The main gold deposits of the metallogenic belt from west to east are Duolanasayi, Saidu, Jinba, Sarbulak, Aktas, and Kekesayi gold deposits. These gold deposits are all controlled by the ductile shear zone and derived secondary shear zone in Irtysh fault zone (Wang et al., 2018a, b; Li et al., 2014; Wang et al., 2011; Xu et al., 2009; Yan et al., 2006). The Irtysh fault is a long-term development fault, which has experienced several active stages such as normal fault-nappe fault-normal fault-nappe fault. Irtysh fault is the boundary of strata division of Altay and Junggar, and it is divided into three sections. The eastern section is Mayin'ebo fault, and the middle section is Fuyun-Xibodu fault. As the western section is covered by the Quaternary, it is generally considered that the Malkakuri fault extends concealedly along the Irtysh valley (Qu and Zhang, 1991). Regionally, Irtysh- Mayin'ebo fault is the main Au migration channel. The regional large faults have the properties of ductile shear zone or nappe to control the spatial distribution of intrusive rock mass, metamorphic facies zone and gold ore belt.
The Markakuli fault is distributed in the direction of NW-SE as a gentle wavy pattern. There are compresso-crushed zones or mylonitized shear zones with widths of hundreds to thousands of meters on both sides of the fault. The fault is characterized by the NW-SE ductile shear deformation in early activities and dominated by brittle activity in later activities (Deng, 2011; Tian and Xiao, 2007). The main magmatic intrusion in the western part of Irtysh gold belt is Habahe plagiogranite intrusion with an exposed area of 800 km2, which is a magma intrusive complex in the Middle Hercynian. Its main lithologies are plagiogranite, monzogranite, quartz diorite and gabbro, and there is a pulsating contact relationship between the lithologies. There are obvious zoning of pluton in which there are many residual rock mass. Some dating studies have been carried out on rocks of different lithologies in the Habahe rock mass (Table 1). The age by the whole-rock Rb-Sr dating and K-Ar dating methods for Habahe rock mass is very young, which can be interpreted as being subjected to late reformation. Due to the difference in lithology and sampling location of the sample, for the same method of zircon U-Pb dating, the granite dating is 390±5 Ma (Cai, 2007) and the monzonitic granite age is 406 Ma (Li et al., 2012). The age of plagiogranite in Jinba gold deposit is 431±3.4 Ma (Wang et al., 2017a), and the age data are relatively old, which may represent an earlier intrusion event. The zircon CL images of plagiogranite in Jinba gold deposit show columnar, short columnar and euhedral crystal indicating that most zircon grains retain the original magmatic zircon zones. Its tectonic environment may be volcanic island arc environment (Wang et al., 2017a).
Methods Test objects Age (Ma) Data sources Zircon SHRIMP U-Pb Habahe rock mass (granite) 390±5 Cai (2007) Whole-rock K-Ar Habahe rock mass (plagiogranite) 284–277 Wang et al. (1996) Whole-rock Rb-Sr Habahe rock mass (plagiogranite) 297±11 Chen et al. (2000) LA-ICP-MS Zircon U-Pb Habahe rock mass (monzogranite) 406 Li et al. (2012) LA-ICP-MS Zircon U-Pb Habahe rock mass (plagiogranite) 431±3.4 Wang et al. (2017a)
Table 1. Age statistics related to the Habahe rock mass
The Fuyun-Xibodu fault is a reverse fault that is located north of the Irtysh River, with a fault strike of 280°–300° and a length of about 135 km. Since the late Late Pleistocene, creep activity has been dominant. Fault fracture zones consisting of crushed migmatite, fault breccia, mylonite and fault gouge have a local width of 150–200 m, with mylonite bandwidth ranging from 10–20 to 100–200 m (Zhou et al., 2007; Wang et al., 1999). The magmatic rocks are less exposed in this area, and intermediate-acid rocks are more distributed, mainly produced in the form of stocks. The quartz porphyry in Sarbulak area is mainly concealed rock mass with obvious Au primary halo and primary halos of related elements (Gong et al., 2009). And the gold residual anomalies in the interior and the margin of the quartz porphyry rock mass are obvious (Zhao et al., 2011). The metallogenic age of the Sarbulak gold deposit is 278.2–216.9 Ma, which belongs to the late Hercynian period. The Rb-Sr isochron age of fluid inclusions is 285±4.3 Ma, and the surface age of Pb-Pb is 304±7 Ma (Wang et al., 2011; Yan et al., 2006). The zircon CL image of the quartz porphyry in the mining area shows black or black reaction edge. Most of the zircon inherits the characteristics of the original zircon. We measured the zircon U-Pb age of the quartz porphyry to be 297.8±1.4 Ma, consistent with the ore-forming age of the Saerbulak gold deposit, which also indicates that the quartz porphyry in the area is closely related to gold mineralization and has good ore-bearing properties. Exposed acidity veins with close relationship with mineralization in the mining area may be derived from deep magmatic activity, which is formed by the upward migration of enriched hydrothermal ore-forming elements due to the structural extrusion-tensile changes.
The Mayinebo fault in the eastern part of the Irtysh gold belt extends more than 90 km, which has the dual characteristics of thrust nappe and left-lateral shear. It has a long and complex evolution history. After the regional large-scale shear-strike-slip activity, there are still local shear activities, which lasts for a long time. The peak period may be 290–270 Ma, and the final end time is about 230 Ma (Zhou et al., 2007; Bo et al., 2000; Wang et al., 1999; Bo, 1996). The magmatic intrusion activity in this area is very active, especially are intermediate-acid dikes in the Middle and Late Hercynian, mainly with diorite and diorite porphyrites, where the contact zone of dikes (bodies) overlaps with the shear zone.
The Jinba gold deposit in the western section occurred in the Habahe plagiogranite rock mass and the Lower–Middle Devonian Ashele Formation. The Markakuli ductile shear zone in the western section of the Irtysh gold belt is the main orecontrolling structure. The ore types are mainly gold-bearing altered diorite vein type, gold-bearing altered rock type and goldbearing quartz vein type. Combined with the results of electron microprobe and SEM/EDS analysis (Table 2), the main metal minerals of the ore are pyrite, magnetite, galena, sphalerite and natural gold. Affected by tectonic deformation, the mylonitization of altered plagioclase granite and altered diorite in Jinba gold deposit is well developed with good ore bearing property (Fig. 2), which may provide an early source for gold mineralization. The Malkakuli ductile shear zone provides space for metallogenic hydrothermal activity and enriches gold in alteration zones and quartz veins formed by tectonic-alteration.
Sample No. Mineral As Fe S Cu Ti Ag Co Au Total quantity Chemical formula JB-ZK15-1-280A Pyrite / 60.33 38.85 / / / 0.04 / 99.22 FeS2 JB-ZK15-1-280B Pyrite / 59.77 39.34 / / 0.06 0.20 0.40 99.77 FeS2 JB-ZK15-1-280C Pyrite / 45.98 53.05 / / / 0.19 0.26 99.48 FeS2 JB-ZK15-1-280D Pyrite 0.04 46.34 53.60 / 0.09 / 0.13 / 100.20 FeS2 JB-ZK15-2-190 Ilmenite / 48.92 / / 51.01 / / / 99.93 FeTiO3 JB-ZK15-2-282A Chalcopyrite / 28.32 44.43 27.20 / / / / 99.95 CuFeS2 JB-ZK15-2-282B Chalcopyrite / 24.81 46.18 28.95 / / / / 99.94 CuFeS2 JB-ZK15-2-177 Pyrite / 49.20 50.02 / / / / 0.58 99.80 FeS2
Table 2. Main metal mineral electron probe analysis results (wt.%) of Jinba gold deposit
Figure 2. Macro and micro characteristics of surrounding rock in Jinba gold deposit. (a) Plagiogranite, strong flow structure, sample No. ZK15-2-146.6; (b) plagiogranite, sample No. ZK15-2-190; (c) cataclastic plagiogranite, mylonitization is well developed, sample No. ZK15-1-348.4; (d) altered mineralized diorite, sample No. ZK15-2-282m; (e) plagiogranite, the plagioclase twin crystal develops, and the amphibole grows after plagioclase, sample No. QJ15-12, cross-polarized light; (f) altered gabbro diorite, columnar amphibole is well developed with moderate pyritization, sample No. QJ15-7, plane-polarized light; (g) plagiogranite, scaly hornblende aggregate and quartz breccia, sample No. QJ15-11, cross-polarized light; (h) gabbro diorite, amphibole has obvious interference color, sample No. QJ15-6, cross-polarized light
The Sarbulak gold deposit is located in the Kalatongke arctic island arc of the northeastern margin of the Junggar Basin, and the north is adjacent to the Irtysh tectonic belt. The total length of the mining area is 18 km, the width is tens of meters to 300 m, and the overall strike is 310°–325°. Gold mineralization is a situation of group aggregation and segmentation mineralization (Fig. 3). The ore body is vein-like, lenticular, saclike, with branching, expansion and contraction characteristics, and the boundary with surrounding rock is clear. The ore is mainly an altered rock type composed of quartz fine mesh veins. The main metal minerals in gold ore are arsenopyrite, pyrite, and natural gold (Table 3, Fig. 4). The main gold-bearing minerals are arsenopyrite and pyrite.
Figure 3. Field features of ore bodies in Sarbulak gold deposit. (a) Altered fracture zone; (b) multistage quartz vein interpenetration
Sample No. Mineral As Fe S Cu Pb Ti Ag Mn Sb Co Ni Zn Total quantity SL15-9 Pyrite 0.11 46.14 52.97 / / / / / / 0.15 0.05 / 99.42 SL15-11A Arsenopyrite 39.19 37.02 23.07 / / / 0.06 0.06 0.05 / / 0.1 99.55 SL15-11B Arsenopyrite 37.85 37.29 23.61 / 0.15 / 0.03 / 0.04 0.03 / / 99 SL15-15 Pyrite 0.22 45.72 53.14 / / / / / 0.09 0.18 0.1 0.11 99.56 Sample No. Mineral As Fe S Cu Pb Ti Ag Te Sb Co Ni Zn Total quantity SL15-17 Chalcopyrite / 30.69 34.22 34.01 / / 0.03 / / 0.03 / / 98.98 SL15-18 Sphalerite / 5.07 34.21 2.06 / 0.04 / / / / / 58.27 99.65
Table 3. Main metal mineral electron probe analysis results (wt.%) of Sarbulak gold deposit
Figure 4. Microscopic photographs of major mineral compositions in Sarbulak gold deposit. (a) Paragenesis of chalcopyrite, sphalerite, arsenopyrite and round strawberry-like pyrite (scanning electron microscope); (b) clusters of strawberry-like pyrite and acicular arsenopyrite (reverberation); (c) pyrite grows along quartz veins (reverberation); (d) pyrite filled along fissures(reverberation); Sp. sphalerite, Apy. arsenopyrite, Ccp. chalcopyrite, Py. pyrite
The Kekesayi gold deposit is located at the junction of the Siberian plate and the Junggar plate, which belongs to the southeast extension of the Irtysh nappe tectonic compression zone (Feng and Zhang, 2009; Wang and Deng, 1998). Due to the influence of Irtysh nappe structure, strong deformation and metamorphism took place in the eastern part of the Irtysh gold belt. Gold mineralization is closely related to tectonic metamorphism and alteration of ductile shear zone. The altered mylonite and gold-bearing quartz veins are the main mineralization types. Alteration is widespread in the mining area with various types, and alteration has certain spatial zoning. Silicification and pyritization are positively correlated with gold mineralization (Wang et al., 2018b). Combined with the results of electron microprobe and SEM/EDS (Table 4), the ore minerals in the mining area are arsenopyrite, pyrite, sphalerite, chalcopyrite, calaverite, joseite, etc (Fig. 5).
Sample No. Mineral Fe S Ag Sb Co Au Zn As Mn Total quantity Chemical formula KK1608A Pyrite 46.45 52.84 / / / / 0.09 / / 99.38 FeS2 KK1608B Pyrite 46.72 53.16 0.07 / 0.04 / / 0.04 0.07 100.1 FeS2 Sample No. Mineral Fe S Ag Sb Co Au Ti Te Bi Total quantity Chemical formula KK1607 Calaverite 4.23 1.53 3.11 0.29 / 28.32 / 49.87 12.91 100.26 AuTe2 KK1603 Joseite / 5.01 0.15 0.23 / / / 34.39 59.77 99.55 Bi2TeS2 KK1606 Hessite 3.01 1.63 57.88 0.1 0.06 / 0.07 35.9 / 98.65 Ag2Te KK1601A Petzite 1.36 / 30.01 / / 26.81 / 41.83 / 100.01 AuAg3Te2 KK1601B Calaverite 7.41 / / / / 36.77 / 55.72 / 99.90 AuTe2
Table 4. Main metal mineral electron probe analysis results (wt.%) of Kekesayi gold deposit
The geological characteristics of Saidu gold deposit and Jinba gold deposit in the northwest part, Sarbulak gold deposit in the middle part and Kekesayi gold deposit in the east part of Irtysh gold belt are summarized and compared in detail (Table 5, Wang et al., 2018a, b, 2017; Wang et al., 2011; Xu et al., 2007; Zhang, 2007; Wang et al., 1999). The main differences of these deposits are as follows: for the geotectonic setting, the Saidu gold deposit and Jinba gold deposit are both the island arc tectonic area of Altai mining area, the Sarbulak gold deposit is the Kalatongke island arc belt in the north-eastern margin of the Junggar Basin, and the Kekesayi gold deposit is the Jiabaosar island arc near the side of the Junggar plate. As far as the ore-bearing strata are concerned, the gold deposits in the western part are Middle Devonian Tuokesalei Formation and Lower–Middle Devonian Ashele Formation, the gold deposit in the middle part is Lower Carboniferous Nanmingshui Formation, and the gold deposit in the eastern part is Lower Devonian Tuorangekuduke Formation. Among mineral assemblages, arsenopyrite in Sarbulak gold deposit contributes significantly to gold mineralization compared with other deposits.
Deposit Jinba Saidu Sarbulak Kekesayi Ore-bearing strata Ashele Formation of Middle Devonian Tuokesalei Formation of Middle Devonian Nanmingshui Formation of Lower Carboniferous Tuoranghekuduke Formation of Lower Devonian Host rocks Plagiogranite, diorite, auriferous quartz veins Auriferous quartz veins, altered phyllite, diorite, plagiogranite porphyry Tuffaceous siltstone, tuffaceous conglomerate and siltstone Mylonite series tectonic rocks Ore-controlling structure Early ductile shear of Maerlakuli fault and secondary brittle fracture Maerlakuli ductile shear belt and derived Tuokuzibayi secondary shear zone Northeast Sarbulak-Aktas fault zone of Moledierbasitao synclinorium Burgen ductile shear zone, Kalaxianger-Lekalatawu fault and Keziletawu fault Intrusive rock Diorite and plagiogranite porphyry veins Diorite and plagiogranite porphyry veins Diorite and gabbro, and plagioclase Diorite, diorite-porphyrite Ore-bearing formations Quartz-gold-pyrite-sulfide Quartz-sericite-tellurium minerals-sulfide-gold Quartz-pyrite-arsenopyrite-gold quartz-sericite-gold-sulfide- calcite chlorite Mineralization alteration Sericitization, chloritization, Silicification, pyritization Silicification, potassic alteration, albitization, sericitization, pyritization, chloritization Arsenopyritization, pyritization, silicification, tourmalinization, sericitization Silicification, sericitization, pyritization, chloritization, calcitization Diagenetic and metallogenic age 431±3.4 Ma 316–272 Ma 278.2–216.9 Ma 283–275 Ma According to Wang et al. (2011); Xu et al. (2007); Zhang (2007); Wang and Deng (1999).
Table 5. Geological characteristics of gold deposits in Irtysh belt
Figure 5. Metallic mineral symbiosis of Kekesayi gold deposit. (a) Coarse-grained pyrite particles (reverberation); (b) limonite formed by oxidation at the edge of rock (reverberation); (c) tellurite occurs as solid solution in pyrite (scanning electron microscope); (d) paragenesis of joseite and hessite coexist in pyrite holes (scanning electron microscope); (e) paragenesis of calaverite and pyrite (scanning electron microscope); (f) petzite occurs in pyrite cracks (scanning electron microscope); Py. pyrite, Lm. limonite, Cav. calaverite, Tel. tellurite, Hes. hessite, Ptz. petzite
These gold deposits have the characteristics of orogenic gold deposits as follows: (a) They occur near the regional Irtysh fault and are controlled by secondary shear zones, with strong regional metamorphism and tectonic deformation and metamorphism, and ductile shearing controls the occurrence of gold orebodies; (b) the ore bodies are mainly vein-like and lenticular in shape, and most of them are distributed along the direction of tectonic line in strike. There are three types of gold mineralization: altered mylonite type, quartz vein type and granite vein type; (c) ore-bearing quartz vein mylonitization has developed, with obvious recrystallization. And the deformation and metamorphism of wall rocks are strong; (d) there are alteration assemblages of medium temperature silicification-beresitization and medium and low temperature sericitization, chloritization and carbonation; (e) the emplacement of intermediate-acid granitoids (veins) not only provides heat, fluid and power for gold mineralization, but also is the main source of gold.
1.1. Tectonic-Magmatic Environment
1.2. Metallogenic Characteristics
The ore-forming fluids of many gold deposits in the Irtysh gold belt have been studied (Wang et al., 2018a, b, c; Wang et al., 2011; Xu et al., 2009; Zhang, 2006). This paper analyses the evolution of gold ore-forming fluids and the relationship with mineralization in the region based on the study of fluid inclusions and H-O-S isotopes. Synchrotron radiation X-ray fluorescence analysis was used to explain the occurrence form and migration process of gold in hydrothermal solution.
The homogenization temperature of fluid inclusions in Saidu gold deposit is 100–300 ℃, and the main stage of mineralization is mainly in 160–200 ℃ (Xu et al., 2009).
The homogenization temperature range of Jinba gold deposit in the early stage of mineralization is 262–401 ℃, and the homogenization temperature range of main metallogenic stage is 200–280 ℃. The ore-forming fluid system is a medium-high temperature, low salinity and low-density system of H2O-NaCl-CO2 (Wang et al., 2018a, 2015). The homogenization temperature range of Sarbulak gold deposit is 230–378 ℃. Its mineralization is multi-phases and multi-stages (Wang et al., 2011). The homogenization temperature range of Kekesayi gold deposit is 121–414 ℃, the main stage of mineralization is mainly in 120–150 ℃. The fluid is high temperature, low salinity and rich CO2 in the early stage. As the deformation of the shear zone increases in the middle and late stages, the fluid evolved into low temperature, low salinity and riched in H2O (Wang et al., 2018b, c, 2017b).
The ore-forming fluids of gold deposits in the Irtysh gold belt have similar evolution characteristics (Table 6): The early and middle stages are characterized by medium high temperature and CO2 rich hydrothermal. And the late stage evolved into a saline solution system with medium low temperature and low salinity. The homogenization temperature of fluid inclusions in the western gold deposit is higher than that in the eastern gold deposit. And Kekesayi gold deposit in eastern is especially strong in structural metamorphism and abundant in CO2 rich inclusions. The physicochemical conditions of mineralization are mesogenetic and mixed fluids of middle-low-temperature hydrothermal.
Deposit Petrography Characteristics of ore-forming fluid Saidu (1) Aqueous solution type (LH2O-VH2O), (2) carbon-rich type (LH2O-LCO2), (3) carbonaceous inclusion riched in N2(LCO2). Th=100–300 ℃, the main stage of mineralization is mainly in 160–200 ℃, ω(NaCl)=0.35 wt.%–9.86 wt.%, ρ=0.76–0.98 g/cm3. Hydrothermal solution is mainly derived from magmatic water. The evolution of fluid from magmatic water in early stage to atmospheric precipitation in late stage. Jinba (1) Aqueous solution type (LH2O-VH2O), (2) carbon-rich type (LH2O-LCO2), (3) carbonaceous inclusion (LCO2). Th=200–400 ℃, the main stage of mineralization is mainly in 200–280 ℃, ω(NaCl)=0.88 wt.%–13.72 wt.%, ρ=0.90–0.95 g/cm3. The evolution of fluid from magmatic water in early stage to atmospheric precipitation in late stage. Sarbulak (1) Aqueous solution type (LH2O-VH2O), (2) carbon-rich type (LH2O-LCO2), (3) carbonaceous inclusion (LCO2). Th=230–378 ℃, ω(NaCl)=0.53 wt.%–5.41 wt.%, Mineralization had multi-phases and multi-stages. The evolution of fluid from magmatic water in early stage to atmospheric precipitation in late stage. Kekesayi (1) Two phase aqueous solution type (LH2O-VH2O), (2) carbon-rich type (LH2O-LCO2), (3) single phase aqueous solution type (LH2O). Th=121–414 ℃, the main stage of mineralization is mainly in 120–150 ℃, ω(NaCl)=0.35 wt.%–10.24 wt.%, ρ=0.6–1.0 g/cm3. High temperature, low salinity and rich CO2 in the early stage. As the deformation of the shear zone increases in the middle and late stages, the fluid evolved into low temperature, low salinity rich H2O.
Table 6. Characteristics of fluid inclusions and ore-forming fluid of several gold deposits in the Irtysh belt
Sulfur isotope characteristics can be used to help solve the problem of the source of ore-forming materials.
The range of δ34S in Saidu gold deposit is 0.31‰–11.41‰ (Li et al., 2007; Zhang, 2006; Chen and Rui, 1997). The range of δ34S in Jinba gold deposit is 3.42‰–8.71‰. Pyrite sulfur isotopes values of diorite dikes and diorite ores in Jinba gold deposit are similar, with a small variation range, indicating that Jinba gold deposit has a homogeneous sulfur source (Wang et al., 2018a). The sulfur isotope of pyrite and arsenopyrite in the ore of Sarbulak gold deposit has been determined (Wang et al., 2011). The sulfur isotope of arsenopyrite measured in this study ranges from -6.1‰–1.2‰, which is close to the sulfur characteristics of meteorites, reflecting that volcanic materials in strata originate from the lower crust or upper mantle. Wang and Deng (1999) deemed that the sulfur in the Kekesayi gold deposit is originated from deep magma. Wang et al. (2006) considered that the ore-forming material was mainly from deep source (mantle source). Zeng et al. (2007) measured that the δ34S of sulfide ranged from -10.009‰–2.819‰, all of which were negative. The results showed that there was no sulfur characteristic of volcanic or magmatic origin. Sulfur may mainly come from tuffaceous siltstone in surrounding rock.
It is obvious from Fig. 6 that sulfur isotopes in quartz vein type gold deposits such as Saidu gold deposit and Jinba gold deposit are relatively enriched with heavy sulfur, which may reflect that the ore forming minerals of this type have more deep metallogenic material. The sulfur isotope values in the ore of Sarbulak gold deposit indicate that the volcanic materials in the strata originate from the lower part of the crust or the upper mantle, which provide the source of sulfur. The δ34S value of some samples in ore of mylonite type gold deposit such as Kekesayi gold deposit is similar to the δ34S value of pyrite in the surrounding rock (Wang and Deng, 1999), which reflected that there are more sulphur in surrounding rock during mineralization. It is also indicated that the process of hydrothermal migration is also the process of mineralizing hydrothermal fluid is continuously extracted from surrounding rocks. The S isotopes are relatively enriched in heavy sulfur in the western gold deposits, and it tends to become lighter in the central gold deposit, and to the eastern gold deposit gradually (Fig. 6). Compared with the source of sulfur, the source of ore forming minerals in western gold deposit is more closely related to magmatic activity, and the structural metamorphism of eastern gold deposit has greater influence on mineralization.
Hydrogen and oxygen isotope compositions of ore-forming fluids are widely used to tracing of ore-forming fluid source, fluid evolution and ore-forming process. On the diagram of δD- δ18OH2O, the δD range of magmatic water is -80‰– -48‰, and that of δ18OH2O is 6‰–9‰. The δD variation range of typical regional metamorphic water is -65‰– -20‰, and that of δ18OH2O is 5‰–25‰ (Sheppard, 1986). The isotope composition of metamorphic hydrothermal fluids varies greatly, which is restricted by the diversity of original rock composition and the wide temperature range of metamorphism. Zhu and Huang (1988) gave that the δD range of metamorphic water was -120‰– -20‰, and that of δ18OH2O was 4‰–25‰. Formulas for this conversion is 1 000ln αQ-H2O=3.306×106×T-2–2.71 (Zhang et al., 1990) Hydrogen and oxygen isotopic compositions of fluid inclusions in Saidu gold deposit, Jinba gold deposit, Sarbulak gold deposit and Kekesayi gold deposit were analysed in this study. The test results are shown in Table 7 and Fig. 7.
Location Sample No. Th (‰) δ18O (‰) δ18OH2O (‰) δDH2O (‰) Saidu gold deposit SD1201 260 11.0 2.08 -105.5 Coarse-grain pyrite quartz vein SD1203 230 11.8 1.45 -97.6 Quartz veins with molybdenite SD1207 230 12.3 1.95 -86.6 Disseminated pyrite quartz vein Jinba gold deposit JB-15-2-177 400 9.4 4.81 -78.00 Disseminated pyrite quartz vein in early metallogenic stage JB-15-2-177 400 9.7 5.11 -78.20 JB-15-2-177 400 9.9 5.31 -78.50 JB-8-3-48.5 280 10.7 1.99 -80.00 Pyrite quartz veins in main metallogenic stage JB-8-3-48.5 280 10.2 1.49 -80.50 Sarbulak gold deposit SL-15-9 310 16.9 9.9 -86.5 White quartz vein SL-15-15 310 18.4 11.4 -76.6 Coarse-grain pyrite quartz vein SL-15-17 310 15.7 8.7 -77.3 Disseminated pyrite quartz vein SL-15-18 310 16.3 9.3 -76 Disseminated pyrite quartz vein Kekesayi gold deposit KK1601B 304 12.7 5.49 -86.9 White quartz vein KK1603 304 10.7 3.49 -82.9 Pyrite quartz vein KK1606 384 11.2 6.25 -82.8 Limonite quartz vein KK1607 344 11.9 5.93 -89 Limonite quartz vein KK1608 345 10.1 4.17 -86.9 Limonite quartz vein with disseminated pyrite Data were tested from the analytical Laboratory Beijing Research Institute of Uranium Geology (ALBRIUG); δ18O (‰): δ18O of quartz
Table 7. Hydrogen and oxygen isotopic compositions of fluid inclusions
The test results and previous tests (Li et al., 2007; Zhang, 2007) in Saidu gold deposit mostly fall within the atmospheric precipitation line, and very few fall within the range of magmatic water and metamorphic water. This indicates that the metallogenic fluid of Saidu gold deposit is a mixture of magmatic water and metamorphic water. The metallogenic fluid is related to magmatic activity in the early stage and it has the participation of atmospheric precipitation in the late stage.
The sample subpoints in Jinba gold deposit are close to the range of magmatic water in the early metallogenic stage, and in the main metallogenic stage, the sample subpoints are within the range of atmospheric precipitation line. This indicates that the metallogenic hydrothermal fluid of Jinba gold deposit evolved from magmatic water in the early metallogenic stage to atmospheric precipitation in the late metallogenic stage.
The subpoints of metallogenic solution in the early stage of Sarbulak gold deposit are distributed in the range of metamorphic water and magmatic water, while in the late stage of mineralization, the subpoints shift to the direction of meteoric water line. The variation range of hydrogen and oxygen isotope composition reflects the multi-stage and multi-stage nature of mineralization. The ore-forming fluid in the superimposed hydrothermal reformation period has the characteristics of multi-sources and is a mixed product of magmatic water and metamorphic water.
Most sample subpoints of the Kekesayi gold deposit fall within the range of metamorphic water, and very few fall within the scope of atmospheric precipitation. This also reflects the metamorphism of the Kekesayi gold deposit is strong, and the metamorphic hydrothermal fluid is involved in mineralization obviously. The tectonic fluid is mainly CO2-rich metamorphic water.
The H-O isotopes of gold deposits in each section of the metallogenic belt all reflect that the ore-forming hydrothermal fluid is a mixture of magmatic water and meteoric water. It indicates that the gold deposits in the orogenic belts in the area are complex in mineralization, and their minerogenetic minerals are characterized by multiple sources.
SRXRF (synchrotron radiation X-ray flourescence) is used to determine the element types and contents in individual fluid inclusion by testing wavelength and spectral intensity of elemental X rays. As a nondestructive analysis testing technology of the physical process is not needed to open the fluid inclusions, it is known as one of the testing methods for trace elements in single fluid inclusion with important application prospects.
The experiment was carried out on the micrometer platform of Shanghai Light Source Hard raybeam line station (BLl5U). The X-ray source used in this experiment is from the hard X-ray microprobe beam line with K-B microfocus in Shanghai Synchrotron Radiation Facility (SSRF). The electron energy of the storage ring of the electron-positron collider is 3.5 GeV, the beam intensity is 260 mA, and the incident light energy is 14.04 keV. The angle between the sample and the detector is 45° when X-ray is incident on the surface of the sample. The X-ray spot size is selected to be 2 μm×2 μm, the step size is set to 2 μm, and the single pixel dot scanning time is 2 s.
In order to find out the relationship between fluid inclusions and mineralization in the metallogenic stage, SRXRF of metal elements in single fluid inclusion have been tested and analyzed. The 16 characteristic elements selected are Au, Ag, Cu, Pb, Zn, W, As, Fe, Cr, Co, Ni, Sn, Sb, Te, Bi and Mn. The experimental samples selected the ideal fluid inclusions in two gold deposits in the gold belt. The sample of Sarbulak gold deposit are gas liquid two phase fluid inclusions in bedding quartz vein parallel to the surrounding rock. The sample of Kekesayi gold deposit is CO2 rich fluid inclusion in quartz vein of metallogenic stage. The results show that (Fig. 8) the relative content of Fe, Pb, Au, As, Zn and Cu relative to the measured fluid inclusions are relatively higher than the background quartz in Sarbulak gold deposit. It is confirmed that fluid inclusions in ore forming fluids are rich in metallogenic material. The above characteristic elements of fluid inclusion No. 2 are mainly concentrated in the gas phase of fluid inclusion.
The relative content of Fe, Au, W, Mn, Zn and Cu are relatively higher (Fig. 9) which indicates the metallogenic elements are enriched in CO2 rich fluid in Kekesayi gold deposit. Vapor-liquid phase separation experiments of metal-bearing supercritical fluids (Zhang et al., 2006) prove that CO2-HCl-NaCl bearing aqueous fluids (in gas phase) may carry gold and copper and transport them from the deep part of the lithosphere to the surface. It suggests that Au and Cu-bearing NaHCO3-HCl-H2O hydrothermal fluids are separated into vapor phase and liquid phases respectively. Therefore, Au and Cu can be distributed in both gas and liquid phases simultaneously, but in most cases, the content of gold and copper in gas phase is higher than that in liquid phase. At the same time, it is found that temperature affects the content of metal in gas and liquid phase.
In recent years, a series of studies have been carried out on the solubility and existing forms of gold and copper in unsaturated hydrothermal gas phase (H2O±HCl) (Zhang et al., 2009; Rempel et al., 2006; Migdisov and Williams, 2005; Archibald et al., 2002, 2001; Migdisov et al., 1999). The results show that gold and copper can exist in the hydrothermal vapor phase with hydrates of AuCl(H2O)3-5, Cu3-4Cl3-4(H2O)6-7.6 respectively, and the hydration number can be changed with temperature and pressure. The solubility of gold and copper in hydrothermal steam is significantly increased relative to a dry system without water.