Data collection and analysis

Before the specific implementation of geological survey, we should systematically collect the data of predecessors' work achievements in the work area and its adjacent areas, get a preliminary understanding of the geological and mineral conditions in the survey area, conduct comprehensive analysis and research in combination with the actual situation, sum up the experience and lessons of predecessors' work, and formulate a feasible, reasonable and correct work plan, so as to make the regional geological survey truly focused, targeted and less detours.

3.2. 1. 1 data collection

Selection and production of (1) topographic map

Generally, the scale of topographic map selected for regional geological survey should be twice that of actual geological survey. 1:250,000 national land survey uses1:50,000 aerial topographic map as the base map; 1:50,000 regional geological survey generally adopts1:25,000 topographic map published by the national surveying and mapping department. For areas without 1:25000 topographic map, one-time topographic-geological mapping method can be adopted, that is, the map can be made directly from aerial photos with corresponding scale, supplemented by 1:50000 topographic map, or 65438 can be collected.

The number of topographic maps collected should be determined according to the grouping of field surveyors and the needs of compiling various results maps. Generally, the topographic map of 1:25000 should be 10 ~ 15, and the topographic map of 1:50000 with high accuracy and good terrain should be 3 ~ 6. Previously used topographic maps need to be papered, flattened and dried in the shade with summer cloth or horse manure paper. The topographic map (quasi-manual map) used by field investigators needs to be cut according to a certain specification (20cm× 16cm), and the unified label should be covered with transparent paper and used in blocks, which is convenient for carrying in the field and can ensure the cleanliness of the original manual map, or a new material "silk cloth" which is resistant to bending, basically does not deform when it meets water, does not change color, and can be written and erased is adopted as the terrain. In addition to collecting topographic maps of the work area, it is also necessary to collect topographic maps around the work area, each with 1 ~ 2 copies, for the use of connecting maps.

(2) Collect geological and mineral data

The collection of geological and mineral data in the work area and its adjacent areas should be from the old to the new, and those outdated and worthless data and those that have been "digested" into later geological achievements should be deleted. 1:50,000 The most valuable basic data of regional geological survey is1:200,000 (or1:250,000), so special attention should be paid to collection. For areas with high degree of research and abundant data, we should mainly collect recent data and integrate them into the measured data through editing or combining editing with testing.

Geological and mineral data mainly include various geological surveys, mineral survey and exploration results, hydrogeological survey data, various related experimental analysis and appraisal data, various related special research documents, scientific research papers and related maps, reports, hand-made drawings, record books and files. The main geological and mineral data of adjacent areas should also be collected.

(3) Collection of geophysical data

Geophysical exploration includes ground geophysical exploration and airborne geophysical exploration. The abundant data obtained are of far-reaching practical significance for exploring, explaining and understanding the underground structural form, the burial conditions of underground ore bodies, the nature of the earth sphere, and discussing the plate movement mode, especially for implementing "three-dimensional geological mapping".

(a) Collecting data on the results of ground geophysical exploration. Ground geophysical methods mainly include magnetic method, electrical method, seismic method and gravity method. When the working area is covered by desert area or Quaternary, it is particularly important to collect the results and data of ground geophysical exploration. In the1:50,000 regional geological survey, magnetic exploration is mainly used to divide structural units, delineate rock masses and faults, and provide prospective areas for further general survey and prospecting.

(b) Collecting data on the results of aerogeophysical exploration. There are many kinds of airborne geophysical data, including airborne magnetic survey, followed by airborne radioactive survey and airborne gravity survey, which were carried out earlier in China and achieved good results.

(4) Data collection of geochemical exploration and heavy sand survey results.

China has completed1:200,000 regional geochemical exploration and heavy sand survey (large-scale surface geochemical exploration and heavy sand survey have also been carried out in some areas), and these results can effectively and prospectively guide the geological survey deployment and implementation of1:50,000 regional geological survey.

(5) collection of remote sensing data

The collection of remote sensing data should be based on the tasks and research contents of regional geological survey, and appropriate aerospace or aviation remote sensing data should be selected. Before data collection, it is necessary to systematically understand the technical parameters and geological characteristics of various remote sensing data, such as spectral interval, spatial resolution, spectral resolution and time resolution, so as to extract geological elements from remote sensing data to the maximum extent.

A. Collection and production of aerial remote sensing photos

Before1:50,000 regional mapping, it is necessary to collect full-color black-and-white aerial photos, color aerial photos, false-color aerial photos, infrared aerial photos and side-looking radar photos with good image characteristics, multiple varieties, multiple bands and multiple scales (Table 3. 1). If the work area is covered by glaciers, deserts or a large area of Quaternary, in order to carry out geological investigation and research on the underlying bedrock, side-looking radar films should be selected; If there are multiple metal occurrences in the work area, large-scale color aerial photographs should be collected; During hydrogeological investigation, infrared aerial photographs or far-infrared scanning images should be collected. If the scale of the existing aerial photos in the work area is too small, you can apply to the aerial photography department to enlarge the photos to a scale close to the requirements of geological survey.

Table 3. 1 Relationship between regional geological survey and aerial photograph scale

After obtaining the aerial data, it should be sorted and compiled in time. Put the aerial photos of the same scale into the bag according to the flight zone, and indicate the map code, flight zone number and photo number on the bag. For the convenience of use, each Zhang Hang should also be numbered in the upper left corner of the back in the following format:

Basic course of regional geological survey

Wherein, the upper part is the picture number, the lower left number is the band number, the middle number is the total number of photos in this band, and the right number represents the number of photos in this band from left to right.

In order to fully understand the continuity and structural framework of geological structures in the survey area, aerial photographs are usually used to sketch the work area and its surrounding areas, and the names or elevations of main features, such as villages and towns, major roads or railways, rivers, lakes, reservoirs and peaks, are marked on each Zhang Hang photograph. In order to avoid soiling aerial photos, labels should be written on transparent paper attached to aerial photos.

B. Collection and production of satellite remote sensing images

1:250,000 remote sensing geological interpretation, mainly multi-spectral remote sensing data with spatial resolution better than 15m; 1:50,000 remote sensing geological interpretation, mainly multi-spectral remote sensing data with spatial resolution better than 5m; For remote sensing geological interpretation with special requirements, the spatial resolution of data should be determined according to the corresponding technical standards.

Generally speaking, the spectral range of remote sensing geological interpretation data is from visible light to short-wave infrared band, so it is necessary to collect thermal infrared band data and extract geological body information with large thermal inertia; The geological survey of vegetation-covered areas can supplement radar data; Appropriate spectral data should be used to extract remote sensing anomaly information, and hyperspectral data should be collected when conditions permit.

The time of remote sensing data should be determined according to the content of special investigation and the geographical environment of the work area, and the time of multi-platform remote sensing data used for fusion processing in the same area should be as consistent as possible. Generally speaking, the best data phase in southern snow-free areas is winter, the best data phase in northern areas is spring and autumn, and the best data phase in mountainous areas with snow all the year round is summer.

When collecting data, you should check the quality of the data. Generally, the distribution area of clouds and snow should be less than 5% of the drawing (in special cases, it can be relaxed to 10%, but the main features cannot be covered), and the speckle noise and bad bands in the image should be as little as possible.

(6) Collection of other information

A. collection of physical geography and economic geography data

Collect information about earthquakes, hydrology, geography, landforms, forests, vegetation, soil, climate, tourism, transportation, local chronicles and even travel notes in this area. Because these data are closely related to determining the survey route, selecting the means of transportation, reasonably determining the field equipment and working period. It is also very important to solve many related geological problems.

B. Collect information on ore prospecting and reporting by the masses.

Collecting information about people's prospecting, reporting and mining history can often provide clues for prospecting and have a multiplier effect on mineral evaluation.

C. Collection of physical information

Including the samples of minerals, rocks and paleontology fossils collected by predecessors in the investigation area and its adjacent areas, as well as physical materials such as rock slices and drilled cores, the collection of these materials can save limited funds and avoid unnecessary repetition and waste.

D. Collecting data on economic development

The agricultural construction and engineering construction in the work area, as well as the suggestions and requirements put forward by local government departments or some large factories and mines on geological work, have important reference value for scientific decision-making and specific implementation plan deployment of regional geological survey, and should also be collected and understood.

E. collection of data such as regional dispatching technical specifications.

With the development of modern social economy, the progress of science and technology and the in-depth development of geological prospecting, the important role and far-reaching significance of regional geological survey are becoming more and more obvious. All countries in the world have formulated detailed regional dispatching norms and technical regulations that are in line with their own reality. These technical specifications and requirements are the basic guarantee for pre-job personnel to cultivate technical literacy and complete regional geological survey, so that employees can carry out their work on the basis of the latest theories and technical methods. Therefore, it is necessary to collect relevant specifications, requirements and relevant guidance documents before work.

3.2. 1.2 Analysis and Utilization of Data

(1) remote sensing image interpretation

Remote sensing images are vivid, with a wide field of vision, and more importantly, various geological information is extremely rich. They have been widely used in the implementation of the new generation1:50,000 regional reconciliation and1:250,000 national land survey, and have received many, fast, good and economical effects. Combining the interpretation of remote sensing images with "digital mapping" can greatly accelerate the pace of regional mapping.

Remote sensing interpretation should run through the whole process of regional geological survey and can generally be divided into four steps: preliminary interpretation, detailed interpretation, comparative interpretation and comprehensive interpretation. Now only a preliminary interpretation is introduced as follows.

A. Principles and requirements of preliminary interpretation

The preliminary interpretation principles of remote sensing images are: easy before difficult, simple after complex, whole after local, structure after lithology.

Easy first, then difficult: it refers to starting from the area where the geological body image reflects the clearest or the previous work has a high degree of research, from the known to the unknown, and gradually expanding to the whole region.

Simplification before copying: refers to the initial interpretation of the structural framework, and then the detailed image characteristics are repeatedly and carefully interpreted.

First the whole, then the part: refers to the combination of a variety of remote sensing images (satellite photos to see the macro, aerial photos to see the micro, color photos identification).

Structure before lithology: it means that the macro interpretation of fault structure in remote sensing images is unique.

The above principles should complement each other and confirm each other in specific applications. At the same time, we must never forget to explain the general principle that must be combined with field exploration (mapping). The specific performance is as follows:

(a) Based on the remote sensing image, according to the task requirements, preliminarily interpret the remote sensing geological elements, understand their regional development characteristics, roughly divide the categories of various elements, preliminarily establish interpretation marks by comparing with the existing data, try to extract the required information, determine the attribute of elements with characteristic interpretation marks, and preliminarily establish image units.

(b) Updating the geographic data of water areas, roads and residential areas collected in the previous period by interpreting the latest time-phase remote sensing images collected. According to the distribution characteristics of regional rocks, structures and other elements, the appropriate survey route is selected.

(c) Digest and absorb the existing geological and remote sensing data, preliminarily grasp the basic geological characteristics and remote sensing image characteristics of the survey area, and make an interpretation sketch with remote sensing image as the main information source and image unit as the unit.

(d) Interpreting the sketch as a transition diagram, and classifying and naming the attributes of the editing unit based on the image. The content and location of reconnaissance work should be marked on the explanatory sketch, and reconnaissance routes should be laid in areas with good traffic conditions, many image units crossing and good outcrops.

(e) In the process of preliminary interpretation and later detailed interpretation, the interpretation card of remote sensing geological elements should be filled in according to the image characteristics of remote sensing geological elements.

B. Contents of the preliminary explanation

(1) Quaternary interpretation: firstly, the boundary between Quaternary loose sediments and bedrock is drawn by using different color and tone information on remote sensing images. Then, based on the landform types (terraces) presented in remote sensing images, the genetic type boundaries of Quaternary are preliminarily drawn.

(2) Fault structure interpretation: mainly refers to linear structure, ductile shear zone, concealed structure, annular structure and active structure. This structure has the best effect in remote sensing image interpretation, because both aerial photos and satellite photos have certain perspective ability, and the background is wide, and various structural features are exposed clearly.

Compared with conventional ground geological survey methods, remote sensing image interpretation can obtain a lot of fault structure information. In the interpretation, firstly, the small-scale remote sensing image is interpreted, which has a wide field of vision and removes many details, which is helpful to identify large faults or deep fault zones, and also to distinguish the level and combination relationship of faults. At the same time, information such as the number of faults, the distance between the same horizontal faults, and the law of rock guiding and ore controlling can also be obtained. Secondly, through the interpretation of large and medium-scale remote sensing images, the specific spatial distribution and mutual shear relationship of fault structures are studied.

Special attention should be paid to the interpretation of ring fault structure, concealed structure and active structure in the interpretation of remote sensing images, which is the most easily overlooked geological structure phenomenon in conventional ground geological mapping, and special attention should be paid to improve the quality of map sheets and the predictability of field investigation in the future.

(c) Interpretation of magmatic rocks: The interpretation of magmatic rocks often uses relatively uniform colors and tones in remote sensing images; Special terrain and unique pincer, radial and annular water system; The massive and non-bedding features of magmatic rocks are manifested in the lack of black and white banded shadows in remote sensing images, which often show circular, equiaxed and semi-circular outlines. Practice has proved that it is very effective to draw the outline boundary of rock mass by using the above characteristics and principles.

(d) Formation lithology interpretation: Remote sensing images can track lithology changes in a large range, which provides us with another new means to study phase transition. It is worth pointing out that the interpretation of lithology must make full use of the geological data existing by predecessors and the local interpretation marks established during the reconnaissance.

The interpretation of sedimentary rocks should grasp the layered nature of sedimentary rocks, which is shown as a strip image on remote sensing images. It is of great practical significance to study the regional bedding variation characteristics of sedimentary sequences on remote sensing images, which is incomparable to conventional ground geological work research.

The interpretation of metamorphic rocks is generally difficult. If the work area is a layered and orderly shallow metamorphic rock series, the interpretation method is similar to that of sedimentary rocks. If the work area is a layered disordered medium-deep metamorphic complex, it can be interpreted according to the interpretation marks of magmatic rocks, and the distribution trend of schistosity should be accurately explained to reflect the regional tectonic framework. For the interpretation of metamorphic rocks, altered rocks can be distinguished by the images on color aerial photographs and TM photos, and the effect is good.

(e) Explain the boundary between folds and unconformities: Remote sensing images have a strong three-dimensional sense, which can directly show the three-dimensional spatial change law of geological structures.

It is more intuitive and convenient to study the types, laws, characteristics and combination of folds through remote sensing images than simply studying them on the ground. Generally speaking, small-scale satellite images have a good effect on studying large-scale fold structures, while large-scale aerial photographs reflect small structures more clearly. In short, the interpretation of folds mainly depends on the symmetry of images or the turning point of beauty.

Angle does not integrate the boundary, which is generally more intuitive and clear in remote sensing images, and the accurate effect of interpretation and sketch is better than that of field sketch.

(f) Determination of necessary occurrence factors: The occurrence of strata, faults and contact surfaces on remote sensing images should be measured by using triangular surface, trapezoidal surface, single-sided mountain and Zhubeiling, and their dip angles should be estimated visually and converted into remote sensing interpretation maps.

Matters needing attention: In the process of comprehensive interpretation of remote sensing images, we should always pay attention to the selection of reconnaissance routes and profile measurement positions.

C. Remote sensing geological interpretation map (draft)

After the above interpretation is completed, the whole map of remote sensing geological interpretation (grass) should be revised, including two parts: inside and outside the map.

The contents of the map include various geological boundaries, geological codes, structural symbols, inking and coloring of occurrence elements (on the reverse side of the transparent map) and so on. The contents outside the drawing include name, scale, legend, drawing label (responsibility table, the same below), drawing frame, etc.

D. compile summary or report of remote sensing geological interpretation.

This paper describes the methods and characteristics of remote sensing technology used in this work, the types, scales, quality and interpretability of remote sensing images, and introduces in detail the interpretable marks (lists) of various geological bodies, the image characteristics of linear, circular and descriptive structures and their geological significance.

It is worth noting that after the compilation of remote sensing geological interpretation map, it is necessary to transfer the interpreted geological boundaries to transparent paper attached to topographic map (hand map) for reference and verification in future geological mapping route investigation.

(2) Analysis and utilization of geological and mineral data

The collected geological and mineral data should be comprehensively sorted out and evaluated in time to determine its reference value.

There are two ways to study the previous literature: one is to read the latest or authoritative summary literature to understand the general situation of the workspace; The second is to read, analyze and study in the order of publication time or investigation. While reading the data, try to complete the arrangement and extraction of the data, fill in the data card and compile relevant maps (such as the map of geological and mineral research degree in the work area).

Drawing up the degree map of geological and mineral research in the work area means using different lines, symbols and figures to indicate the scope of work, the nature of work, the proportion of work and the investigation time, and numbering the data. Important actual data should be drawn on the research degree map (such as mountain engineering controlling ore body, drilling position, important sampling points and fossil points, etc.). ).

(3) Arrangement of other materials

The results of geochemical exploration, heavy sand and geophysical exploration carried out by predecessors in the work area are comprehensively sorted out, and the comprehensive map of geochemical exploration, heavy sand and geophysical exploration anomalies in1:50,000 work area is compiled for reference and verification in future geological surveys.