“Mineral” means geological resources which are inorganic matters having definite or slightly variable chemical components and physical properties, whether requiring smelting or tempering before being put to use or not, and includes coal, oil shale, marble, metal and slag derived from metallurgy, underground brine, stones as prescribed by the Ministerial Regulation to be ornamental stones or industrial stones, and clay or sand as prescribed by the Ministerial Regulation to be industrial clay or industrial sand, but does not include water or rock salt.

Figure 1 Map showing distribution of continental terranes in Thailand and adjacent areas (data from Wang et al., 2001; Fontaine, 2002; Ueno,2003; Chaodumrong et al., 2004).

Thailand is situated on the southern margin of South-East Asia and consists of two microcontinents; Shan-Thai and Indochina joining together during middle Triassic due to continent-continent collision. Prior to their collision and suturing, these two microcontinents have similarly tectonic evolutions which result in continental accretion of each mincrocontinent. The similarity is characterised as the subduction of oceanic crust underneath the two microcontinents but in opposite direction during late Permian. Consequently, paired orogenic belt of similar stratigraphic sequences and paleolatitudes are obviously present in both tectonic area and divided Thailand into three geological provinces as western province, central province and eastern province (Figure 1).

The western and eastern provinces which flank central province are Shan-Thai and Indochina microcontinents, respectively. These microcontinents consist of Precambrian crystalline basement rocks, while the central province are composed of approximately N-S trending fold belts of Paleozoic to Mesozoic marine sequences and subdivided into Sukhothai fold belt in the west and Loei fold belt in the east. These fold belts have generally N-S trend of volcanic rocks which are parallel to each other and are bound in the south by a strike-slip fault, namely Chao-Phraya fault. At the present, western part of Thailand and western half of eastern coast of Thailand are the portions of Shan-Thai microcontinent. The whole Khorat Plateau, on the other hand, is part of Indochina microcontinent (Bunopas & Vella, 1983; Sitthithaworn & Wasuwanich, 1992).

According to the tectonic model which suggested by Bunopas & Vella (1983), metallogenic Provinces in Thailand (Figure 2) can be divided into three regions and sub-regions as follows:

Northeastern province, including Sakon Nakhon and Khorat basins, can be distinguished from the adjacent fold belts or others geological province of Thailand mainly by the abrupt change in elevation and magnetic intensity patterns. This contrast generally follows the edge of Khorat plateau.

The stratigraphic sequences of Khorat plateau consist mainly of Mesozoic continental red beds and some basalt fields in the south. The deposits of Uranium-copper, potash, and rock salts in both Sakon Nakhon and Khorat basins well indicate the mineralization style that can be found in continental environment (Sitthithaworn & Wasuwanich, 1992).

Figure 2 The metallogenic map of Thailand show metalligenic provinces and subprovinces (Sitthithaworn, 1990a).

The western boundary of Central province is identified on the basis of mineralization styles. It begins form west of Changwat Chiang Rai and running southwardly along eastern outline of Khun Tan granitic batholiths until intercepts the Lan Sang strike-slip fault at Changwat Tak. The eastern boundary is Northeastern province, while one of the southern parts of Central province is believed to be situated in Cambodia (Sitthithaworn & Wasuwanich, 1992).

The Cenral province is subdivided into three subprovinces as Suknothai in the west, Loei in the east, and Pha Som in the middle.

The western volcanic belt is mostly late Permain-early Triassic and lies in between Silurian-Devonian and Carboniferous metavolcanic rock. The volcanic belt begins from Changwat Chiangrai and runs southwestwardly to Changwat Tak. The main distribution of metamorphic rocks should be in western belt while minor in Sukhothai subprovince. These metavolcanic rocks also represent an old island arc and trench systems while the western volcanic belt is a younger one. Although the position of the older arc and trench system are not clearly defined, the younger volcanic arc trench probably lay in between Changwat Lampang and Changwat Phrae because the volcanic rock exposed between the 2 provinces are succeeded by basal volcanic conglomerate and other volcanic clast-existing marine sedimentary rocks of Lampang group that suggest volcanic arc environment.

On the east side of the Permian-Triassic arc system there are late Triassic-early Jurassic volcanic belt aligns obliquely to the older belt. The relative wide-spread distribution of copper, stibnite, barite and fluorite deposits and to a lesser extent, gold, galena, manganese and wolfram deposits along the Permian-Triassic volcanic in Sukhothai subprovince are the group of minerals commonly found in volcanic arc system. Furthermore, types of deposit of these minerals are in vertical spectrum of the arc system starting from epithermal deposit down to epizonal pluton association.

Due to the tectonic setting, Loei subprovince is similar to Sukhothai subprovince in being an island arc caused by subduction, and both of them generally have the belts of volcanic rocks parallel to each other. The noticeable difference, however, are the exposure of volcanic and intrusive rocks as well as the known mineralization styles. More intrusive and volcanic rock are exposed in Loei subprovince. These intrusive rocks are commonly associated with andesite, rhyolite and andesitic tuff, and generally produce skarn deposits of iron and copper (usually malachite and chalcopyrite). In some relatively well studied areas, such as the Phu Lon, significance amounts of native gold, electrum, silver and molybdenite in affiliation with magnetite and chalcopyrite have been reported. All the mentioned deposits imply the predominance of lower level in vertical spectrum deposits normally found in island arc system.

Pha Som subprovince conspicuously differs from the previous subprovinces in many aspects such as tectonic setting, mineralization styles and lithology. This subprovince appears as a narrow strip of mafic-ultramafic rocks. The extending trend is interpreted to be shifted southwardly around southeast of Changwat Uttaradit passing Changwat Phitsanulok, Changwat Nakhonsawan and finally intercept Chao-Phraya fault around Changwat Phranakhon Siayuthaya.

Only two chromite occurrences have been found in this subprovince. The first one occurs in serpentinite together with magnesite, asbestos, and talc in Changwat Uttaradit. Another one has been found as blocks in serpentinite and as cobbles along gullies in Changwat Prachinburi.

Western province, including western part of northern Thailand as well as western and southern Thailand, is a part of Shan-Thai microcontinent. It mainly consists of Precambrian to middle Paleozoic rocks with which granite batholiths and stocks are frequently associated, except some areas in southern Thailand which Carboniferous to Permain pebbly mudstones of Phuket and Kang Krachan groups are predominant. This association of these rocks has not been found in other province.

Mineralization styles within Western province are what commonly found in continental setting since this province is a part of Shan-Thai microcontinent. Variety of deposit types is common in Western province but tin and tungsten deposits are the obvious indications of continental setting. Hydrothermal deposits of stibnite, barite, lead and fluorite are also found but postdated igneous intrusions.

Due to the obviousness of lithology and mineral deposits, Western province is classified into four subprovinces as follows:

Tin and tungstern deposits are predominated within this subprovince, while stibnite, barite, zinc and fluorite deposits are subordinate. Iron and lead deposits are very minor. Tin and tungsten in this subprovince are mainly found as dissemination and hydrothermal veins in granite or country rocks, and to a lesser extent, as pegmatite and replacement.

Similarly with Chaing Mai subprovince, Kanchanaburi subprovince has predominately galena deposits while stibnite, zinc and fluorite are subordinate. The most important galena deposit in Kanchanaburi subprovince is the replacement type in Ordovician limestone. The concentration of lead in the limestone is still controversial as hydrothermal or sedimentary origin. However, tin deposits may probably be essential if thoroughly exploration is made.

A unique lithology of Chumphon subprovince which comprises of Kang Krachan and Phuket group pebbly mudstones is similar to the adjacent Permian to Carboniferous Mergui formaton in Myanmar. The predominant deposits in this area are tin placers and disseminated tin in granite while placer gold deposits are also found scattering. However, the cause of the uniqueness is still ambiguous.

Nakon Si Thammarat subprovince resembles to the first two subprovinces in lithology. A hydrothermal magnetite-specularite deposit has been found at Amphoe Chawang, Changwat Nakon Si Thammarat.

For conclusion, Western province is the province of tin, tungsten, lead, zinc, stibnite, gold, fluorite, barite, and iron deposits.

Mineral deposits of metal in Thailand are described as follows:

Tin

Major tin productions are mostly from offshore. Some are from continental deposits, mainly in mountain ranges running north to south along the west of the country. Most of tin are excavated from both onshore and offshore placer deposits, where gravel pumping and dredging mining methods are appropriate. Tin deposits were primarily found in granitic rocks or their adjacent wall rocks in forms of veinlets, pegmaties, aplites, greisens and dissemination in granites. Associated wolframite is occasionally found. In addition, cassiterite is also found in the contact area between granite and limestone producing skarn-type tin-deposit of so-called tactite.

Tungsten

Tungsten, likely wolframite has been recovered from many tin mines of both placer and vein deposits. Ferberite deposit was found in Nakhon Si Thammarat Province, and Phrae Province.

The deposit at Khao Soon area was found in brecciated silicified mudstone. None of igneous rocks has been observed in the nearby area. Scheelite was found in Chiang Rai Province. The deposit is found in tactite and schist originated by contact-metasomatism between biotite granite and limestone-shale.

Iron

Most of iron minerals in Thailand were found as small deposits in Loei Province. These are contact metasomatic deposits where iron occurs in form of hematite and magnetite.

Copper

Porphyry copper deposits were found in Loei Province, and appeared to be high potential areas for copper in Thailand. Magnetite and gossans were found on the surface of Phu Hin Lek Fai area where malachite grains can be traced in the weathered diorite porphyry along the trench. The other copper deposit, Phu Lon, Nong Khai Province, is one of the high potential areas for copper and gold. Chalcopyrite, pyrite, and gold-silver are the main minerals found in the mineralized zone. The chalcopyrite and pyrite are found as veins, veinlets and disseminated ores throughout garnet skarn. Sphalerite was also found as inclusions within chalcopyrite in small amount.

Generally copper occurrences were mentioned in many locations, in the area of igneous rocks containing malachite and azurite, but none of them are shown to be the economic deposit.

Zinc

The well-known zinc deposit, at Mae Sot district of Tak Province, has been exploited since 1984 by Pa Daeng Industry Co., Ltd. The main ore minerals at Pa Daeng deposit are hemimorphite (Zn₄Si₂O₇(OH)₂.H₂O) and smithsonite (ZnCO₃). Minor amounts of zinc carbonate minerals, hydrozincite (2ZnCO₃.3Zn(OH)₂) and loseyite [(ZnMn), (OH)₁₀(CO₃)₂] are present. The ore body can be divided in two main parts, by which the western part of the ore body is dominantly hemimorphite in calcareous sandstone, where the eastern part is dominantly smithsonite in limestone of Triassic age.

Gold

Gold occurrences in Thailand have been reported in several localities. Most of them are placer deposits, derived from primary vein deposits. Gold-bearing quartz veins are commonly observed in granite, diorite, volcanic, and some metamorphic rocks. Native gold was also found as very small inclusions in chalcopyrite vein. Copper ores and porphyry copper deposits in Loei Province probably contain some native gold as an inclusion.

Mineral Resources Potential

According to the airborne geophysical surveys and the interpretation, several mineral commodities are considered to have high potential in many areas throughout the country, as described above. However, the extensive exploration is needed for future development.

Figure 3 Mineral Distribution Map of Thailand (Thawat Japakasetr and Pairatt Jarnyaharn, 1992)

Metallic minerals forming massive sulphide ores of lead, zinc, copper and associated minerals seem to have a great potential among other commodities and require the detailed ground follow-up survey. Gold deposits within or nearby porphyry copper and in epithermal volcanic areas are very interesting. Since primary gold in quartz veins have been investigated, numbers of gold occurrences are discovered with some having high grade ore. It is, therefore, considered that gold is another mineral potential in Thailand for exploitation in the near future. Moreover, modern exploration technology would give rise to the better understanding and recovery of the known deposits.

The two major mines for lead and silver at Kanchanaburi Province (Song Toh), and for zinc at Mae Sot (Pa Daeng), Tak Province, have been in production for years. Stratabound occurrences will probably yield further discoveries of lead, zinc, and silver with modern exploration in these areas.

Copper mineralization was found associated with volcanic rocks and porphyry in some areas. Thailand has volcanic rock which could host massive sulphide deposits, especially in the areas where airborne electromagnetic anomalies are considerably high.

Thailand is known as a major fluorite, barite and antimony province. Some deposits, especially for barite, are considered to be the indicator for gold and base metals.

Vast reserve of rock salt in the Cretaceous Maha Sarakam Formation on the Khorat Plateau is undoubtedly inexhaustible. Potash deposits of carnallite and sylvite, found in some areas on the Khorat Plateau, are also considerably of economic value.

Some mineral resources showing a possibility to be a good potential in the future are Rare Earth and heavy minerals, which have been discovered from offshore areas and in the vicinity of tin mines. Dolomite deposits probably are much more extensive than presently recognized. Potential for chromium and nickel deposits in the vicinity of ultra-mafic rocks in northern Thailand are moderately favorable.

Clay and feldspar potential appears to be substantial, and sources are widely distributed throughout Thailand. Limestone and granitic rocks for dimension stones in ornamental and construction purposes are now one of the main activities in mining industry, and have a very high potential in the future.

Furthermore, the expansion of exploration for industrial minerals, such as clay minerals for ceramics, limestone for cement factory and other purposes are increased annually. The production of raw material in this commodity will be of great benefit to the economics of the country for a long period of time.