P-T-X conditions of hydrothermal fluids and precipitation mechanism of stibnite-gold mineralization at the Wiluna lode-gold deposits,Western Australia: conventional and infrared microthermometric constraints   总被引：15，自引：0，他引：15  

Steffen?Gerd?HagemannEmail author  Volker?Lüders 《Mineralium Deposita》2003,38(8):936-952

The Wiluna lode-gold deposits are located in the Archean Wiluna greenstone belt, in the northern sector of the Norseman-Wiluna belt in the Yilgarn Craton of Western Australia. They are hosted in subgreenschist facies meta-basalts, and controlled by the Wiluna strike-slip fault system and associated shear veins and breccias. The 13 individual lode-gold deposits have produced around 115 t Au from 1901 to 1946 and 1986 to today. Historically, they also produced 38.3 t As and 3.5 t Sb. Gold formed in two stages: stage 1 gold-pyrite-arsenopyrite is finely disseminated in the wallrock and breccia fragments, whereas stage 2 gold-stibnite is located in massive shear veins and breccia matrix, as fracture-fill and in banded-colloform textured veins. Stibnite-gold orebodies only occur in some of the deposits (e.g., Moonlight and northern part of the West Lode) and also display a restricted vertical extent, being preserved only in the uppermost 200 m of stibnite-bearing lodes.Petrographic, conventional, and infrared microthermometric and laser-Raman analysis on stibnite-bearing quartz veins and breccias reveal that the antimony- and gold-rich hydrothermal fluid was of mixed H₂O-NaCl-CO₂±CH₄ type. Microthermometric measurements reveal maximum homogenization temperatures of 340 °C (average 290±25 °C), and a wide range of salinities between 0.2 and 23 eq. wt% NaCl. Aqueous-carbonic fluid inclusions contain variable X_CO2+CH4 (0.03 to 0.82), with the carbonic phase containing a maximum X_CH4 of 0.21.Combined petrographic and microthermometric evidence suggests that the fluid inclusion properties reflect fluid immiscibility of a low-salinity, medium X_CO2+CH4, homogeneous parent fluid at about 290 °C and pressures between 700 and 1,700 bar. Fluid immiscibility was triggered by cyclic pressure release during fault-zone movement. The decompression (adiabatic cooling) of the hydrothermal fluids shifted the ore fluid to lower temperatures, significantly reduced the degree of stibnite undersaturation, and caused stibnite to precipitate. The deposition of stibnite reduced the ore-fluid H₂S concentration, thereby destabilized gold bisulfide complexes in solution, and caused gold precipitation locally. This mechanism explains the intimate spatial association of stibnite and gold in quartz veins and breccias in the stibnite-gold orebodies at Wiluna.Editorial handling: B. Lehmann  相似文献   

Towards a Higher Comparability of Geothermometric Data obtained by Raman Spectroscopy of Carbonaceous Material. Part I: Evaluation of Biasing Factors   总被引：1，自引：0，他引：1  

Nils K. Lünsdorf  Istvan Dunkl  Burkhard C. Schmidt  Gerd Rantitsch  Hilmar von Eynatten 《Geostandards and Geoanalytical Research》2014,38(1):73-94

Raman spectroscopy of carbonaceous material (RSCM) is frequently used to determine metamorphic peak temperatures from the structural order of carbonaceous material enclosed in metasediments. This method provides a quick, robust and relatively cheap geothermometer. However, the comparability of the RSCM parameter is low as there are at least three major sources of biasing factors. These sources are the spectral curve‐fitting procedure, the sample characteristics itself and the experimental design including the used Raman system. To assess the impacts of the biasing factors on RSCM, a series of experiments was performed. The experiments showed that curve‐fitting is strongly influenced by individual operator‐bias and the degrees of freedom in the model, implying the need for a standardised curve‐fitting procedure. Due to the diversity of components (optics, light detection device, gratings, etc.) and their combinations within the Raman systems, different Raman instruments generally give differing results. Consequently, to estimate comparable metamorphic temperatures from RSCM data, every Raman instrument needs its own calibration. This demands a reference material series that covers the entire temperature calibration range. Although sample heterogeneity will still induce some variation, a reference material series combined with standardised curve‐fitting procedures will significantly increase the overall comparability of RSCM data from different laboratories.  相似文献   

Megabenthic recolonization in an experimentally disturbed abyssal manganese nodule area 1     

Hartmut Bluhm  Gerd Schriever  Hjalmar Thiel 《Marine Georesources & Geotechnology》2013,31(4):393-416

The near total removal of manganese nodules during commercial deep‐sea mining will destroy the habitat of the benthic hard‐bottom fauna within the mined areas and result in the formation of a soft‐bottom community of lower diversity. In 1989 the first large‐scale and long‐term experiment, DISCOL, was initiated in the abyssal tropical southeastern Pacific Ocean to study the impact of disturbances similar to ocean mining on the deep‐sea fauna. The megabenthic assemblage and the recolonization of the disturbed area were monitored during three cruises of the German research vessel SONNE by use of an Ocean Floor Observation System with real‐time TV and “photo‐on‐command” capabilities. The results of the image analyses of the baseline and three postimpact studies demonstrate not only a direct impact within the disturber tracks, but also an apparent impact on areas that were not primarily disturbed. Commercial mining will create a sediment plume, which will drift away with near‐bottom currents and also affect animals outside the mined areas. Reduction of environmental effects remains an important objective during development of future nodule collector systems.  相似文献   

Response of a River Catchment to Climatic Change: Application of Expanded Downscaling to Northern Germany   总被引：1，自引：1，他引：0  

Dirk-Ingmar Müller-Wohlfeil  Gerd Bürger  Werner Lahmer 《Climatic change》2000,47(1-2):61-89

We used the technique of expanded General Circulation Model (GCM) downscalingto derive time series of daily weather for the analysis of potential climaticchange impact on a river catchment in Northern Germany. The derived timeseries was then fed into a spatially distributed hydrological model tosimulate various water balance components and river discharge. All componentsof this modelling approach are known to provide fairly accurate results undernormal (current) climatic conditions. Hydrological time series, theirstatistics and spatial patterns of various water balance components, resultingfrom a `business-as-usual' emission scenario, were analysed. The simulationresults showed that if everything apart from climate is held constant, asignificant increase in river discharge may be expected in the coming decadesas a consequence of increased rainfall amounts. Although the modellingapproach provides an operational way of performing watershed climate changeimpact studies, many uncertainties still have to be considered.  相似文献   

The role of beach morphology on coastal cliff erosion under extreme waves          下载免费PDF全文

Claire Earlie  Gerhard Masselink  Paul Russell 《地球表面变化过程与地形》2018,43(6):1213-1228

Erosion of hard‐rock coastal cliffs is understood to be caused by a combination of both marine and sub‐aerial processes. Beach morphology, tidal elevation and significant wave heights, especially under extreme storm conditions, can lead to variability in wave energy flux to the cliff‐toe. Wave and water level measurements in the nearshore under energetic conditions are difficult to obtain and in situ observations are rare. Here we use monthly cliff‐face volume changes detected using terrestrial laser scanning alongside beach morphological changes and modelled nearshore hydrodynamics to examine how exposed cliffs respond to changes in extreme wave conditions and beach morphology. The measurements cover the North Atlantic storms of 2013 to 2014 and consider two exposed stretches of coastline (Porthleven and Godrevy, UK) with contrasting beach morphology fronting the cliffs; a flat dissipative sandy beach at Godrevy and a steep reflective gravel beach at Porthleven. Beach slope and the elevation of the beach–cliff junction were found to influence the frequency of cliff inundation and the power of wave–cliff impacts. Numerical modelling (XBeach‐G) showed that under highly energetic wave conditions, i.e. those that occurred in the North Atlantic during winter 2013–2014, with H_s = 5.5 m (dissipative site) and 8 m (reflective site), the combination of greater wave height and steeper beach at the reflective site led to amplified wave run‐up, subjecting these cliffs to waves over four times as powerful as those impacting the cliffs at the dissipative site (39 kWm^‐1 compared with 9 kWm^‐1). This study highlighted the sensitivity of cliff erosion to extreme wave conditions, where the majority (over 90% of the annual value) of cliff‐face erosion ensued during the winter. The significance of these short‐term erosion rates in the context of long‐term retreat illustrates the importance of incorporating short‐term beach and wave dynamics into geomorphological studies of coastal cliff change. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Beach recovery from extreme storm activity during the 2013–14 winter along the Atlantic coast of Europe     

Guillaume Dodet  Bruno Castelle  Gerd Masselink  Timothy Scott  Mark Davidson  France Floc'h  Derek Jackson  Serge Suanez 《地球表面变化过程与地形》2019,44(1):393-401

The storm sequence of the 2013–14 winter left many beaches along the Atlantic coast of Europe in their most eroded state for decades. Understanding how beaches recover from such extreme events is essential for coastal managers, especially in light of potential regional increases in storminess due to climate change. Here we analyse a unique dataset of decadal beach morphological changes along the west coast of Europe to investigate the post-2013–14 winter recovery. We show that the recovery signature is site specific and multi-annual, with one studied beach fully recovered after 2 years, and the others only partially recovered after 4 years. During the recovery phase, winter waves primarily control the timescales of beach recovery, as energetic winter conditions stall the recovery process whereas moderate winter conditions accelerate it. This inter-annual variability is well correlated with climate indices. On exposed beaches, an equilibrium model showed significant skill in reproducing the post-storm recovery and thus can be used to investigate the recovery process in more detail. © 2018 John Wiley & Sons, Ltd.  相似文献   

Beach cusp morphodynamics     

Gerhard Masselink  Bruce J. Hegge  Charitha B. Pattiaratchi 《地球表面变化过程与地形》1997,22(12):1139-1155

Detailed measurements of three-dimensional beach cusp morphology were made on a steep gradient, low energy, microtidal beach in Perth, Western Australia. During the field campaign a variety of wave conditions and tidal ranges were experienced, and these differing hydrodynamic conditions were reflected in a consistent pattern of morphological changes to the beach cusp system. A useful parameter to delineate between trends of cusp destruction and re-formation appeared to be the surf similarity parameter ξ = tan β/√I₀/L₀, where H₀ is offshore wave height, L₀ is deep water wave length and tan β is beach gradient. For ξ < 1·2 the beach cusps were planed off, whereas cusp morphology was enhanced when ξ > 1·2. A small storm was experienced at the start of the field campaign period and resulted in considerable erosion of the beach face. The cusp morphology across the lower beachface was destroyed, but a subtle remnant of the pre-storm cusp morphology was preserved on the upper beachface. When cusps reformed after the storm, under the influence of declining wave conditions, they appeared at the same location and with the same dimensions as the pre-storm cusp morphology. Hence, it is considered that the cusp re-formation was controlled more by the antecedent morphology than the hydrodynamic conditions. This indicates that positive feedback between swash hydrodynamics and beachface morphology, necessary to form beach cusps, does not require a large variation in relief. © 1997 John Wiley & Sons, Ltd.  相似文献