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Using constrained inversion of gravity and magnetic field to produce a 3D litho-prediction model

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doi: 10.1111/1365-2478.12484
Authors:Mahmoodi, Omid; Smith, Richard S.; Spicer, Bill
Author Affiliations:Primary:
Laurentian University, Department of Earth Sciences, Sudbury, ON, Canada
KGHM International, Canada
Volume Title:Geophysical Prospecting
Source:Geophysical Prospecting, 65(6), p.1662-1679. Publisher: Blackwell on behalf of the European Association of Geoscientists & Engineers (EAGE), Houten, Netherlands. ISSN: 0016-8025
Publication Date:2017
Note:In English. 47 refs.; illus., incl. 2 tables
Summary:Geologically constrained inversion of gravity and magnetic field data of the Victoria property (located in Sudbury, Canada) was undertaken in order to update the present three-dimensional geological model. The initial and reference model was constructed based on geological information from over 950 drillholes to constrain the inversion. In addition, downhole density and magnetic susceptibility measured in six holes were statistically analysed to derive lower and upper bounds on the physical properties attributed to the lithological units in the reference model. Constrained inversion of the ground gravity and the airborne magnetic data collected at the Victoria property were performed using GRAV3D and MAG3D, respectively. A neural network was trained to predict lithological units from the physical properties measured in six holes. Then, the trained network was applied on the three-dimensional distribution of physical properties derived from the inversion models to produce a three-dimensional litho-prediction model. Some of the features evident in the lithological model are remnants of the constraints, where the data did not demand a significant change in the model from the initial constraining model (e.g., the thin pair of diabase dykes). However, some important changes away from the initial model are evident; for example, a larger body was predicted for quartz diorite, which may be related to the prospective offset dykes; a new zone was predicted as sulfide, which may represent potential mineralisation; and a geophysical subcategory of metabasalt was identified with high magnetic susceptibility and high density. The litho-prediction model agrees with the geological expectation for the three-dimensional structure at Victoria and is consistent with the geophysical data, which results in a more holistic understanding of the subsurface lithology. Abstract Copyright (2017), European Association of Geoscientists & Engineers.
Subjects:Airborne methods; Boreholes; Deep-seated structures; Density; Diabase; Dikes; Diorites; Geophysical methods; Geophysical surveys; Gravity field; Gravity methods; Igneous rocks; Intrusions; Inverse problem; Magnetic methods; Magnetic properties; Magnetic susceptibility; Neural networks; Paleomagnetism; Physical properties; Plutonic rocks; Prediction; Quartz diorites; Surveys; Three-dimensional models; Canada; Eastern Canada; Ontario; Sudbury District Ontario; Sudbury Structure
Coordinates:N462500 N465000 W0804500 W0814000
Record ID:809535-17
Copyright Information:GeoRef, Copyright 2021 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom
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