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Identification of intrusive lithologies in volcanic terrains in British Columbia by machine learning using random forests: the value of using a soft classifier

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posted on 2023-05-20, 18:34 authored by Kuhn, S, Matthew CracknellMatthew Cracknell, Anya ReadingAnya Reading, Sykora, S
Identifying the location of intrusions is a key component in exploration for porphyry Cu ± Mo ± Au deposits. In typical porphyry terrains, in the absence of outcrop, intrusions can be difficult to discriminate from the compositionally similar volcanic and volcanoclastic sedimentary rocks in which they are emplaced. The ability to produce lithological maps at an early exploration stage can significantly reduce costs by assisting in planning and prioritization of detailed mapping and sampling. Additionally, a data-driven strategy provides opportunity for the discovery of intrusions not identified during conventional mapping and interpretation. We used Random Forests (RF), a supervised machine learning algorithm, to classify rock types throughout the Kliyul porphyry prospect in British Columbia, Canada. Rock types determined at geochemical sampling sites were used as training data. Airborne magnetic and radiometric data, geochemistry, and topographic data were used in classification. Results were validated using First Quantum Minerals’ geologic map, which includes additional detail from targeted location and transect mapping. The petrophysical and compositional similarity of rock types resulted in a noisy classification. Intrusions, particularly the more discrete, were inconsistently predicted, likely due to their limited extent relative to data sampling intervals. Closer examination of class membership probabilities (CMPs) identified locations where the probability of an intrusion being present was elevated significantly above the background. Indeed, a large proportion of mapped intrusions correspond to areas of elevated probability and importantly, areas were highlighted as potential intrusions that were not identified in geologic mapping. The RF classification produced a reasonable lithological map, if lacking in resolution, but more significantly, great benefit comes from the insights drawn from the RF CMPs. Mapping the spatial distribution of elevated intrusion CMP, a soft classifier approach, produced a map product that can target intrusions and prioritize detailed mapping for mineral exploration.

History

Publication title

Geophysics

Volume

85

Issue

6

Pagination

B249-B258

ISSN

0016-8033

Department/School

School of Natural Sciences

Publisher

Soc Exploration Geophysicists

Place of publication

8801 S Yale St, Tulsa, USA, Ok, 74137

Rights statement

© 2020 The Authors. Published by the Society of Exploration Geophysicists. All article is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) License (CC BY). See http://creativecommons.org/licenses/by/4.0/.

Repository Status

  • Open

Socio-economic Objectives

Copper ore exploration

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