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Title: Factors governing the development of fluorspar orebodies in the North Pennine orefield
Author: Smith, F. W.
ISNI:       0000 0001 3434 6235
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 1974
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The present knowledge of the structure of the North Pennines is reviewed. Vein orebodies are found to occupy cavities formed by combinations, in varying proportions, of strike and dip displacements on irregular fault planes, the dimensions of the orebodies being determined by those of the cavities. "Bonanza" vein orebodies occur where vein systems intersect major belts of washout channel sandstones within Namurian strata. Fluid inclusion studies show that the lead-zinc-fluorine ores of the fluorite zone of the orefield were carried in brines of 20.2 to 25.6 equivalent weight per-cent NaCl salinities and were deposited during brine cooling within o the temperature range from 211 to 119 c. The published solubility data of fluorite in brines of these characteristics indicate that some 5.05 x 101 2 tonnes of brine would have been required in order to deposit the total fluorite content of the orefield. Three main phases in the evolution of the mineralization can be distinguished, an early, possible~ higher temperature, quartz-chalcopyrite-pyrite-marcasite phase, a main ore-depositing phase and a late, lower temperature, quartz-carbonate phase. Consideration of the geometry of ore body systems suggests that feeder conduits must have existed between sub-horizontally-disposed orebody cavities. These were located chiefly at fracture or vein intersections. Detailed fluid inclusion studies of individual orebodies show temperature maxima at such feeder intersections. Trace element analysis of fluorite by X.R.F. shows that the contents of yttrium, cerium and lanthanum are also highly enriched at feeder sites. This has been used as a means of locating intersecting velns within partially developed orebodies. In combination, the fluid inclusion and trace element techniques enable determination of hydrothermal flow directions in vein systems. Mineralization of the Red Vein of Weardale has been studied in detail using structural interpretation, fluid inclusions and trace element analysis of fluorite. The dimensions of the major orebodies have been delimited, indicating iiipossible targets for exploration. Application of the analytical methods to fluorite veins ln the Derbyshire and Central Pennine orefields was unsuccessful ln locating intersections. Results from the Cornubian orefields, however, appear promising. Fluid inclusion determinations have been made on minerals from a number of other orefields in Britain and abroad, some of which had not been previously studied. Trace element analysis of 690 fluorites of varying provenance indicates that the yttrium content may be useful in showing the ultimate source of the fluorite-depositing brine. Fluorites carrying more than about 80 - 90 ppm Yare associated with igneous sources. Fluorites carrying much lower concentrations of Yare characteristically, though not inevitably, from deposits of the Mississippi Valley, or telethermal type of deposit. Fluorites from the North Pennine veins carry high concentrations of Y, in the general range 120 to 815 ppm, and the ore brines are thus considered to have had an ultimately magmatic source.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available