Geophysical Expression of Low Sulphidation Epithermal Au-Ag Deposits and Exploration Implications –Examples from the Hokusatsu Region of SW Kyushu, Japan–     

Craig A. FEEBREY  Hajime HISHIDA  Ken YOSHIOKA  Ken NAKAYAMA 《Resource Geology》1998,48(2):75-86

Abstract: Low sulphidation epithermal Au-Ag deposits constitute a major exploration target for many mining companies worldwide. These deposits are commonly characterized by quartz vein systems which formed at temperatures often in the range 150–250°C giving rise to major alteration halos. Accompanying mineralization and associated alteration is the destruction and redistribution of magnetite in the host rocks and the formation of various K-bearing minerals such as adularia, illite and alunite. These alteration halos can often cover an area of at least several square kilometres and as such have the potential to be detected during reconnaissance geological surveys utilizing high resolution airborne aeromagnetic and radiometric sensors.
Analysis of airborne magnetic and radiometric data recently acquired over the Hokusatsu Region of SW Kyushu indicates that major low sulphidation epithermal Au-Ag deposits are characterized by several distinct geophysical features varying with the degree of post-mineralization cover and level of erosion. Several deposits coincide with extensive magnetic "flat" and high radiometric K–counts. In addition, several workers have shown that a very close association exists between Bouguer gravity highs and epithermal Au mineralization in the Hokusatsu Region. The combined use of areomagnetics, radiometrics and gravity data therefore provides an exceptionally effective approach to exploration for low sulphidation epithermal Au–Ag deposits in the Hokusatsu Region of Japan.  相似文献   

Mudslide plug flow within channels     

D. Craig 《Engineering Geology》1981,17(4):273-281

The methods used to monitor five cases of plug flow in mudslides in east County Antrim, Northern Ireland, are given. Assuming the mudslide material acts as a Bingham substance, the five cases are analysed. The results show a general agreement between the observed and predicted behaviours. An analysis derived to model submarine landslide behaviour is employed to represent the five plug-flow cases, and the results are reasonably close to those achieved in former analyses.  相似文献   

Predicted relative sea-level changes (18,000 years B.P. to present) caused by late-glacial retreat of the Antarctic Ice Sheet     

James A. Clark  Craig S. Lingle 《Quaternary Research》1979,11(3):279-298

Predictions of global changes in relative sea level caused by retreat of the Antarctic Ice Sheet from its 18,000 yr B.P. maximum to its present size are calculated numerically. When combined with the global predictions of relative sea-level change resulting from retreat of the Northern Hemisphere ice sheets, the results may be compared directly to observations of sea-level change on the Antarctic continent as well as at distant localities. The comparison of predictions to the few observations of sea-level change on Antarctica supports the view that the Antarctic Ice Sheet was larger 18,000 years ago than at present. The contribution of the Antarctic Ice Sheet to the total eustatic sea-level rise is assumed to be 25 m (25% of the assumed total eustatic rise). If as little as 0.7 m of this 25-m rise occurred between 5000 yr B.P. and the present, few mid-oceanic islands would emerge. If the Antarctic Ice Sheet attained its present dimensions by 6000 yr B.P., however, and if the volume of the ocean has remained constant for the past 5000 years, numerous islands throughout the Southern Hemisphere would emerge. It is suggested that a thorough study of Pacific islands, believed by some to have slightly emerged shorelines of Holocene age, would yield useful information about ocean volume changes during the past 5000 years, and hence on the glacial history of the Antarctic Ice Sheet.  相似文献   

Systematics of the spinel structure type     

Roderick J. Hill  James R. Craig  G. V. Gibbs 《Physics and Chemistry of Minerals》1979,4(4):317-339

Systematic trends in the geometry of 149 oxide and 80 sulfide binary and ternary spinels have been examined from the standpoint of ionic radius and electronegativity. The mean ionic radii of the octahedral and tetrahedral cations, taken together, account for 96.9 and 90.5% of the variation in the unit cell parameter, a, of the oxides and sulfides, respectively, with the octahedral cation exerting by far the dominant influence in sulfides. The mean electronegativity of the octahedral cation exerts an additional, but small, influence on the cell edge of the sulfides. The equation a=(8/3√d)d _tet+(8/3)d _oct, where d _tet and d _oct are the tetrahedral and octahedral bond lengths obained from the sum of the ionic radii, accounts for 96.7 and 83.2% of the variation in a in the oxides and sulfides, respectively, again testifying to the applicability of the hard-sphere ionic model in the case of the spinel structure. Comparison of observed and calculated u values for 94 spinels indicates that up to 40% of the experimentally measured anion coordinates may be significantly in error. In addition to these compounds, u values are given for 52 spinels for which no data have previously been determined. Diagrams are presented for the rapid interpretation of the internal consistency of published data and the prediction of the structural parameters of hypothetical or partially studied spinels.  相似文献   

In memoriam     

H. Craig 《Earth and Planetary Science Letters》1980,49(2):261-262

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FEM solution of the Navier-Stokes equations for vortex shedding behind a cylinder: experiments with the four-node element     

Philip M. Gresho  Robert L. Lee  Craig D. Upson 《Advances in water resources》1981,4(4):175-184

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Measurement of the effect of particle size variation on the detrital remanent magnetization to anhysteretic remanent magnetization ratio in some abyssal sediments     

Craig Amerigian 《Earth and Planetary Science Letters》1977,36(3):434-442

Deposition experiments have been carried out to measure the effect of particle size variation on the relationship between detrital remanent magnetization (DRM), anhysteretic remanent magnetization (ARM), and geomagnetic field intensity in sediments.Foraminiferal ooze from a box core taken in the Columbian Basin south of Jamaica was separated into several particle size ranges and redeposited in the laboratory in known magnetic fields. The intensity and alternating field (AF) demagnetization characteristics of the DRM and a subsequently applied ARM were compared for the various particle size ranges.The results show a variation of DRM/ARM ratios with particle size. The DRM intensities and directions indicate that particle sizes greater than 38 μm do not contribute significantly to the DRM of the total sediment. ARM intensities for larger particle sizes and particle size analysis of the whole sediment indicate that the fraction greater than 38 μm does make a significant contribution to the total ARM of a sample. Use of the DRM/ARM ratio in experimental measurements of magnetic paleointensity indicates that the method is unsatisfactory for sediments having a significant fraction of magnetic particles larger than 38 μm. It is also shown that, for sediments having a significant fraction of high-coercivity magnetic grains, the relative orientation of the ARM and DRM will affect ARM intensities, making necessary the use of corrected ARM and DRM intensities for ratio calculations.  相似文献   

Biogeochemical and hydrographic controls on chromophoric dissolved organic matter distribution in the Pacific Ocean     

Chantal M. Swan  David A. Siegel  Norman B. Nelson  Craig A. Carlson  Elora Nasir 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2175-2192

Recent in situ observations of chromophoric dissolved organic material (CDOM) in the Pacific Ocean reveal the biogeochemical controls on CDOM and indicate predictive potential for open-ocean CDOM in diagnosing particulate organic matter (POM) remineralization rates within ocean basins. Relationships between CDOM and concentrations of dissolved oxygen, nutrients and inorganic carbon in the subthermocline waters of the Pacific reflect the relative influences of water mass ventilation and water-column oxidative remineralization. Apparent in situ oxygen utilization (AOU) accounts for 86% and 61% of variance in CDOM abundance, respectively, in Antarctic Intermediate Water and North Pacific Intermediate Water. In the deep waters of the Pacific below the zone of remineralization, AOU explains 26% of CDOM variability. The AOU–CDOM relationship results from competing biogeochemical and advective processes within the ocean interior. Dissolved organic carbon (DOC) is not statistically linked to the CDOM or AOU distributions, indicating that the majority of CDOM production occurs during the remineralization of sinking POM and thus potentially provides key information about carbon export. Once formed in the ocean interior, CDOM is relatively stable until it reaches the surface ocean where it is destroyed by solar bleaching. Susceptibility to bleaching confers an additional tracer-like quality for CDOM in water masses with active convection, such as mode waters that appear as subsurface CDOM minima. In the surface ocean, atypically low CDOM abundance highlights a region of unusually extreme oligotrophy: the subtropical South Pacific gyre. For these hyper-oligotrophic waters, the present CDOM observations are consistent with analysis of in situ radiometric observations of light attenuation and reflectance, demonstrating the accuracy of the CDOM spectrophotometric observations. Overall, we illustrate how CDOM abundance in the ocean interior can potentially diagnose rates of thermohaline overturning as they affect regional biogeochemistry and export. We further show how relative surface ocean CDOM abundances are driven in large part by processes occurring in the deep layers of the ocean. This is particularly significant for the interpretation of the global surface distribution of CDOM using satellite remote sensing.  相似文献   

Observations of Fire–Atmosphere Interactions and Near-Surface Heat Transport on a Slope     

Craig B. Clements  Daisuke Seto 《Boundary-Layer Meteorology》2015,154(3):409-426

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Three-dimensional benchmark for variable-density flow and transport simulation: matching semi-analytic stability modes for steady unstable convection in an inclined porous box     

Clifford I. Voss  Craig T. Simmons  Neville I. Robinson 《Hydrogeology Journal》2010,18(1):5-23

This benchmark for three-dimensional (3D) numerical simulators of variable-density groundwater flow and solute or energy transport consists of matching simulation results with the semi-analytical solution for the transition from one steady-state convective mode to another in a porous box. Previous experimental and analytical studies of natural convective flow in an inclined porous layer have shown that there are a variety of convective modes possible depending on system parameters, geometry and inclination. In particular, there is a well-defined transition from the helicoidal mode consisting of downslope longitudinal rolls superimposed upon an upslope unicellular roll to a mode consisting of purely an upslope unicellular roll. Three-dimensional benchmarks for variable-density simulators are currently (2009) lacking and comparison of simulation results with this transition locus provides an unambiguous means to test the ability of such simulators to represent steady-state unstable 3D variable-density physics.  相似文献