'Institute of Geological Sciences of the National Academy of Sciences of Ukraine'
Abstract
A brief investigation of low-grade copper mineralisation associated
with a small, talc-alkaline porphyry intrusion of Caledonian age is
described.
Geological mapping has delineated a small stock of biotite-feldspar
2
porphyry, 0.25 km in area, intruded into a sequence of Dalradian schists
and quartzites with inter-bedded epidiorites. Disseminated sulphides occur
within the porphyry and the hornfelsed epidiorite but do not normally
, exceed 3% of the rock by volume. Assays of both rock types obtained maximum
levels of 0.24% Cu. Hydrothermal alteration is prominent within the
porphyry, with the widespread development of sericite and kaolinite.
Subsequent faulting apparently exerted some control on the present limits
of alteration and mineralisation. Several small strata-bound lenses of
massive sulphide within the metasediments were recorded but were not
investigated in detail.
Geochemical rock-sampling delineated a strong arcuate copper anomaly
over the northern epidiorite/porphyry contact and a more subdued anomaly
along the southern faulted contact. Molybdenum shows a similar distribution
but is more closely confined to the porphyry. Overburden sampling
demonstrated that little or no metal dispersion occurred within the overlying
till, and stream sediment sampling of the catchment area showed that
concentrations of copper decrease to background levels within 1 km of the
intrusion. 1
Induced polarisation (IP) surveys produced a clearly defined grouping
of chargeability anomalies around the edges of the porphyry stock but these
showed no increase in magnitude at depth. Above background chargeability
values recorded over the centre of the intrusion increase markedly towards
the margins , possibly reflecting a pyritic halo. Most resistivity 'lows' coincide with fault zones and the results of a total intensity magnetometer
1
survey showed that, while most magnetic anomalies occur over epidiorites,
I
significant anomalies are also produced in the vicinity of fault zones.
The results of the geological, petrographic, geochemical and
I
geophysical studies demonstrate the presence of several features
: characteristic of 'porphyry copper style' mineralisation but the small
1
surface area and low grade of the deposit, combined with a lack of
encouraging geophysical responses at depth, suggest that there is little
II chance of discovering an economic orebody by exploratory drilling
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