A number of important deposits with distinctive characteristics have been formed in this area.
1. Geological evolution and ore-controlling geological structural conditions
There are Sinian, Ordovician shallow metamorphic flysch formation and Devonian-Middle Triassic stable sedimentary caprocks in this area. Jurassic-Cretaceous volcanic and intrusive activities were strong.
1. Geological evolution
Yongmei sag has undergone several stages of evolution, such as basement formation, basin formation and development, basin end and transformation. The oldest stratum exposed in this area is Taoxi Formation in Wuping area at the junction of Fujian and Jiangxi. Its original rock is pyroclastic sedimentary rock mixed with volcanic rock, and its metamorphic degree belongs to low amphibolite facies. The Sm-Nd isochron age of metamorphic intermediate-basic volcanic rocks is (1825129) Ma. Together with Proterozoic granitoids, it constitutes the pre-Sinian metamorphic basement in the depression area, which is the first basement. Transgression occurred in the Sinian belt until Ordovician, forming offshore facies flysch, which was slightly metamorphic and folded due to Caledonian movement, and became the second set of metamorphic basement in this area. Silurian began to rise in this area.
The middle and late Devonian gradually subsided (earlier in Guangdong, in the middle Devonian), and the basin began to form. In the Early Carboniferous, there was Ansha Formation and then Woodland Formation, both of which belonged to continental clastic rock formation, representing the early face of the basin. In the Middle Carboniferous, with the deepening of the depression, transgression began to form a basin, which extended to the Early Permian, forming a set of sedimentary strata of fine clastic rocks, limestone and siliceous rocks in shallow sea. During the middle Carboniferous Weining period, there were at least two depression centers in the basin. Once on the Longyan-Dehua line, the center is located in the Makeng area of Longyan. Due to the thinning of the crust and the upwelling of the mantle, volcanic rocks such as basalt (andesite) overflow in the Jingshe Formation. The other center is located in Yushui area of Meizhou, where the submarine tension before the sedimentation of Hutian Group caused volcanic activity and jet heat flow activity. Jingshe Formation and Hutian Group are a set of very special and important metallogenic strata, which will be further elaborated below. By the end of Permian, due to the oscillation of the earth's crust, a set of coal-bearing strata deposits alternating between land and sea was formed, and amphibole-diorite, granodiorite and adamellite invaded at the same time. In the early Triassic, relatively stable marine sediments were restored, and the seabed cracked again, which led to a large area of heat flow increase, which led to amphibolite and thermal metamorphism in the sedimentary strata of Xikou Formation.
Influenced by Indosinian movement, the Middle Triassic began to uplift, once regressed into land, and some intermediate-acid granites invaded. However, it began to subside in the late Triassic and lasted until the early Jurassic. Early Jurassic began to gradually retreat to the southwest. Finally, there are residual basins only in the southwest of the basin, from Yongding to Meizhou. Influenced by the early Yanshanian movement, many tensile fractures appeared in the Late Triassic-Early Jurassic basin. Therefore, andesite volcanic rocks erupted in the strata of Wenbinshan Formation in Late Triassic. In the early Jurassic Fankeng Formation, however, there was a basic-acid bimodal volcanic eruption (at that time, the upper mantle of the source region reflected by basalt was equivalent to metasomatic type), and there were corresponding intrusions, including intermediate-acid intrusions such as pyroxene diorite and granodiorite, and acid intrusions such as adamellite and potash granite. The continental volcanic activity began in the Middle Jurassic, and finally ended the development period of the basin.
The late Jurassic basin entered the transition period, and many places in the area were covered by continental volcanic rocks and invaded by various intermediate-acid granites. In the early Cretaceous, it developed into a fault block structure and formed some deep fault zones (Shanghang-Xiao Yun fault). Various superimposed volcanic basins were formed along the fault zone, accompanied by the intrusion of subvolcanic rocks and porphyries, and the intrusion of various rock masses and strains in the late Yanshan period, including intermediate-acid intrusive rocks related to mineralization. Previously, under the influence of Indosinian movement and Yanshan movement, the sedimentary strata in the basin formed folds and faults, resulting in a series of nappe-detachment structures, which often became favorable structures for ore control.
2. Analysis of ore-controlling structure
Ore-controlling structures include basement structure and caprock structure.
At present, little is known about the structure of the first basement (Taoxi Formation). Recently, the Fujian Provincial Coordination Group suggested that there may be a nuclear complex structure, and the structure of the second basement (Sinian-Ordovician) is a series of NE-trending folds and shear zones formed by Caledonian orogeny. The NE-trending structure formed secondary uplift and depression, which controlled the paleogeographic environment of transgression deposits in the Variscan period, such as carbonate deposits in the Laohudong Formation along the Jiangle-Wuping line, which were obviously distributed along the NE-trending secondary depression. On the south side are Hufang-Yongding Uplift and Datian-Longyan Depression. These depressions and uplifts of the basement have formed Mingxi-Wuping composite anticline, Hufang-Yongding composite anticline and Datian-Longyan composite anticline in the caprock. The core of compound syncline is generally composed of Carboniferous-Permian carbonate rocks or coal measures strata. The upper Devonian and lower Carboniferous clastic rocks are exposed on both wings. The core of the compound anticline consists of Lower Paleozoic and Sinian, or was invaded by Variscan-Indosinian granite.
There are large faults in the caprock structure in NE, NEE, NW and NS directions, especially the fault groups in NE and NW directions (Figure 4- 15). The NE Zhenghe-Dabu fault, which runs through the eastern part of this area, is composed of a series of faults with steep dip in the southeast, which basically controls the distribution of Paleozoic sediments and late Jurassic volcanic eruption zones, and there are large-scale intrusions of Hercynian-Indosinian and early Yanshanian granites, and the late Yanshanian granite porphyry strains related to mineralization are also distributed along this zone. In addition, there is the NE-trending Guangze-Wuping fault.
The NW-trending Shanghang-Xiao Yun deep fault was formed later and only developed in the Early Cretaceous. The surface is composed of several large faults striking northeast, which obviously controls the distribution of late Mesozoic sedimentary-volcanic eruption and early Yanshanian granite, and also controls the distribution of small rock bodies related to mineralization in late Yanshanian. The Moho depth map shows that it is a NW-trending change zone, and the Yong 'an-Jinjiang fault is parallel to it.
This area has experienced multi-stage and multi-cycle orogeny: each cycle has formed some nappe detachment structures, most of which were incomplete before Mesozoic, but the Indosinian nappe structure in Yongmei Depression is still clear and can be divided into two NE-trending belts, namely Mingxi-Shanghang nappe structure belt and Nanping-Longyan nappe structure belt. They all move from northwest to southeast, tend to the northwest, and the dip angle is relatively slow. This led to the overlapping of Sinian-Cambrian, Upper Paleozoic and Indosinian granites. During the Yanshanian period, both belts showed signs of superimposed transformation. The nappe structure and decollement structure not only control the deposit, but also cause the loss or repetition of the ore bed, which must be paid attention to when prospecting.
3. Magmatic rocks
Volcanic rocks in this area include small volcanic sedimentary clastic rocks formed in Sinian-Ordovician, Carboniferous submarine basic-neutral lava and pyroclastic rocks (socio-economic formation), late Triassic intermediate-acid volcanic rocks (Wenbinshan formation), early Jurassic marine basic-neutral lava and late Jurassic-early Cretaceous continental volcanic rocks. The earliest intrusive rocks in this area are Caledonian granites, but Variscan-Indosinian granites and early and middle Yanshanian granites are the most developed, and late Yanshanian granites are scattered, but they belong to important ore-forming source rocks.
The Caledonian is dominated by intrusive rocks (383 ~ 428 Ma), mainly distributed between Guangze-Wuping and Zhenghe-Dabu faults. It is gneiss biotite adamellite-gneiss biotite granite. Its ISr value is 0.7082 ~ 0.7 168, and εNd(t) value is -4 ~- 18, which belongs to crustal remelting granite.
Fig. 4- 15 division map of metallogenic belt in Yongmei sag.
● Large-super-large deposits, small and medium-sized deposits and occurrences.
Ⅱ- 1. Datian-Meizhou metallogenic belt, Ⅱ-1-Datian ore concentration area, Datian Longfengchang lead-zinc mine, Datian Jianai lead-zinc mine and Dianguanzhan copper mine, Datian Longshan Qi lead-zinc mine and Datian Shangcai lead-zinc mine; ⅱ- 1-2- Longyan ore concentration area, (12) Longyan makeng iron mine; Ⅱ-1-3—Meizhou ore concentration area, (14) Meizhou Songxi silver-antimony mine and Meizhou Yushui copper mine Ⅱ-2. Shanghang-Yongding metallogenic belt, ⅱ-2-1-Zijinshan ore field ore concentration area, (1 1.
The intrusive rocks from Variscan to Indosinian (240 ~ 390 Ma) are mainly distributed in the axis of compound anticline in Yongmei depression zone or intruded along faults. It belongs to the product of rifting and spreading period, mainly adamellite, followed by granite and granodiorite, and the ISr value is greater than 0.709 (0.7096 ~ 0.7438+08). The INd value is less than 0.5122 (0.5169 ~ 0.51202), and it is mainly remelted granite. Carboniferous high-titanium basalt-basaltic andesite, with ISr value of 0.7076 ~ 0.7097, belongs to mantle source area, and Longyan Makeng (Dehua Yangshan) iron mine is related to it.
The magmatic rocks in the late Triassic-early Jurassic extensional fault depression area (208 ~ 184 Ma) are composed of high-titanium bimodal andesite basalt (diorite)-rhyolite (granite), with low strontium and high neodymium isotope initial ratio. Among them, the ISr value of early Jurassic andesite basalt is 0.7045, εNd(t) value is-1. 1, the ISr value of diorite-monzonite is 0.704 1 ~ 0.7043, and εNd(t) value is+3.02 ~+. Rhyolite is 0.7065, mainly distributed in Longyan, Yongding and Meizhou. There are subvolcanic porphyry-hydrothermal tin, copper and molybdenum deposits in the Yaozi area of Shangxiahu, south Yongding.
In the middle and late Jurassic (166 ~ 138 Ma), southwest Fujian was composed of biotite adamellite, granite and rhyolite, with ISr value of 0.707 1 ~ 0.7 165438 and εNd(t) value of-7.468.
The Cretaceous continental spreading rift period (136 ~ 90 Ma) was distributed along the Shanghang-Xiao Yun fault zone. Granodiorite-granite series and bimodal combination of trachyte-trachyte and rhyolite have ISr values of 0.7066 ~ 0.7 106 and εNd(t) of -2.3 ~-7.9, which are mixed sources of crust and mantle (syntectic remelting type) and are related to porphyry-volcanic hydrothermal copper deposits and rhyolite.
4. Deep structural characteristics
The deep geological data obtained by the following geophysical methods mainly reflect the characteristics since Cretaceous. Yongmei sag is generally located in the middle mantle depression zone between the slow mantle uplift zone in northwest Fujian and the steep mantle slope zone in east Fujian. It crosses Zijin-Chaoanmo uplift belt in the south and extends in the direction of NEE. The mantle depression belt in central Fujian is generally NE-NE, and the Moho depth is 32 ~ 36 km. The Moho surface in Hua 'an area is as deep as 36 kilometers, which is called Hua 'an Mantle Depression.
The western part of this area crosses the mantle uplift belt in the northwest of Fujian, showing a northeast trend. The buried depth of Mohs surface is 30.5 ~ 32km, and there is mantle uplift in Shunchang and Ninghua, with the buried depth of 30.5km and 3 1km respectively.
Quanzhou-Heishui section crosses Datian, Yong 'an and other places in this area. The comprehensive study shows that there is obvious heterogeneity between the crust and the upper mantle, and there are layered and truncated cone-shaped low-speed bodies in the middle and lower crust with a depth of 12 ~ 25 km. The thickness of lithosphere in this area is in the transition zone from west (Shicheng 1 10km) to east (Quanzhou 50 ~ 60 km).
The obvious heterogeneity of the upper crust and upper mantle in horizontal and vertical directions in this area is the source of tectonic-magmatic-mineralization in this area. In particular, the low-velocity bodies commonly existing in the middle and lower crust may be related to basalts of different times in the study area, such as C 1, J 1, K 1, K2, E, N, etc. It is speculated that they are the products of intraplate hot spots caused by the instability of mantle heat flow column-mantle boundary layer. Therefore, the long-term evolution of mantle heat flow column and the effect of multi-stage diapir upwelling on the crust are the deep-seated controlling factors for the formation of large-scale deposits in Yongmei ore concentration area.
Two. Regional mineralization, metallogenic series and metallogenic types
The mineralization in this area is closely related to the geological evolution of this area and the related major geological and structural events. The main regional mineralization includes: porphyry-subvolcanic, marine deposit, submarine jet and magmatic intrusion contact metasomatism. The mineralization, metallogenic series and metallogenic types in this area are shown in Table 4-9.
Table 4-9 Overview of Mineralization, Metallogenic Series and Metallogenic Types in Yongmei Depression
① Yong 'an Li Fang barite deposit was formed by Ordovician marine deposits, and it is not described because it does not belong to the scope of this special study.
In addition, there is iron mineralization related to intermediate-acid continental volcanism in Late Triassic in Xiaxikeng, Anxi, and tin, niobium and tantalum mineralization related to early Jurassic subvolcanic rocks in Upper and Lower Yongding Lake.
Three. Description of each metallogenic belt
Fig. 4- 16 Structural Schematic Diagram of Weining Basin in Southwest Fujian, Yongmei Depression
According to the metallogenic series, this area is only divided into two metallogenic belts: one is the Pb-Zn-Ag-Cu metallogenic belt of Hualixi in Datian-Meizhou and Indosinian marine basin, which is further divided into three metallogenic units according to the distribution of deposits, namely Datian Pb-Zn-Ag-Cu concentrated area, Liancheng-Yongding Pb-Zn-Ag-Cu concentrated area and Meizhou Cu-Pb-Zn-Ag (Sb) metallogenic area; Another metallogenic belt is the gold-copper metallogenic belt in Shanghang Yanshan superimposed volcanic basin (in fact, it is the Zijinshan ore field, which is composed of various deposits (points) in the ore field) (Figure 4- 15). It should be pointed out that the existing data show that there was a rift zone in the Weining period of Carboniferous in southwest Fujian, and the known distribution locations are Lufeng in Shanghang, Dachi in Longyan, Yongdingchang, Makeng in Longyan and Yangshan in Dehua. The connection line is a NE-oriented zone, which is roughly parallel to the Nanping-Ninghua rift in the north (Figure 4-65438+), and the basalt activity in Makeng area is the strongest. According to the exploration data of iron ore area, there are at least three layers of basalt from carbonate rock, and the vast majority of silica content is between 45% and 50%. Plagioclase brand AN43 ~ 74 belongs to China-Labrador rock and basalt. Basalt is the direct roof of main iron ore bodies or interbedded with iron ore beds. There are many jasper lumps in the iron ore body, and the siliceous iron layer at the bottom may be the product of volcanic hot springs. The maximum thickness of the stratum passing through the She Formation here can also reach 176m ... indicating that the Makeng area is both a center of extension and depression, which obviously controls the formation of iron ore. In addition, there are some important iron deposits in the rift zone, such as Luoyang, Pantian, Zhongjia and Yangshan, which shows that it also has regional ore-controlling function. Just because iron ore is not the research object of this topic, the factors of this rift zone are not considered when dividing the mining area. Although there are molybdenum minerals associated with Makeng and Luoyang iron mines and lead-zinc minerals associated with Zhongjia and Yangshan iron mines, they are all products of epigenetic superposition.
1. Datian-Meizhou variscan-Indosinian basin Pb-Zn-Ag-Cu mineralization area (Ⅱ-1)
There are three kinds of mineralization in the area: one is contact metasomatism related to magmatic intrusion; One is a submarine jet; The other is porphyry mineralization.
(1) Datian Pb-Zn-Ag-Cu enrichment area (Ⅱ-1-1)
Located in the northeast margin of the basin, there are many deposits (spots) characterized by sulfur (including syngenetic sulfur), which should be related to the semi-closed paleogeographic environment at that time. The sedimentary discontinuity at the end of Early Carboniferous contributed to the preconcentration of ore-forming metal elements. Magmatic intrusions in Indosinian and Yanshan periods supplemented new ore sources, and at the same time, various nappe detachment structures occurred widely, which became a good space for ore body positioning. Therefore, almost all deposits in the ore concentration area belong to the layered skarn type formed by contact metasomatism, and the detachment structure between limestone and its upper and lower clastic rocks generally becomes the formation place of skarn bodies and ore bodies. The following is an example of Longfengchang deposit.
Datian longfengchang lead-zinc mine, hence the name "longfengchang style". The mining area is an inverted syncline structure, and gently inclined detachment faults and fracture zones are widely developed between Qixia Formation limestone and its upper and lower clastic rocks. The porphyritic biotite granite of Lingdou pluton in Indosinian period intruded by superposition. Layered skarn belt is formed in overlapping intrusive contact zone and gently inclined fault zone. The main ore bodies are layered-lenticular in skarn. There are rhyolite cryptoexplosive breccia in the mining area, which is transformed into granite porphyry in depth, as shown in Figure 4- 17. The ore body in the detachment structure between limestone and clastic rocks in the lower woodland formation is mainly pyrite, and there are siderite residues, which indicates that it is of syngenetic sedimentary origin. However, the ore bodies in the detachment structure between limestone and clastic rocks in Shangwenbishan Formation are mainly polymetallic mines. The deposit scale is medium.
Figure 4- 17 Geological Profile of Line 57 in Longfengchang, Datian, Fujian Province
(Modified according to the data of Minxi Team, 1995)
1- four yuan; 2- Tongziyan Formation; 3- Wenbishan Formation; 4- Chuanshan Formation-Qixia Formation; 5- woodland group; 6- cryptoexplosive breccia; 7- Hercynian-Indosinian granite; 8— Faults and quantity; 9— Fault fracture zone; 10- false integral surface; 1 1- alteration boundary; 12- marble; 13— skarn; 14- pyrite ore body; 15- zinc ore body; 16- copper ore body
A number of deposits of the same type are densely distributed in the ore concentration area, which is characterized by being distributed around an intrusive rock mass. For example, Longfengchang deposit is distributed around Lingdou rock mass, and Longshanqi, Jian 'ai and Shangcai deposits are distributed around Tangquan rock mass (late Yanshanian).
It is worth mentioning that Jian 'ai layered skarn deposit and Dianguanzhan porphyry deposit are closely associated in space and related in genesis, thus forming a * * * combination series of layered skarn and porphyry, as shown in Figure 4- 18.
Figure 4- 18 Geological Profile of Line 305 of Jianai Electric Irrigation Station in Datian County, Fujian Province
(slightly modified according to Minxi team, 1994)
1- conglomerate; 2- marble; 3— Siltstone; 4— Fine grained sandstone; 5— Silicified siltstone; 6— Mudstone; 7— Granite porphyry; 8- mixed diorite porphyrite-granodiorite porphyrite; 9-layer skarn lead-zinc ore body; 10- porphyry disseminated copper ore body; 1 1- manganese ore body; 12- Fault and number; 13-ore-bearing breccia
(2) Houtian-Dapai Iron, Copper, Lead and Zinc Concentrated Area (Ⅱ-1-2)
From Houtian of Longyan to Yongdingkan, copper, lead and zinc are strongly mineralized. In addition to the large iron deposit related to submarine volcanic activity in Makeng, there are ten small deposits and occurrences. Mineralization is mostly layered and quasi-layered, distributed in C 1-C2, P 1q-D 1w, and part of it occurs in the contact zone between intermediate-acid rock mass and carbonate rock.
(3) Meizhou Cu-Pb-Zn-Ag (Sb) metallogenic region (Ⅱ-1-3)
Located at the southwest end of Yongmei sag, this metallogenic area is the area with the earliest transgression and the latest regression. There are two typical deposits in this area: Songxi in Meizhou and Yushui in Meizhou. Its mineralization and metallogenic type are unique.
Figure 4- 19 Geological Map of Songxi Ag-Sb Deposit in Meixian County, Guangdong Province
(According to Team 9 13)
1- four yuan; 2- Lower member of Zhangping Formation; 3, 4 and 5 —— Upper member of Zhangping Formation; 6, 7, 8, 9— the upper section of Jinji Group; 10,11-the middle section of Jinji Group; 12- basalt; 13- ore body, mineralized fracture zone; 14- failure; 15- Geological boundary
In the late Indosinian movement of Songxi Ag-Sb deposit in Meizhou, Yongmei depression began to retreat to the southwest, and Meizhou remained a residual basin for a long time. The upper member of Jinji Formation of Lower Jurassic in the mining area (equivalent to Fankeng Formation in Fujian) is a set of marine sediments in stagnant environment, which is composed of black carbonaceous shale mixed with sandstone and limestone, and some intermediate-basic volcanic rocks overflow, indicating that magma and volcanic hydrothermal solution gushed out due to basin bottom tension. There are some late quartz porphyry and diabase intrusive rocks in the mining area, and fracture zones are developed. Minerals such as silver and antimony are likely to come from submarine volcanic hydrothermal solution, but the enrichment methods are different. According to relevant data, silver-rich minerals are mostly produced in carbonaceous shale above intermediate-basic volcanic rocks, with the highest grade of 1 750× 10-6, in which pyrite is mostly strawberry-shaped. In sandstone, the silver content is very low. There are many kinds of silver minerals, including crimson silver, argentite, stibnite, brittle silver, tetrahedrite, stibnite, silver-bearing jamesonite, stibnite and natural silver. Antimony is mainly concentrated in the silicified fracture zone of faded carbonaceous shale above the silver ore body, with the highest grade of 43.5%, and its mineralization combination is stibnite-Yingshi, pyrite, sphalerite, arsenopyrite and various silver-antimony disulfide salts. Silicification is the most important alteration type, which develops linearly on both sides of the vein, as shown in Figure 4- 19. Mineralization has certain vertical zonation: Ag-Sb mineralization is above 60m, and Ag mineralization is below 60m, especially 60 ~ 100 m is the best part of silver ore. The homogenization temperature of the timely inclusion is determined to be 195 ~ 235℃, which belongs to low temperature, and the sulfur isotope δ34S is 0.52 ‰ ~ 2.8 1 ‰. The isotopic age of mineralized rocks is (159.2 4.7) ma (k-ar) on the surface and (159.2) Ma (k-Ar) in the deep. All these indicate that mineralization has obvious epigenetic characteristics. It is likely that the metal components in the source bed were activated and migrated under the influence of Yanshanian magmatic intrusion and tectonic fragmentation. Silver is mainly absorbed by black shale near the surface and re-enriched, while antimony migrates upward to the fracture zone for filling and enrichment. Therefore, the deposit should belong to the composite metallogenic type, that is, the main enrichment of silver is the adsorption of black shale, and antimony is the recharge of medium-low temperature hydrothermal solution. This deposit is an important metallogenic type newly discovered in recent years. The proved deposits are large in scale, and the No.4 ore body alone contains 2,500-3,000 tons of silver and 77,000 tons of antimony. There are good geochemical anomalies of silver and antimony on the surface, which can be used as prospecting indicators.
The Yushui Cu-Pb-Zn deposit in Meizhou is the only typical massive sulfide deposit in this area, which is located at the southwest end of Yongmei sag. The ore body is layered and locally cystic. Its ore-bearing location is located at the bottom of the middle-upper Carboniferous above the unconformity surface at the top of the lower Carboniferous clastic rock, and its horizon is basically the same as that of Longyan Makeng Iron Mine. There is a thin tuff on the floor of the seam, which is mainly composed of pyroclastic materials with micro-bedding structure, which should be the product of distant volcanic migration. There are hematite, siderite and jasper siliceous rocks in siltstone of coal seam roof, as shown in Figure 4-20. Among them, hematite has colloid structure and local spherulite structure, jasper has stripe structure and pyrite has strawberry structure. All these are enough to prove that it belongs to marine sedimentary origin, and jasper layer, as an iron-siliceous rock, shows that it is the product of jet hydrothermal process. The ore body intersects with diabase porphyrite. The wall rock alteration is mainly silicification, followed by chloritization, sericitization, pyritization and calcitization.
Figure 4-20 Profile of Yushui Copper Mine 1 Orebody in Meixian County, Guangdong Province
(According to the data of Yushui Copper Mine)
1- Hutian Formation of Middle-Upper Carboniferous; Lower Carboniferous 2- Central Formation; 3- carbonate rocks; 4— Siliceous layer (jasper); 5— Siltstone; 6— Medium-fine grained quartzite; 7- tuff; 8- hematite; 9- siderite; 10- massive chalcopyrite; 1 1- porphyry copper deposits and lead-zinc deposits; 12- massive disseminated ore body 0- weakly mineralized hydrothermal altered sandstone; Ⅰ-Medium-fine grained timely sandstone with polymetallic mineralization and strong alteration; Ⅱ-massive polymetallic deposit; Ⅲ-polymetallic mineralized chert; Ⅳ —— polymetallic mineralized carbonate rocks; Ⅴ —— Weakly mineralized carbonate rocks
The deposit is covered by Mesozoic volcanic rocks and belongs to concealed-semi-concealed deposit. Although the proven reserves are moderate, it is of great significance to explain regional mineralization and indicate the prospecting direction. There are high radioactive anomalies near the mining area, which can be used as prospecting indicators.
2. Gold-copper mineralization area in Shanghang Yanshan superimposed volcanic basin (Ⅱ-2)
In the early Cretaceous, there was a NW-trending superimposed volcanic basin along the Shanghang-Xiao Yun deep fault zone in Shanghang area, which was superimposed on the sedimentary strata of the Variscan-Indosinian marine basin. On the northeast side of the volcanic basin, the late Jurassic acid granite invaded first, and then the early Cretaceous deep intermediate-acid magma erupted, forming a set of medium-deep intrusive rocks-porphyry-subvolcanic rocks and volcanic eruption rocks. The Zijinshan-Luobulin gold, silver and copper (molybdenum) ore concentration area (or Zijinshan ore field) was formed in this geological environment. Among them, the Zijinshan large copper-gold deposit belongs to the sulfate type (high sulfur type) deposit unique to the study area. At the same time, there are cryolite and sericite (low sulfur type) deposits formed by epithermal process in the west of the ore field, which are isomorphic to the porphyry copper-molybdenum deposit in Luobuling, forming a relatively complete subvolcanic-porphyry metallogenic series. There are Tongkeng copper mine in the contact zone between limestone and rock mass of Qixia Formation and Judy lead-zinc mine in the contact zone between Xikou Formation and rock mass of Lower Triassic. The fifth chapter introduces Zijinshan copper-gold mine.