The earliest formal basic geological survey in this area began at 1958, when the regional geological survey brigade of Guangdong Geological Bureau conducted1∶ 200,000 regional geological survey. 1974 ~ 198 1 year, Hainan Geological Brigade of Guangdong Geological Bureau conducted geological survey in Shimenshan-Chaishuling molybdenum polymetallic mining area, about 10km south of Baolun Gold Mine, and identified many small and medium-sized molybdenum polymetallic deposits. Panxi Geological Brigade of Sichuan Bureau of Geology and Mineral Resources made a detailed survey of the basic geology in the northern part of Baolun mining area during the regional geological survey of 1988 ~ 199 1 ∶ 50,000 peak amplitude and Ledong amplitude. Subsequently, the Geological Brigade of Hainan Provincial Bureau of Geology and Mineral Resources carried out the ore occurrence inspection and civilian mining investigation on Baolun Gold Mine. Since 1996, in order to cooperate with the investigation of gold resources in this area, the regional geological survey brigade of Hainan Provincial Geological Comprehensive Survey Institute has carried out two regional geological surveys of1:50,000 near the Baolun gold mine area, and completed1:50,000 Liu Huang maps and 1000 regional geological survey reports in 2000. The report made a detailed basic geological study of the mining area and its south.
The exploration, development and comprehensive research of this deposit are of great significance to the local economic development and the general survey of gold deposits in Hainan Island.
1 regional metallogenic geological environment
1. 1 geotectonic unit
The deposit is located at the southwest end of Qiongzhong anticlinorium in the southern margin of South China Fold System, at the intersection of east-west Jianfengling-Diaoluo fault, Jiusuo-Lingshui fault, northeast Lingao-Wang Lou fault and Laocheng-Lingtou fault, and belongs to the edge of Ledong Basin.
1.2 regional stratum
In this area, the Mesoproterozoic Great Wall Baoban Group deep metamorphic rock series, Silurian shallow metamorphic rock series, Cretaceous continental sedimentary rock series and Indosinian and Yanshanian granites are mainly distributed (figure 1). The crystalline basement of the Baoban Group is distributed in the west of the mining area, and its lithology is migmatite, plagioclase gneiss and syenite mica schist. It is in fault contact with the overlying Silurian Tuolie Formation. Tuolie Formation is mainly distributed in the middle of the mining area, which is the ore-bearing stratum of gold deposits, and it is distributed in the NE-SW direction. The northwest and west are in intrusive contact with Jianfeng rock mass, and the southeast and east are superimposed with Cretaceous Lumuwan Formation, and they are in fault contact. The lower member of Tuolie Formation is mainly sericite phyllite with a thickness of > 560 m; The middle part of Tuolie Formation is mainly carbonaceous phyllite, with a thickness of 849 meters ... The Cretaceous strata are distributed in the east of the mining area and consist of Lumuwan Formation and Wanbao Formation. The Lower Cretaceous Lumuwan Formation is mainly composed of glutenite, gravelly sandstone mixed with purplish gray thick layered gravelly crystalline tuff and purplish red tuff, which are in fault contact with the Tuolie Formation and the upper part is integrated under the Upper Cretaceous Wanbao Formation. Wanbao Formation is mainly composed of glutenite and gravelly sandstone.
1.3 regional tectonic framework
Faults and fold structures are well developed in the mining area. The fault structures mainly include the NE No.8 Mountain-Tiewanling thrust fault (F 1) and the NNW ore-controlling fault zone. The fold structure is mainly Haogangling anticline.
The No.8 Mountain-Tiewanling fault (F 1) is distributed in the east of the mining area, showing NE direction, with both ends protruding out of the figure and being 16km long. Width 1 ~ 5m. The overall strike of the fault is NE27, with NW dip angle of 34 ~ 85. The upper wall is Tuolie Formation and the lower wall is Lumuwan Formation, which is a thrust fault. There are many secondary imbricate overthrust cracks on the local upper wall according to the distribution of lens bodies of the corresponding time pulse and silicified pulse. Seriphization, silicification and chloritization are common in fault zones. According to the field outcrop and strain measurement, the fault suffered from strong compressive deformation.
Figure 1 Regional Geology and Gold Deposit Distribution Map of Baolun Gold Deposit
(adapted from Huang et al. 200 1)
1- Quaternary sediments; 2- Cretaceous red clastic rocks and continental volcanic rocks; 3- Permian sandstone, slate and limestone; 4- Carboniferous sandstone, slate and limestone; 5- Silurian clastic rocks and mudstone mixed with limestone; 6- Ordovician clastic rocks and limestone; 7- CAMBRIAN clastic rocks and carbonaceous siliceous rocks mixed with phosphorite; 8— Silurian calcareous formation consists of timely sandstone, quartzite and hematite siltstone mixed with hematite layer; 9— Gneiss, schists, quartzites and migmatites of Baoban Group in the Great Wall System of Mesoproterozoic; 10- Yanshanian basic a-acid volcanic rocks and subvolcanic rocks; 1 1- Yanshanian gabbro and diabase; 12- Yanshanian granitoids; 13- Indosinian granitoids; 14— Variscan-Indosinian granite; 15— variscan gabbro; 16- variscan granitoids; 17— Mesoproterozoic granite and granodiorite; 18- failure; 19- ductile shear zone; 20- large rock gold deposit; 2 1- medium-sized rock gold deposit; 22— Xiaoyan gold deposit; 23— Rock gold deposit and mineralization point; 24— Medium-sized placer gold deposit
The NNW-trending fault zone is mainly distributed in Tuolie Formation, passing through the late Triassic granite northward. Eight fracture zones have been found in the mining area, including five ore-bearing fracture zones (Figure 2), which are almost equidistant and parallel. Generally, the spacing of the fracture zone is 50 ~ 80m, the overall strike is 330 ~ 355, the dip angle is 240 ~ 265, the local dip angle is 60 ~ 75, and the dip angle is 55 ~ 82. The length of the fracture zone is 400 ~10 ~ 30m, and the width is generally10 ~ 30m, the maximum. The fault zone has good zonation, generally the center is filled with gold-bearing quartz veins, and the two sides are silicified phyllite and fractured silicified phyllite in turn.
Haogangling anticline is distributed in Tuolie Formation in Haogangling area, about 1.5km long and about 0.8km wide in the area. Its axis trace is NNW, the core is phyllite in the lower member of Tuolie Formation, the two wings are carbonaceous phyllite in the middle of Tuolie Formation, and the east wing is cut by NE-trending thrust fault, but the middle of Rutlie Formation is not exposed. East wing formation attitude: 61~ 88 ∠ 58 ~ 88; Formation attitude in the west wing: 230 ~ 245 ∠ 60 ~ 80, with lateral dip angle of 40 ~ 60. The NW-trending ore-bearing fracture zone is located from the turning point of Haogangling anticline to the core, which may form a giant structure in the east, and was later transformed by Indosinian and Yanshanian magmatic intrusion and Yanshanian thrust structure.
Fig. 2 Geological map of Baolun Gold Mine
Plan a; Type b profile
K2b—— Lower member of Wanbao Formation of Upper Cretaceous; S 1t2——the middle section of the lower Silurian Tolie Formation; S 1t 1- Lower member of Tolie Formation of Lower Silurian; T2ξγ- Late Triassic syenite.
1- structural fracture zone; 2— Ore body and serial number; 3- timely pulse; 4- fracture; 5- occurrence; 6-exploration line and number; 7- phyllite; 8- chlorophyllin; 9— Vein-crossing tunnel and its number; 10- inclined shaft and number; 1 1- appears (personal data)
1.4 regional magmatism
There is strong magmatic activity in the area, mainly late Triassic Jianfeng superunit biotite syenite granite, which is distributed in the northwest of the mining area, and Yanshanian granite is mainly distributed in the southeast of the mining area.
1.5 metallogenic unit
The metallogenic units in the area are I-5 South China metallogenic domain, II- 15 South China metallogenic province and III-5 1 Hainan metallogenic belt.
2 Geological characteristics of mining area
2. 1 ore-bearing strata
The middle-deep metamorphic rock series of the Mesoproterozoic Baoban Group, the shallow metamorphic clastic rock series of the Silurian Tuolie Group and the clastic sedimentary formation of the Lower Cretaceous Lumuwan Group in this area are important gold-bearing horizons, which constitute regional prospecting indicators.
Although the gold deposits in this area occur in various strata or strata such as granite, most of them are distributed in the deep metamorphic rocks of Baoban Group. The Au abundance of amphibolite schist and muscovite quartz schist in baoban group is 5 ~ 8 times higher than the Clark value in the crust (table 1), and they are the main source beds of gold deposits in the island.
Table 1 Au abundance value of metamorphic strata in Hainan Island
The original gold content in the metamorphic strata of Shilu Group is also high. The analysis results show that quartzite and quartz sandstone in Shilu Group have the highest Au content, followed by diopside and sericite quartz schist, all of which are 3 ~ 8 times higher than Clark value of the earth's crust (table 1). This shows that the source bed of associated gold deposits in Shilu area of the island may be Shilu Group, which is also a favorable horizon for gold mineralization.
2.2 magmatic rocks
Magmatic rocks occupy a considerable proportion in the whole ore-bearing Wuzhishan area, and many gold spots are directly produced in granite, but different gold mining areas or gold mining areas have different forms of expression.
Tunchang and Nankai gold mining areas, gold veins occur in the outer contact zone of granite bodies in the late Yanshan period; There are Yanshanian granitoids in Wenfu gold mining area. Daiya gold deposit is directly produced in Yanshanian granite magma.
There are a large number of Yanshanian granodiorite porphyry dikes in Gezhen shear zone, which are in the same direction as the ore-controlling structure and formed in the same tectonic-magmatic period, and there may be concealed rock masses in the deep part.
2.3 Ore-controlling structure
The gold deposit in this island is obviously controlled by structure. According to the regional tectonic framework, five gold belts correspond to the east-west and north-east structures respectively.
The occurrence of gold deposits (spots) in this area is mainly related to the NE-trending structure, and the gold deposits in the NE-trending ore belt generally occur obviously in the NE-trending fault zone or its secondary faults. However, the gold deposits in the east-west metallogenic belt are controlled by a series of regional-scale NE or NW faults. In the same NE-trending fault, the location of the deposit may be related to the occurrence change of the fault and the intersection of east-west or northwest structures. For example, Ledong gold deposit is located at the intersection of east-west and northeast structures, and the distribution of gold deposits in Gezhen shear zone is obviously related to the position change of shear zone in the strike.
2.4 surrounding rock alteration
Alterations closely related to mineralization mainly include silicification, sericitization, chloritization, carbonation, pyritization and muscovization, and occasionally albitization.
The horizontal zoning of surrounding rock alteration is obvious. Gold deposits generally change regularly from the main fault surface to the outside (footwall), from pyrite silicified rock to pyrite sericite → sericite → silicified granite → potash feldspar granite. The vertical zoning also has certain rules. From shallow large-area silicified altered rocks to various altered rocks in the middle, the symbiotic halo is the widest, followed by Ag halo and Cu halo is the narrowest. The silver halo is widest in the middle of the ore body, while the zinc and copper halos are narrower. The copper halo in the lower part of the ore body is the widest and the silver-zinc halo is the narrowest. The inner zone of lead, gold and silver in horizontal zoning is basically consistent with the position of ore bodies. Copper moves outward and zinc moves inward.
3 Geological characteristics of ore bodies
3. 1 deposit (entity) characteristics
The main ore section of the Baolun gold deposit is the Haogangling ore section located in the north of the mining area, with its scope roughly centered on Haogangling and extending to Wanglouhe River in the north, with an area of about 65,438 0.3 square kilometers, about 560 meters in the south, 500 meters in the east and 500 meters in the west. At present, 19 ore body has been delineated, in which vein I is located in the middle of the ore section, with an area of 0. 13km2. The ore body consists of gold-bearing quartz veins and gold-bearing altered rocks. The boundary of gold-bearing quartz vein is clear, and the boundary between gold-bearing altered rock and surrounding rock phyllite is unclear, showing a gradual transition relationship, which is mainly determined by grade.
The ore bodies are all distributed in the ore-bearing fracture zone (Figure 2). There are 14 ore bodies in the Tr 1 ore-bearing fracture zone, 1 ore-bearing fracture zone in Tr2, 1 ore-bearing fracture zone in Tr3, two ore-bearing fracture zones in Tr4 and 1 ore-bearing fracture zone in Tr5. Ore bodies are mostly veined, lenticular and lenticular. The occurrence of ore body is basically consistent with the ore-bearing fracture zone, with strike of 325 ~ 355, tendency of SWW, local tendency of NEE, and dip angle of 65 ~ 85. The exposed elevation of ore bodies is generally 270 ~ 5 10m, and the elevation of ore bodies controlled by tunnels is generally 320 ~ 130m, with individual (V 1-3) controlled to -25m. The length of ore body is generally 160 ~ 1 100 m, the average thickness is 0.45 ~ 4.86 m, and the thickness variation coefficient is 14% ~ 95%. The average ore body grade is1.61×10-6 ~ 29.48×10-6, the individual grade is 98.05× 10-6, and the grade variation coefficient is 41. V 1-3 ore body is the main ore body in Baolun mining area, which is distributed in the ore-bearing fracture zone Tr 1 with no outcrop on the surface. It belongs to concealed ore body, with strike of 325 ~ 345, dip to SWW, local dip to NEE, and dip angle of 65 ~ 85. The ore body consists of gold-bearing quartz veins and gold-bearing altered rocks. Gold-bearing quartz veins are veined and lenticular, with a strike of 708 meters and an inclination of 720 meters, which is characterized by staged enrichment. The gold concentration centers are distributed in the elevation range of 300-350 meters along the 104 line and the 25-1/kloc-0 line. Gold-bearing altered rocks are veined, distributed on both sides of gold-bearing quartz veins, and have a gradual transition relationship with surrounding rock phyllite, which is delineated according to grade. The grade of gold-bearing altered rock type ore is generally 2.70×10-6 ~ 4.18×10-6, which is much lower than that of gold-bearing quartz vein type ore. The ore body strike control length is 3 10m, the maximum dip angle is 4 15m, the average thickness is 2.62m, the maximum average thickness of a single project is 7.49m, and the thickness variation coefficient is 72%, which is a relatively stable type. The average grade of the ore body is 29.48× 10-6 (obtained by the weighted average of the average grade of a single project), the highest grade of a single sample is 282.70× 10-6, and the coefficient of grade variation is 164%, which is extremely uneven. The ore body is inclined to the south, and the lateral dip angle can reach 45.
3.2 Ore composition
The main metal minerals in ore minerals are pyrite, pyrrhotite and natural gold; The secondary metal minerals are arsenopyrite, nickel-bearing pyrite, chalcopyrite, sphalerite, galena, natural bismuth, biotite, chalcopyrite, biscite, jamesonite, jamesonite, trace iron-arsenic mixture, sulfur-iron mixture, gold-bismuth mixture and sulfur. The main gangue mineral is timely; The minor gangue minerals are muscovite, sericite, chlorite, calcite, rutile and clay minerals.
The natural types of ore in Baolun Gold Mine can be divided into two types: the chronological pulse type and the altered rock type, with the former being dominant. According to the different mineral assemblages, the quartz-vein ore can be further divided into gold-bearing quartz-vein type, gold-bearing carbonate-quartz-vein type and gold-bearing polymetallic sulfide type.
3.2. 1 auriferous quartz vein type
The total amount of metal minerals is relatively low, generally 1% ~ 5%, and locally it can reach 10% ~ 15%, mainly sulfide (sulfide), natural metal, bismuth compound and telluride. Sulfides are mainly pyrite and pyrrhotite, with a small amount of chalcopyrite, sphalerite, galena and arsenopyrite. There are many kinds of bismuth compounds, tellurides and natural metals, including natural bismuth, biotite, gold-bismuth alloy, chalcopyrite, bismutite, bismutite, Baksanite, bismutite, bismutite, bismutite and bismutite. Gangue minerals are mainly light black chronological, and the chronological content can reach more than 90%. A small number of sericite, rutile, chlorite and calcite veinlets are found locally.
3.2.2 Gold-bearing carbonate-time pulse type
The total amount of metal minerals is about 5%, and local 15% ~ 20%, mainly pyrite, sphalerite and galena, with a small amount of chalcopyrite and pyrrhotite; The gangue minerals are ivory quartz (60% ~ 70%) and calcite (20% ~ 35%).
3.2.3 Types of gold-bearing polymetallic sulphides
The content of metal minerals is 5% ~ 20%, mainly pyrite and galena, followed by sphalerite, chalcopyrite and a small amount of arsenopyrite; Gangue minerals are mainly timely (50% ~ 80%) and calcite (10% ~ 25%), with a small amount of sericite, chlorite, rutile and carbonaceous.
3.2.4 Types of gold-bearing altered rocks
Metal minerals include pyrite, pyrrhotite, natural gold and arsenopyrite, but the total amount is low; Sericite and timely gangue minerals constitute the main body of this kind of ore.
The ore type and main mineral composition of Baolun gold deposit are relatively simple, but the trace minerals, especially bismuth minerals, are complex, and the gold mineralization enrichment is closely related to the high bismuth content, especially in the main ore body and high-grade ore. There are more than a dozen bismuth-bearing minerals in Baolun gold deposit, including natural metals, alloy minerals (intermetallic compounds), sulfides, sulfates, tellurides and bismuth compounds. These minerals are rarely reported in chronological vein deposits, and even less in Mesozoic and Cenozoic epithermal deposits. At present, hydrothermal vein-type gold deposits with a wide variety of bismuth minerals such as Baolun are rare.
The fineness of gold minerals is 921~ 968; The particle size of natural gold in Baolun Gold Mine is coarse, with macro gold-gold accounting for 34.4%, gold particles 1.4mm, fine gold accounting for 17.5% and micro gold accounting for 48. 1%. The occurrence of gold is mainly an independent mineral of gold, followed by bismuth (black bismuth gold ore) and sulfide (sulfur gold bismuth ore) of gold. There are also traces of gold in other gold-bearing minerals in the form of isomorphism or mixture, all of which are hyperdispersed gold; The embedded forms of gold are as follows: ① Fracture gold. Gold minerals (and gold mineral aggregates) are embedded in veinlets or crystal caves between grains of vein-like synbiotics or other minerals (such as pyrite) formed in the early stage; 2 package gold. Fine-grained gold minerals distributed in the form of inclusions in gold-bearing minerals (such as pyrite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite and Yingshi) are ultra-dispersed gold, which is difficult to detect under ordinary microscope. With the help of electron probe and electron microscope scanning, it is confirmed that trace gold or invisible gold is distributed in related gold-bearing minerals.
3.3 Ore Composition and Mineralization Stage
The ore structure includes automorphic granular, semi-automorphic granular, allomorphic granular, metasomatic residual, solid solution separation, mosaic, sieve-like, skeleton crystal, scale crystallization and fragmentation. The ore structure is disseminated, reticulate, breccia, spotted, banded, flaky and folded.
Mineralization stages are divided into gold/bismuthate stage, gold/pyrite stage, polymetallic/sulfide mineral stage and carbonate stage.
4 genetic analysis of the deposit
4. 1 Characteristics of fluid inclusions
It can be seen from Table 2 that the fluid inclusions in the Baolun gold deposit are mainly round, oval, rice-shaped or hexagonal, and a few are tubular. Most inclusions are banded along the fault, and the inclusions are generally small, generally between 7 ~14 μ m. Microscopic observation shows that the ore-forming fluid of inclusions has no signs of boiling. The three-phase inclusions containing CO2 are relatively large, 10 ~ 25μ m, and the CO2 content is relatively high.
Table 2 Characteristics of timely fluid inclusions in gold-bearing quartz veins in Baolun Gold Mine.
4.2 Physical and chemical conditions
The measured homogenization temperature of fluid inclusions is between137 and 280℃, the capture temperature of fluid inclusions is between 207 and 309℃, the ore-forming fluid density is between 0.783 and 0.975 g/cm3, and the salinity is between 2.68% and 7.15% (Table 3). Medium temperature and high mineralization temperature indicate that mineralization is related to magmatic thermodynamics and hydrothermal solution, not to epithermal gold deposits.
4.3 Isotopic geochemical characteristics
4.3. 1 sulfur isotope
The δ34S of ore in Baolun gold deposit is -2.3 ‰ ~ 0. 1 ‰ (Table 4), with a small variation range and very concentrated. This shows that the homogenization degree of sulfur isotope is high in the process of mineralization, which shows that sulfur in gold deposits is closely related to magmatic rocks. Therefore, the sulfur in the ore may mainly come from the metamorphic rocks of the Tuolie Formation, but it is obviously influenced and mixed by the sulfur in the remelted granitic magmatic rocks. Compared with other gold deposits in China, the sulfur isotopic composition of Baolun gold deposit is richer in light sulfur than that of Zhilingtou gold deposit in Zhejiang and Hebaoshan gold deposit in Fujian. The specific ore-forming materials mainly come from metamorphic rocks of Dabeiwu gold deposit in Jiangxi and Xiaobanwu gold deposit in Fujian, and the specific ore-forming materials mainly come from sedimentary rocks. The Haigou gold deposit in Jilin is obviously rich in heavy sulfur. This is similar to the Qifengcha gold mine in Beijing, where the ore-forming materials mainly come from metamorphic rocks and some from magmatic rocks. (Chen Bailin, 200 1).
Table 3 Characteristics of ore-forming fluid inclusions in Baolun gold deposit
Note: Tested by Institute of Deposit Geology, Chinese Academy of Geological Sciences, calculated according to the phase diagram of He Zhili (1982)NaCl-H2O system.
Table 4 Sulfur Isotopic Composition of Gold Ore in Baolun Gold Deposit
Note: Institute of Geology, Chinese Academy of Sciences, the test method is high temperature oxidation, and the instrument model is MAT-25 1. These data are relative to the international standard CDT.
4.3.2 Isotopes of carbon, hydrogen and oxygen
The oxygen isotope composition of Baolun gold deposit is δ 18O =1.0 ‰ ~11.7 ‰, and the hydrogen isotope is δ D =-6 1 ‰ ~-62 ‰ (Table 5 According to Clayton's relationship between oxygen isotope fractionation and temperature in time-water system, δ 18O time -δ 18O water = A (106t-2)+B (when T ≈ 200 ~ 500℃, A = 3.38, b).
Oxygen, hydrogen and carbon isotopic compositions of chronological and fluid inclusions H2O and CO2 in ores of Baolun gold deposit.
Note: δD and δ 18O are V-SMOW standards, and δ 13C are V-PDB standards. Source: ① According to Wang Pingan and others, the samples were determined by MAT-25 1 mass spectrometer in Institute of Mineral Resources, Chinese Academy of Geological Sciences. The total accuracy of the method was 3 ‰, δ 13C, δ 6544. ② According to Li and the temperature range of 170 ~ 330℃, calculate the δ 18O value of fluid water.
Hydrogen and oxygen isotope projection map of ore in Baolun gold deposit.
1~ 3 —— Baolun Gold Mine (sampled in this paper, tested by Institute of Deposit Geology, Chinese Academy of Geological Sciences); 4- Altun Dapinggou gold deposit; 5- Fujian Xiaoban Gold Mine; 6- Dabeiwu Gold Mine in Jiangxi; 7— Zhilingtou Gold Mine in Zhejiang (δ D = 8 δ 18O- 10)
The projection point is located at the left edge of the magmatic water area and the lower left corner of the metamorphic water area, indicating that the ore-forming fluid is mainly magmatic water and/or metamorphic water, and the influence of atmospheric precipitation is small. Combined with the historical analysis of geological evolution, the regional metamorphism of Silurian Tolie Formation occurred in Judong, Variscan and Indosinian. Although there is relatively strong dynamic metamorphism in this area (such as Gezhen ductile shear zone), the dynamic metamorphism in this area is not obvious, and it is more likely that the ore-forming fluid comes from magmatic water between metamorphic water and magmatic water. The hydrogen and oxygen isotopic composition of Baolun Gold Mine is similar to that of Xiaoban Gold Mine and Dapinggou Gold Mine in Fujian, but it is less affected by atmospheric precipitation. Compared with Zhilingtou Gold Mine, a volcanic hydrothermal gold mine with obvious sources of atmospheric precipitation, the influence of atmospheric precipitation is much smaller. Compared with Dabeiwu gold deposit in Jiangxi province, where ore-forming fluid mainly comes from magmatic hydrothermal solution, the influence of atmospheric precipitation is still very small. Therefore, the ore-forming fluid of Baolun gold deposit is mainly magmatic water mixed with metamorphic water, which is less affected by atmospheric precipitation, reflecting the close relationship between ore-forming fluid and Mesozoic magmatic activity.
4.4 Rare Earth Elements
Gold ore is rich in light rare earth, and the europium anomaly is not obvious or no anomaly, which is similar to the surrounding rock phyllite. However, it is obviously different from the heavy rare earth enrichment type of granite around the mining area and the strong negative anomaly of europium, and the values of (La/Sm)N, (La/Tb)N and (Sm/Nd)N are also closer to the surrounding rock phyllite, which is different from granite (Table 6). However, the value of gold deposit (Yb/Lu) is between granite and phyllite, and the value of δEu is the main source of other ore-forming materials. The above characteristics show that the ore-forming materials mainly come from metamorphic rocks of surrounding rocks, and are only partially influenced by the composition of granite.
Table 6 Rare Earth Element Content and Characteristic Value of Baolun Gold Mine and Its Surrounding Rock Ore
Note: The data are tested by the National Geological Experimental Testing Center, in which granite and phyllite are the results of plasma spectrum analysis, and gold ore samples are the results of plasma mass spectrometry analysis.
Therefore, although metamorphic rocks are the main ore-forming materials, they have obvious magmatic mixing characteristics, reflecting that mineralization is closely related to Mesozoic remelting granite.
It should be pointed out that a large number of gold deposits at home and abroad are related to syntectic granite, but the granite closely related to gold deposits in this area has the characteristics of rare earth elements and petrology of crustal remelting granite, and has strong crystallization differentiation. Can this explain from another angle that the gold in Baolun Gold Mine mainly comes from stratigraphic metamorphic rocks?
4.5 metallogenic age
Fresh biotite exposed in Jianfengling granite near the mining area was sampled (the sample was taken from the middle of the rock mass) and its age was determined by 40Ar-39Ar fast neutron activation method. Results It is confirmed that the emplacement age of the rock mass is 236.6±3.5Ma (integer age), and it can be confirmed that the rock mass was formed in the early Indosinian period (Table 7).
Dating data of biotite 40Ar-39Ar fast neutron activation method in Jianfengling granite body, Hainan.
Note: The integration age is 236±3.5Ma, and the isochron age is 243 3.5 Ma (3 ~10 data); Sample mass m = 82.80 mg, irradiation parameter j = 0.09712; The sample testing unit is Institute of Geology, Chinese Academy of Geological Sciences; The sampling site is Jianfengling quarry, which is the same as that of zircon age samples of Wang Daying et al. (2000).
According to the 40Ar-39Ar fast neutron activation dating of hydrothermal muscovite in chronological vein ore, the plateau age is 219.410.63ma, and the isochron age is 218.87 2.51Ma+0ma, which are very close. From the plateau age, the accurate metallogenic age of the Baolun gold deposit is 220.0 ~ 265,438+08.8 Ma. In addition, Li et al. measured the K-Ar age of hydrothermal illite in ore as 216.4 3.1Ma, and Liu Yulin et al. measured the K-Ar age of muscovite in vein as 22 1. 3.3 milliamps.
Table 8 Fast Neutron Activation Dating Data of 40Ar/39Ar.
sequential
Note: The plateau age is 219.4 0.6 Ma, and the isochron age is 218.9 2.5 Ma (6 ~1/phase data); Sample mass m = m = 61.85 mg; ; Irradiation parameter j = 0.008 206 The sample testing unit is Institute of Geology, Chinese Academy of Geological Sciences.
4.6 genesis of the deposit
The characteristics of ore-forming fluid inclusions and hydrogen and oxygen isotopes show that the ore-forming fluid is mainly magmatic water, with some metamorphic water participating, and the influence of atmospheric precipitation is relatively small. The geochemical background of ore-forming elements, sulfur isotopes, rare earth elements and initial strontium ratios reflects that the mineral source is mainly metamorphic rocks, but some of them come from magmatic rocks. The source of ore-forming materials and fluids reflects that mineralization is closely related to magmatism. Therefore, the Baolun gold deposit belongs to the magmatic hydrothermal gold deposit controlled by faults and fractures in the shallow metamorphic rock series of the Tuolie Formation of the Lower Silurian.
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(Author Zhang Yanchun)