Selection of geological prospecting breakthrough

With the rapid development of China's industrial and agricultural modernization and urbanization, the contradiction between the increasing demand for resources and the shortage of resources is increasingly apparent. Many metal deposit resources have been in a state of "high dependence" for a long time, and the shortage is rigid. Obviously, a new breakthrough in prospecting is an important task of geological and mineral work today.

1) The essence of "prospecting breakthrough" lies in revealing the law. Through the hard work of several generations of geologists, the regional geological survey team of Shanxi Bureau of Geology and Mineral Resources has successively completed the regional geological survey in the northeast of Shanxi Province at the scale of1:200,000 and1:50,000, and integrated and sorted out the regional geological survey data. On this basis, according to the rock-controlling and ore-controlling model of tectonic-magmatic active belt, the overlapping areas of Mesozoic transitional syntectic intermediate-acidic hypabyssal intrusive rocks, subvolcanic magmatic active belt and regional fault structural belt in different directions are established, which is an important symbol for searching for polymetallic deposits. On this basis, through modern new technologies and methods such as geophysical exploration, geochemical exploration and remote sensing, it has become a breakthrough working mode of comprehensive geological exploration and prospecting to extract ore-induced anomaly information, delineate prospecting targets and favorable prospecting areas, and comprehensively analyze massive data to provide beneficial "ore omen information" for metallogenic prediction.

2) Give play to the guiding role of geological metallogenic theory in geological prospecting behavior, and promote prospecting breakthrough. Zhu Xun (1982), the former Minister of Geology and Mineral Resources, published the article "On Prospecting" more than 30 years ago, and discussed the theoretical basis of the feasibility of "prospecting" from two aspects of metallogenic geological theory and philosophical theory. First, according to the principle of dialectical materialism epistemology, it is impossible to know the whole picture of any mineral deposit through one prospecting practice, but it is necessary to constantly understand this process through practice-understanding-practice-re-understanding, so as to obtain a more comprehensive understanding. For example, the evaluation process of Baoziwan gold deposit was discovered by different geological prospecting units after many twists and turns; Diaoquan mining area was assessed as a copper mine in 1950s, and it was found to be a silver-gold ore body with industrial value during mining. Chaishuling gold deposit was discovered 40 years after the geological exploration of Houyu copper-molybdenum mine ended. Therefore, re-exploration and re-analysis of prospecting clues that have not been positively or negatively evaluated may completely gain new understanding different from the past. Secondly, according to the analysis of mineral deposit theory and philosophical theory, it is necessary to have good metallogenic geological conditions to form industrial deposits. However, in the area where the metallogenic geological conditions of a certain deposit are distributed, there are usually not only isolated points of known deposits, but also other deposits with similar metallogenic geological conditions around them. This provides a theoretical basis for re-prospecting around known mines. Later, Cheng (1994) and Chen Yuchuan (1994) gave a new expression to this theory through the concepts of metallogenic series and metallogenic model, and evolved into a new metallogenic series theory. It extends the traditional research method of single genesis, single type and single model of ore deposit science to the research field of regional, comprehensive and four-dimensional evolution, makes a more scientific explanation of the basic problems in ore deposit science, such as metallogenic history, ore deposit zoning and metallogenic mechanism, and discusses the basic geological problems of ore deposit science and metallogenic theory at a deeper level, which has important practical significance for improving the scientific foresight of geological prospecting.

The total area of the above nine forecast areas is about 7 000 km2. How to optimize the geological prospecting breakthrough will be an important way to realize the rapid prospecting breakthrough. According to the basic principles of metallogenic geological law and metallogenic series theory in northeast Shanxi, the following aspects are the breakthrough points to accelerate the breakthrough of geological prospecting.

(1) Deep and surrounding areas of Tadi volcanic basin

The following favorable metallogenic geological conditions are known in this area.

The top of Jurassic volcanic rocks in Tadi volcanic basin is Upper Jurassic Donglingtai Formation (J3d, thickness 100 ~ 150m), and the lower part is Middle Cascade Mountain Formation (J2t, thickness 25 ~ 2040m) and Jiulongshan Formation (J2j, thickness 15 ~ 572m).

In addition to the known Tainashui, Diaoquan and Xiaoyan ore bodies, there are a series of concealed ore bodies such as Diaoquan-Xiaoyan, Tainashui, Sunjiazhuang, Niejiagou, Xunzhuang and Baibeibao along the NW-trending and NE-trending faults.

The comprehensive anomalies of heavy sand minerals such as gold, silver, copper, lead, zinc, tungsten, bismuth and molybdenum, and the comprehensive anomalies of multi-element river sediments and other geochemical elements are distributed in the annular zone around Tadi volcanic basin. Among them, the comprehensive anomalies of Diaoquan-Xiaoyan and Tainashui are ore-induced anomalies.

This area is adjacent to Lion (county) low-temperature hydrothermal gold deposit and skarn copper, zinc and gold deposit prediction area.

Cambrian-Ordovician carbonate strata are widely distributed in the northern and eastern margins of Tadi volcanic basin, and faults are developed, which is beneficial to hydrothermal metasomatism and the formation of metallogenic series of skarn deposits. All these indicate that the deep and surrounding areas of Tadi volcanic basin have good metallogenic conditions and prospecting prospects.

(2) Yanggao-Tianzhen area

This area is a part of the Au-Pb-Zn polymetallic metallogenic belt between Yinshan secondary fault block and Taihang secondary fault block in northern China, and it is connected with Au-Pb-Zn prediction areas in Lion and Zhangjiakou areas in Hebei province in the east. In geological structural units, two secondary structural units, Yinshan and Taihang secondary fault block, run vertically from north to south, with developed fault structures, frequent activities of acid intrusive rocks and subvolcanic magma in Indosinian and Yanshanian periods, and extensive polymetallic mineralization.

The basement fault, its derivative fault and * * yoke fault of the east-west Datong-Yangyuan Si-Mg layer run through the whole area, and together with Shangyi-Chicheng and Zhangjiakou faults in northern Hebei Province, they form the boundary between Yinshan secondary fault block and Taihang secondary fault block. The NW-trending Tanghe fault (including the Wang Jiabao and Zhongzhuangbao Si-Mg faults) overlaps with the EW-trending Yanggao-Tianzhen fault, which is an area with frequent magmatic intrusions in Indosinian and Yanshanian periods.

Different from the south-central part of northeast Shanxi, this area is not only the overlapping area of east-west and northwest tectonic-magmatic activities, but also the overlapping area of Indosinian and Yanshan mineralization, which is a favorable factor that other prediction areas do not have.

Jidong area is also a polymetallic ore concentration area, which is in the same structural unit as Yanggao-Tianzhen prospecting breakthrough. That is, on both sides of the boundary between Yinshan secondary fault block and Taihang secondary fault block, most gold, lead and zinc deposits are controlled by the same east-west deep fault zone. Zhangjiakou-Xuanhua area is one of the famous gold concentration areas in the northern margin of North China fault block, and there are many gold deposits (spots) 100, including two large ones in Xiaoyingpan and Dongping, six medium ones, and many small ones in100. Because these gold mines are mostly distributed in the triangle of Xuanhua-Chongli-Chicheng, they are called the "Golden Triangle" of Hebei Province. Xiaoyingpan gold deposit is one of the large-scale time-dependent gold deposits in Hebei Province. Up to now, more than 200 gold-bearing quartz veins have been discovered, and the surrounding rocks are deep metamorphic rocks of Jining Group. The metallogenic age and Baoziwan gold deposit belong to Indosinian-Yanshan period.

Between Shangyi-Fengning-Longhua fault and Kangbao-Weichang fault in Hebei Province, there are Caijiaying gold-lead-zinc mine, Niuquan-Yingfangzi silver-lead-zinc mine, Pengjiagou silver mine, volcanic-subvolcanic Xiaoqianying silver mine and Beichagoumen lead-zinc silver mine in the southern margin of Yinshan secondary fault block. There are magmatic hydrothermal silver-bearing lead-zinc deposits in Yinfang, Fengning and Caijiaying in Zhangbei. The volcanic mechanism at the intersection of faults is a favorable metallogenic structure, and the middle and small subvolcanic rocks in the late Yanshan period have obvious relationship with mineralization.

The regional geological background, structural unit affiliation, metallogenic age, metallogenic regularity, tectonic-magmatic ore-controlling factors and metallogenic series combination of these ore-concentrated areas and typical deposits are the same as those in Yanggao-Tianzhen area. However, the known deposit abundance is much inferior, indicating that there is still a lot of prospecting space in this area.

(3) Yixingzhai-Santaishan, Yaoyu-Lingyunkou-Zhongmugou areas in Fan Shi.

Yixingzhai gold deposit is the only known large-scale gold deposit in northeast Shanxi, which belongs to the time-related vein type gold deposit with subvolcanic magmatic hydrothermal origin. It was formed in the NW Yanshanian tectonic magmatic active zone from Wutai Mountain to Hengshan Tailong, and it belongs to the same geological tectonic background as the Chafang Iron Mine, Houyu Copper-Molybdenum Mine and Gengzhuang Gold-Silver Mine. In space and time, it is closely related to the mesophilic and hydrothermal activities in the late Yanshanian acid-acid hypabyssal and ultrahypabyssal volcanic magmatism. Up to now, although more than half of industrial reserve has been mined, in order to find a new breakthrough, it is necessary to further study and analyze the genetic type, metallogenic series and genetic combination of this gold deposit.

1. In addition to gold and silver deposits, there are also large molybdenum ore bodies in Yixingzhai mining area.

Such as mo beside pulse 7? Ore body 1 is located in different boreholes of exploration lines 0, 1 and 3, with a thickness of 17. 18 ~ 95.00 m and a tungsten (molybdenum) content of 0.04% ~ 0. 16% (Table 6-) W (Mo) content in borehole ZK 19 is 0.3033% at the highest in the range of 241.27 ~ 244.64m; From 256.30 to 260.6 1 m, the highest content of w(Mo) is 0.3879%; From 275.29 to 29 1.59 m, the highest content of w(Mo) is 0.8150%; The maximum content of w(Mo) is between 303.24~330.80 m, which is1.1032%; The borehole ZK 18 is 233.57~237.57 m, and the maximum w(Mo) content is 0.28%. 249.2 1 ~ 305.43 m, and the highest content of w(Mo) is 2. 1696%. However, these molybdenum ore bodies have been completely destroyed within the scope of gold mining.

Table 6-3 Mo of No.7 gold vein in Yixingzhai gold mining area? Elements of 1 orebody

According to the geological characteristics of typical porphyry copper or molybdenum deposits at home and abroad, these porphyry deposits seem to be consistent with orogenic belts on a global scale; This remarkable relationship is most obvious in Mesozoic and Cenozoic porphyry deposits around the Pacific Ocean. In orogenic belts, porphyry deposits occur in island arcs and active continental margins.

Regionally, porphyry deposits are mostly related to regional structures and controlled by regional deep and large fault structures. The emplacement of ore-forming magma is controlled by fault structures, especially at the intersection of faults in different directions. Strong fracture zone is a zone with high permeability, which is conducive to the emplacement of ore-forming rocks and the accumulation and precipitation of ore-forming materials, so it is a particularly important ore-controlling structure.

The basic characteristics of porphyry deposits are as follows: ① Porphyry deposits are generally located in or near intermediate-acid intrusions. Ore-hosting rocks are related to long-time intrusions in space and genesis. At least one intrusive facies in the complex is porphyry. ② The intrusions related to porphyry deposits are shallow, generally less than 4 km deep, and most of them are 1 ~ 2 km. The ore-forming rock mass can be surrounded by any kind of rock (layer), but it must be the surrounding rock with a large number of cracks. These faults are one of the important factors controlling mineralization. (3) Ore types are mainly distributed in rock mass, and most of them are fine (reticulate) veins in surrounding rock. Large-scale vein mineralization far away from ore-forming rock mass has appeared one after another. ④ Some porphyry deposits also have Pb-Zn-Ag satellite deposits or mineralization points, medium-low temperature heavy sand mineral anomalies and geochemical anomalies of medium-low temperature metallogenic indicator elements, indicating that the deposits are horizontally zoned. It is related to skarn deposits, cryptoexplosive breccia deposits and fracture-filled metasomatic deposits. ⑤ Primary ore is composed of altered rocks containing sulfide minerals veinlets and disseminated bodies, and is rich in sulfide minerals such as pyrite. Supergene minerals are restricted by natural environmental conditions, and are generally divided into different deep (thick) leaching zones, oxidized ore zones, mixed ore zones, secondary sulfide-enriched zones and primary ore zones from top to bottom. ⑥ Intrusions and surrounding rocks related to porphyry deposits generally have hydrothermal alteration caused by hydrothermal filling and metasomatism to varying degrees, forming a stable altered mineral assemblage zoning, that is, alteration zoning. ⑦ The metallogenic age of porphyry deposits is dominated by Mesozoic and Cenozoic. ⑧ Porphyry deposits are based on magmatic-hydrothermal genetic model. Ore-forming materials come from time-related and genesis-related intrusions, and multi-stage hydrothermal system develops in any kind of surrounding rock inside and above the genesis-related intrusions. This hypothesis holds that ore-forming magma intrudes into the upper crust and crystallizes along the surrounding rocks and the bottom edge of magma chamber. With the supersaturation of volatiles in magma, ore metals are strongly separated from many other components and then enter the volatile phase, that is, magma is rich in a large number of volatiles and high concentrations of ore-forming elements during crystallization. When the increased fluid pressure exceeds the static pressure and the tensile strength of overlying rocks, these rocks will rupture, so that hot water gas and liquid will flow out quickly and enter the new expansion space for precipitation and mineralization. These open spaces include cracks and cryptoexplosive breccia systems in the upper part of rock mass and surrounding rock.

Comparing the geological characteristics of these typical porphyry deposits, the geological characteristics of Yixingzhai gold (molybdenum) deposit and Houyu copper-molybdenum deposit are basically the same except for the different regional geological structural backgrounds. Yixingzhai gold (molybdenum) deposit occurs on the concealed ore-forming rock mass (see Figure 4-9), and Houyu copper, molybdenum and gold bodies occur in the ore-forming rock mass and its upper surrounding rock respectively. With the deepening of the understanding of the genetic types of ore deposits, different evaluations of metallogenic prospects will change.

2. Fully understand the horizontal zoning phenomenon of Yixingzhai gold (molybdenum) deposit and carry out peripheral prospecting.

According to the distribution trend of geochemical anomalies of gold and silver elements and anomalies of heavy sand minerals in Yixingzhai-Santailing area of Yingxian County, Fan Shi, the anomaly trend in Yixingzhai-Santailing area is northwest; The abnormal trend of Santiaoling-Yaoyu-Hunyuan Woyangchang and alfalfa is close to the north-south direction; The abnormal trend between Hunyuan Alfalfa-Yindongwa and Baiyinsi-Xiao Mu Gully turned northeast. The gold mineralization of Yixingzhai (Mo) gold deposit, Santiaoling and Yaoyu, and the lead, zinc and silver mineralization of Baiyinsi and Yindong 30 are included as a whole. With the gradual elevation of the terrain, vertical zoning and horizontal zoning of different mineralization element combinations appear respectively. Therefore, the metallogenic series combination of Yixingzhai gold (molybdenum) deposit can extend to Lingyunkou area in Hunyuan along the NNW direction through Sandaoling and Yaoyu in Yingxian County.

Based on the theoretical analysis of the genesis and zoning of gold (molybdenum) deposits in Yixingzhai, we should pay attention to the * * * combination of gold, copper and molybdenum deposits in the future prospecting work. According to many examples of foreign deposits, porphyry molybdenum deposits have an important feature, that is, they are closely related to porphyry copper deposits, and most of them are related to or associated with * * *, belonging to two members of the same metallogenic series. According to the average grade and relative content of copper and molybdenum in ores, Carten( 1993) classifies porphyry deposits into four types: ① porphyry copper deposits. Copper is almost the only recyclable metal, and the average grade of molybdenum is ≤0.02%. ② Porphyry Cu-Mo deposit. As the main metal or crude product of Cu, 0.02%≤w(Mo)≤0.05%. ③ Porphyry molybdenum-copper deposit. As a metal by-product, Cu (Mo) > 0.05%. ④ Porphyry molybdenum deposit. Copper is almost unrecoverable, and tungsten (molybdenum) is more than 0.05%. When evaluating Yixingzhai gold (molybdenum) deposit, all geological exploration projects have not been systematically analyzed from the perspective of gold and copper. Therefore, it is still a practical and theoretical problem that needs to be treated cautiously whether there will be porphyry copper-molybdenum deposits in Yixingzhai and porphyry gold deposits in Houyu copper-molybdenum deposits.

Based on the analysis of metallogenic regularity and zoning phenomenon of Yixingzhai gold (molybdenum) deposit, it is suggested that Sandaoling, Yaoyu, Yingxian and Hunyuan Lingyunkou-Zhongmugou areas should be included in the comprehensive geological exploration scope.

(4) Daixian Tanshang and Wutai Haoditang areas.

As mentioned above, there are 8 cryptoexplosive breccia tubes around the shallow intrusions and subvolcanic rocks exposed in Tanshang area of Daixian county, 7 cryptoexplosive breccia tubes in Haoditang area of Wutai county, 4 cryptoexplosive breccia tubes in Yixingzhai mining area and 4 cryptoexplosive breccia tubes in Hunyuan Chakou volcanic fault basin. These cryptoexplosive breccia tubes are clustered and concentrated in a small area, pyrite is strongly altered, and copper, molybdenum, lead, zinc and silver are generally mineralized to varying degrees. In order to strengthen the deep prospecting work, high-precision geophysical exploration should be taken as a breakthrough to find the hidden ore-forming rock mass and related deposits at the root of the cryptoexplosive breccia tube in the areas where these cryptoexplosive breccia tubes are distributed in clusters (Figure 6-4 and Figure 6-5).

Figure 6-5 Schematic diagram of porphyry copper mine system in andesite volcanic root zone.

(According to Zhou Ping 20 10)

It indicates the possible relationship between mineralization zoning and porphyry copper deposits and skarn, stratabound recumbent, veined and epithermal precious metal deposits.

Figure 6-5 is the metallogenic model established by Sinelair(2006) according to the geological characteristics of copper deposits in Chile. This model, which is the same as the relationship between trunk and root, inspires us in understanding. In areas where cryptoexplosive breccia tubes are concentrated, especially in areas where multiple cryptoexplosive breccia tubes are concentrated, modern scientific and technological means are used to search for hidden rock masses at the roots and associated magmatic hydrothermal polymetallic deposits.

Figure 6-5 shows the metallogenic model of concealed porphyry copper deposits related to small subvolcanic porphyry intrusions, which comprehensively reflects the connotation of magmatic hydrothermal metallogenic system. The main types and ore-forming sites of deposits related to large hydrothermal systems are skarn type, metasomatic (layered) zinc, lead, silver, gold deposits, various base metal and precious metal vein deposits and cryptoexplosive breccia ore-hosting deposits.

It is assumed that magma intrusion is located in the upper crust, and crystallization occurs along the surrounding rock and the bottom margin of magma chamber. With the supersaturation of volatile matter in magma caused by crystallization, ore metals and many other components are strongly separated into volatile phases. When the increased fluid pressure exceeds the hydrostatic pressure or the tensile strength of overlying rocks, cryptoexplosive breccia is formed, and at the same time, hydrothermal fluid quickly flows out and enters the newly generated open space for precipitation and mineralization. Although these open spaces include fractures and breccia systems in rock mass and surrounding rock, they are located in different parts of the space relative to ore-forming rock mass. Therefore, the vertical and horizontal zoning of the deposit is formed. Whether there is a subvolcanic mechanism as shown in Figure 6-5 and a metallogenic model of Mesozoic subvolcanic magmatic hydrothermal polymetallic deposits in Northeast Shanxi as shown in Figure 5- 1 will be one of the important issues that need to be seriously demonstrated vertically in the future comprehensive exploration work.

(5) In the horizontal direction of the deposit, pay attention to the overlapping areas of different metallogenic geological structural factors and different metallogenic stages.

For example, the Tanghe tectonic-magmatic active metallogenic belt is not only the largest NW-trending arc Mesozoic tectonic-magmatic active metallogenic belt in northeast Shanxi, but also has three overlapping parts with other tectonic-magmatic active metallogenic belts, which should be a more favorable metallogenic site. One node is the overlapping part of the north and the nearly east-west Gao Xiangyang-Tianzhen Indosinian-Yanshan tectonic-magmatic active metallogenic belt; The second node is located in the north-central part of the Tanghe tectonic-magmatic metallogenic belt. The main host rocks are magnetite quartzite and mica quartz schist of Jingangku Formation of Wutai Group in the north of Lingqiu, and it is located in the overlapping part of the east-west regional greenstone gold deposit and the abnormal belt. The third node is located in the southeast section of the Tanghe tectonic-magmatic metallogenic belt and the overlapping part of the Huang Qi-Wulonggou giant Yanshanian tectonic-magmatic metallogenic belt in northeast Hebei. Theoretically, these parts should be conducive to mineralization.