3. 12. 1. 1 The basic geological work, which is mainly based on geological mapping, is the key to the breakthrough of prospecting in the mining area.
The degree of basic geological work in mining area is the leading factor restricting the breakthrough of prospecting in mining area. Through the prospecting practice in the mining area in recent years, the breakthrough in understanding the metallogenic regularity in the following two aspects has played a positive role in the exploration work.
A new understanding of (1) metallogenic environment has laid a theoretical foundation for prospecting in this area.
1) Based on the analysis of regional geological evolution, it is considered that the mineralization in this area is related to the collision orogeny of North China plate and Siberia plate in Variscan period, which is an island arc or continental margin arc orogenic environment and has favorable conditions for the formation of typical porphyry deposits. The porphyry-epithermal metallogenic system in this area was established for the first time, and the replacement resource prospecting was carried out according to the new prospecting idea, and breakthrough new progress was made. The types of vein and porphyry mineralization, as well as the zoning laws of different mineralization elements such as gold, copper and molybdenum are established.
2) The prospecting criteria of different mineralization types in the mining area are established, and the zoning characteristics of mineralization and alteration are preliminarily studied, which lays the foundation for the next prospecting. Gold mineralization is closely related to silicification, and horsetail filiform smoky gray timely veinlets and reticular veins are the main prospecting indicators. Associated alteration includes sericitization, chloritization, epidotization, pyritization and carbonation.
(2) The structural system analysis of the ore field is the key to the breakthrough of the ore field.
According to the structural mapping of the ore field, the "rhombic lattice" ore-controlling structural model of the northwest and northeast fault structures of the ore field is established, the No.2 ore belt is re-delineated, and the "node ore-controlling" model and the volcanic crushing mechanism ore-controlling model are put forward. Especially high-precision remote sensing data (such as ETM, SPOT, QuickBird, etc. ) plays an important role in identifying the structural system of ore field.
3.12.10.2 geochemical exploration method is an effective indicator for prospecting in exposed bedrock area.
Geochemical survey of 65,438+0 ∶ 50,000, 65,438+0 ∶ 65,438+0,000 cuttings (soil) and geochemical profile survey of 65,438+0 ∶ 2000 have been carried out in the mining area, and there are obvious geochemical anomalies in the mining area. The discovery of 1 ore belt. The edge anomaly of ⅱ ore belt was found, which played a guiding role in re-understanding the ore-bearing nature of ⅱ ore belt. The problem is that this method can only indicate the exposed area of bedrock, but the geochemical exploration method is not applicable, or the conventional geochemical exploration method has limitations. For example, the main ore body in the ⅱ ore belt is located under modern aeolian sand. It is precisely because of this reason that the No.2 ore belt has not been discovered by predecessors, and this prospecting has spent a lot of time exploring the ore-bearing parts of the main ore body because of this factor. It is necessary to develop geochemical prospecting methods in sand-covered areas of Inner Mongolia.
3. 12. 1.3 Electrical and electromagnetic methods have a certain guiding role in the establishment of tectonic system.
Most of the working areas are located in the coverage area, and it is difficult to carry out basic geological work, not only on the surface, but also in the deep. In particular, the ore-forming geological bodies related to mineralization-intermediate-acid magmatic rocks are mostly concealed rocks, and the three-dimensional spatial distribution characteristics of structures, the key factor of ore control, need to be obtained by effective geophysical exploration methods. In this work, the high-density electrical method and EH4 continuous conductivity profile measurement are carried out, and the results show that geophysical prospecting methods have certain guiding role in the establishment of structural system. Especially through EH4 and high-density electrical survey, the existence of ⅱ ore belt is recognized, but little information is provided about the specific ore-bearing parts and the location of concealed rock mass. This time, the effect of using geophysical prospecting method to guide ore prospecting is not obvious, not because of the method itself, but because our work is not systematic and the work deployment is only superficial, so it is impossible to analyze the geological problems of the ore field macroscopically and comprehensively.
3.12.10.4 The key to deep exploration is a lot of engineering control.
Under the guidance of correct deposit model, geophysical deep mapping technology and geochemical deep penetration technology, it can be inferred that there may be some kind of ore body in the deep. However, to confirm whether there is an ore body in the deep and how large it is, there must be a lot of engineering control, intensive deep drilling and continuous downward excavation. Especially in this work area, there are few outcrops and unclear geological conditions, which need bold engineering verification.
3. Significance and Enlightenment of the Discovery of12.2 Deposit
3. 12.2. 1 The first large-scale independent concealed porphyry gold deposit in the northern margin of North China plate.
The northern part of North China Plate is an important gold polymetallic metallogenic belt in China. For a long time, the focus of metallogenic research and the main energy of prospecting in this area have been concentrated on the northern margin of North China Plate (landmass). Mineralization is mainly controlled by Precambrian crystalline basement, regional deep fault zone and Mesozoic volcanic-magmatic activity. Obviously, the magmatic rock belt, a typical island arc (continental arc) structure which is very beneficial to mineralization, has not been paid attention to because there are few formed gold deposits found in this area. However, worldwide, the trench-arc basin environment related to plate subduction is one of the most important metallogenic backgrounds of copper-gold deposits. That is to say, as long as there is a trench-arc basin environment related to plate subduction, a typical porphyry copper-gold polymetallic deposit will be found in it. Therefore, in the island arc structure-magmatic belt of the typical trench-arc-basin system in the northern part of the North China Plate, no porphyry deposit matching its environment has been found for a long time, which has become a mystery in the fields of geology and mineral deposits.
Bili alloy deposit is an independent large-scale high-grade porphyry gold deposit, which was first discovered in the northern margin of North China Plate, and is typical and representative (Ge Liangsheng et al., 2009). From one side, it is proved that the Paleozoic island arc accretion zone in the northern part of North China Plate, which has been neglected for a long time, is not only a very important metallogenic geological environment, but also a mineral deposit type that matches the environment, and has very prominent characteristics. Thus, to some extent, an important scientific problem that has long puzzled people in this field has been solved. As the porphyry deposits are distributed in clusters and belts, it is certain that similar deposits will be found in the similar environment of this area and this area with the gradual advancement and deepening of prospecting and exploration, which shows that the determination of the discovery process and type of deposits has important demonstration significance for the search and exploration of similar deposits in similar geological environment in this area.
3. 12.2.2 New evidence of late Paleozoic convergent plate tectonic system in northern North China plate.
Chen Yanjing et al. (20 10) pointed out that the deposit is a unique and complex geological body, which is often the result of the comprehensive action of various geological processes, and records the evolution of the earth more comprehensively or completely, avoiding the one-sidedness that some simple geological bodies can only give some information. Among all kinds of geological bodies, only the ore deposit is a geological body that has undergone a lot of engineering exploration, and its three-dimensional shape, internal structure, elements and mineral composition characteristics and their changes have been revealed in detail and accurately, which makes the understanding of geodynamic evolution based on the study of ore deposits more reliable. Deposit is the product of metallogenic system, so the formation of metallogenic system also has the guiding significance of geodynamics.
Although the ancient Asian Ocean gradually closed from west to east, the Central Asian orogenic belt was characterized by strong continental accretion in Paleozoic, and the extensive development of magmatic arc and magmatic-fluid metallogenic system in late Paleozoic is an indisputable fact (Chen Yanjing, 20 10). However, whether the Late Paleozoic magmatic arc can extend to the "inner mongolian axis" area in the northern margin of the North China Craton and form important deposits is generally less or unclear. On the other hand, on the premise of acknowledging the Paleozoic accretion process in the northern margin of North China plate, there are different understandings about the time limit of plate accretion and the spatial configuration of accretion structural units.
Chen Yanjing et al. (20 10) concluded that the late Paleozoic magmatic arc developed in the northern margin of the ancient land of North China, and the spatial scope of the magmatic arc was centered on "inner mongolian axis" as a whole, and its duration increased from west to east, and the eastern part of Jilin may be delayed to early Triassic. In addition, there may be two main periods of island arc magmatism in late Paleozoic: early and late. The first stage occurred in Devonian-Carboniferous, with a time limit of 380 ~ 324 Ma. The rock assemblage consists of syenite, monzonite, monzodiorite and basic rocks (pyroxene and amphibole). The rock mass mainly comes from the partial melting of the lithospheric mantle and is mixed with ancient crustal materials. Alkaline rocks are mostly distributed in the south of inner mongolian axis, and their distribution is restricted by deep faults near east-west, which is related to Dongping Gold Mine and Hadamengou Gold Mine, and also to altered rocks in the contact zone between Houxianyu boron ore body and diorite vein. The argon-argon plateau age of phlogopite is (386.53 3.9) Ma (MS-DW =1.4) (Tang Haoshu et al., 2000). However, it is uncertain whether magmatic activity and related deposits can represent the characteristics of magmatic rocks on the active continental margin, because they are all produced in the North China plate. The second stage of magmatic activity is Late Carboniferous-Permian, which is widely distributed. The lithologic combination is mainly hornblende gabbro, diorite, quartz diorite, granodiorite and granite, and the emplacement age of the rock mass is 324 ~ 259 Ma. Petrochemistry is characterized by calc-alkaline-high potassium calc-alkaline, aluminum-like and silica content changes. Granitic rocks generally have the characteristics of type ⅰ granite and adakite. Most Carboniferous rocks (such as Longhua, Bolono and Hushiha) have low εNd(t) values (-17.1~-1.5) and zircon εHf(t) values are low (-38.3). The characteristics of rock assemblage, petrochemistry and isotope geochemistry show that it was formed on the continental margin of Andes, which is related to the subduction of the ancient Asian ocean plate to the North China block, and formed a number of deposits, such as Chehugou porphyry copper-molybdenum deposit in Inner Mongolia (Wandeng, 2009), Hadamiao porphyry gold deposit (Ludeng, 2009), Xiaoxinancha porphyry-skarn copper-gold deposit in Jilin, etc. The Rb-Sr isochron age of vein chalcopyrite in Chehugou deposit is (260 14) Ma (Wandeng, 2009), and the Re-Os isochron age of disseminated molybdenite is (258 3) Ma; The zircon LA-ICP-MS age of porphyry zircon in Hadamiao gold deposit is (271.8 3.3) Ma (Lu et al., 2009). SHRIMP zircon age of ore-bearing high-magnesium diorite in Xiaoxinancha is (257 3) Ma. The discussion in this paper shows that there are indeed island arc magmatic mineralization events related to late Paleozoic plate subduction in this area.
Late Paleozoic granitoids in Bilihe and Hadamiao areas are located in the accretion zone in the northern part of North China Plate, but not in the northern edge (inner side) of North China Plate. From its petrogeochemical characteristics, it reflects the characteristics of island arc or continental margin arc tectonic-magmatic environmental products; In time, they were formed in the early and late Variscan period (272 ~ 254 Ma). At this time, this area is at the end of the early Paleozoic Wendurmiao-Xilamulun proliferation process and the accelerated stage of the late Paleozoic Erdaojing-Chagannuoer proliferation process. Considering that the ancient Asian ocean was gradually closed from west to east, the Bilihe-Hadamiao area in the Late Paleozoic may be affected by these two accretion processes at the same time, and its magmatic activity may be controlled by subduction at two different depths in the north and south, and its geochemical characteristics show the complexity of magmatic rocks with both island arc and continental margin arc characteristics. On the one hand, it reflects that the Bainaimiao island arc may extend eastward to Xianghuang Banner, and on the other hand, it represents the existence of subduction of the northern ocean crust plate, thus providing new evidence for the establishment of a convergent tectonic system related to the subduction of the ancient Asian ocean in the northern margin of the North China plate from the perspective of ore deposits.
3. 12.2.3 Some understandings of basic geology in northern North China deserve further discussion.
The basic geological work in northern North China has a history of nearly a hundred years. The understanding of the regional tectonic evolution of Bainaimiao-Xianghuang Banner, where Bilihe Gold Mine is located, has also been deeply studied. Although it is acknowledged that the northern part of North China Plate has experienced the process of plate margin rift from Proterozoic to Mesoproterozoic, continental margin proliferation from Mesoproterozoic to Paleozoic and Mesozoic intracontinental tectonic activity, this does not mean that people have no problems in understanding the characteristics of strata, structure and magmatic activity. In the previous discussion, we have pointed out that a set of intermediate-basic and intermediate-acid volcanic rocks exposed in this area, that is, the so-called upper Jurassic Manitu Formation and Baiyinlaolao Formation, have long been considered as the products of Mesozoic intracontinental volcanic rift (fault) basins. At the same time, it is considered that the formation of these volcanic rift basins is related to the intensification of the westward subduction of the East Pacific plate since Mesozoic. Through regional comparison, it is determined that it was formed in the late Jurassic. A large number of purplish red granite porphyries (veins) intruded into it, so it is also considered to be the product of Mesozoic (Yanshanian) magmatic activity. This understanding is widely accepted by people and written in classical literature such as regional geology. However, the U-PBS PIM dating results of molybdenite Re-Os and single zircon in different types of granites, such as granodiorite porphyry and granite porphyry, which invaded the Manitu Formation and Baiyaolao Formation in Bilihe area show that they were formed in the early Late Paleozoic with a time of about 254 ~ 27 1 Ma. This proves from the side that the intrusive volcanic rocks will not be later than this time, so it can't be the product of Mesozoic magmatism, but more likely the result of island arc volcanic magmatism in the early Late Paleozoic. This shows that the age of some lithostratigraphic units in the northern margin of North China Plate needs to be further determined. This has a great influence on the evolution of geological structure, the law and nature of magmatic activity and the regional tectonic framework in this area. Because, if the volcanic rocks belonging to Mesozoic were actually formed in the Late Paleozoic, it shows that there was no such strong volcanic magmatism in this area in Mesozoic, and there was no volcanic-sedimentary action in this period, which further shows that this area was actually in a state of uplift and erosion during this period, and no so-called rift volcanic basin was formed. NE-trending structures are mostly neotectonics, and as a remote effect of the Pacific plate subduction to the west, no obvious fault depression and uplift have been formed.
3. 12.2.4 Breakthrough of typical demonstration of national crisis gold mine replacement resource exploration.
According to the resource statistics of 4 15 large and medium-sized mines of 25 major metal minerals in China, there are 192 mines (accounting for 46.2%) facing different degrees of resource crisis. At present, it is an urgent task for many mines to strengthen the exploration and prospecting of replacement resources in the deep and periphery of mines, find new replacement resources, prolong the life of mines, maintain social stability and expand social employment. This can not only alleviate the shortage of resources, promote the sustainable development of mining industry, but also contribute to the employment and social stability of workers in mining areas and mining cities, and protect the security of national resources, which has important social and economic significance (Zhai Yusheng, 2004). However, due to the lack of timely exploration, many mines are facing a serious resource crisis to varying degrees. According to the National Survey of Resource Potential of Crisis Mines (Gold Mines) (Report of 2008), among 120 large and medium-sized gold mines, 107 have resource crises (including severe, moderate and mild) in different degrees, accounting for 89.2% of all surveyed mines, and some of them have reached the closure level. Only 9 mines have no resource crisis, accounting for 7.5% of all surveyed mines.
Although the main gold mines in eastern China have experienced long-term mining, on the surface, most of the resources are on the verge of exhaustion, but most of them still have great prospecting potential in the deep and surrounding areas. Some mine management departments have to close down because they don't pay attention to detailed geological research and exploration and reserve resources. In fact, it is irresponsible to society and resources. On the other hand, some mines are facing the situation of decreasing resources. It is not effective to organize mine technicians and even invite some domestic experts and scholars to study and guide the exploration of mine resources at different levels. This phenomenon should be analyzed from two angles. First, whether the potential of mine resources has been scientifically and reasonably analyzed and evaluated. Only the mines that are scientifically considered to have prospecting potential can have the basis and premise of exploration breakthrough; Second, whether the organization of mine geological research and exploration is scientific and appropriate. Mine geological research and exploration is a practical scientific work. Pure theoretical research may get a lot of guidance, but it can't meet the urgent demand for resources in a short time. Therefore, according to the actual situation of the mine, how to formulate a reasonable and effective combination of prospecting ideas and technical methods is of great significance for accelerating the breakthrough of prospecting for replacement resources in crisis mines.
As mentioned earlier, the Bilihe Gold Mine in Inner Mongolia is a serious resource crisis mine with a service life of less than 2 years. Through this scientific research and prospecting work, a major breakthrough in the exploration of replacement resources has finally been achieved, which can be regarded as a typical successful exploration of replacement resources in gold mines in China.
3. 12.2.5 Prospecting and exploration mode has broad prospects for popularization and application in similar areas.
The central and eastern Inner Mongolia is located in the transitional zone between the Gobi desert in the northwest and the grassland in the southeast. The terrain in this area is relatively flat, with low sand dunes and wide seasonal valleys in some areas. Drought and lack of rain, affected by strong winds and dust, are generally covered by aeolian sand to varying degrees. Although the overburden is generally not thick, rock outcrops are quite limited. This special geological landscape has obviously influenced the deployment and implementation of prospecting work, and has become an important problem restricting the breakthrough of geological prospecting in this area.
The previous prospecting practice in this area shows that the traditional idea of geochemical anomaly prospecting by measuring soil and river sediments, that is, evaluating anomalies mainly according to their own properties and existing experience, can play a good prospecting effect in other areas, but it is facing challenges or exposing disadvantages in this area. For example, there are common regional geochemical anomalies without gold in this area, but there are gold ore bodies. On the contrary, significant mineralization has not been found in areas with unusually good gold after repeated work. The main reasons for this anomaly are the interference of aeolian sand, gentle landform and underdeveloped water system on geochemical anomalies. In addition, even if the same prospecting method is used, the specific application in different landscape areas is different. For example, as far as geochemical exploration is concerned, sampling methods, layout of sampling points, sampling media, depth and sample processing methods should be set according to the characteristics of different regions. Therefore, the remote work of regional basic geology and geophysical and geochemical exploration should be carried out in strict accordance with the corresponding specifications, and the geochemical exploration work with strong purpose mainly serving the actual needs of ore prospecting can be flexibly considered according to the actual situation.
In the scientific research and exploration of Bilihe mining area in Inner Mongolia, geological, geophysical and geochemical exploration and remote sensing work of different scales have been deployed. In terms of means and methods, they are all traditional technical methods, and there is nothing new. However, from the specific deployment and implementation, work content and problem-solving level of each method, it has obvious pertinence and emphasis. The main purpose of remote sensing geological work is to basically find out the structural system that controls mining areas and deposits from a larger regional perspective. Because of the poor outcrop, people don't pay much attention to the extraction of alteration information that people often do; The geological survey is mainly to find out the geological characteristics and mineralization alteration characteristics of the mining area, with emphasis on the identification and appraisal of volcanoes, subvolcanic structures and porphyry bodies, and pay attention to the time pulse on the surface and structural fracture zones that may become mineralization targets; The main purpose of deploying geochemical exploration work is to verify the authenticity of anomalies and provide mineralization information for the next step. Profile setting and sampling adopt short profile method, aiming at structural alteration zone, etc. As far as possible, the sampling medium is mainly cuttings, and individual cuttings may not be sampled, but the interference of aeolian sand must be eliminated to make the results more reliable. The deployed geophysical exploration work is mainly aimed at the fault and its ore-bearing evaluation, and the geophysical exploration technology with complementary precision in shallow and deep parts is selected. Through the organic cooperation of the above work, combined with various methods and means to obtain comprehensive analysis and evaluation of the results information, the goal of exploration breakthrough is approached step by step, and the purpose of the work is finally achieved.
3. 12.2.6 Promoting the stable and sustainable development of regional economy has great economic and social benefits.
The discovery of the Bilihe porphyry gold deposit has made new contributions to the regional economic development and the gold industry in China. The proven resource reserves can extend the service life of the mine 130 years according to the production scale of the existing mine with an annual output of 60,000 tons. Expand the mine production scale, with an annual production scale of 300,000 t and a service life of 30 years, which can stabilize employment 1 10,000 people. According to the current price and 80% resource utilization rate, the potential economic value exceeds 4 billion yuan.