Fortune-telling in Hongmiaogou _ Are witches allowed in Hongmiaogou?

Heicigou Gold Mine, Subei Mongolian Autonomous County, Gansu Province

Heicigou Gold Mine is located 30 kilometers south of Yanchiwan Township, Subei County, Gansu Province. It is a formed gold deposit discovered in the south of Danghe River in recent years. 333+334 1 resource is about 20× 103kg, which belongs to structural altered rock type gold deposit (Xie Qun, 2003), and the scale of the deposit is medium.

The geological survey of rock gold in this area began in the mid-1990s. Through the verification and geological investigation of geochemical anomalies in this area, the Geophysical Team of Gansu Geological Exploration Bureau has successively discovered Heicigou Gold Mine, Jiagongtai Gold Mine, Zhenxingliang Gold Mine, Xiaoheicigou Copper Mine, Langchagou Gold Mine, Donghonggou Gold Mine and Banjiegou Gold Mine, and it is considered that this area is mainly associated with copper and gold, including arsenic, mercury, antimony and lead. During this period, Jiuquan Geological Team of Gansu Provincial Bureau of Geology and Mineral Resources also conducted a general survey of gold deposits in this area, and found a number of gold mineralization points through abnormal inspection. The gold 15 and 14 detachments of the former armed police carried out a general survey of placer gold in this area and found Dongshanwan gold mine.

1 regional metallogenic geological environment

1. 1 geotectonic unit

The structural position of the deposit belongs to the early Paleozoic rift zone of Danghe South Mountain in the middle of early Paleozoic in the northern margin of Qaidam plate.

1.2 regional stratum

The exposed strata are mainly volcanic rocks, clastic rocks and glutenite of Ordovician and Silurian, and the Devonian and later strata are partially exposed, which are composed of clastic rocks, mudstone and carbonate rocks with alternating land and sea. The exposed rocks are mainly late Caledonian granitoids, including Jijiaogou medium-fine diorite (), Heicigounao quartz diorite () and Jiagongtai plagioclase granodiorite (), as well as some granite dikes, diorite porphyrite dikes and diabase dikes.

1.3 regional tectonic framework

The folds and faults in this area are developed, and they are distributed in NW-SE direction, which constitutes the remarkable structural characteristics of Wulandaban Mountain. The folds mainly include Wulandaban-Heicigounao, Zhazigou-Wuyagou syncline and Qingshuigou Nanshan syncline. Faults are arranged parallel to the fold axis, mainly including Qingshuigou-Dabinggou, Qingshuigou-Yulekun Qigande, Dabaishigou, Wulanban-Dashagou and Heicigou (Figure 1).

The NWW-trending Qingxiaogounao-Gangbolidaling fault in this area starts from Qingxiaogounao in the west, runs to the east of Gangbolidaling in the east, passes through Wulanban and Dabinggou, and extends 130km, with a fault bandwidth of 100 ~ 300m. The structural rocks are mostly powdery, with strong flakes and folds locally, and the fault plane tends to the northeast with an inclination angle of 65430. It plays an important role in magmatic activity and mineralization in the region, and controls the overall distribution of deposits (points) and geochemical anomaly zones.

The deep fault activity in the east-west direction will be more conducive to the connection between the study area and the North Qilian orogenic belt, which is also the most direct reason for the development of late Caledonian magmatic intrusive rocks at the intersection of the northwest fault and the east-west fault in this area, and may be the direct channel of magmatic activity in this area. However, metal mineralization in this area is closely related to magmatic activity, which leads to the characteristics of east-west zoning and northwest clustering of metal minerals in this area.

Secondary extensional, extensional and torsional faults, ductile shear zones and fault groups originating from both sides of deep faults are the migration channels of ore-bearing hydrothermal solution, as well as the favorable space for hosting ore, and are the direct ore-controlling structures that control the emplacement of ore bodies. Heicigou gold deposit is controlled by the NW-trending reverse fault of Wulanban-Dashagou, and the ore-controlling structure is the NW-trending ductile shear fracture zone. The stronger the fracture of tectonic rocks in the structural fracture zone, the stronger the mineralization alteration, and the mineralization develops in the structural fracture zone with ductile shear characteristics. Jiagongtai gold ore-forming belt is located in the NW-trending and NE-trending structural foliations (in the direction of rock mass), and the NE-trending and NW-trending structural foliations in the southeast of rock mass are also favorable ore-forming sites. The ore-hosting structure of Haxiongzhang Gold Mine is a NNW-NNE fault zone. Dongshanwan Gold Mine is controlled by NE-trending faults, nearly EW-trending compression-torsion thrust faults and their secondary parallel compression zones, and the intersection of EW-trending faults and NE-trending faults is the most favorable metallogenic space.

Figure 1 Zone Main Fault Structure and Secondary Structure Zoning Map

1- Late Paleozoic-Mesozoic sedimentary basin; 2- Silurian strata; 3- Ordovician strata; 4- Proterozoic strata; 5- Ordovician volcanic rocks; 6- Caledonian magmatic intrusive rocks.

Ⅰ—Northern basement uplift area; Ⅱ-central fault fold area; Ⅲ —— Southern fault depression area. ① Zhazigou-Wulanda Bangoukou fault; (2) Qingshui Gounao-Gumuborida Ridge Fault; ③ Qingshuigou South-Yulekun Qigande Fault; ④-Wu Keke-Banzhazigou-Da Dorg fault; ⑤-Hongmiaogou-Chergand-Heicigou-Great Gardeler Fault; ⑥ —— The Great Halleteng River Fault-Yadaotai-Haxiongzhang Fault.

1.4 regional magmatism

Regional magmatic activity is influenced by the evolution of regional geological structure, and volcanic activity develops in addition to strong magmatic intrusion. It is characterized by concentrated magmatic activities, mainly in the early Paleozoic; The formed magmatic rocks have a single lithology, mainly composed of intermediate-acid volcanic rocks and granitic magmatic intrusive rocks, and the magmatic rocks are mainly distributed in the west of the work area in space (Figure 2).

Fig. 2 Distribution map of regional magmatic rocks

Q- four yuan; N- Neogene; Late Paleozoic; Silurian system; O- Ordovician; Platinum Proterozoic

1- magmatic intrusive rocks; 2- Early Ordovician volcanic rocks

The evolution of magmatic rocks is consistent with the geological evolution of the study area. From early to late, from collision intrusive rocks to late or late orogenic intrusive rocks, the acidity and alkalinity of magmatic rocks gradually increase. According to the occurrence characteristics and isotopic dating of magmatic intrusive rocks in the region, magmatic intrusion activities in the region are mainly concentrated in three periods: early East Caledonian, middle Caledonian and late Caledonian. During the early Caledonian magmatic intrusion, the Da Dorg ultrabasic rock body was formed in the north of Danghe River, and some Zhazigou bedrock was formed in the study area, which was eroded by the medium-term intrusive rocks, but it is difficult to distinguish it from the medium-term intrusive rocks. Therefore, the magmatic rocks formed by magmatic intrusion in this area are mainly in the middle and late stages.

Magmatic intrusions related to mineralization in this area mainly occurred in the middle and late Caledonian. The main lithology is granodiorite, plagiogranite, plagioclase granite porphyry and various dikes. Polymetallic mineralization in this area is closely related to magmatic activity in late Caledonian, and magmatic rocks play an extremely important role in controlling mineralization. The main features are as follows:

1) The rock mass is ore-bearing or is itself a mineralized body, and the ore-bearing rock mass is mainly plagiogranite with intermediate acid intrusion, such as the whole rock mineralization in Jiagongtai Gold Mine and the 13 vein in Jijiaogou Gold Mine.

2) Hydrothermal alteration and time-dependent mineralization of gold in rock mass, such as Jiagongtai Gold Mine, Haxiongzhang Gold Mine, Dongshanwan Gold Mine and Zhenxingliang Gold Mine.

3) Altered rock type and time-dependent pulse type mineralization exist in the contact zone between rock mass and surrounding rock and the surrounding rock fracture zone nearby, especially in Jiagongtai gold deposit, Dongshanwan gold deposit and Haxiongzhang gold deposit.

4) The multiple activities of magma and the fracture structure formed in the early rock mass are favorable parts for the emplacement of ore bodies.

The gold content of small intermediate-acid rocks in the late Caledonian in this area is high, with the average gold content of Jiagongtai plagiogranite being 8.5× 10-9 and Zhenxing beam plagioclase granite porphyry being 20.76× 10-9. These rocks are small and closely related to mineralization.

The isotopic data of discovered deposits show that the ore-forming hydrothermal solution of gold and polymetallic deposits in this area is magmatic hydrothermal solution, and the sulfur source has the characteristics of deep source. According to the sulfur isotopic composition characteristics of sulfide in Heicigou gold mine, Jiagongtai gold mine and Dongsanwan gold mine, the variation range of δ34S‰ is -4.8 1 ~-3.8 1, which is small and close to meteorite sulfur. Combined with the hydrogen and oxygen isotopic composition and geological characteristics of Dongsanwan gold deposit, Heicigou gold deposit and Jiagongtai gold deposit, it can be determined that these three deposits are closely related to magmatic activity.

1.5 metallogenic unit

The deposit is located in the northern Qaidam metallogenic belt of Qilian metallogenic area in Qin-Qi-Kun metallogenic domain.

2 Geological characteristics of mining area

2. 1 ore-bearing strata

The main body of Heicigou gold deposit is located in the Ordovician conglomerate layer, controlled by faults, about 4km north of Jiagongtai granite body. The strata exposed in the mining area are mainly middle-upper Ordovician, which can be divided into 5 lithologic sections and 4 sedimentary facies from old to new. The first and second lithologic members are shallow sea facies, which are composed of various volcanic (terrigenous) clastic rocks; The third lithologic member is volcanic ash-mudflow facies, which is deposited in the slope zone; The fourth lithologic member is fluvial delta facies deposit, which is composed of mudstone, sandstone and conglomerate. The fifth lithologic member is clastic rock deposited in shallow-semi-shallow marine facies. The fourth lithologic member is the main ore-bearing layer, and gold mineralization is generally developed (Figure 3).

2.2 magmatic rocks in mining area

Magmatic rocks are well developed in the mining area, and the emplacement of rock masses is mostly controlled by secondary fault structural zones, and they are exposed sporadically in the form of rock clusters, dikes (or dykes). Lithology is mainly syenite diorite, and quartz monzonite can also be seen. The edges of monzonite are mostly interspersed with surrounding rocks, and the interior is rich in surrounding rock breccia, sometimes with condensed edges and keratinization, showing the characteristics of hypabyssal emplacement. In addition, the mineralization of the rock mass is obvious, which is closely related to the formation of gold deposits in Heicigou area. The important gold bodies in the mining area are located near the contact zone inside and outside the rock mass.

2.3 Ore-controlling structure

The structure that controls the occurrence of ore bodies in the mining area is Heicigou fault zone, which is basically consistent with the axis of Wulanban-Heicigou brain syncline, with strike of 125 and dip angle of 70 ~ 80. The rocks in the fault zone are broken and altered strongly, and mylonitized rocks and mylonite can be seen, which reflects that the fault is active and complex, and may be a ductile-brittle long-life fault, and its secondary fault is an important ore-controlling structure in this area.

Fig. 3 Geological schematic diagram of Heicigou gold mine area

Q- four yuan; Ss, Sst, Sls and SLSG-Silurian grayish green sandstone, tuffaceous sandstone, interbedded sandstone slate and interbedded glutenite; CG- Carboniferous conglomerate; δ— diorite; η-quartz monzonite. 1- fracture and number; 2- Ore (mineralized) body

2.4 surrounding rock alteration

The mineralization alteration in this area is mainly controlled by the fault zone, and the alteration types are mainly carbonation, sericitization, silicification, iron carbonation, arsenopyrite, pyritization and amphibole.

The surrounding rocks in the ore-controlling fracture zone are strongly altered, and the alteration intensity is positively correlated with the mineralization intensity of metal sulfide and gold. The stronger the alteration, the better the mineralization. Alteration zoning is not obvious. The edge of the ore belt is weakened by corrosion, mainly carbonization and sericitization, with a small amount of pyritization. The internal alteration of the ore belt is strong, mainly silicification, iron carbonation and arsenopyrite, followed by pyritization and sericitization.

2.4. 1 silicification

It is fine-grained and rod-shaped and evenly distributed in time. In some places, it is reticulate and banded, which indicates that it occurs under dynamic conditions. Silicification and structural deformation are synchronous. The mineralization most closely related to silicification is pyritization, followed by arsenopyrite.

Carbonization of iron

It is mainly manifested by the uniform infiltration of fine irregular particles, and the closely associated metal mineralization is self-shaped spear-shaped and needle-shaped arsenopyrite, which uniformly infiltrates dust spots.

Seriphization

Most of them are recrystallized from original argillaceous materials, which have gradually turned into muscovite, and the related gold mineralization is not obvious.

carbonize

It is the product of low temperature, one is the recrystallization of calcareous cement in primary clastic rocks, and the other is calcite veinlets and reticular veins filled in tensile fractures in the later stage of mineralization, neither of which is closely related to mineralization.

Metal mineralization

It is mainly arsenopyrite, disseminated by fine dust spots, needle-shaped and spear-shaped, which is closely related to gold mineralization, followed by pyrite.

cornification

It is developed in the surrounding rock of the north wall of the ore belt (floor surrounding rock), with biotite amphibole as the main one and andalusite amphibole as the second. Each mineralization has obvious zonation in space, and antimony gold, lead gold and copper gold mineralization are located on both sides of Heicigou gold deposit in turn.

3 Geological characteristics of ore bodies

3. 1 deposit (entity) characteristics

Heicigou Gold Mine is divided into three mining areas, namely, Heicigou Gold Mine, Hongshishan Gold Mine and Jindongpo Gold (Antimony) Mine (Figure 3). The proven metal contents of the former two are 15.404× 103kg and 0.664× 103kg respectively, and the latter is not sufficiently controlled and is estimated to be smaller than the former two. The ore belt in Heicigou mining area is produced in Ordovician, and its overall shape is controlled by ancient delta facies, which is layered, layered and lenticular, and the thickness of ore body changes with the change of sedimentary facies (Figure 4). The shape of the ore body is controlled by the interlayer structure in the conglomerate layer and occurs in the fault zone and footwall conglomerate, showing the characteristics of altered rock-type gold deposits. See table 1 for the changes of ore body thickness and grade of the three exploration lines.

Table 1 Changes of Ore Body Thickness and Grade in Different Exploration Lines

3.2 Ore composition

According to natural types, the ores in Heicigou Gold Mine can be divided into oxidized ores and primary ores. The former is mainly formed by the influence of late tectonic activities and surface weathering and leaching, accompanied by primary minerals, all of which are banded (Figure 4) and generally occur near the surface. Primary ores include conglomerate type, cataclastic conglomerate type, structural altered rock type and chronological network vein type. Pyrite in ore is veined, massive and disseminated, mainly distributed in cements and fractures, and there are also veined and disseminated pyrite in gravel.

Fig. 4 Section of Heicigou Gold Mine 140 Exploration Line

1- oxidized ore body; 2- Primary ore body; 3— Siltstone; 4- conglomerate; Penttuff

The metal minerals in the ore are mainly arsenopyrite and pyrite, followed by sphalerite, chalcopyrite, galena, magnetite and limonite. The arsenopyrite is yellow-white, and some surfaces have yellow-brown oxide films. The crystal form is needle-shaped and spindle-shaped, and it is mostly filled in the edge of carbonate vein or its cracks in the form of veinlets. Pyrite is self-crystallized, with pentagonal dodecahedron and polycrystal, followed by strawberry, which is one of the gold-bearing minerals. Non-metallic minerals include quartz, sericite, calcite, dolomite and apatite.

The content of metallic minerals in structural altered rock-type gold ore is generally less than 5%, among which fine-spotted, spear-shaped and needle-shaped arsenopyrite are the main ones, and the particle size is generally less than < 0.00 1mm, with uniform dissemination.

The metallogenic elements of gold mineralization are as (> 400× 10-6), Sb (> 40× 10-6) and Au (average 1.3989× 10-6), and other elements are Ag and Mo. Therefore, antimony and arsenic can be used as indicator elements for gold prospecting, especially arsenic can be used as a direct indicator element for gold mineralization. It also shows that the formation temperature of gold mineralization is low, and it is a medium-low temperature deposit, which is consistent with the occurrence of colloidal pyrite. The average gold content of this kind of ore is1×10-6 ~ 2×10-6, and the highest is 5.9× 10-6.

The content of metallic minerals in timely vein ores is generally < 10%, and the mineral particles are coarse. Due to the different combinations of metal minerals, different ore-bearing veins have been formed. The element combination of chronological vein mineralization is obviously different from altered rock type. The average content of mineralized metal elements is higher than that of gold (1.84× 10-6), silver (> 5× 10-6) and molybdenum (1 1.22× 65448). Lead (1403× 10-6), zinc (897× 10-9), arsenic (> 400× 10-6), antimony (38.60×/kloc-0) At the same time, in addition to the above metal minerals, there may be bismuthite and molybdenite.

Natural gold and silver-gold deposits exist in microscopic-ultramicroscopic state. Microscopically, it can be seen that gold minerals exist in the cracks of gangue minerals in the form of particles < < 0.00 1mm, and are wrapped in time. The particle size statistics are shown in Table 2.

Table 2 Particle size statistics of gold minerals

Note: The data source is the geological survey report of Heicigou Gold Mine and Jiagongtai Gold Mine in Subei Mongolian Autonomous County, Gansu Province, Gansu Geophysical Exploration Team, 1996.

Artificial heavy placer gold is golden yellow or slightly white flake, filamentous and granular, with the maximum particle size of about 0.02mm, generally below 0.0 1mm, and it is analyzed by electron probe as natural gold and silver-gold ore (Table 3).

Table 3 Electron probe w(B)/% of natural gold and silver-gold ore

Note: The data source is the geological survey report of Heicigou Gold Mine and Jiagongtai Gold Mine in Subei Mongolian Autonomous County, Gansu Province, Gansu Geophysical Exploration Team, 1996.

3.3 Division of Metallogenic Stages

ⅰ: The early time-dependent pulse-type polymetallic gold mineralization stage (early time-dependent pulse-type mineralization stage) is the earliest, with the development of time-dependent pulse and calcite time-dependent pulse, rich in coarse cubic pyrite, chalcopyrite, galena and chalcocite, distributed in massive veins, and the associated gold content in this mineralization stage is also high.

Ⅱ: gold mineralization stage of structural altered rock type, which can be divided into two sub-stages. Ⅱ-1:the sub-stage of silicification-pyritization was formed at the same time as structural schistosity and structural fragmentation, and the alteration was mainly silicification, followed by sericitization. Metal mineralization is characterized by the development of pentagonal dodecahedral pyrite, which is an important period of gold mineralization. Ⅱ-2: iron carbonation-arsenopyrite sub-stage, slightly later than silicification stage, characterized by iron carbonation and arsenopyrite development, with colloidal pyrite locally developed, indicating that the formation temperature is low. It can be seen that arsenopyrite takes pentagonal dodecahedron pyrite as the core and grows radially or around it, indicating that arsenopyrite is formed later than pentagonal dodecahedron pyrite. This sub-stage is the most important period of gold mineralization, and the gold grade can reach 5.85× 10-6. In addition, arsenopyrite can also be directly superimposed on the early time-dependent vein mineralization.

Ⅲ: The gold (antimony) mineralization stage of the chrono-pulse type (late chrono-pulse type) is characterized by the development of the chrono-pulse of stibnite, and the metallic mineral is only massive stibnite. The average gold content of veins is 0.543× 10-6. The time-related vein mineralization of stibnite can also be directly superimposed on the early time-related vein mineralization, so it can be seen that stibnite occurs in the form of network vein and block along the early time-related vein fault.

Ⅳ: Carbonization stage, which is the late stage of mineralization with weak mineralization, marks the end of gold mineralization.

Although the above-mentioned metallogenic stages are slightly sequential in time, they are mostly superimposed in space and can also be produced separately.

4 genetic analysis of the deposit

4. 1 isotope geochemical marker

The sulfur isotopic composition of Heicigou gold mining area is shown in Table 4. The δ34S of pyrite and stibnite has little change, which is close to that of meteorite sulfur, reflecting its close genetic relationship with magmatic activity. The W(Co)/w(Ni) value of pyrite indicates that the gold deposits in this area are related to magmatic hydrothermal solution.

Table 4 Sulfur Isotopic Composition of Heicigou Gold Deposit

Table 5 Analysis Results of Trace and Rare Earth Elements

Note: Data were tested by Nuclear Industry Testing and Experimental Center, 2003.

4.2 Rare Earth Elements

From the analysis results of trace elements and rare earth elements in ores, rocks and strata (table 5), it can be seen that the contents of trace elements and rare earth elements in different ores of Heicigou Gold Mine are quite different, indicating that their genesis is complex and can be roughly divided into three groups: the first group is that Nb, Ta, Zr and Hf are strongly depleted and Eu is enriched, indicating that the source area may be deep; Secondly, heavy rare earths are relatively scarce, and there is no Eu anomaly, which may be closely related to strata; Third, the weak deficit of heavy rare earths and the negative anomaly of Eu may be related to magmatic activity in this area.

4.3 Discussion on deposit types

Heicigou gold deposit has obvious stratabound characteristics. First of all, the ore body is strictly controlled by the interlayer fracture in the conglomerate layer, and occurs in the conglomerate in the structural fracture zone and its footwall, which is layered, layered and lenticular. Primary ores are mainly conglomerate type and cataclastic conglomerate type. Although there are NW-trending veins (bodies) in Jindongpo gold (antimony) mining area of Hongshishan gold mining area, the scale is small and not mineralized. If only two corpuscles are used, secondly, the study of sedimentary facies and gold content in the mining area shows that the intensity of gold mineralization has a certain relationship with sedimentary facies and gravel content. The gold content of conglomerate cemented with silica is good. With the decrease of gravel content, the particle size becomes smaller and the gold content tends to decrease. Thirdly, the wall rock on the upper wall of the gold mineralization belt is a negative anomaly belt with a bandwidth of 150m, which indicates that gold mineralization is closely related to the wall rock at the time of mineralization.

The Heicigou gold deposit is different from the typical stratabound gold deposit (Lande gold deposit) and the traditional magmatic hydrothermal gold deposit. As mentioned above, some scholars classified it as a Rand-type gold deposit, others thought it was the result of the trinity of strata, structure and magmatic rocks, but they did not clearly classify it, and some scholars thought it was an altered rock-type gold deposit. This shows that the type of Heicigou gold deposit is controversial, and it is really difficult to give a clear type. According to the data of rare earth, trace elements and isotopes of the Heicigou gold deposit, the main ore-forming materials of the deposit often come from the deep, which is related to magmatic activities, rather than from the conglomerate layer, which obviously does not conform to the characteristics of stratabound gold deposits, and it is also inconsistent with the facts to classify the deposit as conglomerate type or stratabound conglomerate type gold deposits. However, judging from the geological characteristics of the deposit, the characteristics of the ore body and the relationship between the ore body and the surrounding rock, the deposit does show some stratabound characteristics, that is, the ore body basically occurs in the structural fracture zone, the horizon is fixed, and the ore grade has certain correlation with the formation lithology, so it is not suitable to classify the deposit as a magmatic hydrothermal gold deposit.

The problems encountered in Heicigou gold mine are typical problems in the geological work of gold mines in western China. In fact, some newly discovered medium and large gold deposits in the west in recent years all show similar characteristics to the Heicigou gold deposit, such as the Yangshan super-large gold deposit in Gansu Province and the Zhaishang medium-sized gold deposit in Minxian County, Gansu Province. All deposits are controlled by certain strata, and strata are not the main providers of ore-forming materials, but magmatic activity is the dominant factor of mineralization (Lu Yanming, 2004).

5 exploration standards

Find the concentrated development area of diorite in time, and find the structural fracture zone near the contact zone with surrounding rock in the diorite development area; Look for strong alteration areas such as silicification, iron carbonation, arsenopyrite, pyritization and time-dependent pulse development areas in the structural fracture zone; Searching for high anomaly zones of gold, antimony and arsenic in primary anomalies.

refer to

Jin Zhipeng, He Jinzhong, Lu Qingshan. 2004. Geochemical Characteristics of Heicigou Gold Ore Field in Subei County, Gansu Province, Gansu Geology, 13 (1): 74 ~ 79.

Liu, Li Houmin, et al. 2003. Gold mineralization related to syenite diorite in Heicigou area of Dangheshan. South China Geology and Mineral Resources, (1): 12 ~ 16.

Fan, Zhao Xinfeng et al. 2004. Geological characteristics and type attribution of Heicigou gold deposit in Gansu Province. Gold Geology, 10 (4): 1 ~ 6.

(Author Zhang Yanchun)