Mineral inclusions in sapphire from the basalt-related deposit in Bo Phloi, Kanchanaburi, western Thailand: indication of their genesis

Abstract

The Bo Phloi gem field in Kanchanaburi Province, Western Thailand, is closely associated with Cenozoic basalts. Blue and yellow sapphire, black spinel, and minor zircon have been mined for over three decades. The mineral inclusions observed in sapphire samples are alkali feldspar, nepheline, hercynitic spinel, zircon, manganiferous ilmenite, silica-rich enstatite, almandine–pyrope garnet, monazite, calcite, sapphirine, biotite–phlogopite mica, and staurolite. Based on their geochemical affinity, these mineral inclusions can be categorized into two main groups: felsic alkaline and contact-metamorphic, which appear to have originated from different processes. These inclusions provide new evidence for proposing a bimodal genetic model. Felsic alkaline origin is evidenced by the occurrence of a felsic alkaline inclusion suite and the REE geochemistry of sapphire-associated zircon, which indicates that most of the sapphires crystallized from a high-alkali felsic melt (probably, in the lower crust). Contact-metamorphic origin is evidenced by the presence of a contact-metamorphic inclusion suite, suggesting that some of these sapphires might also have originated from metasomatized crustal rocks and a contaminated melt along the contact zone of a basaltic intrusion (probably, in the upper mantle or lower crust).

Petrogenesis of alkaline basalt-hosted sapphire megacrysts. Petrological and geochemical investigations of in situ sapphire occurrences from the Siebengebirge Volcanic Field, Germany

“…Notably, there is no correlation between the mineral inclusion suite and the minor and trace element compositions of the host sapphires. Interestingly, many inclusions in the sapphires are carbonates, which have only been described previously in sapphires associated with alkaline basaltic volcanism from the Bo Phloi gemfield in Kanchanaburi, western Thailand (Khamloet et al 2014). Furthermore, the U-bearing inclusions thorite, thorianite and Pyrochlore and Columbite Group minerals are of great interest, as they potentially allow to date the age of the sapphire crystallization using the U-Pb chronometer.…”

Zircon Xenocrysts from Cenozoic Alkaline Basalts of the Ratanakiri Volcanic Province (Cambodia), Southeast Asia—Trace Element Geochemistry, O-Hf Isotopic Composition, U-Pb and (U-Th)/He Geochronology—Revelations into the Underlying Lithospheric Mantle

“…Isolated RVP zircon xenocrysts differ from many other zircon xenocryst suites that are commonly spatially associated with corundum xenocrysts either in multimineralic xenoliths or as discrete crystals in heavy mineral separates, e.g., Bo Phloi and Chanthaburi-Trat regions in Thailand (Piilonen, unpublished data, [98,99]), South Vietnam [100], Loch Roag, Scotland [97], and Lava Plains, NE Australia [10,12]. Such zircons associated with corundum, either as xenocrysts or as corundum-hosted inclusions, have consistently higher Hf (>1 wt % and up to 4.5 wt % HfO 2 ) and often negative Eu anomalies, which suggests evolved, likely peraluminous corundum-bearing sources (Figure 11).…”

Cause analysis of chatoyancy of sapphires from Shandong, China

“…3 As a gemstone, sapphire is one of the most valuable gemstones and is produced in many countries worldwide, for example, Myanmar, Thailand, Sri Lanka, Australia, etc. [4][5][6][7] The sapphire ores in the Shandong province are the largest reserves and have the best quality in China; it is located in the western part of the Tan-Lu fault zone, southeast of the North China Craton. 8 To the best of our knowledge, the gemological properties, mineralogical properties, chromogenic mechanism, color modication and inclusion study of Shandong sapphires have been investigated systematically and thoroughly.…”