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The programme examines the use of Concordia graphs for studying uranium-lead isotopic ages and how a study of stable isotopes of hydrogen and oxygen can lead to an understanding of the origin of ce...rtain rocks and ore deposits.
Metadata describing this Open University video programme
Module code and title: S333, Earth science topics and methods
Item code: S333; 01; 1976
First transmission date: 14-03-1976
Published: 1976
Rights Statement:
Restrictions on use:
Duration: 00:25:00
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Producer: Peter Clark
Contributors: Jullian Pearce; Robert Pidgeon; Simon Shepherd; Richard Thorpe
Publisher: BBC Open University
Keyword(s): Atomic lattice; Concordia graph; Copper deposits; Hydrogen; Hydrothermal origin; Hydrous minerals; Oxygen; Standard Mean Ocean Water; Uranium-lead isotopic ages; Zircon crystals
Footage description: Richard Thorpe introduces the programme. He holds a Geiger counter to a granite specimen to demonstrate its radioactivity. Using an animation, Thorpe explains the uranium-lead half life and how its measurement can be used to date rocks. Thorpe examines a thin section of the granite under the microscope. He points out the pleochroic halos and zircon crystals. Thorpe explains the importance of zircon for dating rocks. Thorpe discusses the importance of the Concordia plot which combines two rates of uranium decay in zircon crystals. Shots of an animated Concordia plot. Thorpe points out lead loss as a possible cause of the discrepancies found in Concordia plots. Shots of zircon crystals under microscope. Shots of lead loss plotted on an animated Concordia graph for zircon crystals. Thorpe demonstrates and explains a method for separating out zircon from granite using a jaw crusher, crown mill, vibrating table, heavy liquids and magnetic separation. Thorpe (voice over) explains how the zircons from a single granite are analysed for uranium and lead. Film shots show the process. Robert Pidgeon discusses the significance, for geochronology of the uranium-lead method of dating. Julian Pearce, using animated graphics showing ratios of isotopes, discusses the basics of stable isotopes of oxygen and hydrogen. He goes on to explain why he is interested in the isotopes of these two elements. Pearce demonstrates some of the physical properties of ordinary and heavy water by checking densities with a hydrometer and boiling points with a thermometer. Pearce next discusses the isotopic composition of sea water (SMOW). The formula for comparing other water with SMOW is captioned. An animated graph plots SMOW against other waters such as meteoric water from various regions of the earth. Pearce gives reasons for the different values. Film shots of steam rising from liquid lava from inside a central African volcano. Shots of researchers taking samples of this steam. Pearce introduces Simon Shepherd. Shepherd with a geological model of Cyprus. Shots of a Cypriot copper mine. Shots of a cross section of the model. Shepherd points out two possible origins for magmatic water. Using two rock samples from Cyprus and an animated graph, Shepherd demonstrates that the water in the samples is probably of sea, rather than magmatic origin. Shepherd uses the cross sectioned model above to explain a possible method for the formation of ore deposits in Cyprus.
Master spool number: 6HT/71780
Production number: 00525_1207
Videofinder number: 1886
Available to public: no