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