Exploration for porphyry-style copper mineralisation near Llandeloy

(Table 2, no. 251, contains elevated levels of some
chalcophile elements (Pb, Mo, As) which are perhaps
indicative of weak epigenetic mineralisation. The erratic
level of alkalis is considered to reflect alteration seen in
thin section, but no regional pattern could be discerned
with variation within one outcrop as great as across the
whole area.
Rock geochemistry, based on available outcrop
sampling therefore failed to give any clear indication of
the presence of disseminated mineralisat ion, a
conclusion which agreed with the stream sediment
sampling, but was in distinct contrast to the findings of a
soil sampling survey and subsequent drilling.
Stream sediment survey
A stream sediment survey was carried out in the
catchment of the Solfach, partly to look for indications
of mineralisation and partly as an orientation study, to
test the effectiveness of drainage sampling as a mineral
exploration technique in this area of low relief with
incised drainage, thick drift cover, sluggish streams and
extensive contamination.
Sampling and analysis
Thirty five sites (Figs. 3, 4) were sampled for water
stream sediment and panned concentrates. Stream
sediment was wet-sieved at site to pass 100 mesh BSS
(0.15 mm) using a minimum of water to retain the clay
St. Brides Bey
Figure 3 Location of drainage survey anomalies
fraction. Samples were dried in the laboratory prior to
grinding in a ball mill for 30 minutes. A 0.5 g split was
analysed for Cu, Pb and Zn by atomic absorption
spectro-photometry (AAS) following digestion in hot
concentrated nitric acid for one hour. was determined
by X-ray fluorescence spectrometry (XRF) followi~~g
grinding of a 12 g subsample in a Itemat mill with
'elvacitel binder and pelletising. A further range of
elements was determined by optical emission
spectroscopy (OES). Detection limits were approxi-
mately 1 ppm for Be; 2 pprn for As; 3 pprn for Cu; 5 ppm
for Pb, B, Zn, Y and Sn; 10 ppm for V, Cr, Co and Ni;
20 ppm for Zr; SO pprn for Mn; 100 pprn for Ba and 0.5%
for Fe.
Constant volume panned concentrates of about 50 g
were made at site from about 4 kg of -8 mesh BSS
(2 mm) stream sediment. Following drying, a 12 g
subsample was ground in a Itemat mill with 3g of
'elvacitel binder for five minutes prior to pelletising and
analysis by XRF for a range of elements. Detection
limits were 2 pprn for Mo and As; 3 pprn for Th and Zn;
5 pprn for Ni; 6 pprn for Mn and Cu; 9 ppm for Sn;
11 ppm for Sb; 13 pprn for Pb; 21 ppm for Ce and 27 pprn
for Ba.
A 30 ml water sample was collected in a plastic screw
top bottle and acidified in the field with 0.3 ml
perchloric acid. The sample was subsequently analysed
by AAS for Cu and Zn without further sample
preparation. Detection limits were approximately
0.02 ppm.
Sample site showing tin content of panned