1. Identify and restore the whole porphyry alteration system through fault structure mapping.
Fig. 4- 1 schematic diagram of structural history of San Manuel-Kalamazoo porphyry copper deposit in the United States (quoted from J. D. Lowell et al.,1970; Zhao, 2008, revised edition)
Mineralization and alteration zoning is the most obvious and characteristic geological prospecting indicator of the deposit, which often plays a decisive role in finding out the existence of the deposit and determining the prospecting direction. The most famous example is the discovery of Kalamazoo porphyry copper deposit in southern Arizona, USA. J. D. Lowell et al. (1970) found standard zoning mineralization and alteration features in the deposit, but they found that only half of the identified alteration zones were left by faulting, so it was inferred that the other half might have been moved to other places. Through the study of fault strike and fault distance, the other half of it, namely San Manuel deposit, was found (Figure 4- 1). The alteration zones of these two deposits combine to form a complete ring. This example strongly illustrates the importance of mineralization and alteration marks, so it is widely used by prospectors. Although the identified alterations are not so complete and "standard", typical alterations such as potash alteration, sericitization alteration, argillization alteration and Pan Qing alteration are common, and they are all regarded as important signs to confirm the existence of ore bodies and guide exploration and deployment.
2. Identification of porphyry alteration system in shallow coverage area by remote sensing and geophysical means.
Identifying the surface porphyry system and delineating its range is the key to realize porphyry copper prospecting. Depending on remote sensing mapping and geophysical investigation, the scope of porphyry metallogenic system in concealed area can be effectively delineated. For example, the Coiavasi deposits in northern Chile include Rosario and Ushina porphyry copper systems. Through the observation of many old mines and mining waste piles in the period of 1978 ~ 1979, it is recognized that the alteration zone centered on Rosario deposit and the exposed edge of Wushna mineralization system have the characteristics of porphyry copper deposits, but the spatial distribution range of the whole porphyry system, especially Wushna mineralization system, is not clear due to the accumulation of thin debris on the surface and the coverage of Miocene gravel layer. In this case, more than 60 boreholes have been drilled, and the exploration effect is not significant. From 65438 to 0990, through satellite image interpretation and geophysical exploration, a circular induced polarization anomaly was circled on the Rosario porphyry copper system, which was characterized by high polarizability and low resistivity. At the same time, anomalies are also delineated in the exposed part of Ugina's leaching iron cap and the area 3km east covered by ignimbrite after mineralization (Figure 4-2). The induced polarization anomaly of Ugina is consistent with a circumferential magnetic anomaly with high circumferential magnetic force, which is a reflection of pyrite halo. Later, it was found that the resistivity less than10ω m was consistent with porphyry copper mineralization.
Figure 4-2 Rosario and Ushina porphyry copper systems in Coyawasi deposit in northern Chile (cited from R. L. Moore et al., 2002) show low resistivity anomalies of these two systems.
The ore holes in Uguina have reached the chalcocite enrichment zone, with a thickness of over 65,438+000m and an average copper content of over 65,438+0%. Borehole drilling is near the mineralized ignimbrite at the edge of bedrock outcrop, because it shows the favorable characteristics of leaching gauze, hematitization and vein interpenetration. At that time, it was found that the position of the hole was still outside the measurement range of induced polarization. After the induced polarization measurement is completed, the circled low-resistance band is interpreted as a reflection of the high-intensity development of veinlets. According to the results of induced polarization, it is determined that ignimbrite covers the whole range of the lower Ugina mineralization enrichment zone (Figure 4-2).
3. Establish the Karamay porphyry molybdenum deposit model to guide the continuous discovery of large molybdenum deposits in the metallogenic belt.
The successful application of the prospecting model of the climax porphyry molybdenum deposit in Colorado, USA, is a classic in the application of the prospecting model. Kelemex deposit is a super-large molybdenum mine mined in the early 20th century. It is believed that the deposit was formed by magmatic intrusion. Later, on the basis of detailed observation and in-depth study, geologists discovered many "abnormal" geological phenomena, which could not be satisfactorily explained by one-time intrusion theory. Based on the inspection and understanding of the old data and the comprehensive analysis of a large number of new data obtained from arduous and meticulous field observation, a prospecting model of multiple intrusions and mineralization of Clemax molybdenum mine is established, that is, Clemax rock plant is a composite rock mass composed of four main rock masses or main intrusion stages, and each rock mass or intrusion stage has a set of hydrothermal products related to its genesis and time. Every magmatic intrusion is accompanied by hydrothermal and mineralization activities, and each intrusion is more intense than the previous one. The model was later fully applied to find new molybdenum deposits in the Colorado metallogenic belt.
(1) The scientific explanation of the late ore-free stage products and their spatial and temporal positions led to the discovery of Henderson concealed molybdenum deposit.
There are many geological similarities between Hongshan area and Clemax area in Colorado metallogenic belt: there are network vein chalcocite mineralization; Both of them are close to tertiary strongly active faults; The ore bodies are all related to composite rock series with the same age and composition. All show multi-stage mineralization and alteration; The types of metal minerals are exactly the same. According to this, if favorable magma and structure are organically combined in time and space, it is possible to form Clemax-type multilayer molybdenum ore bodies in the deep part of Hongmanting area. In order to check the best molybdenum anomaly, on the basis of detailed analysis, a test borehole was drilled in the northwest of Redmont, exposing the edge of Henderson ore body. Through further work, at 1963, a large deposit with a depth of 9 14 ~ 1067 m was identified.
(2) A large molybdenum deposit in emmons Mountain was found by comparing the geological parameters of the deposit model.
The discovery of Henderson molybdenum deposit not only confirmed the correctness of Clemax molybdenum deposit model, but also enriched the content of the model. Using the newly improved model parameters, the discovery of the Emmonshan molybdenum deposit was effectively guided (J. A. Thomas, 1982).
There are many similarities between molybdenum deposits in Redmont area and Klaimax area, but there are also some important differences: the underlying rocks in Redmont area are fresh granite porphyries, while Klaimax area is typical porphyries; There are a lot of Precambrian metamorphic rocks in Clemax area, but there are relatively few such rocks in Redmount area. Compared with Henderson ore body, hydrothermal alteration zone is more complete. According to these differences, the existing deposit model is further revised.
Mount Emmons is located in the midwest of Colorado metallogenic belt. 1968 When evaluating the potential of non-ferrous metal resources in Redewell basin in the north of emmons, scattered rhyolite fragments containing molybdenite were found in the intrusive breccia tube, and the characteristics of this molybdenum-bearing rock were similar to those of Clemax-type molybdenite parent rock. During the period of 1970 ~ 1972,1borehole was drilled on the surface exposed rhyolitic breccia tube. As a result, a shallow non-ferrous metal mineralization zone and two deep low-grade molybdenum mineralization zones, namely upper and lower Redewell molybdenum ore bodies, were discovered. This discovery caught the attention of the company. They believe that many important parameters of discovered molybdenum deposits are similar to those of Clima porphyry molybdenum model, and it is hopeful to find more abundant and larger molybdenum deposits in this area. According to the comparison with Clemax and Henderson molybdenum deposits, a preliminary exploration plan is made. Among them, the extension of two molybdenum deposits in Redewell basin was delineated by drilling, and the distribution of altered rocks and time veins in Redewell basin was studied by detailed mapping of the rest areas of Mount Emmons. In the summer of 1976, after the initial plan was completed, a 750m-deep borehole was drilled to verify the target area in the periphery of Radle Di Basin in southern Shandong, emmons, and the 240m lower part of the borehole exposed the widely developed quartz-pyrite-molybdenite veinlets. After 1977 ~ 1978, the ore reserve of a large molybdenum deposit is 1. 56 × 108t, and the average grade of MoS2 is 0. 43%, buried depth of 420 meters.
(2) According to the metallogenic system and zoning model of the deposit, the deep metallogenic prediction is made.
The model from known to unknown analogizes the distribution and evolution of prospecting in deep space of metallogenic system, which improves the accuracy of deep prospecting prediction. The ore zoning model and structural control model established according to the known deposits are compared in the periphery to find the same type of deposits as the known deposits. This strategy has played an important role in the prospecting of the periphery of known deposits, and there are countless successful examples. Especially in recent years, with the great discovery of deep prospecting, people have gradually discovered that the recognized zoning pattern in the plane can basically be seen in the vertical direction. Therefore, it is of great practical significance to establish a spatial zoning model of ore deposits to guide ore prospecting.
Fig. 4-3 schematic diagram of continuous crustal mineralization of Archean vein gold deposits (quoted from D. I. Groves, 1993)
1. continuous crustal metallogenic model of Archean vein gold deposits
Since the late 1980s, many high-temperature (> 700℃) hydrothermal vein-type gold deposits have been found in Archean granulite facies rocks, and some low-temperature (< 180℃) hydrothermal vein-type gold deposits have also been found in sub-greenschist facies rocks. These discoveries have greatly changed people's previous understanding and revised some traditional concepts. Therefore, D.I. Groves of Australia (1993) put forward the "continuous crustal metallogenic model of Archean vein gold deposits" on the basis of summarizing previous studies (Figure 4-3). According to this model, vein gold deposits occur in metamorphic rocks from greenschist facies to granulite facies, and gold deposits can be formed continuously at different vertical depths, at least involving the crustal profile above 15km. Gold deposits in different metamorphic rocks belong to a group of continuous syngenetic deposit combinations, but these three types of gold deposits are different in metallogenic structural conditions, alteration combination of surrounding rocks, ore mineral combination and occurrence state of gold. The model does not reflect the vertical distribution of gold mineralization in the same mining area, but generally reflects the distribution characteristics of a series of gold deposits in the regional scope, thus unifying the evolution of metallogenic system with the evolution of deposits with different depths.
2. Vertical superposition model of porphyry copper metallogenic system and epithermal metallogenic system.
Figure 4-4 is a summary of the distribution of gold (copper) deposits in Chile by R.H. Sillitoe (1991). The essence of this model is that the high sulfide epithermal gold mineralization in Chile often develops on the porphyry mineralization centered on the intrusive body, while the low sulfide epithermal deposits and the deep contact metasomatic and vein gold deposits occur on the edge of porphyry mineralization (Figure 4-4). This model has been confirmed by the discovery of a large number of mineral deposits on the west coast of the Pacific Rim, and provides an important idea for the potential prediction of deep mineral resources. The model suggests that, on the one hand, attention should be paid to searching for porphyry copper (gold) deposits in the deep part of epithermal deposits, for example, super-large far-southeast porphyry copper deposits have been produced under the arsenic-bearing copper-gold bed in Lebanto, far southeast of the Philippines; On the other hand, it is necessary to pay attention to whether there is an associated relationship between epithermal deposits and porphyry copper deposits in the plane because of the different denudation degrees of the deposits in space.
Figure 4-4 Occurrence positions of several typical gold deposits in Chile relative to the idealized porphyry system (quoted from R. H. Sillitoe, 199 1).
3. Balkan-Carpathian porphyry copper model R. H. Sillitoe (1979) Based on the study of porphyry copper deposits in the former Yugoslavia and Romania, the Balkan-Carpathian porphyry copper model was put forward. This is a four-in-one composite deposit model, that is, the porphyry body is a porphyry copper deposit with 0.45% ~ 0.6% copper and a small amount of Au and Mo. There are skarn-type copper deposits at the contact between ore-bearing rocks and Mesozoic carbonate rocks, and the copper grade increases; There are metasomatic lead-zinc deposits in Mesozoic carbonate strata; There are massive sulfide deposits (black ore type) contemporaneous with porphyry bodies in the upper volcanic cover. The ore-bearing porphyries in this model are contemporaneous diorite, diorite, granodiorite, andesite and tuff. The surrounding rocks are Mesozoic carbonate rocks, and the alteration includes K-feldspar, sericitization, qingpanlithization and silicification. If the surrounding rocks are not carbonate rocks, skarn deposits will not be formed. At this time, the model is mainly composed of massive sulfide deposits in the upper volcanic rocks and porphyry copper deposits in the lower porphyry bodies (Figure 4-5).
Figure 4-5 Balkan model of porphyry copper deposit (quoted from R. H. Sillitoe,1979; Wang Zhitian et al., 1994)
Some European countries have discovered new porphyry copper deposits by using this model. For example, in the Boer copper mine area of Tymark, the former Yugoslav Republic of China, on the basis of studying the regional metallogenic model and exploring the relationship between porphyry copper ore and massive sulfide, the porphyry copper ore body in the deep part of the system was discovered under massive sulfide ore bodies (chalcopyrite, cerulete and pyrite) by using this model (Figure 4-6).
Figure 4-6 Profile Diagram of Boer Deposit in the Former Yugoslavia (quoted from Wang Zhitian et al., 1994)
Porphyry copper deposits were also found 600 meters below the massive sulfide copper deposit in Rexk, Hungary. This mine is an old mine of 1850. At that time, only minerals near the surface were mined. In 1959, after detailed surface mapping, it was decided to drill four deep holes, which showed that lead and zinc were abundant, and it was decided to drill 12 hole again, in which two large areas were drilled with medium and low grade copper deposits, which were porphyry copper deposits later discovered. In fact, the porphyry copper deposits here were encountered in the past oil drilling, but the Balkan porphyry copper deposit system was not mastered at that time, and attention was only paid to finding massive sulfide deposits. It was not until 1968 discovered that there might be a deep porphyry copper deposit that large-scale exploration began, thus discovering this concealed porphyry ore body and finding abundant associated skarn deposits.
4. Spatial distribution pattern of jet deposited (SEDEX type) lead-zinc deposits and reticulated copper deposits.
Jet-deposited (SEDEX type) lead-zinc deposits and reticulated vein copper deposit sometimes coexist in space. For example, there are Jurassic jet deposited lead-zinc deposits in western Cuba. There are both layered SEDEX lead-zinc deposits and reticulated copper deposits in this area. Some deposits include SEDEX lead-zinc deposits and reticulated copper deposits. There are also SEDEX-type lead-zinc deposits associated with copper deposits in other parts of the world, such as Mount Isa deposit in Australia, Tom deposit in Cserven Basin, Rammelsberg deposit in Germany, Hogge deposit in Inner Mongolia, China and Tanyaokou deposit.
5. Spatial distribution model of "four floors" copper mine
Some deposits in different times in the same metal-metallogenic province may be reactivated and enriched by older ore-forming materials in the crust after later geological processes; Some sediments do not come directly from the ancient basement, but from the deep, such as the lower crust or upper mantle. Both cases show that in a specific area, the same mineral may be produced in different periods because the geochemical province may provide sufficient sources of ore-forming materials, but different types of deposits may be produced because of different geological processes in different periods, so the mineralization in different periods is inherited. The most typical example is the "four generations under one roof" copper mine sequence in Sichuan and Yunnan, which is referred to as the "four-layer" copper mine model (Li Gongju, 199 1), that is, the Dahongshan volcanic jet (fluid) hydrothermal-sedimentary metamorphic copper (iron) deposit related to the basic porphyry formation. Secondly, the sedimentary-jet Dongchuan copper (iron) deposit related to terrigenous clastic (including pyroclastic)-carbonate formation, and then the syngenetic sedimentary-reformed glutenite, dolomite-type copper deposit (Lanniping type) and diagenetic epigenetic-hot brine sand (shale)-type copper deposit (Yunnan Chinese type) formed in terrestrial strata in Diwa area. This is not a simple "four generations under one roof" (Figure 4-7). Mineralization is not only inheritance, but also regeneration and multicycle.
6. Trinity deposit model
In the middle and lower reaches of the Yangtze River, "multi-integrated" copper polymetallic deposits (skarn type, porphyry type and layered massive sulfide type) have been formed, represented by Chengmenshan. Skarn-type deposits are formed in the contact zone between granodiorite porphyry and limestone, porphyry copper-molybdenum deposits are formed in rocks of quartz porphyry and granodiorite porphyry, and layered massive sulfide deposits are formed on limestone of Huanglong Formation in Middle Carboniferous and sandstone of Wu Tong Formation in Upper Devonian (see model 12 for details).
(three) according to the geological prospecting model, organize mineral exploration work.
Geological model is essentially a regular understanding of metallogenic environment, metallogenic process and controlling factors, so it can undoubtedly play a guiding role in the exploration of new deposits. As far as the geological model is concerned, it can guide the exploration of the periphery and depth of the known ore belt. Here are two examples to illustrate.
1. According to the known geological prospecting model, drilling in the peripheral system of the known ore belt directly leads to the discovery of the deposit.
In the Spansai porphyry copper mine in Chile, because the local bedrock is covered under the "South American Prairie", the application of geophysical and geochemical exploration methods is not effective, so drilling is arranged at both ends of the known mine along the metallogenic structural belt; Then summarize the data and determine the next exploration target area according to the intersection of faults. Finally, a new deposit was discovered by grid drilling. From the application of the method, drilling played a key guiding role in the discovery of the deposit in this case. However, if there is no geological knowledge based on geological prospecting model, it is difficult to arrange drilling work of 9000m in this area. After drilling for 30000m, no ore was found, which eventually led to the discovery of this deposit.
Figure 4-7 "Four-story" copper mine model in Sichuan-Yunnan area of China (quoted from Li Gongju, 199 1)
Papu Parlane deposit in Carlin-type gold belt in the United States has basically understood the geological characteristics of this ore belt from the perspective of regional metallogenic belt. This is also the deposit discovered during trawling in the covering area around the known deposit in 1990s. Archimedes gold deposit is also located in Carlin gold belt, which was discovered in a famous mining area with a mining history of more than 50 years. This is the result of a simple and effective exploration plan. Although the cuttings sampling of the old cave showed the existence of gold mineralization for the first time, geochemical exploration did not play a further role in the exploration plan, because the ore body was covered under the overlying strata after mineralization. Geophysical prospecting is not used in exploration work, but mainly depends on advanced geological model and "edge-expanding" drilling.
2. Re-evaluate the known ore occurrences according to the geological prospecting model, leading to a major breakthrough in prospecting.
This paper takes the discovery process of Winston Lake deposit in Ontario, Canada as an example to illustrate. 1952, Zenmac metal mining co., ltd completed the exploration of a small zenith deposit. The deposit is a compact massive sphalerite deposit with a reserve of 12. 8 × 104t, zinc grade 23%, copper content 0. The zenith deposit is located in the transition zone between gabbro and metamorphic pyroxenite gabbro. The deposit is lenticular, dipping to NE, with an inclination of 35 ~ 45 and a thickness of several centimeters to13.4m.. ..
The unique geological background of Tianding deposit aroused great interest of Yingqiao Copper Company (CFC) at that time. In order to evaluate the ore-bearing prospect in this area and look for larger deposits, CFC Company completed the geological survey and rock geochemical survey in this area in June1978+1October. The researchers tried to combine the circled anomalies with the genesis of zenith sediments to conduct a comprehensive study. The host rock of Tianding deposit is gabbro, which is a geological anomaly. Gabbro layer intrudes between the underlying altered calc-alkaline felsic volcanic rocks and the overlying unaltered pillow tholeiite basic volcanic rocks. Predecessors have put forward two explanations for the genesis of the Tianding deposit. One is that it is a vein-like epigenetic ore source, and the other is that it is magmatic. According to the results of general survey and detailed investigation, CFC company believes that the genesis of Tianxiang deposit is related to volcanic massive sulfide deposition. Based on this, CFC company established a geological model, that is, the zenith deposit was interpreted as a large volcanic massive sulfide xenolith from the in-situ large deposit at the top of felsic volcanic rocks. Figure 4-8 shows the cross section of the model.
Figure 4-8 zenith deposit in Lake Winston, Canada and its relationship with ore source (quoted from P. W. A. Severin et al., 1989)
To verify the above explanation, CFC company drilled 8 diamond holes in 198 1. Four of them were drilled in the exploration lease of CFC company. Three of these four holes are used to study pyrite beds (spatially related to cordierite-amphibole alteration zone in felsic volcanic rocks), and the fourth hole is used to verify weak maximum-minimum coupled electromagnetic method (Max min), very low frequency (VLF) and magnetic anomalies in gabbro located in the northwest of Tianding deposit. The other four boreholes were drilled in the exploration lease of Zenmac Metal Mining Company to verify the proposed geological model. The results of the first four holes are disappointing, and the results of the last four holes are encouraging. They found out the downward projection position of the exposed flint volcanic ash layer, and its depth was125 ~ 250 m. The chert volcanic ash layer is located at the top of felsic volcanic rocks east of the overlying cordierite-amphibole alteration zone. In addition, the borehole passes through a gas injection formation, containing 0. 4. 57% zinc. 3m interval and 7m thick dispersed mineralized interval containing 1% copper.
After that, CFC company decided to carry out drilling pulse electromagnetic method (PEM) investigation based on drilling results and previous exploration experience, especially in LacDufault mining area in northwest Quebec.
Five transmitting coils with the same size (100m × 100m) are used in the borehole PEM measurement (Figure 4-9), so that excitation can be carried out in multiple directions, and the position, shape and size of the conductor can be inferred according to the abnormal curves of different excitation positions. The measurement was carried out in hole DDH Z0 4. Results A strong anomaly was detected, and the sign of the anomaly changed from early to late on each trajectory, indicating that the anomaly belongs to a typical "edge" anomaly. The anomaly center is located at a depth of 245 meters, and sulfide mineralization with a thickness of several millimeters can be seen. The abnormal curves measured by emission at different positions are similar in shape, indicating that there is a good plate conductor. In addition, the amplitudes of the responses of the north and south transmitting coils are approximately equal, indicating that the plate-like body is continuous in this direction. Judging from the response of the east-west transmitting coil, the plate-shaped body should be inclined to the east and extend downward, which is consistent with the observation of geophysical anomalies and geological inference on the ground. Another noteworthy anomaly is that the sign of the abnormal response obtained by the west transmitting coil is basically reversed and the amplitude is smaller. This can be explained by the coupling relationship between primary field and exciton. According to the vector direction of the primary field, it can be inferred that the coupling between the primary field of the west transmitting coil and the downward inclined plate conductor is the worst, and the directions of the primary field and the secondary field are basically opposite, so this abnormal phenomenon appears.
According to the interpretation results of borehole electromagnetic survey and geological inference, hole Z0 5 was laid in June 1982 to verify the PEM anomaly of borehole. As a result, Z0 5 borehole encountered a thickness of 2. 1m, containing copper 1. 10%, zinc content 19. 1 1%, silver content 220. The gold content is 0. 73g/t. The ore belt is located at the bottom of gabbro bedrock 300 meters below the surface. Through the above series of comprehensive exploration, this hidden massive sulfide deposit in Winston Lake was discovered.
The geological model of the deposit and the geophysical model in the well play a very important role in the discovery of the deposit. Through a series of exploration activities, it is finally realized that the zenith deposit is only an xenolith of volcanic massive sulfide deposit derived from the large in-situ Winston Lake deposit.
Fig. 4-9 results of pulsed electromagnetic measurement of borehole in Winston Lake, Canada (quoted from P. W. A. Severin et al., 1989).