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Porphyry style copper mineralisation at Black Stockarton Moor, south-west Scotland

Brown, M.J.; Leake, R.C.; Parker, M.E.; Fortey, N.J.. 1979 Porphyry style copper mineralisation at Black Stockarton Moor, south-west Scotland. Institute of Geological Sciences, 100pp. (WF/MR/79/030) (Unpublished)

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Abstract/Summary

Reconnaissance soil sampling within the catchment of streams containing anomalous levels of copper in drainage samples led to the discovery of disseminated copper mineralisation in the Black Stockarton Moor area of Galloway, Scotland. Analysis of aeromagnetic data and of a gravity survey of the area, previously mapped as an irregular complex of dykes, suggested that the region was underlain by laminar bodies of granodiorite. Geological mapping r evealed the presence of a major Caledonian multiphase subvolcanic complex intruding LOvler Palaeozoic turbidi tes, to the west of the Criffe! granodioritic plutonic complex. An induced polarisation survey delineated an arcuate anomaly about 6 km long and the resul t s of a simultaneous geochemical soil survey showed a zone with anomalous levels of copper (> 140 ppm to 5500 ppm) in the southern part of the area to be essentially paralle l to the IP anomaly but partially displaced to the east. A series of three deep angled drill holes and nine shallow holes sited on geochemical and geophysical anomalies confirmed the widespread presence of both veinlet and disseminated pyrite and copper mineralisation of the porphyry type. The Black Stockarton Moor subvolcanic complex is a composite of minor intrusive rocks, the ear l iest phase of which, comprising porphyri te dyke swarms, granodiorite sheet intrusions, small granodiori te stocks, breccia pipes, vent agglomerates with plugs of basic rock and a few basic dykes, predates the adjacent multiphase Crlffel plutonic complex. The second phase of subvo lcanic activity postdates the plutonic rocks and comprises intense en-echelon s igmoidal swarms of porphyrite dykes sharply discordant to the earliest phase rocks. A minor third phase consists of linear porphyrite dykes closely associated with fault - ing. Chemical analysis and mineralogical examination of the borehole material indicates that regular zonation can be observed in the style and intensity of both mineralisation and hydrothermal alteration. This zonation is regular fr om west to east across the IP and soil anomalies. A propylitic alteration zone with the development of chlorite. epidote and minor sericite in igneous rocks and of calcite , quartz, jasperoid, chlorite, amphibole, epidote and albite in sedimentary rocks occurs to the wes t . Within this zone hematite gradually gives way to increasing amounts of pyrite from west t o east. The propylitic zone passes into a sericitic alteration zone where sedimentary rocks are frequently bleached and igneous rocks pink or orange-coloured containing secondary quartz, chlorite and muscovite. Pyrite is most conspicuous within rocks of the outer sericite zone, the outcrop of which coincides roughly with the axis of the IP anomaly. Further east pyrite decreases but chalcopyrite and bornite with some chalcocite become relatively conspicuous and copper levels are the highest attained (in the 400 ppm to 1100 ppm range). save for isolated highly br·ecciated sections. Chemical zonation shows relative enrichment in Mn, Zn, As and Pb in the outer propyli tic zone, Ba in the serid tic 1 zone and Cu in the inner sericitic zone while As, Sb and Au are markedly concentrated with Cu and Mo in isolated brecciated sections

Item Type: Publication - Report (UNSPECIFIED)
Programmes: BGS Programmes > Other
Funders/Sponsors: Department of Industry
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed
NORA Subject Terms: Earth Sciences
Date made live: 01 Nov 2010 16:15
URI: http://nora.nerc.ac.uk/id/eprint/11871

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