OF CARBONATE-HOSTED LEAD-ZINC DEPOSITS OF THE KOOTENAY ARC ( 82 FEast Half )
Fieldwork for this study consisted of a preliminary investigation and sampling of carbonate-hosted lead-zinc deposits within the Kootenay arc. Lead isotope data from galena were also determined at The University of British Columbia. Carbonate-hosted lead-zinc deposits in the Kootenay arc have been characterized as either concordant or transgressive types based on field characteristics (Fyles, 1966). In general, the transgressive mineralization occurs as vein or replacement deposits that are enriched in silver. The concordant deposits are stratiform  and  contain  a  simple  base metal sulphide mineral suite with little or no precious metals. The concordant deposits have also been referred to as the Salmo or Remac-type, after several large deposits in the Salmo camp. Lead isotope data from deposits in the Kootenay arc have been used to interpret and explain the source of lead and the ore-forming processes responsible for these deposits. Lead isotope plots for the Remac-type deposits do not conform to lead growth curves constructed for lead-zinc deposits from this region, nor can they be adequately interpreted as the result of lead mixing or lead inheritance. A thorough analysis and comparison of the ore and gangue mineralogy, stratigraphy, and trace element and isotope geochemistry from these conformable Remac-type deposits and the younger Metaline-type deposits will provide an improved understanding of the regional ore-forming process.
Average lead isotope growth curves for shale-hosted zinc-lead deposits, Canadian Cordillera
Average lead isotope growth curves for shale-hosted zinc-lead deposits have been constructed empirically for a large but well-defined tectonic segment of the Canadian Cordillera. The model defined is applicable to the dating of galena-lead from shale-hosted deposits in the Selwyn basin and in the Ogilvie, Richardson, Wernecke, and Mackenzie Mountains, in the Eastern fold belt, and in much of the Omineca crystalline belt. This area of the cordillera generally had a coherent geochemical evolution. Lead for deposits was extracted from sediments which had been deposited along the western margin of the North American craton and which were derived largely from upper crustal crystalline rocks that formed the western part of the Canadian Shield.The average shale growth curves involve three stages of evolution. The third (most recent) stage of the three-stage model, starts at 1.89 m.y. and evolves to 0 m.y. with mu of 12.16 and omega of 49.09. The first two stages follow the two-stage model of Stacey and Kramers (1975). The model allows precise model age estimates, with an error generally less than 0.05 m.y., to be made for deposits of known age. This is particularly useful in property evaluation during exploration because in many cases the certainty of a syngenetic or epigenetic origin can control future philosophy about exploration and/or evolution of a deposit or an area. Model ages, in concert with stratigraphic information, commonly indicate the likelihood of epigenetic or syngenetic origins.
The crystal structure of stilpnomelane. Part II. The full cell
Summary The structural formula of stilpnomelane averaged from 37 representative literature analyses and based on the determined structure is (Ca,Na,K)4(Ti0·1Al2·3Fe35·5Mn0·8Mg9·3)[Si63Al9](O,OH)216·nH2O. Ferrostilpnomelanes have up to 12 R 3+ cations in the octahedral sheet, ferristilpnomelanes commonly have between 24 and 30 R 3+ cations, rarely up to 37. The two groups can be distinguished by accurate X-ray powder diffraction, ferrostilpnomelanes having d 001 less and a greater than have ferristilpnomelanes. The unit cell is triclinic, a = b∼21·8 Å, γ = 120°, d 001∼12·2 Å, P . Hexagonal groups or ‘islands’ of 24 silicon-oxygen tetrahedra co-ordinate to the octahedral sheet, the centres of the ‘islands’ are displaced by 5a/12, 8b/12 on either side of the octahedral sheet as a result of warping of this sheet to permit articulation with the smaller tetrahedral sheet. The 24-tetrahedra ‘islands’ are linked laterally by 6-member rings of inverted tetrahedra, which in turn link at their apices to like rings connecting the next sheet of ‘islands’. Thus a single tetrahedral layer is 4 tetrahedra thick and has symmetry 6/m. The 6-member rings of tetrahedra act as hinges permitting up to 0·5 Å extension or contraction of the tetrahedral sheet to accommodate variations in the octahedral sheet dimensions with varying R 2+/R 3+ ratio.