During radiometric investigation at Mawlait, significant uranium mineralisation (0.024-0.22%U 3 O 8 ) was located mainly within the small pegmatite (garnet bearing quartzofeldspathic rock), which are locally segregated within migmatite at Umiang River section. Pink granite and granite gneisses are the dominant lithounits of the study area showing fertile character and spotty radioactivity at several places. Radioactivity in these rocks is mainly contributed by discrete uraninite grains along with some zircon and xenotime. Granites are peraluminous, low-Ca in nature and their geochemical signatures suggest derivation from a felsic source. Discriminant diagrams using Rb, Nb and Y indicate 'within plate' to 'volcanic arc' nature of the rock. The uraniferous pegmatitic veins within migmatite appear to have formed due to localised metamorphic segregation during late stage of anatexis. Petromineralogical and geochemical studies suggest that the uranium mineralisation in granitic-pegmatitic rocks of the area is mainly syn-magmatic type.

Petrographic studies of Proterozoic pyriteferous granitoids forming basement for upper cretaceous Mahadek sediments from Wahkyn area reveal interesting textural peculiarities of Pyrite. These pyrites also reveal interesting structural peculiarities. The three textural pyrite varieties found in the granitoids are: framboidal, colloform and recrystallised which appear both as composite aggregate as well as independent units. Various textures and variation in reflectivity, microhardness and elemental distribution of the pyrites are described. Average Co/Ni ratio along with the textural manifestation of these pyrites attests their sedimentary origin.In Wahkyn area, the core samples from several vertical boreholes (drilled up to a maximum depth of 93.40 m) were studied. Thickness of Mahadek sediments including basal conglomerate in the boreholes vary from 47.95 to 88.20 m and basement granitoids vary from 0.85 m to 5.40 m. The studied samples represent depths of 53.30 to 93.40 m and were drawn from depths of 0.5 m to 1.0 m below the sediment -basement contact.This paper describes the petrography, ore petrography and chemistry of pyrites occurring in the basement granitoids of Wahkyn area of West Khasi hills, Meghalaya.

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