Vlad Kaminski

Improving modelling of AEM data affected by IP, two case studies

Modelling IP parameters, including dispersive resistivity, from AEM data showing clear IP effects is possible. Using the spatially constrained inversion approach, with forward response that account for the full Cole and Cole model, we recover realistic chargeability and “IP corrected “resistivities sections from two VTEM datasets, from Canada and Australia. The “IP corrected” resistivity sections often show better agreement with known geological features, while improving dramatically the data fit, with respect to those obtained without IP modelling. While the majority of the IP effect originate from shallow chargeable layers, there seems to be some positive correlation between an isolated deep chargeable anomaly and known base metal deposit location.

Using helicopter electromagnetic "HEM… surveys to identify potential hazards at coal-waste impoundments: Examples from West Virginia

We have used 14 multifrequency helicopter-borne electromagnetic HEM surveys to determine the internal structure and integrity of mine-impoundment structures in West Virginia, U.S.A. — the first time such technology has been applied in this way and apparently well suited for such activities. The HEM surveys identified areas of concern in each of the impoundments investigated. In most cases, these were areas where filtrate was emerging high on the downstream embankment and represented an erosion risk. Of greater concern, the HEM survey identified thick bodies of slurry that remained unconsolidated and were buried deep beneath the embankment’s crest of some impoundments. Ground confirmation activities indicated that HEM survey interpretations provided an accurate representation of the conductivity distribution within coal-waste impoundments. We then interpreted the conductivity/depth images from the HEM surveys to provide a snapshot of hydrologic conditions that existed within the impoundment at the time of the survey. Resistivity profiles were obtained at the inactive impoundment along segments of flight lines from the HEM survey. HEM and resistivity surveys detected a conductive layer at a depth of about 7 m that was interpreted to be unconsolidated coal slurry. The methods also detected conductive bodies at a depth of about 26 m that were interpreted to be flooded mine works. Resistivity surveys from these segments corroborated HEM data, thereby providing independent confirmation of the HEM data and its processing. The resistivity and HEM surveys indicated a resistive surface layer where the coarse coal refuse was placed. Beneath the resistive surface layer is a conductive layer of unconsolidated or partially consolidated coal slurry. These highly loaded bodies of unconsolidated slurry are susceptible to solifluction, which can threaten embankment stability. Underground mine workings were identified in the HEM data from one impoundment.

Joint 3D inversion of muon tomography and gravity data

Cosmic rays of muons are a natural, abundant, highlypenetrating particle flux that continuously shower the earth’s surface and penetrate hundreds of meters underground. Muons are attenuated as they pass through matter so that flux below ground is dependent on the total integrated mass traversed by the particles. Recently, sensors have been placed in existing tunnels to observe the muon flux for brown-field mining applications. We have developed an algorithm to invert muon tomography data, along with gravity data, to recover a 3D distribution of density contrast. The difference in physics between muon ray-paths and gravity data provides a unique insight into the subsurface.

Joint Interpretation of AEM and Aeromagnetic Data Acquired over the Drybones Kimberlite, NWT (Canada)

A time domain electromagnetic and a magnetic surveys were conducted by a VTEM system in 2005 over Drybones kimberlite (Canada). The EM data, showing IP effect, were inverted using the modified AarhusINV code with Cole-Cole modeling while for the magnetic data we used a new inversion algorithm considering vertical profiles (soundings) of data at different altitudes. The comparison of the inverse models, i.e. susceptibility, resistivity and chargeability, was performed along a profile for which a geological cross-section has been drawn basing on drilling information. The results revealed the different sensitivity of methods with respect to the geological structures at Drybones bay. However we show how the cooperation of the TDEM and aeromagnetic data in the studied area can lead to a better understand of the structures at depth.

Joint inversions of two VTEM surveys using quasi-3D TDEM and 3D magnetic inversion algorithms

In the current paper, we present results of a joint quasi-three-dimensional (quasi-3D) inversion of two versatile time domain electromagnetic (VTEM) datasets, as well as a joint 3D inversion of associated aeromagnetic datasets, from two surveys flown six years apart from one another (2007 and 2013) over a volcanogenic massive sulphide gold (VMS-Au) prospect in northern Ontario, Canada. The time domain electromagnetic (TDEM) data were inverted jointly using the spatially constrained inversion (SCI) approach. In order to increase the coherency in the model space, a calibration parameter was added. This was followed by a joint inversion of the total magnetic intensity (TMI) data extracted from the two surveys. The results of the inversions have been studied and matched with the known geology, adding some new valuable information to the ongoing mineral exploration initiative. We present the results of a joint quasi-3D inversion of two VTEM datasets, flown over a VMS-Au prospect in northern Ontario, Canada, six years apart from one another. The TDEM data were inverted jointly using the spatially constrained inversion (SCI) approach and verified against known geology.

Using ERA Low Frequency E-field Profiling And UBC 3D Frequency-domain Inversion to Delineate And Discover a Mineralized Zone In Porcupine District, Ontario, Canada.

A low-frequency resistivity survey using ERA electrical profiling (middle gradient array) has been completed over a nickel prospect in Porcupine District, Ontario, Canada. The results of this EM-Resistivity were used to calculate the apparent resistivity and were further inverted using UBCGIF 3D Frequency Domain Inversion Software, EH3DInv. The results of the inversion have shown the anomalous distribution of electrical properties, consistent with a known geological contact between metavolcanic rocks and an ultramafic pluton. The conductive zone has been interpreted to be located in the interval between 70 and 120 meters.