(1) Characteristics of aeromagnetic anomalies
This type of aeromagnetic anomalies are concentrated in the Damiao-Tougou-Xiayuan area of ??Chengde, spreading in an east-west direction. In addition, there is 73-39 (Northern Town) in Luquan City in the Taihang Mountains, which also falls into this category.
The ore-bearing parent rocks that cause such anomalies are mostly anorthosite and sourite, and a few are gabbro. Anorthosite and sourite are not strongly magnetic, so the aeromagnetic anomalies directly reflect the iron-phosphorus ore bodies. existence. This type of aeromagnetic anomaly is generally superimposed on the background of large-scale positive magnetic anomalies caused by rock masses. The anomalies are mostly elliptical in shape, ranging from hundreds of meters to thousands of meters. The long axis is mostly in the east-west or northeast direction, and the intensity is Higher, the ΔT value is mostly between 500 and 2000nT, the maximum intensity is above 3000nT, and the gradient is steep. The larger the abnormality scale, the higher the abnormality intensity.
Among these anomalies, 76-116 (Luoguozigou), 59-18h (Hongshanzui), and 59-18a (Heishan) are large deposits. 59-18b (Maying) and 59-18c (Tougou) are medium-sized mineral deposit anomalies, and the rest are small-scale mineral deposit anomalies. 76-116 (Luoguozigou) is expected to become a very large vanadium-titanium magnetite and iron-phosphorus deposit anomaly, and the 59-18a (Heishan) anomaly area has great potential for finding iron-phosphate ore and vanadium-titanium magnetite. potential.
59-18h (Hongshanzui) is a large-scale anomaly (Figure 4-55), located to the west of Pingquan County. The aeromagnetic anomaly was discovered in 1959 and was thought to be caused by metamorphic iron ore. In 1960 Ground inspection confirmed that it is basic to ultrabasic rock mass. The anomaly is elliptical, with a long axis of 3.5km and a short axis of 1.8km. The gradient is steep and the intensity is high. The maximum value is 4280nT. There is a negative anomaly on the north side with a minimum value of -1000nT. The anomaly is consistent with the exposed basic rock mass. The rock mass is an east-west elliptical rock strain with an exposed area of ??5.5km2. The rock mass is divided into two major rock belts, namely the biotite hornblende gabbro belt and the potash-length mixed biotite hornblende monzonite belt. The body is found in the biotite hornblende gabbro belt. The mineral belt is distributed in an annular shape. The annular belt is 4000m long, 80-210m thick, and the thickest is 280m. Containing P2O5 is generally 2~4, TFe9~17, TiO20.22~3.5, and has copper mineralization. In 1972, through surface survey and evaluation by the Fourth Geological Team, the on- and off-balance sheet ore reserves were 20877.79×104t, P2O5567.0×104t, iron ore 2504.66×104t, and TiO2589.87×104t. The scale of ultra-poor iron ore reaches large scale. The northern part is mined by Chenggang, and the southern part is mined by civilians.
Figure 4-55 59-18h aeromagnetic ΔT anomaly contour plan (unit: nT)
1:200,000 regional geochemical anomalies are composed of 17 elements, with P is mainly P, accompanied by elements such as F, Ba, Sr, Y, La, Fe, Co, Ni, Ti, etc. P and F are inner band concentrations, La and Sr are middle bands, and the rest are outer bands.
(2) Examples of basic rock type iron-phosphate deposits
1. Luoguozigou iron-phosphate ore and vanadium-titanium magnetite
Located in Chengde City 3km north of the Damiao mining area, the aeromagnetic anomaly number is Jic-79-116.
(1) Discovery process
In 1956, the geophysical exploration team of the Geological Bureau of the Ministry of Heavy Industry conducted a 1:2000 magnetic method of 2.04km2 with the purpose of finding vanadium-titanium magnetite. The earliest geophysical exploration work in the area, the 1:100,000 aeromagnetic survey in 1959 classified this anomaly as the Damiao anomaly, without a separate number.
This area was not taken seriously until the Maying iron-phosphate ore was discovered in the 1970s. In 1975, based on the work of the 10th Geological Team, the 4th Geological Team carried out a detailed investigation, and in 1976 it was transferred to exploration. , and 1:5000 magnetic method was used for 3.75km2. The exploration work was completed in 1978, and it became a large iron-phosphorus deposit. In recent years, low and gentle geomagnetic anomalies have been verified by drilling, and large-scale vanadium-titanium magnetite bodies have been discovered in the depths.
In 1979, Team 904 of the Aeronautical Geophysical Exploration Brigade of the Ministry of Geology conducted a 1:50,000 aeromagnetic survey and detected a large-scale and very regular aeromagnetic anomaly, numbered 79-116.
From 1979 to 1981, the Hebei Geophysical Exploration Team conducted another large-area ground magnetic survey of 1:10,000.
(2) Geological overview of the mining area
The iron-phosphorus ore body occurs in the norite in the western part of the Heishan basic complex. The western end of the ore body is in fault contact with the Mesozoic fault basin, and the northern end of the ore body is in fault contact with the Mesozoic fault basin. , the east is in intrusive contact with anorthosite, and the southeast and south are also in fault contact with anorthosite.
The lithology of the rock mass is anorthosite and norite. The structures in the area are dominated by faults, including northeast, north-east, north-west, north-south and other faults, which cause the ore body to be cut.
The alterations of surrounding rocks include sodium zoisitization, amphiboletization, chloritization, talcization, etc.
The mining area consists of two iron-phosphate ore body groups, Luoguozigou and Dawusugou. The Luoguozigou ore body group is located in the south, extending northwest, with an area of ??0.35km2. There are 22 iron-phosphate ore bodies, among which No. Ⅰ to Ⅲ are larger, with No. Ⅲ being the largest, 750m long and 180-350m thick. No. Ⅰ is 550m long, 20-100m thick, and has a small extension depth. No. Ⅱ is 250m long and 30~40m thick. There is no pinch-out trend at the maximum oblique depth of 500m in the ore body. The ore body trends southeastward and dips toward the northeast.
In the chloritized anorthosite surrounding the iron-phosphate ore bodies, penetrating vanadium-titanium magnetite veins of 50 to 100 meters are common. There are a total of 55 ore bodies, all of which are small in scale.
The grade of the iron-phosphate ore body is stable, with P2O53~6 in the ore, with an average of 4.47; TFe12.12~20.85, with an average of 18.19; TiO23~7, with an average of 5.7; V2O50.05~0.12, with an average of 0.118.
Through exploration, the Luoguozigou ore body has obtained iron-phosphate ore reserves of 21927.8×104t, metallic titanium 1247.2×104t, metallic vanadium 25.93t, and metallic cobalt 1.99×104t. It is a low-grade large-scale comprehensive mineral deposit.
The Dawusugou iron-phosphate ore body group is located in the north, with a length of 1200m, a width of 50-300m, and an area of ??0.21km2. It is composed of 12 iron-phosphate ore bodies and 22 vanadium-titanium magnetite bodies. Among them, the largest iron-phosphate ore body is 1200m long, with an average thickness of 93m on the surface and an average thickness of 194.58m in the borehole. The ore body is plate-shaped, trending northeast, tilting southeast, and with an inclination angle of 50° to 52°. The iron-phosphate ore reserves are found to be 10702×104t, which is also a large-scale low-grade comprehensive mineral deposit.
(3) Magnetism of rocks and ores
The main magnetic parameters of rocks and ores in the area are listed in Table 4-7.
Vanadium-titanium magnetite and iron-phosphate ore have the strongest magnetism, followed by chloritized anorthosite and norite. Anorthosite has only very weak magnetism and cannot be measured by a magnetic scale.
Table 4-7 Magnetic parameters of rock ore in Luoguozigou mining area
(4) Magnetic anomaly characteristics
A. Aeromagnetic anomaly (Figure 4-56)
Figure 4-56 79-116 aeromagnetic ΔT anomaly contour plan (unit: nT)
1:50,000 aeromagnetic results, the anomaly is superimposed on the positive magnetic field background, The 1000nT isoline is closed and presents an elliptical anomaly in the north-south direction, nearly 3000m long and nearly 2500m wide. The anomaly peak is close to the south, with a maximum value of 3230nT, indicating that the anomaly intensity is lower in the north and higher in the south. There is also a small equiaxed anomaly with a maximum value of 1860nT adjacent to the north. There are no negative anomalies around positive anomalies.
B. Geomagnetic anomaly (Figure 4-57)
Geomagnetism is a ΔZ anomaly group, which can be divided into Luoguozigou (M-21) and Dawusugou (M- 23) Two abnormal groups.
The Luoguozigou anomaly group is located in the south. The 3000nT isoline is a whole, and the 5000nT isoline is divided into several anomalies. The overall distribution is northwest, and the maximum value of the anomaly is nearly 1×104nT. It is consistent with the Luoguozigou iron-phosphate ore body and the vanadium-titanium magnetite body group in the southeast (Figure 4-57).
The Dawusugou anomaly group is located in the north, and the 3000nT contours are also a whole, spreading in the northeast direction. The 5000nT contours have a smaller range, with a maximum value of 7000nT, which is similar to that of Dawusu Valley. The Gou iron-phosphate ore bodies are consistent.
From the perspective of the range and intensity of ΔZ anomaly, the Dawusugou anomaly is not as good as the Luoguozigou anomaly. Therefore, the aeromagnetic anomaly reflected in the aeromagnetic anomaly is that the intensity is high and the range is large in the south, while the intensity is low and the range is small in the north. .
Figure 4-57 Luoguozigou ΔZ geological comprehensive plan (unit: nT)
The two anomaly groups of Luoguozigou and Dawusugou are both in strong positive magnetic fields On the background (M-24), the 2000nT contour includes all the anomalies of the two anomaly groups, clearly reflecting the two-level superposition characteristics of the anomaly. The east side shows the low-value, wide and gentle part of the anomaly. In Section 19 (Fig. 4-58) and Section VII (Figure 4-59), the gentle anomaly is particularly obvious on the right side of the section. In addition, there are no negative values ??around, so it is inferred that there are larger magnetic bodies in the depths. Analysis of surface and drill core parameters shows that the anorthosite and chloritized anorthosite in the abnormal area are weakly magnetic. It is inferred that the cause of the low and gentle background anomaly is the iron-phosphate ore and vanadium-titanium magnetite buried deeply. Comprehensive reflection.
Figure 4-58 Comprehensive cross-section of Luoguozigou magnetic anomaly 19 exploration line
In summary, the low and gentle anomaly is a 2500m long, 1300m wide, trending NNE and dipping The magnetic body in the south-east east, calculated from section VII (Figure 4-59), has an inclination angle of 77°, a top burial depth of 510m, a center burial depth of 1100m, and a bottom extension of 1260m. The effective magnetization intensity is 7470×10-3A/m. Magnetic field reflection of iron-phosphate ore body and vanadium-titanium magnetite body. It is recommended to verify the deep hole. The hole is located at ZK4 in section VII and the design hole depth is 1000m.
It has been verified that holes 2401 and 2402 have found the first iron ore layer at 120-220m, which is 60-100m thick. It is the main iron ore layer of the sardine type iron ore (numbered layer 21). Hole ZK2401 The output is at a hole depth of 1074.20-1245.00m and a true thickness of 121m; the ZK2402 hole is produced at a depth of 1094.97-1251.45m. There are 3 layers of ore with a true thickness of 115.5m. The ore type is dense disseminated ore and is connected along the strike. In addition, hole ZK2402 contains hornblende pyroxenite type iron ore at hole depth of 1391.76~1905.80m. This type of ore was not found in hole ZK2401 due to its shallow hole. It has been confirmed that this ore system is a deep hidden ore body with a large scale and is expected to become the largest vanadium-titanium magnetite deposit in the Damiao area.
2. Montenegro vanadium-titanium magnetite and iron-phosphate ore
See the first section of this chapter.