Chemistry and genesis of Ree bearing gemstones from the North West Frontier Province, Pakistan

Khan, Ehtesham Ullah (2009) Chemistry and genesis of Ree bearing gemstones from the North West Frontier Province, Pakistan. (MSc(R) thesis), Kingston University, .


Alkaline granites have high K + Na vs Si ratios. Some of the best studied of these are in the Kola Province of NW Russia where they are characterized by high Rare Earth Element (REE) concentrations which stabilize a remarkable range of rare REE-rich minerals. The northern part of the Indian Plate in northern Pakistan is intruded by a number of Upper Carboniferous alkaline complexes including the Ambela and Warsak plutons. As in the Kola Peninsula, the alkaline granites of northern Pakistan host a range of REE-rich minerals. Many of these are of gem quality. Zagi Mountain is located in the Warsak area of the Mulla Ghori tehsil of the Kyber Agency, part of the North West Frontier Province of Pakistan. The area is underlain by granites of the Warsak igneous complex. The Warsak complex is made up of a series of sill-like alkaline granites, micro-granites, gabbros and dolerites. The granitic rocks contain aegirine, riebeckite and astrophyllite. The granites are rich in the rare earth elements and contain a number of REE-bearing gem minerals. These include bastnaesite-(Ce), parasite-(Ce), monazite-(Ce), xenotime-(Y), titanite, genthelvite, eudideymite together with non REE-bearing grossular garnet, quartz and zircon. (Khan & Marwat, 2007). Analytical data presented here document the chemistry of light REE bearing bastnaesite, parisite and monazite, and heavy REE bearing xenotime. Most of the REE phases are located along fractures and veins or in vugs and show good crystal shapes. These textures are typical of minerals precipitated into open space fillings from hydrothermal fluids. This suggests fractionation of the REE into late stages of the alkaline magma prior to their being partitioned into hydrothermal fluids.

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