Precious metal minerals

All countries in the world attach great importance to the exploration and development of gold deposits. The world's gold resources are widely distributed, but unbalanced. According to the statistics of the US Geological Survey, by the end of 1998, the gold reserves were 45000t, and the reserve base was 72000t (excluding China and other countries with no public data). Countries with large reserves include South Africa, the former Soviet Union, the United States, Canada, Australia, Brazil and other resource-rich countries. South Africa accounts for about half of the world's gold resources, accounting for 48% of the world's gold reserves, and Brazil, the former Soviet Union and the United States each account for about 12% of the total resources.

Gold deposits can be formed in different geological periods, geological tectonic environments and rock types. There are many types of primary gold deposits, and the main types of exploration and exploitation of primary gold deposits are: ① Precambrian shield and greenstone belt gold deposits in platform area, including Helmlow gold deposit in Canada and Homstak gold deposit in the United States; ② Gold-bearing uranium conglomerate gold deposits in Proterozoic primitive geosyncline depression, including Witwatersrand gold deposit in South Africa; (3) Carlin-type gold deposits in Paleozoic fold areas of the United States and Mulongtao-type gold deposits in Uzbekistan; (4) Mesozoic and Cenozoic gold deposits related to volcanic rocks, subvolcanic rocks and small intrusions, including Pogra and Lihir Island gold deposits in Papua New Guinea, Akpan-Antamokai gold deposits in the Philippines and Mo Ling gold deposits in Japan; ⑤ Modern placer gold deposits and ⑤ associated gold deposits. Among them, 1 and 2 are concentrated in Precambrian, accounting for 70% of the world's gold reserves; Four types are concentrated in Mesozoic and Cenozoic, accounting for about 25% of the world's gold reserves; Three types of gold deposits in Paleozoic strata account for about 5%. It can be seen that the world's gold reserves are concentrated in "one old and one new".

Since 1980s, the global gold prospecting has reached an unprecedented level, and a large number of large and super-large gold deposits have been discovered. In particular, the United States, Canada, Australia, Brazil, Japan and Papua New Guinea have made great breakthroughs and progress in gold prospecting and exploration. For example: ① The maclaurin gold deposit in California, USA was discovered in 198 1 year, with a gold reserve of 100t and an average grade of 4.98g/t. The deposit is a reticulate vein-like disseminated gold deposit occurring in volcanic rocks and sedimentary rocks, and the ore body occurs in silicified tuff. ② There are 2 1 gold deposits within 72km of Carlin-type gold belt in the United States, and the total recoverable reserves at the end of 1026t, of which Jinkeng (3 19t) and HouBates deposit (55 1t) are the largest. The original exploration depth of Carlin-type gold belt is between 100 ~ 300 m, all of which belong to fine disseminated gold deposits in low-grade sedimentary rocks. Since 1987 implemented the deep drilling plan, the Carlin-type gold belt has made outstanding prospecting achievements, and a series of high-grade large-scale gold deposits have been discovered in the deep part of the mining area. In recent years, high desert gold deposits (60t, grade 10.3 ~ 20.6g/t) and turquoise gold deposits (155t, grade 12g/t) have been discovered below 450m. It can be seen that the Carlin-type gold belt still has great potential for deep prospecting. (3) The Hermlow gold deposit in Ontario, Canada was discovered in 1982, with a reserve of 597t and a grade of 7.78g/t, belonging to Archean greenstone belt. ④ The Tongdela gold deposit in northwest Canada is located 240Km northeast of Yelonev, and it was found in 1982, with a reserve of 150t and a grade of 6.20 g/t. The deposit is located in steep felsic pyroclastic rocks in Archean volcanic belt and controlled by shear structure. ⑤ The Lingshui gold mine in Kyushu, Japan was discovered in 1980, with a reserve of 120t and a grade of 80g/t. Together with the Yamada and Shenshan gold mines discovered nearby, the total reserve is about 260t, and the average grade is close to 70g/t, which belongs to the Tertiary epithermal type or hot spring type. In recent years, an extra-large gold-bearing vein rare in the world has been discovered in this mining area, with a reserve of 40-50 tons and a grade of 20-25 g/ton ... ⑥ Poguela gold deposit in Nga province of Papua New Guinea has developed from a small gold deposit before the 1970s (with a reserve of only a few tons) to an extra-large gold deposit in the 1990s, with a reserve of 420 tons and a grade of 3.7 g/ton, and its mineralization is related to. ⑦ Papua New Guinea volcanic Alisher gold mine (573 tons, grade 3.4 g/ton). (8) Selina-mockel greenstone gold deposit in former Czechoslovakia. Pet-name ruby Pedala gold deposit in lower weathered rock of placer gold mine in Bala state, Brazil. The newly discovered super-large gold deposits since 1980s include: gold deposits such as Refuxio (recoverable reserves 103t) and Lacoipa (126t) in Marikonga epithermal gold-porphyry gold belt in Chile, and the geological reserves of gold in the whole belt have exceeded 400-500t; Fort Knox porphyry copper-gold deposit, Alaska, USA (Au >124t); Great progress has also been made in the prospecting of porphyry copper-gold deposits and volcanic gold deposits in the volcanic region around the Pacific Ocean, such as the Grisberg skarn-porphyry copper-gold deposit (1200t, grade 1.8g/t) and the Batu Xijiawu porphyry gold deposit. Dibidio porphyry gold deposit was discovered in the Philippines; Cartier porphyry gold deposit was discovered in Australia; Cerro Cassel and pascua porphyry gold deposits were discovered in Chile; Porina and Gaby porphyry gold deposits were discovered in Peru and Ecuador respectively. Juno and Knoxville porphyry gold deposits and MacDonald volcanic gold deposits have been discovered in the United States. At present, the volcanic areas around the Pacific Ocean are still working and developing. Nizhdanin (475t, 5g/t) from Yakutia, the former Soviet Union; Meskoye gold mine in Madanga (277 tons, grade 12g/ ton); Kumtor gold mine in Kyrgyzstan (3 16t, grade 4.4g/t), Ametist gold mine in kamchatka peninsula (96t, grade 16g/t), etc. In addition, in recent years, the gold reserves of some famous old gold mining areas have obviously expanded. For example, several gold deposits with hundreds of tons of reserves have been newly discovered in the Rand gold mine area of South Africa, and large gold-bearing ancient conglomerate gold deposits have been discovered in the deep part of the basin. Dominica's "Laocun" gold mine reserves have expanded to more than 600 t, and since the 1990s, old stratum gold mines and lateritic gold mines have also been discovered. Large gold deposits have been found in Archean greenstone belts in Tanzania and Venezuela, and early Proterozoic greenstone belts in Mali and Niger. A very large Precambrian black shale type gold (platinum) deposit was discovered in Russia. A large lateritic gold deposit (390t, grade 1.25g/t) was discovered in the stratigraphic distribution area of Venezuela 19 1.00 (ancient square, 1994, He Jinxiang, 1998) greenstone belt.

During this period, gold exploration in China developed rapidly and achieved the most brilliant achievements since the founding of the People's Republic of China. Many large gold mines have been discovered and proved. It is worth noting that promising fine disseminated gold deposits have been discovered in Permian and Triassic in southwest Guizhou, forming a "gold mineralization prospect area in southwest Guizhou", which is known as the "golden triangle" in Yunnan, Guizhou and Guangxi and has become a new gold base in China. Since then, Sichuan, Gansu, Shaanxi, Ningxia and other provinces (regions) have successively discovered this type of gold deposits, and discovered a new "golden triangle" area, further broadening the field of gold prospecting. In addition, a number of new gold deposits have been discovered in the old mining areas and old gold belts in Jiaodong and Xiaoqinling areas, such as Taitai super-large gold deposit, Guangdong Yunkai Jiaojia altered rock type gold deposit, Hainan Baoban and other gold deposits, as well as the recently discovered Baolun gold deposit rich in chronological veins. Some new types of gold deposits have also been discovered, such as granite type (porphyry type? ) gold mine; Potash feldspar granite vein gold deposit was discovered in Inner Mongolia. Iron hat type gold deposit discovered in Xinqiao, Anhui. The great progress in recent ten years is mainly to continue to discover new greenstone belt-type gold deposits and expand reserves; Many large shear zone gold deposits have been discovered. A major breakthrough has been made in the prospecting of fine disseminated (Carlin-type) gold deposits.

According to the types of gold deposits in China, we should focus on looking for epithermal (volcanic-subvolcanic), fine disseminated (Carlin), altered rock and greenstone gold deposits. While emphasizing the search for independent gold deposits, we should also pay attention to the search for gold-bearing polymetallic deposits, especially the research and analysis of structures.

The world is rich in gold resources and widely distributed. Its reserves and reserve base account for 58% and 80% of the total resources, respectively, while reserves account for 73% of the reserve base, indicating that gold exploration is relatively high. However, the static guarantee years of reserves and reserve base are 2 1 year and 29 years respectively, which can only guarantee the output of 2 1 the first 20 years of the century. However, since 1970s, the gold exploration fever has continued. Since 1980s, many large-scale gold mines have been discovered, and the resource potential of gold mines in the world is still great, especially in the southwest Pacific and Latin American countries. The prospect of gold exploration is considerable, the reserves will continue to increase, and the degree of protection will be further improved.

2) Silver

According to the statistics of the US Geological Survey, the world silver reserves and reserve base in 1998 were 28× 104t and 42× 104t respectively. Silver mines are widely distributed, and their reserves are mainly concentrated in Mexico, Canada, the United States, Australia, Peru and other countries, accounting for 57% of the world's total reserves. About two-thirds of the world's silver resources come from nonferrous and precious metal deposits, such as copper, lead, zinc and gold. , 1/3 are the main silver-producing vein deposits. Although the latest discovery is the primary gold and silver deposit, it is predicted that the huge reserves and resources in the future will come from the discovery of base metal deposits with by-product silver. The world's silver resources are mainly distributed in three giant silver-bearing structural belts, namely, the Pacific Rim belt, the Mediterranean belt and the Mongolia-Okhotsk belt. The distribution of silver metallogenic areas is regular, and they all occur in the ocean-land transitional metallogenic system. The main silver metallogenic areas in the Mesozoic-Cenozoic fold belt are also related to the junction of ore-bearing structures in the ocean continent. The silver mineralization age of the largest transitional metallogenic system is Oligocene-Miocene. The second transitional metallogenic system is the Cretaceous-Paleogene silver polymetallic metallogenic area in the rift zone and adjacent fold zone of the Atlantic and Arctic ridges. The main types of silver deposits are: ① epithermal deposits related to Mesozoic and Cenozoic volcanic rocks and subvolcanic rocks; ② Intermediate-temperature hydrothermal silver nonferrous metal deposit; ③ Medium temperature liquid Ag-Co-Ni deposit; ④ metasomatic silver deposits in carbonate, etc.

According to the combination of host rocks and main useful elements, the main types of silver deposits are: ① silver deposits hosted in continental volcanic rocks and subvolcanic rocks; ② Silver-bearing sulfide deposits in marine calc-alkaline volcanic rocks and volcanic sedimentary rocks; ③ Ag-Pb-Zn metasomatic deposits in carbonate rocks and skarns; ④ Ag-Pb-Zn deposits in metamorphic rocks and clastic sedimentary rocks; ⑤ Ag-Co-Ni-Bi-As vein deposits occur in Precambrian metamorphic volcanic rocks, sedimentary rocks and diabase; ⑥ Syngenetic sedimentary deposits dominated by sandstone and mudstone. Because most silver deposits are associated with other metal deposits, the metallogenic theory, deposit model, geology and geophysical and geochemical exploration methods of various gold, lead, zinc and copper deposits can be used for the exploration of corresponding types of silver deposits. Prospecting should be based on the geological structure environment, ore-hosting rocks and mineralization types of each region, and the corresponding exploration methods should be reasonably selected.

According to the different combinations of ore-bearing rocks and metals, Baige et al. (1994) proposed that the silver deposits in China can be divided into 8 categories and 29 subtypes, among which the contact altered rock series and tectonic fractured altered rock series occurring in volcanic rocks are the most important. It is mainly distributed in the platform margin, fold system, especially in the coastal Pacific tectonic magmatic activity area. The metallogenic epoch is dominated by Mesozoic and Proterozoic. Independent silver deposits and silver-gold deposits are mostly continental volcanic rocks and structurally fractured altered rocks. Marine volcanic rocks related to mineralization are mostly spilite porphyry series, while continental volcanic rocks and intrusive rocks are mainly intermediate-acid calc-alkaline rocks. The source beds and ore-bearing strata of silver are mainly Proterozoic and Paleozoic. The migration and location of silver deposits are mostly controlled by structures, and rational use of comprehensive prospecting methods is an effective means to find silver quickly and economically.

China has accelerated the prospecting, exploration and development of silver deposits in recent ten years, and has become a major silver resource country in the world, with good metallogenic geological conditions and considerable resource prospects. Although the world is rich in silver resources, it is mainly associated deposits with limited development and utilization. The static guarantee period of existing reserves and reserves base is 20 years and 30 years respectively. It can be seen that the guarantee degree of reserves is not high, so it is necessary to strengthen exploration, especially to find independent silver deposits with silver as the main product.

3) Platinum group metals

According to the statistics of the US Geological Survey, the reserves and reserve bases of 1998 platinum group metals are 70600t and 77500t respectively, which are highly concentrated in South Africa, Russia, Canada and the United States, accounting for 98% of the world's total reserves. Among platinum group metals, the output of platinum and palladium accounts for about 90%, and other metals account for about 10%. Platinum group metals account for the vast majority of the world's total reserves, and the main types of deposits for exploration and exploitation are:

(1) Cu-Ni sulfide-type platinum group metal deposits related to basic-ultrabasic rocks. This kind of deposit is the most important source of platinum group metal reserves and output in the world. At present, the platinum group metals in the world's three major platinum-producing countries mainly come from such deposits, and the representative deposits are: copper-nickel sulfide-platinum group metal deposits in Bushveld complex, South Africa (platinum group metals are the main products, and metals such as copper, nickel and cobalt are by-products); The copper-nickel sulfide deposit containing platinum group metals in Norilsk of the former Soviet Union and the copper-nickel sulfide deposit containing platinum group metals in sudbury.

(2) Chromite-type platinum group metal deposits related to basic-ultrabasic rocks. This kind of deposit is becoming more and more important. In the early 1980s, platinum group metal deposits related to UG-2 chromite deposit were discovered in Bushveld complex in South Africa, which almost doubled the reserves of platinum group metals in South Africa. Platinum-containing layer mainly produces platinum group metals, and chromite is recovered as a by-product. In addition, the platinum mines in Urals of the former Soviet Union, Ethiopia and Alaska of the United States also belong to this type.

(3) Placer gold deposits. There is little difference between platinum placer and placer of other minerals. Platinum deposits are of eluvial type, slope type and alluvial type. Distributed in Colombia, the United States, Canada and the former Soviet Union. This kind of deposit is a secondary type, and its reserves account for only a few percent of the world's total reserves, and its role is gradually decreasing.

(4) Other types. In addition to the above types, the following six kinds of deposits containing platinum group metals have been discovered: ① black shale copper deposits containing platinum (such as Zehistan copper mine in Poland); (2) Platinum deposits occurring in various copper and gold veins (such as Persian deposits in Nevada, USA); ③ Porphyry copper-molybdenum deposits containing platinum group metals (disseminated copper-molybdenum deposits) (such as Clemex④ platinum-bearing chalcopyrite copper deposits in the United States (such as Urals in the former Soviet Union); (5) Platinum-bearing cassiterite-sulfide deposits (such as some deposits in the Far East of the former Soviet Union); ⑥ Platinum-bearing uranium sulfide deposits (such as Ontario, Canada).

The exploration and research of platinum group metals are mainly concentrated in basic-ultrabasic rocks, and the intrusion of platinum group metals into Precambrian layered rocks in magmatic rocks has great industrial potential. For example, Bushveld in South Africa, great rock wall in Zimbabwe and Stilwater in Montana, USA. In addition to layered rock bodies, the mineralization of platinum group metals may also be related to basic-ultrabasic rock bodies belonging to other formations, and these intrusions have various metallogenic characteristics (copper-nickel sulfide, chromite, titanomagnetite, etc.). In recent years, we have actively studied ophiolite belts, especially those in the Mediterranean. The enrichment of platinum group elements has been found in both intrusive rocks and volcanic rocks. Platinum group metals have been found in silicate phase invading ultrabasic rocks. Komatiite-type iridium-rich nickel sulfide deposit related to differentiated ultrabasic rocks in volcanic rocks of Precambrian greenstone belt has a good prospecting prospect. Uranium, gold and platinum group metal ores, which can be used as new sources of platinum group metal resources, have been found in Proterozoic sediments in Saskatchewan, Canada. Selenium, antimony and bismuth are the indicator elements of abnormal platinum group elements, and there are a large number of platinum group metal selenides. Some hydrothermal uranium veins are also rich in platinum group elements, so it is necessary to study platinum group metals in uranium ore composition carefully. The general survey of platinum group metal placer is also an urgent task; In the future, special attention should be paid to the new types of platinum group metals, namely, sediments (magnesium deposits, ferromanganese crusts and high-carbon shale) and extrusive rocks (olivine trachyte in mainland China and glassy andesite in ocean region) in ancient and modern basins. For example, we should study the iron-magnesium deposits in the Pacific Ocean, whose platinum group metal content is 65,438+000 times that of similar continental sediments, and cobalt crusts generally contain platinum.

It is worth emphasizing that most important PGE-containing mineralization discovered in recent years coincides with gold mineralization, such as the super-large mesothermal "dry valley" gold deposit in Neoproterozoic sedimentary rocks related to black shale in Siberia, Russia. This unconventional gold and platinum deposit occurs in Uzbekistan, Kyrgyzstan and Brazil. For China, we should also pay attention to various metal deposits related to Neoproterozoic-Early Paleozoic black shale. Some important and even world-class large gold deposits and gold-platinum deposits have been discovered in the eastern part of the former Soviet Union. China should attach importance to the study of metallogenic environment and ore-controlling conditions and creatively promote the prospecting of this kind of deposits.

In short, the global platinum group metal resources are rich, with sufficient reserves and high degree of protection. According to the average annual output of 283t, the static guarantee period of platinum group metal reserves and reserve base is 19 1 year and 223 years respectively. However, due to the high concentration of platinum group metals, countries still need to carry out continuous exploration to ensure supply.