Mineral reconnaissance drainage sampling in the late 1970s identified gold in heavy mineral
concentrates collected from a number of localities in the Ochil Hills. Subsequent detailed sampling
of these localities showed that alluvial gold is present over a large area of the central Ochils and
extends eastwards to the Firth of Tay. The most anomalous catchment, Borland Glen, near Glen
Devon, was the focus for further integrated geological, geochemical, and geophysical studies.
The geology of Borland Glen comprises a series of Lower Devonian andesitic lavas and pyroclastics
intruded by a diorite body and porphyry dykes. Minor hydrothermal alteration is visible at surface.
A large induced polarisation anomaly was found near the watershed between Borland Glen and
Coul Burn and was interpreted as a steep-sided zone of disseminated pyrite with associated
hydrothermal alteration. Overburden sampling proved gold and mercury anomalies over the same
area.
Seven boreholes were drilled to a maximum depth of 102 m to investigate the source of the IP and
overburden geochemical anomalies. Intense hydrothermal alteration and brecciation were found to
have affected the lavas and pyroclastics in the central, IP-anomalous zone and were accompanied
by major pyritisation with associated minor base metal sulphides. Gold values in the drillcore reach
a maximum of 505 ppb Au and it is concluded that the bedrock source of the alluvial gold has not
been proved. However, the intense hydrothermal alteration in the setting of an evolved calcalkaline
volcanic complex is indicative of a large epithermal system, and a more fertile source may
yet be discovered in the area. Other gold sources are indicated in the central Ochils and further
detailed investigations are thought to be warranted
