Integrated geophysical imaging of a concealed mineral deposit: A case study of the world-class Pebble porphyry deposit in southwestern Alaska

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. B317-B328 ◽  
Author(s):  
Anjana K. Shah ◽  
Paul A. Bedrosian ◽  
Eric D. Anderson ◽  
Karen D. Kelley ◽  
James Lang
Keyword(s):  
Magnetic Susceptibility ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Geophysical Methods ◽  
Analytic Signal ◽  
Magnetotelluric Data ◽  
Porphyry Deposit ◽  
Glacial Sediments ◽  
Conductivity Anomalies ◽  
Geophysical Imaging

We combined aeromagnetic, induced polarization, magnetotelluric, and gravity surveys as well as drillhole geologic, alteration, magnetic susceptibility, and density data for exploration and characterization of the Cu-Au-Mo Pebble porphyry deposit. This undeveloped deposit is almost completely concealed by postmineralization sedimentary and volcanic rocks, presenting an exploration challenge. Individual geophysical methods primarily assist regional characterization. Positive chargeability and conductivity anomalies are observed over a broad region surrounding the deposit, likely representing sulfide minerals that accumulated during multiple stages of hydrothermal alteration. The mineralized area occupies only a small part of the chargeability anomaly because sulfide precipitation was not unique to the deposit, and mafic rocks also exhibit strong chargeability. Conductivity anomalies similarly reflect widespread sulfides as well as water-saturated glacial sediments. Mineralogical and magnetic susceptibility data indicate magnetite destruction primarily within the Cu-Au-Mo mineralized area. The magnetic field does not show a corresponding anomaly low but the analytic signal does in areas where the deposit is not covered by postmineralization igneous rocks. The analytic signal shows similar lows over sedimentary rocks outside of the mineralized area, however, and cannot uniquely distinguish the deposit. We find that the intersection of positive chargeability anomalies with analytic signal lows, indicating elevated sulfide concentrations but low magnetite at shallow depths, roughly delineates the deposit where it is covered only by glacial sediments. Neither chargeability highs nor analytic signal lows are present where the deposit is covered by several hundred meters of sedimentary and volcanic rocks, but a 3D resistivity model derived from magnetotelluric data shows a corresponding zone of higher conductivity. Gravity data highlight geologic features within the deposit, including shallow diorite sills that locally contain higher-grade mineralization. The results thus show ways in which an integrated survey approach might be used to distinguish zones of potentially economic mineralization.

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.

scholarly journals Joint Gravity and Seismic Reflection Methods to Characterize the Deep Aquifers in Arid Ain El Beidha Plain (Central Tunisia, North Africa)

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1310
Author(s):  
Hajer Azaiez ◽  
Hakim Gabtni ◽  
Mourad Bédir
Keyword(s):  
Seismic Reflection ◽  
Large Scale ◽  
Seismic Analysis ◽  
Gravity Data ◽  
Geophysical Methods ◽  
Gravity Anomalies ◽  
Integrated Approach ◽  
Central Tunisia ◽  
Deep Aquifers ◽  
Advanced Analysis

Electric resistivity sounding and tomography, as well as electromagnetic sounding, are the classical methods frequently used for hydrogeological studies. In this work, we propose the development and implementation of an original integrated approach using the unconventional hydro–geophysical methods of gravity and seismic reflection for the fast, large–scale characterization of hydrogeological potential using the Ain El Beidha plain (central Tunisia) as an analogue. Extending the values of vintage petroleum seismic reflection profiles and gravity data, in conjunction with available geological and hydrogeological information, we performed an advanced analysis to characterize the geometry of deep tertiary (Oligocene and Eocene) aquifers in this arid area. Residual and tilt angle gravity maps revealed that most gravity anomalies have a short wavelength. The study area was mainly composed of three major areas: the Oued Ben Zitoun and Ain El Beidha basins, which are both related to negative gravity trends corresponding to low–density subsiding depocenters. These basins are separated by an important NE–SW trend called “El Gonna–J. El Mguataa–Kroumet Zemla” gravity high. Evaluation of the superposition of detected lineaments and Euler deconvolution solutions’ maps showed several NE–SW and N–S relay system faults. The 3D density inversion model using a lateral and vertical cutting plane suggested the presence of two different tectonic styles (thin VS thick). Results from the gravity analysis were in concordance with the seismic analysis. The deep Oligocene and Eocene seismic horizons were calibrated to the hydraulic wells and surrounding outcrops. Oligocene and Eocene geological reservoirs appear very fractured and compartmented. The faulting network also plays an important role in enhancing groundwater recharge process of the Oligocene and Eocene aquifers. Finally, generated isochron maps provided an excellent opportunity to develop future comprehensive exploration surveys over smaller and more favorable areas’ sub–basins.

Classifying Copper-Molybdenum-Gold Porphyry Deposit Alteration using Magnetic and Spectral data

2021 ◽  
Author(s):  
Oliver Dixon ◽  
William McCarthy ◽  
Nasser Madani ◽  
Michael Petronis ◽  
Steve McRobbie ◽  
...  
Keyword(s):  
Machine Learning ◽  
Magnetic Susceptibility ◽  
Spectral Data ◽  
Learning Algorithm ◽  
Copper Production ◽  
Magnetic Data ◽  
Machine Learning Algorithm ◽  
Porphyry Deposit ◽  
Remanent Magnetisation ◽  
Magnetic Remanence

<p>Copper is one of the most important critical metal resources needed to achieve carbon neutrality with a projected increase in demand of >300% over the next half century from electronics and renewables.  Porphyry deposits account for most of the global copper production, but the discovery of new reserves is ever more challenging. Machine learning presents an opportunity to cross reference new and traditionally under-utilised data sets with a view to developing quantitative predictive models of hydrothermal alteration zones to guide new, ambitious exploration programs.</p><p>The aim of this study is to demonstrate a new alteration classification scheme driven by quantitative magnetic and spectral data to feed a machine learning algorithm. The benefits of an alteration model based on quantitative data rather than subjective observations by geologists, are that there is no bias in the data collected, the arising model is quantifiable and therefore easy to model and the process be fully automated. Ultimately, this approach aids more detailed exploration and mine modelling, in turn, reducing the extraction process carbon footprint and more effectively identifying new deposits.</p><p>Presented here are magnetic susceptibility and shortwave infrared (SWIR) data collected from the KazMinerals plc. owned Aktogay Cu-Mo giant porphyry deposit, eastern Kazakhstan, which has a throughput of 30Mtpa of ore. These data are cross referenced using a newly developed machine learning algorithm. Generated autonomously, our results reveal twelve statistically and geologically significant clusters that define a new alteration classification for porphyry style mineralisation. Results are entirely non-subjective, reproducible, quantitative and modellable.</p><p>Importantly, magnetic susceptibility measurements improve the algorithm’s ability to identify clusters by between 29-36%; enhancing the sophistication of the included magnetic data promises to yield substantially better statistical results. Magnetic remanence data are therefore being complied on representative samples from each of the twelve identified clusters, including hysteresis, isothermal remanent magnetisation (IRM) acquisition, FORC measurements, natural remanent magnetisation (NRM) and anhysteretic remanent magnetisation (ARM). Through collaboration with industry partners, we aim to develop an automated means of collecting these magnetic remanence data to accompany the machine learning algorithm.</p>

scholarly journals PHYSICAL-MECHANICAL PROPERTIES OF METAVOLCANIC ROCKS OF THE MOUNTAIN CRIMEA

2018 ◽  
Vol 13 (4-5) ◽  
pp. 36-51
Author(s):  
J. V. Frolova ◽  
V. V. Ladygin ◽  
E. M. Spiridonov ◽  
G. N. Ovsyannikov
Keyword(s):  
Mechanical Properties ◽  
Magnetic Susceptibility ◽  
Volcanic Rocks ◽  
Low Grade ◽  
Secondary Mineral ◽  
Grade Metamorphism ◽  
Clastic Rocks ◽  
Metavolcanic Rocks ◽  
Physical Density ◽  
Characteristic Values

The article considers the petrogenetic features of the volcanogenic rocks of the Middle Jurassic age of the Mountain Crimea and analyzes their influence on physical (density, porosity, water absorption, and magnetic susceptibility) and physical-mechanical properties (strength, modulus of elasticity, and Poisson's ratio). Among volcanogenic strata there are subvolcanic, effusive and volcanogenic-clastic rocks. All volcanic rocks were altered under the influence of the regional low-grade metamorphism of the zeolite and prehnite-pumpellyite facies, which resulted in a greenstone appearance. Among the secondary mineral the most common are albite, chlorite, quartz, adularia, sericite, calcite, pumpellyite, prenite, zeolites, epidote, sphene, and clay minerals. It is shown that low-grade metamorphism is characterized by heterogenious transformations: there are both slightly modified, practically fresh differences, and fully altered rocks. Tuffs are usually altered to a greater extent than effusive and subvolcanic rocks. In general, effusive and volcanogenic-clastic rocks differ markedly in their physicalmechanical properties, which is due to the peculiarities of their formation: the former are substantially more dense and stronger, less porous and compressible. However, these differences are leveled as a result of intensive changes in mineral composition and porosity in the process of low-grade metamorphism. The most characteristic values of metavolcanite properties were revealed. It is shown that among all studied parameters, the magnetic susceptibility most clearly correlates with the degree of rocks alteration.

scholarly journals Geology and geophysics at the archeological park of Vulci (central Italy)

2014 ◽  
Vol 57 (1) ◽  
Author(s):  
Marco Marchetti ◽  
Vincenzo Sapia ◽  
Adriano Garello ◽  
Donatella De Rita ◽  
Alessandra Venuti
Keyword(s):  
Electrical Resistivity ◽  
Magnetic Susceptibility ◽  
Cultural Heritage ◽  
Central Italy ◽  
Geophysical Methods ◽  
Archaeological Sites ◽  
Local Authorities ◽  
Resistivity Tomography ◽  
Geological Information ◽  
Geological Map

<p>The Vulci archeological site was object of interest by the Soprintendenza ai beni culturali dell’Etruria meridionale (Italian government department responsible for southern Etruria’s cultural heritage) since the beginning of the 20th century. In 2001, the Ministero dei Beni Culturali (Italian ministry of cultural heritage) along with the local authorities, opened a natural-archeological park. In this area, it lies most of the ancient Etruscan city of Velch (today known by its Latin name, Vulci) including the Osteria Necropolis that is the object of this study. Recently, new archaeological excavations were made and the local authorities needed major geological information about the volcanic lithotypes where the Etruscans used to build their necropolis. The aim of this study is to define the geological and geophysical characteristics of the rock lithotypes present in the Vulci park. For this purpose, a geological map of the area (1:10000) has been realized. Moreover, two different geophysical methods were applied: measurements of magnetic susceptibility and electrical resistivity tomography. Magnetic susceptibility analyses clearly identify magnetic contrasts between different lithotypes; the characteristics of the pyroclastic flow that originated the Sorano unit 2 and its vertical facies variations are well recorded by this parameter that along with lithostratigraphic observations provides information about the depositional conditions. Two electrical resistivity tomographies were performed, which show the Sorano unit 2 thickness to be of c. 7 m with resistivity values ranging from 200 to 400 Ω·m. This kind of multidisciplinary approach resulted to be suitable to study this type of archaeological sites, revealing that areas characterized by a relevant thickness and wide areal extension of volcanic lithotypes can be a potential site where Etruscans might have excavated their necropolis.</p>

Constructing piecewise-constant models in multidimensional minimum-structure inversions

Geophysics ◽  
2008 ◽  
Vol 73 (1) ◽  
pp. K1-K9 ◽  
Author(s):  
Colin G. Farquharson
Keyword(s):  
Gravity Data ◽  
Model Structure ◽  
Iteratively Reweighted Least Squares ◽  
3D Inversion ◽  
Magnetotelluric Data ◽  
2D Inversion ◽  
Piecewise Constant ◽  
Text Type ◽  
Current Minimum ◽  
Modified Algorithm

A modification of the typical minimum-structure inver-sion algorithm is presented that generates blocky, piecewise-constant earth models. Such models are often more consistent with our real or perceived knowledge of the subsurface than the fuzzy, smeared-out models produced by current minimum-structure inversions. The modified algorithm uses [Formula: see text]-type measures in the measure of model structure instead of the traditional sum-of-squares, or [Formula: see text], measure. An iteratively reweighted least-squares procedure is used to deal with the nonlinearity introduced by the non-[Formula: see text] measure. Also, and of note here, diagonal finite differences are included in the measure of model structure. This enables dipping interfaces to be formed. The modified algorithm retains the benefits of the minimum-structure style of inversion — namely, reliability, robustness, and minimal artifacts in the constructed model. Two examples are given: the 2D inversion of synthetic magnetotelluric data and the 3D inversion of gravity data from the Ovoid deposit, Voisey’s Bay, Labrador.

Temperature, strain rates, and rheology: the key parameters controling strength variations in the Australian lithosphere

2020 ◽  
Author(s):  
Magdala Tesauro ◽  
Mikhail Kaban ◽  
Alexey Petrunin ◽  
Alan Aitken
Keyword(s):  
Heat Flow ◽  
Seismic Tomography ◽  
Seismic Velocity ◽  
Gravity Data ◽  
Geophysical Methods ◽  
The Other ◽  
Crust And Upper Mantle ◽  
Large Variability ◽  
Other Hand ◽  
Australian Plate

&lt;p&gt;The Australian plate is composed of tectonic features showing progression of the age from dominantly Phanerozoic in the east, Proterozoic in the centre, and Archean in the west. These tectonic structures have been investigated in the last three decades using a variety of geophysical methods, but it is still a matter of debates of how temperature and strength are distributed within the lithosphere. We construct a thermal crustal model assuming steady state variations and using surface heat flow data, provided by regional and global database, and heat generation values, calculated from existing empirical relations with seismic velocity variations, which are provided by AusREM seismic tomography model. The lowest crustal temperatures are observed in the eastern part of the WAC and the Officer basin, while Central and South Australia are regions with anomalously elevated heat flow values and temperatures caused by high heat production in the crustal rocks. On the other hand, the mantle temperatures, estimated in a previous study, applying a joint interpretation of the seismic tomography and gravity data, show that the Precambrian West and North Australian Craton (WAC and NAC) are characterized by thick and relatively cold lithosphere that has depleted composition (Mg# &gt; 90). The depletion is stronger in the older WAC than the younger NAC. Substantially hotter and less dense lithosphere is seen fringing the eastern and southeastern margin of the continent. Both crustal and mantle thermal models are used as input for the lithospheric strength calculation. Another input parameter is the crustal rheology, which has been determined based on the seismic velocity distribution, assuming that low (high) velocities reflect more sialic (mafic) compositions and thus weaker (stiffer) rheologies. Furthermore, we use strain rate values obtained from a global mantle flow model constrained by seismic and gravity data. The combination of the values of the different parameters produce a large variability of the rigidity of the plate within the cratonic areas, reflecting the long tectonic history of the Australian plate. The sharp lateral strength variations are coincident with intraplate earthquakes location. The strength variations in the crust and upper mantle is also not uniformly distributed: In the Archean WAC most of the strength is concentrated in the mantle, while the Proterozoic Officer basin shows the largest values of the crustal strength. On the other hand, the younger eastern terranes are uniformly weak, due to the high temperatures.&lt;/p&gt;

Unsupervised delineation of landfill geometries based on geophysical imaging results

2020 ◽  
Author(s):  
Matthias Steiner ◽  
Werner Chwatal ◽  
Andreas Freudenthaler ◽  
Adrian Flores Orozco
Keyword(s):  
Geophysical Methods ◽  
Subjective Perception ◽  
Random Walker ◽  
Upper Austria ◽  
Base Points ◽  
Imaging Results ◽  
Refraction Seismic ◽  
High Gradients ◽  
Geophysical Imaging

&lt;p&gt; Environmental aspects and the growing interest in the economical exploitation of landfills urges the need for cost-efficient workflows providing information with high spatial resolution. Especially for landfill mining, a detailed characterization of the landfill geometry and the waste composition is critical to assess the economic potential. Geophysical methods have proven to fulfill these requirements since they permit to collect data in a quasi-continuous manner. However, the subjective perception of the geophysical imaging results might bias the interpretation, e.g. the characterization of the landfill boundaries and the estimation of waste volumes. To overcome such shortcomings, we present here an unsupervised method for the post-processing of geophysical imaging to identify subsurface interfaces associated to e.g. landfill geometries, waste variation etc. Our methodology is applicable for results obtained with a single method, or the combination of different geophysical methods, e.g. refraction seismic tomography (RST), electrical resistivity tomography (ERT) or induced polarization (IP). Assuming strong contrasts in the retrieved physical properties associated to interfaces, our method computes the magnitude of the gradient vector for each point in the resolved model. In the next step, a random walker algorithm converts the gradient magnitude image into a binary image permitting to obtain the contours of subsurface regions characterized by high gradients. Originating from the centroid for such a region further base points are determined and used in the final step to compute shape and location of the corresponding interface. To demonstrate the applicability of our method we present here results obtained for a landfill located in Upper Austria, where RST, ERT and IP data were collected along several transects. Our results demonstrate that the method proposed here has the potential to enhance geophysical investigations of landfills by permitting an improved interpretation of the imaging results, as required, for instance to estimate waste volume.&lt;/p&gt;

Combining ExoMars’ Ma_MISS and Drill data

2020 ◽  
Author(s):  
Alessandro Frigeri ◽  
Maria Cristina De Sanctis ◽  
Francesca Altieri ◽  
Simone De Angelis ◽  
Marco Ferrari ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Water Content ◽  
Large Scale ◽  
Mechanical Response ◽  
European Space Agency ◽  
Volcanic Rocks ◽  
Space Agency ◽  
Geophysical Imaging

&lt;p&gt;The ExoMars Rover and Surface Platform planned for launch in 2022 is a large international cooperation between the European Space Agency and Roscosmos with a scientific contribution from NASA.&amp;#160; Thales Alenia Space is the ExoMars mission industrial prime contractor.&amp;#160;&lt;/p&gt; &lt;p&gt;Besides sensors and instruments characterizing the surface at large scale, the ExoMars&amp;#8217; rover Rosalind Franklin payload features some experiments devoted specifically to the characterization of the first few meters of the Martian subsurface. These experiments are particularly critical for the main ExoMars objective of detecting traces of present or past life forms on Mars, which may have been preserved within the shallow Martian underground [1].&lt;/p&gt; &lt;p&gt;Rosalind Franklin will be able to perform both non-invasive geophysical imaging of the underground [2] and subsurface &lt;em&gt;in situ&lt;/em&gt; measurements thanks to the Drill unit installed on the rover. The Drill has been developed by Leonardo and its purposes are 1) to collect core samples to be analyzed in the Analytical Laboratory Drawer (ALD) onboard the Rover and 2) to drive the miniaturized spectrometer Ma_MISS within the borehole.&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt; &lt;p&gt;Ma_MISS (Mars Multispectral Imager for Subsurface Studies, [3]) will collect mineralogic measurements from the rocks exposed into the borehole created by the Drill with a spatial resolution of 120 &amp;#956;m down to 2 meters into the Martian subsurface.&lt;/p&gt; &lt;p&gt;Rocks are composed of grains of minerals, and their reaction to an applied stress is related to the mechanical behavior of the minerals that compose the rock itself. The mechanical properties of a mineral depend mainly on the strength of the chemical bonds, the orientation of crystals, and the number of impurities in the crystal lattice.&lt;/p&gt; &lt;p&gt;In this context, the integration of Ma_MISS measurements and drill telemetry are of great importance.&amp;#160; The mechanical properties of rocks coupled with their mineralogic composition provide a rich source of information to characterize the nature of rocks being explored by ExoMars rover&amp;#8217;s drilling activity.&lt;/p&gt; &lt;p&gt;Within our study, we are starting to collect telemetry recorded during the Drill unit tests on several samples ranging from sedimentary to volcanic rocks with varying degrees of weathering and water content.&amp;#160; In this first phase of the study, we focused our attention on the variation of torque and penetration speed between different samples, which have been found to be indicative of a particular type of rock or group of rocks and their water content.&amp;#160;&amp;#160;&lt;/p&gt; &lt;p&gt;We are planning to analyze the same rocks with the Ma_MISS breadboard creating the link between the mineralogy and the mechanical response of the Drill.&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt; &lt;p&gt;This will put the base for a more comprehensive and rich characterization of the &lt;em&gt;in situ&lt;/em&gt; subsurface observation by Rosalind Franklin planned at Oxia Planum, Mars in 2023.&amp;#160;&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Acknowledgments: &lt;/strong&gt;We thank the European Space Agency (ESA) for developing the ExoMars Project, ROSCOSMOS and Thales Alenia Space for rover development, and Italian Space Agency (ASI) for funding the Ma_MISS experiment (ASI-INAF contract n.2017-48-H.0 for ExoMars MA_MISS phase E/science).&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;[1] Vago et al., 2017. Astrobiology, 17 6-7. [2] Ciarletti et al., 2017. Astrobiology, 17 6-7. [3] De Sanctis et al., 2017. Astrobiology, 17 6-7.&lt;/p&gt;

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