Microdiamond grade as a regionalised variable – some basic requirements for successful local microdiamond resource estimation of kimberlites     

Stiefenhofer  Johann  Thurston  Malcolm L.  Bush  David E. 《Mineralogy and Petrology》2018,112(2):673-684

Microdiamonds offer several advantages as a resource estimation tool, such as access to deeper parts of a deposit which may be beyond the reach of large diameter drilling (LDD) techniques, the recovery of the total diamond content in the kimberlite, and a cost benefit due to the cheaper treatment cost compared to large diameter samples. In this paper we take the first step towards local estimation by showing that micro-diamond samples can be treated as a regionalised variable suitable for use in geostatistical applications and we show examples of such output. Examples of microdiamond variograms are presented, the variance-support relationship for microdiamonds is demonstrated and consistency of the diamond size frequency distribution (SFD) is shown with the aid of real datasets. The focus therefore is on why local microdiamond estimation should be possible, not how to generate such estimates. Data from our case studies and examples demonstrate a positive correlation between micro- and macrodiamond sample grades as well as block estimates. This relationship can be demonstrated repeatedly across multiple mining operations. The smaller sample support size for microdiamond samples is a key difference between micro- and macrodiamond estimates and this aspect must be taken into account during the estimation process. We discuss three methods which can be used to validate or reconcile the estimates against macrodiamond data, either as estimates or in the form of production grades: (i) reconcilliation using production data, (ii) by comparing LDD-based grade estimates against microdiamond-based estimates and (iii) using simulation techniques.

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The role of intracontinental deformation in supercontinent assembly: insights from the Ribeira Belt,Southeastern Brazil (Neoproterozoic West Gondwana)   总被引：1，自引：0，他引：1       下载免费PDF全文

Vinícius T. Meira  Antonio García‐Casco  Caetano Juliani  Renato P. Almeida  Johann Hans D. Schorscher 《地学学报》2015,27(3):206-217

In this study, we challenge the multiple collision model for the tectonic evolution of the Neoproterozoic Ribeira Belt in Southeastern Brazil. New U–Pb SHRIMP data reveal Palaeoproterozoic (2153 ± 15 Ma) and Cryogenian (783 ± 6 and 768 ± 8 Ma) granitic rocks in the Embu Domain, and detrital zircon data of metasedimentary units from the Embu and Costeiro domains suggest a coherent tectonic evolution for the whole Ribeira Belt. Rather than by multiple collisions, these data are best explained by a simpler tectonic model involving continent (craton)‐volcanic arc collisions in the Dom Feliciano and Brasilia belts that led to intracontinental crustal thickening of the adjacent thinned hinterland (Ribeira Belt) at ~640–610 Ma, followed by widespread post‐collisional magmatism and rift‐related sedimentation at ~600–540 Ma. We suggest that intracontinental orogeny is a relevant process during supercontinent assembly, as illustrated here by the evolution of significant parts of the Brasiliano orogen.  相似文献   

Late orogenic rebound and oblique Alpine convergence: New constraints from subsidence analysis of the Austrian Molasse basin   总被引：1，自引：1，他引：0  

Johann Genser  Sierd A.P.L. Cloetingh  Franz Neubauer   《Global and Planetary Change》2007,58(1-4):214

Subsidence analysis of 16 wells in the Austrian Molasse basin documents major spatial and temporal changes in tectonic subsidence as well as a late-stage surface uplift. The timing of the main phase of tectonic subsidence shifted from early Oligocene in the western part of the peripheral foreland to the early Miocene in the eastern part. These temporal and spatial changes in tectonic subsidence reflect a change from oblique dextral to sinistral convergence between the Alpine nappe stack and its foreland. The main phase of sediment accumulation was delayed to the early Miocene and led to the infill of the basin and a major second, sediment-load driven phase of basement subsidence. Sediment accumulation rates in the basin reflect the build-up of topography in the Alpine mountain chain. Since approximately 6 Ma a pronounced regional uplift of the entire Molasse basin has taken place, marking the transition from lateral extrusion to orthogonal contraction within the Alpine system and deep-seated changes in geodynamic boundary conditions, possibly due to delamination of previously thickened lithosphere. Surface uplift is contemporaneous with similar processes in extra-Alpine Central Europe, where it is interpreted to reflect intra-plate stress changes.  相似文献   

Coordinated Ocean-ice Reference Experiments (COREs)     

Stephen M. Griffies  Arne Biastoch  Claus Böning  Frank Bryan  Gokhan Danabasoglu  Eric P. Chassignet  Matthew H. England  Rüdiger Gerdes  Helmuth Haak  Robert W. Hallberg  Wilco Hazeleger  Johann Jungclaus  William G. Large  Gurvan Madec  Anna Pirani  Bonita L. Samuels  Markus Scheinert  Alex Sen Gupta  Camiel A. Severijns  Harper L. Simmons  Jianjun Yin 《Ocean Modelling》2009,26(1-2):1-46

Coordinated Ocean-ice Reference Experiments (COREs) are presented as a tool to explore the behaviour of global ocean-ice models under forcing from a common atmospheric dataset. We highlight issues arising when designing coupled global ocean and sea ice experiments, such as difficulties formulating a consistent forcing methodology and experimental protocol. Particular focus is given to the hydrological forcing, the details of which are key to realizing simulations with stable meridional overturning circulations.The atmospheric forcing from [Large, W., Yeager, S., 2004. Diurnal to decadal global forcing for ocean and sea-ice models: the data sets and flux climatologies. NCAR Technical Note: NCAR/TN-460+STR. CGD Division of the National Center for Atmospheric Research] was developed for coupled-ocean and sea ice models. We found it to be suitable for our purposes, even though its evaluation originally focussed more on the ocean than on the sea-ice. Simulations with this atmospheric forcing are presented from seven global ocean-ice models using the CORE-I design (repeating annual cycle of atmospheric forcing for 500 years). These simulations test the hypothesis that global ocean-ice models run under the same atmospheric state produce qualitatively similar simulations. The validity of this hypothesis is shown to depend on the chosen diagnostic. The CORE simulations provide feedback to the fidelity of the atmospheric forcing and model configuration, with identification of biases promoting avenues for forcing dataset and/or model development.  相似文献   

Multiproxy Analyses of Stratigraphy and Palaeoenvironment of the Late Palaeolithic Grabow Floodplain Site,Northern Germany     

Johann Friedrich Tolksdorf  Falko Turner  Knut Kaiser  Eileen Eckmeier  Mareike Stahlschmidt  Rupert A. Housley  Klaus Breest  Stephan Veil 《Geoarchaeology》2013,28(1):50-65

Changing river courses and fluctuations of the water table were some of the most fundamental environmental changes that humans faced during the Late Glacial, particularly as these changes affected areas intensively used for settlement and resource exploitation. Unfortunately, only a few stratigraphies have been documented in the North European plain that show the interaction between river development, vegetation history, and occupation by Late Palaeolithic humans. Here, we present the results of detailed stratigraphical studies (pedology, archaeology, chrono‐, tephra‐, and palynostratigraphy) at the Federmesser site Grabow 15 located in the broad Elbe River valley. The research aimed to produce a model of site formation based on a multiproxy approach, relating the local evidence to the palaeoenvironmental and settlement history of the wider region. After deposition of fluvial sands during the Late Pleniglacial in a braided setting, the river course developed locally toward a meandering system at the transition from the Older Dryas to the Allerød, while periodic flooding led to the deposition of floodplain sediments during the early Allerød. The floodplain was settled by people of the earliest “Federmessergruppen,” who are believed to have chosen this open floodplain area along the river for collecting and processing amber of local origin. Their artifacts became embedded in the aggrading floodplain sediments. In the late Allerød, floodplain sedimentation ceased and a Fluvisol‐type soil developed, indicating a trend toward geomorphic stability. The Fluvisol was then covered by silty floodplain sediments due to a rising water level during the late Younger Dryas resulting in the cessation of human occupation in the area. Subsequent organic‐rich Late Glacial/Holocene sediments preserved the settlement remains to the present.  相似文献   

Patterns of decadal-scale Arctic warming events in simulated climate   总被引：1，自引：1，他引：0  

Alexander Beitsch  Johann H. Jungclaus  Davide Zanchettin 《Climate Dynamics》2014,43(7-8):1773-1789

Pronounced positive decadal-scale temperature anomalies occurred in the Arctic region in the first half of the twentieth century, an episode known as the early twentieth century warming (ETCW). Analyzing a 3,000-year unperturbed climate simulation performed with the Max Planck Institute Earth System Model, we demonstrate that internal variability of the Northern Hemisphere climate system is sufficient to reproduce warm events matching the observed ETCW. We perform a superposed epoch analysis on simulated data and identify 26 Arctic warming episodes compatible with the ETCW. The simulated events reproduce, in their ensemble average, magnitude as well as spatial and temporal extent of the observed ETCW. In individual realizations, the ETCW-like events indicate that different patterns of internally generated decadal Arctic warming are possible, including pan-Arctic warming events. We investigate the dynamics that typically lead to the simulated warming events: positive oceanic heat transport anomalies that form in the North Atlantic initialize the warming events and trigger an ocean-ice-albedo feedback in the Barents Sea region. The consequent reduction in sea-ice extent leads to enhanced multi-year surface warming through strengthened ocean heat release to the atmosphere. The oceanic heat transport anomalies reduce to pre-event levels around the year of the maximum warming. However, the warming events typically lasts for another 5–7 years until the sea-ice extent recovers to pre-event conditions.  相似文献   

Analytical 2D GNSS PVT solutions from a hyperbolic positioning approach     

Johann Dambeck  Benjamin Braun 《GPS Solutions》2013,17(3):309-326

GNSS receivers estimate 3D antenna position and receiver clock bias when at least four satellites are tracked. If only three satellites are available, a 2D antenna position solution is still possible. We derive an almost exact algorithm for the determination of two possible antenna positions and the corresponding receiver clock biases based on pseudorange measurements to three GNSS satellites and a height measurement. The two ambiguous solutions exactly reflect the same height measurement. One of the solutions can be eliminated if some prior knowledge of the user position, for example, near the Earth, is available. In general, a less accurate height measurement gives a less accurate 2D GNSS solution, and vice versa. The determination of the receiver antenna position is based upon the intersection of two confocal hyperboloid sheets and the ellipsoid, resulting in a hyperbola along which the user is located. The algorithm is verified by numerical computations.  相似文献   

Time calibration of sedimentary sections based on insolation cycles using combined cross-correlation: dating the gone Badenian stratotype (Middle Miocene, Paratethys, Vienna Basin, Austria) as an example     

Johann Hohenegger  Michael Wagreich 《International Journal of Earth Sciences》2012,101(1):339-349

Cross-correlation between insolation intensities and a combination of sedimentary characters is introduced to obtain precise time calibration of sedimentary cycles. The first step is to transfer the section scale into ages using power spectra comparing the main periods with orbital cycles, while in the second step the standardized values of sedimentary signals are cross-correlated with the standardized insolation curve. As an example for the applicability of the method, we investigated calcium carbonate, organic carbon in a 9-m sampled section from the historical Badenian stratotype at Baden/Sooss (Lower Austria). Comparing courses of geochemical parameters between the historical stratotype and a nearby drilled 102-m scientific core resulted in continuation of the core section into the stratotype. Cross-correlation between magnetic susceptibility (MS) combined with the negatively correlated calcium carbonate content of the drilled section on the one side and summer solar insolation at 65° northern latitude on the other resulted in an extremely significant correlation between −14.221 and −13.982 Ma. This is younger than the before estimated time frame (−14.379 to −14.142 Ma) based on cross-correlation between MS and the orbital 100-kyr eccentricity and 41-kyr obliquity cycles. The direct continuation of the drilled section by the stratotype covering a time span of 17.7 kyr consequently dates the Badenian stratotype between −13.982 and −13.964 Ma. Therefore, the upper limit of the stratotype, assigned to the Early Badenian, puts it close to the Langhian/Seravallian boundary at −13.82 Ma, demonstrating the need for revising the Badenian stratigraphic subdivision based on orbital cycles, especially the middle Badenian Wielician substage.  相似文献   

Geochronology and geochemistry of a dyke–host rock association and implications for the formation of the Bavarian Pfahl shear zone, Bohemian Massif     

Wolfgang Siebel  Ulrich Blaha  Fukun Chen  Johann Rohrmüller 《International Journal of Earth Sciences》2005,94(1):8-23

To place constraints on the formation and deformation history of the major Variscan shear zone in the Bavarian Forest, Bavarian Pfahl zone, SW Bohemian Massif, granitic dykes and their feldspar-phyric massive host rock (so-called palite), zircons were dated by the U–Pb isotope dilution and Pb-evaporation methods. The dated samples comprise two host rocks and four dykes from a K-rich calc-alkaline complex adjoining the SW part of the Bavarian Pfahl shear zone. The palites, which appear to be the oldest magmatic rocks emplaced in the shear zone, yield ages of 334±3, 334.5±1.1 Ma (average ²⁰⁷Pb/²⁰⁶Pb-evaporation zircon ages) and 327–342 Ma (range of U/Pb zircon ages) suggesting a Lower Carboniferous age for the initiation of the Pfahl zone. Absence of inherited older cores in all investigated zircons indicates that incorporation of crustal zircon material has played virtually no role or that the melting temperature was very high. Determination of the dyke emplacement age is complicated by partial Pb-loss in most of the fractions analysed. This Pb-loss can be ascribed to higher U content of the dyke zircons compared to those from host rock. Upper discordia intercept ages of the different dykes range from 322±5 to 331±9 Ma. The dykes are pre- to synkinematic with respect to penetrative regional mylonitisation along the Pfahl zone, and the upper intercept ages provide a maximum age for this tectonic event.  相似文献   

Evolution of quartz microstructures and textures during polyphase deformation within the Tauern Window (Eastern Alps)     

Walter Kurz  Wolfgang Unzog  Franz Neubauer  Johann Genser 《International Journal of Earth Sciences》2001,90(2):361-378

The interior of the Tauern Window exposes underplated Penninic continental lithosphere and the overlying obducted Penninic oceanic crust within a large antiformal dome in the internal zone of the Eastern Alps. These units have been affected by a polyphase deformation history. Generally, three deformation events are distinguished. D₁ is related to underplating of, and top-to-the-N nappe stacking within, the Penninic continental units of the Tauern Window. Deformation stage D₂ is interpreted to reflect the subsequent continent collision between the Penninic continental units and the European foreland, D₃ is related to the formation of the dome structure within the Tauern Window. During thickening of continental lithosphere and nappe stacking (D₁), and subsequent intracontinental shortening (D₂), these tectonic units have been ductilely deformed close to a plane strain geometry. Conditions for the plastic deformation of the main rock-forming mineral phases (quartz, feldspar, dolomite, calcite) have prevailed during all three phases of crustal deformation. Generally, two types of quartz microstructures that are related to D₁ are distinguished within the Tauern Window: (a) Equilibrated and annealed fabrics without crystallographic preferred orientations (CPO) have only been observed in the central part of the southeastern Tauern Window, corresponding with amphibolite-grade metamorphic conditions. (b) In the northeastern and central part of the Tauern Window microstructures are characterized by quartz grains that show equilibrated shape fabrics, but well preserved CPO with type-I cross girdle distributions, indicating a deformation geometry close to plane strain. During D₂, two types of quartz microstructures are distinguished, too: (a) Quartz grains that show equilibrated shape fabrics, but well-preserved CPO. The c-axes distributions generally are characterized by type-I cross girdles, locally by type-II cross girdles, and in places, oblique single girdle distributions. (b) A second type of quartz microstructure is characterized by highly elongated grains and fabrics typical for dislocation creep and grain-boundary migration, and strong CPO. This type is restricted to the southern sections of the western and eastern Tauern Window. The c-axis distributions show type-I cross girdles in the western part of the Tauern Window and single girdles in the southeastern part. In the western part of the Tauern Window, a continuous transition from type (b) microstructures in the south to type (a) microstructures in the north is documented. The microstructural evolution also documents that the dome formation in the southeastern and western Tauern Window has already started during D₂ and has continued subsequent to the equilibration during amphibolite to greenschist facies metamorphism. D₃ is restricted to distinct zones of localized deformation. D₃-related quartz fabrics are characterized by the formation of ribbon grains; the c-axes show small-circle distributions around the Z-axis of the finite-strain ellipsoid. During exhumation and doming (D₃), deformation occurred under continuously decreasing temperatures.  相似文献