Petrographic and geochemical evidence for hydrothermal evolution of the North Deposit,Mt Tom Price,Western Australia     

Warren?Spencer?ThorneEmail author  Steffen?Gerd?Hagemann  Mark?Barley 《Mineralium Deposita》2004,39(7):766-783

High-grade iron mineralisation (>65%Fe) in the North Deposit occurs as an E-W trending synclinal sheet within banded iron formation (BIF) of the Early Proterozoic Dales Gorge Member and consists of martite-microplaty hematite ore. Three hypogene alteration zones between unmineralised BIF and high-grade iron ore are observed: (1) distal magnetite-siderite-iron silicate, (2) intermediate hematite-ankerite-magnetite, and (3) proximal martite-microplaty hematite-apatite alteration zones. Fluid inclusions trapped in ankerite within ankerite-hematite veins in the hematite-ankerite-magnetite alteration zone revealed mostly H₂O–CaCl₂ pseudosecondary and secondary inclusions with salinities of 23.9±1.5 (1, n=38) and 24.4±1.5 (1, n=66) eq.wt.% CaCl₂, respectively. Pseudosecondary inclusions homogenised at 253±59.9°C (1, n=34) and secondary inclusions at 117±10.0°C (1, n=66). The decrepitation of pseudosecondary inclusions above 350°C suggests that their trapping temperatures are likely to be higher (i.e. 400°C). Hypogene siderite and ankerite from magnetite-siderite-iron silicate and hematite-ankerite-magnetite alteration zones have similar oxygen isotope compositions, but increasingly enriched carbon isotopes from magnetite-siderite-iron silicate alteration (–8.8±0.7, 1, n=17) to hematite-ankerite-magnetite alteration zones (–4.9±2.2, 1, n=17) when compared to the dolomite in the Wittenoom Formation (0.9±0.7, 1, n=15) that underlies the deposit. A two-stage hydrothermal-supergene model is proposed for the formation of the North Deposit. Early 1a hypogene alteration involved the upward movement of hydrothermal, CaCl₂-rich brines (150–250°C), likely from the carbonate-rich Wittenoom Formation (¹³C signature of 0.9±0.7, 1, n=15), within large-scale folds of the Dales Gorge Member. Fluid rock reactions transformed unmineralised BIF to magnetite siderite-iron silicate BIF, with subsequent desilicification of the chert bands. Stage 1b hypogene alteration is characterised by an increase in temperature (possibly to 400°C), depleted ¹³C signature of –4.9±2.2 (1, n=17), and the formation of hematite-ankerite-magnetite alteration and finally the crystallisation of microplaty hematite. Late Stage 1c hypogene alteration involved the interaction of low temperature (~120°C) basinal brines with the hematite-ankerite-magnetite hydrothermal assemblage leaving a porous martite-microplaty hematite-apatite mineral assemblage. Stage 2 supergene enrichment in the Tertiary resulted in the removal of residual ankerite and apatite and the weathering of the shale bands to clay.Editorial handling: B. Lehmann  相似文献   

Seasonal metal remobilization in the sediments of Great Bay,New Hampshire     

Mark E. Hines  Wm. Berry Lyons  Peter B. Armstrong  William H. Orem  Mary Jo Spencer  Henri E. Gaudette  Galen E. Jones 《Marine Chemistry》1984,15(2):173-187

Concentrations of dissolved iron, manganese, molybdenum, copper, and organic carbon (DOC) were measured in the pore waters from surficial sediments of a temperate estuary to delineate seasonal metal remobilization from 1978 through 1980. Iron and DOC data were collected for 31 months and covaried inversely and exponentially. Iron dissolution occurred during the spring and during periods of active bioturbation with concentrations as high as 18 mg 1^?1. Iron values were low during winter due to oxidation to ferric oxides. The lack of active bioturbation during the summer of 1978 allowed for the nearly complete removal of iron as a monosulfide precipitate. However, bioturbation resumed during the summer of 1979 and 1980 and dissolved iron concentrations as high as 10 mg 1^?1 were observed at those times. The iron and DOC data were a qualitative measure of bioturbation activity. Dissolved manganese, molybdenum, and copper data were collected for 18 months during 1978 and 1979. All three metals displayed spring maxima covariate with iron, suggesting that they behaved chemically like iron and/or were associated with iron- or manganese-rich phases during this time of the year. In general, manganese and molybdenum varied temporally with iron while copper concentrations mimicked iron variations only during the spring.  相似文献   

The use of partitioned matrices in geophysical inversion problems     

Call Spencer 《Geophysical Journal International》1985,80(3):619-629

Summary. The parameters in many geophysical inverse problems may be partitioned so as to separate them into two distinct sets. This separation might be on the grounds of physical differences between the two sets, or it might be for computational reasons. In this paper, methods for making estimates of one or other set of parameters unbiased by uncertainty in the other set are summarized. It is shown that these procedures, which are characterized by asymmetric resolution matrices, are not equivalent to the generalized inverse solution. The properties of various matrix inverses used to obtain solutions are discussed in relation to the usual least-squares and minimum-norm conditions. Finally, a new algorithm for calculating the generalized inverse, in terms of the inverses of partitions, is given.  相似文献   

More seismic evidence on the location of Grenville basement beneath the Appalachians of Quebec-Maine     

Carl Spencer  Alan Green  James Luetgert 《Geophysical Journal International》1987,89(1):177-182

Summary. High-quality multichannel seismic (=133 fold) and refraction/wide- angle reflection (1 to 3 km receiver spacing and 30 to 60 km shot spacing) data have been collected across the northern Appalachians in Quebec, and Maine. An integrated interpretation of the seismic data from the southeastern Quebec-western Maine region provides strong evidence that the rocks of the predominantly oceanic "Dunnage" zone are allochthonous having been thrust westwards over Precambrian Grenville basement during and subsequent to the closing of the Iapetus Ocean.  相似文献   

WHAT FUTURE FOR SINGAPORE'S PRIVATE BUSES?     

Andrew H. Spencer  Ph.D.    Lee Meng Hye  M.B.A.  A.C. A.  Chan Foo Tuck  B.Soc.Sc. 《Singapore journal of tropical geography》1989,9(2):125-140

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Real-Time GPS Data Transmission Using VSAT Technology     

Michael E. Jackson  Chuck Meertens  Oivind Ruud  Spencer Reeder  Warren Gallaher  Chris Rocken 《GPS Solutions》2002,5(4):10-19

The University NAVSTAR Consortium (UNAVCO) Boulder Facility is assessing Very Small Aperture Terminal (VSAT) technology for near real-time transmission of GPS data from a remote receiver to a central processing facility. The study is motivated by the need for a robust, cost-effective data communications solutions to transfer GPS data from remote sites where no other communication alternatives exist. Future large-scale plate boundary deformation initiatives using spatially dense networks of GPS will require receivers to be located where the science dictates, and not the power or communications infrastructure. For other applications, such as determining rapid GPS orbits and time transfer, there is a push toward reducing the latency in GPS data used to produce GPS data products and differential corrections (Talaya & Bosch, 1999; Jackson, Meertens, & Rocken, 2000; Muellerschoen, Bar-Sever, Bertiger, & Stowers, 2001), and to support upcoming Low Earth Orbiting (LEO) missions requiring low latency, 1-s GPS data. In this paper we evaluate two Ku-band systems, the Nanometrics Libra VSAT and the StarBand 2-way satellite Internet VSAT. The Nanometrics system test results show that continuous, 1-s GPS data can be streamed from multiple remote stations within the VSAT footprint, quality checked, and delivered for processing with a <2.5-s latency (mean 1.2 s) and a 99.8% reliability. Benefits of the Nanometrics system include global coverage, control of bandwidth allocation and data hub, and the low power draw of the system. Negatives include the cost of hub and remote infrastructure and the need to negotiate landing rights issues on a country-by-country basis. The UNAVCO Facility currently operates a Nanometrics hub and three remote VSAT systems. The StarBand system showed 98.9% reliability with a maximum latency of 10.2 s (mean latency 1.7 s) for 1-Hz GPS data and an average uplink speed of 31.7 kbps. Benefits of the StarBand system include the cost and small profile of the remote antenna. Negatives include coverage limited to coterminous United States and the high power draw of remote systems. ? 2002 Wiley Periodicals, Inc.  相似文献   

Effects of coal dust on species composition of mosses and lichens in an arid environment     

Sherry Spencer 《Journal of Arid Environments》2001,49(4):843

A wind-borne plume of coal dust has been deposited on the soil and vegetation next to a coal storage area at a power generation plant in Oregon (U.S.A.). Correlated with the deposition of coal dust were significantly increased soil temperatures, decreased pH, and increased moisture-holding properties. Some heavy metal concentrations were also higher on the plume. These differences are possibly responsible for the lower frequencies and diversity of lichen species on the plume. Moss diversity, frequency and percent cover are similar on and off the plume with the exception of Ceratodon purpureus. The increased cover of C. purpureus may be attributed to heavy metal tolerance on the plume.  相似文献   

Catastrophes and earth history. The new uniformitarianism : Edited by W. A. Berggren & John A. Van Couvering. 464 pp. Princeton University Press, Princeton, U.S.A. $19.50     

Spencer G. Lucas  Adrian Hunt 《Cretaceous Research》1985,6(4):387-389

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Great Salt Lake,and precursors,Utah: The last 30,000 years     

Ronald J. Spencer  M. J. Baedecker  H. P. Eugster  R. M. Forester  M. B. Goldhaber  B. F. Jones  K. Kelts  J. Mckenzie  D. B. Madsen  S. L. Rettig  M. Rubin  C. J. Bowser 《Contributions to Mineralogy and Petrology》1984,86(4):321-334

Sediment cores up to 6.5 m in length from the South Arm of Great Salt Lake, Utah, have been correlated. Radiocarbon ages and volcanic tephra layers indicate a record of greater than 30,000 years. A variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation; these include acoustic stratigraphy, sedimentologic analyses, mineralogy, geochemistry (major element, C, O and S isotopes, and organics), paleontology and pollen.The results indicate that prior to 32,000 year B.P. an ephemeral saline lake-playa system was present in the basin. The perennial lake, which has occupied the basin since this time, rose in a series of three major steps; the freshest water conditions and presumably highest altitude was reached at about 17,000 year B.P. The lake remained fresh for a brief period, followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present Great Salt Lake. The lake remained at low elevations, and divided at times into a north and south Basin, until about 8,000 year B.P. Since that time, with the exception of two short rises to about 1290 m, the lake level has remained near the present elevation of 1280 m.  相似文献   

Geosecs II,the 1970 North Atlantic station: Hydrographic features,oxygen, and nutrients     

D.W. Spencer 《Earth and Planetary Science Letters》1972

Profiles of salinity, temperature, oxygen and nutrients for a station at 35°46.5′N and 67°59.8′W show the influence of the five major sources of deep water in the North Atlantic Ocean. The presence of distinct, identifiable cores of water types, far removed from their sources, together with linear relationships between salinity and both oxygen and silicate in the deep water suggest that horizontal mixing processes predominate over vertical dissipation and in situ production or loss processes in determining the distribution of these tracers in the deep western Atlantic Ocean.  相似文献