Geophysical evidence for a concealed eastern extension of the Tanygrisian microgranite and its possible relationship to mineralisation

A Bouguer anomaly low in the Blaenau Ffestiniog
area is interpreted as being due to a concealed
eastward extension of the Tanygrisiau microgranite.
The geophysical evidence suggests that the granite,
seen at outcrop at Tanygrisiau, 1 km south-west of
Blaenau Ffestiniog, continues north-westwards at
a shallow angle and that the general form of the
intrusion is tabular, decreasing in width downwards
The geological evidence supports this interpretation
and also the existence of the extension to the
east (suggested by the geophysical evidence). The
magnetite-bearing granite is also thought to be
responsible for a pronounced aeromagnetic
anomaly which has a form supporting the gravity
evidence for the eastward extension of the granite
body but requires the extension of a magnetic
body down to a depth of 15 km.
The mineralisation in the area consists of
sulphide-bearing quartz veins occupying mainly
north-easterly trending faults. There are
insufficient mineral occurrences to produce any
clear correlation but the distribution of the veins
seems to be mainly coincident with the southern
flank of the concealed granite.