| Reference Type | Journal (article/letter/editorial) |
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| Title | Rubidium-strontium age studies and geochemistry of acid veins in the Freetown complex, Sierra Leone |
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| Journal | Mineralogical Magazine | ISSN | 0026-461X |
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| Authors | Beckinsale, R. D. | Author |
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| Bowles, J. F. W. | Author |
| Pankhurst, R. J. | Author |
| Wells, M. K. | Author |
| Year | 1977 (December) | Volume | 41 |
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| Issue | 320 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/doclib/MinMag/Volume_41/41-320-501.pdf+ |
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| DOI | doi:10.1180/minmag.1977.041.320.12Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 2826 | Long-form Identifier | mindat:1:5:2826:8 |
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| GUID | 0 |
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| Full Reference | Beckinsale, R. D., Bowles, J. F. W., Pankhurst, R. J., Wells, M. K. (1977) Rubidium-strontium age studies and geochemistry of acid veins in the Freetown complex, Sierra Leone. Mineralogical Magazine, 41 (320) 501-511 doi:10.1180/minmag.1977.041.320.12 |
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| Plain Text | Beckinsale, R. D., Bowles, J. F. W., Pankhurst, R. J., Wells, M. K. (1977) Rubidium-strontium age studies and geochemistry of acid veins in the Freetown complex, Sierra Leone. Mineralogical Magazine, 41 (320) 501-511 doi:10.1180/minmag.1977.041.320.12 |
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| In | (1977, December) Mineralogical Magazine Vol. 41 (320) Mineralogical Society |
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| Abstract/Notes | SummaryThe stratigraphical limits on the age of the Freetown intrusion, Sierra Leone, are very wide, yet the intrusion has not previously been accurately dated by isotopic methods, despite a number of attempts. Rubidium-strontium dating of acid veins contemporaneous with the early stages of the prolonged cooling history of the intrusion provides an age of 193 ± 3 Ma. The veins consist of quartz and orthoclase with relict minerals, principally plagioclase, from thehost gabbro. Electron-microprobe analysis of the altered minerals of the veins, and the petrography of the vein and adjacent host gabbro clearly demonstrate that the veins were formed from a granitic fraction, differentiated in situ from the surrounding solid gabbro with the assistance of a hydrous fluid phase within the incipient vein. This assertion is supported by the identical, low value of the initial 87Sr/86Sr ratio (0·70389) obtained from both the acid and basic rocks, and the technique described here may be useful in dating other, similar, intrusions. |
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