The metallogenic sub-series belongs to the metallogenic series of Luoan block deposits distributed in Mianchi-Yima area, Henan Province. The metallogenic belt is about 20 kilometers long from east to west, 2 ~ 2.5 kilometers wide from north to south, and covers an area of 100 square kilometers.

During the Triassic period, due to the uplift of the earth's crust, the distribution of large-scale sedimentary basins in the interior of North China Platform gradually narrowed, and the sedimentary basins were limited to Jiyuan and Yima in the early Jurassic.

A set of coal-bearing formations, mainly feldspathic sandstone, siltstone, carbonaceous claystone and coal seam, were deposited in the early and middle Jurassic in Yima Basin, distributed in the middle of the basin. In the late Jurassic, due to the influence of Yanshan movement, the crustal movement in this area changed from overall ups and downs to local depressions and faults. At this time, Mianchi-Yima area became a deep depression basin, during which massive conglomerate with poor sorting and unclear bedding was deposited, and the sedimentary environment changed from early calm freshwater lake facies to intermountain jet and alluvial fan facies.

Cretaceous sporadic outcropped in the south of the basin, distributed on the Jurassic. The lower series is mainly composed of pink and gray tuffaceous sandstone, tuffaceous glutenite and siltstone. The Upper Series is a set of reddish-brown conglomerate layers with a small amount of gray-green thick argillaceous siltstone.

Mianchi-Yima basin is surrounded by Triassic, with complete outcrops in the north and east and sporadic distribution in the south and west. The sediment is a set of clastic rock series from lakeside facies to limnetic facies in continental basin. The clastic rocks of the lower series are purplish red and grayish purple, which are composed of timely sandstone, feldspar timely sandstone, sandy claystone, sandy shale and siltstone. The rocks in the lower part of the Middle Series are mainly purplish red, the rocks in the middle part are interbedded with purplish red, purplish gray and yellowish green, and the rocks in the upper part are mainly yellowish green and brownish yellow. This series is mainly composed of feldspathic sandstone and claystone with a small amount of shale. Claystone often contains calcareous nodules with calcareous conglomerate at the bottom. The lower part of the Upper Series is yellow-green, beige feldspar sandstone, calcareous siltstone and sandy claystone sandwiched with thin coal seams, and the upper part is grayish yellow, grayish green and gray, which is composed of feldspar sandstone, silty claystone, claystone and coal lines.

At the end of Triassic, affected by Indosinian movement, the crust in this area uplifted and the surrounding area of Mianchi Yima uplifted. Later, the early and middle Jurassic coal-bearing formations of lakeshore swamp facies were deposited in the basin, and the tectonic environment was in a stable ascending and descending movement. During the early Jurassic coal-accumulating period, the sedimentary environment was relatively calm and lasted for a long time. From the end of Jurassic to the beginning of Cretaceous, influenced by Yanshan movement, fault structures developed, which destroyed the integrity of Jurassic sedimentary basin, formed a small fault depression and deposited a set of Cretaceous molasse formations.

Second, the ore-controlling geological conditions

(1) stratum

The formation of coal can not be separated from favorable sedimentary environment, and it exists in specific sedimentary rock series. Therefore, the controlling effect of stratum on coal mine (rock stratum) is obvious.

1. Yima Formation

This formation belongs to the Middle-Lower Jurassic, which is the coal-bearing stratum of this metallogenic subsystem. Yima area is well developed, and the representative profile is shown in Figure 4-9.

Fig. 4-9 Section of Yima Formation (J 1-2y) of Middle and Lower Jurassic in the west of Yima Open-pit Mine.

(According to Jiaozuo Mining Institute 1982, slightly modified)

Overburden: Neogene conglomerate.

Mineralization of Main Minerals and Metallogenic Series of Deposits in Henan Province

inconformity

Yima Formation of Middle and Lower Jurassic (J 1-2y) is124.7m thick.

1 1. Gray-white, gray-green and red clay layer 5.9m

10. Black dense massive claystone containing siderite layer. Production of bivalve shellfish. Ostracoda, Ostracoda and Fish Scale Fossils18.3m.

9. The middle coal is 4.6m with dark brown sandstone and clay rock.

8. The upper gray-black and black claystone and sandy claystone are sandwiched with gray thick siltstone and thin coal seam, and the lower gray-black thick siltstone and sandy claystone. Contains a large number of animal and plant fossil fragments 7.8m

7. Gray thick-thick siltstone mixed with thin black sandy clay rock. The top is black sandy claystone and claystone. Rich in plant fossils15.4m.

6. Medium-fine grained feldspar quartz siltstone mixed with calcareous fine sandstone, with thick khaki layer, 20.7m.

5. Light gray thin-layer medium-fine grained sandstone mixed with gray siltstone. The bottom is 6.8m gray-white medium-thick fine-grained calcareous seasonal sandstone.

4. Light gray thick layer fine grained timely sandstone mixed with thin gray sandy claystone17.7m.

3. Gray medium-thick siltstone. Contains 9.5 million plant fossils.

2. Bottom coal, thin layer containing carbonaceous claystone, siltstone and carbonaceous siderite,13.0m.

1. Sand and conglomerate layers, usually converted into gravel claystone or interbedded with sandstone and claystone, with a thickness of 5.0m.

inconformity

Underlying stratum: Tanzhuang Formation of Upper Triassic (T3t)

2. Ma 'ao Formation

The stratum belongs to the Middle Jurassic, and the lower member is grayish yellow, grayish green, purplish red and grayish white sandy clay and claystone, mixed with sandstone and conglomerate, and the bottom is thick conglomerate. The upper member is brick red sandy claystone mixed with grayish green and grayish yellow sandy clay and conglomerate. The sedimentary thickness is156 ~196m, which is mainly lacustrine sediments.

3. Upper Jurassic

The lower part of the series is red conglomerate mixed with sandstone and clay rock, and the upper part is brown and gray thick conglomerate mixed with gravel. It belongs to a set of alluvial fan conglomerate. The thickness is 393 ~ 446 m.

According to the Jurassic sedimentary rock assemblage and lithological characteristics, coal-forming mainly occurred in the early Jurassic, and the coal mine was controlled by the Yima Formation of the Middle and Lower Jurassic.

(2) Lithofacies palaeogeographic characteristics

The Jurassic sediments in this area generally inherited the sedimentary environment of the Late Triassic. Due to the continuous uplift of the North China platform, the lake basin was further narrowed, leaving only Mianchi-Yima and Jiyuan small basins in the early Jurassic. According to sedimentary rock assemblage and lithologic characteristics, Mianchi-Yima basin belongs to lakeside swamp facies in early Jurassic. Yima Formation contains a large number of plant fossils, mainly ferns and gymnosperms, and animal fossils mainly include bivalves, arachnids and ostracods. Coal is formed under weak reduction and reduction conditions. In the middle and late Jurassic, the basin sediments were lake facies and intermontane alluvial fan facies, which was not conducive to the formation of coal.

(3) Paleoclimatic characteristics

In the Late Permian, the climate of North China Platform changed to hot, dry and little rain, and the Carboniferous and Permian coal accumulation periods ended. This climatic feature lasted until the Middle Triassic. After the Middle Triassic, the climate gradually turned to warm, humid and rainy, which was beneficial to plant growth and reproduction. After the late Early Jurassic, it turned into a dry-hot climate. The coal formation from Carboniferous to Permian and Jurassic shows that climate plays an important role in coal formation.

(4) Ore-controlling structure

In the process of diagenesis and mineralization, geological structure and geological structure always complement each other. The lithologic characteristics of sediments and different types of rock combinations in the basin can often reflect the geological and tectonic environment in the process of diagenesis and mineralization.

Indosinian movement lifted the basement of Yima area in Mianchi, forming Jurassic inland lake basin, which provided a place for coal accumulation. According to the characteristics of sedimentary rock series of Yima Formation, the early Jurassic lake basin was in a stable ascending and descending movement, and the sedimentary facies belonged to lake swamp facies. The accumulation speed of humus is basically consistent with the subsidence speed of the basin, which makes the coal accumulation last for a long time and becomes a balanced compensation basin, which provides good geological structural conditions for the generation and accumulation of coal. By the middle and late Jurassic, the crustal movement was frequent. The tectonic environment has been in an unstable state, and climate change has led to the end of the coal accumulation period. At the end of Jurassic, due to the influence of Yanshan movement, fault structures developed in this area, which destroyed the coal seam.

Three. Metallogenic characteristics

(1) coal-bearing strata

The coal-bearing strata in this area belong to Yima Formation of Middle and Lower Jurassic. The bottom of this formation is sand and conglomerate, composed of bluish gray and grayish white medium-coarse grained sandstone, containing quartzite and timely sandstone gravel. With a thickness of 0.9 ~ 59m, the lower part is gray siltstone, medium-fine grained feldspar sandstone mixed with carbonaceous claystone and thick coal seam (coal 1- coal 2); The upper part is gray-black claystone mixed with sandy claystone and siltstone, containing middle coal and upper coal 1- coal 2. The upper coal and aluminum clay rocks in the eastern part of the coalfield are often eroded. The thickness of coal-bearing strata is between 26 ~136 m.

Coal measures strata are exposed in the axis of Mianchi syncline and distributed in Qian Qiu, Changcun, Yima, Yangcun, Gengcun and other places, with a dip angle of 65438+00 ~ 25.

(2) Coal seam production characteristics and spatial changes.

There are 2 ~ 5 coal seams in the coal-bearing series, with a total thickness of about 2 1m and a coal-bearing coefficient of 28.26%. Each coal seam from bottom to top is:

1. Bottom coal 1

Located on the conglomerate at the bottom of coal-bearing measures. The roof is fine sandstone and siltstone, the floor is claystone and carbonaceous claystone, and there is direct breccia locally. Coal seams are mainly developed in the shallow and middle-deep parts of the western metallogenic belt, and merge with bottom coal 2 when they extend to the deep part. The structure of coal seam is complex, with 6-7 layers of gangue, up to 12 layers, the thickness of gangue is generally 0.0 1 ~ 1.72 m, and the lithology is mostly clay rock and carbonaceous mudstone. The thickness of coal seam is generally between 0.24-2 1.76m, with an average thickness of 8.5 1m and a local thickness of 31m. The coal seam is unstable along the strike and belongs to local mining.

2. Bottom coal 2

Located in the lower part of coal-bearing rock series, the roof and floor are clayey rocks. The distribution of coal seams in the metallogenic belt is stable, and the thickness of coal varies from 0.39 m to 7.56 m, which is generally recoverable. The structure of coal seam is complex, generally containing 2 ~ 6 layers of gangue, up to 19 layers, and the thickness of gangue is 0.03 ~1.85 m.

3. China Coal

Located in the middle of coal-bearing rock series. Generally, the coal seam is 4m thick, which is basically stable and recoverable in most areas. The roof and floor are claystone or mudstone, and the floor in some areas is fine sandstone. The coal seam structure is simple, with 2 ~ 3 layers of gangue, and the thickness of single layer of gangue is 0.03 ~1.42 m.

4. Upper coal

Located in the upper part of coal-bearing measures, 8 m away from China Coal12 ~/KLOC-0. The roof and floor are clayey rocks. This coal seam is only developed in the west of the ore field, and often divides into two layers of coal with a distance of about 2 m. The upper coal 1 is 0.09~8.93m thick, with an average thickness of 2. 12m, which is unstable and locally recoverable. The upper coal seam 2 is 0.82 ~ 2.84 m thick, with an average thickness of 1.85m, which is complicated in structure and locally recoverable.

From the development degree, spatial distribution and coal seam structure of coal seams in different parts of coal-bearing series, it can be seen that coal accumulation has an evolutionary trend from strong to weak from morning till night, and the thickness of coal seams is from large to small; The thickness of coal seam changes greatly and is unstable, and the phenomenon of branch and merger of coal seam is complex, with many dirt bands.

(3) Coal quality characteristics

The coal quality of different horizons is also different. The bottom coal is medium ash, low sulfur and low phosphorus long flame coal. It is blocky and granular, fragile, easily weathered and prone to spontaneous combustion. The composition of coal and rock is mainly bright coal, followed by semi-dark and dark coal, belonging to semi-bright and bright type. Low calorific value. China coal belongs to medium-low ash, sulfur-rich lignite-long flame coal, semi-bright type. The upper coal is medium-low ash and medium sulfur-rich lignite, which belongs to semi-bright type. See Table 4-5 for the changes of coal composition in each coal seam.

Table 4-5 Table of Coal Quality Analysis Results of Each Coal Seam in Yima Coalfield

As can be seen from the table, with the increase of coal seam level, the metamorphic degree and calorific value of coal decrease; The content of ash and sulfur in coal tends to increase gradually. Compared with Carboniferous-Permian coal, its metamorphic degree and calorific value are relatively low, and its volatile content is generally higher, generally higher than 15% ~ 20%.

(4) metallogenic mechanism and metallogenic model

Yima-style coal mines were produced in the early and middle Jurassic and distributed in the middle of Mianchi-Yima Mesozoic sedimentary basin. The coal-forming mechanism is basically the same as that of Late Carboniferous-Permian, but the metallogenic background and age are different. Yima coal was formed in inland lake and swamp environment. In the early Jurassic, the climate was warm and humid with abundant rain. The plants in the swamp grow and reproduce intensively, which provides rich materials for the formation of coal. However, the transformation of plant residues into coal goes through two stages, namely peat stage and coalification stage. According to the rock assemblage and coal seam characteristics of Yima Formation of coal-bearing series, the tectonic conditions of the basin during the coal accumulation period are favorable for the formation of coal, and the rate of swamp decline and peat accumulation remain in balance for a long time. From the early Jurassic to the middle Jurassic, this kind of balance compensation gradually weakened, resulting in the thickness of coal seam becoming thinner from bottom to top. The whole basin is in a stable subsidence movement. Peatization transforms plant residues in surface swamps into humus (peat); Peat layer sinks deep with the decline of basin basement, and the upper part is covered with thick sediments and surface water. Under the influence of overlying sediment pressure and deep temperature, peat (sapropelic) layer is coalified and gradually solidified into lignite, long-flame coal and so on.

To sum up, the process of Yima coal mine (layer) metallogenic model is as follows:

Mineralization of Main Minerals and Metallogenic Series of Deposits in Henan Province