3. 1.2. 1 mining geology
The strata in the mining area are mainly exposed in the Paleoproterozoic Jingshan Group and the Anji Village schist section of Cenozoic Quaternary Lugezhuang Formation (Figure 3. 15). The lithology of the former is biotite schist, biotite granulite, diopside granulite mixed with diopside marble, etc. Intrusive rocks in the mining area are developed, including fine-grained amphibolite gneiss and amphibolite biotite in Huilongkuang rock mass of Qixia rock suite in Neoarchean, fine-grained adamellite gneiss in Zhao Bei rock mass of Dingshuang rock suite in Proterozoic, and Mesozoic lamprophyre, diorite porphyrite, pegmatite and chronological veins. Among them, Qixia suite is in the form of inclusion, and the double-roof suite intrudes into Jingshan Group in the form of nearly north-south banded bedding. F 1 fault structure is developed in the mining area, which is mainly distributed along the contact zone between the Proterozoic Jingshan Group and the Proterozoic double-roof rock suite, and is biased to one side of the double-roof rock suite. North-northeast, inclined to the west, with an inclination of about 65; The surface is intermittently exposed about 2800m, with a width of 0.8 ~15 m; Obvious scratches and steps can be seen along the fracture surface, and structural lenses (plate Ⅳ-1) are developed, showing left-lateral compression and torsion, and ductile shear zones are developed locally, which is the ore-controlling structure in the mining area.
Table 3.7 Typical deposit type characteristics of orogenic mesogenic deposits in Jiaodong area
Fig. 3. 15 Geological Schematic Diagram of Tea Mine Area
(According to the revision of Shandong Third Institute of Geology and Mineral Exploration in 2006)
1-gravelly sand and clayey silt; 2- biotite schist and granulite mixed with diorite marble; 3- Fine-grained adamellite gneiss; 4- Fine grained amphibole gneiss and amphibole biotite; 5- biotite plagioclase gneiss; 6- Wuyun schist; 7— occurrence of rock stratum; 8— Flake peeling occurs; 9- cataclastic dikes and their number; 10- gold ore body and its number; 11-the location of the trench; 12- drilling position; 13- Baseline, exploration line and number
3. 1.2.2 Geology of the deposit
(1) Mineralization zone and ore body characteristics
At present, only the 1 mineralization zone is found in the mining area, which is controlled by the F 1 fault and consists of cataclastic rocks, breccia, sericitized kaolin granite and silicified granite. The mineralized zone is 230m long and 4.20 ~ 7.20m wide, with an overall strike of 0 ~ 20 and a west dip of 55 ~ 70. Among them, 1 ore body, the occurrence is consistent with the alteration zone; The exposed surface is 48m long, with a thickness of 0.66~2.29m, an average thickness of 2.09m, an inclined depth of 15m and an occurrence elevation of+175 ~+ 188m. Gold grade (1.21~ 5.77) ×10-6, with an average of 2.17×10-6; The antimony grade is 2. 17% ~ 20.67%, with an average of 9.82%.
(2) Ore characteristics
There are two main types of ore: stibnite sericitized cataclastic rock and stibnite sericitized kaolin granite (plate Ⅳ-1~ plate Ⅳ-6), in which stibnite sericitized kaolin granite ore is folded. The metal minerals in the ore are mainly stibnite and pyrite, with a small amount of galena, pyrrhotite, sphalerite and chalcopyrite. Among them, stibnite is mostly distributed in the form of heteromorphic-automorphic granules, needles or aggregates, in the form of veins, reticulate veins, blocks or disseminated, with scratches on local surfaces, flaky twins and extrusion deformation, with the content as high as 65%. There are a few stibnite in sericitized kaolin granite-type ores. Gangue minerals mainly include quartz, sericite, feldspar, kaolin, calcite and biotite. Ore structures are generally self-shaped-semi-self-shaped granular structures, agglomerated twin structures, metamorphic structures and so on. Ore structures are vein-like, reticulate vein-like, massive, dense massive, breccia-like, disseminated and so on. (plate IV-7 ~ plate IV- 12).
(3) Surrounding rock and surrounding rock alteration
The surrounding rock of the ore body is mainly gneiss fine-grained adamellite. Wall rock alteration includes silicification, sericitization, kaolinization and limonite mineralization, all of which are closely related to antimony gold mineralization.
(4) Metallogenic stage and mineral generation sequence.
According to the microscopic identification results and field geological characteristics, the mineralization in this area can be divided into two stages: hydrothermal mineralization stage and supergene oxidation stage, in which the former includes four stages, namely: ① sericitization stage, which mainly develops sericitization alteration, produces early sericite and quartz, accompanied by a small amount of coarse pyrite crystals, a small amount of disseminated stibnite and pyrrhotite; (2) In the metallogenic stage of Yingshi-stibnite, silicification is strong, and authigenic-semi-authigenic stibnite is produced in large quantities as veinlets, reticulate veins and disseminated minerals, accompanied by galena, pyrite, sphalerite and chalcopyrite. ③ In the stage of sericite-kaolinite-stibnite mineralization, massive stibnite is mainly formed, and the nonmetallic minerals are mainly sericite, kaolin and carbonate. A small amount of chlorite, epidote and other minerals are developed along the peripheral cracks. ④ In the chrono-carbonate stage, a small number of chrono-carbonate veinlets were mainly formed in the late stage of mineralization. In the supergene oxidation stage, kaolin, stibnite and limonite are mainly formed.
3. 1.2.3 Study on fluid inclusions
In this paper, the isochronous fluid inclusions in strongly silicified gold-antimony ore in tea mining area are studied, which basically represent the fluid characteristics in the metallogenic stage of isochronous-stibnite ore.
Petrographic characteristics of (1) inclusions
The types of inclusions studied are mainly gas-liquid two-phase inclusions, which are composed of water phase () and bubbles () at room temperature, mostly round, oval, long and irregular. The size of inclusions is 2 ~ 16 micron, mostly 4 ~ 6 micron, and the gas-liquid ratio 10% ~ 50%, mostly 65438.
Table 3.8 Test Results of Fluid Inclusions in Tea Mining Area
(According to the fluid inclusion laboratory test of Jilin University, 20 13)
(2) Uniform temperature, salinity and density
The freezing point temperature (Ti) of the measured inclusions is-11.0 ~-1.7℃. The uniform temperature is between 209.9 and 294.6℃, and the peak value is between 230 and 280℃. The calculated salinity (NaCleq) ranges from 2.89% ~ 15.04%, with a peak value of 9% ~ 13% and an average value of 9. 18%. The density ranges from 0.80 to 0.93 g/cm3, and the peak value is concentrated between 0.83 and 0.89 g/cm3 (Figure 3. 16), with an average value of 0.87g/cm3. Generally speaking, the fluid in the Yanshi-stibnite mineralization stage in the tea mining area is a medium temperature, low salinity and low density fluid.
Fig. 3. Histogram of homogeneous temperature, salinity and density of ore-forming fluid in Yingshi-Sb mineralization stage in16 tea mine area.
(3) Metallogenic pressure and depth
According to the results of micro-temperature measurement of inclusions and Shao Jielian's empirical formula (1990), the pressure range of ore-forming fluid in tea mining area is 18.32 ~ 32.63 MPa, with an average of 25.31MPa. . According to the piecewise fitting method proposed by Sun Fengyue et al. (2000), the relationship between fluid pressure and depth of Xibusen (1994) fault zone is estimated, and the corresponding formation depth ranges from1.83 to 3.26 km, with an average of 2.53km.
To sum up, the study of isochronous fluid inclusions in the strong antimony silicide gold mine in the tea mine shows that the ore-forming fluid in the hydrothermal mineralization of the tea mine is moderate temperature (209.9 ~ 294.6℃), medium and low salinity (2.89% ~ 15.04%) and low density (0.80 ~ 0.04%).
3. 1.2.4 characteristics of trace elements and rare earth elements
In this study, five samples with different salinity were tested for trace elements and rare earth elements (Table 3.9), and the sample analysis was completed by Beijing Institute of Geology of the Nuclear Industry. From the normalized distribution pattern diagram of rare earth elements in chondrites (Figure 3. 17), it can be seen that the distribution curve is relatively gentle to the right, light rare earth elements are relatively rich, heavy rare earth elements are relatively deficient, and the fractionation of light and heavy rare earth elements is not obvious. From the Eu anomaly, the long-distance sillimanite schist, silicified limonite schist and stibnite schist have obvious negative Eu anomaly, while amphibole adamellite gneiss and silicified sericitized granite have positive Eu anomaly, and the latter Eu anomaly is relatively obvious, indicating that the source of ore-forming materials has little to do with the granite gneiss in the ore-bearing country. On the contrary, a small amount of ore-forming materials may come from Jingshan Group.
Table 3.9 Analysis Results of Trace Elements and Rare Earth Elements in Rocks and Ores in Tea Mining Area Unit: 10-6
sequential
Fig. 3. 17 spider web diagram of standardization of rare earth chondrites and trace elements in surrounding rocks and ores of tea mining area
The lithology of ckh- 1 ~ 5 is the same as that in table 3.9.
Trace element analysis shows that antimony is positively correlated with copper, lead, zinc, cesium, thallium and indium, and negatively correlated with lithium and barium. Compared with altered granite gneiss, ores (CKH-4 and CKH-5) are rich in Sb and the above positive related elements, and Ba elements are obviously brought out in large quantities, which is related to the formation of barite. At the same time, from the change of elements, it can be seen that the ore samples and adamellite gneiss samples have similar changing trends, showing some inheritance, and the latter may provide some ore-forming materials.
3. 1.2.5 sulfur isotope characteristics
This time, three stable isotope samples of sulfur were collected. The sample is single mineral stibnite in I- 1 orebody primary gold-antimony ore. The sulfur isotopic composition δ34S is +6.8‰, +7. 1‰ and +7.8‰ respectively, with a small change range, which is basically consistent with the metal sulfides in Wangjiazhuang and Xingjiashan mining areas of Fushan, and both fall into the granite range, indicating the source of sulfur.
3. 1.2.6 Genesis of the deposit
In the antimony-gold deposit of Cha Mine, the ore body is strictly controlled by the fault zone, and the host rock is fine-grained adamellite altered in the fracture zone, with strong wall rock alteration, antimony-gold mineralization and multi-stage mineralization. Isotopic composition shows that mineralization is related to deep ore-forming materials and ore-forming fluids. At the same time, different levels of magmatism can provide heat source and drive the hydrothermal circulation of groundwater, continuously extract gold-forming substances from strata, migrate to favorable fault zones for precipitation and enrichment, and form gold deposits. The deposit is a mesothermal vein deposit. Compared with the metallogenic characteristics of orogenic gold deposits (Groves et al., 1998) (Table 3. 10), it is considered that Chakuang gold-antimony deposit belongs to orogenic type and belongs to orogenic epithermal gold-antimony deposit. Genesis can be compared with Dachang Au-Sb deposit in Qinghai, East Kunlun orogenic belt (Zhao, 2004). The formation of the deposit is roughly consistent with the hydrothermal vein-type gold deposits in Qixia, Penglai and its west, and it is also the product of tectonic hydrothermal activity in the late Yanshan period of Mesozoic. However, the mineralization in this mining area is far away from the main part of the rock mass (heat source) and the mineralization depth is small, so the mineralization temperature is low, and it shows continuous mineralization in the crust together with other orogenic gold deposits in other areas (Groves et al., 1998). At the same time, the occurrence of epithermal antimony-gold mineralization in the vertical Hecha mine also shows that there is less erosion, good preservation conditions and great potential for finding orogenic gold deposits in this area.
Table 3. Comparison of main characteristics between10 tea gold-antimony deposit and orogenic gold deposit
Note: The data of orogenic gold deposits and Dachang gold antimony deposits are quoted from Zhao (2004); This book is the information of gold and antimony deposits in tea mines.