Thailand – Gem Origins Overview
Southeast Asian gem province centred on Chanthaburi, Trat, Kanchanaburi, Bo Phloi, and Bo Rai; world leader in corundum heat treatment and trading.
Introduction
Thailand hosts one of Southeast Asia's most important gem-producing and gem-processing provinces, centred on Cenozoic alkali basalt fields in the east (Chanthaburi-Trat) and west (Kanchanaburi). Bo Rai, Trat Province, was the dominant global ruby source during the 1970s–1980s; Keller (1982) noted Thailand had become "the world's major source of gem ruby" after Mogok's decline. [1]
Diagnostic significance for Thai corundum is the basaltic geochemical signature: high iron (above 600 ppm), a strong 451/460/470 nm iron absorption triplet, and weak to inert long-wave UV fluorescence, contrasting sharply with marble-hosted material from Mogok or Kashmir. Basalt-suite inclusions (zircon with radiation halos, ilmenite, enstatite, feldspar) confirm geological parentage.
Though Bo Rai is largely exhausted, Bangkok and Chanthaburi remain the world's dominant corundum trading and heat-treatment centres, processing rough from Cambodia, Vietnam, Burma, and East Africa. [2] The market remains active for independent buyers sourcing rough directly in the region, as recounted in a gemmologist's first-hand account of buying rough in Chanthaburi. Thailand is also the global hub for blue zircon, converting Cambodian rough by oxidising heat treatment. [3]
Geological Context
All Thai corundum deposits share a basaltic origin:
Basaltic Province
- Setting: Cenozoic intraplate alkali basalt fields along the Indochina block
- Age: Neogene to Quaternary volcanic activity
- Transport: Corundum crystallised at mantle depth and was transported to the surface by alkali basalt magmas
- Concentration: Gems accumulate in alluvial and eluvial placers derived from weathered basalt
- Chemistry: Basaltic environment imposes high-Fe, low-Cr signature on corundum – the defining geochemical contrast with marble-hosted Mogok ruby
Tectonic Context
- Post-subduction intraplate extension of the Indochina microplate
- Multi-stage sapphire formation at Bo Phloi reflects separate pulses of basaltic magmatism
- Same Southeast Asian alkaline basalt province as Cambodian Pailin field; deposits merge across the border
Mining Areas
| District | Province | Products | Status |
|---|---|---|---|
| Bo Rai | Trat | Ruby (historic 'Siam ruby') | Largely exhausted |
| Bo Welu / Khlung | Chanthaburi | Ruby, blue/yellow sapphire | Limited activity |
| Bo Phloi | Kanchanaburi | Blue and yellow sapphire | Mostly closed, well-studied |
| Kanchanaburi town area | Kanchanaburi | Blue sapphire | Historic |
Production History
Thailand's rise and evolution as a gem hub:
Rise to Prominence
- 1970s–1980s: Thailand became the world's dominant ruby source after Mogok production declined; Keller (1982) noted Thailand had become "the world's major source of gem ruby" following "the recent drastic decline in production from the classic ruby mines of Burma" [1]
- Bo Rai ruby production peaked in the 1970s–1980s; now essentially exhausted
Treatment and Trading Hub
- Bangkok and Chanthaburi developed into the world's dominant ruby and sapphire heat-treatment and trading centres
- Thailand pioneered the technology of heating Thai and Burmese rough to dissolve silk and improve colour [2]
- Material from Thailand, Cambodia, Vietnam, Burma, and East Africa is routinely treated and traded through Chanthaburi
Zircon Trade Hub
Beyond ruby and sapphire, Thailand is the global centre for blue zircon production:
- Cambodian and Vietnamese zircon rough is imported to Chanthaburi and Bangkok
- Heat treatment in oxidising conditions at 900–1000°C converts brownish rough to the prized "blue zircon" colour [3]
- Thailand exports the majority of the world's faceted blue zircon
Basaltic vs Marble-Hosted Corundum
References
- ↑ 1. Keller, P. (1982). The Chanthaburi-Trat Gem Field, Thailand. Gems & Gemology, 18(4), 186–196. DOI: 10.5741/gems.18.4.186.
- ↑ 2. Shor, R.; Weldon, R. (2009). Ruby and Sapphire Production and Distribution: A Quarter Century of Change. Gems & Gemology, 45(4), 236–259. DOI: 10.5741/gems.45.4.236.
- ↑ 3. Read, P. (2014). Gemmology (3rd ed.). Butterworth-Heinemann. DOI: 10.4324/9780080507224.