Beishan Gold Mine belongs to Naomaohu Township, Yiwu County, Xinjiang. It is 40 kilometers northeast of Naomaohu Township. Geographical coordinates are 95 09' 29 "~ 9511'/kloc-0" east longitude. 43 56 ′ 38.2 ″ ~ 43 57 ′ 22.7 ″ north latitude. Hami City is 240 kilometers from Yiwu County to Naomaohu Township, mostly asphalt roads, and 40 kilometers from Naomaohu Township to the mining area is a simple road, which is convenient for all vehicles.
The working area belongs to low mountain and hilly landform, with high terrain in the north and low terrain in the south, with an altitude of 620 ~ 662 m and a relative height difference of less than 50 m ... Irregular annual rivers with dendritic dry valleys have small precipitation and large evaporation. The surface is mostly covered by sediments, and the thickness of the covering layer is about 0.3 ~1m. The region has a typical continental climate with dry heat in summer, with an average temperature of 38℃ and a maximum temperature of 50℃. It is cold in winter, with an average temperature of-10℃ and a minimum of -23℃. March to August is a windy season, and the wind force is generally 6 ~ 8, and the maximum can reach12; In addition, there are sandstorms and sand blowing.
There is no one in the local area. The nearest residential area is Naomaohu Township, which belongs to an important farming and animal husbandry area in Yiwu County. There are perennial rivers on the surface of Naomaohu Township, with sufficient water, which can ensure the production and domestic water in the mining area.
Second, the regional geology
Beishan gold deposit is located in the eastern part of Siberian plate and Buke-Santanghu island arc in the early Late Paleozoic. The regional exposed strata are mainly the second subgroup of Zhuomubasitao Formation of Lower Devonian and the first subgroup of Nanmingshui Formation of Lower Carboniferous, followed by Putaogou Formation of Neogene and Quaternary diluvium. The second subgroup () of Zhuomubastao Formation is a set of marine basic volcanic lava and intermediate-acid pyroclastic rocks, which are normal sedimentary clastic rocks with several layers of coal lines. The Putaogou Formation (N2p) is a set of inland lake sediments, and its lithology is orange-red glutenite and light gray silty clay mixed with glutenite.
According to the occurrence, the types of magmatic rocks in this area can be divided into two types: intermediate plutonic intrusive rocks and hypabyssal-ultrahypabyssal intrusive rocks. Medium-deep intrusive rocks, the first type of intrusive rocks are small and scattered, represented by gabbro and diorite; The second type of intrusive rocks are large-scale and widely distributed, represented by quartz diorite and granodiorite. The third type of intrusive rocks is small in scale, mainly distributed in the southeast of the area, represented by granite. Shallow-ultrashallow intrusive rocks are characterized by small rock masses and sporadic outcrops. The main rock types are diabase (porphyrite), diorite porphyrite, plagioclase fine-grained rock and granite porphyry.
The tectonic line in the area is mainly NW -NWW, with faults as the main part and folds as the auxiliary part. There are three main fault directions: NW -NWW formation, NE-NNE formation and NNW formation. Among them, the northwest -NWW group is the most developed. Strong cleavage and fragmentation occurred along the fault zone, which controlled a series of magmatic rocks. In addition, a large number of volcanic institutions can be seen in the Carboniferous in the northwest and southeast of this area.
The main minerals in this area are gold, copper, iron, sulfur, alunite, sodium nitrate and zeolite.
Three. Mining area geology
The strata exposed in the (1) mining area are mainly acidic pyroclastic rocks of the second subgroup () of the Lower Devonian Zhuomubastao Formation, and normal sedimentary rocks of the Tertiary and Quaternary systems. The second subgroup () of the Lower Devonian Zhuomubastao Formation occupies the main part of the mining area, which is mainly composed of (silicified) dacite tuff, andesite tuff and basaltic crystalline tuff. Generally speaking, the lithology changes from neutral to intermediate acid from west to east, and tuff crystalline limestone is the boundary marker layer between andesite tuff and dacite tuff. Silicified dacite tuff is only partially exposed in dacite tuff, and basaltic crystalline tuff is distributed in dacite tuff in block form, and the two are in a transitional state with no obvious boundary. The Neogene Pliocene Putaogou Formation (N2p) is tongue-shaped and distributed in the northwest of the mining area. The lithologic combination is silty conglomerate, argillaceous rock and clayey rock.
Quaternary Holocene (Q4) is distributed in the low-lying area in the middle of the mining area. Mainly aeolian sand and gravel, covering the surface, with a thickness of 30 ~ 50 cm, which is not filled in on the mining area map.
(2) Structure
The tuff of the second subgroup of Zhuomu Bastao Formation was sampled and analyzed, and the silica content of the three samples was low, ranging from 48.28 to 52.82. Medium alkalinity, K2O+Na2O is 4.24 ~ 4.72; K2O/Na2O < 1, ranging from 0.024 to 0.24 (Table 5- 1 1). The structural form of the mining area is dominated by faults, of which NW-NWW formation is the most prominent, followed by NE-NNE formation and NNW formation. Three groups of faults have laid the basic structural framework of this area, and the surrounding triangle area controls the mining area, mineralization and abnormal distribution in the mining area. The strike of ore-hosting faults is complex and diverse, with dense spatial distribution, and most of them are tensile-shear composite. The specific features of main faults and ore-hosting structures in this area have been discussed in the third chapter of this book, and they are not repeated here (Figure 5- 10).
(3) Magmatic rocks
The magmatic rocks in the mining area are all the products of the second intrusion in the middle of Variscan. Rock types are complex, mainly diorite (porphyrite), diabase (porphyrite) (see plate VII- 1), plagioclase fine-grained rock, followed by quartz diorite, granite and andesite (porphyrite). According to petrochemical analysis, the alkalinity is moderate, Rietmann index is 6 1.68 ~ 3.30, which is generally calc-alkaline, and K2O/Na2O ratio is 0.099 ~ 0.32. The magmatic rocks in this area have a characteristic evolution law. From morning till night, from basic to intermediate acidity and acidity, the abundances of SiO2 _ 2, K2O+Na2O, K2O/Na2O, Rb/Ba, LREE/HREE and Au all increase obviously (Table 5- 1 1), indicating that gold mineralization and late epithermal are intermediate acidity.
Table 5- 1 1 petrochemical analysis results of various rocks in Beishan mining area (wB/%)
Four. geology of ore deposits
(A) the characteristics of the ore belt
Ore belt refers to a strip belt controlled by surface engineering and containing 1 to several ore bodies. There are 1 1 ore belts in this area, and the ore belts have different trends, generally extending 150 ~ 220m, with the longest 400m, the shortest 40m, the widest 2 ~ 8m, the widest 19.6m and the narrowest 0.8m, in which/kloc-. V and No.6 ore belts are large in scale, with chrysotile sericitization along the ore belt and characteristic yellow surface. See table 5- 12 for the basic characteristics of each ore belt.
Table 5- 12 List of Gold Belt Features
(2) Ore body characteristics
There are 26 ore bodies delineated in the area (> 1g/t), most of which occur in gold belts, and the host rock is pyrite sericite (see Figure 3-9). Four occur in the secondary fracture zone in or near the F 1 fault zone, and the ore-bearing rocks are cataclastic rocks or timely carbonate veins. The length of a gold mine is generally 40 ~ 80m, the longest 160m and the shortest 30m, the apparent thickness is generally 1 ~ 3m, the thickest is 8m, and the thinnest is 1m, and the grade is generally10 ~ 3.50g/t.
(3) Ore type, structure and material composition
According to the mineral composition of the ore, the ore can be divided into five natural types, namely pyrite sericite type, chronological vein type, polymetallic sulfide type, silicified carbonate vein type and plagioclase fine-grained rock type. Among them, topaz sericite type is the most important; The timely vein is silicified by pyrite sericite and mainly distributed in the center of the vein. Polymetallic sulfide types often occur in deep holes or shafts of ore bodies; Silicified carbonate vein type mainly occurs in F 1 fault, and plagioclase fine-grained rock type is only distributed in plagioclase fine-grained dike.
The ore structure is dominated by autotype-isomorphic granular structure, followed by emulsion drop structure, erosion skeleton structure, inclusion structure and fragmentation structure.
The ore structures are mainly star-shaped disseminated structures, followed by veinlets, reticular disseminated structures and massive structures.
The main ore minerals are native gold and pyrite, followed by chalcopyrite, sphalerite, galena, arsenopyrite, limonite, sky blue, tetrahedrite, jarosite, malachite, white titanium ore, white iron ore, native copper, ilmenite and chalcopyrite. Gangue minerals are mainly syenite, sericite and calcite, followed by biotite, epidote, diaspore, rutile, chlorite, plagioclase, kaolinite, chalcedony, zoisite, tourmaline, gypsum, zeolite, apatite, chlorophyllin and sphene.
The chemical composition of ore varies with the type of ore. Pyrite sericite ore is relatively rich in gold, silver, arsenic, antimony, tin and titanium. Seasonal carbonate minerals are relatively rich in gold, lead, manganese and nickel. (Table 5- 14).
Table 5- 13 List of Ore Body Features
sequential
(4) Alteration of surrounding rock and prospecting index
The main types of wall rock alteration in mining area are silicification, pyritization, sericitization, kaolinization, carbonation, chloritization, epidotization and so on. Among them, silicification, pyritization and sericitization are closely related to gold, and kaolin is a sign of near ore.
It can be seen from Table 5- 1 1 that compared with tuff surrounding rocks, the main elements brought in by sericitization of pyrite are SiO2 and K20, and the main elements brought out are Fe2O3, CaO, MgO, Na2O and P2O5. In the late stage of strong silicification, the only constant element brought in is SiO2 _ 2, and most other constant elements are brought out.
In order to investigate the migration and change of trace elements in the process of surrounding rock alteration, the IV vein and surrounding rock were sampled in profile, and the results are shown in Table 5- 15 and Figure 5- 1 1.
Table 5- 14 Mineral Chemical Composition Table
Table 5- 15 Contents of Trace Elements in Chrysotile and Surrounding Rock
Fig. 5-11Ⅳ-1trace element content curve of ore vein
As can be seen from Table 5- 15 and Figure 5- 1 1, most of the elements have a characteristic bimodal distribution. However, there are differences in specific details, among which the peaks of Au, Ag, As and Sb are the sharpest, reflecting the drastic changes in content. The highest content is in pyrite sericite, and the lowest content is in tuff surrounding rock, which is higher than the tuff in the corresponding vein, indicating that this group of elements comes from ore-forming hydrothermal solution and has been brought in. The peak values of Fe group elements Cr, V, Ti, Co and Mn are the most gentle, reflecting that the content changes little. The highest content is at the edge of chrysotile sericite, which corresponds to the frequent clayey phenomenon between chrysotile sericite and tuff. The content of Fe group elements is lower than that of tuff in the time pulse, indicating that this group element may not change much or increase in the sericitization stage of chrysotile, but it is obviously brought out in the silicification stage. The content curves of sulfur-loving elements Cu, Pb, Zn, Mo and Sn are between the first two, but the difference is that except Pb, the content of sulfur-loving elements is equivalent to that of tuff surrounding rock in the corresponding pulse, and only Pb is the highest in the corresponding pulse. The above characteristics show that this group of elements was brought in at the early stage of sericitization of chrysotile, and changed little at the later stage of silicification. Compared with the same group of elements, Pb lags behind and tends to be enriched in the later stage of silicification.
The prospecting criteria in this area mainly include intermediate-acid late-stage rock mass related to the formation of subvolcanic complex, multi-stage active structural alteration fracture zone, sericitization, silicification, kaolinitization and limonitization of pyrite, combination of gold, arsenic, antimony and copper, lead and zinc elements, high-power IP high-phase anomaly and so on.
Verb (abbreviation for verb) potential customer comment
Based on the comprehensive analysis of geological, geophysical and geochemical data of the mining area, it is considered that the mining area has important prospecting prospects and is worth further work.
(1) Deep part of the known mineralized area (east of the mining area)
The types of surface dikes in the east of the mining area are complex, mineralization and alteration are common, and the structural conditions are favorable. I-VII ore belt has been discovered. It is known that the occurrence of ore belt is generally steep, and the strike is not far, but the downward extension depth is large, and the grade also tends to become rich downward. Veins bifurcate at the upper part of the profile and compound at the lower part, reflecting shallow surface erosion and little weathering damage. According to the drilling data of Team 704, granodiorite porphyry was found in the deep part, so a new mineralization type may appear downward.
(2) West of the mining area
There are NW-trending and NW-trending faults in the west of the mining area, and the surface is mostly diorite (porphyrite), diabase (porphyrite) and plagioclase fine-grained rock. The grade of gold sampled by the exploratory trench in the ore belts ⅵ and ⅷ are all higher than1g/t. At the request of the special group, the "305" project office carried out comprehensive geophysical scanning in this area at 1999, and found a nearly north-south trend, with a length of 2km and a width of 1km, and a nearly annular high-phase electrical anomaly. Because there is no carbonaceous shale in this section, it is inferred that the anomaly is a reflection of sulfide. High-precision magnetic survey corresponds to the weak magnetic background area, and it is speculated that the deep part may be an intermediate-acid rock intrusion. Gold, arsenic, antimony and other elements have high value anomalies. The remote sensing center of the former Ministry of Geology and Mineral Resources also identified the gold prospecting target area through color infrared remote sensing. According to the analysis of the above data, we think that the prospect of searching for deep large subvolcanic porphyry gold deposits in the west of the mining area is great, so we should make a decisive decision and immediately invest in further in-depth work and deep drilling verification on the basis of the existing work.