Chigou area is located in the south of Qiushan ore concentration area, on the north side of Yang Shan-Fengzhen fault (Figure 3-36), only 20km away from Shangdan suture zone in the north, and adjacent to Fengzhen-Yangshan deep fault with multi-phase activities in the south. The stratum of Chigou copper (molybdenum) mining area is a set of shallow metamorphic fine clastic rocks-carbonate rocks in Chigou Formation of Middle Devonian, with widespread keratinization and local skarnization around the rock mass. Chigou Formation is divided into three lithologic sections from bottom to top: the first lithologic section (D2ch 1) is developed with timely sandstone and silty slate; The second lithologic member (D2ch2) is developed with thin-to-medium-thick layered hornfelted timely sandstone and biotite timely amphibole. Calcareous silty slate and biotite silty slate are developed in the third lithologic member (D2ch3). The strata in the mining area strike nearly east-west, and tend to the north, with an inclination angle of 40 ~ 60. Fault structures are developed, mainly in the near east-west direction, followed by NNE and NE. Among them, F 1 and F2 faults are the main rock-controlling and ore-controlling faults, which control the zoning distribution of mineralized alteration zones and porphyry groups, while ne-trending faults control the shape of porphyry groups.
Figure 3-36 Regional Geological Map of Chigou Copper (Molybdenum) Deposit
Shuangyuangou-Tudigou-Chigou small acidic rocks invaded Chigou Formation, and seven small (porphyry) rocks (Figure 3-37) were exposed on the surface of Chigou porphyry rock mass (group), all of which were small in scale, of which 1 rock mass was large, with an area of 0.06km2, and the rest were only 0.001~ 0.06km2.. Ⅱ-ⅶ rock mass is porphyritic quartz diorite and porphyritic diorite, which belongs to intermediate-acid hypabyssal-ultrashallow facies, and is irregular in plane, with vein strike near SN (Ⅲ rock mass is presumed to be columnar porphyry rock mass); From south to north (I-ⅶ), it shows the evolution trend from acidic to moderately acidic. The formation of rock mass groups is controlled by the intersection of NWW-trending faults and Chigou normal faults (including NE-trending secondary faults), and all the rock masses intrude into the Devonian Chigou Formation, showing an intrusive or fault contact relationship with it. Copper-molybdenum mineralization is mostly developed near the internal and external contact zone between rock mass and surrounding rock.
Figure 3-37 Geological Schematic Diagram of Chigou Copper (Molybdenum) Deposit
Geochemical analysis shows that the rocks in Chigou copper mine are obviously poor in silicon (W (SiO _ 2) = 57.34% ~ 69.07%), rich in alkali (W (H2O+Na2O) = 6.66% ~ 8.75%) and high in potassium (w (H2O) = 2.92% ~ 5./kloc. Figure 3-38). The content of MnO in rock mass is low (0.03% ~ 0. 19%), and the content of Al2O3 is low (14.29% ~ 16.25%). The main components are Feot (2.33% ~ 7.29%) and MgO (0.90). Rock geochemical analysis shows that Chigou rock mass has the same evolution trend as the small rock mass in Lengshuigou, Xiaguanfang, Xiaohekou, Yuanjiagou and Yuanzijie areas, indicating that they are the evolution products of the same magma source area.
Figure 3-38 SiO _ 2-H2O Diagram of Rock Mass in Zhashui-Yangshan Ore Concentration Area
2. Geological characteristics of the deposit
(1) ore body characteristics
Chigou deposit is mainly composed of Chigou concealed molybdenum mineralization belt, 1 copper (molybdenum) mineralization belt, Fusanggou skarn copper mineralization belt and No.4 copper mineralization belt.
1) Buried Molybdenum Mineralization Zone: Molybdenum Mineralization Zone is located in the east of the mining area, starting from syenite porphyrite (Line 9) in the east and reaching Chigoukou in the west. The surface mineralization is weak and the deep mineralization is enhanced. Molybdenum mineralization occurs in interlayer fracture zones and fractures in the form of veinlets and network veins.
2) 1 Copper (Molybdenum) Mineralization Zone: This mineralization zone is located on the south side of adamellite and is in contact with surrounding rock. At present, the controlled mineralization zone is about 65 meters long and 5.7 meters thick, with copper grade of 0. 1 1.28% and the highest copper grade of 0.33%. The analysis of ground and borehole shows that the occurrence of adamellite is complex, irregular in plane, deep and steep in north, and generally shows east-west trend; Molybdenum-bearing copper-mineralized rock mass, the ore body is buried deeply, molybdenite is mainly developed in the deep part of the contact zone in the rock mass, and chalcopyrite is distributed in the deep part of the surrounding rock of epidote, chloritization and amphibolite in the outer contact zone.
3) Fusanggou skarn type copper mineralization belt: This mineralization belt consists of I, II and III ore bodies, which are located near Line 3, 14 and Line 7 ~ 15 in the north of the mining area respectively. Among them, 1 ore body controls a skarn-type copper mineralization body with a width of 0.9 m and a length of 50 m, with a copper grade of 2.34%, and the ore body is generally layered.
4) copper mineralization zone Ⅳ: This mineralization zone is distributed between lines 13 ~ 17, and quartz diorite Ⅳ is a concealed ore body in the internal and external contact zone. Six copper ore bodies delineated by 0.2% cut-off grade are basically distributed in quartz diorite, and their shapes are controlled by concealed rock bodies. It is speculated that the deep part of the rock mass is connected into a whole, and chalcopyrite is distributed near the upper and lower boundaries of the rock mass in the form of veinlets.
(2) Mineralization and alteration types
According to the field geological observation, indoor identification and comprehensive research, Chigou rock mass and surrounding rock are strongly altered, and the main alteration types are hornblende, potassium silicate, pyrite sericitization and Pan Qingyan (Figure 3-39), followed by kaolin and skarnization. Among them, keratinization and skarnization are distributed in the middle and upper strata of gullies, and the rock-controlling faults are planar banded; Potassium silicate, sericitization, kaolinization and peridotite are mainly distributed in the rock mass or near the outer contact zone, which is closely related to copper (molybdenum) mineralization.
The ore structure is dominated by metasomatic texture filling, followed by solid-melt separation structure; Ore structures are mainly disseminated structures and veinlets disseminated structures, followed by breccia structures and colloid structures. Metal minerals are mainly pyrite, chalcopyrite and a small amount of molybdenite.
3. Petrographic characteristics of Chigou rock mass
The surface exposed area of Chigou rock mass is small, mostly irregular strands and dikes, which are cut into several sections by surrounding rocks. Through geological mapping, it shows that the surrounding rocks have developed large-scale alteration, including skarnization and amphibolite, amphibolite basically develops outward around the rock mass, skarnization is mainly located in the north side, including diopside. Where there is rock mass, obvious alteration will occur. Yuanjiagou, Xiaohekou, Yuanzi Street and Shuangyuangou are characterized by ring shape, and the alteration in other areas is characterized by east-west direction, indicating that there are huge bedrock in the deep. The high-precision magnetic anomaly in Chigou mining area shows that the intrusion direction of rock mass is from Baishagou rock mass to Chigou rock mass (class ⅳ rock mass). Therefore, this area has good prospecting geological conditions. In order to determine the petrographic characteristics of deep rock branches and their differences from surface rock masses, from 2008 to 2009, based on a large number of geological mapping, geochemical anomaly anatomy and high-precision magnetic scanning of the surface, a detailed study on the microscopic characteristics of petrography was carried out.
Chigou Ⅰ rock mass is a small rock mass with east-west distribution, with three branches exposed on the surface, with a length of 80 ~ 434m, a width of/kloc-0 ~ 1 60m and an area of about 0.06km21No.rock mass has obvious porphyritic structure. Porphyries include potash feldspar (Kfs), plagioclase (Pl), biotite (Bi) and amphibole (Hr). The matrix is fine, mainly composed of syenite, potash feldspar and plagioclase (Figure 3-40), and it is adamellite.
Rock body Ⅱ is a SN- strike dike, with a length of 278m, a width of 22 ~ 76m and an area of about 0.02km2. The rock is anisotropic and mainly composed of biotite (5%), amphibole (15%), plagioclase (40%), potash feldspar (20%) and syenite (5.
There are three east-west branches exposed on the surface of No.3 rock mass, which are 32 ~ 70m long and 2 ~ 40m wide, with an area of about 0.00 1km2. The rocks are porphyritic, and the porphyritic crystals are mainly composed of potash feldspar, quartz and biotite (Figure 3-40). The biotite is transformed into chlorite (Chl) and acicular rutile (Ti), which belongs to diorite porphyrite.
Rock mass Ⅳ is irregularly branched, with a length of 32 ~ 90m, a width of 26 ~ 70m and an area of about 0.006km2 The rock is porphyritic, mainly composed of potash feldspar, syenite, plagioclase and biotite (Figure 3-40). The biotite is eroded into tapestry, with authigenic pyrite and abnormal chalcopyrite in the middle and porphyritic quartz-bearing diorite.
Rock mass ⅴ is large in scale, with SN- strike vein along its long axis, 450m long, 20 ~124 m wide and an area of about 0.02km2 The rock is of anisotropic structure, mainly composed of syenite, plagioclase and amphibole, and most of biotite is changed into chlorite, which is quartz-bearing diorite.
Figure 3-39 Characteristics of Main Mineralization Alteration Types in Chigou Copper Mine Area
ⅵ and ⅶ rock masses are very small in scale and are dike-like. Rock mass ⅵ is124m long and 48m wide. The rocks are porphyritic, mainly composed of plagioclase, potash feldspar and amphibole. Hornblende is diorite porphyrite with a small amount of chloritization, and the rock mass is characterized by the development of a large number of authigenic magnetite (Figure 3-40).
Through detailed microscopic observation of different rocks and branches closely related to mineralization in the deep, it is considered that 1 rock mass has typical porphyritic structure, followed by No.3 rock mass, and the porphyritic structure of No.2 and No.4 rock mass is not obvious. The deep branches related to mineralization are similar to those of No.2 and No.4 rock bodies, and the potash feldspar granite veins seen in ZK 170 1 are obviously different from those in 1-VI rock body and 13 borehole.
Figure 3-40 Microscopic photos of rocks in Yangshan Chigou area.
Fig. 3-4 1 chigou ⅰ-ⅵ zircon U-Pb isotopic age.
4. Age of diagenesis and mineralization
On the basis of detailed field observation and microscopic observation, I-ⅵ rocks were selected for MC-LA-ICP-MS zircon U-Pb dating. Re-Os isotopic dating of molybdenite was carried out. Systematic dating studies show that the crystallization age of the first rock mass is (146 1) Ma, that of the second rock mass is (148 1) Ma, and that of the third rock mass is (141/) Ma. No age. Rock mass ⅴ is (140 1) Ma, and rock mass Ⅱ is. ⅵ rock mass is (146 1) Ma. Xiaochigou pluton was formed in 140 ~ 148 Ma (Figure 3-4 1 molybdenite Re-Os dating shows that the mineralization age is 148 Ma (Figure 3-42), which is consistent with the formation age of pluton, indicating that the intrusion of pluton is related to mineralization in time, space and origin.
To sum up, Chigou copper mine belongs to porphyry copper mine.
Figure 3-42 Re-Osmium Isotopic Isochronous Age of Molybdenite in Chigou Copper Mine