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How do you find an orebody? Where do you start looking? This programme is the first of three linked programmes which examine a massive new lead-zinc discovery in Ireland. It is at Navan, in County... Meath, about 30 miles north of Dublin. This orebody will become the largest lead-zinc mine in Europe, and will probably rank amongst the top ten mines in the world, Navan is used as a case study for mining. In this first part Dr. Stephen Drury gives the broad geological setting, and shows how a geochernical survey showed up zinc anomalies in the soil. This was followed up by a geophysical survey, (an Induced Potential Survey), which gave promising results. These paved the way for a much more rigorous and expensive bore-hole survey, which ultimately proved the existence of the orebody, and its size and grade. Dr. Richard Thorpe discusses the origin of the ore, the replacement of the Carboniferous Limestone; and goes on to show how the temperature of formation of the orebody might be worked out from the silver content and from fluid inclusions. Other speakers include a field geologist at Navan, and the Chief Geologist for Tara Mines Ltd.
Metadata describing this Open University video programme
Item code: S26-; 05
First transmission date: 30-03-1974
Published: 1974
Rights Statement:
Restrictions on use:
Duration: 00:24:13
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Producer: Peter Clark
Contributors: Stephen Drury; Richard Thorpe
Publisher: BBC Open University
Keyword(s): Bore-hole survey; Geochemical survey; Geophysical survey; Induced potential survey; Ireland; Lead-zinc; Navan; Orebody
Subject terms: Mining engineering--History
Footage description: Stephen Drury with a map of the British Isles. On it are marked areas of carboniferous limestone. Drury points out areas where the limestone has become strongly mineralised. Shots of a Derbyshire mine. Aerial shots of Cheddar Gorge showing exposed carboniferous limestone. Shots of peat deposits in Ireland being exploited. The carboniferous limestone lies deep under the soil here. Drury explains why very little was known about mineral deposits in Ireland up to 1960. Shots of map of Ireland showing the extent of the carboniferous limestone outcrop. Lead, copper and gold deposits are marked. These mineral deposits are from older mine workings around the coast. Drury, gives a brief listing of the geological makeup of Ireland. Shots of a histogram showing areas under exploratory licence in Ireland from 1956-1972. Shot of a map of Ireland showing the area being explored for minerals in 1972. This is compared with the map showing carboniferous limestone content. They are almost identical. Commentary by Drury explains how Tara Mines Ltd. carried out a geo-chemical survey at Navan. Shots of soil samples being taken and analysed in the laboratory. An atomic absorption spectrophotometer is used to analyse the soil samples. Brian Byrne, chief geologist for Tara Mines Ltd. gives the results of the geocherrical survey in the area. Map of the area around Navan shows the zinc anomaly which was discovered during the geo-chemical survey. Aerial shot of the same area. Commentary by Drury discusses the possibility of an ore body being present. Film sequence shows part of an induced potential geophysical survey being carried out in the same area. This follows up the geochemical survey. Commentary by Drury explains the procedure and principles involved. Map of the area around Navan shows the extent and location of the geophysical survey. Shot of a graph showing the plot for one of the lines of the induced potential survey. Shots of a mobile drilling rig at work during a bore hole survey of the Navan area. Commentary by Drury explains what is happening. Several close up shots of the equipment being used including the drill bit. Brian Byrne discusses the results of the bore-hole survey at Navan. Map of the area shows drill hole sites. Drury with a 3 dimensional model of the ground at Navan. Bore holes and the ore body are indicated. Drury explains the sort of predictions a mining company can make based on models of this sort. Richard Thorpe with a piece of drill ore from Navan. He points out the various minerals present. This is a Micrograph of a section of the sample. Thorpe points out more of the minerals and fossils found there. Cross section diagram of the rock formation at Navan. The ore body is marked. Another cross section diagram shows the rocks at Tynagh. Here too the ore body is marked, together with other geological features. Thorpe points out that all the ore bodies discovered in Ireland have similar geological settings. Geological map used to back up his point. Thorpe begins discussion on the origins of ore bodies. Sean Finlay, exploration geologist at Navan, discusses possible origins of ore bodies at Navan. He uses a core sample to aid his discussion. Thorpe discusses methods which might be used to determine the origin of an ore body. He begins by explaining how a knowledge of the temperature of the ore body at time of formation can give clues to its origin. Thorpe explains two methods: 1. Silver content method. Temperature at time of formation determines silver conten in lead sulphide. Model of a lead sulphide crystal used as an aid. Graph shows silver content at various temperatures. Thorpe, Richard of Fluid inclusion method. Temperature at formation determines characteristics of fluid inclusions. Shots of micrographs showing fluid inclusions at various temperatures. The evidence of the application of the 2 methods above suggests some form of hydrothermal origin of ore bodies. Drury sums up the programme by discussing the potential of mineral exploitation at Navan. Shots of the mine at present (1973) and model showing future development.
Master spool number: 6HT/71234
Production number: 00525_1005
Videofinder number: 2797
Available to public: no