1. Geological background
Fenghuangzui Formation (Arf) of Archaean Dantazi Group in this area is the oldest exposed stratum (Figure 5-7a), mainly distributed in the middle of the target area. The lithology is mainly strongly migmatized amphibole, amphibole granulite, biotite granulite and multilayer marble. Near Sandaogou, a large area of Archean homogeneous migmatite (Jzh) is exposed. Mesoproterozoic basic complex intruded into Archean strata along deep faults, and its lithology was amphibole and pyroxene amphibole. A large area of early Proterozoic adamellite is exposed on the north side of Tiematugou, and a small area of variscan potash feldspar granite is exposed on the south side. A large area of early Proterozoic metamorphic diorite is exposed in the west of the target area. NEE fault and NE fault are very developed in this area.
There is only one kind of small iron ore known in this area, that is, Tiematugou small vanadium-titanium magnetite. The ore body occurs in basic-ultrabasic rocks, and the genesis of the deposit belongs to late magmatic deposits.
2. Geophysical characteristics
Magnetic field characteristics: In the aeromagnetic △T contour map (Figure 5-7d), the target area is in a large-area rising positive magnetic field, and the negative magnetic anomalies on the north side are distributed in a nearly east-west belt; After the polarization treatment of the original magnetic field (Figure 5-7c), the whole anomaly moves northward, the associated negative anomaly disappears in the north, and a negative anomaly zone near east-west direction appears in the south. On the basis of polarization, the vertical first derivative processing eliminates the influence of background field, and the local abnormal characteristics are more obvious. The east-west strong magnetic anomaly belt on the north side of Sandaogou-Hongqi line is about 18km long, and Tiemataogou small deposit is located on the east side of the strong magnetic anomaly belt. On the plane section (Figure 5-7b), the abnormal curve of Tiematagou shows a narrow and sharp spike-shaped strong magnetic anomaly with an intensity of 40km. The abnormal curve of Sandaogou is relatively weak and gentle, and its intensity is about 1000nT.
Gravity field characteristics: from west to east, the gravity field value shows a gradual increase trend; In the residual gravity field, the target area is in the high-value anomaly area near the east-west strike, and the gravity and magnetic anomalies are in good agreement. Tiematugou iron mine is located in the southeast gradient zone of elliptic residual high anomaly.
Compared with geological and mineral maps, strong magnetic and gravity anomalies correspond well with ultrabasic rocks.
3. Local anomaly analysis
Five aeromagnetic anomalies related to iron ore were screened out (Table 5-4), among which Ji C-1960-17A-1is located near Tiemagou Iron Mine.
Table 5-4 List of Key Anomalies in Baiqi Township-Tiematagou Target Area
(1) Ma Tietu gully anomaly (Hebei C- 1960- 17A) and pot kiln anomaly (Hebei C-1960-17a).
Tiemataogou anomaly (Hebei c-1960-17a-1) is close to the known iron mine (Tiemataogou iron mine). On the1:50,000 geological map, the anomaly center is located in the late Archean ultrabasic rocks, and there are Archean Fenghuangzui Formation in the anomaly range, and mottled small potash granite is exposed in the south. In the magnetic field, the anomaly curve is a sharp magnetic anomaly with high intensity and steep gradient, accompanied by a negative anomaly with amplitude of 5570nT on the north side.
Figure 5.7 Geological and Mineral Map and Geophysical Analysis Map of Sandaogou Target Area
A- geological and mineral map; B- aeromagnetic △T plane profile; C- aeromagnetic △T polar contour map; D- aeromagnetic △T contour map; Residual gravity contour map; F— Plane diagram of vertical first derivative isoline of aeromagnetism.
1- four yuan; 2- Jurassic Zhangjiakou Formation; 3- Jurassic Baiqi Formation; 4- Jurassic Mentougou Formation; 5- Archaean Taipingzhuang Formation; 6- Archaean Fenghuangzui Formation; 7 —— Taibei Yubaimiao Formation; 8— Medium-grained granodiorite; 9- amphibole rock, pyroxene amphibole rock; 10— eclogite; 11-plagioclase; 12-metamorphic medium-coarse diorite; 13- metamorphic coarse-grained granite; 14- homogeneous migmatite; 15 —— known ore-induced anomaly; 16 —— Inferring ore-induced anomalies; 17 a known iron ore location; 18- target range
The basin kiln anomaly (Hebei C- 1960- 17A) is located in the southwest of Tiematagou anomaly (Hebei C-1960-17a-1). On the 1:50000 geological map, the anomaly center is close to the NEE strike fault zone, with ultrabasic rocks in the late Mesoproterozoic in the north, banded migmatized metamorphic rocks in the south, and Archaean Fenghuangzui Formation in the south of the metamorphic zone. In the magnetic field, it is similar to the aeromagnetic anomaly of Hebei c-1960-17a-1,and it is also a spike-shaped strong magnetic anomaly with high intensity and steep gradient, accompanied by a negative anomaly with an amplitude of 77 15nT on the north side. According to the aeromagnetic isoline map of1:50,000, Hebei c-1960-7a anomaly and Hebei C- 1960- 17A-1anomaly are two high-value points in the same near east-west elliptic anomaly. On the aeromagnetic contour map of 1:200000, two anomalies have been integrated.
According to the geological environment and characteristics of aeromagnetic anomalies, it is inferred that aeromagnetic anomalies are caused by ultrabasic rocks and iron ore bodies.
In June of 20 1 1 year, the project team investigated the anomaly and found that large-scale open-pit mining of iron ore had been carried out in the anomaly area (Xinglong Mining Company), and the total iron grade of iron ore was generally above 10%, and some reached above 20%. According to the statistical results of magnetic susceptibility, the magnetic susceptibility of ultrabasic rocks is generally 7000×10-5 ~ 9000×10-5Si, and the magnetic susceptibility can reach tens of thousands×10-5Si after iron mineralization. The magnetic susceptibility of Archean metamorphic rocks is generally several hundred×10-5Si and several thousand×10-5Si. The magnetic susceptibility of granite is generally 300×10-5 ~ 500×10-5Si, and that of iron ore is generally 30,000×10-5 ~ 40,000×10-5Si, with individual reaching 70,000×.
According to the qualitative research results and physical property measurement data, the aeromagnetic profiles passing through the abnormal centers of Hebei C- 1960- 17A and Hebei C-1960-17A-1are inversed, and the results are shown in Figures 5-8 and 5-9. The inversion results show that there are iron ore bodies in ultrabasic rocks, and the shallow ore bodies have low grade, low magnetic susceptibility and strong magnetism due to weathering. The effective magnetization of tiemataugou magnetite body is 12.86A/m, 3 1.3 1A/m, 42.88A/m, and that of Yao Bin magnetite body is 2 1.54A/m, 42.88a/m.
Fig. 5-8 2.5D inversion result of aeromagnetic anomaly in Hebei c-1960-17a-1.
1- Early Proterozoic granodiorite; 2- migmatized metamorphic rocks; 3- Archaean single tower group; 4- Late Archean ultrabasic rocks; 5- 4 yuan; 6— Inferring magnetite; 7- Proterozoic plagioclase; 8— aeromagnetic survey curve; 9— Calculation curve; 10- flying altitude; 1 1— Effective magnetization direction and effective magnetization.
(2) The north anomaly of Sanitation Gully (Hebei C- 1 960-1001), the east anomaly of Sanitation Gully (Hebei C- 1960- 1002) and the lower wopu anomaly (Hebei C-1002)
Fig. 5-9 2.5D inversion result of aeromagnetic anomaly of Hebei C- 1960- 17a.
1- Early Proterozoic granodiorite; 2- Archaean single tower group; 3- Late Archean ultrabasic rocks; 4- 4 yuan; 5— Inferring magnetite; 6- Jurassic volcanic rocks; 7— aeromagnetic survey curve; 8— Calculation curve; 9- flying height; 10-effective magnetization direction and effective magnetization; 1 1- section direction
Three aeromagnetic anomalies are located in a large area of metamorphic diorite in early Proterozoic, and the Fenghuangzui Formation is exposed sporadically in some areas. Late Archean ultrabasic rocks are distributed near the anomaly in the form of east-west dikes. In the magnetic field, the abnormal curve is weaker and gentler than Tiematougou, and the abnormal intensity is 1000 ~ 1340 nt. According to the magnetic parameters measured in Tiemataogou area, the magnetic susceptibility of Archean metamorphic rocks is generally several hundred 10-5SI, and some reach several thousand × 10-5SI. It is speculated that the three aeromagnetic anomalies may be caused by metamorphic diorite, ultrabasic rock and Fenghuangzui metamorphic rock, and the local high magnetic anomalies may be related to the sedimentary metamorphic iron ore in the old strata.
4. Target evaluation
The main prospecting type in this area is magmatic iron ore, followed by sedimentary metamorphic iron ore.
The target area is close to Montenegro-Damiao known iron ore area, and the metallogenic environment is the same as Montenegro-Damiao area. Tiematugou anomaly is characterized by strong magnetic and gravity magnetic anomalies in geophysical field, which is of good directive significance for finding vanadium-titanium magnetite and chromite. Although open-pit mining has been carried out at present, it is unknown whether deep exploration has been carried out. According to the results of aeromagnetic quantitative calculation, the iron ore resources in Baiqi-Tiematugou area are very large (about 65.438+0.89 billion tons). In addition, there are local aeromagnetic anomalies in the Archean old strata in the west of the target area, which also has certain iron ore prospecting potential.
To sum up, the target area is classified as Class A. ..