1. Regional geophysical characteristics
On the regional Bouguer gravity map, Kebutai Iron Mine is located on the gravity height axis delineated by the △g isoline of -230× 10-5m/s2, and the gravity height decreases in an arc from west to east, from -2 16× 10-5m/s2 to-226× 65433.
On the aeromagnetic △T contour map, the iron ore area is at the boundary of different magnetic fields. There is a negative magnetic field in the north, and the negative background field is sandwiched with a NW magnetic anomaly zone. There is a chaotic high-frequency band in the south, which is a part of the high-frequency band in the Gongnaisi River area. It spreads in the east-west direction, and the intensity is generally 200 ~ 500 nt. The vertical derivative can be decomposed into several local magnetic anomalies, and the iron ore area is located in one of them (Figure 3-37).
1:25000 aeromagnetic field is located in the transition zone between high magnetic field background and low flat negative magnetic field background, which is a local high magnetic anomaly superimposed on high magnetic field background. The closed circle of 400nT isoline is oval, with major axis 1km and minor axis 0.6km, and △Tmax is 1 145 nt, which is higher than the background value. This anomaly is related to the rich maghemite and hematite in iron ore.
Summary of geophysical prospecting criteria: The iron ore belongs to sedimentary metamorphic iron ore, mainly hematite, and it is difficult to predict by magnetic survey. Weak magnetic anomalies and strong magnetic anomalies are closely related to magnetite and volcanic rocks.
2. Ore controlling factors
See table 3- 14 for the elements of kebutai iron mine.
Table 3- 14 Table of Regional Metallogenic Elements of Kebutai-Chagangnuoer Marine Volcanic Iron Deposit
Fig. 3-37 Geological, Mineral and Geophysical Analysis Diagram of Kebutai Iron Mine Typical Deposit (modified according to the data of Xinjiang Bureau of Geology and Mineral Resources)
3. Metallogenic model
(1) regional geological background
Shikebutai iron deposit is located in the Awulale Rift Zone of the Esek-Ili Block in the Late Paleozoic. The main structural lines in the area are distributed in the east-west direction, forming a gentle syncline structure with steep north and gentle south, and the fault structure is not developed. The exposed strata in the mining area are mainly Lower Permian and Middle Carboniferous. Variscan intrusive rocks are exposed in the south of the mining area.
(2) Metallogenic geological environment
The ore-bearing stratum is the first member of the Upper Carboniferous Iski Rick Formation, which is in fault contact with the second member of the Iski Rick Formation, and the south is cut by the late Carboniferous intrusive rocks. The rock type combination of ore-bearing strata is: basic rock-intermediate rock-acid rock marine volcanic eruption-sedimentary formation, and carbonate rock-chemical sedimentary formation in some areas, with an exposed thickness of 2043.24m. Generally, it undergoes ductile → brittle deformation, forming schist andesite, schist tuff, thousands of rhyolite porphyries → sericite quartz schist, dolomite quartz schist, schist (mylonite foliation).
The isotopic geological age of the volcanic rocks of the Iskilik Formation in Turgongsayi area was determined by the whole rock rubidium strontium method, and the result was 320 1 1 Ma. The age of this stratum is Late Carboniferous.
(3) Ore deposit combination, distribution and occurrence
The mining area is about 4km long and about 1.3km wide. The mining area consists of six ore sections: main ore section, west ore section, east ore section, southwest ore section, south ore section and Luobei ore section. Among them, the ore bodies in the main ore section are convex mirrors with thick middle and thin sides, with as many as 14 layers, length of 1200m, total thickness of 70m and single layer thickness of 1 ~ 15m. The ore bodies of other ore groups are thinner than the main ore section, and only consist of 1 ~ 2 layers, with poor continuity, ranging from tens of meters to hundreds of meters in length and a thickness of 1 ~ 5m. The ore body is layered, quasi-layered and convex mirror-shaped, and the ore body is banded and layered. The output of each coal seam is strictly limited by horizon, and the occurrence is consistent with surrounding rock. Coal seam and surrounding rock fold synchronously. The lithofacies of coal seam, its roof, floor and interlayer changes greatly, and the phenomenon of pinch-out appears again along the strike. Wall rock alteration is undeveloped, sericitization, chloritization and silicification are weak. Massive copper-bearing pyrite with a thickness of 12m and a copper grade of 0.96% was observed under the iron ore layer at the depth of zk210/0/borehole 150m. In addition, sericite phyllite containing pyrite with a thickness of more than 100 m was found in the lower wall of the iron mine bed, and pyrite was distributed in massive or disseminated form.
(4) Ore types and mineral assemblages
The natural types of ores are massive hematite and chalcopyrite. Its mineral composition: metallic minerals include hematite, specularite and limonite; Pyrite, chalcopyrite, magnetite, sphalerite and galena; Gangue minerals include ruby, timely, sericite and chlorite; Barite, calcite, tourmaline.
Ore grade The average grade of total iron is 56.66%, and the highest grade can reach 66.78%. Ore industry types: rich minerals containing jasper hematite and rich minerals containing polymetallic hematite. The whole mining area is rich in iron ore resources, accounting for 70%. Harmful impurities in ore: the average content of sulfur is 0.278%, phosphorus is less than 0.05%, and silica is mostly 5% ~ 10%.
(5) Ore texture and structure
The ore structure is dominated by semi-automorphic crystals, followed by automorphic-heteromorphic crystals, which constitute fine crystal structure, fibrous, needle-like aggregate and granular structure. The ore structure is dominated by dense massive structure, followed by schistose structure, banded structure, disseminated structure and veinlets.
(6) Mineralization stage and distribution
Shikebutai iron deposit was formed in volcanic sedimentary origin, and different ore bodies were formed in different volcanic stages under the same metallogenic environment. Metallogenic stage in the later stage of volcanic eruption: in the later stage of volcanic eruption, after large-scale violent eruption, the relative eruption is weak, mainly volcanic gas and liquid, containing a lot of ore-forming materials and volatiles, drifting into hot sea water. After decomposition, new minerals are formed. In the reducing environment of seawater, the plasmas of Cu2++, Pb2++, Zn2 ++ and Fe2 ++ are sulfur-loving and active, and combine with S2 ions in seawater to form new minerals, such as pyrite, chalcopyrite and sphalerite. Under stable conditions, massive copper-bearing pyrite bodies are formed. Volcanic overflow mineralization stage: during the intermission of volcanic activity, the slurry composed of hematite and silica colloid gushed out of the volcano and flowed down the slope of the volcano to the center of the basin. Due to the unstable sedimentary environment, a triad of hematite, jasper and barite is formed, which is distributed on massive copper-bearing pyrite.
(7) Division and distribution of mineralized alteration zones
There are many types of hydrothermal alteration in mining areas, including silicification, sericitization, pyritization, carbonation, siderization, kaolin and specularite. However, the distribution is limited, mostly in the contact zone outside the rock mass, near the interval zone, regional metamorphic products, recrystallization of original rock minerals and so on. However, the wall rock alteration related to mineralization is very weak, with only local silicification, sericitization and chloritization phenomenon. There is no obvious alteration in the surrounding rock near the mine, there is no direct or indirect relationship between the formation or enrichment of ore bodies and mineralization alteration, and there is no difference in rock alteration between the ore-bearing bottom and the non-ore-bearing bottom.
(8) Physical and chemical conditions of mineralization
According to the data of oxygen isotope analysis, it is concluded that the metallogenic temperature of jasper and hematite is 295℃. This value may represent the diagenetic and metallogenic temperature, and the seawater temperature should be less than this value during hematite-jasper deposition.
According to the temperature measurement data of inclusions, the mineralization temperature of Shikebutai iron mine is 295℃, and the mineralization temperature of specularite-barite is 190 ~ 250℃.
The homogenization temperature of barite is 158 ~ 252℃, and that of Jasper is 130 ~ 152℃, with an average of 186℃ and salinity ω (NaCl) = 3./kloc-0.
Oxygen isotope: The calculation results show that the δ 18O value of ore-forming water in Kebutai Iron Mine is close to 6, that is, close to the value of magmatic water. That is, it may be related to submarine volcanic eruption.
According to the research of Guilin Institute of Geology and Mineral Resources (1996), the results are as follows:
The δ34S of four pyrite samples with sulfur isotope characteristics are -3.7 ‰ ~ 6. 1 ‰, with an average value of -5.03‰, and the δ34S of layered barite is+12.9%, indicating that the sulfur source of metal sulfides in this area is mainly the mixture of mantle-derived sulfur and seawater sulfur brought by deep volcanic eruption.
Characteristics of hydrogen and oxygen isotopes The hydrogen and oxygen isotopic compositions of hematite and ruby samples fall within the range of magmatic water, while other samples fall near the range of magmatic water, indicating that the ore-forming fluid of the deposit comes from magma and seawater.
Lead isotope characteristics reflect that the ore-forming materials in this area come from the upper mantle or the deep source area of the crust.
The initial ratio of strontium in hematite with strontium isotope characteristics is 0.7037 and 0.7062, which indicates that the ore-forming material comes from deep crust or upper mantle and is related to submarine volcanic eruption.
(9) Genetic mechanism of the deposit
Shikebutai iron deposit belongs to volcanic-sedimentary iron deposit. The iron ore layer and copper-bearing massive sulfide under it are the products of submarine volcanic eruption at different stages in the same metallogenic environment. The metallogenic mechanism is that in the late or intermittent period of volcanic eruption, large-scale magmatic eruption has stopped, but volcanic eruption continues. These acidic hot gas liquids, which are rich in ore-forming materials, gush out along faults or volcanic passages, constantly migrate to the basin, interact with seawater, and precipitate due to changes in physical and chemical conditions. Among them, Cu(Pb, Zn) and other elements with strong sulfur affinity are dissolved in seawater in a relatively reducing environment. As the ore pulp spewed out from the crater, the ore-forming process continued to flow to the center of the basin, and elements such as iron, silicon, barium and manganese were enriched in the ore pulp. Under the condition of weak acid oxidation, a large number of hematite, lenticular ruby and layered barite hematite are formed, which constitutes barite-ruby-hematite formation. Ba-Si-Fe Trinity is a ore-bearing thermal fluid generated by submarine volcanic eruption, which interacts with seawater in the basin. This shows that the genesis of iron (copper) deposits in this area is volcanic eruption and overflow sedimentary iron (copper) deposits formed in different stages under the same metallogenic environment. The metallogenic model is shown in Figure 3-38.
Figure 3-38 Metallogenic Model of Kebutai Iron Mine
(10) prospecting criteria
The first member of the Upper Carboniferous Rick Formation in Iski is the main ore-bearing horizon of Shikebutai Iron Mine.
The ore-bearing strata are a set of shallow-sea pyroclastic sedimentary rocks.
The surrounding rocks near the mine are fine tuff, pozzolanic tuff, tuff sandstone and siltstone, which are often rich in iron and are grayish purple and purplish gray. Purple layer is usually a possible near-ore sign.
Ruby interlayer and lens are common in iron deposits. They are the products of the same environment and closely related. Ruby has weathering resistance and can be used as a prospecting indicator.
The activation rate of hematite is obviously different from that of surrounding rock, so it is possible to find hematite by electrical method.
The ore-bearing strata contain a small amount of magnetite and manganese magnetite, and the ore-bearing strata can be roughly delineated by magnetic method.