Radiometric ages and other isotopic data bearing on the evolution of Archaean crust and ores in the Kuhmo-Suomussalmi area, eastern Finland

The Archaean greenstone-gneiss terrain in the Kuhmo-Suomussalmi district in eastern Finland has been isotopically studied in connection with regional bedrock mapping and local mineral exploration projects. The studies have aimed at testing correlations of lithologic units in partly poorly exposed areas, determining times of ore formation and obtaining ore genetic information in order to better understand the general evolution of the Archaean formations within the Fennoscandian Shield. Isotopic results on 63 zircon and titanite fractions from 13 samples, common lead analyses of 14 sulphide separates from two mineral prospects and 33 whole rock Pb-Pb analyses warrant the following conclusions: 1) Although some dates in excess of 3 Ga have been determined from the Finnish Archaean, most of the granite gneiss terrain was formed between 2.85 and 2.65 Ga with a major period of rock formation from about 2.75 to 2.69 Ga. 2) The majority of the metavolcanic rocks within the Kuhmo-Suomussalmi greenstone belt are 2.79 Ga old, but the meta-andesites of the Luoma Group are distinctly older at 2.97 Ga. 3) The Taivaljärvi Ag-Zn-Pb deposit appears to be syngenetic with the local metavolcanic rocks and is thus 2.79 Ga old. Its lead probably represents the initial lead of both mafic and felsic metavolcanic rocks in the area. 4) When compared to the Abitibi region in Canada, the available Pb-Pb data may suggest a heterogeneous Archaean mantle, but as even this study shows, common lead data is inconclusive evidence, as it may be easily influenced by later hydrothermal processes

An international study of the quality of national-level guidelines on driving with medical illness

BACKGROUND: Medical illnesses are associated with a modest increase in crash risk, although many individuals with acute or chronic conditions may remain safe to drive, or pose only temporary risks. Despite the extensive use of national guidelines about driving with medical illness, the quality of these guidelines has not been formally appraised. AIM: To systematically evaluate the quality of selected national guidelines about driving with medical illness. DESIGN: A literature search of bibliographic databases and Internet resources was conducted to identify the guidelines, each of which was formally appraised. METHODS: Eighteen physicians or researchers from Canada, Australia, Ireland, USA and UK appraised nine national guidelines, applying the Appraisal of Guidelines for Research and Evaluation (AGREE II) instrument. RESULTS: Relative strengths were found in AGREE II scores for the domains of scope and purpose, stakeholder involvement and clarity of presentation. However, all guidelines were given low ratings on rigour of development, applicability and documentation of editorial independence. Overall quality ratings ranged from 2.25 to 5.00 out of 7.00, with modifications recommended for 7 of the guidelines. Intra-class coefficients demonstrated fair to excellent appraiser agreement (0.57-0.79). CONCLUSIONS: This study represents the first systematic evaluation of national-level guidelines for determining medical fitness to drive. There is substantive variability in the quality of these guidelines, and rigour of development was a relative weakness. There is a need for rigorous, empirically derived guidance for physicians and licensing authorities when assessing driving in the medically ill