Aerial photography project

Geophysical and geochemical exploration methods can usually play the role of strategic prospecting methods in metallogenic (regional) prospecting, especially the development of ultra-low density regional geochemical exploration technology, which provides a feasible way to "quickly grasp the overall situation and gradually narrow the target area", which is well proved by the regional geochemical exploration sweeping plan carried out in some countries and regions in the world. For example, the U.S. Department of Energy's uranium resources evaluation plan in the 1970s, the Canadian national regional geochemical exploration plan in the 1980s, Nord carlot plan in Norway, Sweden and Finland in northern Europe, and the national regional geochemical exploration plan in China have greatly promoted the mineral exploration in the metallogenic belt.

As far as a certain area is concerned, it is necessary to carry out regional geophysical exploration from a regional perspective, which can quickly narrow the target area and make a major breakthrough in prospecting. For example, in the 1990s, Newmont launched a large-scale geochemical survey plan in Indonesia, and quickly discovered geochemical anomalies above the Xijiawu and messer deposits in Ba Du from a regional perspective, so it achieved the purpose of verifying geochemical anomalies by tracing outcrops and surface geological mapping, and quickly discovered two super-large deposits in Ba Du Xijiawu and messer. Even in the old areas with a certain degree of work, flexible application of geochemical methods will achieve corresponding prospecting results. For example, in June1978165438+1October, Holstek Company proposed to start from the region, and screen ore occurrences or anomalies to find ore deposits through several levels of work such as reconnaissance inspection, detailed investigation and target area evaluation. Under the guidance of this idea, according to the known deposit model and rock sampling, geochemical anomalies were discovered, gold mineralization outcrops were discovered through anomaly inspection, and maclaurin's large gold deposit was confirmed through drilling. According to the point of view from regional to local, in the exploration of new areas, traditional geochemical exploration methods are used to quickly grasp the overall situation, gradually narrow the target area and achieve a breakthrough in mineral exploration; In the exploration of old areas, either new geochemical exploration methods are adopted to realize the transformation from regional to local, or new theories and methods are applied to re-understand the existing geochemical data, emphasizing the revealing of ore-controlling geological factors from the regional geochemical background and the revealing of the structure and characteristics of geochemical anomalies from different dynamics, so as to effectively screen prospecting areas.

Although geophysical prospecting method is an indirect prospecting method in general, once the ore-controlling factors of the deposit are determined, it is possible to convert geophysical prospecting information into direct prospecting information, so that geophysical prospecting method can play the role of strategic method. Especially in the area covered by the surface, it is necessary to study the application conditions of geophysical methods with large detection depth in order to transform geophysical information into information directly related to ore prospecting. For example, the Elsa Mountain mining area in the northwest of Queensland, Australia, is one of the largest producing areas of copper, lead and silver in the world, and its mining history has been more than 100 years. The early exploration activities here were mainly concentrated on Proterozoic rock outcrops. Since 1980s, the exploration target has been partly transferred to Mesozoic sedimentary rock coverage area. In this area, there are mainly copper and gold deposits hosted by sedimentary rocks related to iron rocks and shear, such as Strarra, Osborne, Elliott, Eloise and Ernest Henry. Because the deposit is completely hidden, the conventional geological exploration methods are greatly limited. In this area, the prospect of copper-gold mineralization is often related to banded iron-bearing formation (BIF), so the banded iron-bearing formation must be determined first when determining the prospect area, among which high-precision aeromagnetic method and ground magnetic survey are generally the most effective methods. Based on this understanding, the ground time domain electromagnetic method has been widely popularized and applied, and it has achieved frequent results. 1985 Newmont Company and China South Locomotive Co., Ltd. jointly undertake risk exploration. On the basis of detailed investigation of surface magnetic method, the fixed and moving loop transient electromagnetic method is used to scan the surface locally, circle a good conductive zone consistent with the magnetic source, and drill holes to reach the mineralized iron strata. Then, the drilling location is further carried out by using magnetic vertical derivative and simulated TEM measurement. It was not until 28 diamond boreholes were drilled that thick coal seams with economic significance were discovered for the first time, and rich ores with a thickness of 32m, 5.8% Cu and 3.28×10-6-6 Au were discovered. Further work since then has determined the scale of Osborne deposit. 1988, BHP company verified the aerial and ground magnetic anomalies in the eastern fold zone of the metallogenic province through TEM measurement, and as a result, the Eloise copper-gold deposit with a thickness of 50 ~ 70m was found under the Mesozoic sedimentary layer. Similarly, based on a similar combination of prospecting ideas and methods, in 199 1 year, Western Australia Mining Company discovered Ernest Henry copper-gold deposit under the 40-50m-thick sediment on the eastern edge of the metallogenic fold belt, which is the largest copper discovery in Australia since the discovery of the Olympic Dam deposit. It can be seen that geophysical methods, mainly high-precision magnetic survey and surface time-domain electromagnetic method, have played a leading role in the new prospecting discoveries in this metallogenic belt in recent 10 years. This is also an example of how to transform indirect information into direct information and achieve a breakthrough in prospecting.

As far as geological work or exploration degree is concerned, in the so-called "new areas" or areas with a certain exploration history, but the regional geological work degree is low for various reasons, the early remote sensing geological work can provide indispensable information for the subsequent field and geophysical and geochemical exploration work selection areas.

The Tertiary porphyry copper belt in Chile is a world-famous metallogenic belt with a long history of mining and exploration. Since 1960s and 1970s, the prospecting work has been clearly arranged by zones, and a number of important deposits have been discovered, at the same time, the understanding of regional geological laws of ore belts has also made a breakthrough. The ore belt widely covers the piedmont gravel layer, and the bedrock outcrops are scattered. Searching for alteration zones closely related to porphyry copper deposits and copper-gold deposits and drawing the main fault zones are the main preliminary work for prospecting. In order to solve the problems of regional exploration quantity, geological mapping and drilling work selection, some mining companies implemented aerial photogrammetry projects in this ore belt in the 1950s and 1970s to solve the "fixed point" problem of further exploration. At the end of 1950s, Chilean exploration company carried out aerial photogrammetry along the "western fault zone" from El Salvador to Cerro Colorado, and further arranged geological mapping, geochemical exploration and drilling at different scales with the abnormal color display related to alteration zone as the target area, and found a number of important porphyry copper deposits such as Quebrada Blanca, Koyavasi and Escondida. In the 1980s, aerial photography geological survey was carried out on the ore belt. According to the color anomalies related to mineralization shown in the altered belt, geological mapping and geochemical exploration were further arranged, thus the Martai and Lobo gold deposits were discovered. According to the same selection-detailed exploration procedure, Lakoipa gold deposit was also discovered. Although it has a history of nearly a hundred years, it was only because of the abnormal color in aerial photographs that the exploration company noticed it in the 1970s and discovered it after further ground exploration.

Indonesia has a superior metallogenic environment for porphyry copper deposits, which was recognized in the late 1960s. In addition, optimistic estimates of copper prices and a series of discoveries in neighboring Papua New Guinea and the Philippines have attracted several large mining companies in Europe and America to engage in risk exploration. At the beginning of exploration work (early 1970s), the main problems faced were the low level of geological work, not only the lack of regional geological data, but also the lack of reliable topographic map data. The exploration work is concentrated in the middle of North Sulawesi and the Hiranchaya ore belt. In addition, there are some contract areas in Java, Central Sulawesi, Nusa Tenggara Islands and Hamahira. The choice of these areas is mainly based on the speculation that the porphyry copper deposits in the Philippines and Papua New Guinea may extend to the northern Sulawesi ore belt in Indonesia respectively. Tertiary calc-alkaline rocks in island arc or continental margin environment are widely distributed in the above areas. The main exploration methods are river sediment survey and rock turnover observation, but due to the lack of topographic and geological data, aerial photography and side-looking radar data collection are arranged before field work as the base map for field exploration and used in the selection area. After further regional exploration, three economically significant copper mineralization areas and several low-grade copper mineralization areas were delineated, and more detailed exploration was carried out in the mining area after the 1980s. Since 1980s, remote sensing data have been widely used in gold exploration and mineral selection in Indonesia, and gold exploration in this period mainly concentrated in Cenozoic magmatic active zones. In the exploration of Weita Island gold deposit, CSR Mining Company firstly analyzed the Landsat imaging data of Nusa Tenggara Islands, and determined several favorable epithermal metallogenic tectonic settings. Then, the1:50,000 photographic geological interpretation was carried out in Weita Island and Li Lang Island. In view of the difficulty of no topographic and geological data in the exploration area, the drainage map is compiled and the prospect area of epithermal or porphyry metallogenic structure is delineated. The key area of photographic geological interpretation is the former land. On this basis, field geological mapping and geochemical sampling are arranged. The follow-up work also confirmed that the abnormal areas in satellite and aerial images are related to strong alteration zones and dikes in volcanic rocks, and many gold and silver deposits with economic significance have been discovered.