Rare earth element mobility during granite alteration: Evidence from southwest England     

D.H.M. Alderton  J.A. Pearce  P.J. Potts 《Earth and Planetary Science Letters》1980,49(1):149-165

Geochemical analyses of granitic rocks from southwest England reveal that the rare earth elements (REE) were potentially mobile during hydrothermal and supergene alteration. In particular, trivalent REE were removed from the system during K-silicate alteration, Eu was lost during sericitic alteration; all REE were lost during tourmalinization, and light REE were lost during chloritization and argillic alteration. The fluids themselves had low concentrations of REE; in only one case (chloritization) were heavy REE introduced during alteration. Analysis of separated minerals indicated that the behaviour of the REE could be partly explained in terms of their different affinities for the primary and secondary assemblages. Thermodynamic calculations indicated that REE mobility is enhanced by the presence of fluorine in the alteration fluids partly because REE form more stable complexes with F than with Cl and partly because elements such as Ti, Zr and P that form REE-bearing minor phases are themselves potentially mobile.  相似文献   

GeoPT2. International Proficiency Test for Analytical Geochemistry Laboratories - Report on Round 2   总被引：1，自引：1，他引：0  

Michael Thompson  Philip J. Potts  Jean S. Kane  Peter C. Webb  John S. Watson 《Geostandards and Geoanalytical Research》1998,22(1):127-156

Results from sixty laboratories participating in GeoPT2, the international proficiency testing programme for analytical geochemistry laboratories, are reported. Compared with 71.3% in the last round, 74.6% of the reported data complied with the laboratories' selected fitness for purpose criteria.  相似文献   

Geostandards and Geoanalytical Research     

Philip J. Potts  Mireille Polv 《Geostandards and Geoanalytical Research》2003,27(3):213-213

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International Association of Geoanalysts'Protocol for the Certification of Geological and Environmental Reference Materials   总被引：2，自引：1，他引：2  

Jean S. Kane  Philip J. Potts  Michael Wiedenbeck  Jean Carignan  Stephen Wilson 《Geostandards and Geoanalytical Research》2003,27(3):227-244

This protocol has been developed by the International Association of Geoanalysts to demonstrate procedures for the certification of geological and environmental reference materials to comply to the fullest extent possible with recommendations of the International Organisation for Standardisation (ISO Guide 35). A practical approach is described on the assumption that certifications will be normally be based on collaborative analysis programmes in which participating laboratories are preselected on the basis of performance in a proficiency testing programme or on the basis of other criteria of merit.  相似文献   

Editorial     

Phil Potts  Mireille Polv 《Geostandards and Geoanalytical Research》2002,26(3):247-247

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The age and growth of hottentot seabream Pachymetopon blochii before and after the South African linefish state of emergency in 2000     

MW Farthing  AC Winkler  K Anderson  S Kerwath  C Wilke  WM Potts 《African Journal of Marine Science》2018,40(2):187-196

The hottentot seabream Pachymetopon blochii is a small-sized (maximum 2.67 kg) sparid endemic to southern Africa. It is an important target in South Africa's Western Cape traditional linefishery, particularly in the absence of more valuable pelagic species (such as Thyrsites atun and Seriola lalandi). In 2000, South Africa's linefishery was declared to be in a state of emergency, and commercial fishing effort was consequently reduced by 70%. A subsequent increase in stock biomass and intraspecific competition, coupled with environmental changes, were hypothesised to have thereafter altered the growth rate of hottentot, from 2000 to 2010. This study aimed to revise outdated age–growth models for the hottentot by using modern techniques (sectioned otoliths), and to compare age–growth relationships before and after the declared linefish state of emergency. The maximum age observed was 19 years, with no difference in the growth rate between sexes (p = 0.39–0.43) or time-periods (p = 0.96). Although the growth rate did not change, there is evidence that the age structure of the stock changed between time-periods as a result of changes in fishing pressure between 2000 and 2010. The enhanced recent growth model for hottentot, described as L_t = 418.063 (1 – e^{?0.104(t – [?4.709])}) (pooled sexes; n = 206), indicates a considerably slower growth rate for this species than was proposed previously using whole otoliths and has major implications for effective stock management.  相似文献   

ISO Best Practices in Reference Material Certification and Use in Geoanalysis     

Jean S. Kane  Philip J. Potts 《Geostandards and Geoanalytical Research》2007,31(4):361-378

The International Organisation for Standardisation (ISO) has published many guides, or technical standards, of great value to analytical geochemists. Two of particular importance are Guide 33 (Uses of Certified Reference Materials) and Guide 35 (Certification of Reference Materials). Both were first developed in the 1980s and undergo regular review and updating by the Reference Materials Committee (REMCO) that operates within ISO. Recent revisions have focused on adding statistical rigour to both guides. Although this offers significant advantages for use by professional metrologists, there are consequent issues of comprehension by the analytical chemists who in fact have the greatest need of them. A major focus of Guide 35 is the development of reference material uncertainties that are in full compliance with the Guide on Measurement Uncertainty (GUM), jointly issued by ISO, IUPAC and others. Guide 35 details handling of uncertainty due to (1) degradation on the shelf and in transport, (2) sample heterogeneity and (3) inter‐method and inter‐laboratory bias, as well as within‐laboratory repeatability. The International Association of Geoanalysts has developed a protocol for reference material certification that applies Guide 35 to the specific needs of the geoanalytical community. The approach being taken by the IAG in developing GUM‐compliant uncertainties for its certified values is presented. Recommendations made in Guide 33 for how a laboratory should compare its own results with certified values in assessing laboratory accuracy are outlined. Additionally, the subject of misusing reference materials is discussed. The apparent misuse occurs because so few CRMs exist that meet critical measurement needs of geoanalytical laboratories and that also meet the rigorous metrological demands of the latest editions of the ISO Guides. All of the focus of the IAG certification programme has been to undertake certifications that would fill gaps in CRM availability and thus serve to limit this misuse.  相似文献   

GeoPT5. An International Proficiency Test for Analytical Geochemistry Laboratories - Report on Round 5   总被引：1，自引：0，他引：1  

Michael Thompson  Philip J. Potts  Jean S. Kane  Stephen Wilson 《Geostandards and Geoanalytical Research》2000,24(1):E1-E28

Results are presented from the seventy two laboratories participating in GeoPT5, round five of the international proficiency testing programme for analytical geochemistry laboratories. The sample for round five, AMH-1 (Mount Hood andesite), was distributed during March 1999 and participating laboratories were asked to analyse the sample using their routine techniques and submit results to the steering by 15th June 1999. In this report, contributed data are listed together with the derived z-scores from which participating laboratories can assess their analytical performance. Z-scores in the range -2 to 2 are considered satisfactory. Z-score values that lie outside this range may indicate unsuspected analytical bias. The distinctive feature of the present round is that AMH-1 is a candidate reference material prepared by the USGS and it is intended that the present proficiency testing data will contribute to the reference material characterisation programme.  相似文献   

Characterization of mesostasis regions in lunar basalts: Understanding late‐stage melt evolution and its influence on apatite formation          下载免费PDF全文

Nicola J. Potts  Romain Tartèse  Mahesh Anand  Wim van Westrenen  Alexandra A. Griffiths  Thomas J. Barrett  Ian A. Franchi 《Meteoritics & planetary science》2016,51(9):1555-1575

Recent studies geared toward understanding the volatile abundances of the lunar interior have focused on the volatile‐bearing accessory mineral apatite. Translating measurements of volatile abundances in lunar apatite into the volatile inventory of the silicate melts from which they crystallized, and ultimately of the mantle source regions of lunar magmas, however, has proved more difficult than initially thought. In this contribution, we report a detailed characterization of mesostasis regions in four Apollo mare basalts (10044, 12064, 15058, and 70035) in order to ascertain the compositions of the melts from which apatite crystallized. The texture, modal mineralogy, and reconstructed bulk composition of these mesostasis regions vary greatly within and between samples. There is no clear relationship between bulk‐rock basaltic composition and that of bulk‐mesostasis regions, indicating that bulk‐rock composition may have little influence on mesostasis compositions. The development of individual melt pockets, combined with the occurrence of silicate liquid immiscibility, exerts greater control on the composition and texture of mesostasis regions. In general, the reconstructed late‐stage lunar melts have roughly andesitic to dacitic compositions with low alkali contents, displaying much higher SiO₂ abundances than the bulk compositions of their host magmatic rocks. Relevant partition coefficients for apatite‐melt volatile partitioning under lunar conditions should, therefore, be derived from experiments conducted using intermediate compositions instead of compositions representing mare basalts.  相似文献   

A numerical study of the effects of wall deformation on earth pressures     

D. M. Potts  A. B. Fourie 《国际地质力学数值与分析法杂志》1986,10(4):383-405

When designing any earth retaining structure it is necessary to estimate the limiting earth pressures. This is usually achieved by assuming a linear pressure distrigution and by using active and passive pressure coefficients obtained by either limit equilibrium, stress field solutions of limit analysis. These coefficients are approximate in a theoretical sense, do not distinguish between modes of wall movement, and provide no pre-failure information. In practice, wall movements are dependent on the construction method and support conditions provided. Any effect of such movements on earth pressures is therefore of practical interest. In this paper the finite element method is used to investigate the effect of the mode of wall movement on the generation of earth pressure. Both smooth and rough walls are considered. It is shown that the distribution of earth pressure is highly dependent on the assumed mode of deformation. The resultant forces on the wall are also affected, but to a lesser degree. The, effect of soil dilatation, the initial horizontal stress and the distribution of soil stiffness with depth are also examined.  相似文献