The Shuiyindong gold deposit in Zhenfeng County, Guizhou Province is located at 21km to the west of the north of Zhenfeng County, with geographical coordinates of 115 31 ′ 11 ″ ~ 115 33 ′ 38 ″ east longitude. 25 31 ′ 11 ″ ~ 25 33 ′ 28 ″ north latitude belongs to Xiaotun Township, Zhenfeng County, and a small part of the western end of the mining area belongs to huilong town, Xingren County, with a mining area of 28km2. In the early 1981s, when investigating the mercury mine in Huijiabao anticline, gold-bearing mineralization was discovered in Xionghuangyan, Shuiyindong mining area, which opened the gold prospecting history of Huijiabao anticline. During 1982 ~ 1983, the prospecting in Shuiyindong area was carried out intermittently, and only the surface oxidized ore bodies controlled by faults were found. At one time, it was considered that there was no further gold prospecting value in the area. In 1983, Zimudang and Taipingdong large-scale gold deposits were discovered in Zimudang area in the western section of Huijiabao anticline. In 1993, the exploration in zimudang gold deposit was completed, and a "two-story" prospecting model was established. In 194, the large-scale metallogenic prediction of Huijiabao anticline was carried out, and the Shuiyindong area was selected as the A-class prospecting target area, and the "downstairs mine" in Longtan Formation was selected as the exploration. In 1995, the blind gold deposit controlled by mercury cave was discovered by drilling verification. Only in June 2114, the exploration of the middle ore section was completed, and the resources/reserves with an average grade of 11.95×11-6 were 54.62 t, making Shuiyindong Gold Mine another super-large gold deposit after Lannigou in the "Golden Triangle" of Yunnan, Guizhou and Guangxi. In recent years, several hundred tons of new resources have been explored, and the Shuiyindong gold deposit is expected to become a super-large deposit.

1 geological background

Shuiyindong gold deposit is located in the north of Carlin-type gold deposit concentration area in southwest Guizhou, and together with a large number of gold deposits such as Lannigou gold deposit, Zimudang gold deposit, Taipingdong gold deposit, Gotang gold deposit, Banqi gold deposit and Yata gold deposit, it has become the main body of the "Golden Triangle" in Yunnan, Guizhou and Guangxi. The tectonic position of the "Golden Triangle" in Yunnan, Guizhou and Guangxi is located in the Youjiang Fold Belt and its junction on the southwest edge of the Yangtze Platform, which belongs to the composite part of the Eurasian plate, the Indian plate and the Pacific Ocean (Han Zhijun et al., 1999).

The exposed strata in this area are mainly Devonian, Carboniferous, Permian and Triassic, which are widely distributed. The Cambrian is only scattered in the southern margin (in Guangxi), and the Jurassic is missing. The Cretaceous-Tertiary (Paleogene) is only scattered in the southwest of Guangnan and Luoping, mainly red sand, mudstone and conglomerate in intermountain fault basins, and the Quaternary is of various types.

The igneous rocks exposed on the surface in this area include continental overflow tholeiite and dyke diabase, alkalescent diabase and alkalescent ultrabasic rock (Table 1).

table 1 geological characteristics of igneous rock assemblage in southwest Guizhou

2 mining area

The mining area is located in Huijiabao gold field in Xingren Anlong gold belt. Spatially, together with Zimuyou and Taipingdong large-scale gold deposits, Lanmuchang large-scale mercury-platinum deposits, Dabatian-type mercury deposits and a number of gold and mercury deposits, it forms the Huijiabao gold-mercury thallium ore field with a length of about 21km near EW direction (Figure 1).

The ore field structure is mainly a short axis anticline of Huijiabao near EW direction, with a length of about 21km and a width of about 6km. Taking Huilong Fault (F18) in the middle of the anticline as the boundary, the stratum in the west section is relatively slow, with a dip angle of 5 ~ 21, and the wings are basically symmetrical; The strata in the eastern section are slightly steep, showing an asymmetric shape with steep north wing and slow south wing. The western section is Zimudang gold mine, which contains two large gold deposits, Zimudang and Taipingdong, and the eastern section is Sanchahe gold mine, with Shuiyindong super-large gold deposit and Xionghuangyan, Zhaojiaping, Puzilong and Zaofanshan gold spots. The anticline is obviously superimposed by the late NE and near-SN structures, and there is a secondary NE anticline, with three groups of faults and interlayer faults (interlayer slip) in EW, NE and SN directions. EW-trending faults are developed near the axis of the anticline, basically parallel to the axis of the anticline, mostly low-angle reverse faults, slightly steep in the shallow part and gentle in the deep part. The F115 fault exposed in the Shuiyindong gold mine area gradually disappeared in the Longtan Formation (P3l) in the deep part. EW-trending faults are ore-bearing faults, which are staggered by later faults together with anticlines. Interlayer structures are mainly developed in the axial and paraaxial parts of anticlines, and are mainly found in Dachang Formation and Longtan Formation, and are important ore-controlling structures in Shuiyindong, Taiping Cave and zimudang gold deposit.

Figure 1 Regional Geological Sketch of Shuiyindong Gold Mine

(according to Guo Zhenchun, 2112)

T1yn-Yongningzhen Formation; T1y—-Yelang Formation; P3c+D-Changxing Formation+Dalong Formation; P3l—-Longtan Formation; 1— anticline; 2-normal fault; 3-reverse fault; 4-Fault with unknown nature; 5-Gold deposit (point); 6-Mercury deposit (point); 7-Thallium deposit; 8— Arsenic occurrence

3 Geological characteristics of ore deposit (body) < P > Shuiyindong gold deposit is a compound concealed deposit which occurs in Longtan Formation of Permian, and the ore body is dominated by stratabound type and supplemented by fracture type. Stratified ore bodies mainly include Ⅲc, Ⅲb, Ⅲa, Ⅱf and Ⅰa (Table 2), which occur in the range of nearly 31m on both sides of the axis of Huijiabao anticline. They are layered and quasi-layered, with the same occurrence as the rock stratum, thin thickness, rich grade, undulating eastward dip, and spatially overlapping multiple ore bodies. Fractured ore bodies occur in gently inclined reverse faults with small fault distance near the axis of anticlines, and are strictly controlled by fault fracture zones.

table 2 characteristics of stratabound ore bodies

fractured ore bodies are composed of "Loushang Mine" controlled by F115 and ore bodies controlled by blind faults such as F162, F163, F164 and F165 in Longtan Formation. "Loushang Mine" occurs in the collapse space of F115 fracture zone and the core of its hanging wall traction anticline, and tends to S. The ore bodies are lenticular and layered, and the ore bodies are scattered and scattered, and only some resources are obtained.

the ore bodies controlled by p>F162, F163, F164 and F165 occur in the fault fracture zone in a lenticular shape, with a dip of SE, and the dip angle is 21 ~ 45. The ore bodies expand and contract, and the fault cuts carbonate rocks, and the fracture zone becomes wider and the ore bodies are thicker. However, when the clay rocks are cut, the fracture zone becomes narrower, and the ore bodies are thin or even locally unacceptable.

3.1 ore-controlling structure

The structure in the Shuiyindong gold mine area is well developed, which is mainly composed of Huijiabao anticline near EW and longitudinal reverse faults distributed along the axis of the anticline, followed by NE, near SN faults and unconformity surface structures.

the huijiabao anticline is a regional structure, and some small anticlines (Zhaojiaping anticline, EW-oriented, about 1.5km long in the area) are superimposed locally, which is a wide, gentle and short-axis anticline near EW-oriented, and some of them are transformed into NW or NNW-oriented due to later transformation. The anticline in the area is about 5.3km long, the stratum at the core is nearly horizontal, the dip angle of the strata at the two wings is 11 ~ 211, and the axial plane is nearly vertical. Shuiyindong gold deposit is located in the middle of the eastern part of Huijiapu anticline, and the ore bodies are mainly distributed within 311m from the axis of the anticline. NE-trending folds are distributed in the southwest of the mining area, with a small scale. Four anticlines and three synclines are developed in * * *, and the axis trace of the surface is nearly parallel, with a length of 1.61～1.91km. The famous Lanmuchang anticline.

EW-trending faults are developed near the axis of anticline, basically parallel to the axis of anticline, mostly low-angle reverse faults, slightly steep in the shallow part and gentle in the deep part. EW-trending faults are ore-bearing faults, which are staggered by later faults together with anticlines. There are F111 and F115 faults in the mining area. F111 controls the output of Puzilong and Zaofanshan gold deposits; F115 is the ore-controlling fault of Shuiyindong gold deposit, which controls the output of Xionghuangyan gold deposit eastward.

NE-trending faults developed a SEries of high-angle tensile and torsional faults with NW dip in the southwest of the mining area, and a series of concealed reverse faults with se dip and dip angle of 28 ~ 45 developed near the axis of Huijiabao anticline, which controlled the production of fractured ore bodies in Shuiyindong Gold Mine.

There is a parallel unconformity surface between the Middle Permian Maokou Formation and the Upper Permian in Shuiyindong mining area, and interlayer faults are formed along the unconformity surface and its vicinity, which controls the occurrence of layered and lenticular flat gold bodies in deep structural alteration variants in the mining area.

3.2 ore characteristics

The metallic minerals formed in hydrothermal period include pyrite, arsenopyrite, white iron ore, realgar, orpiment, stibnite and Cinnabar. Pyrite is dominant, arsenopyrite often occurs with pyrite, and stibnite, Cinnabar, realgar and orpiment are distributed in veinlets, which are only found in Ia ore bodies and fractured ore bodies. Non-metallic minerals are mainly Shi Ying, dolomite and calcite, with fluorite, chalcedony and clay minerals. These minerals often form the following * * * assemblages: Shi Ying-dolomite, Shi Ying-fine pyrite-arsenopyrite, Shi Ying-calcite-realgar-orpiment-stibnite-Cinnabar and coarse pyrite-white iron ore. The main structures of ore are lamellar, biological remains, disseminated, lumpy and veinlets; The structure is mainly self-granular, strawberry, biological illusion and replacement.

the ore phase analysis results are shown in table 3.

table 3 results of mineral phase analysis w(Au)/11-6

note: the data in the table are analyzed by Guizhou 115 geological brigade laboratory and tested by HYX-3A fluorescence analyzer.

Pyrite is the main carrier of gold, which can be divided into sedimentary pyrite and hydrothermal pyrite. Pyrite in the former is mostly strawberry-shaped or authigenic cube and pentagonal dodecahedron crystal, with large particle size and strip (grain) shape. Pyrite particles were fine and disseminated in hydrothermal stage. Four kinds of pyrite with different morphologies and structural features: strawberry-shaped, bioclastic-shaped, coarse-grained, and fine-grained.

3.3 sequence of surrounding rock alteration and mineral formation

The surrounding rock alteration mainly includes silicification, dolomitization and pyritization, followed by hydrothermal alteration such as arsenopyrite, male (female) yellowing, clayey and fluoridation. Among them, silicification, dolomitization and pyritization (accompanied by arsenopyrite) are closely related to gold deposits, and all gold deposits have these three alteration characteristics. Gold deposits (mineralization) often occur in areas with strong alteration and superposition of various alterations, and rocks without alteration or with single alteration contain no or low gold content.

the hydrothermal mineralization of gold deposits can be divided into three stages, and the corresponding mineral assemblages and formation sequence are listed in table 4.

Table 4 Mineralization sequence of Shuiyindong gold deposit

4 Geochemical characteristics

4.1 Major elements

The ores of Shuiyindong gold deposit are divided into three categories. Carbonate rock type (impure limestone), siliceous breccia type (breccia claystone, breccia siltstone and breccia limestone) and calcareous sandstone type (calcareous sandstone and calcareous siltstone). Among them, carbonate type ore is the main ore, followed by breccia type ore, and calcareous sandstone type ore only occurs in P3l1 small ore body. See Table 5 for the main chemical compositions of carbonate type ores. See Table 6 for ore composition analysis of different ore bodies.

4.2 trace elements

The main rock types of the ore-bearing rock series of Shuiyindong Gold Mine include limestone, marl, mudstone, argillaceous siltstone and siliceous rock, etc., and generally have very high contents of As, Sb, Cu and Tl, which are much higher than those in normal similar rocks, among which As is hundreds of times higher than those in similar rocks. As, Sb, Cu and Tl are the characteristic indicator elements of gold mineralization in Shuiyindong gold deposit.

table 5 main chemical composition w (b)/%of carbonate-type ores

note: the data were analyzed and tested by the key laboratory of mineral deposit geochemistry of China academy of sciences, with total chemical analysis method.

the original contents of Au, As, Cu, Sb and Tl in all kinds of rocks (bAsed on unaltered samples) are not much different, and their changes are far lower than those caused by mineralized alteration. The ratio of average values of au, as, Cu, Sb and Tl in mineralized rocks to similar unaltered rocks is as high as tens to hundreds. Among them, Au, As and Tl are the highest. Au, As, Cu, Sb, Tl and Pb in the ore-bearing rock series are significantly increased compared with the same kind of unaltered rocks, while Ti, Sc, Nb, Ta, Zr, Hf, V, Cr, Co, Sn, Ga, Ge, Cd, Rb, Cs, Ba, Mn, Zn, Th and REE have little change.

Table 6 Composition analysis results of ore combination samples

Note: The data were analyzed and tested by the Key Laboratory of Deposit Geochemistry of China Academy of Sciences; Chemical total analysis and plasma mass spectrometry.

4.3 rare earth elements

The content of rare earth elements in ore bodies ranges from 11.8× 11-6 to 37.1× 11-6, with an average of 21.8×11-6. The δEu value is between 1.88 and 1.21, with an average of 1.13. Except for a few samples with weak negative anomalies, there are no Eu anomalies or positive anomalies. The average σ ΣREE of surrounding rock is 241.9×11-6, and the average δEu value is 1.11, with no abnormality. The average σ ΣREE ratio and δEu value of the ore-free rocks in the same horizon as the ore body are 48.1×11-6 and 1.81 respectively, showing weak negative anomalies. The average σ ΣREE of limestone is 9.59×11-6, and the average δEu is 1.65, with negative anomalies (Table 7).

Table 7 Rare Earth Element Analysis Results and Characteristic Parameters w(B)/11-6

Note: Ⅲc-4 and Ⅲc-5 are siliceous type ores, and the others are tuffaceous bioclastic limestone type ores; The surrounding rock is 6 pieces on average, and the lithology is mainly clay rock and siltstone, with a small amount of limestone; Two ore-free sections are average, and the lithology is limestone with more tuff. According to Shen Wenjie et al, 2115.

4.4 isotope

The sulfur isotope analysis results of Shuiyindong Gold Mine are shown in Table 8. See Table 9 for lead isotopic composition and related parameters of hydrothermal pyrite in the ore.

Table 8 Sulfur Isotope Analysis Results of Shuiyindong Gold Mine

(According to Liu Jianzhong, 2116b)

Table 9 Lead Isotope Composition and Related Parameters of Hydrothermal Pyrite in Shuiyindong Gold Mine Ore

Note: δ β = (β-β m)/β m× 1111; Δγ ＝（γ-γm）/γm×1111； β = 217 Pb/214 Pb of the sample; γ = 218 Pb/214 Pb of the sample; β m = 217 Pb/214 Pb of the mantle = 15.33; γ m = 218 Pb/214 Pb of the mantle = 37.47; The testing unit is Isotope Laboratory of Yichang Institute of Geology and Mineral Resources. According to Liu Jianzhong, 2116b.

4.5 characteristics of inclusions

The shape of inclusions is isolated and irregular, and the negative crystal shape is its characteristic, with a diameter of 5 ~ 61μ m, and most of them are 11 ~ 51μ m.. According to the phase characteristics of inclusions at room temperature (25℃) and the phase changes during freezing, the types and composition of inclusions can be divided into four categories: liquid, gas, gas-liquid phase VCH4+N2+CO2+H2O, and CO2-rich fluid inclusions.

The results of temperature measurement and pressure measurement of fluid inclusions show that the homogenization temperature of fluid inclusions is 211 ~ 221℃ and the salinity is 5% ~ 6% during the main mineralization period. The pressure of ore-forming fluid ranges from 1111× 115 to 2111× 115, which shows the properties of overpressure fluid. It has the characteristics of medium-low temperature and ultra-high pressure hydrothermal mineralization.

reference

Guo Zhenchun. 2112. Two-story model of Huijiabao gold field in southwest Guizhou and its prospecting significance. Gold Geology, 8 (4): 18 ~ 23

Han Weijun, Wang Yangeng, Feng Jizhou, etc. 1999. Gold Geology and Exploration in Southwest Guizhou. Guiyang: Guizhou Science and Technology Press <