32 research outputs found
Disseminated sulphide mineralisation at Garbh Achadh, Argyllshire, Scotland
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
Mineral reconnaissance at the Highland boundary with special reference to the Loch Lomond and Aberfoyle areas
Serpentinite bodies at the Highland Boundary in
the Loch Lomond and Aberfoyle areas are
extensively altered to magnesite-quartz and
ferroan-dolomite-quartz rocks. Silicification was
probably initiated before conversion to carbonate.
Relict textures indicate that the serpentinites were
derived from peridotitic precursors, but one
unaltered ultrabasic sample comprises mainly
chromian diopside. Chromite geochemistry and
hornblende-schist mineralogy rein force the ophiolitic
character of the serpentinite-spilite-blackshale-
chcrt assemblage of the Highland Border.
Magnetic and VLF traverses across the Highland
Boundary fracture-zone near Helensburgh
identified several anomalous zones. One may be
due to a concealed serpentinitic sheet.
The most mineralised serpentinite body
showed chromium values in the range 1000 to
3035 ppm. Such concentrations arc not encouraging
for the small serpentinites at Loch Lomond
and Aberfoyle, but may be significant regarding
larger serpentinites elsewhere at the Highland
Border
Lead, zinc and copper mineralisation in basal Carboniferous sediments at Westwater, south Scotland
A zioneo f lead, zinc and copperm ineralisatioins developedo ver a minimum
I of 4 km of strikeo f basal Carboniferoucse mentstoneg roup sedimentsa nd
immediatelyu nderlyingB irrenswarkL avas atwestwater,n ear Laqholm in south
Scotland. Grades so far obtained from sparse rock exposures and from shallow
boreholes
a fissure
sulphides
are usuallyO .l-O.j%o f combinedm etals over 1-2 m of thickness,bu t
vein of higher grade and a relativelyt hick zone of disseminated
were also located. Galena, sphalerite,c halcopyritea ndbaryte
occur mainly in thin dolomitev eins but disseminationosf galenaa re also
presenti n sandstoneu nits. The mineralisatioins of low temperaturet ype
I
was emplaceda long northeasterlyt rendingn ormal faultsa nd cross faults
regardeda s late Carboniferouisn age.
and
Mineralisatiohna s been controlledb y faulting,r egionalf aciesv aziation
and local lithologicalv ariationa s well as by stratigraphipco sition. These
controlsa re applicablei n furthere xplorationo f Lower Carboniferourso cks in
both south and central Scotland. The heavy mineral fraction of stream sediment
is the optimums amplingt ype in reconnaissanceex plorationo f areas of calcareous .
rocks such as the Lower Carboniferouso f south Scotlanda nd basal till sampling
is the most effectivem ethod of follow-upe xplorationi n those areas where
glaciald epositsa re widespreada nd often thick
Investigation of stratiform sulphide mineralisation at Meall Mor, South Knapdale, Argyll
A co-ordinated geochemical-geophysical-geological investigation of copper
mineralisation in the Meal1 ?46r area, South Knapdale, Argyll was carried 0th
in 1976 and followed by a drilling programme of 3 shallow holes in early 1977.
The mineralisation occursin a zone of weak stratiform sulphide mineralisation
(the pyrite zone) with a strike length of 1Okm in the Upper &ins Quartz&e
of the Middle Dalradian.
The geochemical drainage survey showed the existence of a strongly anomalous
distribution of Cu and Sb in the Abhainn Srathain draining south from .
Meal1 M&- and detailed soil sampling over the pyrite zone outlined a broad
area enriched in copper. Deeper soil sampling confirmed the anomalously
high copper values and a coincident IP anomaly was found stretching from
Meal1 M& south to the old mine workings on Abhainn Srathain, and is probably
caused by a local enrichment of pyrite and chalcopyrite within the pyrite
zone.
Three boreholes were drilled; two on coincident geochemical and geophysical
anomalies, and the third beneath the old mines at Abhainn Srathain. Copper
values in the first two holes range up to 0.24% Cu over 4.27m, but up to
1.06% Cu over 2.67m in the third and this enrichment may be related to a
later remobilisation of the disseminated chalcopyrite. The results of subsequent
drilling at two other sites are given in Appendix III
Mineral exploration for zinc, lead and baryte in Middle Dalradian rocks of the Glenshee area, Grampian Highlands
Drainage surveys and airborne geophysical surveys of a
600 km2 area from Blair Atholl to Braemar identified
several targets near Glenshee within the Ben Eagach
Schist, the host formation of the Aberfeldy deposits, lying
30 km along the Dalradian strike to the SW. Integrated
geological, geochemical and geophysical surveys have
been carried out over these targets. The extensive cover of
peat and glacial overburden, particularly over the softer
lithologies of the formation, hinders geological mapping
and near-surface leaching has destroyed most of the
sulphide. The presence of base metals and baryte is best
shown by detailed drainage sampling and the sulphidebearing
graphitic schist can be traced through drift
covered ground by VLF-EM, IP and SP surveys. Six
shallow boreholes were drilled on the basis of the
geochemical and geophysical anomalies and mapping of
the available outcrops.
Zinc-lead mineralisation has been found in the elastic
lower member of the Ben Eagach Schist as well as in the
upper member of graphitic schist. Vein baryte with minor
base metals is present in the Ben Lui Schist, a higher
Middle Dalradian formation, in southern Glenshee.
The detailed information available for the Glenshee
area is listed in the Data Package. A charge of &lOOO will
be made for a copy of this information, consultation with
staff, drillcore examination and for the time of staff required
to make a short field visit to the area
Geophysical investigation of chromite-bearing ultrabasic rocks in the Baltasound-Hagdale area, Unst, Shetland Islands
Economic deposits of chromite were discovered in Unst, Shetland
Islands in the early part of the nineteenth century and extraction
continuedi ntermittentlyu ntil exhaustiono f the known near-surface
deposits in 1945. Since it is likely that further comparable deposits
exist at shallow depth, detailed geophysical smeys employing
2
magnetic and electrical methods were carried out over ? km of the area
of known mineralisationt o test the feasabilityo f detectinga nd
delineatingt hem. Seven of 16 small positive gravity arumaJ.ie&se
tested by shallow boreholes but only two were attributed to chromite
concentrations.T he gravity anomaliesa t the other borehole sites
remain unexplained; they may be due to unidentified variations in bedrock
density at depth; they may be
of weathering and the thickness of
in overburden thickness
Polymetallic mineralisation in Carboniferous rocks at Hilderston, near Bathgate, central Scotland
Five boreholes in the vicinity of the ancient Ag-Ni-Pb
mine at Hilderston, near Bathgate have yielded new
stratigraphic, mineralogical and geochemical information.
These results, together with a critical reexamination
of old records, are interpreted in relation to a
palaeo-environment profde across a volcanic island with
coastal lagoon and fringing reef deposits, as proposed by
Jameson (1980).
Stratabound Zn-Pb mineralisation occurs in the lower,
argillaceous part of the Petershill Limestone, which was
deposited in an anaerobic lagoon on the edge of a volcanic
landmass during the Lower Carboniferous Epoch (Lower
Limestone Group, Vi&an Stage). The best intersection
shows 8 m of mineralised limestone, with underlying carbonaceous
mudstone (1 m) and tuffaceous seat rock
(2 m), having an average concentration of 0.14 % Pb and
0.66% Zn and maximum values of 0.6% Pb and 3.1%
Zn in the carbonaceous mudstone. Further drilling was
subsequently carried out in order to investigate possible
lateral extensions of the stratabound mineralisation and to
test for mineralisation in similar lithologies and geological
environments at other stratigraphic levels, and a report
on the results will be available at Edinburgh.
Late-Carboniferous hydrothermal veins occur within
the Petershill Limestone and in immediately overlying
elastic sediments, where they are cut by E-W faults and
quartz-dolerite dykes. At Hilderston Mine two
assemblages are recognised in the vein: Ba-Fe-
Ni-Co-Ag-As on a dyke margin adjacent to the elastic
sediments and Fe-Pb-Zn-S at lower levels adjacent to
the limestone. Zones of alteration in the dolerite dykes
carry hydrocarbons and weak Ba-Fe-Cu-F mineralisation.
No potentially-valuable vein deposits were
discovered in the present investigation