Inversion of airborne geophysics over the DO-27/DO-18 kimberlites — Part 3: Induced polarization

2017 ◽  
Vol 5 (3) ◽  
pp. T327-T340 ◽  
Author(s):  
Seogi Kang ◽  
Dominique Fournier ◽  
Douglas W. Oldenburg
Keyword(s):  
Time Domain ◽  
Geophysical Methods ◽  
Induced Polarization ◽  
Three Dimensions ◽  
Data Set ◽  
Time Constants ◽  
Airborne Geophysics ◽  
Petrophysical Model ◽  
Time Domain Electromagnetic ◽  
Conductivity Models

The geologically distinct DO-27 and DO-18 kimberlites, often called the Tli Kwi Cho (TKC) kimberlites, have been used as a testbed for airborne geophysical methods applied to kimberlite exploration. This paper focuses on extracting chargeability information from time-domain electromagnetic (TEM) data. Three different TEM surveys, having similar coincident-loop geometry, have been carried out over TKC. Each records negative transients over the main kimberlite units and this is a signature of induced polarization (IP) effects. By applying a TEM-IP inversion workflow to a versatile time domain EM (VTEM) data set we decouple the EM and IP responses in the observations and then recover 3D pseudo-chargeability models at multiple times. A subsequent analysis is used to recover Cole-Cole parameters. Our models demonstrate that both DO-18 and DO-27 pipes are chargeable, but they have different Cole-Cole time constants: 110 and 1160 μs, respectively. At DO-27, we also distinguish between two adjacent kimberlite units based on their respective Cole-Cole time constants. Our chargeability models are combined with the density, magnetic susceptibility and conductivity models to build a 3D petrophysical model of TKC using only information obtained from airborne geophysics. Comparison of this final petrophysical model to a 3D geological model derived from the extensive drilling program demonstrates that we can characterize the three main kimberlite units at TKC: HK, VK, and PK in three dimensions by using airborne geophysics.

Three dimensional inversion of multisource time domain electromagnetic data

Geophysics ◽  
2013 ◽  
Vol 78 (1) ◽  
pp. E47-E57 ◽  
Author(s):  
Douglas W. Oldenburg ◽  
Eldad Haber ◽  
Roman Shekhtman
Keyword(s):  
Time Domain ◽  
Maxwell’S Equations ◽  
High Performance ◽  
Maxwell's Equations ◽  
Sulfide Deposit ◽  
3D Inversion ◽  
Data Set ◽  
Electromagnetic Data ◽  
Backward Euler ◽  
Time Domain Electromagnetic

We present a 3D inversion methodology for multisource time-domain electromagnetic data. The forward model consists of Maxwell’s equations in time where the permeability is fixed but electrical conductivity can be highly discontinuous. The goal of the inversion is to recover the conductivity-given measurements of the electric and/or magnetic fields. The availability of matrix-factorization software and high-performance computing has allowed us to solve the 3D time domain EM problem using direct solvers. This is particularly advantageous when data from many transmitters and over many decades are available. We first formulate Maxwell’s equations in terms of the magnetic field, [Formula: see text]. The problem is then discretized using a finite volume technique in space and backward Euler in time. The forward operator is symmetric positive definite and a Cholesky decomposition can be performed with the work distributed over an array of processors. The forward modeling is quickly carried out using the factored operator. Time savings are considerable and they make 3D inversion of large ground or airborne data sets feasible. This is illustrated by using synthetic examples and by inverting a multisource UTEM field data set acquired at San Nicolás, which is a massive sulfide deposit in Mexico.

Inductive induced polarization effect in heliborne time-domain electromagnetic data for uranium exploration, northern part of Cuddapah Basin, India

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. B109-B120 ◽  
Author(s):  
Veldi Ramesh Babu ◽  
Indrajit Patra ◽  
Shailesh Tripathi ◽  
Sridhar Muthyala ◽  
Anand K. Chaturvedi
Keyword(s):  
Time Domain ◽  
Induced Polarization ◽  
Uranium Mineralization ◽  
Cuddapah Basin ◽  
Text Data ◽  
Argillic Alteration ◽  
Uranium Exploration ◽  
Time Domain Electromagnetic ◽  
Text Response ◽  
Lithologic Unit

The Peddagattu, Lambapur, Chitrial and Koppunuru uranium deposits along the northern margins of the Cuddapah Basin are confined to the middle Proterozoic unconformity interface between Archean basement granites and the overlying resistive quartzites. Negative transients observed in the coincident loop heliborne time-domain electromagnetic (HTEM) data over these deposits (occurring in outliers) are believed to be due to thick polarizable conductive zones occurring along the unconformity. Similar negative HTEM responses are recorded over the Gorukunta Tanda outlier. A ground spectral induced polarization (SIP) survey conducted over the outlier and ground geologic observations indicated an altered basement/regolith with thickness up to 5 m below 20–30 m thick quartzite. Interpretation of Cole-Cole parameters computed from the SIP data indicated a change in the dispersion. These Cole-Cole parameters were used in modeling negative HTEM data assuming a polarizable plate placed in a layered earth at a depth of approximately 50 m using the CSIRO LeroiAir program. A negative [Formula: see text] response in the late channels indicated that the negatives can be explained in terms of inductive induced polarization effects. Modeling of HTEM [Formula: see text] data for the profile through the Lambapur uranium deposit and the Gorukunta Tanda reveals the presence of a polarizable lithologic unit at a depth of approximately 40 m. This unit is interpreted as an argillic alteration of basement, with the presence of clay and/or disseminated sulfides as evidenced from the core extracted from the boreholes at depths below the highly resistive quartzite. Uranium mineralization is closely associated with altered basement and sulfides along the unconformity where the distinct negative electromagnetic (EM) signature is recorded. Furthermore, there exists a good correlation between the uranium mineralization grade and the thickness versus the averaged late-channel negative HTEM response over the known deposits. The negative EM response helped in locating the new target areas for uranium exploration.

scholarly journals Modeling induced polarization effects in helicopter time domain electromagnetic data: Synthetic case studies

Geophysics ◽  
2017 ◽  
Vol 82 (2) ◽  
pp. E31-E50 ◽  
Author(s):  
Andrea Viezzoli ◽  
Vladislav Kaminski ◽  
Gianluca Fiandaca
Keyword(s):  
Time Domain ◽  
A Priori ◽  
Induced Polarization ◽  
Earth Model ◽  
Model Parameters ◽  
Model Approximation ◽  
Generic Models ◽  
Time Domain Electromagnetic ◽  
Airborne Electromagnetic ◽  
Priori Information

We have developed a synthetic multiparametric modeling and inversion exercise undertaken to study the robustness of inverting airborne time-domain electromagnetic (TDEM) data to extract Cole-Cole parameters. The following issues were addressed: nonuniqueness, ill posedness, dependency on manual processing and the effect of constraints, and a priori information. We have used a 1D layered earth model approximation and lateral constraints. Synthetic simulations were performed for several models and the corresponding Cole-Cole parameters. The possibility to recover these models by means of laterally constrained multiparametric inversion was evaluated, including recovery of chargeability distributions from shallow and deep targets based on analysis of induced polarization (IP) effects, simulated in airborne TDEM data. Different scenarios were studied, including chargeable targets associated with the conductive and resistive environments. In particular, four generic models were considered for the exercise: a sulfide model, a kimberlite model, and two generic models focusing on the depth of investigation. Our study indicated that, in cases when relaxation time ([Formula: see text]) values are in the range to which the airborne electromagnetic is most sensitive (e.g., approximately 1 ms), it is possible to recover deep chargeable targets (to depths more than 130 m) in association with high electrical conductivity and in resistive environments. Furthermore, it was found that the recovery of a deep conductor, masked by a shallower chargeable target, became possible only when full Cole-Cole modeling was used in the inversion. Lateral constraints improved the recoverability of model parameters. Finally, modeling IP effects increased the accuracy of recovered electrical resistivity models.

scholarly journals tTEM20AAR: a benchmark geophysical data set for unconsolidated fluvioglacial sediments

2021 ◽  
Vol 13 (6) ◽  
pp. 2743-2752
Author(s):  
Alexis Neven ◽  
Pradip Kumar Maurya ◽  
Anders Vest Christiansen ◽  
Philippe Renard
Keyword(s):  
Time Domain ◽  
Reliable Method ◽  
Geophysical Inversion ◽  
Quaternary Deposits ◽  
Data Set ◽  
Time Domain Electromagnetic ◽  
Inversion Techniques ◽  
Alpine Environments ◽  
The Magnetic Field ◽  
Depth Of Investigation

Abstract. Quaternary deposits are complex and heterogeneous. They contain some of the most abundant and extensively used aquifers. In order to improve the knowledge of the spatial heterogeneity of such deposits, we acquired a large (1500 ha) and dense (20 m spacing) time domain electromagnetic (TDEM) data set in the upper Aare Valley, Switzerland (available at https://doi.org/10.5281/zenodo.4269887; Neven et al., 2020). TDEM is a fast and reliable method to measure the magnetic field directly related to the resistivity of the underground. In this paper, we present the inverted resistivity models derived from this acquisition. The depth of investigation ranges between 40 and 120 m, with an average data residual contained in the standard deviation of the data. These data can be used for many different purposes: from sedimentological interpretation of quaternary environments in alpine environments, geological and hydrogeological modeling, to benchmarking geophysical inversion techniques.

Modeling induced polarization effects in helicopter time-domain electromagnetic data: Field case studies

Geophysics ◽  
2017 ◽  
Vol 82 (2) ◽  
pp. B49-B61 ◽  
Author(s):  
Vladislav Kaminski ◽  
Andrea Viezzoli
Keyword(s):  
Time Domain ◽  
Signal To Noise Ratio ◽  
Mineral Exploration ◽  
Induced Polarization ◽  
Electromagnetic Transients ◽  
Additional Information ◽  
Time Domain Electromagnetic ◽  
Airborne Electromagnetic ◽  
Cole Model ◽  
Inversion Techniques

Induced polarization (IP) effects are becoming more evident in time-domain helicopter airborne electromagnetic (AEM) data thanks to advances in instrumentation, mainly due to improvements in the signal-to-noise ratio and hence better data quality. Although the IP effects are often manifested as negative receiver voltage values, which are easy to detect, in some cases, IP effects can distort recovered transients in other ways so they may be less obvious and require careful data analysis and processing. These effects represent a challenge for modeling and inversion of the AEM data. For proper modeling of electromagnetic transients, the chargeability of the subsurface and other parameters describing the dispersion also need to be taken into consideration. We use the Cole-Cole model to characterize the dispersion and for modeling of the IP effects in field AEM data, collected by different airborne systems over different geologies and exploration targets, including examples from diamond, gold, and base metal exploration. We determined how multiparametric inversion techniques can simultaneously recover all four Cole-Cole parameters, including resistivity [Formula: see text], chargeability [Formula: see text], relaxation time [Formula: see text], and frequency parameter [Formula: see text]. The results obtained are in good agreement with the ancillary information available. Interpretation of the IP effects in AEM data is therefore seen by the authors as providing corrected electrical resistivity distributions, as well as additional information that could assist in mineral exploration.

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