Geology of Ore Deposits

Geology of Ore Deposits. Vol. 47. No. 4. 2005, pp. 309-325, Translated from Geologiya Rudnykh Mestorozhdenii, Vol. 47. No. 4. 2005. pp. 342-359. Original Russian Text Copyright © 2005 by Gatinsky. English Translation Copyright © 2005 by Pleiades Publishing. Inc.

Tectonics and Geodynamic Prerequisites of Mineral Resource Distribution in the Indochina Region Yu. G. Gatinsky Vernadsky State Geological Museum, Russian Academy of Sciences, ul. Mokhovaya 11, Moscow, 125009 Russia Received November 29. 2004

Abstract—The tectonic structure of the Indochina Region is determined by the development of Precambrian continental crustal blocks and foldbelts of different age located between them. Using the method of lateral structural-lithologic analysis, it was found that contrasting processes occurring in the territory from the end of the Proterozoic to the present time: these were, on the one hand, destruction and rifting and, on the other hand, accretion and orogeny. The former were associated with the splitting of Gondwana; the latter resulted in the accretion of Laurasia and then Eurasia. This led to the interference and mutual overlapping of various geodynamic environments, accompanied by magmatism of different types and the origin of various mineral resources. Tectonic events favored generation in the Tethyan and Pacific belts of Southeast Asia of elongated zones with base and rare metal mineralizations and deposits of iron ores, chromites, and copper. Destruction processes and anorogenic magmatism formed isolated areas of Cu-Ni and PGE mineralization and deposits of bauxites, rare and rare earth metals, and gold. Large hydrocarbon fields were concentrated in Cenozoic superimposed depressions and on recent shelves. In view of the above, the Indochina Region holds one of the leading places in Asia in diversity of mineral deposits and prospects for a further increase in mineral-raw material resources.

INTRODUCTION activity processes of different types developed inside The Indochina Region occupies the continental part stable blocks and their folded framework. The combi- of Southeast Asia, involving the Indochina and Malay nation of these opposite processes brought about a peninsulas and adjacent shelves (Fig. 1). In the west, it complicated overlapping and interference of elongated is bordered by the slopes of the Rakkhain Range, by the zones and isolated areas of diverse mineral resources Ganges and Brahmaputra lowlands, and by the Bay of that was first mentioned by Gatinsky et al. (1978). Later Bengal and Andaman Sea shelf zones, and, in the east, works on the relationship between tectonics and miner- by the South China Sea shelf. The northern boundary of ageny in the region were published in the 1980s the region is conventionally drawn along 25°-27° N. (Hutchison, 1982, 1989; Gatinsky, 1986). Since that This territory is occupied by Myanmar, Thailand, west- time, new data have appeared and several economically ern Malaysia, Singapore, Laos, Cambodia, and Viet- significant areas of mineral resources have been discov- nam and partly by southern and southeastern China, ered. The recent synthesis of data on the metallogeny of northeastern India and Bangladesh, and northwestern Asia (Mineral..., 1999) and large and superlarge ore Sumatra (Indonesia). deposits of the world encouraged this research (Rundquist et al, 2004, 2005). The inclusion of adjacent areas of China into the region should be particularly noted. Most tectonic structures and metallogenic belts of the Indochina Pen- TECTONIC STRUCTURE insula continue into these areas, and their consideration would be incomplete if restricted by a narrow geo- The rigid framework of the region consists of Pre- graphic framework. Nearly all researchers of the cambrian continental crustal blocks, which are ancient Indochina Region, from earlier (Blondel, 1929) to platforms and median massifs that are fragments of recent (Gatinsky, 1986; Hutchison, 1989; Metcalfe, Middle Phanerozoic continents and microcontinents 1995), have regarded the adjacent territories of south- (Fig. 1). The majority of rigid blocks were previously ern and southeastern China as parts of the Indochina parts of Gondwana. They broke off at various times Region. during rifting and drifted to the north together with The tectonic structure of the region is characterized Paleotethyan and Tethyan lithospheric plates (Gatinsky by a combination of stable Precambrian crustal blocks et al., 1978; Gatinsky, 1986; Gatinsky and Hutchison, and mobile foldbelts occurring between them. During 1987; Metcalfe, 1995). Collision of the blocks with the Phanerozoic, the block accretion caused active oro- Laurasia and, beginning with the Mesozoic, with Eur- genesis in mobile belts. Simultaneously, anorogenic asia led to the development of Phanerozoic mobile foldbelts, which formed at the places of passive and active Address for correspondence: Yu.G. Gatinsky. E-mail: [email protected] margins of blocks and oceanic-type basins separating

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them. As for the blocks themselves, they, or at least affected by magmatism associated with the formation their inner areas, remained stable for a long time and of active continental margins of various types. This will then were overlain by gently dipping covers of moder- be discussed in more detail in the next section of the ate thickness and have not undergone any significant paper. disturbances. The mobile belts, on the contrary, have experienced intense dislocations, being transformed The southern edge of the Yangtze block (Huang, 1978), a great part of which is situated in eastern Asia into linear fold-thrust structures. The latter are charac- (VII), occurs north of the preceding block. In northern terized by sharply different gradients of the thickness of Vietnam and southern China, the basement of the block deposits across their strike and repeated development is composed of gneisses and schists with interbeds of of metamorphism and magmatism, often affecting mar- Paleoproterozoic ferruginous quartzites, which form gins of neighboring stable blocks. The method of lateral isolated nuclei of early stabilization (2300-2070 Ma, structural-lithologic analysis, which consists in com- K-Аг method) (Gatinsky et al., 1973; Ren et al., paring structural-lithologic sections within definite 1999). These nuclei are welded by Mesoproterozoic time intervals, made it possible to determine the alter- more weakly metamorphosed terrigenous- nation of geodynamic styles in each time interval, or, in volcanogenous and carbonate rocks dated at 1760- other words, to define the stages of the evolution of the 1050 Ma (Rb-Sr method). The final stabilization of the region (Gatinsky, 1986). basement took place 850-800 Ma (Huang, 1984; The Indosinia block (Blondel, 1929), or the Indosin- Shui, 1988). The total thickness of these rocks exceeds ian median massif, about 1000 x 600 km in size, occu- 10 km. The cover is composed of Neoproterozoic and Phanerozoic deposits 4.5-5 km thick, mostly marine pies the central place in the structure of the Indochina and, in upper parts, lagoon- and terrestrial-type. In Region (V; here and below, Roman numerals given in the marginal zones of the block, cover rocks display parentheses correspond to structure numbers in Fig. 1). irregular meta-morphism and block folding and are The basement of the block, forming the Kontum emer- intruded by mag-matic rocks of different age under gence in Vietnam and Laos, is composed of Archean the influence of events in adjacent mobile belts. and Paleo- and Mesoproterozoic gneisses, schists, and These events first occurred in the Silurian-Devonian amphibolites, with a total thickness of no less than 7- and Jurassic-Cretaceous. In addition, in the late 8 km, metamorphosed in the granulite and amphibolite Permian-Triassic, the considered part of the Yangtze facies {Geology..., 1990). The isotopic age of rocks block was affected by rifting accompanied by basic and (most likely, rejuvenated) does not exceed 2300- contrast magmatism (Gatinsky, 1986). 1810 Ma (K-Ar method). Apparently, a similar basement underlies the submerged part of the block in Cam- The third large stable block of the region is Sinobur- bodia and Thailand (Hahn et al., 1986). However, a bur- mania (III) (Gatinsky et al., 1978), known in other ied Early Paleozoic aulacogen, the Sekong zone, was schemes as a southeastern part of the "Cimmerian con- identified between that part of the block and the Kon- tinent," Sinoburmamalaya, or Sibumasu (Sengor, 1979; tum emergence (Tri et al., 1986). Basement rocks dis- Hutchison, 1982; Metcalfe, 1995; etc.). The block play intricate folding, migmatization, and abundant about, 500 km wide, extends from south to north for intrusions of Proterozoic and younger granitoids. Two 2500 km, embracing northeastern Sumatra, the Malay main epochs of regional metmorphism are clearly Peninsula, the western Indochina Peninsula, and adja- defined, 2300 and 530 Ma (the latter corresponds to cent area of southern China. Large Cenozoic strike-slip Pan-Gondwana rejuvenation). The block cover, with a faults cut the block into isolated segments, shifted rela- total thickness of 6 km, is represented by shallow-water tive to each other. The largest of them, the Shan plateau marine Neoproterozoic-Paleozoic deposits and by con- segment, is situated in northeastern Myanmar. The basement of the block is composed of Paleoproterozoic tinental red-colored Mesozoic beds widely spread in rocks, unconformably overlain by a Mesoproterozoic the Korat Plateau in Thailand. The marginal zones of sequence, and was completely stabilized about 900 Ma the block in Central Vietnam, Laos, Thailand, and Cam- (Bender, 1983). The cover is made up of slightly bodia, in the Late Paleozoic and Early Mesozoic, were

Fig. 1. Tectonic scheme of the Indochina Region and adjacent territories. The structures on the shelf are shown on the basis of data of Yu.G. Zorina and A.A. Chistyakov (Gatinsky et al.., 1984). (1) Blocks of Precambrian continental crust (ancient platforms and median massifs and adjacent paleoshelf zones confined to them); (2) Phanerozoic mobile bells (fold structures originated at the site of paleobasins of the oceanic type and transitional zones between them and ancient blocks); (3) large Cenozoic superimposed depressions on the continent; (4) recent shelves; (5) some paleorifts in ancient continental crustal blocks; (6-9) faults ((a) crustal. (b) mantle-crustal), proved and assumed on the basis of (6) geological-geophysical. (7) geomorphological, (8) cosmogeological. and (9) complex data; (10-13) faults of kinematic type: (10) strike slip, (11) transform, (12) thrust, and (13) normal; (14) local structures prominent in the seafloor relief ((a) positive, (b) negative). (I—IX) Blocks: (I) Indostan, (II) Irrawadia, (III) Sinoburmania, (IV) Kuantan, (V) Indosinia, (VI) Phuhoat, (VII) Yangtze, (VIII) Cathaysia, (IX) Hainan; (X-XVI) mobile belts: (X) Arakan, (XI) central Myanmar, (XII) Thai-Malay-West Yunnan, (XIII) Viet-Lao, (XIV) Vietbac-Guangxi, (XV) Natuna-South Vietnam. (XVI) Sunda.

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deformed Paleozoic and Mesozoic terrigenous-carbon- latest Silurian (Shui, 1988). In the marginal parts of the ate deposits, the thickness of which in the Shan plateau Viet-Lao belt (XIII), folding and intrusion of synoro- reaches 5 km. Belts of Triassic and Cretaceous grani- genic granites occurred prior to the accumulation of toids occur on the eastern and western flanks of the Lower Devonian molasse and mostly influenced Lower block, respectively. They were formed under conditions Paleozoic deposits. In the axial zone of the belt, how- of active continental margins and collision zones. ever, these events took place at the end of the Devonian Smaller Precambrian crustal blocks are represented and the beginning of the Carboniferous, while the by fragments that either broke off from large blocks greater part of the Devonian section is represented by a during rifting, namely, Kuantan (IV), Phuhoat (VI), and deformed flysch complex (Tri et al., 1986; Gatinsky, Cathaysia (VIII), or were previously parts of Gond- 1986; Geology..., 1990). wana and then, at various times, joined Eurasia, such as The Thai-Malaya-West Yunnan belt, the largest in Irrawadia (II) and Hainan (IX) (Gatinsky, 1986). the region, 250 km wide, extends for more than 3000 km. The mobile belts that separate the blocks mentioned, The major folding (Indosinian) in it is recorded in the irrespective of the time of folding, are similar in compo- Late Triassic (mid-Norian stage). This belt, composed sition; in lower parts, they are dominated by ophiolites of Silurian-Middle Triassic rocks, continues far into and terrigenous-cherty deepwater deposits; in middle Central Asia through eastern Tibet and the southern part, by gray wackes and island arc volcanics; and, in the branches of the Kunlun Range (Ren et al., 1999). The upper part, by flysch complexes. The thickness of their Central Myanmar belt (XI), previously referred to as sections in different belts ranges from 5-7 km (XIII) to the East Burma belt (Gatinsky, 1986), is made up of 15-20 km (X). In many cases, the marginal zones of the Upper Paleozoic, Triassic, and Jurassic strata. In the belts are formed by thick folded terrigenous-carbonate Mid-Cretaceous, they underwent folding and enclose sequences of paleoshelves (miogeosynclinal zones). an extended belt of Cretaceous Sn-bearing granites (the They are intensely tectonized, with dominating linear northern part of the famous Burma-Malaya granite folding and thrusts; host intrusions of synorogenic S- belt). Farther to the northwest, the Central Myanmar type granites; and are overlain by red-colored or varie- belt continues between northern and southern Tibet. gated molasses with a sharp unconformity. Similar in age, the Natuna-South Vietnam belt (XV) is In the Indochina Region, the age of deformed com- represented in the area considered only by its marginal plexes and major folding, which corresponds to the zone in the southeastern Indochina Peninsula, being time of collision and amalgamation of neighboring mostly concealed under shelf sediments. The Arakan blocks, progressively decreases from east to west. At belt (X) is situated in the extreme west of Myanmar and the northeastern edge of the Vietbac-Guangxi belt the adjacent area of eastern India. It consists of thick (XIV), the time of folding alters in a southwesterly Upper Cretaceous and Paleogene strata, crumpled into direction from Vendian (the latest Proterozoic) to the folds at the end of the Oligocene and the beginning of

Fig. 2. Distribution of principal mineral resources in the Indochina Region and adjacent territories defined by their geodynamic settings (modified after Gatinsky (1986)). (I) Continental-marginal belts of the Malay type and collisional belts of the "continent-continent" type with dominating hydrothermal and skarn Sn. W, and Sb mineralization and, in some cases Mo, Pb, and As; (2) the same of the Andean type, mainly with Cu-porphyry mineralization and with Au, Ag, Pb, Zn, and Mo and occasionally Fe (skarns); (3) the same of the Cordillera type with hydrothermal and skarn Fe, Cu, and Pb mineralization and, in some cases. Zn and Au; (4) ophiolitic belts and complexes of deepwater basins and volcanic island arcs on the oceanic crust with chromites; Cu-massive sulfide mineralization, and Ni, Zn, Mn; (5) intracontinental rift zones with low-temperature mineralization of fluorite, Hg and Sb, in some cases, with volcanogenic base metal mineralization (Pb, Zn, and Ag); (6-8) areas related to plumes, hot spots, and prerift reworking of the continental crust with a leading role of magmatism: (6) of trap formation (Cu, Ni, and Pt), (7) subalkaline granitoid (Sn, W, Та, and Nb), (8) subalkaline and alkaline with carbonatites (Cu, Au, and REE); (9) areas with proved and potential bauxite occurrence; (10) large and most representative medium ore deposits and isolated ore districts reported in (Mineral.., 1999; Electronic..., 2004; Rundquist el al., 2004); (11) main oil-and-gas-bearing basins: (I) Assam (India), (II) Bengal (India, Bangladesh), (III) Irrawady (Myanmar), (IV) Gulf of Thailand (Thailand. Malaysia, Cambodia. Vietnam), (V) Mekong (Vietnam). (1-42) Deposits and groups of deposits {Electronic..., 2004; Rundquist et al., 2004; Mineral..., 1999): (1) Dongchuan, Cu, stratiform; (2) Shizishan, idem; (3) Getang, Au, hydrothermal; (4) Lamuchang, Hg, hydrothermal; (5) Yata, Au, hydrothermal (China); (6) Mwetaung, Ni, weathering crust; (7) Badwin, Pb-Zn, massive sulfide (Myanmar); (8) Dahongshen, Cu, Fe, stratiform; (9) Simatang, Hg, stratiform; (lO)Mahao, Sb. stratiform; (11) Maxiong, idem: (12) Shanhu, W-Sn. hydrothermal; (13) Gejiu, Sn-W, Cu, Pb, skarn; (14) Laoyunshan, W, hydrothermal; (15) Damingshan, idem, China; (16) Xiangquyen, Cu, Au, REE. hydrothermal; (17) Quyxa, Fe, weathering crust; (18) Paclang, Au, hydrothermal (Vietnam); (19) Youmapo. W, skarn; (20) Shilu, Cu-Mo, skarn (China); (21) Monywa, Cu, porphyry (Myanmar); (22) Banphuc. Ni-Cu, massive sulfide (Vietnam); (23) Doimok, W, skarn, hydrothermal (Thailand); (24) Phunyuon. Fe, skarn (Laos); (25) Quyhop, Sn, placer; (26) Langmo, Au, hydrothermal and placer; (27) Codinh. Cr, magmatic (Vietnam); (28) Maelama, W, hydrothermal: (29) Samaeng, W, skarn, hydrothermal; (30) Loei, Cu, Au. skarn (Thai- land); (31) Thachkhe, Fe, skarn (Vietnam); (32) Phuhin, Cu, porphyry (Thailand); (33) Nongson, coal, U, sedimentary; (34) Bong- mieu, Au, hydrothermal and placer; (35) Dacnong, bauxites, weathering crust: (36) Tranang, Au, hydrothermal and placer (Viet- nam); (37) Phanga, Sn, placer; (38) Nakhon Sithammarat, idem; (39) Phuket, idem (Thailand): (40) Kinta-Beatrice, Sn, Ta-Nb, skarn. pegmatite; (41) Sungey Lembing, Sn, skarn, hydrothermal; (42) Kuala Langat, Sn, placer (Malaysia).

GEOLOGY OF ORE DEPOSITS Vol. 47 No, 4 2005 Main types of ore deposits in the Indochina Region according to (Lung, 2004; Makeev and Politov, 1991; Mineral.. 2004; Stepanov et al., 1983; Electronic..., 2004; Bender, 1983; Geology..., 1990; Geology..., 1984; Mineral..., 1999)

No. Metal Main ore mineralization types Country Tectonic position (in Geodynamic setting Mineraliza- Instances of deposits (in parentheses, number of of formation tion age parentheses, number in Fig. 2) structures in Fig. I) and their dimensions, resources (P, predicted resources), and content of useful components

1 Iron Hematite-magnetite-skarn Vietnam Miogeosynclinal zone Active margin of Cordil- Late Paleo- Thachkhe (31), large, 544 mln. t of the Viet-Lao mobile lera type (reworked zoic of ore, 59% Fe belt (XIII) former passive margin)

2 Laos Phunyuon (24), large, 1 bin. t of ore (P), 42-67.7% Fe

3 Residual in ancient weathering Vietnam Yangtze block (VII) Intracratonic Paleozoic Quyxa (17), medium, 124 mln. t crust after ferruginous quartzites of ore, 54-55% Fe, 3% Mn

4 Titanium Marine beach placers // Indosinia block (V) Cenozoic Dezi (not shown in Fig. 2); medium (?), 50-100 kg/m3 of ilmenite, 1-3 kg/m3 of rutile

5 Chrome Magmatic chromite, and placer // Viet-Lao mobile belt Fragments of ancient Early Paleo- Codinh (Nuynya) (27), large, 8 (XIII) oceanic crust in a colli- zoic mln. t of ore, 44.3-51.9% Cr2O3, sion zone 1.8-4.9 kg/m3 of placer chromite

6 Nickel Residual in weathering crust after Myanmar Arakan mobile belt (X) Collision zone Cenozoic Mwetaung (6), medium, 10 mln. t ultramafic rocks of ore (P), 1.19-3.0% Ni

7 Nickel- Copper-nickel sulfide in mafic Vietnam Yangtze block (VII) Borders of paleorift zone Late Permi- Banphuc (22), medium, 120 000 t copper and ultramafic rocks an-Early of Ni, 40 000 t of Cu, 0.49-4.78% Triassic Ni, 0.75-1.63% Cu

8 Copper Stratiform in volcanogenic-sedi- China ft Active continental margin Permian- Dahongshen (8), large and other mentary rocks of Andean type Triassic deposits of this type in southern China (1,2)

9 Copper Copper-skarn Thailand Indosinia block (V) Active continental margin Permian- Loei (30), medium of Andean type Triassic

10 Copper-molybdenum-skarn China Cathaysia block (VIII) Active continental margin Late Juras- Shilu (20), medium of Malay type sic-Creta- ceous Table. (Contd.) No. Metal Main ore mineralization types Country Tectonic position (in Geodynamic setting Mineraliza- Instances of deposits (in parentheses, number of of formation tion age parentheses, number in Fig. 2) structures in Fig. 1) and their dimensions, resources (P, predicted resources), and content of useful components

11 Copper Polyformational copper-rare- Vietnam Yangtze block (VII) Area of continental crust Paleogene Xiangquyen (16), medium, earth skarn and hydrothermally intraplate reworking by 551000 t of Cu, 333000 t of total sulfidized shear zones alkaline intrusions REE oxides, 34.4 t of Au, 0.6- 1.3% Cu, 0.63-9.7% REE, 0.46- 0.55 g/t Au

12 Porphyric in acid effusives Myanmar Irrawady block (II) Active continental margin Neogene Monywa (21), medium, 313600 t of Andean type of Cu, 0.66-0.88% Cu

13 Lead-zinc Galena-sphalerite-quartz sulfide // Sinoburmania block (III) Early Paleo- Badwin (7), large, 5-8% Pb, 3- zoic 6% Zn, 0.9% Cu, 550 g/t Ag

14 Alumini- Residual gibbsite in laterite Vietnam Indosinia block (V) Intracratonic Cenozoic Dacnong (35), large and other um weathering crust after Cenozoic southern Vietnam deposits with basalts total resources of 6.7 bln. t of bauxites (P), 35-39% A12O3

15 Tin Polyformational cassiterite-skarn, China Yangtze block (VII) Area of continental crust Cretaceous Gejiu (13), superlarge ore dis- cassiterite-sulfide, and cassiterite- intraplate reworking by tricts, 1.4 mln. t of Sn, 0.5% Sn, silicate, placer subalkaline granites 0.8 kg/m3 of placer cassiterite

16 ft Polyformational cassiterite-skarn Malaysia Kuantan block (IV) Active continental margin Cretaceous Sungey-Lembing (41), large and cassiterite-silicate hydrother- of Malay type mal 17 f/ Polyformational cassiterite-skarn Sinoburmania block (III) Areas of subalkaline Late Carbon- Kinta-Beatrice (40), superlarge, and cassiterite-sulfide hydrother- granites iferous > 10000 t of Sn concentrate, mal in carbonate rocks 1.34% Sn, as well as columbite and tantalite

18 Placer Malaysia Sinoburmania block (III) Intracratonic (washing Cenozoic Kuala Langat (42), superlarge, out of area of Late Car- 0.1-0.4 kg/m3 of cassiterite, as boniferous subalkaline well as columbite and tantalite granites)

19 Tin Placer Vietnam Phuhoat block (VI) Intracratonic (washing Cenozoic Quyhop (25), medium placer ar- out of area of Paleogene ea, 0.1-1.0 kg/m3 subalkaline granites) Table. (Contd.) No. Metal Main ore mineralization types Country Tectonic position (in Geodynamic setting Mineraliza- Instances of deposits (in parentheses, number of of formation tion age parentheses, number in Fig. 2) structures in Fig. 1) and their dimensions, resources (P, predicted resources), and content of useful components

20 Tin Placer Thailand Mobile belt of central Washing out of granites Cenozoic Phuket (39), large, and other plac- Myanmar (XI) in active margin of Malay er deposits of southern Thailand type (37, 38), 0.2-0.4 kg/m3 21 Tungsten Greisen hydrothermal China Vietbac-Guangxi mobile Distal zone of active mar- Late Juras- Damingshan (15), large belt (XIV) gin of Malay type sic-Creta- ceous 22 Molybdenite-scheelite-skarn Thailand Sinoburmania block (III) Collision zone Late Triassic Doimok (23), medium, and other similar deposits of western Thai- land (28, 29) 23 Antimony Quartz antimonite, hydrothermal // Active margin of Malay Triassic Pakhan (not shown in Fig. 2), me- type dium (?), 0.6-5.0% Sb 24 Mercury Hydrothermal China Yangtze block (VII) Paleorift zone // Lamuchang (4), medium 25 Rare-earth Polyformational fluorite-carbon- Vietnam Yangtze block (VII) Area of alkaline intru- Paleogene Dongpao (not shown in Fig. 2), (Ce group) ate (bastnaesite-parisite) hydro- sions large, and other deposits of north- thermal and residual in weathering ern Vietnam with total reserves crust after alkaline rocks of 9.38 mln. t (P) of ore, from 0.3-0.7% to 20-30% of total sum of REE oxides, 0.001% Та2О5, 0.026-0.15 Nb2O5 26 Uranium Sedimentary in coal-bearing se- Indosinia block (V) Intracratonic graben Late Triassic Nongson (33), medium, quences 3000-5000 thou. t U3O8 (P) 27 Gold Gold-antimonite hydrothermal China Yangtze block (VII) Paleorift zone Triassic Getang (3), medium 28 Gold Gold-quartz hydrothermal and Vietnam Yangtze block (VII) Borders of a paleorift Late Permi- Langmo (26), medium, about placer zone an-Early 10-15 g/t in veins, 0.3-0.5 g/m3 Triassic in placers 29 Polyformational gold-sulfide- ft Indosinia block (V) Active margin of Cordil- Late Paleo- Bongmieu (34), medium, 193 t quartz veined and stratiform in lera type zoic (P), 3.1-11.39 g/t Au and 3-5 g/t black shales and placers Ag in ore, 0.5-2.4 g/m3 Au in placers 30 Gold-sulfide-quartz hydrother- Natuna-southern Viet- Active margin of Malay Late Juras- Tranang (36), medium, 130 t (P), mal (arsenic type) and placers nam mobile belt (XV) type sic-Creta- 5-20 g/t in veins, 0.5-1.0 g/m3 in ceous placers T E C T O N I C S A N D G E O D Y N A M I C P R E R E Q U IS I T E S 317

Level of eluvial development before mining

Roof of limestones before mining

Fig. 3. Section of the Beatrice cassiterite-skarn deposit (40), western Malaysia {Geology..., 1988). ( I ) Cassiteriie-bearing pipe; (2) granites; (3) Paleozoic crystalline limestones. F, faults. the Miocene (Bender, 1983). The continuation of the Major coal reserves are associated mainly with belt is traced in the north between the Himalayas and Mesozoic and less frequently with Upper Paleozoic Southern Tibet and in the south in the Andaman and strata of rigid block covers and superimposed depres- Nicobar Islands and southwestern Sumatra, which is a sions in mobile belts. Large-scale deposits of the latter part of the Sunda mobile belt (XVI). type are located in northern Vietnam, on the Bacbo Bay coast (Late Triassic Honggay coal basin). In a number Essential for the tectonic structure of the region are of deposits in central Vietnam (33; here and below, Ara- large Cenozoic superimposed depressions and pale- bic numerals in parentheses correspond to deposit num- orifts, several of which are shown in Fig. 1, and numer- bers in Fig. 2), Mesozoic coal-bearing beds contain ura- ous faults of various types and different formation nium (Mineral..., 1999). Brown coal deposits, widely depth. These faults are united in the NW (most clearly developed in Thailand and Vietnam, are assigned to identified and stable), NE, N-S, and W-E (most likely, Cenozoic superimposed depressions. the youngest) fault systems (Gatinsky et al., 1984). The following ore mineral resources may be mentioned as most significant for the economy of the region (table). GENERAL CHARACTERIZATION OF MINERAL RESOURCE DISTRIBUTION Iron ores form deposits of metasomatic origin (up to 59 wt % Fe) in Vietnam and Laos (24, 31). Metamor- The Indochina Region contains diverse mineral phogenic ores, such as ferruginous quartzites, are of a resources (Fig. 2). The main oil and gas fields are lower grade, but in weathering crust the Fe concentra- assigned to recent shelves, continental slopes, and large tion in them increases to 55 wt % with a 3 wt % Mn Cenozoic depressions on the continent. The richest content (17) (Geology..., 1990). among them are the Irrawady (III, Fig. 2); Gulf of Thai- Manganese ores are represented by hydrothermal- land (IV); and, particularly, Mekong (V) basins (Min- sedimentary deposits in Paleozoic carbonate rocks and, eral..., 2004). in a few cases, by weathering crusts. Chromites were

GEOLOGY OF ORE DEPOSITS Vol. 47 No. 4 2005 Fig. 4. Geological sections of the Thachkhe iron ore deposit (31) in central Vietnam (Stepanov et al., 1983). (1) Loose Cenozoic deposits; (2) Late Paleozoic granitoids; (3-5) Thachkhe Devonian Suite: (3) hornfels and slate, (4) carbonate rocks, (5) idem with shale interlayers; (6) skarn; (7) brucite marble; (8) magnetite ores; (9) oxidized hematite ores; (10) pre- ore fault zone; (11) other faults. (I-VII) Sections.

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Fig. 7. Scheme of the geological structure of the Quyhop district (25) in Vietnam (Geology..., 1990). ( I ) Alluvium; (2) alluvium with cassiterite placers; (3) Jurassic-Lower Cretaceous siltstones, tuffstones, and rhyolites; (4) shales, tuffstones, and conglomer-ates of the Middle Triassic; (5) Carboniferous-Permian limestones; (6) Lower Carboniferous shales and limestones; (7) Ordovi-cian-Silurian calcareous shales, limestones, sandstones, and conglomerates; (8) Neoproterozoic- Lower Cambrian schists, quartz-ites, and gneisses; (9) Paleogene granites; (10) Paleozoic granites; ( 1 1 ) cassiterite-quartz occurrences; (12) cassiterite-sullide occurrences; (13) faults. larger northern part of the (Early Cretaceous) Burma- belts in the form of giant pipelike orebodies at the con- Malaya belt belongs to this type. Within this belt, in tacts of granites with carbonate rocks. This may be Thailand, along with large Sn and W deposits (23, 26, illustrated by the Beatrice pipe in the Kinta valley in 28, and 37-39), quite a number of small Sb and CaF2 western Malaysia (Fig. 3), from which 9000 t of tin deposits (not shown in Fig. 2) were discovered. As a concentrates were produced (Geology..., 1988). Sn and result, this country became a leader in producing these W bedrock and placer occurrences are shown in Fig. 2 mineral products (Mineral..., 2004). The Cathaysia belt (deposits 12, 14, 15, 19,23,28, 29, 37-39, 41, and 42). (Late Jurassic-Cretaceous), located in southeastern In some cases, hydrothermal Au occurrences are present China, is also of Malay type. It continues in the north- in these belts, as was recorded in South Vietnam (36). eastern direction into South Korea and in the southwestern into South Vietnam. 2. Continental-marginal belts of the Andean type evolve above the young, heated, gently dipping and, In their metallogeny, these belts resemble collision therefore, light and floating oceanic lithosphere. They belts of "continent-continent" type (for instance, the commonly develop on thick (up to 40-50 km) mature western Malay Peninsula at the end of the Triassic) or continental crust with high subduction rates and active "continent-island arc on continental crust" type (the overthrusting of the continental plate onto the oceanic eastern part of the same peninsula at the end of the Pale- one. A tectonotype of such belts is found in the Andes, ozoic and beginning of the Mesozoic) (Geology..., while, in southeastern Asia, they are represented by the 1988). The youngest "continent-continent" belt Late Cenozoic belt on the islands of Sumatra and Java appeared in the Himalayas in the Cenozoic. During col- (Gatinsky et al., 2000). The latter belt is characterized lision, the continental crust thickness sharply increased by porphyry copper, and, more rarely, skarn deposits (in the Himalayas and Tibet, up to 60-70 km (Ren et bearing base metals, gold, and silver. The continuation al., 1999). The richest Sn skarn deposits developed in of the Late Cenozoic active margin of the Sunda Islands these

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Fig. 8. Geological map of the Xiangquyen deposit (Geology..., 1990). ( I ) Lower Cambrian apatite-bearing metasedimentary rocks; (2-4) Proterozoic rocks: (2) gneisses, (3) mica schists and metasomatites, (4) gneisso-granites; (5) shear zone; (6) orebodies. was established in western Myanmar where the large of this type extends through northeastern Laos and Monywa porphyry copper deposit is located (21) Vietnam, and an Early Mesozoic belt, from southern (Bender, 1983). Similar belts are reconstructed for the China to central Thailand, while a Cenozoic belt is Early Paleozoic and Late Mesozoic in the west of the recorded in western Myanmar. Chromite deposits are Shan plateau in Myanmar (7) and in the Late Paleozoic common in alpine-type ultramafics (27); nickel, in in southern China (1,2, and 8), Laos and Thailand (30 weathering crust after ultramaflc rocks (6); and copper, and 32), and probably in western Cambodia (Gatinsky, in massive sulfide ores, still poorly explored in the 1986). region. 3. Cordillera-type continental-marginal belts are 5. Zones of intracontinental rifting are characterized associated with initial reworking of former passive by a bimodal volcanic association. The latter may be margins with immature continental crust. Skarns, gen- accompanied by volcanogenic Pb-Zn-Ag mineraliza- erated here in carbonate rocks at the contacts with gran- tion (Jurassic-Cretaceous sequences in the Tule district ite-granodiorite intrusions, are characterized by Fe, of northern Vietnam (Geology..., 1990). The shoulders Cu, and Pb ore mineralization, along with hydrother- of rifts often exhibit low-temperature mercury, anti- mal Zn, Pb, Au, and Cu occurrences. In the Indochina mony, and fluorite ore mineralizations and barite Region, the largest belt of this type extends from the deposits, along with average-temperature gold mineral- Xiengkhuang plateau in Laos through the Trungson ization. One of the most clearly distinguished belts of Range and Kontum emergence into northern Cambo- this type (Early Mesozoic) stretches in the northeast- dia. It was formed within the Late Paleozoic active mar- erly direction through southern China along a large Tri- gin of the Indosinian block (Gatinsky, 1986). Sulfide- assic paleorift (3, 4, 5, 9, 10, and 11). Gold-quartz quartz gold deposits (34) and vein lead-zinc occur- deposits within the borders of the Early Mesozoic rences occur here along with skarn iron deposits (24 Songda rift in northern Vietnam (Gatinsky, 1986) and and 31), one of the largest of which is shown in Fig. 4. the placers related to them are illustrated in Fig. 5. Among potential ore-bearing areas, there are three 4. Ophiolitic belts comprise complexes of ancient notable major ones. oceanic crust and the upper mantle of deepwater oceanic and marginal basins, nonvolcanic frontal arcs, and 6. Areas of trap formation magmatism of the rifted submarine terraces, as well as island arcs on oceanic continental crust are made up of continental tholeiites, crust. In many cases, they occupy an allochthonous subalkaline olivine basalts, differentiated stratified gab- position over more ancient complexes. A Paleozoic belt bro-norite intrusions, and gabbroids, which contain Ti-

GEOLOGY OF ORE DEPOSITS Vol. 47 No. 4 2005 TECTONICS AND GEODYNAMIC PREREQUISITES 323 magnetite and sulfide copper-nickel ore mineraliza- DISCUSSION tion. These areas, formed at the end of the Permian and The above-mentioned belts and areas embrace the beginning of the Triassic, are widespread in southern majority of zones in the Indochina Region promising China and northern Vietnam (22), where they were for ore mineral resources. Figures 1 and 2 show that ore developed prior to the Triassic rifting (Gatinsky, 1986). deposits, including large and superlarge ones, are for Recently, higher than normal planinum mineralization the most part concentrated in zones where tectonic has been revealed in a number of such areas in Vietnam structures of different types are crossed by metallo- (Polyakov et al., 1990; Thanh, 1994). genic zones, distinguished on the basis of geodynamic factors. Several areas deserve special attention. 7. Areas of granitoid magmatism of high alkalinity 1. The northwestern part of the Shan plateau in east above hot spots and paleoplumes enclose cassiterite- ern Myanmar, north of Mandalay and Baoshan in quartz, wolframite-quartz, and cassiterite-sulfide southern China. This part of the Sinoburmania block hydrothermal deposits, as well as skarns and rare metal was repeatedly reworked into continental-marginal vol- pegmatites with cassiterite and tantalo-niobates. The cano-plutonic belts. The large base metal massive sul- Mesozoic area of the Jos plateau in Nigeria is a classic fide Badwin deposit is situated here (7). Jadeite depos- example of such structures. The author was the first to its occur among rocks in the ophiolite belt (central reveal them in the Indochina Region (Gatinsky, 1986). Myanmar) overthrusting an ancient block, and the The most illustrative example is the Gejiu ore district in Mogou Proterozoic gneisses of the basement host ruby southern China (13), made up of Triassic terrigenous- deposits. Late Cenozoic (about 15 Ma) alaskite granites carbonate sequences cut by Late Mesozoic granites and alkaline rocks are also developed here (Bender, (Fig. 6). This area contains a considerable part of the Sn 1983). ore reserves of China, about 1400 thousand tons {Elec- 2. The southern China district, east of Kunming. tronic..., 2004), and large Be, W, Nb, and Та reserves. This area, situated at the border of the Triassic paleorift Another example is the Quyhop district in the northern zone, is undoubtedly promising for Sb, Hg, and Au part of central Vietnam, where the Sn ore mineraliza- deposits (3, 4, 5, 9, 10, and 11). The superposition of tion is related to subalkaline Paleogene granites occur- the neighboring Late Mesozoic continental-marginal ring in Neoproterozoic-Lower Cambrian crystalline volcano-plutonic Cathaysia belt (12, 14, and 15) pro- rocks. These bedrock sources produced rich of eluvial- vides an opportunity for revealing new rare metal alluvial cassiterite placers in the district (Fig. 7). occurrences. 3. The well-known Gejiu district in southern China The third area is connected with Carboniferous sub- and the adjoining territory of northern Vietnam—the alkaline granites in the northwestern Malay Peninsula, Fansipan Range and Hongha River. The area is charac- in the Kinta River valley. This area contains rare metal terized by widespread Cretaceous-Paleogene granites pegmatites with cassiterites and tantalo-niobates {Geol- and alkaline rocks along with Permian-Triassic differ- ogy..., 1988). The available geological data suggest entiated mafic-ultramafic intrusions at the borders of that similar areas may occur in the southern Malay Pen- the Triassic Songda rift. This environment led to the insula and in southern Vietnam (Gatinsky, 1986). appearance of a unique combination of ore mineralizations. These are sulfide copper-nickel ores, probably 8. The last type of the promising areas distinguished with PGE minerals (22); tin, tungsten, beryllium, and in the scheme is associated with Late Mesozoic-Ceno- tantalo-niobate mineralizations (13); and complex cop- zoic alkaline intrusions. This type is, most likely, also per-gold-rare-earth mineralization (16) probably asso- influenced by paleoplumes. Such areas are known in ciated with alkaline rocks and carbonatites (Palabora different parts of the region. However, their connection type?). In addition, there are metamorphosed phospho- with mineralization was reliably established only in rites (Laokay apatites) and Fe-enriched weathering northern Vietnam. Here, in the Xiangquyen (16) and crusts after magnetite quartzites (17). It may be sug- Namxe districts, there are outcrops of Paleogene grano- gested with a large degree of confidence that this area deserves further investigation. syenites, alkaline granites, shonkinites, and other alkaline rocks. The presence of carbonatites is also sug 4. Central Vietnam north of Vinh. This zone is gested {Geology..., 1990). The sulfide copper-gold and known for its Sn deposits in association with young highly alkaline granites (25), gold-quartz occurrences rare-earth (Ce group) ore mineralization associate with and gold placers at the Triassic paleorift (26) borders, intrusive rocks, which are hosted by Precambrian and and chromites in Paleozoic ophiolites (27). In this case, Lower Cambrian metamorphic rocks (Fig. 8). Orebod- as in the preceding one, there are encouraging pros- ies are located in ancient shear zones. Figure 8 does not pects for widening the mineral-raw material base. show Paleogene alkaline intrusive rocks exposed far- 5. One of the new most promising areas may be ther west. The prospects of this copper-gold-sulfide- identified farther south, in central Vietnam, in the north type mineralization, still insufficiently explored, may of the Kontum emergence. This part of the Indosinia be significant. block was repeatedly cut by intrusions of different age,

GEOLOGY OF ORE DEPOSITS Vol. 47 No. 4 2005 324 GATINSK Y both on the side of mobile belts of the Tethys zone in ACKNOWLEDGMENTS the Paleozoic and beginning of the Mesozoic and on the The author is grateful to V.I. Kazansky and side of the Pacific belt in the Late Mesozoic and Ceno- zoic. The Bongmieu gold-sulfide-quartz deposit (34) I.V. Murav'eva for useful remarks and valuable consul- has been developed here since the middle of the last tations while preparing the manuscript for print. century; its Au resources amount to 193 t (Mineral..., This work was supported by a grant from the Presi- 1999). Dozens of new Au deposits and occurrences of dent of the Russian Federation (grant no. NSh- the same type were recently discovered in this district, 99.2003.5) and by Fundamental Research Program in particular, in Neoproterozoic metamorphosed car- no. 5 of the Division of Earth Sciences, Russian Acad- bonaceous black shales (Lung, 2004). A uranium emy of Sciences. occurrence was discovered in Triassic coals of the Nongson deposit (33). Minor Late Cretaceous-Paleo- REFERENCES gene intrusions of potassic granites, also Au-bearing, are encountered in this district. 1. F. Bender, Geology of Burma (Gebruder Borntraeger, 6. There are good prospects for discovering new rare Berlin, 1983). metal occurrences in northwestern Thailand, where the 2. F. Blondel), "Les mouvements tectoniques de l'Indochine overprint of several tectonic and metallogenic belts of francaise," in Proceedings of the 4th Pacific Science different types has been reconstructed. Skarn and Congress, (Java, Jakarta, 1929), Vol. 2. hydrothermal W deposits (23, 28, and 29) and abundant 3. Electronic Data Base on Large and Super-large Depos antimony and fluorite occurrences occur in the district. its of Ore and Non-ore Minerals of the World, Ed. by Small areas of alkaline intrusions of Cretaceous age D. V. Rundquist (GGM, Moscow, 2004). were also noted. 4. Yu. G. Gatinsky, Lateral Structural-Lithologic Analysis 7. The famous Phuket (37 and 39) and Kinta Valley (Nedra, Moscow, 1986) [in Russian]. (40) Sn-bearing districts in the Malay Peninsula have 5. Yu. G. Gatinsky and Ch. S. Hutchison, "Calhaysia, been almost exhausted, though the ore-bearing zone Gondwana and the Palaeolethys in the Evolution of Con south of Kuala Lumpur is of interest. The superlarge tinental Southeast Asia," Geol. Soc. Malaysia Bull. 20, Kuala Langat placer cassiterite deposit (42) is situated 179-199(1987). here, and the zone encloses Carboniferous and Late 6. Yu. G. Gatinsky and A. Ya. Kochetkov, "Principal Types Cretaceous subalkaline granites. Carboniferous gran and the Tectonic Position of Au Ore Mineralization in ites show rather high Sn, Та, and Nb contents (Hutchi Southeast Asia," Dokl. Ross. Akad. Nauk 376 (1), 76-79 son, 1982). In the waters adjacent to the Malacca Strait (2001). and South China Sea, powerful dredges are used to 7. Yu. G. Gatinsky, Yu. P. 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