Dajing mining area is located at the southern end of Daxing 'anling, and the geotectonic position is located in the middle of Hualixi geosyncline fold belt in Xing 'an, and the secondary structural unit is anticlinorium in Linxi-Keyouzhongqi. The metallogenic belt belongs to Lianhuashan-Dajingzi Cu-Pb-Zn-Sn ore belt.
1. Brief description of mine geology
(1) stratum
Dajing mining area is mostly covered by Quaternary aeolian sand, alluvial clayey silt and gravel, and the exposed stratum is mainly upper Permian Linxi Formation, which is scattered. Linxi Formation (P3l) is a set of normal sedimentary rocks of freshwater lake facies, which can be divided into four lithologic sections from bottom to top, and only the first lithologic section and the second lithologic section are exposed in the mining area. Its lithology is mainly siltstone, followed by argillaceous siltstone and fine-grained and medium-grained composite sandstone, with marl thin layers or lenses locally.
(2) Structure
The structure of the mining area is dominated by faults and broken structures, and the fold structure is not developed. The main fold is an open arc syncline-Tulengzigou syncline. Faults in the mining area are mainly divided into four groups: northeast, nearly north-south, northwest and northwest. Among them, NW and NW mainly exist in the form of ore body or dike filling in the mining area, and the rock and ore control is very obvious, which is the main ore-hosting structure in the area.
(3) Magmatic rocks
There are no large intrusive rocks exposed in Dajing mining area, but dike rocks are very developed, belonging to basic-intermediate acid subvolcanic rocks, which often appear in groups and belts and invade the fracture zone of Linxi Formation in the form of dikes, dykes and bedrock. The types of dikes are mainly basaltic porphyrite, andesite porphyrite, lamprophyre and dacite porphyry, and some are porphyrite. The first three are closely related to mineralization. According to the K-Ar dating of the whole rock, the andesite porphyry and the dacite porphyry are products of the early Yanshanian period (133 ~ 155 Ma).
2. A brief description of the characteristics of the deposit
(1) ore body characteristics
Hundreds of veins have been controlled in the mining area, with a length of 3 kilometers from east to west and a width of 2.5 kilometers from north to south, which are produced in groups and belts. According to the distribution characteristics of ore bodies, it can be roughly divided into three ore zones: north, middle and south, and each ore zone is divided into several vein groups, most of which are concealed ore bodies. The ore bodies occur in irregular vein, compound vein, staggered vein and beaded shape, and are mostly filled in the NW-trending and NW-trending composite fault zones. They are often S-shaped in plane, with soothing waves in the inclined direction, and some expansion and contraction or branching and compounding phenomena. The boundary between most veins and surrounding rocks is very clear, a few veins are disseminated, and most ore bodies are phosphorus-containing siltstone as surrounding rocks.
The strike length of ore body is generally 200 ~ 700 m, and the longest is >1200 m; The dip depth is generally 200 ~ 600 m, the extension of ore bodies is generally greater than the extension depth, and the extension of a few ore bodies is similar to or even greater than the extension depth. The thickness of the ore body is generally 0.5 ~ 1.5m, and the maximum thickness is 8.7m, with the phenomenon of expansion and contraction. The general occurrence law of ore bodies is obvious. Most ore bodies change in strike from 290 to 325, and most of them are around 365,438+00. It tends to NE, and the dip angle changes greatly, from 25 to 75. The general change trend is slower to the west of the 46 th line, generally 25 ~ 45. The east of Line 46 is steep, generally 45 ~ 65. The local change is large, which is characterized by a sharp turn along the strike and dip, making the ore body in a broken line shape on the plane and a ladder shape on the section.
(2) Ore type and structure
There are three main ore types in Dajing mining area, namely, Cu-Sn-Ag ore, Pb-Zn-Ag ore and its composite Cu-Sn-Pb-Zn ore. In addition to the main types, there are pyrite ores, which often occur in the upper and lower walls of the main ore body, sometimes replacing the main ore body, causing the interruption of industrial ore bodies.
The ore structure is mainly heteromorphic-semi-automorphic granular structure, followed by solid solution separation structure, interstitial structure, mosaic structure, rare colloid structure, unequal particle crushing structure and skeleton crystal structure; The common ore structures are vein structure, reticulate vein structure and massive structure, followed by banded structure, and disseminated-punctate structure and breccia structure are rare. Cavity structure is only found in some tin mines, and honeycomb structure is not developed, but only exists in local areas near the surface.
Specimen name oreNo containing tin, silver and copper. DB028- 1 Early Yanshanian Stratigraphic Age
Atlas of large ore specimens from typical mines in China
The sample is copper yellow, grayish black, medium-coarse crystalline structure, vein-like and banded structure. Ore minerals mainly include chalcopyrite, cassiterite, marmatite, galena and various silver-bearing minerals. Gangue minerals are timely, carbonate minerals and a small amount of andalusite. Copper grade is 2. 16%, silver grade 139.5438+0g/t, and tin grade is 0.64%.
Genetic types of dajing silver-copper deposit in Chifeng city, inner Mongolia autonomous region genesis of subvolcanic medium-low temperature hydrothermal veins