Figure Description

[0024] Figure 1 A flowchart illustrating a method for reconstructing paleohydraulic conditions in a sedimentary basin, provided by this invention.

[0025] Figure 2 This is a stratigraphic distribution map of a certain region during the 22 Ma period.

[0026] Figure 3 This is a lithological distribution map of a certain region during the 22 Ma period.

[0027] Figure 4 This is a topographic map of a certain region during the 22 Ma period.

[0028] Figure 5 A paleohydrodynamic environment map of a certain region during the 22 Ma period;

[0029] In the diagram: 1-Upper Cretaceous Mingshui Formation; 2-Upper Cretaceous Sifangtai Formation; 3-Upper Cretaceous Nenjiangzu Formation; 4-Upper Cretaceous Yaojia Formation, Sections 2 and 3; 5-Upper Cretaceous Yaojia Formation, Section 1; 6-Upper Cretaceous Qingshankou Formation; 7-Fault; 8-Structural boundary; 9-Mudstone; 10-Sandstone; 11-Recharge area; 12-Drainage area; 13-Surface water watershed; 14-Inferred paleoriver; 15-Inferred catchment area; 16-Surface water runoff direction; 17-Groundwater runoff direction of Yaojia Formation aquifer. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] like Figure 1 As shown, the present invention provides a method for reconstructing paleohydrodynamic conditions in a sedimentary basin, comprising the following steps:

[0034] Step 1: Determine the tectonic evolution process and uranium mineralization stages of the study area.

[0035] Step 1.1: Determine the tectonic evolution process of the study area

[0036] Within the study area, existing rock apatite fission track dating data were collected. When the data was insufficient, additional rock samples were collected for apatite fission track dating. The main tectonic evolution stages of the study area were determined by combining the above data with the regional tectonic evolution history.

[0037] Step 1.2: Determine the uranium mineralization stages

[0038] For uranium deposits in the study area, existing uranium-lead isotope data of uranium ore were collected. When the data was insufficient, additional uranium ore samples were collected for uranium-lead isotope analysis. Using the above data, the isochron ages of the uranium deposits were uniformly calculated and fitted to determine the main mineralization periods of the uranium deposits.

[0039] Step 1.3: Determine the stratigraphic age of the last uranium mineralization period (t).

[0040] By comparing the tectonic evolution stages obtained from step 1.1 with the uranium mineralization periods calculated from step 1.2, the relationship between tectonic evolution and uranium mineralization periods in the study area is analyzed. Each large-scale tectonic uplift activity will cause sedimentary discontinuities in the regional strata. If the last large-scale tectonic activity coincides with the last large-scale uranium mineralization period (t), it is considered that the last large-scale tectonic activity led to uranium mineralization in the study area during period t. Based on the regional stratigraphic timescale, the sedimentary discontinuity period and overlying strata of the last uranium mineralization period (t) are determined.

[0041] Step 2: Drilling Data Extraction

[0042] Collect and organize geological logging data from various boreholes in the study area. Using the sedimentary discontinuity period where the last uranium mineralization period (t) determined in step 1.3 is located as the boundary point, remove all the overlying strata data determined in step 1.3. Extract the data of the uppermost strata, uppermost lithology, and uppermost strata elevation (i.e., the underlying strata, underlying lithology, and the top surface elevation of the underlying strata at geological time t of each borehole) for each borehole after removing the overlying strata data.

[0043] Step 3: Drawing the graphic

[0044] Based on the underlying strata, underlying lithology, and elevation data of the top surface of the underlying strata extracted in step 2 for each borehole at geological time t, a stratigraphic distribution map, a lithological distribution map, and a topographic map for geological time t are drawn respectively.

[0045] Step 4: Reconstructing ancient hydrodynamic conditions

[0046] Based on the stratigraphic distribution map, lithological distribution map, and topographic map drawn in step 3, and taking into account the stratigraphic, lithological distribution, and surface undulation, a paleohydrodynamic environment map is compiled using a map containing elements such as stratigraphy, structure, and topography as the base map. The flow direction and watershed of surface water and groundwater are roughly drawn; ancient rivers and lakes are inferred and drawn; secondary hydrodynamic units are delineated; and the recharge and discharge areas of the target mineral strata are delineated to reconstruct the paleohydrodynamic environment at that time.

[0047] like Figure 2-4 As shown, taking the reconstruction of paleohydrodynamic conditions during the last mineralization period in a certain region as an example, this invention provides a method for reconstructing paleohydrodynamic conditions in a sedimentary basin, comprising the following steps:

[0048] Step 1: Determine the tectonic evolution process and uranium mineralization stages of the study area.

[0049] Step 1.1: Determine the tectonic evolution process of the study area

[0050] Within the study area, a total of 89 existing rock apatite fission track dating data were collected, and a total of 6 rapid uplift events were identified, located at 76 Ma, 68 Ma, 51 Ma, 31 Ma, and 23 Ma.

[0051] Step 1.2: Determine the uranium mineralization stages

[0052] For uranium deposits in the study area, a total of 105 uranium-lead isotope data of existing uranium ore were collected. After uniformly performing isochron age calculation and fitting, six major mineralization periods were obtained: 87 Ma, 68 Ma, 65–69 Ma, 56–60 Ma, 47–50 Ma, 26–29 Ma, and 22 Ma.

[0053] Step 1.3: Determine the stratigraphic age of the last uranium mineralization period (t).

[0054] Comparing the tectonic evolution stages obtained from step 1.1 with the uranium mineralization periods calculated from step 1.2, it can be concluded that uranium mineralization is controlled by tectonic evolution. Furthermore, the last large-scale tectonic activity in 23 Ma coincides with the last large-scale uranium mineralization period in 22 Ma. It can be considered that the large-scale tectonic activity in 23 Ma led to uranium mineralization in the study area during the 22 Ma period. According to the regional stratigraphic timescale, 22 Ma is at the end of the Oligocene sedimentary hiatus. The overlying strata during this sedimentary hiatus mainly include the Da'an Formation (N2d), the Taikang Formation (N2t), and the Quaternary (Q).

[0055] Step 2: Drilling Data Extraction

[0056] A total of 221 borehole data were collected and organized within the study area. Taking the Oligocene sedimentary hiatus period at which the last uranium mineralization period of 22 Ma, as determined in step 1.3, occurred as the boundary, all data of the overlying Da'an Formation (N2d), Taikang Formation (N2t), and Quaternary (Q) strata determined in step 1.3 were removed. After removing the overlying strata data, the uppermost strata, uppermost lithology, and uppermost strata elevation of each borehole (i.e., the underlying strata, underlying lithology, and the elevation of the top surface of the underlying strata at the geological time of 22 Ma for each borehole) were extracted.

[0057] Step 3: Drawing the graphic

[0058] Based on the underlying strata, underlying lithology, and elevation data of the top surface of the underlying strata extracted in step 2 for each borehole during the geological period of 22 Ma, a stratigraphic distribution map, a lithological distribution map, and a topographic map for the geological period of 22 Ma are drawn respectively.

[0059] Step 4: Reconstructing ancient hydrodynamic conditions

[0060] Based on the stratigraphic distribution map, lithological distribution map, and topographic map drawn in step 3 at 22 Ma, and taking into account the stratigraphic, lithological distribution, and surface undulation, a paleohydrodynamic environment map is compiled using a map containing elements such as stratigraphy, structure, and topography at 22 Ma as the base map. The flow lines, runoff directions, and watersheds of surface water and groundwater in the study area at 22 Ma are roughly drawn. Paleorivers and paleolakes are inferred and drawn, and secondary hydrodynamic units are delineated. The recharge area, runoff area, and discharge area of ​​the target mineral strata are delineated, and the paleohydrodynamic environment at that time is analyzed.

[0061] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0062] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for reconstructing palaeohydrodynamic conditions in a sedimentary basin, characterized in that, Includes the following steps: Step (1): Determine the tectonic evolution process and uranium mineralization stages of the study area; Step (1) specifically includes: Step (1.1): Determine the tectonic evolution process of the study area; In the study area, collect existing rock apatite fission track dating data. If the data is insufficient, it is necessary to collect additional rock samples for apatite fission track dating. Combine the above data with the regional tectonic evolution history to determine the main tectonic evolution stages of the study area. Step (1.2): Determine the uranium mineralization period; For uranium deposits in the study area, collect existing uranium ore uranium lead isotope data. If the data is insufficient, supplementary uranium ore samples need to be collected for uranium lead isotope analysis. Use the above data to uniformly calculate and fit the isochron age of the uranium deposit to obtain the main mineralization period of the uranium deposit. Step (1.3): Determine the stratigraphic age of the last uranium mineralization period t; compare the tectonic evolution stages obtained from step (1.1) with the uranium mineralization periods calculated from step (1.2), analyze the relationship between tectonic evolution and uranium mineralization periods in the study area. Each large-scale tectonic uplift activity will cause sedimentary discontinuities in the regional strata. If the last large-scale tectonic activity coincides with the last large-scale uranium mineralization period, it is considered that the last large-scale tectonic activity led to uranium mineralization in the study area during time period t. Determine the sedimentary discontinuity period and overlying strata where the last uranium mineralization period t is located based on the regional stratigraphic timescale. Step (2): Drilling data extraction; Collect and organize geological logging data from various boreholes in the study area. Using the sedimentary discontinuity period where the last uranium mineralization period t determined in step (1.3) is located as the boundary point, remove all the overlying strata data determined in step (1.3). Extract the uppermost strata, uppermost lithology, and uppermost strata elevation data of each borehole after removing the overlying strata data. Step (3): Drawing; Based on the underlying strata, underlying lithology and the elevation of the top surface of the underlying strata of each borehole at geological time t extracted in step (2), draw the stratigraphic distribution map, lithological distribution map and topographic map for geological time t respectively; Step (4): Reconstruct ancient hydrodynamic conditions; Based on the stratigraphic distribution map, lithological distribution map and topographic map drawn in step (3), and taking into account the stratigraphic, lithological distribution and surface undulation, a paleohydrodynamic environment map is compiled using a map containing stratigraphic, structural and topographic elements as the base map. The flow direction and watershed of surface water and groundwater are roughly drawn; ancient rivers and ancient lakes are inferred; secondary hydrodynamic units are delineated; and the recharge and discharge areas of the target mineral strata are delineated to reconstruct the paleohydrodynamic environment at that time.

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