Ruby mines: every major deposit named and explained

Mogok Stone Tract: the named mining localities

The Mogok Stone Tract covers approximately 400 square kilometres in the Mandalay Region of Myanmar, centred on the town of Mogok at approximately 22.9°N, 96.5°E. Within this broad area, gem mining has been documented at dozens of specific localities. The following are the principal named mining areas with documented geological and production character.

Kyatpyin

Kyatpyin is one of the most consistently productive named localities within the Mogok Stone Tract. Located northeast of the town of Mogok, Kyatpyin's mines work primary marble-hosted corundum in bedrock and secondary gravel deposits derived from the marble. The geology here shows the classic Mogok marble sequence: white to pale grey calcite marble with alternating dolomitic bands, carrying ruby in pockets and stringers where the chromium-bearing metamorphic fluids concentrated during crystallisation. Kyatpyin rubies show the low iron, strong fluorescence character of the best Mogok material. Some of the documented fine specimens with clear Mogok provenance in museum collections and private holdings are attributed to Kyatpyin by dealers with long histories in the valley (Hughes, R.W., Ruby and Sapphire, 1997, pp. 108–115; Ward, F., Rubies and Sapphires, Gem Book Publishers, 1991, pp. 12–18).

Thurein Taung

Thurein Taung, a mining area whose name means roughly "elephant mountain" in Burmese, represents one of the more active primary mining areas in recent decades. Work here involves hard-rock extraction from primary marble formations at higher elevation, a more capital-intensive operation than working alluvial gravels but one that accesses fresh, undisturbed primary material rather than the secondary gravel deposits that have been largely picked over at valley level. Material from Thurein Taung has been documented in Lotus Gemology field reports as contributing to current production of fine-quality Mogok rough (Lotus Gemology field reports, lotusgemology.com; Hughes, 2017, updated field notes).

Bernardmyo (Bernardmyaing)

Bernardmyo is historically significant and frequently cited in 19th and early 20th century records of Mogok production. British colonial records from the period when the British Burma Ruby Mines Company held the mining concession (1887–1925) reference Bernardmyo among the productive localities worked during that period. Historical records from the company's annual reports, quoted in Hughes (1997), indicate significant production of gem-quality material from this area. Current production from Bernardmyo is reportedly modest compared to historical levels, consistent with the general pattern of declining accessibility of the richest alluvial and near-surface primary deposits across the valley (Hughes, 1997, pp. 112–116; British Burma Ruby Mines Company records as referenced in Hughes).

Wetloo

Wetloo is a mining area northwest of Mogok town associated with primary marble workings at depth. Material from Wetloo has been associated with particularly fine spinel production alongside ruby; the marble formation here produces both gem species, and dealers in Mogok historically purchased mixed parcels containing ruby, spinel, and occasionally sapphire from Wetloo miners (Hughes, 1997, pp. 113–114).

Pyan Gaung

Pyan Gaung is known for producing some of the largest crystals in the Mogok tract, though large crystals do not always translate to gem-quality material. The geology here shows thicker marble horizons with larger crystal growth pockets, which produces coarser crystal sizes. Fine gem-quality material from Pyan Gaung is documented, and large rough crystals from this area have appeared in the Yangon and Mogok trading markets (Hughes, 1997, p. 113).

Kyauk Pyat Thar

This locality, sometimes transliterated differently in various English-language sources, is associated with a higher proportion of ruby in gneiss and schist rather than pure marble: the contact zone between marble and metamorphic gneiss can produce ruby with slightly different inclusion populations from the pure marble-hosted stones. Contact zone rubies may show inclusions of biotite, sillimanite, or other minerals from the surrounding gneiss in addition to the calcite typical of pure marble-hosted stones. This mixed inclusion suite is one basis on which laboratories sometimes distinguish different Mogok localities, when the data is sufficient (Lotus Gemology field notes; Gübelin Gem Lab archive).

Secondary (alluvial) deposits: the valley floor gravels

Across the valley floor and lower slopes of the Mogok Stone Tract, alluvial gravel deposits (called "byon" in Burmese) have been worked for centuries. These secondary deposits contain rounded ruby crystals liberated from the primary marble by erosion and concentrated by water action. The alluvial deposits are generally more accessible than primary workings and have been the primary source of production for most of the valley's history. They are now largely worked out at shallow depths: serious new production increasingly requires either deeper alluvial excavation (pit mining with water pumps) or hard-rock primary quarrying. The alluvial material from Mogok tends to show some abrasion of crystal faces and rounded edges from transport, distinguishable under magnification from the sharper-edged crystals found in primary workings (Hughes, 1997, pp. 108–112; Ward, 1991, pp. 12–20).

Star ruby localities: Kyaukme and adjacent areas

The Mogok Stone Tract and adjacent areas of northern Myanmar also produce star rubies: stones with oriented rutile silk dense enough to produce a six-rayed asterism when cut as cabochons. Star ruby localities within and adjacent to Mogok tend to produce corundum with higher rutile content, sometimes at the expense of transparency. The finest star rubies in world museum collections, including the DeLong Star Ruby (100.32 carats, in the American Museum of Natural History, New York) and the Rosser Reeves Star Ruby (138.7 carats, Smithsonian Institution), are attributed to Burmese origin broadly, most likely from the Mogok/Kyaukme area (AMNH collection records; Smithsonian collection records).

Mong Hsu, Shan State, Myanmar: deposit structure and production history

Mong Hsu is located in southern Shan State, approximately 250 kilometres southeast of Mogok at approximately 21.0°N, 97.0°E. The deposit was discovered as a commercial gem ruby source in 1992 by local farmers and quickly became one of the world's largest ruby supply sources by volume, though not by top quality (Hughes, R.W., Ruby and Sapphire, 1997, pp. 136–145).

Geological structure

The Mong Hsu deposit is hosted in marble of the same broad metamorphic belt as Mogok, but the specific geological context differs: the marble here shows different secondary mineral populations, different fluid inclusion types, and different trace element chemistry in the rubies produced. The most notable characteristic of Mong Hsu ruby in the rough is the strong colour zonation: a dark purplish-blue core (caused by iron-titanium interactions in the crystal growth conditions) surrounded by a red rim (from chromium). Unheated Mong Hsu rough shows this blue core clearly and is essentially unsaleable without treatment.

High-temperature heat treatment (1,800°C or above, significantly hotter than the treatment used for most Mogok material) dissolves the iron-titanium interaction causing the blue core, producing a more uniform red across the stone. After treatment, Mong Hsu rubies can show fine red colour. However, the high-temperature treatment required produces specific telltale features under microscopic examination: fully dissolved silk (rutile needles completely absent), specific types of rutile discoids around solid inclusions, and sometimes tension fractures around inclusions caused by the thermal shock of the treatment cycle. These features allow laboratories to identify the combination of Mong Hsu origin and high-temperature heat treatment reliably (GIA Gems and Gemology; Gübelin Gem Lab; SSEF technical notes on Mong Hsu treatment).

Production scale and market impact

At its peak in the mid-to-late 1990s, Mong Hsu was producing a large fraction of global commercial ruby supply by weight. The deposit flooded the market with heated commercial material that changed pricing structures for mid-grade heated rubies. Its long-term impact was to establish heat treatment as standard rather than exceptional for commercial ruby, and to create the infrastructure for high-temperature treatment in Bangkok that persists today (Hughes, 1997, pp. 136–145; Wise, R.W., Secrets of the Gem Trade, 2nd ed., Brunswick House Press, 2016, pp. 75–78).

Namya, Kachin State, Myanmar: the north Myanmar ruby

Namya is located in Kachin State, far northern Myanmar, in a geological setting distinct from the Mogok and Mong Hsu deposits to the south. The deposit, which became commercially known in the late 1990s and 2000s, produces marble-hosted ruby in the upper Chindwin/Kachin geological terrane. Namya rubies have been documented and studied by gem laboratories, and the deposit has its own trace element and inclusion signature that distinguishes it from Mogok, though the two share the marble-hosted low-iron character (Lotus Gemology field reports; GIA research notes on northern Myanmar ruby).

Namya is notable for producing rubies with a slightly different colour distribution than classic Mogok: some Namya material shows vivid colour with a more orangey secondary hue than the classic purplish-red of Mogok. Fine unheated Namya rubies have been certified by major laboratories and have appeared in fine gem auctions, though volume is limited. The political situation in Kachin State, which has been subject to ongoing conflict, has made consistent production difficult (Lotus Gemology, lotusgemology.com).

Montepuez, Mozambique: block by block

The Montepuez ruby deposit in Cabo Delgado Province, northern Mozambique, is operated primarily by Gemfields plc through its subsidiary Montepuez Ruby Mining Limitada (MRM), which holds a 36,000-hectare mining concession granted in 2011. Within this large concession area, production is concentrated in several named blocks that have been identified through systematic exploration as having the highest ruby concentration and quality (Gemfields corporate reports and operational updates, gemfields.com).

Maninge Nice block

The Maninge Nice block (the name translates roughly as "good place" in the local language) is the primary production block within the Montepuez concession and the source of most of the higher-quality material Gemfields has sold at its tender auctions. The geology here shows the ruby-bearing amphibolite and graphitic gneiss sequence described in the origin article, with ruby occurring in primary hard-rock formations as well as secondary elluvial (near-surface, not transported far from primary source) deposits. The elluvial deposits at Maninge Nice have been the most productive in recent years, with bulldozer-assisted stripping of the laterite overburden exposing the ruby-bearing soil horizon (Gemfields operations reports; Lotus Gemology field reports on Mozambique, lotusgemology.com).

Glass block

The Glass block, so named for the glassy, transparent character of some of the ruby rough found there, produces material with a slightly different morphological character from the Maninge Nice block. Glass block rubies tend to have higher transparency as rough crystals, which correlates with potentially better face-up clarity after cutting. Some of the finest quality unheated Mozambican rubies that have appeared in international auction markets have been attributed to Glass block production (Gemfields operational updates; Lotus Gemology).

Ntorro block and other concession areas

The broader concession area includes additional named blocks including Ntorro and others that are in various stages of exploration and development. The full extent of the Montepuez deposit's gem-quality potential has not been exhaustively mapped, and Gemfields continues geological exploration within the concession boundaries (Gemfields annual reports 2014–2024, gemfields.com).

Artisanal mining areas adjacent to the concession

Significant artisanal and small-scale mining (ASM) occurs on land adjacent to the Gemfields concession, operated by individual miners and informal cooperatives. Material from ASM miners enters the market through local traders in the nearby town of Montepuez and eventually reaches Bangkok, Jaipur, and other cutting centres. ASM Mozambican material is often indistinguishable by laboratory analysis from Gemfields-mined material, since it comes from the same geological deposit. The existence of ASM activity means that "Mozambique, Montepuez" on a laboratory certificate does not imply Gemfields chain of custody: it is a geological origin statement, not a supply chain certification (Gemfields corporate responsibility reports; Lotus Gemology field notes).

Luc Yen, Yen Bai Province, Vietnam: sub-deposits and localities

The Luc Yen mining district is located in the mountainous Yen Bai Province of northern Vietnam, approximately 300 kilometres northwest of Hanoi at approximately 22.1°N, 104.7°E. Mining here accelerated from the late 1980s as Vietnam's economic reforms (Doi Moi) opened the country to external trade (Hughes, 1997, pp. 148–158; Lotus Gemology field reports on Vietnam).

Khoan Thong and Nuoc Ngap localities

Within the Luc Yen district, the Khoan Thong and Nuoc Ngap areas are the principal ruby-producing localities. The geology is marble-hosted, similar to Mogok in its broad character: the Luc Yen carbonate sequence is part of the same Indosinian metamorphic belt that extends from Tibet through Myanmar and into northern Vietnam. The local marble shows calcite and dolomite mineralogy, producing rubies with calcite inclusions similar in some respects to Mogok material, though with different fluid inclusion populations that help laboratories distinguish the two origins (Lotus Gemology; Hughes, 1997, pp. 152–154).

Khoan Thong is the area most associated with fine-quality Luc Yen ruby. Some of the finest Vietnamese rubies reaching international auction markets have been attributed to this locality by dealers with direct sourcing relationships. The marble here shows a distinctive secondary mineral assemblage including specific amphibole and feldspar minerals that produce diagnostic inclusions in the hosted rubies (Lotus Gemology field reports).

Nuoc Ngap and the flooded mine problem

The name "Nuoc Ngap" translates roughly as "flooded water" in Vietnamese, reflecting the geological reality of this mining area: ruby-bearing marble occurs below the local water table in several areas, requiring continuous pumping during extraction. The Nuoc Ngap deposit has produced significant quantities of commercial to fine ruby, including star ruby material with well-formed asterism. Water management is the primary operational challenge here (Hughes, 1997, p. 153; Lotus Gemology).

An Phu and Truc Lau localities

An Phu and Truc Lau are secondary localities within the Luc Yen district that produce smaller quantities of ruby alongside the primary production areas. Material from these localities tends to be more commercial in quality, mixed with the broader Luc Yen production stream. The trace element and inclusion profiles of Luc Yen material as a whole are well-documented by major laboratories, though sub-locality precision within Luc Yen is not yet standard laboratory practice (Lotus Gemology field reports).

Quy Chau, Nghe An Province, Vietnam

Quy Chau is located in Nghe An Province in north-central Vietnam, approximately 400 kilometres south of Luc Yen at approximately 19.6°N, 105.0°E. The deposit differs geologically from Luc Yen: while both are marble-hosted, the Quy Chau marble sequence shows different secondary mineralogy, producing rubies with a distinctly different trace element profile and inclusion population (Hughes, 1997, pp. 155–157; Lotus Gemology).

Quy Chau rubies typically show a more distinctly purplish hue than Luc Yen material, sometimes appearing quite violet-red, reflecting different chromium-iron-titanium trace element ratios. The finest Quy Chau stones are fine gems, but the proportion of the production reaching fine quality is lower than at Luc Yen. Commercial quality Quy Chau rubies are commonly found in the Hanoi and Ho Chi Minh City gem markets, often alongside sapphire from the nearby Quy Hop sapphire deposit (Lotus Gemology; Hughes, 1997).

Jegdalek, Afghanistan: deposit structure and current status

The Jegdalek ruby deposit is located in Sarobi District, Kabul Province, Afghanistan, approximately 70 kilometres east of Kabul at approximately 34.6°N, 69.8°E. The deposit sits at an elevation of approximately 2,300 metres in the rugged mountains of the Laghman range (Ward, F., Rubies and Sapphires, 1991, pp. 35–38; Hughes, 1997, pp. 160–168).

Geology of Jegdalek

Jegdalek is a marble-hosted ruby deposit in the Kabul Block metamorphic terrane, a geological unit with ancient Precambrian basement that experienced later metamorphic overprinting. The marble host at Jegdalek shows calcite with dolomite and minor graphite, producing rubies with calcite inclusions similar to Mogok in type, though with a different spatial distribution and paragenesis. The trace element profile of Jegdalek rubies, particularly the iron-to-chromium ratio and the specific gallium and vanadium concentrations, is distinctive enough that major laboratories can reliably identify the origin (Gübelin Gem Lab; AGL; SSEF).

Jegdalek rubies at their finest show strong fluorescence under UV and in natural daylight, similar to Mogok marble-hosted stones. The colour tends toward a slightly stronger purplish secondary hue than classic Mogok, a character some collectors specifically seek. Fine unheated Jegdalek rubies are legitimate top-tier stones. Their market price relative to Mogok reflects the prestige premium for Mogok's thousand-year history rather than any consistent inferiority of the stones themselves at comparable quality levels (Wise, 2016, pp. 78–80).

Production history and access constraints

Jegdalek has been mined intermittently for centuries: Mughal records and earlier Afghan trade documentation mention rubies from this area. The British Geological Survey documented the deposit during the colonial period. Modern commercial production has been constrained by Afghanistan's political instability. Periods of significant production occurred in the 1960s and 1970s under relatively stable conditions, and again briefly in the early 2000s. Since then, access has been difficult and production sporadic. Most Jegdalek rubies in current circulation come from older production that has been held in private hands or traded through Pakistani and Indian dealers who historically had access to the region (Hughes, 1997, pp. 160–165; Ward, 1991, pp. 35–38).

Didy and Andilamena, Madagascar: the island's two ruby characters

Madagascar's ruby production divides into two distinct geological types that produce commercially very different material: the basalt-hosted deposits centred on Andilamena and Vatomandry, and the marble-hosted deposit at Didy. Understanding this distinction is essential for anyone buying Madagascar-origin ruby (Lotus Gemology field reports on Madagascar; GIA Gems and Gemology research notes on Didy).

Andilamena and Vatomandry: basalt-hosted commercial production

Andilamena is located in the Alaotra-Mangoro Region, central-eastern Madagascar. The ruby deposit here is associated with alkali basalt volcanism, similar in geological character to the Thai and Cambodian deposits. The rubies show high iron content, weak fluorescence, and typically require heat treatment to produce commercially acceptable colour. Andilamena became a significant commercial production area from the late 1990s, contributing to global supply of heated commercial ruby at competitive price levels.

Vatomandry, on the eastern coast of Madagascar, is another basalt-related ruby locality producing broadly similar material. Commercial heated Madagascar ruby from these basalt-hosted sources is traded through Antananarivo dealers and eventually reaches the Bangkok and Jaipur cutting markets (Lotus Gemology field reports).

Didy: the marble-hosted exception

Didy is located in the Alaotra-Mangoro Region, approximately 300 kilometres north of Antananarivo. The deposit was identified as commercially significant around 2012 when fine-quality ruby with marble-hosted character began appearing in Bangkok and at international auction houses. The geology at Didy shows marble and calc-silicate rocks hosting chromium-bearing corundum, producing rubies with low iron content and fluorescence character more similar to Mogok than to the basalt-hosted Madagascar sources.

Major laboratories including Gübelin, AGL, and SSEF have documented and defined the Didy origin signature: specific mineral inclusions (calcite, apatite, and certain amphibole minerals characteristic of the Malagasy marble sequence), combined with trace element profiles distinguishable from both Mogok and the basalt-hosted Madagascar material. Fine unheated Didy rubies have been offered at Christie's and Sotheby's and have achieved prices reflecting their marble-hosted quality, positioned below Mogok but competitive with other mid-premium origins (Gübelin Gem Lab; Lotus Gemology; Christie's Geneva results).

Thailand: Chanthaburi-Trat and the treatment centre geography

Thailand's ruby-producing areas are concentrated in the Chanthaburi-Trat region in the southeastern corner of the country, near the Cambodian border. The principal ruby-producing areas include Bo Rai (Trat Province) and the broader Chanthaburi gem field. These are alkali basalt-hosted deposits of the type described in the fluorescence section: high iron, dark colour requiring heat treatment, weak fluorescence (Hughes, 1997, pp. 185–196; Ward, 1991, pp. 50–60).

Bo Rai, Trat Province

Bo Rai was historically the most productive Thai ruby locality, producing significant quantities of dark red ruby from basalt-derived secondary deposits worked by open-cast and pit mining. Production has declined substantially from peak levels as accessible deposits became exhausted. Bo Rai rubies are typically dark, with strong colour but little luminosity: the high iron content produces this character. The stones almost universally require heat treatment to reach commercial quality (Ward, 1991, pp. 50–52).

Chanthaburi's role as treatment hub

Chanthaburi's importance to the ruby market today is less as a production centre (Thai production has largely declined) and more as a treatment hub. The town contains dozens of heating workshops that treat ruby rough and finished stones from Myanmar, Mozambique, Madagascar, Vietnam, and other sources. The "Bangkok treatment" for ruby, meaning the high-temperature heat treatment in oxidising or reducing atmospheres, was largely developed and refined in the Chanthaburi-Bangkok corridor. Understanding that "Bangkok heated" refers to a treatment location rather than an origin location is important for accurate reading of trade documentation (Wise, 2016, pp. 75–80).

How laboratories identify specific mines within an origin

The question of mine-level origin determination, as distinct from country or region-level origin determination, represents the frontier of gemological science. Here is the current state of what is and is not achievable.

What inclusion microscopy can and cannot do

Different named localities within the Mogok Stone Tract show subtly different secondary mineral assemblages in the host marble, which are reflected in the inclusion populations of the hosted rubies. Kyatpyin rubies may show different calcite morphology or different fluid inclusion character from Pyan Gaung material. These differences are real and documented in the Gübelin archive and in Lotus Gemology's published field research. However, the overlap between localities is substantial, and the reference database for mine-level identification is less comprehensive than for country-level identification. Trained laboratory gemologists can sometimes suggest a more specific locality based on inclusion evidence, particularly for very well-characterised stones or when a specific unusual mineral inclusion is present. This remains a specialist judgment rather than a standardised procedure (Gübelin Gem Lab archive; Lotus Gemology field research; Gübelin and Koivula, Photoatlas of Inclusions, 1986).

What LA-ICP-MS trace element analysis can do

Laser ablation mass spectrometry provides trace element concentrations at parts-per-million levels across a panel of elements including iron, titanium, vanadium, gallium, chromium, magnesium, and others. For country and regional origin determination, the trace element profiles are robust and well-documented: the difference between Mogok and Mozambique is measurable and statistically significant. For sub-locality determination within a country, the data is more equivocal: different localities within Mogok show overlapping trace element ranges because they share the same broad geological environment, differing only in local detail. LA-ICP-MS adds confidence to country-level determinations and can help distinguish broad regional types (marble-hosted vs basalt-hosted, for example) but mine-level precision within a country remains beyond routine laboratory capability for most origins (Gübelin Gem Lab; SSEF; AGL methodology documentation).

Isotope analysis: the emerging frontier

Stable isotope analysis, particularly oxygen and carbon isotopes from carbonate inclusions in marble-hosted rubies, offers the potential for more refined provenance determination. The isotopic composition of the carbonate host marble varies by geological terrane and even by locality within a terrane, reflecting differences in the original limestone precursor and the metamorphic fluid history. Research programs at Gübelin and in academic institutions have explored this approach, with promising results for distinguishing marble-hosted ruby origins that are difficult to separate by trace elements alone (Gübelin Gem Notes, published research summaries). This technique is not yet routinely applied in standard commercial certificates but represents the direction in which mine-level identification is moving.

Source: Gübelin, E.J. and Koivula, J.I., Photoatlas of Inclusions in Gemstones (1986); Gübelin Gem Lab origin methodology documentation (gubelingem.com); AGL technical notes (aglgemlab.com); Lotus Gemology field reports (lotusgemology.com); Hughes, R.W., Ruby and Sapphire (1997/2017). Reliability assessments reflect current laboratory practice.

Sri Lanka: Ratnapura and Elahera districts

Sri Lanka's ruby and sapphire production is concentrated in two districts: Ratnapura (the "city of gems") in Sabaragamuwa Province, and Elahera in Central Province. Both are alluvial gem gravel districts where corundum extracted from primary metamorphic basement rocks has been transported and concentrated in river and valley gravels over geological time (Hughes, 1997, pp. 170–185).

Ratnapura district

Ratnapura, located approximately 100 kilometres southeast of Colombo, is the historic centre of Sri Lankan gem mining. The district's gem gravels (called "illam") are worked in pits 3 to 10 metres deep, following the gem-bearing gravel layer. Ratnapura produces a wide variety of gem species from the same deposits: sapphire, ruby, chrysoberyl (including alexandrite), spinel, garnet, topaz, tourmaline, and zircon may all occur in a single pit. The mixture of species is diagnostic: Sri Lankan origin for ruby is associated with this multi-species occurrence, while Mogok ruby occurs in a more restricted species assemblage (primarily ruby, spinel, and sapphire from marble, without the variety of species found in Sri Lankan metamorphic basement alluvials).

Elahera district

Elahera in Central Province produces sapphire as its primary gem species but also yields ruby from the same metamorphic alluvial system. The Elahera material tends to be smaller crystal sizes and higher proportion of near-gem or subgem quality compared to Ratnapura. The gem trading infrastructure in the nearby town of Embilipitiya handles material from both districts (Hughes, 1997, pp. 175–182; Ward, 1991, pp. 60–70).