Southeast Asia | Main distribution of tin mines in Indochina
The Indochina Peninsula in Southeast Asia is located at the intersection of the eastern section of the Tethys tectonic domain and the western circum-Pacific tectonic domain. It is one of the most active and complex regions in the world. It has undergone tectonic evolution, magmatic activity, metamorphism and mineralization in different periods such as the Hercynian, Indosinian and Yanshanian periods [1-9], and has dual mineralization characteristics of the Tethys-Himalayan mineralization domain and the circum-Pacific mineralization domain [10]. The mineralization in this area is complex and diverse, and it is rich in important mineral resources such as copper, nickel, chromium, gold, and potassium salt [11-13]. In particular, it is distributed with the world-famous Southeast Asian tin belt [14-15]. The tin reserves in the Southeast Asian tin belt account for nearly 80% of the world's tin reserves. In recent years, some important tin deposits have been newly discovered [15-16], which have attracted much attention.
Division of tectonic units and distribution of tin deposits in the Indochina Peninsula of Southeast Asia
The Indochina tin belt in Southeast Asia is located at the intersection of the Tethys-Himalayan metallogenic domain and the West Pacific circum-Pacific metallogenic domain. It is one of the most important metallogenic belts in the world and is the southward extension of the Sanjiang tin belt in southwest China and the South China metallogenic belt. The formation of the Indochina tin belt in Southeast Asia is restricted by a specific metallogenic geological tectonic environment. The regional tectonic pattern controls the distribution of magmatic rocks and strata, and also controls the spatial distribution of tin deposits. Based on the geotectonic background, tectonic unit pattern, geological tectonic evolution characteristics, intrinsic control factors of tin deposit mineralization and spatial distribution characteristics of tin deposits in the study area [48-53], this paper divides the Indochina tin belt in Southeast Asia from west to east into three major tin belts and seven tin sub-belts: the Mogok-Mawlamyine-Tanlinthayi-Phuket tin belt (I), the Kengtung-Chiang Rai-Chiang Mai tin belt (II) and the Viet Bac-Trang Son-Kon Tum-Dalat tin belt (III) (Figure 1, Table 2).
2.1 Mogok-Mowlamyine-Tarinthayi-Phuket tin ore belt (I) The Mogok-Mowlamyine-Tarinthayi-Phuket tin ore belt is located on the western edge of the Baoshan-Shan Thai landmass, extending in a nearly north-south direction. It is connected to the Tengchong tin ore belt in China to the north, and extends to central Myanmar (Mowlamyine and Taninthayi) to Phuket, Thailand to the south. It is one of the longest and most important tin (tungsten) ore belts in the world. According to the tectonic unit pattern and the intrinsic control factors of tin ore mineralization, the Mogok-Mowlamyine-Tarinthayi-Phuket tin ore belt (I) is further divided into two tin ore sub-belts: the Mogok-Mowlamyine tin ore sub-belt (I1) and the Taninthayi-Phuket tin ore sub-belt (I2) based on the Meiping fault zone as the boundary (Figure 1). The Mogok-Mawlamyine tin mining sub-zone (I1) is located on the east side of the Sagaing Fault Zone. The exposed strata are mainly Paleoproterozoic, Carboniferous-Permian and Quaternary. The magmatic rocks are mainly Cretaceous granites that are distributed in a large-scale belt in a near north-south direction[32]. Tin mineralization is mainly related to Cretaceous granites. The Taninthayi-Phuket tin mining sub-zone (I2) is located on the west side of the Ranong Fault Zone. The exposed strata are mainly Carboniferous-Permian and Quaternary. The magmatic rocks are composed of Cretaceous and Triassic granites that are distributed in a large-scale belt, mainly Cretaceous granites[32]. Tin mineralization is mainly related to Cretaceous and Triassic granites.
There are more than 70 known tin deposits (sites) in the Mogok-Mawlamyine-Taninthayi-Phuket tin belt, including 6 large-scale deposits and 9 medium-sized deposits[47]. The exposed strata in this tin belt are mainly Paleoproterozoic, Carboniferous-Permian and Quaternary, and the magmatic rocks are mainly the large-scale Late Mesozoic Tengchong-Mogok-Lanong magmatic arc[32]. A large-scale belt-like granite belt is developed in the Tengchong-Mogok-Lanong magmatic arc (Figure 1). The granite is mainly composed of S-type and I-type granites, with S-type granites being the main ones[39]. Tin mineralization is mainly controlled by the Tengchong-Mogok-Lanong magmatic arc granite belt. Almost all tin deposits (sites) in this tin belt are distributed in the contact zone between S-type granites and Carboniferous-Permian. The mineralization age of tin deposits is Cretaceous-Paleogene, and the main mineralization types are: hydrothermal vein tin deposits, such as the large tin (tungsten) deposit in Bilaoke, Thailand, and the medium-sized tin (tungsten) deposits in Maoqi and Tuwakmin, Myanmar;
Weathering crust-alluvial tin deposits, representative of which are the large-scale placer tin deposit in Phang Nga Bay, Thailand, and the medium-sized placer tin deposits in Haidain and Kambao, Myanmar [32-33].
2.2 Kengtung-Chiang Rai-Chiang Mai tin mining belt (II) The Kengtung-Chiang Rai-Chiang Mai tin mining belt (II) is located at the junction of the two tectonic units of the Baoshan-Shan Thai block and the Simao-Nampang intermediate block. It extends in a northeast direction, connected to the Lancang River tin mining belt in China to the north, and terminates at the Meiping fault zone in the south (Figure 1). It is an important part of the tin mining belt of the Indochina Peninsula in Southeast Asia. According to the pattern of geotectonic units, the Kengtung-Chiang Rai-Chiang Mai tin mining belt (II) is further divided into two tin mining sub-belts, the Kengtung-Chiang Rai tin mining sub-belt (II1) and the Chiang Mai tin mining sub-belt (II2), with the Nanhe Chengyi ophiolite belt as the boundary (Figure 1). The main part of the Kengtung-Chiang Rai tin mining sub-belt (II1) is located on the eastern edge of the Baoshan-Shan Thai block and the west side of the Nanhe Chengyi ophiolite belt; the main part of the Chiang Mai tin mining sub-belt (II2) is located on the western edge of the Nanbang intermediate block and the east side of the Nanhe Chengyi ophiolite belt. There are more than 20 known tin deposits (points) in the Kengtung-Chiang Rai-Chiang Mai tin belt (II), including one large deposit. Tin mineralization is mainly distributed in Chiang Rai, Chiang Mai and Tak in northern Thailand. The exposed strata in the Kengtung-Chiang Rai-Chiang Mai tin belt are mainly Late Paleozoic, Mesozoic and Cenozoic. The magmatic rocks are mainly Late Paleozoic-Triassic Kengtung-Chiang Rai-Chiang Mai magmatic arc with a large-scale, near north-south belt distribution[32]. The Kengtung-Chiang Rai-Chiang Mai magmatic arc has a large-scale Triassic granite belt, which is composed of S-type and I-type granites, with S-type granites being the main ones[39]. Tin mineralization is mainly related to the Kengtung-Chiang Rai-Chiang Mai magmatic arc granite belt. The average Sn content of the granites in the belt is 64×10⁻⁶, which is 20 times the average Sn content of granites in the world (3×10⁻⁶)[10]. Almost all tin deposits (points) in the belt are distributed in the contact zone between S-type granites and late Paleozoic and Mesozoic-Cenozoic strata. The tin mineralization age in the Kengtung-Chiang Rai-Chiang Mai tin belt is the Triassic-Cretaceous period, and the main mineralization types are: skarn-type tin deposits, such as the Bokeo large-scale tin deposit; hydrothermal vein-type tin deposits, such as the Tanmalat large-scale tin deposit and the Labo medium-sized tin deposit; residual-alluvial tin deposits, such as the Samoeng large-scale placer tin deposit [32-33].
2.3 Northern Vietnam-Truong Son-Kon Tum-Dalat tin ore belt (III) The Northern Vietnam-Truong Son-Kon Tum-Dalat tin ore belt (III) spans two tectonic units, the Indochina Block and the South China Block, from south to north. It is located on the eastern edge of the Indochina Block and the southern edge of the South China Block. It is connected to the Gejiu-Maguan tin-tungsten-lead-zinc-silver-antimony metallogenic belt in China to the north. The main part is located in Vietnam (Figure 1). The exposed strata in this tin ore belt are mainly Paleozoic, Mesozoic and Cenozoic. The magmatic rock types are complex and diverse, mainly intermediate-acidic intrusive rocks [32]. The Bukang magmatic arc and the Kon Tum-Dalat magmatic arc, which are closely related to tin mineralization, are developed (Figure 1). Taking the Me Jiang-Ma Jiang ophiolite belt and the Truong Son-Da Nang fault zone as the boundaries, the Northern Vietnam-Truong Son-Kon Tum-Da Lat tin mining belt can be roughly divided into three tin mining sub-belts from north to south: the Northern Vietnam tin mining sub-belt (Ⅲ1), the Truong Son tin mining sub-belt (Ⅲ2) and the Kon Tum-Da Lat tin mining sub-belt (Ⅲ3) (Figure 1).
(1) Northern Vietnam Tin Mineral Sub-Belt (III1) The Northern Vietnam Tin Mineral Sub-Belt is located at the southern edge of the South China Block and the northern part of the Mojiang-Majiang ophiolite belt. It is connected to the Gejiu-Maguan Sn-W-Pb-Zn-Ag-Antimony mineralization belt in the north and ends at the Mojiang-Majiang ophiolite belt in the south. The main part is located in the Thanh Hoa-Ha Giang area in northern Vietnam (Figure 1). There are more than 10 known tin deposits (points) in this tin mineralization sub-belt. The belt contains Proterozoic basement metamorphic rock series and Triassic, Jurassic-Cretaceous remelting granites that are closely related to tin mineralization [54]. The mineralization period of the tin deposits is mainly the Yanshanian period, and the main mineralization types are: hydrothermal vein-type tin deposits, such as the large tin deposit in Pia Oac, the large tin-tungsten deposit in Thien Ke and the medium-sized tin deposit in Noi Phao in Xuanhua Province; and residual-alluvial tin-tungsten deposits, such as the medium-sized placer tin-tungsten deposit in Pia Oac [32-33].
(2) Truong Son Tin Mineral Sub-Belt (III2) The Truong Son Tin Mineral Sub-Belt is located between the Mojiang-Majiang ophiolite belt and the Truong Son-Da Nang fault zone (Figure 1). There are more than 10 known tin deposits (points) in the belt. The exposed strata in the Truong Son Tin Mineral Sub-Belt are mainly Ordovician-Cretaceous, and the Late Paleozoic-Triassic Bukang magmatic arc is developed. The Bukang magmatic arc develops Paleozoic and Mesozoic granite belts. The tin mineralization in the Truong Son Tin Mineral Sub-Belt is mainly distributed in the contact zone of the granite belt. The main types of tin deposits in the Truong Son Tin Mineral Sub-Belt are: high-temperature hydrothermal type, such as the large-scale Nam Batan tin deposit in Khammouane Province, Laos and the medium-sized tin deposit in Ha Tinh Province, Vietnam; residual placer tin deposits, such as the medium-sized San To medium-sized tin deposit and Kwai Ho medium-sized tin deposit in Nghe An Province, Vietnam [32-33]. (3) Kontum-Dalat tin mining sub-belt (III3) The Kontum-Dalat tin mining sub-belt is located in the Dalat Hercynian fold belt on the eastern edge of the Indochina block in the South China Sea, and is distributed in a northeast direction. This tin mining sub-belt has developed Proterozoic basement metamorphic rock series, Devonian-Carboniferous sedimentary metamorphic formations and Kontum-Dalat magmatic arc. The intrusive rocks are mainly Hercynian and Yanshanian granites. Tin mineralization is mainly related to the Late Cretaceous porphyritic granite small bodies. Tin deposits (points) are mainly distributed in the interior and contact zones of the Hercynian and Yanshanian granite belts. The mineralization type of tin deposits is mainly hydrothermal vein type, such as the large tin-tungsten deposit in Da Trai [32-33].
