The Taconite Inlet Lakes Project: a systems approach to paleoclimatic reconstruction     

R. S. Bradley  M. J. Retelle  S. D. Ludlam  D. R. Hardy  B. Zolitschka  S. F. Lamoureux  M. S. V. Douglas 《Journal of Paleolimnology》1996,16(2):97-110

A comprehensive study of meteorological, hydrological, limnological and sedimentological conditions in the watersheds of density-stratified (meromictic) lakes around Taconite Inlet, Northern Ellesmere Island, N.W.T., Canada was carried out from 1990–1992. Lakes C1 and C2 contain seawater trapped by isostatic uplift as the former embayments became isolated from the sea. These lakes, and Lake C3, contain varved sediments which provide an annually resolvable paleoclimatic record. By studing the major systems influencing sedimentation in one of these lakes (Lake C2) a better understanding of the climatic controls on varve formation, and hence on the paleoclimatic signal in the varved sediment record, was obtained. The varves of Lake C2 provide a proxy record of summer temperature for the region.This is the first in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.  相似文献   

Commentary and critique of “accounting for mineral resources: Issues and BEA's initial estimates”     

DeVerle Harris  Michael Rieber 《Natural Resources Research》1996,5(1):7-21

The Bureau of Economic Analysis (BEA), U.S. Department of Commerce, in keeping with broad international efforts to green national gross domestic product (GDP) accounts, has attempted to create satellite accounts for mineral depletion. The present paper criticizes the BEA's unit rent measure of resource depletion, which is based upon Hotelling's pure theory of exhaustion. Following a thorough criticism of Hotelling's theory as a real-world model of mineral prices, practical issues related to the treatment of recycling, exploration, definition of reserves/resources, and their valuation/exploitation are introduced. For crude oil and natural gas and the nonfuel minerals, specific application problems of joint products and residuals complicate BEA's assumptions and efforts.  相似文献   

The effects of solar and ionospheric parameters on seasonal variation of 6300 Å line emission at Calcutta     

S. K. Midya  R. Chattopadhyay 《Earth, Moon, and Planets》1996,74(2):123-129

The purpose of this paper is to find correlation between OI 6300 Å line intensity with solar and ionospheric parameters. A critical study have been made and the following important results are obtained:

(i)	Solar flare index plays more important role for the emissions of 6300 Å line than other solar parameters.
(ii)	Intensity of 6300 Å line increases linearly with the increase of solar flare index.
(iii)	Virtual height plays more important role than critical frequency for the emission of 6300 Å line-intensity.
(iv)	Possible explanation of this type of variation is also presented.

  相似文献   

Spectroscopic observations of parsamian 21     

É. S. Parsamian  K. G. Gasparian  G. B. Ohanian 《Astrophysics》1996,39(2):121-125

This work presents spectroscopic observations of Parsamian 21, which has been shown recently by Staude and Neckel to be a fuor-type star. A list of identified absorption lines is given. The results are compared with previous spectroscopic observations over the period 1966–1990. It is shown that the H line profile changed during this period; according to the observations of 1986, the center of the H absorption line was shifted by –140 km/sec from ₀ and reached –600 km/sec at the line edge. It follows from the presented lightcurve that the star has undergone brightness variations of nearly three magnitudes and most likely became a fuor before 1902.Translated fromAstrofizika, Vol. 39, No. 2, pp. 227–235, April–June, 1996.  相似文献   

First Byurakan Spectral Sky Survey. Late-type stars. VIII. Zone + 80 ≤ δ ≤ + 90°     

K. S. Gigoyan  V. V. Hambaryan 《Astrophysics》1996,39(4):310-314

The eighth list of late-type stars of spectral classes M and C detected on the plates of the First Byurakan Spectral Sky Survey (FBS) in the zone +80 +90° is presented. Of the 79 objects detected, 67 are new discoveries (66 M stars and one carbon star); 16 objects are unidentified IRAS sources. The equatorial coordinates, spectral classes, and magnitudes are given.Translated fromAstrofizika, Vol. 39, No. 4, pp. 523–529, November, 1996.  相似文献   

The origin of accretionary lapilli   总被引：1，自引：0，他引：1  

J. S. Gilbert  S. J. Lane 《Bulletin of Volcanology》1994,56(5):398-411

Experimental investigations in a recirculating wind tunnel of the mechanisms of formation of accretionary lapilli have demonstrated that growth is controlled by collision of liquid-coated particles, due to differences in fall velocities, and binding as a result of surface tension forces and secondary mineral growth. The liquids present on particle surfaces in eruption plumes are acid solutions stable at 100% relative humidity, from which secondary minerals, e.g. calcium sulphate and sodium chloride, precipitate prior to impact of accretionary lapilli with the ground. Concentric grain-size zones within accretionary lapilli build up due to differences in the supply of particular particle sizes during aggregate growth. Accretionary lapilli do not evolve by scavenging of particles by liquid drops followed by evaporation — a process which, in wind tunnel experiments, generates horizontally layered hemispherical aggregates. Size analysis of particles in the wind tunnel air stream and particles adhering to growing aggregates demonstrate that the aggregation coefficient is highly grain-size dependent. Theoretical simulation of accretionary lapilli growth in eruption plumes predicts maximum sizes in the range 0.7–20 mm for ash cloud thicknesses of 0.5–10 km respectively.  相似文献   

Gold mineralization in As-rich mesothermal gold ores of the Bogosu-Prestea mining district of the Ashanti Gold Belt,Ghana: remobilization of “invisible” gold   总被引：1，自引：0，他引：1  

A. H. Mumin  M. E. Fleet  S. L. Chryssoulis 《Mineralium Deposita》1994,29(6):445-460

The Bogosu-Prestea mining district of southwestern Ghana is a 33 km section of the Early Proterozoic Ashanti Gold Belt. Greenschist facies carbonaceous and carbonate-bearing turbidites and greywackes, and mafic dikes host numerous economic mesothermal gold deposits. Structurally higher ores in the Bogosu concession have brittle deformation and consist of disseminated-sulphide lodes in tectonically-disrupted sedimentary rocks and carbonate-altered mafic dikes. Most gold occurs as micrometre-size particles in arsenian pyrite, and as invisible gold in arsenian pyrite and arsenopyrite. The structurally deeper ores of the adjoining Prestea concession are associated with brittle-ductile deformation and consist of extensive crack-seal quartz-veins and graphitic shear zones. Only minor amounts of invisible gold were detected; in these deeper lodes, gold occurs dominantly as abundant microscopic and larger particles in sulphide/arsenide minerals and in gangue. The gold distribution patterns revealed by SIMS microprobe analysis and ion maps, EMP and colour staining suggest that most of the primary gold in the Bogosu-Prestea system precipitated in solid-solution with sulphide/arsenide minerals. However, post-depositional concentration and redistribution occurred, in increasing degree with: 1) increase in metamorphic/hydrothermal gradients in the gold system (depth), 2) decrease in the refractory properties of the host mineral, and 3) increase in the amount of post-depositional, host-mineral recrystallization and deformation. Gold evolved from primary solid-solution within sulphide/arsenide minerals, to colloidal and micrometre-size particles concentrated in voids, fractures and internal grain boundaries, and finally to microscopic and larger particles at sulphide/arsenide grain margins and in the gangue assemblage. The general conclusions presented here are applicable to As-rich gold deposits of all ages, worldwide. The presence of gold in late fractures is insufficient evidence for late-stage introduction of gold in mesothermal gold systems.  相似文献   

Solubility of Pt and Pd sulfides and Au metal in aqueous bisulfide solutions   总被引：5，自引：0，他引：5  

P. Pan  S. A. Wood 《Mineralium Deposita》1994,29(5):373-390

An experimental study of the solubility of Pt and Pd sulfides and Au metal in aqueous bisulfide solutions was conducted at temperatures from 200° to 350 °C and at saturated vapor pressure. A 500-mL Bridgemantype pressure vessel constructed of titanium, and equipped with a motor-driven magnetic stirrer was employed. The pH and the oxidation state were buffered by the coexistence of H₂S/HS^–/SO _inf4 ^sup2– . The pH at temperature was calculated to be in the range 5.91–9.43, and S was 0.3–2.2 m. Under the experimental conditions, the measured solubility of gold is about two to three orders of magnitude greater than that of either platinum and palladium, and the measured solubility of platinum is, in general, approximately equal to that of palladium, in molal units. The solubilities are found to be in the range: platinum 4–800 ppb, palladium 1–400 ppb, and gold 2–300 ppm. The solubility data can be modeled adequately using the following reactions: Au+H₂S+HH^–=Au(HS) ₂ ^– +1/2H₂ (K₁₄); PtS+HS^–+H⁺=Pt (HS) ₂ ⁰ (K₁₅); PdS+HS^–+H⁺=Pd (HS) ₂ ⁰ (K₁₆); PtS₂+H₂=Pt (HS) ₂ ⁰ (K₂₁).With equilibrium constants determined as follows (errors represent two standard deviations): Preliminary measurements of the solubilities of metallic Pt, Pd and Au as hydroxide complexes were also conducted using a second titanium pressure vessel, at temperatures of 200° to 350 °C and vapor saturation pressure, with pH and the oxidation state controlled or buffered by adding known amounts of NaOH and H₂ gas. The concentration of NaOH was in the range 0.01–1.3 m, and the partial pressure of H₂ at 200 °C was 62–275 bars, initially. Under the temperature and pressure conditions of these experiments, the solubility of platinum in 1 m NaOH solution is less than 100 ppb, that of palladium is less than 10 ppb and that of gold is less than 0.2 ppm; and in 0.01 m NaOH solutions, both Pt and Pd solubilities are less than 1 ppb. These data indicate that the contributions of hydroxide complexes to the total solubilities in the bisulfide runs, where the pH was in the range of 5.9–9.4, are negligible. The concentrations of both Pt and Pd as bisulfide complexes in the Salton Sea geothermal system predicted using the stability constants determined in this work agree very well with those values measured by McKibben et al. (1990). This calculation strongly suggests that the PGE are transported in moderately reducing, near neutral hydrothermal fluids as bisulfide complexes, as is gold. However, the much lower maximum solubility of the PGE relative to gold severely constrains models of re genesis, and may explain the relative rarity of hydrothermal PGE deposits compared to the relative abundance of hydrothermal Au deposits.  相似文献   

Aqueous alteration of the Bali CV3 chondrite: evidence from mineralogy, mineral chemistry, and oxygen isotopic compositions     

Keller LP  Thomas KL  Clayton RN  Mayeda TK  DeHart JM  McKay DS 《Geochimica et cosmochimica acta》1994,58(24):5589-5598

A petrographic, geochemical, and oxygen isotopic study of the Bali CV3 carbonaceous chondrite revealed that the meteorite has undergone extensive deformation and aqueous alteration on its parent body. Deformation textures are common and include flattened chondrules, a well-developed foliation, and the presence of distinctive (100) planar defects in olivine. The occurrence of alteration products associated with the planar defects indicates that the deformation features formed prior to the episode of aqueous alteration. The secondary minerals produced during the alteration event include well-crystallized Mg-rich saponite, framboidal magnetite, and Ca-phosphates. The alteration products are not homogeneously distributed throughout the meteorite, but occur in regions adjacent to relatively unaltered material, such as veins of altered material following the foliation. The alteration assemblage formed under oxidizing conditions at relatively low temperatures (<100 degrees C). Altered regions in Bali have higher Na, Ca, and P contents than unaltered regions which suggests that the fluid phase carried significant dissolved solids. Oxygen isotopic compositions for unaltered regions in Bali fall within the field for other CV3 whole-rocks, however, the oxygen isotopic compositions of the heavily altered material lie in the region for the CM and CR chondrites. The heavy-isotope enrichment of the altered regions in Bali suggest alteration conditions similar to those for the petrographic type-2 carbonaceous chondrites.  相似文献   

Cordierite-garnet-sillimanite-quartz equilibrium: I. New experimental calibration in the system FeO−Al2O3−SiO2−H2O and certain P-T-X H2O relations     

Biswajit Mukhopadhyay  Michael J. Holdaway 《Contributions to Mineralogy and Petrology》1994,116(4):462-472

The equilibrium in which hydrous Fe-cordierite breaks down to almandine, sillimanite, quartz, and water was previously experimentally determined by Richardson (1968) and Holdaway and Lee (1977) using QMF buffer and by Weisbrod (1973) using QIF buffer. All these studies yielded similar results — a negative dP/dT slope for the equilibrium curve. However, based on theoretical arguments, Martignole and Sisi (1981), and based on Fe-Mg partitioning experiments on coexisting cordierite and garnet in equilibrium with sillimanite and quartz, Aranovich and Podlesskii (1983) suggested that this equilibrium curve has a positive dP/dT slope and its position depends on the water content of the equilibrium cordierite. We have redetermined this equilibrium using a much improved tecnique of detecting reaction direction, and cordierite starting material that contained virtually no hercynite. Hercynite was present as a contaminant in the cordierites of previous experimental studies and possibly reacted with quartz during the experimental runs to expand the apparent stability field of Fe-cordierite. We synthesized Fe-cordierite from reagent grade oxides at 710°C and 2 kbar (using QMF buffer) with two intermediate stages of grinding and mixing. The cordierite has a unit cell volume of 1574.60 ų (molar volume=23.706 J/bar) and no Fe³⁺ as indicated by X-ray diffraction and room temperature Mössbauer studies respectively. Reaction direction was concluded by noting20% change of the ratios of intensities of two key X-ray diffraction peaks of cordierite and almandine. Our results show that the four-phase equilibrium curve passes through the points 2.1 kbar, 650°C and 2.5 kbar, 750°C. This disagrees with all previous experimental studies. H₂O in the Fe-cordierite, equilibrated at 2.2 kbar and 700°C and determined by H-extraction line in the stable isotope laboratory, is 1.13 wt% (n=0.41 moles). H₂O content of pure Mg-cordierite equilibrated under identical conditions and determined by thermogravimentric conditions and determined by thermogravimetric analysis is 1.22 wt% (n=0.40). Similar determinations on Fe-cordierite and Mg-cordierite equilibrated at 2.0 kbar and 650°C show 1.27 wt% (n=0.46) and 1.47 wt% (n=0.48) of H₂O respectively. Thus, H₂O content appears to be independent of Fe/Mg ratio in cordierite, a conclusion which supports previous experimental determinations. The experimentally determined equilibrium curve represents conditions of P_H2O=P_total. From this we calculated the anhydrous curve representing equilibrium under conditions of X _H2O ^V =0.0. A family of calculated equilibrium curves of constant n _H2O ^Cord cut the experimentally determined curve at a very small angle indicating a slight variation in n _H2O ^Cord in cordierite in equilibrium with almandine, sillimanite, and quartz under the conditions of constant X _H2O ^V . Ancther set of calculated equilibrium curves, each representing constant a _H2O ^V demonstrate that the slopes of the curves vary with X _H2O ^V , and are all positive in the full range of 0.0X _H2O ^V 1.0.  相似文献