The genesis of sediment-hosted,exhalative zinc + lead deposits   总被引：2，自引：0，他引：2  

M. J. Russell  M. Solomon  J. L. Walshe 《Mineralium Deposita》1981,16(1):113-127

Large sediment-hosted lead+zinc deposits like Mount Isa, McArthur River, Navan, Rammelsberg and Sullivan form a distinctive group characterised by stratiform, syngenetic sulphide ores that formed in local basins on the sea floor as a result of protracted hydrothermal activity accompanying continental rifting. Generally there is a development of a sedimentary pre-ore phase mineralization often featuring manganese followed by zinc±lead, iron and chert. Lower main phase zinc+lead lenses are usually almost devoid of copper but Cu tenors increase toward the middle or top of the ore sequences. Hanging wall trace element haloes are common. These characteristics are accounted for by deriving the ore solutions from subsurface convective circulation of modified highly saline seawater. The circulation is initiated during rifting and driven by a high geothermal gradient. As a result of continued extensional strain and cooling of the rock column the brittle-to-ductile transition zone is depressed and the circulation penetrates to greater depth with time. Of the ore metals the downward-penetrating convection fluids first leach and transport zinc and lead, but with increasing temperature are later able to leach and transport some copper. Unless convective circulation ceases the metal sequence generally reverses as the cooling phase sets in. The minimum distance separating major coeval orebodies of this type is 18 km which is a function of the size of the convective systems.  相似文献   

Silurian Sedimentation in the South Qilian Belt: Arc-Continent Collision-related Deposition in the NE Tibet Plateau?     

YAN Zhen  FU Changlei  Jonathan C. AITCHISON  ZHOU Renjie  Solomon BUCKMAN  CHEN Lei 《《地质学报》英文版》2020,94(4):901-913

The South Qilian belt mainly comprises an early Paleozoic arc-ophiolite complex, accretionary prism, microcontinental block, and foreland basin. These elements represent accretion-collision during Cambrian to Silurian time in response to closure of the Proto-Tethyan Ocean in the NE of the present-day Tibet Plateau. Closure of the Proto-Tethyan Ocean between the Central Qilian block and the Oulongbuluke block and the associated collision took place from NE to SW in a zipper-like style. Sediment would have been dispersed longitudinally SW-ward with a progressive facies migration from marginal alluvial sediments toward slope deep-water and deep-sea turbidites. This migration path indicates an ocean basin that shrank toward the SW. The Balonggongga'er Formation in the western South Qilian belt represents the fill of a latest Ordovician-Silurian remnant ocean basin that separated the Oulongbuluke block from the Central Qilian block, and records Silurian closure of the Proto-Tethyan Ocean and subduction beneath the Central Qilian block. However, alluvial deposits in the Lajishan area were accumulated in a retro-foreland basin, indicating that continent-continent collision in the eastern South Qilian belt occurred at c. 450–440 Ma. These results demonstrate that the Proto-Tethyan Ocean closed diachronously during early Paleozoic time.  相似文献   

An ML scale for Eastern Dharwar Craton and adjoining regions     

Sharma  Aman  Vashisth  Divakar  Naresh  B.  Suresh  G.  Raju  P. Solomon  Raghavan  R. Vijaya  Srinagesh  D. 《Journal of Seismology》2021,25(5):1251-1263

  相似文献   

Zn–Pb–Cu volcanic-hosted massive sulphide deposits: criteria for distinguishing brine pool-type from black smoker-type sulphide deposition     

M. Solomon  F. Tornos  R. R. Large  J. N. P. Badham  R. A. Both  Khin Zaw 《Ore Geology Reviews》2004,25(3-4):259-283

Eight Zn–Pb–Cu massive sulphide deposits that appear to have formed on the sea floor (seven in Spain, one in Tasmania) are believed to have been precipitated in brine pools, based on the salinities and temperatures of fluid inclusions in underlying stockworks. Comparing the geological features of these deposits with those of the Zn–Pb–Cu massive sulphide ores of the Hokuroku Basin, Japan, which have formed as mounds from buoyant fluids of low salinity, shows that brine pool deposits have: (1) potentially very large size and tonnage, and high aspect ratio, (2) higher Zn/Cu and Fe/Cu values, (3) no evidence of chimneys, (4) relatively abundant framboidal pyrite and primary mineral banding, (5) reduced mineral assemblages (pyrite-arsenopyrite/pyrrhotite), and minor or rare barite in the massive sulphide, (6) associated stratiform and/or vein carbonates, (7) relatively unimportant zone refining, (8) lack of vertical variation in sphalerite and sulphur isotopic compositions, and (9) evidence of local bacterial sulphate reduction. Application of these criteria to the Rosebery deposit in Tasmania, for which there are no fluid inclusion data, leads to the conclusion that the southern section was deposited as separate lenses in a brine-filled basin or basins. Other potential candidates include Brunswick no. 12 and Heath Steele (Canada), Woodlawn and Captains Flat (New South Wales), Hercules and Que River (Tasmania), and Tharsis and the orebodies at Aljustrel (Spain and Portugal). Recently published fluid inclusion data for Gacun (China) and Mount Chalmers (Queensland) suggest that not all ores deposited from highly saline fluids have reduced mineral assemblages.  相似文献   

Micromycetes from the Saline Arubotaim Cave: Mount Sedom, The Dead Sea Southwestern Shore, Israel     

Isabella Grishkan  Eviatar Nevo  Solomon P. Wasser 《Journal of Arid Environments》2004,57(4):431

We examined the soil microfungal community of the saline Arubotaim Cave, Israel. A total of 68 species from 28 genera were isolated. The most prominent features of the cave mycobiota were: the prevailing number of melanin-containing micromycetes; the abundant presence of the Aspergillus species; a comparatively large share of sexual ascomycetes; and the spatial and temporal variation of the mycobiota composition. Nine species were considered as a characteristic micromycete core for the cave. Many of the micromycetes isolated are distributed worldwide. This confirms the conclusion of many mycologists working in areas with saline and arid soils that there is no specific halophilous mycobiota characteristic for these soils.  相似文献   

Biogenic hydrocarbons in fluid inclusions from the aberfoyle tin-tungsten deposit, Tasmania, Australia   总被引：3，自引：0，他引：3  

C. F. Hoffmann  R. W. Henley  N. C. Higgins  M. Solomon  R. E. Summons 《Chemical Geology》1988,70(4):287-299

Trace components in fluid inclusions from the Aberfoyle tin-tungsten deposit in Tasmania, Australia, were examined by thermal decrepitation-mass spectrometry. The technique involves the decrepitation of fluid inclusions by stepwise heating in the source of a mass spectrometer. In addition to water, other species identified were carbon dioxide and hydrocarbons. Detailed analysis of these hydrocarbons showed that they ranged in carbon number from C₁ up to at least C₃₃ and probably comprised, in part, biological marker compounds, previously unreported in such high-temperature environments. Their presence suggests that the fluid responsible for mineralisation was not entirely magmatic but contained a non-magmatic component evolved through fluid-rock interaction in the sedimentary country rocks.  相似文献   

Velocities of compressional and shear waves in limestones   总被引：2，自引：1，他引：2  

Solomon Assefa  Clive McCann  Jeremy Sothcott 《Geophysical Prospecting》2003,51(1):1-13

Carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties (porosity and permeability) mainly resulting from various diagenetic processes (compaction, dissolution, precipitation, cementation, etc.). These complexities make prediction of reservoir characteristics (e.g. porosity and permeability) from their seismic properties very difficult. To explore the relationship between the seismic, petrophysical and geological properties, ultrasonic compressional‐ and shear‐wave velocity measurements were made under a simulated in situ condition of pressure (50 MPa hydrostatic effective pressure) at frequencies of approximately 0.85 MHz and 0.7 MHz, respectively, using a pulse‐echo method. The measurements were made both in vacuum‐dry and fully saturated conditions in oolitic limestones of the Great Oolite Formation of southern England. Some of the rocks were fully saturated with oil. The acoustic measurements were supplemented by porosity and permeability measurements, petrological and pore geometry studies of resin‐impregnated polished thin sections, X‐ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores. It is shown that the compressional‐ and shear‐wave velocities (V_p and V_s, respectively) decrease with increasing porosity and that V_p decreases approximately twice as fast as V_s. The systematic differences in pore structures (e.g. the aspect ratio) of the limestones produce large residuals in the velocity versus porosity relationship. It is demonstrated that the velocity versus porosity relationship can be improved by removing the pore‐structure‐dependent variations from the residuals. The introduction of water into the pore space decreases the shear moduli of the rocks by about 2 GPa, suggesting that there exists a fluid/matrix interaction at grain contacts, which reduces the rigidity. The predicted Biot–Gassmann velocity values are greater than the measured velocity values due to the rock–fluid interaction. This is not accounted for in the Biot–Gassmann velocity models and velocity dispersion due to a local flow mechanism. The velocities predicted by the Raymer and time‐average relationships overestimated the measured velocities even more than the Biot model.  相似文献   

数字流域水系构建方法浅析   总被引：14，自引：1，他引：14  

李春红  任立良  达卫特  王美荣 《水文》2002,22(6):1-4

基于辽河水系老哈河流域栅格DEM数据,分别采用数字高程流域水系模型(DEDNM)、河流工具RiverTools、地理信息系统Arcview软件,根据地形提取水系信息,构建数字流域,并分析比较了三者在凹陷区域识别、水系、子流域及其拓扑关系生成方面的差异。总的来说,数字高程流域水系模型的可修改性较好;而RiverTools软件可视化程度高,使用方便,并具备强大的图示和地形分析功能;Arcview基于地理信息系统(GIS)更易于进行二次开发。  相似文献   

The effect of particle precipitation events on the neutral and ion chemistry of the middle atmosphere: II. Odd hydrogen     

S. Solomon  D.W. Rusch  J.C. Gérard  G.C. Reid  P.J. Crutzen 《Planetary and Space Science》1981,29(8):885-893

A one dimensional time-dependent model of the neutral and ion chemistry of the middle atmosphere has been used to examine the production of odd hydrogen (H, OH, and HO₂) during charged particle precipitation. At altitudes above about 65 km, odd hydrogen production depends on the ionization rate, and the atomic oxygen and water vapor densities. Odd hydrogen production is shown to exhibit diurnal and other time dependent variations during such an event at these altitudes, and the assumption that two odd hydrogen particles are always produced per ionization is reexamined.  相似文献   

Issues in sediment toxicity and ecological risk assessment   总被引：8，自引：0，他引：8  

Chapma PM  Ho KT  Munns WR  Solomon K  Weinstein MP 《Marine pollution bulletin》2002,44(4):271-278

This paper is based on a facilitated Workshop and Roundtable Discussion of key issues in sediment toxicology and ecological risk assessment (ERA) as applied to sediments that was held at the Conference on Dredged Material Management: Options and Environmental Considerations. The issues addressed included how toxicity is defined and perceived, how it is measured, and how it should be used within the context of ERA to support management decisions. The following conclusions were reached regarding scientific considerations of these issues. Toxicity is a measure of hazard and not a risk per se. Thus, toxicity testing is a means but not the end to understand risks of sediments. Toxicity testing cannot presently be replaced by chemical analyses to define hazard. Toxicity test organisms need to be appropriate to the problem being addressed, and the results put into context relative to both reference and baseline comparisons to understand hazard. Use of toxicity tests in sediment ERAs requires appropriate endpoints and risk hypotheses, considering ecological not just statistical significance, and recognizing that hazard does not equate to risk. Toxicity should be linked to population and community response to support decision-making, assessing possible genotypic adaptations that can influence risk estimates, and addressing uncertainty. Additionally, several key scientific issues were identified to improve future sediment ERAs, including the need to improve basic understanding of ecological mechanisms and processes, recognition of variability in the assessment process, and an improved focus and ability to assess risks to populations and communities.  相似文献