St Andrews Research Repository

St Andrews University Home
View Item 
  •   St Andrews Research Repository
  • Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)
  • Geography & Geosciences (Previous name for currents schools of Earth & Environmental Sciences and ...)
  • Geography & Geosciences Theses
  • View Item
  •   St Andrews Research Repository
  • Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)
  • Geography & Geosciences (Previous name for currents schools of Earth & Environmental Sciences and ...)
  • Geography & Geosciences Theses
  • View Item
  •   St Andrews Research Repository
  • Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)
  • Geography & Geosciences (Previous name for currents schools of Earth & Environmental Sciences and ...)
  • Geography & Geosciences Theses
  • View Item
  • Login
JavaScript is disabled for your browser. Some features of this site may not work without it.

Mineralogy, petrology and geochemistry of Caradocian phosphorites, N. Wales, U.K.

Thumbnail
View/Open
NeetaSaigalPhDThesis.pdf (36.21Mb)
Date
07/1985
Author
Saigal, Neeta
Supervisor
Walton, E. K. (Ewart Kendall)
Funder
Overseas Research Grant
Continental Oil Company
Leckie Trust
St Andrew University Post-Graduate Studentship
Metadata
Show full item record
Altmetrics Handle Statistics
Abstract
Caradocian phosphorite nodules sampled from the Powys county of N. Wales, U.K. have been investigated in order to characterize the deposit geochemically, mineralogically and petrographically and to evaluate their mode of formation. Nodules are the main form of phosphorite although phosphatized organic fragments and oolitic grains are also present. On the basis of petrographio characteristics, nodules are grouped into two types; Type I nodules (with abundant organic material) and Type II nodules (with abundant clay minerals). Mineralogical compositions of the phosphorite nodules reflect varying degrees of dilution of the phosphate material, francolite, by authigenic and detrital minerals. Examination with the scanning electron microscope of freshly fractured surfaces of nodules suggests that the apatite formed authigenically as a direct chemical precipitate. Surfaces of abundant siliceous spicules and other organic fragments as well as some minerals appear to be favoured sites for apatite nucleation. Geochemical studies showed significant impoverishment of lattice elements and enrichment of non-lattice elements in both types of nodules. Chemically the phosphorite nodules may be described in terms of four major components: SiO2, CaO, P2O5 and F. The average concentrations of trace elements present in these nodular phosphorites were compared with an average concentration in marine shales. The enrichment and/or depletion largely suggested precipitation from sea water. The proposed model of phosphorite formation involves inorganic (or biochemical) precipitation of apatite within pore waters of anoxic sediments and subsequent concentration of the apatite by physical processes. Oxidation of organic material during sulphate reduction is the main source of phosphate. This is supported by the very light delta13c isotopic composition of structural carbonate present in the francolites. These studies have also shown that these phosphorites have undergone differential leaching during weathering processes with the development of secondary phosphate: minerals, decarbonation of francolite and removal of many major and minor elements.
Type
Thesis, PhD Doctor of Philosophy
Collections
  • Geography & Geosciences Theses
URI
http://hdl.handle.net/10023/15566

Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.

Advanced Search

Browse

All of RepositoryCommunities & CollectionsBy Issue DateNamesTitlesSubjectsClassificationTypeFunderThis CollectionBy Issue DateNamesTitlesSubjectsClassificationTypeFunder

My Account

Login

Open Access

To find out how you can benefit from open access to research, see our library web pages and Open Access blog. For open access help contact: openaccess@st-andrews.ac.uk.

Accessibility

Read our Accessibility statement.

How to submit research papers

The full text of research papers can be submitted to the repository via Pure, the University's research information system. For help see our guide: How to deposit in Pure.

Electronic thesis deposit

Help with deposit.

Repository help

For repository help contact: Digital-Repository@st-andrews.ac.uk.

Give Feedback

Cookie policy

This site may use cookies. Please see Terms and Conditions.

Usage statistics

COUNTER-compliant statistics on downloads from the repository are available from the IRUS-UK Service. Contact us for information.

© University of St Andrews Library

University of St Andrews is a charity registered in Scotland, No SC013532.

  • Facebook
  • Twitter