scholarly journals Three-dimensional imaging of a Ag-Au-rich epithermal system in British Columbia, Canada, using airborne z-axis tipper electromagnetic and ground-based magnetotelluric data

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. B1-B12 ◽  
Author(s):  
Juliane Hübert ◽  
Benjamin M. Lee ◽  
Lijuan Liu ◽  
Martyn J. Unsworth ◽  
Jeremy P. Richards ◽  
...  
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Three Dimensional ◽  
Data Sets ◽  
Borehole Data ◽  
Magnetotelluric Data ◽  
Electric Field Amplitude ◽  
Epithermal System ◽  
Geologic Model ◽  
Felsic Volcanic

We have evaluated results from a study combining airborne z-axis tipper electromagnetic (ZTEM) and ground-based magnetotelluric (MT) data to image an epithermal system in British Columbia. The spatially coincident use of these two methods allowed for a direct comparison of both data sets in the overlapping frequency band and showed that both measurements were consistent. Inversion of just the ZTEM data suffered from the lack of electric field amplitude information, which could be provided by the MT data. Three-dimensional inversion modeling of the two individual data sets was performed. Models of electrical resistivity derived from both data sets were consistent and could be correlated with the geological and structural setting of the mineralization. Gold is associated with disseminated pyrite and marcasite in quartz-sericite-altered felsic volcanic rocks and intrusions, especially near the contact with mafic volcanic rocks and a late diorite intrusion. The quartz-sericite alteration yields a conductivity anomaly, relative to the more resistive mafic country rocks. Although ZTEM and MT do not possess the resolution of the geologic model derived from borehole data, our model agrees well with a regional assessment of the deposit.

scholarly journals Geophysical properties of an epithermal Au-Ag deposit in British Columbia, Canada

2018 ◽  
Vol 6 (4) ◽  
pp. T907-T918
Author(s):  
Bahman Abbassi ◽  
Li Zhen Cheng ◽  
Jeremy P. Richards ◽  
Juliane Hübert ◽  
Jean M. Legault ◽  
...  
Keyword(s):  
British Columbia ◽  
Magnetic Susceptibility ◽  
Volcanic Rocks ◽  
Magnetization Vector ◽  
Direct Access ◽  
Vector Model ◽  
High Potassium ◽  
Epithermal System ◽  
Magnetic Inversion ◽  
Felsic Volcanic

The Newton Au-Ag deposit is an intermediate sulfidation state epithermal system in British Columbia, Canada. Multiple types of geophysical data are interpreted and evaluated with drillcore petrophysical, geochemical, and geologic observations to better understand the geophysical signature of the Newton epithermal system. Airborne [Formula: see text]-ray data sets indicate elevated emission counts of K, eTh, and eU over the Newton epithermal system, which are caused by hydrothermal alteration. Drillcore [Formula: see text]-ray measurements also indicate high potassium concentrations related to the K-rich phyllosilicates in the form of argillic and quartz-sericite alteration assemblages. Magnetization vector inversion (MVI) is used to recover an unconstrained 3D magnetization vector model of the system on regional and deposit scales. The regional MVI has resolved a deep concentric-shaped low magnetic zone that is interpreted as a porphyry system beneath the epithermal deposit. At the deposit scale, 3D direct current (DC) resistivity and induced polarization (IP) inversion, and unconstrained MVI revealed finer details of the epithermal system architecture. Cooperative DC/IP and magnetic inversion, at the deposit scale, constrained the magnetic susceptibility model and recovered a more precise susceptibility image of the epithermal system that is well-matched with borehole geology. The integrated geophysical interpretation helped to resolve several 3D latent geologic features in places without direct access to drillcore samples. We identified four petrophysical domains based on the three cooperatively inverted physical properties, including electrical resistivity, IP chargeability, and magnetic susceptibility. The combined geophysical models differentiated porphyritic intrusions (chargeability/susceptibility lows), disseminated sulfides (resistivity lows and chargeability highs), a Cu-rich zone in mafic volcanic rocks (susceptibility/chargeability highs and resistivity lows), and an Au-Ag-Cu-rich zone with silicification in felsic volcanic rocks (chargeability/susceptibility lows and resistivity highs). These petrophysical domains also provide useful exploration vectors for identification of similar epithermal systems.

scholarly journals Geochemistry, geochronology, and fluid inclusion study of the Late Cretaceous Newton epithermal gold deposit, British Columbia

2016 ◽  
Vol 53 (1) ◽  
pp. 10-33 ◽  
Author(s):  
Lijuan Liu ◽  
Jeremy P. Richards ◽  
S. Andrew DuFrane ◽  
Mark Rebagliati
Keyword(s):  
British Columbia ◽  
Gold Deposit ◽  
Late Cretaceous ◽  
Gold Mineralization ◽  
Volcanic Rocks ◽  
Fluid Inclusion Study ◽  
Epithermal Gold ◽  
Epithermal Gold Deposit ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks

Newton is an intermediate-sulfidation epithermal gold deposit related to Late Cretaceous continental-arc magmatism in south-central British Columbia. Disseminated gold mineralization occurs in quartz–sericite-altered Late Cretaceous felsic volcanic rocks, and feldspar–quartz–hornblende porphyry and quartz–feldspar porphyry intrusions. The mineralization can be divided into three stages: (1) disseminated pyrite with microscopic gold inclusions, and sparse quartz–pyrite ± molybdenite veins; (2) disseminated marcasite with microscopic gold inclusions and minor base-metal sulfides; and (3) polymetallic veins of pyrite–chalcopyrite–sphalerite–arsenopyrite. Re–Os dating of molybdenite from a stage 1 vein yielded an age of 72.1 ± 0.3 Ma (published by McClenaghan in 2013). The age of the host rocks has been constrained by U–Pb dating of zircon: Late Cretaceous felsic volcanic rocks, 72.1 ± 0.6 Ma (Amarc Resources Ltd., unpublished data, reported by McClenaghan in 2013); feldspar–quartz–hornblende porphyry, 72.1 ± 0.5 Ma; quartz–feldspar porphyry, 70.9 ± 0.5 Ma (Amarc Resources Ltd., unpublished data, reported by McClenaghan in 2013). The mineralized rocks are intruded by a barren diorite, with an age of 69.3 ± 0.4 Ma. Fluid inclusions in quartz–pyrite ± molybdenite ± gold veins yielded an average homogenization temperature of 313 ± 51 °C (number of samples, n = 82) and salinity of 4.8 ± 0.9 wt.% NaCl equiv. (n = 46), suggesting that a relatively hot and saline fluid likely of magmatic origin was responsible for the first stage of mineralization. Some evidence for boiling was also observed in the veins. However, the bulk of the gold mineralization occurs as disseminations in the wall rocks, suggesting that wall-rock reactions were the main control on ore deposition.

The thickness of Neogene and Quaternary cover across the central Interior Plateau, British Columbia: analysis of water-well drill records and implications for mineral exploration potential1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia. 2Geological Survey of Canada (GSC) Contribution 20100036; Mineral Deposit Research Unit (MDRU, Department of Earh and Ocean Sciences, The University of British Columbia) Contribution p-261.

2011 ◽  
Vol 48 (6) ◽  
pp. 973-986 ◽  
Author(s):  
Graham D.M. Andrews ◽  
Alain Plouffe ◽  
Travis Ferbey ◽  
James K. Russell ◽  
Sarah R. Brown ◽  
...  
Keyword(s):  
British Columbia ◽  
Mountain Pine Beetle ◽  
Mineral Exploration ◽  
Three Dimensional ◽  
Research Unit ◽  
Mineral Deposit ◽  
Basic Knowledge ◽  
Data Sets ◽  
University Of British Columbia ◽  
Water Well

Analysis of over 10 000 water-well records has been used to produce new depth-to-bedrock maps for areas around five cities on the central Interior Plateau of central British Columbia: 100 Mile House, Prince George, Quesnel, Vanderhoof, and Williams Lake. Hitherto, exploration for mineral and hydrocarbon resources has been hampered by a lack of basic knowledge of the thickness of Neogene and Quaternary lithologies. Interpretation of these new maps provides first-order constraints on the localization of thick drift in pre-Late Wisconsinan bedrock paleovalleys, some of which are now buried. Basalt lavas of the Chilcotin Group are restricted to erosional remnants of previously extensive sheets emplaced onto an older peneplain. Our results confirm that the Neogene and Quaternary cover is primarily controlled by paleotopography and is generally thin and patchy across much of the region. Increased understanding of the three-dimensional distribution of cover produces a corresponding increase in the utility of geological, geochemical, and geophysical exploration techniques, and a reduction in the risk for future mineral exploration activities, especially when combined with more sophisticated data sets.

Geostatistical Joint Interpretation of Gravity and Magnetotelluric Data of the US Cordillera

2021 ◽  
Author(s):  
Mohammad Shehata ◽  
Hideki Mizunaga
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Data Sets ◽  
Spatial Expansion ◽  
Magnetotelluric Data ◽  
Data Set ◽  
Entire Area ◽  
Mean Values ◽  
Local Means ◽  
The Us

<p>Long-period magnetotelluric and gravity data were acquired to investigate the US cordillera's crustal structure. The magnetotelluric data are being acquired across the continental USA on a quasi-regular grid of ∼70 km spacing as an electromagnetic component of the National Science Foundation EarthScope/USArray Program. International Gravimetreique Bureau compiled gravity Data at high spatial resolution. Due to the difference in data coverage density, the geostatistical joint integration was utilized to map the subsurface structures with adequate resolution. First, a three-dimensional inversion of each data set was applied separately.</p><p>The inversion results of both data sets show a similarity of structure for data structuralizing. The individual result of both data sets is resampled at the same locations using the kriging method by considering each inversion model to estimate the coefficient. Then, the Layer Density Correction (LDC) process's enhanced density distribution was applied to MT data's spatial expansion process. Simple Kriging with varying Local Means (SKLM) was applied to the residual analysis and integration. For this purpose, the varying local means of the resistivity were estimated using the corrected gravity data by the Non-Linear Indicator Transform (NLIT), taking into account the spatial correlation. After that, the spatial expansion analysis of MT data obtained sparsely was attempted using the estimated local mean values and SKLM method at the sections where the MT survey was carried out and for the entire area where density distributions exist. This research presents the integration results and the stand-alone inversion results of three-dimensional gravity and magnetotelluric data.</p>

scholarly journals Multiphysics data modeling and imaging for exploration in the southern Rocky Mountains

2018 ◽  
Vol 6 (3) ◽  
pp. SG59-SG78 ◽  
Author(s):  
Maria Soledad Velasco ◽  
David Alumbaugh ◽  
Emmanuel Schnetzler
Keyword(s):  
Cross Sections ◽  
Predictive Analytics ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Data Sets ◽  
Mathematical Framework ◽  
Magnetotelluric Data ◽  
Land Access ◽  
Southern Rocky Mountains ◽  
Well Data

We carried out a multidata geophysics study in southern Colorado to explore for [Formula: see text] reservoirs in an area where seismic imaging is very limited due to the mountainous terrain, the presence of high-velocity volcanic rocks, and difficulty in obtaining land access permits. We have developed a modeling/interpretation methodology using ground magnetotelluric data as well as airborne magnetic and electromagnetic data combined with public domain gravity data and existing well and seismic data. We used the integration of these data sets to produce a series of 2D and 3D geophysical models that reveal basin architecture previously poorly defined through the analysis of limited seismic and well data alone. We found that this type of analysis aids in decreasing uncertainty in the interpreted geologic cross sections and a better understanding of the structural complexities of the region. Through the application of machine learning methods, we are also able to integrate several data sets into a mathematical framework resulting in a predictive model of spatial [Formula: see text] distribution. The integration of the interpretations from all data sets, predictive analytics results, and knowledge of [Formula: see text] production, allows us to delineate areas of interest for further exploration.

Imaging an Ag-Au rich epithermal system in British Columbia, Canada, with airborne ZTEM and ground magnetotelluric data

2013 ◽  
Author(s):  
Juliane Hubert ◽  
Benjamin Lee ◽  
Martyn Unsworth ◽  
Jeremy Richards ◽  
Doug Oldenburg ◽  
...  
Keyword(s):  
British Columbia ◽  
Magnetotelluric Data ◽  
Epithermal System

Inversion for magnetic anomalies of arbitrary three‐dimensional bodies

Geophysics ◽  
1990 ◽  
Vol 55 (10) ◽  
pp. 1321-1326 ◽  
Author(s):  
X. Wang ◽  
R. O. Hansen
Keyword(s):  
Three Dimensional ◽  
Large Data ◽  
Magnetic Anomalies ◽  
Large Data Sets ◽  
Data Sets ◽  
Inversion Algorithm ◽  
Geologic Model ◽  
Profile Inversion ◽  
Inversion Techniques ◽  
Medicine Lake

Two‐dimensional (profile) inversion techniques for magnetic anomalies are widely used in exploration geophysics: but, until now, the three‐dimensional (3-D) methods available have been restricted in their geologic applicability, dependent upon good initial values or limited by the capabilities of existing computers. We have developed a fully 3-D inversion algorithm intended for routine application to large data sets. The algorithm based on a Fourier transform expression for the magnetic field of homogeneous polyhedral bodies (Hansen and Wang, 1998), is a 3-D generalization of CompuDepth (O’Brien, 1972). Like CompuDepth, the new inversion algorithm employs thespatial equivalent of frequency‐domain autoregression to determine a series of coefficients from which the depths and locations of polyhedral vertices are calculated by solving complex polynomials. These vertices are used to build a 3-D geologic model. Application to the Medicine Lake Volcano aeromagnetic anomaly resulted in a geologically reasonable model of the source.

Distribution of Paleogene and Cretaceous rocks around the Nazko River belt of central British Columbia from 3-D long-offset first-arrival seismic tomography

2014 ◽  
Vol 51 (4) ◽  
pp. 358-372 ◽  
Author(s):  
Draga Talinga ◽  
Andrew J. Calvert
Keyword(s):  
British Columbia ◽  
Seismic Velocity ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Hydrocarbon Exploration ◽  
P Wave ◽  
Velocity Models ◽  
First Arrival

Across the Nechako–Chilcotin plateau of British Columbia, the distribution of Cretaceous sedimentary rocks, which are considered prospective for hydrocarbon exploration, is poorly known due to the surface cover of glacial deposits and Tertiary volcanic rocks. To constrain the subsurface distribution of these Cretaceous rocks, in 2008 Geoscience BC acquired seven long, up to 14.4 km, offset vibroseis seismic reflection lines across a north-northwest-trending belt of exhumed sedimentary rocks inferred to be part of the Taylor Creek Group. P-wave velocity models, which are consistent with sonic logs from nearby wells, have been estimated using three-dimensional first-arrival tomography to depths ranging from 1 to 4 km. Igneous basement can be identified on most lines using the 5.5 km/s isovelocity contour, which locates the top of the basement to an accuracy of ∼400 m where its depth is known in exploration wells. There is no general distinction on the basis of seismic velocity between Cretaceous sedimentary and Paleocene–Eocene volcanic–volcaniclastic rocks, both of which appear to be characterized in the tomographic models by velocities of 3.0–5.0 km/s. The geometry of the igneous basement inferred from the velocity models identifies north-trending basins and ridges, which correlate with exposed rocks of the Jurassic Hazelton Group. Identified Cretaceous sedimentary rocks occur beneath less negative Bouguer gravity anomalies, but the original distribution of these rocks has been disrupted by later Tertiary extension that created north-trending basins associated with the most negative gravity anomalies. We suggest that Cretaceous sedimentary rocks, if deposited, could be preserved within these basins if the rocks had not been eroded prior to Tertiary extension.

Computer-aided methods for 3-D visualization of serial sections and thick biological specimens

1992 ◽  
Vol 50 (2) ◽  
pp. 1060-1061
Author(s):  
Mark Ellisman ◽  
Maryann Martone ◽  
Gabriel Soto ◽  
Eleizer Masliah ◽  
David Hessler ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Three Dimensional ◽  
Neuritic Plaque ◽  
Dimensional Structure ◽  
Data Sets ◽  
Molecular Physiology ◽  
Research Activities ◽  
Computer Aided ◽  
Dimensional Reconstruction

Structurally-oriented biologists examine cells, tissues, organelles and macromolecules in order to gain insight into cellular and molecular physiology by relating structure to function. The understanding of these structures can be greatly enhanced by the use of techniques for the visualization and quantitative analysis of three-dimensional structure. Three projects from current research activities will be presented in order to illustrate both the present capabilities of computer aided techniques as well as their limitations and future possibilities.The first project concerns the three-dimensional reconstruction of the neuritic plaques found in the brains of patients with Alzheimer's disease. We have developed a software package “Synu” for investigation of 3D data sets which has been used in conjunction with laser confocal light microscopy to study the structure of the neuritic plaque. Tissue sections of autopsy samples from patients with Alzheimer's disease were double-labeled for tau, a cytoskeletal marker for abnormal neurites, and synaptophysin, a marker of presynaptic terminals.

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