Platinwm-bearing Rocks in the Lizard District. 518 
are found, apparently derived by interaction between intrusive and 
country rock. 
The ultrabasic bosses, which Dr. Rastall indicated as the possible 
sources of platinum, cover the centre and south-west of the 
Peninsula, and also appear as small intrusions in other parts. 
They consist of massive serpentine, and three main varieties 
have been previously outlined namely: Dunite-serpentine to 
the north, bastite-serpentine in the centre and south-east, and 
tremolite-serpentine to the west. The constant association 
of platinum with ultrabasic centres of dunite has been else- 
where noted, and it was considered that search around this mass of 
serpentine should prove most profitable. The dunite serpentine 
is a light-coloured rock, greyish-green, whitish or bluish in colour, 
very streaky, and containing octahedra and grains of magnetite 
and chromite. Its mass is on the highest central part of the Lizard 
plateau, and from the watershed streams arise which flow north to 
the Helford river, and east, south, or west to the sea. The alluvial 
bodies are very narrow and shallow, and contain little gravel, being 
mainly composed of clayey silt, and therefore not very favourable 
to the presence of mineral placers. No mineral deposits are known 
within this serpentine, which is exposed over an area of about 
24 square miles. 
The first tests were made by panning the surface of the alluvials 
with a small pan to recover any minerals of high specific gravity 
which might be present. The concentrates obtained were examined 
and found to consist of magnetite, a little chromite, and particles 
of dunite-serpentine, but no visible platmum. However, it was 
decided to assay the concentrates, and after fusion with litharge 
and fluxes, and cupellation of the resulting lead buttons, two minute 
beads of platinum were obtained weighing respectively 4 mg. and 
‘35mg. These were tested and definitely proved to be platinum. 
They indicate values of approximately 1-0 mg. Pt. per cubic ft. of silt. 
One of these beads was unfortunately mislaid, but the other remains 
in the custody of Mr. E. H. Davison, Lecturer in Geology at the 
School of Mines, Camborne. 
As these values had been obtained from the surface silt of the 
alluvials, and as there was a strong probability of increased values 
being found near bedrock, it was decided to carry on further research. 
A prospecting licence was obtained and a pit sunk in one of 
the alluvials, near Tregadjack Farm, samples being taken at various 
depths and at bedrock. The results obtained were disappointing, 
from the economic point of view, as the alluvial proved to be fine 
silt down to bedrock, and there was practically no concentration of 
gravel or sand. A greater quantity of heavy concentrate per cubic 
foot was obtained near bedrock, but on this being examined it was 
found to be exactly similar to the previous ones, and contained no 
visible platinum. Samples from the stream beds were also obtained 
which, on panning, yielded similar concentrates. 
VOL. LYIII.—NO. XI. 33 
