I. intrusive rocks
The surface of Fujiawu granodiorite porphyry is trapezoidal, 650m long in NE direction and 300m wide in NW direction, with an area of 0.2km2 (Figure 2-34). The rock mass is inserted in the direction of NW3 10, and the lateral dip angle is about 40. The downward trend of rock mass has obviously increased, reaching the elevation of -—200m, while the horizontal cross-sectional area has increased to 0.8km2, and the long axis direction of rock mass profile has also turned from NE to NW. The boundary of rock mass is straight and there are few lateral branches.
The main rock mass and surrounding rock are in intrusive contact, and the contact boundary is clear, showing a sudden change relationship. There are several meters wide contact angle breccia in some areas, and the breccia is mainly composed of surrounding rocks.
The main rock mass causes a certain degree of contact metamorphism to the shallow metamorphic surrounding rock, and the metamorphic degree of the footwall is usually higher than that of the footwall. According to the metamorphic degree, it can be divided into two zones, the inner layer is hornfel zone and the outer layer is porphyry phyllite zone.
Figure 2-34 Geological Map of Fujiawu Copper Deposit
1-foreshock and the third lithologic member of Jiudu Formation; 2— The second lithologic member of Jiudu Formation of Pre-Sinian system; 3— The first lithologic member of Jiudu Formation of Pre-Sinian system; 4- chlorite (epidote)-hydromica phyllite (metamorphic tuff); 5- chlorite (epidote)-hydromica phyllite (metamorphic tuff); 6- timely muscovite phyllite (metamorphic tuff); 7-6 and 7 are not scored; 8— timely muscovite granodiorite; 9- chlorite (epidote)-hydromica granodiorite porphyry; 10- chlorite (epidote)-hydromica-potash feldspar granodiorite porphyry; 1 1- diorite porphyrite; 12-metamorphic diabase; 13— gabbro-pyroxenite; 14-fine felsic; 15- contact angle conglomerate; 16- geological boundary; 17-flaky occurrence; 18- alteration zone boundary; 19- anticline and its tendency; 20—— Syncline and its tendency; 2 1- failure; 22- pyrite
According to geophysical data, it is speculated that Fujiawu, Tongchang and Zhushahong composite porphyries converge into a large concealed rock mass at the depth of 1800m, because Tongchang rock mass has been inserted into the bottom of Zhushahong rock mass more than 800 meters underground.
Fujiawu granodiorite porphyry minerals, according to the quantitative statistics under the microscope (area%): corresponding time 18 ~ 23, with an average of 20.5; Plagioclase (mainly feldspar) ranges from 43 to 55, with an average of 48.5; Potash feldspar ranges from 13 to 18, with an average of15.5; Amphibole is 7 ~ 10, with an average of 8.3; The biotite ranges from 3 to 7, with an average of 4.8. The composition of accessory minerals in Fujiawu main rock mass is (10-6): magnetite ranges from 847 to 9674, with an average of 5261; The apatite is 130 ~ 52 1, with an average of 351; 0.3 ~ 289 sphene, average145; Zircon ranges from 133 to 255, with an average of 194. The chemical composition of rocks is listed in Table 2-23, and compared with similar rocks in China and the world. Table 2-24 gives the CIPW value of Fujiawu porphyry. This paper summarizes the main oxide characteristics of porphyry bodies.
Table 2-23 Chemical Composition and Comparison of Fujiawu Porphyry Table 2-23 Petrochemical Composition of Fujiawu Porphyry
Table 2-24 CIPW value of Fujiawu porphyry (WB/%)
The content of SiO2 _ 2 is between 64.27% and 66.13%, with an average of 65.05%, which is higher than the average of granodiorite in China and close to the average of granodiorite in the world. Al2O3 changes from 15.34% to 16.67%, with an average value of 15.74%, which is lower than that of similar rocks in China and the world. Fe2O3+FeO ranges from 3.55% to 4.98%, with an average of 4.20%, which is also lower than the average quality of similar rocks in China and the world. MgO changes from 65438 0.36% to 2.90%, with an average value of 65438 0.69%, which is relatively lower than the average value of granodiorite in China and the world. CaO is 2.89% ~ 4.66%, with an average of 3.57%, which is slightly lower than the average of granodiorite in China and the world. Na2O+K2O is 6.37% ~ 7.65%, with an average of 7.08%, which is higher than the average of granodiorite in China and the world. Especially the content of K2O is high, which constitutes the main characteristics of porphyry petrology.
The K-Ar isotopic age of the K-feldspar vein in Fujiawu granodiorite porphyry is 157Ma, and that of the K-Ar isotopic age of the K-feldspar vein in the surrounding rock of the mining area is 152Ma.
Two. geology of ore deposits
Orebody: See Table 2-25 and Figure 2-35 for the morphological occurrence characteristics of Fujiawu orebody. The central axis of copper-bearing porphyry tends to NW with an inclination of 40 ~ 20. The ore body at the top of the rock mass has been denuded, and the ore body in the contact zone around the upper part of the rock factory is well preserved, so the ore body is a hollow cylinder inclined to the northwest, and the horizontal section is annular. The enrichment center of copper-molybdenum mineralization is roughly consistent with the structural faults and fault-intensive zones in the internal and external contact zones. The intensity of copper mineralization is roughly symmetrical with the contact zone, and a single copper body is distributed in the deep part of the deposit, especially in most contact zones of porphyry bodies. The mineralization continuity in the main ore body is very good, and there are few inclusions.
Table 2-25 Morphological Characteristics of Ore Bodies in Fujiawu Copper Deposit
Figure 2-35 Section and Plan of Fujiawu Ore Body.
1-Cu (0.4%) ore body; 2- granodiorite porphyry
Ore minerals: the ore minerals of Fujiawu are basically similar to those of copper factory. Please refer to the description in the section of Copper Factory, which will not be repeated in this section. The main metal sulfides in the ore are pyrite 3.30%, chalcopyrite 1.39% and chalcocite 0.053%. Pyrite: chalcopyrite: molybdenite is 2.4 ∶ 1 ∶ 0.038. Chalcopyrite accounts for more than 90% of copper minerals, followed by bornite, tetrahedrite and chalcocite.
Ore structure: basically similar to copper factory, so I won't repeat this part.
Ore reserves, grade and chemical composition: Fujiawu deposit has a copper reserve of 2,572,600 tons and a copper grade of 0.501%; Molybdenum reserves 167845t, molybdenum grade 0.033%. Associated gold content is 0.055g/ton, cobalt content is 0.0024%, and selenium content is 0.00 15%. Primary ore is mainly primary copper sulfide, which usually accounts for about 90% of copper reserves, secondary copper sulfide accounts for 5% ~ 10%, and copper oxide and copper sulfate account for less than 5%. Besides copper, beneficial elements is also related to copper, gold, silver, rhenium, nickel, cobalt, sulfur, selenium, tellurium, titanium, potassium and platinum group elements. The harmful impurity elements in the ore are mainly arsenic, zinc and magnesium. The average arsenic content is 0.007%, zinc content is usually less than 0.0 1%, and magnesium oxide is generally less than 2%, which meets the requirements of current industrial indicators.
Third, the surrounding rock alteration.
The wall rock alteration of Fujiawu deposit is basically similar to that of copper factory, but the altered mineral content is different. Therefore, table 2-26 can be compared with the table of copper factory.
Table 2-26 Comparison of mineral composition changes in different alteration zones of Fujiawu porphyry copper (molybdenum) deposit Table 2-26 Rock mineral content in alteration zone of Fujiawu porphyry copper (molybdenum) deposit
Note: * Calculated by × 10-6; Other contents are in%.
The alteration process of Fujiawu deposit is described as follows:
Potassium silicate alteration: mainly occurs in the form of isochron-potash feldspar veins. The K-Ar isotopic age of potassium feldspar veins is 152 ~ 157 Ma, which is far from that of granodiorite porphyry, indicating that the potassium silicate alteration was formed together with the late porphyry magma and is an independent fluid phase of the late porphyry magma and surrounding rocks. Potassium silicate alteration products are mainly potassium feldspar, followed by biotite, anhydrite and albite.
Chrono-sericite-chloritization: K-Ar isotopic age of altered sericite is 1 12Ma, at which time the crystallization of granodiorite porphyry has been separated for a long time. During this period, the tectonic movement caused a dense fracture zone in the upper contact zone of porphyry, but the volatile fluid rich in alkali was continuously discharged from the lower magma chamber, which led to the convective circulation of Tianshui, forming a mixed fluid phase, and finally caused rocks (porphyry, phyllite, etc.) around the contact zone. ) mainly through hydrolysis. Amphibole and biotite decompose into sericite, and iron and hydrogen sulfide combine to form a large number of pyrite, thus forming the Yanshi-sericite-chloritization belt.
Carbonate-sulfation: In the later period of consolidation in magma chamber, there is still some residual heat, which drives the convective circulation of Tianshui, and the physical and chemical conditions of thermal fluid slowly restore the state of the crust surface. The alteration formed in this stage is mainly calcite, dolomite, ankerite and gypsum, followed by manganese siderite, fluorite, barite and zeolite.
Fourth, stable isotopes.
Sulfur Isotope: See Table 2-27 for the sulfur isotope composition of sulfide in Fujiawu and its vicinity, while the sulfur isotope δ34S of sulfate varies from -0.6‰~ 1.0‰, with an average value of 0.48 ‰; The sulfur isotope δ34S value of sulfide in sulfur ore is 0.5 ‰ ~ 1.3 ‰, with an average value of 0.97‰. This shows that the sulfur isotopic composition of sulfide in Fujiawu and sulfur mine is uniform, which is basically close to meteorite sulfur. The sulfur isotope δ34S of Fujiawu sulfate ranges from 6.1‰ to 7.6 ‰, with an average value of 7. 1‰ (Table 2-28). This shows that the sulfur isotope composition of sulfate is very different from that of seawater. The sulfur source of these sulfates is not from seawater sulfate, but mainly from deep sulfur source.
Table 2-27 Sulfur Isotopic Composition of Sulfide in Fujiawu Copper Deposit
Table 2-28 Sulfate and Sulfur Isotope Composition of Fujiawu Copper Deposit Table 2-28 Sulfate and Sulfur Isotope Composition of Fujiawu Copper Deposit
Table 2-29 Oxygen Isotope Composition of Fujiawu Copper Deposit
Table 2-30 Analysis Results of Timely Fluid Inclusions in Fujiawu Copper Deposit Table 2-30 Composition of Fluid Inclusions in Shi Ying of Fujiawu Copper Deposit
Note: According to Institute of Geology of Ministry of Metallurgical Industry 1984.
Table 2-3 1 Analysis Results of Elements and Components Related to Mineralization in Fluid Inclusions of Fujiawu Copper Deposit Table 2-3 1 Elements and Components Related to Mineralization in Fluid Inclusions of Shi Ying in Fujiawu Copper Deposit
Note: According to Institute of Geology of Ministry of Metallurgical Industry 1984.
Oxygen isotope: The oxygen isotope composition of Fujiawu is shown in Table 2-29. Table 2-29 shows the evolution trend of the reaction between porphyry and mixed fluid, and the mixed fluid is composed of granodiorite magma oxygen gradually evolving into Tianshui oxygen isotope.
Verb (abbreviation of verb) fluid inclusion
The fluid inclusions in Fujiawu deposit include gas inclusions, multiphase inclusions, gas-liquid inclusions and CO2-containing inclusions, and the gas-liquid ratio usually varies from 65,438+00% to 40%, with a few reaching 50% to 80%. The daughter minerals of multiphase inclusions mainly include halite, sylvite and anhydrite. The volume content of CO2 in CO2-bearing inclusions ranges from 10% to 15%. The diameter of most fluid inclusions is between 5- 10μm, and a few are larger than 10 μm. The homogeneous temperature range of most fluid inclusions is 140 ~ 360℃, and a few reach 540 ~ 680℃. The analysis and test results of timely sulfide inclusions are shown in Table 2-30, and the elements and components related to liquid phase mineralization are shown in Table 2-3 1.
The ratio of main ions in fluid inclusions is: [K+]/[Na+] varies from 0.144 to 5.245, with an average of1.557; [Ca2+]/[Mg2+] ranged from 0.269 to 6.4 16, with an average of 2.099; The range of [Cl-]/[F-] is 20.433 ~ 246.077, with an average of 96.560. In addition, fluid inclusions contain different ore-forming elements, including copper ranging from trace to 1430× 10-6 and lead ranging from trace to 80× 10-6. Zinc ranges from trace to 1 150× 10-6, and molybdenum ranges from trace to 220× 10-6.
Discussion on the genesis of intransitive verb deposit
Fujiawu copper mine is located on the uplift side of the junction zone between Tailong and Qiantang Depression in the south of the Yangtze River. The magmatic emplacement, hydrothermal alteration and mineralization of Yanshanian epithermal granodiorite porphyry were controlled by the deep fault zone in northeastern Jiangxi. During the Yanshan period, andesite magma erupted in Wuyuan-Dexing-Yiyang-Dongxiang area. The emplacement of hypabyssal-ultrahypabyssal porphyry rock mass is an organic part of the intermediate-acid volcanic eruption, which is likely to belong to the pipeline facies of this volcanic eruption. Mesoproterozoic Shuangqiaoshan Group is regarded as a source bed by some geologists because it is rich in ore-forming metals. The ore body is located at the top of Yanshanian calc-alkaline composite granodiorite porphyry and surrounding rock, and is considered as the main contributor to mineralization. The main geological characteristics of Fujiawu deposit, such as hydrothermal alteration and mineralization, can be compared with typical porphyry deposits, so it is classified as porphyry copper (molybdenum) deposit.