During the late Silurian to early Devonian, end-Caledonian sinistral transpression caused movement on a series of N to NE trending strike slip faults that transected the Dalradian terrain. One of this set of faults, the Tyndrum Fault, was active from the end of the Caledonian orogeny to after Permo-Carboniferous times. Detailed mapping of fault zone fractures and veins has revealed a long and complicated movement history involving both sinistral and dextral strike-slip fault movement. Reactivation involved both the formation of new structures and the utilisation of old structures The Tyndrum Fault hosts both economic lead-zinc and gold-silver-telluride mineralisation. The gold-silver mineralisation occurred in a sinistral strikeslip fault set adjacent to the Tyndrum Fault probably before 410Ma. The leadzinc mineralisation occurred at - 340 Ma in a dextral strike-slip movement and is hosted by the Tyndrum fault plane and in subparallel fractures. Many episodes of quartz mineralisation have also occurred. Individual mineralisation episodes show a cyclic character, with hydrothermal brecciation and cataclastic events. When distinctive mineralising fluids were pumped through the fault, individual groups of cycles may be recognised. Several cycles were responsible for the gold mineralisation. An initial hydrothermal brecciation deposited quartz and pyrite. Electrum was adsorbed onto this pyrite in a following cataclastic event, and several more cycles of hydrothermal brecciation and cataclasis occurred. The lead-zinc mineralisation occurred by a similar mechanism, and these cycles may be related to the earthquake process. Stable isotopic ratios from veins containing the gold mineralisation have been determined. 0180 values for quartz ranged from +10 to +15 %0. oD values from water in fluid inclusions ranged from -91 to -34%0. 034 S val ues ranged from +0.25 to +8%0 for pyrite. Later lead-zinc veins in the vicinity gave 034S values of +50/00 for galena. Fluid inclusion studies indicated the gold-bearing veins were formed from C02 -rich, low salinity, unmixed fluids. The 't values of. 290-350°C probably represent true trapping temperatures. The isotopic ratios of the mineralising fluid were calculated as between -1.0 to +6.80/00 fa r sulphur and for oxygen as between +3.6 to 6.8%0. Comparison with nearby .porphyry-style mineralisation suggests an original magmatic origin for the mineralising fluid but there may be an influence from a meteoric component. The sulphur isotopic ratios suggest a mainly country rock source, though a magmatic component is also apparent.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:582123 |
| Date | January 1990 |
| Creators | Curtis, Sara Francis |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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