Investigation into distribution of the platinum group elements, South Harris, Isle of Lewis, Scotland

A programme of field sampling was carried out in May 1991 to investigate the distribution of the platinum group elements (PGE) over the South Harris Complex. The Complex is situated at the southern end of the Isle of Lewis, and lies some 60 km off the north-west coast of Scotland. The project area covers approximately 70 km2, rising from sea level to 460 m. Much of the ground below 100 m is covered by blanket peat and its associated wet and dry-heath vegetation, with occasional ice-smoothed outcrops. The higher ground affords locally excellent exposure. Drainage samples were collected from 65 stream locations and rock samples from 93 sites. The range of lithologies sampled include those of the intrusive complex and its marginal metamorphic belts (Figure 1). The locations of rock and drainage sample sites are shown in Figure 2. Rock samples were collected from surface exposures, with several points on each outcrop sampled to produce a representative sample. Drainage sampling was carried out in order to establish the distribution of the prospective elements over poorly exposed ground. This involved the collection of two size fractions in the field by wet screening. A coarse fraction (-2 mm) was processed by panning from an initial volume of 4 litres to produce a 150 ml concentrate. The stream sediments were screened at 150 microns then bagged with minimal water loss in order to retain the colloidal fraction. XRF analysis on pressed powder pellets was carried out by the Analytical Chemistry Unit of the BGS. The suites of elements determined are as listed in their respective tables.