Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Charoitite

Charoitite is the name used localy to refer to a rock consisting of more than 50 vol.% of charoite. Charoitites occur in about 25 localities along the southern margin of the Little Murun pluton. These are collectively known as the "Lilac Rock" charoite deposit (Fig.1).

Fig.1: Schematic geological map of the Lilac Rock deposit. 1: Quaternary rocks; 2: carbonatites and related rocks; 3: charoitites, 4: fenites, 5: nepheline syenites, 6: pseudoleucite syenites, 7: porphyritic syenites, 8: alkaline syenites, 9: sedimentary carbonate rocks, 10: sandstones and quartrites, 11: granite gneisses; 12: fenitized granite gneisses, 13: fault zones; 14: geological contacts.

Charoitites vary from purely mono-mineral rock torocks with variable proportions of charoite, quartz, aegirine, and K-feldspar. Other minerals such as tinaksite and canasite are typically found as accessories.
Depending on the geologicd setting, four types of charoite-bearing rocks have been distinguished by Borisov (1985). The charoitites of type I occur as thin (2-3 cm) veins of fine-grained massive charoite in aegirine fenites developed in the country sedimentary rocks: sandstones, shales and gneisses. The second and third types occur in breccia zones, and are represented by nests and veins of texturally diverse charoite (type two) and blocks of charoitite (type three). The charotites of type four are found at the contact with carbonatites. The charoitites of types two and three are mined commercially.

A typical sample of charoitite consists of rounded grains of quartz and microcline, as well as euhedral crystals and stellate aggregates of greenish black aegirine, honey-yellow tinaksite and greenish grey frankamenite set in a groundmass of charoite demonstrating a diversity of colours and textures. Charoitites from some localities within the Lilac Rock deposit also contain large subhedral crystals of pearly-white platy fedorite and pale bluish green pectolite and brownish-red miserite, as well as platy crystals of tokkoite, commonly in intergrowths with tinaksite.
In addition to the textural diversity, charoite shows a broad spectrum of colours from lilac to brown and grey, often within the same hand-specimen. as shown by several studies Mn²⁺ e Mn³⁺ ions are responsible for the colour and cathodoluminescence of charoite.

The nature of charoitites-forming processes has been a subject of scientific debate. Until now, two major hypotheses have been proposed. Vorob'ev et al. (1983) suggest a magmatic origin for the charoite-bearing rocks. According to Vladykin et al. (1994), the composition of microinclusions in the minerais of charoitites supports the "magmatic" hypothesis and shows that the charoite rocks crystallised from a fluid-saturated melt corresponding to differentiates of ultrapotassic magmas. However, the majority of researchers interpret charoitites as a typical example of metasomatic rocks.

Murun Complex

Mesozoic K-alkaline intrusions are abundant at the Aldan shield and they are distributed in the northern part with a strike roughly parallel to the NE-SW trending Mongolia-Okhotsk orogenic belt (Fig.2). This orogenic belt is a reflection of subduction of the Mongolia-Okhotsk oceanic plate. The Mongolia-Okhotsk Ocean closed at the Carboniferous in the west and in the Late Cretaceous in the east.

Fig.2: Tectonic sketch map of Mesozoic Siberia and East Asia. Arrows show time when particular parts of the Mongolia-Okhotsk Ocean closed. After Kostyuk et al. (1990).

By the time of magmatism at the Malyy Murun, the Mongolia-Okhotsk subduction ceased at the central part of the orogenic belt and thus Early Cretaceous magmatism at the Malyy Murun massif represents a post-subduction process, which was coeval to rifting at the central part of the Mongolia-Okhotsk orogenic belt.
The Malyy Murun massif (ca.48 km²) is a part of a larger Murun ultrapotassic complex (150-180 Km²), which consists of the Bolshoy (Great) Murun, Malyy (Little) Murun, and Dagaldyn massifs (Fig 3). The Malyy Murun and Dagaldyn massifs are Early Cretaceous and Early Jurassic, respectively. The Bolshoy Murun massif is not yet dated.
The northern part of the Malyy Murun syenite massif is bounded by skarns at the contact with the carbonate wall rocks. The southern part of the massif is bounded by quartz sandstones, where a broad contact aureole of fenites developed. All known outcrops of charoitite rocks were found within fenites.

Fig.3: Geologic map of the Murun ultrapotassic complex and a cross-section at the Stary prospecting site. After Vorobyev (2008).

The complex was discovered in the late 1930-s - early 1940-s by the VG Ditmar expedition. Since then, dozens of scientists have been involved in the geological exploration of Murun.
As this exploration progressed, the complexity of the geological and tectonic situation at Murun became increasingly evident. The Murun complex is, perhaps, best known for a suite of Ca-rich fenitic rocks developed from the Proterozoic carbonaceous sandstones. Beginning in the 1960-s, a number of new minerals of unusual composition and structure have been discovered in the fenites. Many of these, including frankamenite and the gemstone charoite, are quite common in the Murun rocks, but have not been encountered anywhere else in the world.
There is no agreement between geologists as to what the composition of the parental magma was, or how the intrusions developed in time, or regarding genetic relationships between the individual petrographic series.

At present, there are two major views on the evolution of the Murun complex:

1) Orlova et al. (1987, 1988) suggest that the complex developed as a single layered lopolith by magmatic differentiation.
2) Ivanyuk & Evdokimov (1991), Mitchell & Vladykin (1996), Konev et al. (1996), (Vladykin, 2000) and others suggests that the individual intrusive phases were emplaced independently as a series of plutonic and hypabyssal bodies. They recognized four magmatic stages in the Malyi Murun Massif:

Early phase: makes up the northeastern part of the massif. It includes the following rocks: (1) Cumulate formations: olivine-spinel rock seggregations with zones of melilite-bearing olivinepyroxene-phlogopite-monticellite rocks, which occur as xenoliths in biotite pyroxenites. (2) Layered complex of ultrabasic ultrapotassic rocks composed of Biotite-pyroxenites, olivine, K-ijolites, leucitic fergusites, and shonkinites.

Major phase: occupies the central part of the massif. It is made up of a horizontally, layered units of various pseudoleucitic, kalsilitic, and biotite-pyroxene-bearing K-feldspathic syenites, whose crystallization terminated in the formation of quartz syenites and dykes and stocks of alkali granites. The pseudoleucitic syenites (synnyrites) in the northeast of the massif form a large body not less than 600 m in thickness.

Volcanic phase: comprises the central and northern parts of the massif. This is a layered flow of leucitic melaphonolites, leucitites, and leucitic lamproites (minette) with zones of tuff breccias. The dyke complex of this phase is formed by leucitic tinguaites, richterite-sanidine lamproites, trachyte-porphyries and syenite-porphyries.

Late phase: It occupies the southeastern part of the massif, covering 10 km2, and is made up of banded layered complex of potassic silicate-carbonate rocks which form 1 to 20-30 m wide bands. These bands are: (1) white microgranular K-feldspathic rocks consisting of K-feldspar with minor admixtures of pyroxene and tinaksite; (2) quartz-calcite-pyroxene-microcline rocks with calcite contents varying from 5 to 20%; (3) pyroxene-K-feldspathic rocks with widely varying contents of both components.
The rocks have diverse structures and textures: banded, spherolitic (for pyroxene), equigranular, fine- and coarse-grained, etc.; (4) essentially pyroxene rocks. This layered banded outcrop contains carbonatites and charoite rocks, which are represented by veins, dykes, and some sill-like formations having no sharp contacts with the silicate-carbonate rocks.

Purple charoite, green aegirine and honey-yellow Tinaksite. Murun Massif, Aldan Shield, Yakutia, Russia.

Purple charoite and green aegirine. Murun Massif, Aldan Shield, Yakutia, Russia

Purple charoite, green aegirine and white-gray feldspar. Murun Massif, Aldan Shield, Yakutia, Russia.

Purple charoite. Murun Massif, Aldan Shield, Yakutia, Russia.

Purple charoite, green aegirine and white-gray feldspar. Murun Massif, Aldan Shield, Yakutia, Russia.

Bibliography

• Mitchell, R. H., & Vladykin, N. V. (1996). Compositional variation of pyroxene and mica from the Little Murun ultrapotassic complex, Aldan Shield, Russia. Mineralogical Magazine, 60(6), 907-925.
• Reguir, E. (2002). Aspects of the Mineralogy of the Muran Alkaline Complex, Yakutia, Russia. National Library of Canada. Bibliothèque nationale du Canada.
• Vladykin, N. V., Viladkar, S. G., Miyazaki, T., & Mohan, V. R. (2008). Geochemistry of Benstonite and Associated Carbonatites of Sevathur, Jogipatti and Samalpatti, Tamil Nadu, South India and Murun Massif, Siberia. Journal of the Geological Society of India, 72(3), 312-324.
• Vladykin, N. V. (2009). Potassium alkaline lamproite–carbonatite complexes: petrology. Genesis, and their reserves, Russ. Geol. Geophys, 50(12), 1443-1455.
• Wang, Y., He, H., Ivanov, A. V., Zhu, R., & Lo, C. (2014). Age and origin of charoitite, Malyy Murun massif, Siberia, Russia. International Geology Review, 56(8), 1007-1019.

Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 1x (Field of view = 9mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 1x (Field of view = 9mm)
Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 1x (Field of view = 9mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)
Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 1x (Field of view = 9mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 1x (Field of view = 9mm)
Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)
Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)
Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 1x (Field of view = 9mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 1x (Field of view = 9mm)
Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 2x (Field of view = 7mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 2x (Field of view = 7mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 2x (Field of view = 7mm)
Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 2x (Field of view = 7mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 2x (Field of view = 7mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 2x (Field of view = 7mm)
Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 2x (Field of view = 7mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 2x (Field of view = 7mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 2x (Field of view = 7mm)
Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 2x (Field of view = 7mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 2x (Field of view = 7mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 2x (Field of view = 7mm)
Fibrous charoite (I order gray) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)
Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (beige color) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (beige color), quartz (colorless) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (beige color), quartz (colorless) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)
Fibrous charoite (beige color) and quartz (colorless) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) and quartz (I order gray-white) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (beige color) and quartz (colorless) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)
Fibrous charoite (beige color) and quartz (colorless) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) and quartz (I order gray-white) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (beige color) and quartz (colorless) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)
Fibrous charoite (beige color), quartz (colorless) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (beige color), quartz (colorless) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (beige color), quartz (colorless) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)
Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (beige color), quartz (colorless) and green aegirine crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. PPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray), quartz (I order gray-white) and aegirine (high interference colors) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (I order gray) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)
Fibrous charoite (I order gray) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)	Fibrous charoite (I order gray) crystals in a charoitite. Murun Massif, Aldan Shield, Yakutia, Russia. XPL image, 10x (Field of view = 2mm)