Flameless Atomic Absorption Determination of Gold and Palladium in Geological Reference Samples

Gold and palladium have been determined in 42 geological reference samples with graphite furnace AAS after aqua regia digestion and SnCl₂-Hg extraction. A brief discussion on the quality of these analyses also is presented.     

Isotopic and Geochemical Constraints on the Origin and Evolution of the Columbia River Basalt

New major and trace element data on over 70 samples are combinedwith a wider knowledge of the regional stratigraphy, and ofthe tectonic evolution of the boundary between the ColumbiaPlateau and the northern margin of the Basin and Range province,to distinguish three subgroups within the Columbia River BasaltGroup (CRBG): the Picture Gorge Basalt; the main sequence ofColumbia River flood basalts, here named the Clarkston Basalt;and the Saddle Mountains Basalt. The subgroups are characterizedby different incompatible element and Sr-, Nd-, and Pb-isotoperatios, and they are interpreted in terms of different sourceregions mobilized under different tectonic conditions. The majordifferences between the subgroups are consistent with partialmelting processes in the upper mantle, and it is argued thatthey reflect previous partial melting episodes which resultedin source regions that were variably enriched and depleted inincompatible elements. The major variations within the PictureGorge and Clarkston Basalt subgroups include increases in theabundances of large ion lithophile elements (LILE) and increasesin the ratios of LILE/high field strength elements (HFSE) whichare interpreted as the addition of a lithospheric/subduction-relatedcomponent. The Picture Gorge Basalt has a depleted isotopic and chemicalsignature on which is superimposed an enrichment of LILE toproduce a trace element pattern similar to that of other 17–0-Mabasalts erupted south of the Olympic Wallowa Lineament. Thispattern is characteristic of volcanism associated with the Basinand Range extensional province, and others have attributed itto a source component derived from an enriched subcontinentallithospheric mantle (SCLM). Of the Clarkston Basalts, the Imnaha and Grande Ronde Basaltsform chemical and isotopic arrays which indicate mixing of componentsfrom two distinct source regions. One had high ratios of LILE/HFSEand light rare earth elements (LREE)/HFSE, and as these arenot common in oceanic basalts, this component is thought tohave been derived from the continental mantle lithosphere. Itsisotope ratios are more enriched (older?) than those of thePicture Gorge Basalt, and its Rb/Sr ratios are much higher thanthose in its source rocks, consistent with preferential mobilizationof LILE at the time of magmatism. The second component was derivedfrom an asthenospheric source similar to that of Hawaii basaltsand is most obviously attributed to mantle plume activity. Basaltsof the Eckler Mountain and Wanapum Formations (smaller, separateformations of the Clarkston Basalt as redefined in this paper)fit this mixing model less well and may represent mixing betweenmore than two components. Flows of the third CRBG subgroup,the Saddle Mountains Basalt, also carry a lithospheric geochemicalsignature and have long been recognized as having more radiogenicisotopic signatures than the other two subgroups. Thus, SaddleMountains flows appear to require a lithospheric source enrichedin LILE at an even earlier time, and we concur with other workersthat the isotopic and chemical evidence implies their derivationfrom subcontinental lithospheric mantle enriched at {small tilde}2000Ma. Within each subgroup, the chemical effects of partial melting,fractional crystallization, and magma mixing processes can allbe distinguished within particular flow sequences. In the ImnahaBasalt variable degrees of partial melting during the generationof the CRBG magmas, and gabbro fractionation within the lowercrust, played major roles in their evolution. In the GrandeRonde Basalt fractional crystallization appears to be restrictedto >10%. The chemical and isotopic data for each CRBG subgroup, and thedifferent sources which those data imply, can be accommodatedin a tectonic model which includes the passing of the Yellowstonehotspot south of the center of the CRBG eruption before significantBasin and Range extension had moved north of the Brothers Faultzone at 15 Ma.     

Mesozoic interaction of the Kula plate and the western margin of north america

Oceanic crust west of North America at the beginning of the Jurassic belonged to the Kula plate. The development of the western margin of North America since the Jurassic reflects interaction with the Kula plate, the Kula-Farallon spreading center and the Farallon plate. The Kula plate ceased to exist in the Paleocene and later developments were caused by interaction of the Farallon plate and, subsequently, collision with the East Pacific Rise.At the beginning of the Jurassic, when spreading between North and South America began, the Kula-Farallon-Pacific triple junction moved to the north relative to North America, and the eastern end of the Kula-Farallon spreading center swept northwards along the continental margin.During the Paleocene, Kula-Pacific spreading ceased and the Kula plate fused to the Pacific plate. Throughout the Mesozoic, subduction of the Kula plate took place along the Alaskan continental margin. When the Kula plate joined the Pacific plate a new subduction zone formed along the line of the present Aleutian chain.Wrangellia and Stikinia, anomalous terrains in Alaska and northwestern Canada respectively, were emplaced by transport on the Kula plate from lower latitudes. Hypotheses which require transport of these plates in the Mesozoic from the “far reaches of the Pacific” ignore the problem of transport across either the Kula-Pacific or Kula-Farallon spreading centers. The interaction of the Kula plate and western North America throughout the Jurassic and the Cretaceous should result in emplacement of these terrains by motion oblique to the continental margin. Tethyan faunas in Stikinia must come from the western end of Tethys between North and South America, not the Indonesian region at the eastern end of Tethys.As the northeastern end of the Kula-Farallon ridge moved northward, the sense of motion changed from right lateral shear between the Kula and North American plates to collision or left lateral shear between the Farallon and North American plates. Left lateral shear along zones analogous to the Mojave-Sonora megashear may have been the means by which anomalous terrains were transported to the southeast into the gap between North and South America forming present day Central America. Such a model overcomes the overlap difficulties suffered in previous attempts to reconstruct the Mesozoic paleogeography of Central America.     

Biogeochemistry, a prospecting tool in the search for mercury mineralization

Summary of biogeochemical prospecting for mercury mineralization in the Pinchi Fault is given. One thousand two hundred and eight plant samples were collected and analyzed for mercury. In mineralized areas the typical mercury content of dried plants was not less than 0.2 and 0.4 μg/g and even concentrations between 0.6 and 1.6 μg/g were observed. In nonmineralized zones at least 90% of the plants contained no more than 0.15 μg/g of mercury. Analytical and sampling procedures are described.     

Attenuation of electrons flux penetrating through the lower ionosphere

The angular variation of elastic and inelastic scattering cross-sections has been calculated and used to study the energy deposition by precipitating electrons with the help of Monte Carlo Method. Monoenergetic, power law electron spectrum with isotropic and monodinational incidence starting at an altitude of 300 km have been used to obtain the angular and energy distributions at certain height intervals. In these calculations constant magnetic field has been used.     

Temperature variation in the mesosphere during solar eclipse

Rocket-borne observations of the extinction of solar hydrogen Lyman-alpha radiation made during the solar eclipses of 20 May 1966 at Karistos for normal and 44% visibility and of 7 March 1970 at East Quoddy for normal, 10% and 0.6% visibility have been used to study the variation of temperature in the mesosphere during these events. It is seen that near the mesopause the decrease of temperature at Karistos is by 20° K for 44% visibility and at East Quoddy by 100° K for 0.6% visibility. Possible causes of these temperature variationsvis-a-vis molecular oxygen and pressure variations have been briefly discussed.     

High temperature calorimetry of sulfide systems

The standard enthalpies of formation of FeS (troilite), FeS₂ (pyrite), Co_0.9342S, Co₃S₄ (linnaeite), Co₉S₈ (cobalt pentlandite), CoS₂ (cattierite), CuS (covellite), and Cu₂S (chalcocite) have been determined by high temperature direct reaction calorimetry at temperatures between 700 K and 1021 K. The following results are reported: $$\Delta {\rm H}_{f,FeS}^{tr} = - 102.59 \pm 0.20kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,FeS}^{py} = - 171.64 \pm 0.93kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_{0.934} S} = - 99.42 \pm 1.52kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_9 S_8 }^{ptl} = - 885.66 \pm 16.83kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_3 S_4 }^{In} = - 347.47 \pm 7.27kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,CoS_2 }^{ct} = - 150.94 \pm 4.85kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Cu_2 S}^{cc} = - 80.21 \pm 1.51kJ mol^{ - 1} ,$$ and $$\Delta {\rm H}_{f,CuS}^{cv} = - 53.14 \pm 2.28kJ mol^{ - 1} ,$$ The enthalpy of formation of CuFeS₂ (chalcopyrite) from (CuS+FeS) and from (Cu+FeS₂) was determined by solution calorimetry in a liquid Ni_0.60S_0.40 melt at 1100 K. The results of these measurements were combined with the standard enthalpies of formation of CuS, FeS, and FeS₂, to calculate the standard enthalpy of formation of CuFeS₂. We found \(\Delta {\rm H}_{f,CuFeS_2 }^{ccp} = - 194.93 \pm 4.84kJ mol^{ - 1}\) . Our results are compared with earlier data given in the literature; generally the agreement is good and our values agree with previous estimates within the uncertainties present in both.     

Mudbank regime off the Kerala coast during monsoon and non-monsoon seasons

Field experiments conducted in the nearshore ocean to understand the dynamics of mudbank off Kerala, south-west coast of India, are highlighted. Real time monitoring of the nearshore ocean off Purakkad, Kerala was accomplished using pressure transducers for nearshore surface wave measurements, and current sensors for nearshore velocity measurements. Comprehensive information on the spatial structure of mudbank was obtained from aerial surveys. Extensive data collected on surface waves and currents in the nearshore ocean, indicate that the infra-gravity (IG) waves (leaky modes and trapped edge wave modes), and far infra-gravity (FIG) waves coupled with strong shoreline reflections and undertow play an important role in the dynamics associated with the mudbanks off Kerala during the monsoon season. During the non-monsoon season evidence for progressive edge waves in the infragravity frequency band, an energetic gravity wave band and a strong undertow with weak reflections was observed.