The Geochemistry And Structural Controls Of Auriferous Shear Zones At Yellowknife, Mackenzie District, Northwest Territories, Canada

The existing stratigraphic and structural subdivisions are refined, and temporal constraints indicate two prograde metamorphic events at Yellowknife. Four generations of structures are identified: (1) brittle syn-volcanic, (2) brittle-ductile, late first metamorphism, (3) brittle, post-first metamorphism, pre second metamorphism, and (4) brittle, post second metamorphism, Proterozoic faults. Gold mineralization occurs in P-shears which became dilatant during seismic-aseismic events after a passive ductile state had been achieved, and is reflected at all scales, from hand sample, stope, orebody, ore zone, to mining camp-scales.;Structural studies at Yellowknife, and geochemical analyses of the igneous rocks are consistent with greenstone belt development in a back-arc basin that accreted obliquely onto an older crustal terrain, with emplacement of shoshonitic lamprophyres during late convergence, post-granite. Geochronological work places this framework into; (1) synvolcanic, at 2,683 Ma, (2) syn-I-type batholith, syn first metamorphism at 2,620 Ma, (3) mineralization between 2,620-2,585 Ma, (4) second metamorphism at 2,585 Ma, and (5) Proterozoic dykes.;Ore-related metasomatic alteration is imparted upon structurally and chemically modified volcanic rocks of the Yellowknife Bay Formation. The chemical composition of these rocks, now chlorite schists reveals a fluid history consistent with metasomatic alteration by large volumes of weakly saline, near neutral, CO{dollar}\sb2{dollar}/CH{dollar}\sb4{dollar}-rich fluids at temperatures near 390{dollar}\sp\circ{dollar} {dollar}\pm{dollar} 15{dollar}\sp\circ{dollar}C, and log f{dollar}\sb{lcub}02{rcub}{dollar} near the pyrite-pyrrhotite transition. Gold mineralization was enhanced by fluid-gas unmixing induced by pressure fluctuations, causing periodic excursions in the Eh of the remaining aqueous fluids, resulting in destabilization of soluble gold complexes, changes in mineral phase relationships and chemistries, and shifts in the {dollar}\delta\sp{lcub}13{rcub}{dollar}C of related carbonates. Pressure fluctuations were promoted by structural discontinuities generated by the intersection of type 1 and 2 structures; the former was reactivated during type 3, to generate the present distribution of mineralization. Related metasomatic effects can be detected up to 100 m from ore zones, within macroscopically unaltered chlorite schists. Later, surface-related fluids locally modified the {dollar}\delta\sp{lcub}18{rcub}{dollar}O of less robust minerals. (Abstract shortened by UMI.

Bringing Agriculture into the GATT: Designing Acceptable Agricultural Policies

Agricultural and Food Policy, International Relations/Trade,

Survey Results and Demographic Data for United Catholic Social Services\u27 Family Services

A summary of demographic data and survey results

Real Estate Risk and Return Expectations: Recent Survey Results

Investment and portfolio studies generally use ex post risk and return data, although expected risk and return data is what should be used. This is probably due to the dearth of such data or the difficulty and/or cost of obtaining it on a current basis. This study reports the results of a survey of major real estate investors and researchers, i.e., large life insurance companies, real estate advisors, large pension funds, and selected academics. The survey examined investment horizon, expectations about inflation, total returns on real estate, distribution between income and appreciation returns, the volatility of real estate returns, and the correlation of real estate returns with stocks returns, bond returns, and inflation. In addition, the study contains results for the above before and after the October 19, 1987, stock market crash.

Effects of Creosote and Cca on Moisture Movement in Southern Pine and Red Oak

A vapocup apparatus was used to determine rates of moisture movement and water-vapor permeability values for CCA- and creosote-treated red oak and southern pine. The average loading for CCA-treated specimens was 6.4 kg/m3 (0.4 lb/ft3) and the average loading for creosote-treated specimens was 168.2 kg/m3 (10.5 lb/ft3). Specimens were subjected to three different relative humidity conditions: 50%, 75%, and 90%. The rates of mass transfer increased exponentially with increasing relative humidity. The rate of moisture movement was greater for southern pine than for red oak, and greater for CCA-treated specimens than for creosote-treated specimens. The water-vapor permeability values were calculated and the values increased exponentially as relative humidity increased. For both species, CCA-treated specimens had the highest water-vapor permeability values and creo-sote-treated specimens the lowest