Mineral
“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.
Geological Settings
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).
Metallogenesis and Metallogenic Provinces
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:
(1)Northeastern Province
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).
(2)Central Province
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.
(3)Western Province
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
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.
Types, Characteristics and Occurrences of Mineral 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.
Manganese
Manganese was found as stratiform, vein type and residual deposits. The ore bodies
are irregular shape and pocket like. Almost all deposits occurred in clastic sedimentary
rocks. Most manganese deposits were reported to have discovered in the northern
part of Thailand and in Loei Province.
Antimony
Antimony deposits in Thailand are mainly vein type, formed along sheared and brecciated
fault zones in sedimentary and granitic rocks. Such veins display irregular form
and, sometimes, pockets. Stibnite and stibiconite are common ore minerals with quartz
and calcite as gangue minerals. Galena and fluorite are associated minerals locally
found in some stibnite veins. The antimony deposits are dominant in the northern
part of Thailand, such as Lampang, Phrae, Chiang Mai and Lamphun Provinces. Few
are found in Surat Thani Province in the South and Chon Buri in the East.
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.
Lead
A large number of lead deposits have been found in Kanchanaburi Province. Galena
ore body and minor sphalerite occur in Ordovician limestone as veins along fractures
and faults, sometimes as irregular veinlets and brecciated mass. Silver is usually
associated with galena. Cerussite has been found on the surface as secondary mineral
in many areas. Ordovician limestone terrain in Kanchanaburi Province is the most
favorable potential area for extensive exploration for lead deposits.
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.
Potentials and Productions of Mineral Resources
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.