A New Round of Bauxite Exploration in Henan Province

(Henan Nonferrous Metals Bureau of Geology and Mineral Resources)

Henan is one of the main producing areas of bauxite in China, and its ore-bearing rock series forms an irregular triangle in Sanmenxia-Zhengzhou-Pingdingshan, with a total distribution area of about 15000km2. The traffic conditions in the bauxite distribution area are good, including Longhai Railway, G3 10 National Highway and Lianhuo Expressway, Beijing-Guangzhou Railway, G 107, G207 and Beijing-Zhuhai Expressway. Urban and rural roads are also connected into a network, and the mining area is also connected with the countryside through gravel roads. The development of aluminum industry in Henan province has the advantages of resources, energy and industry. At present, the output of bauxite, alumina and electrolytic aluminum in Henan Province ranks first in China, and it has become an important aluminum industrial base in China. Large alumina enterprises such as Henan Branch, Zhongzhou Branch, East Hope (Sanmenxia) Aluminum Company, Cayman Company of Hangzhou Jinjiang Group, Xiangyi Aluminum Company, Xiangjiang Wanji, Sino-American Aluminum Company and Pingdingshan Huiyuan have formed an annual alumina production capacity of 8 million tons, and the annual consumption of bauxite is about 22 million tons. Alumina enterprises have strong demand for bauxite resources. However, the rapid development of aluminum industry needs the full guarantee of basic resources (bauxite). As far as the proven bauxite resource reserves in our province are concerned, the sustainable development of aluminum industry is facing the severe challenge of insufficient bauxite resource guarantee, and the production capacity, annual supply and annual consumption are seriously unbalanced; The insufficient supporting capacity of bauxite resources has become a bottleneck restricting the sustainable development of aluminum industry.

Good development conditions, huge resource potential and serious resource bottleneck make the new round of bauxite exploration time tight, task heavy and pressure heavy. It is necessary to study major issues from the perspective of prospecting and exploration-summarize and understand the metallogenic regularity of bauxite, select key areas, clarify policy and technical issues, and make breakthrough progress as soon as possible.

Review of bauxite exploration and scientific research in the past 50 years

After more than 50 years of bauxite exploration and research since the founding of New China, a number of important bauxite resource points have been discovered, and some important knowledge of metallogenic regularity has been formed.

By the end of 2006, 74 bauxite deposits have been discovered in Henan Province, with a total resource reserve of 572.23 million t, of which the basic reserve is 200.77 million t. The basic reserves and resources account for 35.09% and 64.95438+0% of the total reserves respectively. Considering the consumption reserves of civil mining that have not been counted, the basic reserves available for industrial design and mining are even less, and a large number of inferred resources need to be explored and upgraded, so the bauxite resources supporting the development of aluminum industry in Henan are seriously insufficient.

According to the distribution characteristics of bauxite caused by paleometallogenic environment and structural changes since Mesozoic, the bauxite in the whole province is divided into seven grade IV metallogenic areas, including Shanxian-Mianchi-Xin 'an aluminum (clay) metallogenic area, Yanshi-Gongyi-Xingyang aluminum (clay) metallogenic area, Dengfeng-Xinmi aluminum (clay) metallogenic area and Yuzhou-Jiaxian aluminum (clay) metallogenic area. Among them, Shanxian-Mianchi-Xin 'an aluminum (clay) metallogenic area has the largest number of large and medium-sized bauxite deposits.

Alumina (clay) minerals come from Carboniferous benxi formation on the ancient denuded crust of Cambrian and Ordovician carbonate rocks. It belongs to the aluminum (clay) soil deposit of carbonate paleoweathering crust, and the ore body is strictly controlled by the denudation topography of paleoweathering crust. The bauxite hosted in Carboniferous benxi formation (C2b) is 30 ~ 80m away from the main coal seam (Er 1 coal seam) hosted in Shanxi Formation of Lower Permian (P 1s). When the buried depth of bauxite is greater than 150m, there are generally mineable coal seams or inedible inferior coal seams in the upper part.

The bauxite-bearing rock series in this area can be divided into three lithologic sections from bottom to top: Lower section (C2b 1): iron clay rock. Gray-white, purple-red, pea oolitic, clastic structure, block and spot structure. The iron content increases gradually from top to bottom. The middle and upper parts are sandwiched with bauxite and clay mineral lenses. The lower part contains massive and oolitic hematite or siderite and pyrite, and some areas are rich in intact iron ore bodies or pyrite bodies. The thickness of this layer is 0 ~ 20.85 m, generally1.50 ~ 5.00 m. The partial loss of this section may lead to the direct contact between bauxite layer and CAMBRIAN and Ordovician limestone. Middle section (C2b2): It consists of bauxite, high alumina clay, hard clay and alumina rock. Rocks and minerals are gray, dark gray, yellow-brown and ochre, with granular, pea-like, bean-like, clastic and cohesive structures, blocky and porous structures. The general thickness is 0.50 ~ 6.00 meters, and the maximum thickness is 75 meters (summer night in Jiyuan). Upper member (C2b3): hard clay ore and clayey shale. Gray, gray, yellowish brown, sometimes with carbonaceous shale or coal lines at the bottom. The thickness of this layer is 0 ~ 20m, generally 0.50~3.00m, and it is the unstable roof of bauxite layer. The boundary between the three is not obvious or a certain paragraph is missing.

Generally speaking, the strata in the mining area are monoclinic with gentle dip angle (5 ~ 20), and the occurrence of ore bodies is consistent with the strata. In space, the overall shape of large bauxite bodies should be a composite shape of irregularly embedded bucket-shaped ore bodies with a thickness of several meters above the average thickness on the background of layered ore bodies with a thickness of one to several meters. The roof of the ore body is relatively flat, and the floor of the ore body is uneven. On the plane, due to the phase transformation and later erosion of bauxite and clay minerals (rocks), bauxite bodies are often irregular, with or without skylights and harbors, and sometimes the boundary shape of ore bodies is complex; In the cross section, it is layered, lenticular (hollow bucket) or a combination of the two, and sometimes there are clay mineral (rock) interlayers. Among them, lenticular ore bodies are often located in the ancient karst caves of carbonate rocks in the chassis because of their large thickness and good ore quality. Generally speaking, the thickness variation curve of large and medium-sized bauxite deposits is single peak, with a wide range of thickness frequency variation, and the thickness variation coefficient is between 80% ~ 100%.

The main mineral component of the ore is diaspore (content 50% ~ 90%), which is usually in the form of particles with a particle size of about 0.0 1mm, and its aggregate is often in the form of oolite, bean, lump or internal debris. The minor mineral components of the ore are kaolinite (less than 20%) and hydromica (less than 10%). The main chemical components of the ore are Al2O3, SiO2, Fe2O3, TiO2, S, Loss, etc. And the content is relatively stable. On average, the content of Al2O3 is 60% ~ 72%, the coefficient of variation is about 10%, the content of TiO2 is 5% ~ 15%, the coefficient of variation is about 50%, and the content of Fe2O3 is 1.5% ~ 10%. The content of S is 0.5% ~ 1.5%, the coefficient of variation is 60% ~ 150%, and the loss is roughly 12% ~ 15%. The average A/S in the mining area is 4 ~ 9.

In 2007, the detailed survey of deep bauxite in Caoyao mining area was completed (looking for aluminum under coal), with an exploration area of 14.655km2, the maximum exploration depth of about 670m, and the resources above Class (333) of 6 1.23 million t (estimated area of about 6.50km2). Due to the continuous exploration of several deep boreholes with large spacing (1600m), there are still (334) kinds of predicted resources in the area of 6 1 10,000 tons, and the resource reserves in the whole mining area exceed 1 100 million tons, reaching a super-large scale. The average thickness of ore bodies in the whole area is 4.98m, the average Al2O3 content is 62.78%, the average S content 1.03%, and the average A/S ratio is 4.8. It is worth noting that, compared with Guangou, Zhuanggou, Fan 'ao and Jiajiaao bauxite deposits in shallow exploration areas (in the north of this area), with the increase of depth, there are still about 1/3 samples with a/s >: 7; The sulfur content increased significantly (the shallow sulfur content was 0.113% ~ 0.153%). The exploration of deep bauxite in Caoyao coal mining area is a major breakthrough in bauxite prospecting in Henan Province, which has important demonstration significance for deep bauxite prospecting in the whole North China platform area.

Two, the new round of bauxite exploration should give priority to the deployment of key areas.

Summarizing the achievements and experiences of bauxite prospecting and scientific research for more than 50 years, the new round of bauxite prospecting and exploration should be deployed in the surrounding areas of the "two dragons and two depressions" in the bauxite metallogenic triangle of our province. The exploration work focusing on upgrading resources is mainly carried out within the scope of existing bauxite "two certificates", which is expected to increase (333) bauxite resources1~10.50 billion t; The prospecting work is mainly carried out in the "two certificates" area of coal mine and the shallow area with a buried depth of 700m m. It is estimated that 450 million tons of bauxite resources can be added.

(1) There is a wood belt uplift around it.

The district includes four counties and cities: Shaanxi County, Mianchi County, Xin 'an County and Jiyuan County. Daimanzhai uplift is a platform uplift area in the Middle Carboniferous of North China Platform, and the surrounding carbonate strata have undergone long-term seawater leaching and laterization. The paleokarst terrain in this area is moderately mature, with vertical rhythm changes of hard clay, bauxite and iron clay in some bauxite-bearing rock series, and coal lines in some bauxite layers indicate the changes of paleoclimate, sea immersion and regression. Suitable metallogenic geological environment, deposition formed a huge bauxite deposit. The ore-bearing rock series of the Upper Carboniferous benxi formation aluminum (clay) mine stretches 100 km in this area. The differential tectonic movement since Mesozoic has formed a large number of structural fault blocks. With Koumenshan and Longtangou faults as the boundary, it can be divided into three secondary ore belts: Qiligou-Jiaodi aluminum (clay) ore belt (western ore belt), Dujiagou-Yushan aluminum (clay) ore belt (central ore belt) and Zhangyaoyuan-Xiaye aluminum (clay) ore belt (eastern ore belt).

This area is an important bauxite metallogenic belt in our province, which has achieved a series of exploration results and is also the key deployment area for a new round of bauxite prospecting. The prospecting for medium-deep bauxite should be deployed in the following eight key areas. Through this work, it is estimated that the reserves of bauxite resources can be increased by 330 million tons;

(1) Looking for a mining area in the middle of Luhualing-Bailang-Chuangshan in Mianchi County. The western ore belt is in the north, with an area of 10km2, a buried depth of 150 ~ 400 m, a pre-acquired resource of 40 million t and A/S ratio of medium to high. This area is adjacent to the Yellow River, and normal faults are developed in the northeast. In the future exploration, we should pay full attention to the hydrogeological conditions in the mining technical conditions.

(2) Zhaozhuang-Wanggudong-Fanjiashan, Shaanxi County, looking for deep mining areas. The western ore belt is in the south, with an area of 10km2, a buried depth of 300 ~ 700 m, and a pre-acquired resource of 20 million tons. The phase transformation of bauxite ore in this section is frequent, the shape of bauxite body is complicated to predict, and the A/S ratio is moderate.

(3) Zhijian-Cai 'ao, Shanxian County, is looking for a deep mining area. The western ore belt is in the east, with an area of 30km2, a buried depth of 300～700m and a pre-acquired resource of 60 million tons. It is located in the lower part of Zhijian coal mine area, and it is expected to find high-grade and large-scale bauxite bodies.

The above three sections are all located to the west of Kumenshan fault. A series of high-angle normal faults that strike northeast and tend northwest constitute the deep boundary of each exploration profile.

(4) Mianchi County Caoyao-Jiajiaao-Lizhuangzhai is located in the middle-deep exploration area. It is located in the west of the middle section of the middle ore belt, with an area of 15km2, a buried depth of 200~700m and a pre-acquired resource of 50 million t ... There may be a large east-west fault in the west of this section, which leads to the decline of the southern plate and the increase of exploration depth. The occurrence of strata in the east is steep, which limits the scope of shallow exploration area and the buried depth is 700 meters.

(5) Guiwu-Duancun-Leigou-Hongyang, Mianchi County, looking for middle-deep mining areas. Located in the middle of the middle ore belt, with an area of 10km2, buried depth of 400 ~ 700 m and pre-acquired resources of 35 million t ... The fold structure in the same metallogenic period may aggravate the phase transformation of alumina (clay) ore, resulting in more complicated bauxite ore body shape.

(6) Tiemen-Yushan in Xin 'an County is located in the middle and deep part of the exploration area. Located in the east of the middle ore belt, it covers an area of 30 square kilometers, with a buried depth of 200 ~ 700 meters and a pre-acquired resource of 50 million tons ... It should be noted that the NW-trending Longtangou fault may constitute the northern boundary of this section, and the occurrence of ore-bearing rock series on both sides of the fault is completely different.

The above three sections are sandwiched between Koumenshan fault and Longtangou fault in the northern wing of Mianchi-Xin 'an syncline basin. The existence of nearly east-west faults in this area may make the ore-bearing rock series descend southward in a stepped way, thus limiting the scope of effective exploration area.

(7) The middle-deep exploration area of Goutou-Jiagou-Shi Si in Xin 'an County. Located in the south of the East Ore Belt, it covers an area of 30 square kilometers, with a buried depth of 350 ~ 700 meters and a pre-acquired resource of 60 million tons ... The occurrence of strata in the south of this section tends to the northeast with a large dip angle, and the north is close to Xiaolangdi Reservoir. The iron and sulfur content in the middle exploration section may be high.

(8) Jiyuan is looking for a mining area in the summer night. Located in the north of the East Ore Belt, it covers an area of 20 square kilometers, with a buried depth of 200 ~ 700 meters, and the pre-acquired resources amount is150,000 tons ... The maturity of ancient karst landform in this area is low, and the ore-bearing rock series is generally nearly north-south, mainly aluminum clay rocks, and its bauxite bodies are mostly isolated islands, with small scale, great thickness variation and high exploration difficulty.

(2) Around Songshan Uplift

The region includes yanshi city, gongyi city, Xingyang, xinmi city, Dengfeng, Yichuan and Yiyang counties. Songshan Uplift is a Tailong area of Middle Carboniferous in North China Platform, and the surrounding carbonate strata have undergone long-term seawater leaching and laterization. The ancient karst terrain in this area is relatively mature, including Yanshi-Gongyi-Xingyang aluminum (clay) metallogenic area, Dengfeng-Xinmi aluminum (clay) metallogenic area and Yiyang-Yichuan aluminum (clay) metallogenic area. The differential tectonic movement since Mesozoic not only cut the ore-bearing rock series into structural blocks of different sizes, but also caused different burial depths and different or even opposite tendencies from uplift.

This area is the earliest bauxite metallogenic belt for prospecting and exploration in our province. There are many ore occurrences and deposits in this area, and a series of achievements have been made in geological exploration. Faults are developed in this area, and the scale of a single bauxite body is medium and small. Bauxite, clay ore and clay rock in ore-bearing rock series have frequent phase transitions, and the internal structure of ore bodies is relatively complex. Bauxite ore has a medium grade, with an average Al-S ratio of 4 ~ 6. In the new round of bauxite prospecting, it is advisable to deploy medium-deep prospecting work in the following two key areas first. Through the work, it is estimated that 30 million tons of bauxite resources will be increased.

Pianqiao-Jiaocun Middle-Deep Prospecting Mining Area in Yanshi County: located on the northern slope of Songshan Mountain, in the western section of Yan-Gongcheng ore belt. The area is 15km2, the buried depth is 250~700m, the pre-acquired resources are150,000 t, there are many NE and NW faults in the area, and karst groundwater is developed, so the future exploration and development should be carefully studied.

Sunpo-Jiagou-Shendian Zhongshen Prospecting Mining Area in Yanshi County: located in the north slope of Songshan Mountain, in the middle section of the Yan-Gongcheng ore belt. The area is 10km2, the buried depth is 2.5-700m, and the pre-acquired resources are150,000 t. The nearly east-west fault in this area limits the exploration scope of bauxite tendency. The NW-trending fault may communicate the hydraulic connection of karst groundwater, which is a problem that needs to be seriously studied in the future exploration and development.

(3) periphery of Yuzhou fault basin

This area includes Yuzhou City and a part of Dengfeng City. Yuzhou fault (depression) basin is a fault depression area since Mesozoic and Cenozoic, which is only geographically attached to the surrounding bauxite-bearing rock series, and has no genetic relationship, and is also different from the bauxite-bearing rock series around the coal-accumulating basin. This area belongs to Yuzhou-Jiaxian bauxite metallogenic area, and the bauxite area around Yuzhou fault (depression) basin is explored and deployed in a unified way to emphasize the existing characteristics and influence of fault structures in this area.

Dishuitan-Fangshan-Mojie medium-deep prospecting area in Yuzhou City: area 15km2, buried depth of 300~700m, pre-acquired resources of 654.38+500,000 t ... The paleokarst landform in this area is not mature, bauxite bodies often exist as isolated lenses with different sizes, and the ore grade is medium and rich.

The Shenhou-Hongchang Zhongshen prospecting mining area in Yuzhou City covers an area of 20 square kilometers, with a buried depth of 250-700 meters and a pre-acquired resource of 20 million tons ... The ancient karst landform in this area is mature, the phase transition between alumina (clay) ore and alumina clay rock is strong, and the shape of bauxite body is complex.

(4) The area around Ruzhou-Baofeng fault (depression)

The area includes Ruzhou City, Jiaxian County, Baofeng County, Lushan County and Shilong District of Pingdingshan City. It belongs to Ruyang-Ruzhou-Baofeng aluminum (clay) metallogenic area. Ruzhou-Baofeng fault depression area is a fault depression area since Cenozoic, but it is geographically dependent on the surrounding bauxite-bearing rock series and has no genetic relationship. The NW-SE fault consistent with the long axis of the depression descends from both sides of the depression to the middle, which increases the buried depth of bauxite-bearing rock series.

Baofeng Han Zhuang-Zhangbaqiao middle-deep prospecting area: with an area of 30km2, buried depth of 150~450m ~ 450m, and pre-acquired resources of 45 million tons ... Generally speaking, this section is northwest-southeast structure, with the maximum buried depth of ore-bearing rock series in the middle of about 450m, which gradually becomes shallower to the two wings. In the future exploration, we should pay attention to the position of the erosion boundary of Cretaceous basalt in the north and the imbricate fault in the northwest-southeast direction in the south. The thickness of bauxite layer in this area is relatively stable, and the ore grade is moderate, with A/S of 4 ~ 5.

With the progress of the new round of bauxite prospecting and exploration, we will find new situations and study new problems, and further deploy favorable areas for bauxite prospecting in the middle and deep parts of the surrounding areas of "two ridges and two depressions" and obtain more exploration results.

Iii. Problems to be solved in the new round of bauxite exploration

The new round of bauxite exploration focuses on the section within the "two certificates" of coal mine, where the bauxite-bearing rock series is buried 700 meters deep and shallow. There are some major problems that need to be studied and solved urgently in terms of policies, technologies and exploration methods.

The Mineral Resources Law of People's Republic of China (PRC) defines the uniqueness and exclusiveness of the ownership of "exploration right and mining right" at the policy level, so there are legal obstacles to bauxite exploration and exploration within the scope of "two certificates" in coal mines.

In fact, the focus of the new round of bauxite exploration is mainly within the scope of coal mine "two certificates" mining rights, which are divided into three types: coal mine goaf, coal mine mining area and coal mine reserved area. Exploring bauxite in "coal mine goaf" has no influence on coal mining, while exploring bauxite in "coal mine preparation area" can greatly improve the control degree of coal seam, and using underground mining engineering in "coal mine mining area" to explore bauxite can greatly save exploration cost. The scope of "mining right" of coal mine does not include the ore-bearing strata of bauxite in the lower part, so the main problem of "aluminum under coal" exploration at the policy level is the enthusiasm of coal mining enterprises and the coordination of interests under the leadership of the government.

Within the scope of coal exploration right, because the exploration grid of bauxite is much denser than that of coal (bauxite survey is equivalent to coal detailed survey or exploration), coal exploration can locate the exploration depth of bauxite relatively accurately, and bauxite exploration can greatly improve the control degree of coal exploration, which is a good thing for two purposes. Under the leadership of the competent government departments, it is entirely possible to make institutional innovations beneficial to the country and enterprises.

On the technical level: at present, domestic bauxite exploration is basically carried out in accordance with the principles and procedures determined by the specifications, and the evaluation period of deposit scale is long; The study of bauxite mineralization law is limited to macroscopic or microscopic characteristics, and it is rarely analyzed and evaluated from the perspective of exploration. Therefore, from the perspective of exploration, systematically analyzing, studying and summarizing the formation conditions and output characteristics of bauxite, as well as the relationship with the maturity of ancient karst landforms, ancient structures and contemporaneous structures, can establish a perfect technical index system for rapidly evaluating the scale of bauxite deposits.

The main contents of the technical index system are: a foundation, five parts and three means.

One foundation: investigation and study based on metallogenic background.

Five parts: ① Ore-bearing rock series: thickness, change and continuity of natural outcrop (or shallow exploration area); Vertical combination characteristics; Weight of ore body. (2) Ore body characteristics: ore body scale and internal structure; Surface mineral content rate and large thickness rate; Characteristic model of ore body. ③ Ore characteristics: mineral composition, chemical composition, change and their relationship; Structure, structure, change and relationship. (4) Ore-controlling structure: paleostructural maturity and paleokarst landform and their relationship; Syngenetic structure and its relationship with ore body characteristics and ore structure. ⑤ Mining technical conditions: main hydrological and engineering geological problems.

Three means: taking geological survey, geophysical survey and reasonable and effective drilling as the main means, clarifying the working methods of various means and emphasizing the effective combination of means.

The key technologies of the new round of bauxite prospecting and exploration are: ① the analysis technology of small structural differences between bauxite basement and caprock; (2) Syngenetic structural analysis technology in bauxite mineralization period; ③ maturity analysis technology of ancient karst landform; ④ Differentiation of physical differences, combination of geophysical methods and target determination technology; ⑤ Coal mine goaf drilling technology; ⑥ Combination of exploration means under different conditions.

In terms of research methods, it emphasizes to look at the problem from the perspective of exploration and the scale of middle view; Highlight the combination of comprehensive research on indoor data and field geological survey; Combination of geological and geophysical exploration; Give full play to the role of computer technology in the study of bauxite mineralization law, the extraction of characteristic parameters of ore bodies and the exploration and simulation of ore deposits.

The new round of bauxite exploration is deep and costly. Because of the geological characteristics of bauxite deposits, it is difficult to realize large-scale systematic control. This requires a breakthrough in the combination of geological analysis technology, geophysical survey technology and exploration methods. Grasp the key points, grasp the key points, narrow the target area and improve the effect.