HEAVY MINERALS IN PRECAMBRIAN QUARTZITE OF THE LESSER HIMALAYA, GARHWAL, INDIA 1

The Preeambrian Gamri Quartzite of the Deoban-Tejam Belt in Garhwal, with its restricted ultrastable heavy mineral assemblages consists primarily of zircon in the northern belt and tourmaline wkh zircon in the southern belt. The ultrastable heavy mineral suite and supermature light fraction of the quartzite seem to have been greatly altered by weathering and abrasion prier to deposition during a prolonged period of pene-planation of source area in the initial stages of geosynclinical development. Absence of tourmaline varieties in the northern belt and basal southern belt reflects compositional changes in the source area, i.e., the Central Crystalline Axis. Regional ateral and vertical variability of important tourmaline varieties has been recognised in the Ga~nri Quartzite with an increasing concentration i stratigraphieally younger horizons of the southern belt near the overlying carbonates. The confirmation of the heavy mineral associations in structurally deformed belts of the Gamri Quartzite is applicable in the tectonic interpretation. I NTRODIJCTION The heavy minerals have been extensively used in lithologic and stratigraphic orrelations, reconstruction of paleogeography and tectonic history of the source and dcpositional areas. In the Himalayan sediments, heavy minerals of the Siwaliks, the Upper Tertiary molasse deposits of the southernmost Sub-Himalaya have been extensively studied, but the heavy minerals of the pre-Tertiary sediments of the Lesser Hi-malaya, so far, have not been worked out. This paper describes heavy mineral assemblages from slightly metamorphosed, Precambrian (;amri Quartzite of the Deoban--Tejam sedi-mentary Belt of Garhwal and Kumaon. The re-sults of this study indicate the utility of the heavy mineral investigations in the paleogeog-raphy, stratigraphy and tectonics of the Lesse