GIS-based spatial and temporal changes of land occupation caused by mining activ

GUO Li-jun, YAN Ya-ya, GUO Li-na, MA Jin-long, LV Ming-yu

1China University of Geosciences (Wuhan), Wuhan 430074, China.

2Hebei Yi Kun Geotechnical Engineering Ltd., Shijiazhuang 050000, China.

3Central South University, Changsha 41000, China.

Abstract: By using multi-source and multi-temporal high resolution remote sensing data and related techniques of remote sensing and geographic information systems, this paper analyzes the spatial and temporal changes of land occupation caused by mine development in four mining areas of eastern Hubei Province from 2011 to 2014, including Chengchao-Tieshan iron-copper polymetallic deposit area, Daye-Yangxin iron-copper polymetallic deposit area,E-Nan mining area, and Wuxue-Yangxin non-metallic mining area along the Yangtze River.The results show that: In the research area, land occupation of energy mine exploitation is small and in scattered distribution, with coal mine occupying the largest area, showing a downward trend in four years； land occupation of metal mines is large and in centralized distribution, with iron mine and copper mine occupying the largest area, showing a downward trend in four years； non-metallic mines are large and in great quantity, with mines of limestone for building and limestone occupying the largest area, showing a upward trend in four years.

Keywords: Remotesensing data； Eastern Hubei Province；Land occupation of mining activities；Spatial change

Introduction

Mineral resource is the important material basis for social and economic development. Mining industry is the leading industry of national economic and social development. In such a long time, people only pay attention to the exploitation of mines and ignore the problem of land occupation caused by mining activities. As a result,the land occupation problem is getting worse.According to the survey, with the expansion of development scale of mines in recent years, mine exploitation takes up a lot of land, which brings great damage to farmland, forest land and unused land, and leads to a series of mine geological disasters which cause serious personal and property losses to local residents. Therefore,strengthening the investigation and supervision of land occupation caused by mining activities has attracted the attention of the whole society (CAO Hui et al. 2014).

In recent years, high resolution remote sensing image has been widely used in the development of mineral resources and the survey, monitoring and evaluation of geological environment. By using multi-source and multi-temporal high resolution remote sensing data, this paper processes and extracts information from the data of research area(four mining areas including Chengchao-Tieshan iron-copper polymetallic deposit area, Daye-Yangxin iron-copper polymetallic deposit area,E-nan mining area, Wuxue-Yangxin non-metallic mining area along the Yangtze River), and reveals the status quo, amount and spatial changes of land occupation caused by mining activities in eastern Hubei from 2011 to 2014. At last, this paper analyzes and studies the final results, providing technical support and decision basis for relevant state departments to understand the status and change of land occupation caused by mining activities, strengthen the supervision of mine area,and develop planning for mining land recovery.

1 Research area and data source

1.1 Research area

The research area includes four mining areas in eastern Hubei Province including Chengchao-Tieshan iron-copper polymetallic deposit area,Daye-Yangxin iron-copper polymetallic deposit area, E-nan mining area and Wuxue-Yangxin non-metallic mining area along the Yangtze River,basically covering the main energy, metal and non-metallic mines in eastern Hubei (Fig. 1). The research area is about 2 089.51 km2, accounting for 2.78% of the total area of eastern Hubei. The research area is located in the Mesozoic copper,gold, iron, lead, zinc, and sulphur metallogenic belt in middle and lower reaches of the Yangtze River,rich in mineral resources of coal, iron, copper, gold and strontium (XIA Jin-long et al. 2009).

Fig.1 Distribution map of the study area

Chengchao-Tieshan iron-copper polymetallic deposit area is located in Ezhou City of Hubei Province. Its tectonic position is in the north edge of the triangle formed by NW-oriented Xiangfan-Guangji fracture, NNE-oriented Tuanfeng-Wenquan fracture and EW-oriented Changyang-Yangxin fracture, which is the transition zone of Yangtze block and North China block. Chengchao-Tieshan iron-copper polymetallic deposit area is located in Daye-Yangxin copper, iron, gold, silver,strontium, lead, zinc, tungsten, molybdenum,pyrite, wollastonite, limestone and coal metallogenic area. Exploited mines in this area are mainly energy mines and metal mines.

Located in hilly and lower mountainous areas,Daye-Yangxin iron-copper polymetallic deposit area has a continental climate, with warm and humid weather and abundant rainfall. Tectonically,it is in the virgation of southwest Hubei, which is located in the fold belt of lower Yangtze platform.It is controlled by the magmatism area in southeast Hubei, which is located in Yanshannian magmatic activity area in the middle and lower reaches of the Yangtze River. This area belongs to the metallogenic belt of middle and lower reaches of the Yangtze River. Surface water flowing through the mine area mainly comes from Donggang River and Xigang River, which eventually converge into Daye Lake. Along the two rivers, there are open pit mining waste rock piles, tailings piles and smelters(ZHANG Xiao-jun and HU Ming-an, 2008).

E-nan mining area is located in the Yanshanian gold, silver, copper, lead and zinc metallogenic belt in the east section of earth's axle of southern Yangtze River. The area is rich in mineral resources such as coal, limestone and marble.

Wuxue-Yangxin non-metallic mining area along the Yangtze River is rich in limestone,cement limestone, limestone for building, marble for building, dolomite, granite, tile clay and other minerals. It is a major non-metallic mining area for building materials in eastern Hubei Province.

1.2 Data source

The satellite remote sensing data of the research area with high resolution obtained from 2011 to 2014 has been used, including the satellite data of SPOT-5 and ZY-102C with a resolution higher than 5 m, the satellite data of ZY-3 and GF-1 with a resolution higher than 2 m, and the satellite data of IKONOS-2, WorldView-2 and Quickbird with a resolution higher than 1 m. Years of remote sensing monitoring and satellite data used are shown in Table 1.

Table 1 Remote sensing data source table

2 Research method

2.1 Remote sensing data processing

Conduct coordinate transformation, atmospheric correction, geometric correction, image intensification, image fusion, mosaic and boarder match and so forth on the satellite data collected in the research area through IKONOS-2,WorldView-2, Quickbird, SPOT-5, GF-1, ZY-3,ZY-102C and IKONOS, so as to meet the requirements for identification and accuracy of information on land occupation for mine development and other relevant activities.

(1) Atmosphere correction

On account of a lack of atmosphere correction module in sub system of remote sensing data processing, the process of atmosphere correction shall be completed by using FLAASH module in the commercial software ENVI. Calibrate the radiation of raw image by sensor parameter, input files upon radiometric calibration into the FLAASH module and read environment parameter in header file when image has shown, thus obtaining the final result of atmosphere correction.

(2) Geometric correction

When remote sensing image is shown, due to the effect of projection method of imaging, uneven sensing medium, earth curvature, topographic relief and other elements, some geometric deformations of gained remote sensing image compared with the target on the earth's surface have shown up. Difference between geometric figures on the image and selected map projection,with distortion of shape or location, mainly shows the displacement, rotation, scaling, curve and so forth. With the help of topographic map and DEM and other control materials, geometric correction can eliminate or decrease image transformation(YANG Xian-huaet al.2012).

(3) Image intensification

Data fusion can obtain high resolution of full color data and multi-spectral color effect.Processed image which takes the maximum advantage of all kinds of information, can better explain and describe the target or the environment that is sensed, making it easier to interpret and convenient to be comprehensively analyzed. Data fusion is performed by different fusion and transform methods such as HIS transform, PCA fusion, ImgSharpen fusion,etc.(ZHANG Zhiet al.2014).

(4) Mosaic and cutting

Mosaic and cutting of image are the necessary processes in image processing. Image mosaic and multi-scenes at the same time phase can complement with each other, and therefore recover the image information lost in thick cloud covering area, which is very important to deal with climatic region with more cloud and rain. Image cutting can cut the image that conforms to the range of work region, decreasing image size and saving processing time.

2.2 Information extraction

(1) Target of information extraction

Main information that needs to be extracted includes: solid waste (such as coal gangue pile,waste dump and hillock) caused by mining activity,and the location, boundary and land occupation type of transfer site (such as mineral pile, coal mine, washing mine field, and dressing plant); the location of mine construction and stope, the category of surface feature, quantity, the range of dynamic change, boundary line and mine varieties(CHANG Ling et al. 2014).

(2) Extraction method

Method that combines computer automatic extraction and manual visual interpretation has been primarily adopted. The computer automatic extraction mainly uses thresholding segregation method to extract whole piece of mine location image, and such method is rapid and accurate. On this basis, with the method of man-machine interactive interpretation and ArcGIS 9.6 software,combined with background knowledge of mining geology, edit and select the mine location image extracted by computer in many aspects such as color, form, landscape and texture according to the spectral signature and space structure of image.

Having completed the interpretation, verify the interpretation result by means of the combination of field and indoor examinations. If the surface feature on the image cannot be recognized, record the specific surface ground and location, take field verification, collect related pictures and GPS coordinate, and amend the figure spots of indoor interpretation (HE Liang-zhu et al. 2013).

2.3 Outdoor examination and information post-processing

Exam the reliability and accuracy of extracted information, check doubtful information, complement missing information, and amend false information. By field examination, arrange and analyze collected data, amend the image that is not consistent with the real object, delete fake image,and complete missing image (QI Xiao-ying et al.2008).

3 Analysis of monitoring results

3.1 Analysis of the status quo of mining area

(1) The occupied area of the mining activity area in the research area is 2 580.31 ha, including mining face-the largest occupied area, which is 1 002.6 ha, accounting for 38.86% of the whole research area; secondly, solid waste materials and transfer site, with areas of 763.34 ha and 784.61 ha respectively, which are 29.58% and 30.41% of the whole research area; mine construction-the smallest occupied area, which is 1.15% of the whole research area. Specific conditions are shown in Fig. 2.

Fig. 2 Research area of different types of mining area

In the four mining areas, Chengchao-Tieshan iron-copper polymetallic mining area has the highest percentage of occupied area, which is 46.13%, mainly because there are a large number of opencast iron mines, solid waste materials piles and transfer sites; the percentage of Yangxin-Wuxue non-metallic mining area is 35.35%, and the occupied area of the transfer site and the solid waste pile is outstanding; the percentage of the other two mining areas, Daye-Yangxin iron-copper polymetallic mining area and E-nan mining area,have a percentage lower than 15%, similarly transfer site and solid waste area have bigger occupied area. Mining surface and solid waste materials pile are main occupied type. Occupied situation of each mining area is shown in Fig. 3.

Fig. 3 Percentage of covering types from each mining area

(2) Main mine types of the research area are energy mine, metallic mine and non-metallic mine.Energy mine has a small occupied scale,distributes loosely, and main type of it is coal mine.Coal mine is mainly underground, such as transfer sites (coal washery and coal cleaning plant) of coal mine and gangue pile occupied area. Occupied areas of coal mine in 2011-2014 are 67.97 ha,39.46 ha, 38.71 ha, 33.09 ha respectively, showing a declining tendency year by year. The main reasons are that coal resource reserve is limited,the price is decreasing, and the gained profit is shrinking, etc.

Metallic mine has large occupied area and concentrated distribution, and the occupied area of iron mine and copper mine are the largest, mainly because the mining scales of the two mines are large, and are mainly opencast working. Stope and refuse dump formed by large scale soil stripping have large occupied area. The occupied areas of iron mines are 918.64 ha, 633.75 ha, 570.03 ha,and 616.05 ha respectively from 2011 to 2014,basically showing a declining trend. The main reasons are that the cost of iron mining is high,production enterprises stop or decrease production due to national policy's effect, and the iron mine demands decrease due to the large quantity of substitute products in the market.

Fig. 4 The covering area chart of each mine type (2011-2014)

Non-metallic mines are large and in great quantity, with mines of limestone for building and limestone occupying the largest area. Non-metallic mines often have large-scale exploitations, mainly using open-pit mining, leading to big stope and large land occupation for generated solid waste.From 2011 to 2014, land occupations of limestone for building are 703.81 ha, 751.73 ha, 700.66 ha and 774.93 ha, which show some fluctuations during the four years. Reason of land occupation growth is that limestone resources in the research area are abundant and widely distributed. With good quality, large reserves, wide uses, high value for development and utilization and broad prospects for development, these limestone resources are widely used in all aspects of the national economy. Reason for land occupation decrease is that under such a long time of extensive growth mode for limestone exploitation and utilization, mining enterprise layout is not reasonable, resulting in increasingly serious conflicts between geological environment and resource development. Besides, this has caused damage to landscape, vegetation, land, atmosphere and other natural resources, leading to geological disasters risks such as landslides in many places.National policies for land recovery and management have imposed some control on the scale and quantity of mine exploitation. Land occupations of mining activities of various ores are shown in Fig. 4.

Fig. 5 The mineral percentage statistics chart in the city of Xianning

(3) Land occupation caused by mining activities in eastern Hubei is mainly distributed in Xianning and Huangshi. Xianning mainly exploits non-metallic mines, in which the land occupation of limestone for building is the largest, which is 28.12 ha/year in average, accounting for 23.97% of the total land occupation area caused by mining activities in Xianning. The second largest land occupation is marble mines used for decoration,which covers 21.58 ha/year in average, accounting for 18.4% of the total occupation. Marble mine accounts for 16.49% of the total occupation and coal mine accounts for 13.27%. Other ores that occupies land mainly include limestone, dolomite,tile clay, calcite and some other non-metallic minerals. Land occupation percentages of various minerals are shown in Fig. 5.

Huangshi mainly exploits metal mines, in which the land occupation of iron ore is the largest,which is 273.7 ha/year in average, accounting for 11.2% of the total land occupation caused by mining activities in Huangshi. The second largest land occupation is copper mine, which covers 101.94 ha/year in average, accounting for 4.17% of the total occupation. Gold mine occupies 12.01 ha/year, accounting for 0.49% of the total occupation. For non-metallic mines, limestone for building occupies the largest area, which is 238.08 ha/years. Other minerals that occupy less land include tungsten ore, molybdenum ore,strontium ore, quartzite and tremolite. The land occupation percentages of various minerals are shown in Fig. 6.

Fig. 6 The mineral percentage statistics chart in the city of Huangshi

(4) As the main type of land occupation,open-pit mining occupies the largest land.Underground mining occupies less land. Land occupation caused by open-pit mining includes 32 ores such as iron, coal, copper, gold, limestone,limestone for cement and limestone for building,covering an area of 2 580.31 ha and accounting for 23.53% of the total occupation. This land occupation is mainly caused by open-pit mining face, transit field and solid waste heap. According to the statistics of land occupation of single opencast mine, there are 364 single opencast mining points. Land occupation of a single opencast mine is 981.65 ha, larger than that of a single underground mine.

There are 14 ores involved in underground mining, which include coal, iron, copper, zinc,tungsten, molybdenum, gold, strontium and so on.There are 140 underground mining points.

3.2 Analysis of change in mining areas

According to the mining area remote sensing data from 2011 to 2014, changing trends of the four mining areas for development have been systematically summarized and analyzed. From 2011 to 2014, total area of mining activities decreased from 2 912.53 ha in 2011 to 2 580.31 ha in 2014, indicating a downwards trend. Detailed information of the changes in mining areas is shown in the following Fig. 7.

Fig. 7 Variation diagram of mining area in the study area

(1) In accordance with the changes in the mine covering areas, legal mining was increasing,reflecting a stricter national monitoring on mining activities and a better outcome of the monitoring;illegal mining decreased from 53.9 ha in 20 122 to 25.88 ha in 2013, having been reduced by half during two years, while the illegal mining jumped to 77.5 ha in 2014 due to the illegal development of private clay minerals mines for bricks and the increasing of previous illegal mine covering area.The significant increase in illegal mining in 2014 requires further control and management; closed or abandoned covering area decreased from 473 ha in 2011 to 255.95 ha in 2014, while a slight increasing trend showed in 2014; no significant change has occurred in the transfer site area; solid waste materials reduced from 1 007.98 ha in 2011 to 784.61 ha in 2014 due to the re-use dump of mining waste and the control and management of the solid wastes; and mine construction area declined from 45.78 ha in 2011 to 29.76 ha in 2014.Detailed information is shown in Fig. 8 and Table 2.

(2）Varieties of minerals developed from 2011 to 2014 decreased year by year. Production of minerals in 2011 such as shale, limestone, shale for cement, diorite and other minerals stopped in 2012,due to the state mining rectification policy and limited reserves of mineral resources. Two new construction sandstone areas covering 0.51 ha showed up during 2012-2014 compared with 2011.

Fig. 8 Area Comparison chart of mine covering area type (2011-2014) (ha)

Table 2 Comparison statistics chart of mine covering area type (2011-2014)

(3) Coal mines dropped from 120 in 2011 to 77 in 2014, a decrease of 34.88 ha in total area. Due to the increase of coal price and labor costs,decrease in demand and development security,development of coal, a kind of energy mines, has involved from the conventional open mines to underground development, reducing the land occupation significantly and environment pollutions caused by coal development. With the control and management by state in recent years, some illegal open/underground coal mines have been shut down, which has further reduced the occupied area of coal mines.

Influenced by resource reserves and environment conditions, iron ore mine covering areas decreased from 396 in 2011 to 304 in 2014, and the total occupied area has been declined by 302.59 ha, almost half of that in 2011; copper ore mine covering areas reduced from 172 in 2011 to 149 in 2014, a decrease of 56.2 ha in occupied area.In addition, gold mine covering areas increased from 6 in 2011 to 19 in 2014, an increase of 26.24 ha in occupied area.

(4) Non-metallic mineral mining is dominated by limestone, among which limestone for construction has the largest area, followed by cement limestone and limestone. Due to reasons of mineral resources reserves and national recovery and management of the mine environment, the number of construction limestone mines dropped from 321 in 2011 to 289 in 2014, but the occupied area grew from 703.81 ha in 2011 to 774.93 ha in 2014;though the number of mines declined, the occupied area has increased, indicating that the urban construction in recent years has stimulated the demand for such resources. Therefore, cement limestone mines increased from 52 in 2011 to 88 in 2014, and at the same time the occupied area nearly doubled by an increase of 196.93 ha from 2011 to 2014; limestone mine covering areas dropped from 123 in 2011 to 96 in 2014, reducing the occupied area by 53.07 ha.

4 Conclusions and suggestions

4.1 Conclusions

(1) Analysis of multi-source and multitemporal remote sensing data shows: Mine covering area among the mining activities in the research area has the is the largest, accounting for 38.86% of the total research area, followed by transfer sites and solid wastes area, 30.41% and 29.58% of the total research area respectively;mine construction accounts for 1.15% of the total research area.

(2) Minerals in the research area mainly are energy mine, metal ore and non-metallic minerals.Energy mines areas are small, and are distributed in a scattered form. Main energy mine is coal mine with a downward trend in coal mining from 2011 to 2014. Metal mining area is large and is distributed in a centralized way. Iron ore and copper ore have the largest area, which shows a declining trend for the past four years.Non-metallic mining is in a large scale and quantity, and the main mining areas are for construction limestone and limestone. Construction limestone and limestone mining from 2011 to 2014 is on the rise.

(3) From the administrative unit, the main mining regions of the research area are Xianning and Huangshi. Mining in Xianning is mainly for non-metallic exploitation, which is dominated by construction limestone, with an average of 28.12 ha/year, accounting for 23.97% of the total area of mining activities in Xianning; mining in Huangshi is mainly for metals, among which iron mine has the largest area, with an average area of 273.7 ha/year, accounting for 11.2% of the total area of mining in Huangshi, and mining area for other minerals is relatively small.

(4) Monitoring of the change of mining area types from 2011 to 2014 shows as follows: legal mine covering area has a upward trend; trend of illegal mining covering area is in a zig-zag pattern,rising after first decreasing; closed and abandoned mining covering area shows an overall downward trend with a slight increase in 2014; changes in the transfer site covering area of the four years are not obvious; solid wastes and mine construction areas have an overall downward trend.

4.2 Suggestions

With the strengthening of the development of the mining industry in Hubei Province and management of relevant government departments,changes in mine development area of the eastern part of Hubei gradually become to level off, and the mining order is getting better year after year.However, due to the waste heaps and mineral pools left by illegal and irrational exploitation, damages to mine environment still exist, causing air pollution, destruction of vegetation, and geological disasters such as soil erosion, collapse, landslides,mudslides, slides and ground cracks and posing a more serious threat to the ecological environment(FENG Chun-tao and ZHENG Juan-er, 2014).Therefore, the reasonable control of resource development is extremely important, and suggestions and countermeasures are also an urgent need for mine development activity.

(1) To develop reasonable rules and regulations to strictly control the mineral development. Adhere to the “lawful, reasonable and environmentallyfriendly mining” principle, divide the planning area based on the restrictions and permissions of laws and regulations and ensure that the exploitation is in line with the overall planning and environmental protection requirements.

(2) To reasonably determine the amount of mineral resources exploitation and utilization, and then carry out the development according to market conditions and national economic situation,achieving dynamic cycle and the balance between current interests and long-term interests.

(3) To use remote sensing technology for real-time supervision on the mining areas to provide detailed data for government departments,so as to strengthen monitoring and approval of mine development area.