Abstract
The microinclusions in cuboid diamonds from Ebelyakh River deposits (northeastern Siberian craton) have been investigated by FIB/TEM techniques. It was found that these microinclusions have multiphase associations, containing silicates, oxides, carbonates, halides, sulfides, graphite, and fluid phases. The bulk chemical composition of the microinclusions indicates two contrasting growth media: Mg-rich carbonatitic and Al-rich silicic. Each media has their own specific set of daughter phases. Carbonatitic microinclusions are characterized by the presence of dolomite, phlogopite, apatite, Mg, Fe-oxide, KCl, rutile, magnetite, Fe-sulfides, and hydrous fluid phases. Silicic microinclusions are composed mainly of free SiO2 phase (quartz), high-Si mica (phengite), Al-silicate (paragonite), F-apatite, Ca-carbonates enriched with Sr and Ba, Fe-sulfides, and hydrous fluid phases. These associations resulted from the cooling of diamond-forming carbonatitic and silicic fluids/melts preserved in microinclusions in cuboid diamonds during their ascent to the surface. The observed compositional variations indicate different origins and evolutions of these fluids/melts.
Highlights
Syngenetic inclusions of minerals, melts, and fluids in natural diamonds suggest a multicomponent environment in the Earth’s deep mantle, where diamonds are formed
The FTIR spectra of the diamonds in this study contain absorption bands related to different phases in the microinclusions
FTIR spectroscopy can be used to verify the dominant major components of these media. These assemblages of daughter phases of microinclusions of different compositions are first studied by transmission electron microscope (TEM) (AEM)
Summary
Syngenetic inclusions of minerals, melts, and fluids in natural diamonds suggest a multicomponent environment in the Earth’s deep mantle, where diamonds are formed. The recent progress of investigations into these polyphase inclusions is obvious from the analysis of numerous works concerning diamond growth media Most of these studies were focused on natural fibrous diamonds containing abundant microinclusions (submicron size inclusions) of the multiphase associations of fluids/melts [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. It is important to note the finding of a fluid rim mainly composed by H4 SiO4 (orthosilicic acid) + H6 Si2 O7 (persilicic fluid), which is a typical feature of diamonds and is found at the interface between mineral inclusions and their diamond hosts [21]. This fluid is detectable by micro-Raman spectroscopy and is present for any Minerals 2019, 9, 50; doi:10.3390/min9010050 www.mdpi.com/journal/minerals
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