The geophysical response of the Goldrush-Fourmile orebody and implications for camp-scale Carlin-type deposit exploration, Cortez District, Nevada

2021 ◽  
Vol 40 (2) ◽  
pp. 122-128
Author(s):  
Lee M. Sampson ◽  
Nicholas C. Williams
Keyword(s):  
Best Practice ◽  
Direct Detection ◽  
Geochemical Modeling ◽  
Ground Surface ◽  
Density Contrast ◽  
Positive Density ◽  
Fine Grained ◽  
Geophysical Surveys ◽  
Sulfide Content ◽  
Surrounding Areas

Since discovery of the Goldrush and Fourmile deposits, numerous geophysical surveys have been acquired over the footprint of mineralization and surrounding areas to focus exploration. The Goldrush-Fourmile system extends more than 7 km in strike length and averages approximately 300 m wide. Most of the orebody lies more than 300 m below ground surface and continues to depths of more than 900 m. Direct detection of the ore system using geophysical tools is impeded by several factors. The system is relatively flat lying and sits in the hinge of a doubly plunging anticline. This gives the shallowest zones a very small lateral footprint. The ore consists of thin strata-bound zones of silica-sulfide mineralization with a tight alteration selvage. Structural controls along faults are limited, with only small displacements. Strong petrophysical contrasts exist between unaltered rock units. Finally, the terrain is rugged. Resistivity inversions of airborne electromagnetic data show that mineralization sits within a complex zone of resistivity responses. Close to intrusions, the host stratigraphy is resistive. Away from intrusions, the same stratigraphic units show highly variable but commonly very low resistivities. This suggests the possibility of redistribution of carbon around intrusions during premineralization metasomatism. Within the orebody, sulfide content increases conductivity within individual formations related to the distribution of fine-grained sooty pyrite. The geometry of the Red Hill Anticline is imaged as a positive density contrast in the observed gravity and geologically constrained gravity inversions. The positive density contrast represents the gross geophysical signature of denser carbonates within the Paleozoic stratigraphy. Magnetic surveys are crucial for mapping the distribution of igneous rocks and potentially hornfelsed sedimentary rocks. The challenges associated with exploring for deeply buried Carlin mineralization notwithstanding, the application of innovative geophysical tools tuned to assess specific geologic questions, combined with best-practice geologic and geochemical modeling, is helping drive exploration for additional Carlin-type mineralization across the Cortez District.

Mise‐a‐la‐masse survey for an auriferous sulfide deposit

Geophysics ◽  
2001 ◽  
Vol 66 (1) ◽  
pp. 70-77 ◽  
Author(s):  
B. B. Bhattacharya ◽  
Dinesh Gupta ◽  
Buddhadeb Banerjee ◽  
Shalivahan
Keyword(s):  
Massive Sulfide ◽  
Sulfide Deposit ◽  
Sulfide Mineralization ◽  
Gold Exploration ◽  
Copper Mineralization ◽  
Geophysical Surveys ◽  
Sulfide Content ◽  
Equipotential Map ◽  
Massive Sulfide Mineralization ◽  
Gold Bearing

A mise‐a‐la‐masse survey was carried out in Bhukia area, Banswara district, Rajasthan, India for auriferous sulfide occurrences. This area was originally surveyed for copper mineralization. Exploratory drilling, however, proved it to be economically not viable. The area was reopened for geophysical surveys when grab samples indicated the presence of gold. Initial geophysical surveys for copper mineralization showed electromagnetic, induced polarization, and resistivity anomalies. At first, one borehole was drilled for gold exploration on the basis of initial geophysical surveys. It encountered massive sulfide mineralization in association with gold. Borehole logging and a mise‐a‐la‐masse survey were carried out in this borehole. Three further boreholes drilled on the basis of the mise‐a‐la‐masse results encountered massive sulfide mineralization in association with gold. One of the three boreholes, 100 m from the first borehole along strike, was used for another set of mise‐a‐la‐masse measurements. A composite equipotential map was prepared using the results of mise‐a‐la‐masse results of both the boreholes. The equipotential contours show a north‐northwest‐south‐southeast trend of mineralization. The boreholes drilled on the basis of the mise‐a‐la‐masse results have delineated a strike length of more than 500 m of gold‐bearing sulfide mineralization. The sulfide content ranges from 10 to 40% and gold concentration ranges from 2 to 6 ppm. The dip and plunge of the lode, as anticipated from the mise‐a‐la‐masse results, are toward the west and north, respectively. Mise‐a‐la‐masse surveys are continuing in the adjoining areas.

scholarly journals Changes in ground deformation prior to and following a large urban landslide in La Paz, Bolivia revealed by advanced InSAR

2018 ◽  
Author(s):  
Nicholas J. Roberts ◽  
Bernhard T. Rabus ◽  
John J. Clague ◽  
Reginald L. Hermanns ◽  
Marco-Antonio Guzmán ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Ground Surface ◽  
Slope Instability ◽  
Small Scale ◽  
Spatial And Temporal Patterns ◽  
La Paz ◽  
Fine Grained ◽  
Measured Displacement ◽  
Optical Satellite Images ◽  
Displacement Patterns

Abstract. We characterize and compare creep preceding and following the 2011 Pampahasi landslide (∼ 40 Mm3 ± 50 %) in the city of La Paz, Bolivia, using spaceborne RADAR interferometry (InSAR) that combines displacement records from both distributed and point scatterers. The failure remobilised deposits of an ancient landslide in weakly cemented, predominantly fine-grained sediments and affected ∼ 1.5 km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8 cm/a and localized parts of the scarp area showed displacements of up to 14 cm/a. Changes in deformation in the 10 months following the landslide are contrary to the common assumption that stress released during a discrete failure increases stability. During that period, most of the landslide toe and areas near the headscarp accelerated, respectively, to 4–14 and 14 cm/a. The extent of deformation increased to cover most, or probably all, of the 2011 landslide as well as adjacent parts of the slope and plateau above. The InSAR-measured displacement patterns – supplemented by field observations and by optical satellite images – indicate that kinematically complex, steady-state creep along pre-existing sliding surfaces temporarily accelerated in response to heavy rainfall, after which the slope quickly achieved a slightly faster and expanded steadily creeping state. This case study demonstrates that high-quality ground-surface motion fields derived using spaceborne InSAR can help to characterize creep mechanisms, quantify spatial and temporal patterns of slope activity, and identify isolated small-scale instabilities. Characterizing slope instability before, during, and after the 2011 Pampahasi landslide is particularly important for understanding landslide hazard in La Paz, half of which is underlain by similar, large paleolandslides.

Holocene deltaic sedimentation along an emerging coast: Nastapoka River delta, eastern Hudson Bay, Quebec

2002 ◽  
Vol 39 (4) ◽  
pp. 505-518 ◽  
Author(s):  
Caroline Lavoie ◽  
Michel Allard ◽  
Philip R Hill
Keyword(s):  
River Delta ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Fluvial Erosion ◽  
Fine Grained ◽  
Isostatic Rebound ◽  
Geophysical Surveys ◽  
Deltaic Sedimentation ◽  
Forced Regression ◽  
Natural Laboratory

Eastern Hudson Bay is characterized by falling relative sea level as a result of post-glacial isostatic rebound, which makes the region a natural laboratory for rapid forced regression, where the evolution of deltaic systems and offshore sedimentation patterns can be studied. A multidisciplinary approach involving airphoto analysis, offshore geophysical surveys, sediment coring, and facies and diatom analyses was used in this study of the Nastapoka River delta. The delta has formed as a result of the fluvial erosion of emerged Quaternary sediments but is mainly subaqueous. Offshore, in the prodelta zone, the oldest deposits are glaciomarine, laid down when the ice front of the receding Laurentide ice sheet stood on the Nastapoka hills some 7700–6800 years BP. Lateral equivalents of this glaciomarine unit are presently exposed on land. The shallow-water platform of the delta shows a thin surficial unit of wave-worked sand that overlies fine-grained, deeper water deposits derived from erosion of clay soils in the river catchment a few centuries ago, probably during periods of intense thermokarst activity. As the isostatic uplift continues, the deltaic platform will gradually emerge and be incised by the river channel.

scholarly journals Changes in ground deformation prior to and following a large urban landslide in La Paz, Bolivia, revealed by advanced InSAR

2019 ◽  
Vol 19 (3) ◽  
pp. 679-696 ◽  
Author(s):  
Nicholas J. Roberts ◽  
Bernhard T. Rabus ◽  
John J. Clague ◽  
Reginald L. Hermanns ◽  
Marco-Antonio Guzmán ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Ground Surface ◽  
Small Scale ◽  
Spatial And Temporal Patterns ◽  
La Paz ◽  
Fine Grained ◽  
Measured Displacement ◽  
Optical Satellite Images ◽  
Displacement Patterns ◽  
Spaceborne Radar

Abstract. We characterize and compare creep preceding and following the complex 2011 Pampahasi landslide (∼40 Mm3±50 %) in the city of La Paz, Bolivia, using spaceborne radar interferometry (InSAR) that combines displacement records from both distributed and point scatterers. The failure remobilized deposits of an ancient complex landslide in weakly cemented, predominantly fine-grained sediments and affected ∼1.5 km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8 cm a−1 and localized parts of the scarp area showed displacements of up to 14 cm a−1. Changes in deformation in the 10 months following the landslide demonstrate an increase in slope activity and indicate that stress redistribution resulting from the discrete failure decreased stability of parts of the slope. During that period, most of the landslide toe and areas near the head scarp accelerated, respectively, to 4–14 and 14 cm a−1. The extent of deformation increased to cover most, or probably all, of the 2011 landslide as well as adjacent parts of the slope and plateau above. The InSAR-measured displacement patterns, supplemented by field observations and optical satellite images, reveal complex slope activity; kinematically complex, steady-state creep along pre-existing sliding surfaces accelerated in response to heavy rainfall, after which slightly faster and expanded steady creeping was re-established. This case study demonstrates that high-quality ground-surface motion fields derived using spaceborne InSAR can help to characterize creep mechanisms, quantify spatial and temporal patterns of slope activity, and identify isolated small-scale instabilities; such details are especially useful where knowledge of landslide extent and activity is limited. Characterizing slope activity before, during, and after the 2011 Pampahasi landslide is particularly important for understanding landslide hazard in La Paz, half of which is underlain by similar large paleolandslides.

Pragmatic approach to quality metrics development in cancer.

2013 ◽  
Vol 31 (31_suppl) ◽  
pp. 60-60
Author(s):  
Donna Chung ◽  
Aniruddha Dwarakanath ◽  
Charlotte Williams ◽  
Kathy Pritchard-Jones ◽  
James Mountford ◽  
...  
Keyword(s):  
Patient Experience ◽  
Cancer Care ◽  
Best Practice ◽  
Local Population ◽  
Quality Measures ◽  
System Level ◽  
Patient Pathway ◽  
Small Set ◽  
Surrounding Areas ◽  
Key Pathways

60 Background: London Cancer aims to use transparency of service and quality measures to drive improvement in cancer care in North and East London and surrounding areas, serving our population of 3.5m people. Whilst the on-going implementation of the National Outcome and Service Dataset for UK is expected to take 18 months we have chosen to develop quality measures with the teams accountable to deliver the service by using available data from a variety of existent sources and illustrate this in value scorecards tracking the patient pathway. Methods: Building on an engagement exercise with patients, clinicians and charities in 2011 to identify which outcomes mattered most to patients, a small set of key pathways metrics was identified for each site specific cancer pathway board to monitor their progress in implementing integrated cancer care. Metrics were selected only if (a) clinically useful, in line with the current work plan and improvement effort; (b) accessible on a recurrent basis and requiring minimal manual effort; (c) facilitate the understanding of the patient pathway; (d) align with London Cancer objectives in improving survival, patient experience, and access to innovation and clinical trials. Pathway boards were invited to contribute with the intention to provide a pathway metrics value scorecards on a quarterly basis. Results: The first set pathway metrics scorecards, with 31 metrics, were published by June 2013. Key items include adherence to established best practice (16), data completeness (6), survival (3), pathway efficiency (3), and patient experience (3). Conclusions: Pathway metrics are reported at a system level, reflecting the care for our local population, against measures that are important to them and will allow visibility of success. Whilst current pathway metric development is limited by the availability of meaningful data we aim to build on the existing metrics in an iterative fashion. For this we are working with stakeholders to improve data quality.

scholarly journals Badania georadarowe kemów jako przykład możliwości zastosowania metod geofizycznych do badania form zbudowanych z drobnoziarnistych osadów klastycznych = GPR surveys of kame hills as an example of geophysical methods being applied to the study of forms built of fine grained clastic sediments

2020 ◽  
Vol 92 (3) ◽  
pp. 423-446
Author(s):  
Piotr Lamparski
Keyword(s):  
Geophysical Methods ◽  
Ice Sheet ◽  
Geological Structure ◽  
Point Of View ◽  
Geological Mapping ◽  
Fine Grained ◽  
Clastic Sediments ◽  
Geophysical Surveys ◽  
Ground Penetrating ◽  
The Way

The Ground Penetrating Radar (GPR) method potentially offers many possibilities for fast and reliable lithostratigraphic sediment models to be developed. From a cognitive point of view, this represents a major simplification and shortening of procedures with which information about sediments can be obtained. And from the point of view of the economy of operations, there can be a significant reduction in costs and time of research in shallow geology and the stratigraphy of areas where unconsolidated clastic sediments are of superficial occurrence. Also noteworthy is the possibility for the results of GPR surveys to be deployed in support of geological mapping, as well as in the shallow exploration of resources and hydrogeological studies.The most major advantage of the GPR method related to the possibility of the structure of forms being observed in full shape. In the absence of large outcrops, geophysical prospection of geomorphological forms is helpful, insofar as we are able to translate the results of geophysical surveys into the actual lithostratigraphic system of sediments building a specific form.Against that background, the research presented in this article forms part of the work to develop radar stratigraphy, as an important support for direct geological research (Huggenberger et al., 1994; Van Overmeeren, 1998; Beres et al., 1999, Overgaard and Jakobsen, 2001; Jakobsen and Overgaard, 2002; Neal, 2004; Lejzerowicz et al., 2014; Żuk and Sambrook Smith, 2015; Lejzerowicz et al., 2018). It also points to the research potential of the GPR method in determining the genesis of form. The discussion on the way kames form has been going on in the literature for years (Niewiarowski, 1959; 1961; Karczewski, 1971; Klajnert, 1978; Jaksa, 2003; Terpiłowski, 2008). The studies presented here do not suffice to allow the matter to be determined comprehensively, even though they do provide for verification of the opinions of previous researchers.The area forming the subject of this article is defined by Niewiarowski (1959) as the dead ice zone because of the characteristic set of forms (dead ice moraines, kames and eskers). Like modern researchers (Terpiłowski, 2008), Niewiarowski points to the importance of sub-Quaternary surface elevations in the formation of cracks in the ice sheet, with this leading on to the formation of kame hills above such elevations. This would also seem to have been one of the reasons for the formation in the mass of ice of lakes whose filling with sediment and melting ice walls took the form of kames.The great advantage of the GPR method lies in its ability to recognise macrostructural sediment patterns in glacilimic forms. This diagnosis allows for the high-probability assessment of the genesis of form, especially in the context of its position being determined in the marginal zone of the ice sheet. Also looking extremely promising is the capacity for the thickness of fine clastic sediments lying on till to be determined using GPR. It allows for the determination of the way in which a given form is rooted.Described as they are in brief only, test results for selected sites serve to confirm the great usefulness of the GPR method in the recognition of shallow lithostratigraphy of clastic sediments. Nevertheless, this should not be the only method used to recognise the geological structure of forms and sediments. Significant interpretation ambiguities mean that the GPR method should act in support of direct lithostratigraphic research, not merely serving as an alternative to it. GPR surveys offer a depiction particularly close to the real one – of sediment present in homogeneous sediments in relation to electrical parameters. Sediments ideal for GPR surveys would for example be fine dry sands or silts – and it is precisely these sediments that built most of the investigated kame forms.

Characterisation and Remediation of Beryllium Waste Pits in the Southern Storage Area at Harwell

2003 ◽  
Author(s):  
Lorimar Fellingham ◽  
Andrew Graham ◽  
Steven Stiff
Keyword(s):  
Best Practice ◽  
Thin Layers ◽  
Permeability Barrier ◽  
Limited Information ◽  
Term Care ◽  
Geophysical Surveys ◽  
Storage Area ◽  
Chemical Wastes ◽  
A Site ◽  
Ground Penetrating

The Southern Storage Area at UKAEA’s Harwell site was used from the late 1940’s through until the late 1980’s for the storage, packaging and disposal of various radioactive and chemical wastes. These included beryllium-contaminated wastes arising primarily from the decommissioning of redundant beryllium fabrication facilities. The latter were buried in five unlined, shallow trenches, each being ∼40–50 m long by 6 m wide and 3–4 m deep. An environmental assessment identified three feasible options for the future of these “Beryllium” Pits. These were full excavation with removal of their contents and surroundings, capping and long-term care and maintenance. These options were studied more extensively to select the best practicable environmental option (BPEO), which was excavation. This paper describes in detail the characterisation and remediation approaches used in identifying, planning and successfully implementing that option. It also compares the actual waste arisings in nature, form and quantities with the expectations from the characterisation investigations. At the project commencement limited information existed from records and past trial pitting on the form and contents of the pits. Thus much more extensive characterisation was necessary to determine their dimensions, identify waste types, volumes and disposal routes and quantify potential hazards for any excavations. The characterisation programme involved planning, setting up a site infrastructure, site clearance, non-intrusive surveying and intrusive characterisation by coring. The pit areas and their immediate surroundings were monitored for radiological contamination, followed by geophysical surveys using magnetometry and ground penetrating radar. Primary and secondary containment systems were then constructed over the pits before coring, sampling and analysis on a predefined grid. There was significant beryllium contamination in all pits with some limited contamination by heavy metals, including mercury, and radionuclides. There were also trace levels of volatile organic solvents. These data provided the basis for planning the remediation. The remediation was successfully undertaken to achieve as a minimum a set of remediation targets for residual chemical and radioactive contamination. These targets were determined from site-specific risk assessments, best practice and waste limits. Each pit was remediated within a sealed and ventilated primary containment inside a secondary weatherproof containment building. A horizontal mining approach was adopted to pit excavation with a small excavator initially placed in a launch pit constructed immediately outside the pit. The excavator worked along the pit removing thin layers of waste from an inclined face ahead of it. The waste was placed into bags on trolleys on rails. It was removed via a posting port. After removal of all of the contents and hazardous materials, the containment was removed. Any further excavation required to meet the remediation targets was undertaken in bulk in the open. After verification sampling the remediation was completed by inserting a low permeability barrier of clay and a bentonite geotextile into the base of the pit and backfilling with compacted clean soil. The remediation was completed with successful achievement of all remediation criteria and minimal impacts on the operators, public and environment.

scholarly journals An Airborne 2-μm Double-Pulsed Direct-Detection Lidar Instrument for Atmospheric CO2 Column Measurements

2017 ◽  
Vol 34 (2) ◽  
pp. 385-400 ◽  
Author(s):  
Jirong Yu ◽  
Mulugeta Petros ◽  
Upendra N. Singh ◽  
Tamer F. Refaat ◽  
Karl Reithmaier ◽  
...  
Keyword(s):  
Column Density ◽  
Direct Detection ◽  
Ground Surface ◽  
Lidar Measurement ◽  
Measurement Sensitivity ◽  
Airborne Measurements ◽  
Alternative Approach ◽  
Lidar Measurements ◽  
High Measurement ◽  
Dry Mixing

AbstractThis study reports airborne measurements of atmospheric CO2 column density using a 2-μm double-pulsed integrated path differential absorption (IPDA) lidar. This new 2-μm IPDA lidar offers an alternative approach to measure CO2 column density with unique features. The online frequencies of this lidar can be tuned to 1–6 GHz from the CO2 R30 absorption line peak. It provides high measurement sensitivity to the lower-tropospheric CO2 near the ground surface. This instrument was flown in the spring of 2014 in a NASA B200 aircraft. The results of these test flights clearly demonstrate the measurement capabilities of this lidar instrument. The CO2 column dry mixing ratio is compared to an in situ CO2 measurement by a collocated NOAA flight. The IPDA lidar measurement is determined to be in good agreement with a 0.36% difference, which corresponds to 1.48 ppm. It is the average difference between the IPDA lidar measurements and the NOAA air samples in the flight altitudes from 3 to 6.1 km.

Stratigraphy and depositional environments of the Late Famennian (Late Devonian) of Southern Belgium and characterization of the Strud locality

2015 ◽  
Vol 153 (1) ◽  
pp. 112-127 ◽  
Author(s):  
JULIEN DENAYER ◽  
CYRILLE PRESTIANNI ◽  
PIERRE GUERIAU ◽  
SÉBASTIEN OLIVE ◽  
GAËL CLÉMENT
Keyword(s):  
Flood Plain ◽  
Depositional Environments ◽  
Seed Plants ◽  
Fine Grained ◽  
Exceptional Preservation ◽  
Invertebrate Diversity ◽  
Water Ecosystems ◽  
Surrounding Areas ◽  
Tetrapod Evolution

AbstractThe Famennian (Upper Devonian,c. 372 to 359 Ma) strata of Belgium have recently received much attention after the discoveries of early tetrapod remains and outstandingly preserved continental arthropods. The Strud locality has yielded a diverse flora and fauna including seed-plants, tetrapods, various placoderm, actinopterygian, acanthodian and sarcopterygian fishes, crustaceans (anostracans, notostracans, conchostracans and decapods) and a putative complete insect. This fossil assemblage is one of the oldest continental – probably fresh-water – ecosystems with a considerable vertebrate and invertebrate diversity. The study of the palaeoenvironment of the Strud locality is crucial because it records one of the earliest and most important phases of tetrapod evolution that took place after their emergence but before their terrestrialization. It raises the question of environmental and ecological conditions for the Devonian aquatic ecosystem and the selection pressures occurring at the onset of tetrapod terrestrialization. The present study characterized the fluvial facies of the Upper Famennian sedimentary rocks of Strud and the surrounding areas. The exceptional preservation of arthropods and plants in the main fossiliferous layers is explained by rapid burial in the fine-grained sediment of the quiet and confined flood plain environment. Newly investigated fossiliferous sections in the Meuse–Samson area led to the description and correlation of key sections (Strud, Wierde and Jausse sections, complemented by the less continuous Haltinne, Huy and Coutisse sections). Moreover, the investigated sections allowed a review of the age of the fossiliferous horizon, which is now definitely considered to be Late Famennian in age.

SUBSURFACE GRAVITY MEASUREMENTS

Geophysics ◽  
1952 ◽  
Vol 17 (2) ◽  
pp. 365-377 ◽  
Author(s):  
George R. Rogers
Keyword(s):  
Gravity Data ◽  
Density Contrast ◽  
Positive Density ◽  
Mine Shaft ◽  
Local Anomaly ◽  
Gravity Measurements

Gravity data were obtained at approximately 100-foot intervals in a vertical mine shaft 2,916 feet deep. The shaft passed through a region of high positive density contrast, and a local anomaly was observed of plus 14.0 gravity units to minus 17.9 gravity units. Calculations for Bouguer densities were carried out with the gravity measurements. A theoretical sphere that closely approximates the observed data and known conditions is derived from the gravity data.

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