The biotite-phlogopite series in fenites from the Loe Shilman carbonatite complex, NW Pakistan

Abstract

The Loe Shilman carbonatite sheet complex comprises an extensive amphibole sovite which is intruded by minor biotite sovite and amphibole ankeritic carbonatite. The carbonatites have fenitized the country rocks to form a metasomatic zone c. 100 m wide of alternating mafic and felsic mica-bearing banded fenites which grade into slates and phyllites. Phlogopite-rich micas occur nearest to the carbonatite contact. The biotites occur in K-feldspar + albite _+ Na-amphibole ___ aegirine and _ phengite fenites produced by the intrusion of the early amphibole sovite. Aegirine buffered the iron distribution and the biotites became more magnesian. Veins cross-cutting the fenites consist of biotite and/or Ba-bearing K-feldspar, and are interpreted to result from solutions emanating from the biotite sovite. The ankeritic carbonatite is responsible for the formation ofphlogopite in the fenites in a c. 3 m wide zone adjacent to the carbonatite, and evidently are the result of fenitizing fluids rich in Mg. Chemical equations calculated to balance the reactions interpreted to have taken place in the fenites suggest that about 10% of the A1 and Si in the protolith was mobilized and moved towards the carbonatites during fenitization, and that the fenitizing solutions were strongly alkaline and oxidizing. K E Y w og D S: biotite, phlogopite, fenite, carbonatite, Loe Shilman, Pakistan.

Temperature-HF fugacity trends during crystallization of calcite carbonatite magma in the Fen complex, Norway

“…K20 is low in the phlogopite, less than 10 wt.%. Low-potassium (alkali deficient) phlo-gopites were reported from the Sarfartoq carbonatite complex, Greenland (Secher and Larsen, 1980) and from fenites in the Loe Shilman_ carbonatite complex, Pakistan (Mian and LeBas, 1987). In the Fen complex, low K in mica has been related to leaching of alkalis during initial post-magnetic re-equilibration or metasomatism (Andersen, 1984(Andersen, , 1989.…”

Micas from the Khaluta carbonatite deposit, western Transbaikal region

“…Micas from aluminosilicate rocks are characterized by high Al, Fe, and Ti contents, whereas micas from ultramafic rocks and limestone are enriched in Mg. The Fe, Al, and Ti contents are higher in micas from fenites than from carbonatites owing to the specific chemical nature of mineral formation (Mian and Le Bas, 1987;Le Bas and Srivastava, 1989). At the Eastern Sayan, Guli, and Kovdor deposits, the depletion of back zones of metasomatic carbonation columns in Al, Fe, and Ti is related to the character of host rocks, the evolution of mineral-forming systems, and variable temperature and pressure (Chernyasheva and Gormasheva, 1966; Pozharitskaya and Samoilov, 1972;Rass, 1980).…”

“…These minerals are also typomorphic of carbonatite complexes, where they occur in both carbonatites and cognate alkaline silicate and metasomatic rocks. Micas were investigated in detail in such well-known carbonatite-bearing complexes as Yacupiranga, Tapiro, and Katalio in Brazil (Brod et al, 2001), Chernigovka in Ukraine (Krivdik et al, 1982), Kovdor and Guli in Russia (Rass, 1980), as well as complexes in India and Pakistan (Le Bas and Srivastava, 1989; Mian and Le Bas, 1987) and the Eastern Sayan complex in Russia (Chernysheva and Gormasheva, 1966;Pozharitskaya and Samoilov, 1972).…”

An Overview of the Carbonatites from the Indian Subcontinent

“…In Purulia area alkali pyroxenite shows sodic fenitization [56] and so is the case with Loe Shilman, Silai Patti, Jawar and Jambil areas of Pakistan where phyllites and gneisses show development of sodic amphiboles and soda feldspars indicating prominent sodic fenitization ( Figure 1). However, increased percentage and grain size of K-feldspar, surrounded by clusters of small globules of albite, increased concentration of biotite near Fe-oxides indicate presence of strong potassic fenitization [15,124,127,128]. Intense potassic fenitization is also known to occur at Khanneshin complex [87].…”