Geochemistry of feldspars from the Ambalavayal Molybdenite Prospect, Kerala

Abstract

Major and trace element geochemistry of coexisting alkali feldspar and plagioclase pairs from granite and alkali feldspars from the associated pegmatites of the Ambalavayal molybdenite prospect in Wynad district, Kerala, are presented. The element levels in both the feldspars show an overall comparability with the values reported from elsewhere. The nature of distribution of elements between coexisting feldspars is generally consistent with their crystal chemical behaviour. X-ray studies of alkali feldspars show a triclinic symmetry with the triclinicity values ranging from 0.2955 for feldspar from the granite to 0.6742 for feldspar from the pegmatite. Mol per cent feldspar end members range from Or_56.43Ab_40.52An_3.05in alkali feldspar of the granite to Or_74.00Ab_22.51An_3.19 in alkali feldspar of the pegmatite. The crystallization temperature of the alkali feldspar-plagioclase pairs in the granite is estimated to be between 704-740°C and that of alkali feldspar in the pegmatite to be between 525-580°C.