First, further strengthen the metallogenic prediction, prospecting and resource exploration of key metallogenic belts.
Modern geological prospecting can generally be divided into three stages: theoretical prediction research, implementation of scientific and technological methods and engineering verification. In the stage of theoretical prediction, we should solve the problem of favorable metallogenic areas and types, that is, solve the problem of prospecting there; The implementation of scientific and technological methods should solve the deployment of land, material, chemistry, remote and other methods and means, and further delineate the target area; Target verification is to solve the problem of deposit location through engineering (pit and drilling) verification. These three stages should run through geological investigation and research. This project should belong to the theoretical prediction stage.
According to the research of this project, five favorable prospecting zones or areas have been preliminarily delineated nationwide, among which three areas are key prediction areas. The following are only suggestions on the deployment and development of the next specific prospecting work in these five areas.
(1) Strengthen the prospecting method and orientation of Jinchuan and its surrounding metallogenic system.
1. Strengthen the study of prospecting methods in Jinchuan and its periphery.
(1) Geological exploration method
The geological characteristics of the deposit can also be used as a prospecting indicator. For example, the diagenetic and metallogenic era is Proterozoic, which naturally leads to the conclusion that the stratigraphic indicator for prospecting is the Precambrian distribution area, and the structural indicator is mainly the structural distribution direction. Signs of ultrabasic rocks: first, the rock mass is a compound rock mass formed by multiple intrusions; Secondly, the rock mass belongs to dunite-lherzolite-plagioclase lherzolite type (or there are lithofacies zones of this type in the rock mass); Third, the rock mass is highly differentiated. The mineral sign is that ultrabasic rocks contain plagioclase, olivine and so on. The combination of metal sulfide is pyrrhotite-pyrite-nickel pyrite-chalcopyrite, in which the appearance of nickel sulfide is the best sign, and it is also beneficial when the content of pyrrhotite is greater than that of pyrite. The petrochemical symbol is m/? < 6, the rock is highly alkaline.
In addition, Jinchuan rock mass is in intrusive contact with its surrounding rock, and the surrounding rock near the contact surface has contact metamorphism, which is also a prospecting indicator worthy of attention. For example, there are olivine fossilization, serpentine, tremolite and diopside in marble (especially metal sulfide mineralization at the same time), and strong biotite and chloritization in migmatite. Because there are contact metasomatic copper-nickel ore bodies in this area, metamorphism of ultrabasic rocks at the edge of rock mass is also an important prospecting indicator, which should be used in combination with geochemical indicators (content and distribution characteristics of ore-forming elements and trace elements, etc.). ).
The oxidation zones of ore bodies and mineralized bodies contain secondary minerals such as limonite, hematite, malachite, azurite, chalcedony, bischofite and jarosite, which are bright colors such as brown, red, blue, green and yellow, and are important prospecting indicators.
(2) Geophysical exploration
A. looking for geophysical signs of ultrabasic rocks
The distinguishing marks between ultrabasic rock anomalies and non-ultrabasic rock anomalies mainly include the following points:
1) Anomaly size: Aeromagnetic anomalies caused by ultrabasic rocks are usually not very large. The smallest one is only reflected on one measuring line. The largest is rarely more than 5 ~ 6 kilometers long and 2 kilometers wide.
2) Abnormal plane shape: ultrabasic rocks are mostly banded, and a few are nearly round with regular shape.
3) Abnormal strength: mostly high, reaching 300~700 nT. A few are weak, ranging from 50 to 200 NT dollars. The abnormal strength is closely related to the buried depth of rock mass. The abnormal strength of exposed rock mass is high, and the abnormal strength of concealed rock mass is weak. In addition, the alteration of ultrabasic rocks is also a factor affecting the abnormal strength. If significant iron removal occurs during alteration, it may lead to the weakening of rock magnetism.
4) Curve shape: ultrabasic rock anomalies are mostly unimodal in profile, with sharp shape and large gradient on both wings, but there are many factors affecting the curve shape. The abnormal curve of exposed rock mass is steep, while that of concealed rock mass is slow. The greater the buried depth, the smaller the peak value and gradient.
5) In addition, the ring structure of remote sensing image is also an indirect sign of concealed rock mass.
B. Geophysical indexes for evaluating ore-bearing property of rock mass
According to the statistical results of physical parameters, the rocks and minerals in Longshoushan area can be divided into three types: the first type of physical body belongs to strong magnetism, low resistance, high polarization and high density, and the corresponding geological body is copper-nickel sulfide ore in the mining area; The second type is physical bodies with strong magnetism, low resistivity, moderate polarization and medium density, and the corresponding geological bodies are ultrabasic rocks; The third kind is the physical body with weak magnetism, low resistivity, low polarization and medium density, and the corresponding geological body is the surrounding rock of ultrabasic rock body.
Compared with the second and third kinds of physical objects (rock mass and its surrounding rocks), the first kind has the highest magnetism, density and polarizability. Therefore, in principle, magnetic, gravity and electrical (ηs) anomalies can be used as indicators to evaluate the ore-bearing property of rock mass. However, due to the limitation of geological and geophysical conditions and the multi-solution of geophysical exploration results, these indicators can only play a good role in prospecting if they have certain objective conditions and are combined with geological and geochemical indicators. The most important conditions are: there are obvious physical differences between the ore body and the surrounding rock, and the ore body is large enough, and its buried depth is not beyond the range that can be detected by relevant methods. Therefore, the main prospecting criteria of this kind of deposits are: ① strong geomagnetic and aeromagnetic anomalies (△ Zmax = 1000 ~ 3000 nt, △ Tmax = 4 ~ 700 nt) with regular shape; ② The apparent polarizability of 6% ~ 2% is abnormal, and its shape, occurrence and range are consistent with magnetic anomalies; ③ The weak Bouguer anomaly of gravity, that is, the local field of about 0.6 ~ 0.8 mg/L, can be obtained; ④ The ore body is dominated by remanence, Jr/ji ≥1; Ultrabasic rocks and surrounding rocks are mainly magnetic, Jr/Ji < 1.
(3) Geochemical prospecting
By comparing the geochemical characteristics of strata, intrusive rocks and deposits in regional geochemical fields, the indicator elements of Cu-Ni magmatic deposits related to ultrabasic rocks are determined to find ultrabasic rocks. Geochemical indexes for judging the ore-bearing property of rock mass are as follows.
A. looking for geochemical indicators of ultrabasic rocks
The Ni-Co high background zone on geochemical map can indicate the distribution range of ultrabasic rock zones.
2) The local anomalies in the Ni-Co high background zone often correspond to ultrabasic rocks. For example, the comprehensive anomalies of chromium, nickel, copper and cobalt are more conducive to finding rock masses.
3) When 3) geochemical anomalies of 3)Cr, Ni, Cu and Co correspond to aeromagnetic anomalies, it indicates that ultrabasic rocks may exist, which is also a sign to judge the nature of aeromagnetic anomalies.
4) The geochemical anomalies of Cr, Ni, Cu and Co caused by ultrabasic rock mass can be found by soil survey when the thickness of Quaternary caprock is not large (< 20m).
5) When the above indicator elements are abnormal along the fault structure, ultrabasic rocks may exist in the adjacent sections of the structural belt.
6) Due to the high content of copper and gold in ultrabasic rocks in this area, the anomaly of copper and gold is also a sign of the discovery of ultrabasic rocks. However, the geological factors affecting the distribution of copper and gold are complex and need to be comprehensively analyzed in combination with the above other indicators.
B. geochemical indicators for judging the ore-bearing property of rock mass
1) The elements of Ni, Cu and Co are high in content, large in dispersion and obviously positively correlated with each other, which is the geochemical characteristic of Cu-Ni ultrabasic rocks.
2) The rock mass has high abundance of S and high contents of NiS, CuS and CoS. There is a positive correlation between Ni and S, which is an important symbol to distinguish between ore-bearing and non-ore-bearing rock masses.
3) By studying the content, distribution, dispersion and correlation of Cr, Ni, Cu, Co, S, V, Ti and other elements, the basic and ultrabasic rocks containing Ni, Cr or V-Ti magnetite can be distinguished.
2. Strengthen the positioning research of Jinchuan and its peripheral metallogenic system.
There are many basic-ultrabasic rocks around Jinchuan in Longshoushan uplift belt 100 km. These rock masses are all in the same tectonic background, and their lithology, surrounding rock and rock geochemical characteristics are the same or very similar. The research results of constant elements show that their causes are also related. Both the determination of the age and the strata in which it is located indicate that Jinchuan and its surrounding rock masses may be the products of the same period. We think that these rocks and Jinchuan rocks were formed at the same time or of the same origin, belonging to the same metallogenic system, which contributed to the mineralization of Jinchuan super-large nickel-copper-platinum deposit, and may be low-gravity high-magnesium ferrosilicate magma without ore during early melting and early emplacement.
The reason why Jinchuan small rock mass becomes a large mine is probably related to its peripheral basic-ultrabasic rock mass. Judging from the metallogenic regularity of magmatic deposits, magmatic activity is an important condition for mineralization, especially multi-stage magmatic activity can cause magmatic differentiation and mineralization; It is an indisputable fact that Jinchuan is a super-large deposit formed by deep melting and multi-stage infiltration We believe that Jinchuan super-large deposit can be formed, there must be a huge metallogenic enrichment center in the deep, and there must be a long-term stable supply of energy and metallogenic materials, which should be related to the continuous magmatic activity in a certain range. At present, Jinchuan rock mass and its surrounding rock mass are small in scale, but widely distributed, extending about 100 km from east to west along Longshoushan uplift belt, and the influence range of magmatic activity is about 100 km. Therefore, it is speculated that the next step in the search for Jinchuan-type super-large nickel-copper-platinum deposit should be to find a new metallogenic system at a distance of 0/00 km from Jinchuan/Kloc.
Over the years, many geologists at home and abroad have done a lot of work in the periphery of Jinchuan, trying to learn from foreign prospecting experience to find large-scale nickel-copper-platinum deposits near Jinchuan, but all failed. This seems to confirm that the small rock mass around Jinchuan is itself an ore-free magma with early melting and early emplacement.
Drawing lessons from Jinchuan metallogenic model and searching for Jinchuan-type super-large nickel-copper-platinum sulfide deposit metallogenic system along the ancient continental margin of North China is the guiding ideology of the next prospecting work.
This project has collected a lot of geological data and invested a lot of geological work. In the western extension of Longshoushan rock belt, there are many small rock bodies exposed in Gao Tai-Linze area, 250 km away from Jinchuan rock body. The lithology and rock geochemical characteristics of 109- 1 and 109-2 basic-ultrabasic rocks are compared with Jinchuan and its surrounding rocks, and it is considered that 109-2 rock mass is similar to Jinchuan and its surrounding rocks in many ways and belongs to the same type of ultrabasic rocks. Coincidentally, there are also rock bodies in Yejili area, which is 100 km away from Jinchuan rock body in Beidashan rock belt. Compared with Jinchuan and its surrounding rocks, Yejili pluton belongs to the same type of ultrabasic pluton in lithology and rock geochemistry. We speculate that these two areas are probably new metallogenic systems similar to Jinchuan super-large nickel-copper-platinum sulfide deposit, and 109-2 rock mass and Yejili rock mass are members of these two metallogenic systems respectively. Searching for super-large nickel-copper-platinum sulfide deposits is to find a new metallogenic system in situ, so these two areas are the key areas for our next prospecting work.
(2) Strengthen the exploration of nickel-rich copper ore and platinum group resources in the border area between Gansu and New Zealand.
In Beishan area (9100 ′ ~ 97 00 ′; North latitude is 40 30' ~ 42 00'. According to the existing exploration results and the research of this project, mafic-ultramafic rocks are well developed, with 96 places according to preliminary statistics. As far as the occurrence of rock mass is concerned, there are two types: small rock mass and bedrock (or rock basin), and the age is mainly from the end of Early Permian to the late Permian, followed by Middle-Neoproterozoic. Among them, most of the small rock masses are steep and the bedrock (or basin) is gently inclined. According to the existing exploration data, although the scale of deposits found in this area is large, nickel and copper deposits are poor. In view of this situation and the results of metallogenic prediction and analysis of this project, the future prospecting work in this area should focus on two types of metallogenic rock bodies (namely, steep small rock bodies and gently inclined rock bodies or rock basins and slabs), and pay attention to finding rich ore bodies and platinum group resources. Specific should also pay attention to the following aspects.
1) On the basis of fully considering the regional metallogenic geological facts of 900 km mafic-ultramafic rock belt in the "Pobei" area of Ruoqiang-Heishan-Mazongshan area in the northern margin of Tarim block, we should also pay attention to the investigation of Heishan, Datoushan, Mazongshan and slope rocks.
2) According to the preliminary study of this project, the existing metallogenic facts and conditions in this area show two dominant types of regional mineralization, namely, the meso-Neoproterozoic steep small rock type similar to Jinchuan type and the gently inclined rock basin or bedrock type under the background of Permian large igneous province. Looking for these two types of deposits should be the future prospecting direction.
3) Strengthen the evaluation of platinum group resources in nickel-poor copper mines. In addition to field basic geological work and systematic sampling, the evaluation should also strengthen the research of indoor testing methods to continuously improve the repeatability and accuracy of test results.
4) Based on the fact that this area is mostly Gobi desert, we should pay attention to the application of geophysical (gravity and magnetic) and remote sensing interpretation methods in regional prospecting.
(3) Resource evaluation and exploration of intrusive rock deposits related to Emeishan basalt in the southwest margin of Yangtze landmass.
According to the research of this project, in the Lijiang-Midu-Jinping Ni-Cu-Pt deposit metallogenic prediction area in the southwest margin of the Yangtze block, the future regional resource evaluation, prospecting and exploration should focus on the intrusive rock deposits related to Emei basalt, and pay attention to the following aspects.
(1) Strengthen basic geology and regional adjustment of key road sections.
The above research results show that mafic-ultramafic rocks are developed in Yongsheng-Lijiang area, especially along the Jinsha River, which is in the same period as Permian basalt. However, in the past, the basic geological work in this area was limited to the regional scale of1:200,000. At present, the regional distribution of intrusions is not clear, and it is necessary to carry out1:50,000 geological survey to find out. This is very important for finding Ni-Cu-Pt magmatic sulfide deposits.
(2) Pay attention to the study of picrite in basalt development zone.
According to the geological comparison data with Norilsk mining area, it is necessary to strengthen the research on the spatial distribution and genetic relationship of picrite in basalt development area in the future prospecting work in this prediction area, because this research will provide more metallogenic information.
(3) Investigation of concealed rock mass in typical areas
In the prediction area, it is very important to study the Fe-Mg-Fe ore-forming rock mass. In addition to strengthening the study of the surface area, it is also very important to study the deep concealed rock mass. Most of the existing ore-forming rock bodies in the study area belong to small rock bodies with limited surface exposure. Therefore, it is necessary to explore the concealed rock mass and provide basis for the selection of prospecting target area. In addition, for mafic-ultramafic rock mass, due to its remarkable density performance and magnetic characteristics, it is also feasible to apply geophysical methods to deep geological research.
(4) Exploration of copper resources in copper-rich horizons.
From Mili-Baoping in Yongsheng to Tuanshan in Binchuan, that is, along the east and west sides of Jinsha River fault, the existing data and the metallogenic facts of several deposits (points) show that there is a copper-rich layer with obviously increased copper abundance at the top of Permian basalt, which has great potential for further prospecting or exploration along this belt.
(5) Attention should be paid to the metallogenic types of Ni-Cu-Pt magmatic sulfide deposits.
In this prediction area and Emeishan igneous province, the discovered types of Ni-Cu-Pt magmatic sulfide deposits are cylindrical (Baimazhai), lenticular small rock mass and layered intrusion (Jinbaoshan). Based on the study of Lijiang, Yongsheng and Binchuan in this project and the comparison with similar deposits in foreign igneous provinces, it is considered that it is very necessary to find layered intrusive deposits in these areas, and it is also the key direction of future work.
(6) Strengthen the study of geochemical profile in the basalt development area of Emei Mountain, and pay special attention to the change law of ore-forming elements such as Ni, Cu and PGE, that is, the change of enrichment and loss, especially the problem of loss horizon, because the research results in Norilsk area show that there is a certain relationship between mineralization and loss horizon.
(4) Strengthen the prospecting for nickel, copper and platinum resources in northern Guangxi and eastern North Tianshan.
The forest movement area in northern Guangxi and the Huangshan belt in the eastern part of northern Tianshan Mountain are two prospecting areas at another level predicted by this project. Although these two areas have carried out prospecting and exploration to varying degrees in the past, further prospecting research is still necessary.
The future work of Huangshan Belt should focus on finding platinum group resources and nickel-rich copper deposits.
In northern Guangxi, the previous work was mainly focused on Baotan area, but the work in the forest-moving area with good metallogenic conditions was relatively weak. Especially due to the geographical conditions at that time, the results of basic geological work could not meet the needs of further prospecting. In order to speed up the geological prospecting work in this area, we suggest setting up a geological survey project in Lindong area as soon as possible, and at the same time deploying1:50,000 regional survey work.
Second, continue to strengthen the research on the basic theory of prospecting and better guide prospecting.
Without theoretical guidance, prospecting will be blind. The discovery of some large-scale deposits in the world is more or less supported by related theoretical research, such as metallogenic background, theoretical analysis of plate structure and regional mineralization, metallogenic model, metallogenic series, etc. These theoretical research plays an important role in regional prospecting. As far as the Ni-Cu-Pt magmatic sulfide deposit studied in this project is concerned, the mineralization is directly related to mafic-ultramafic rocks. The research results of diagenetic process, regional distribution law, metallogenic process, metallogenic mechanism and metallogenic model of mafic rocks will still be an important basis for finding Ni-Cu-Pt magmatic sulfide deposits.
The regional metallogeny of Ni-Cu-Pt magmatic sulfide deposits has been studied by predecessors (Tang Zhongli, 2004; Li, 1996), the preliminary study shows that the genesis of Ni-Cu-Pt magmatic sulfide deposits is special, mainly magmatic detachment mineralization, but also hydrothermal superposition mineralization (Tang Zhongli, 1989), but in general, this kind of deposit is still a type of deposit that depends on magmatic detachment. The same is true abroad. The known Ni-Cu-Pt magmatic sulfide deposits in China are all products of magmatic detachment mineralization (Tang Zhongli, Ren Duanjin, etc. , 1989). Therefore, the regional metallogenic research of this kind of deposits mainly focuses on the metallogenic background and the stage of metallogenic geological evolution.
The preliminary study shows that there are 15 metallogenic series of Ni-Cu-Pt magmatic sulfide deposits in China, which are mainly concentrated in the Middle Neoproterozoic and Late Paleozoic Hercynian. In terms of regional distribution, these metallogenic series are mainly concentrated in the peripheral areas of North China, Tarim, Yangtze and Qilian, Tianshan, Junggar and Kunlun orogenic belts. Strengthening the study of these metallogenic series and further finding out their temporal and spatial distribution and formation background will play an important role in the future regional prospecting and exploration, especially the resource exploration and deployment in the western region.
Thirdly, strengthen the theoretical model of prospecting.
Since sudbury was discovered by 18 in 1980s, the exploration and development of Ni-Cu-Pt magmatic sulfide deposits have been going on for more than a century, and hundreds of such deposits have been discovered all over the world. Looking back, the prediction and prospecting of these deposits generally go through three stages, namely, geological theory prediction stage, scientific and technological method implementation stage and engineering verification stage. In the theoretical research stage, the theoretical research and summary of existing metallogenic models are very beneficial to the discovery of new deposits, such as the metallogenic model of Norilˊsk-Talnakh belt in Siberian dark rock series related to continental overflow basalt and the metallogenic model of small rock mass in China, which have played an active role in early prediction and prospecting. According to the research of this project in China, the in-depth theoretical study of these two types of metallogenic models will still be the main content of prospecting work in the future.
4. Looking for the most potential deposit type.
Magmatic sulfide deposits related to ultramafic rocks and mafic rocks can be divided into four types according to the main ore-forming element combination and enrichment concentration:
1) Co-and Pt-bearing deposits dominated by nickel and copper;
2) Nickel-based deposits containing copper, cobalt and platinum;
3) Nickel and copper deposits dominated by platinum group elements;
4) Copper and zinc deposits. Among them, type 4) deposits are rarely found at present, only reported in China and Finland. The most famous example is the Delny deposit in Qinghai, China.
Tang Zhongli (1995) classified Ni-Cu-Pt magmatic sulfide superlarge deposits into five types:
1) Proterozoic syenite-gabbro deposit related to ancient crater (sudbury);
2) Small intrusive deposits related to continental margin cracking after Proterozoic (Jinchuan and Woyisai Bay);
3) Phanerozoic intrusive deposits related to continental rift, equivalent to overflow basalt (Norilsk-Thallner belt);
4) Komati-related deposits in Archean greenstone belt (agnew in western Australia and Darkis Mountain in Thompson Kanbar);
5) Sulfide and platinum group deposits in the Paleoproterozoic continental layered intrusive complex (Bushveld et al.).
According to the research results of this project, the most potential deposit types in China are small intrusive deposits related to continental margin cracking and orogenic belt interior, and deposits related to continental overflow basalt intrusion, which are also the types that should be paid special attention to in future prospecting. As far as the combination types of ore-forming elements are concerned, the emphasis should be placed on the first three categories.
Five, strengthen the research and prospecting in the new area
The so-called new area refers to areas that have not been investigated or studied in the past, such as the periphery of North China ancient land and Yangzi ancient land and the outer mountainous areas, the northeastern margin of Tarim and the junction of Altai and Junggar, the northern, western and southern margins of Tarim and the surrounding areas of Qaidam, and the contact zones of orogenic belts in different periods. Among the key prospecting targets predicted in this project, Lijiang-Jinping area and Beishan area at the junction of Gan Xin belong to the new area, so these two areas should be strengthened first in the next prospecting work.