Exploration Geophysics Exploration Geophysics Society
Journal of the Australian Society of Exploration Geophysicists
RESEARCH ARTICLE

Relationship between bulk mineralogy and induced polarisation responses in iron oxide-copper-gold and porphyry copper mineralisation, northern Chile

Sebastián Aguilef 1 6 Jaime Araya Vargas 2 Gonzalo Yáñez 3 4 5
+ Author Affiliations
- Author Affiliations

1 Servicio Nacional de Geología y Minería (SERNAGEOMIN), Santa María 0104, Santiago 7520405, Chile.

2 GFZ German Research Centre for Geosciences, Telegrafenberg 14473, Potsdam, Germany.

3 Departamento de Ingeniería Estructural y Geotécnica, Pontificia Universidad Católica de Chile, Avda. Vicuña Mackenna 4860, Santiago 7820436, Chile.

4 Millennium Nucleus for Metals Tracing along Subduction (NMTM, 130065), Plaza Ercilla 803, Santiago 8370450, Chile.

5 GEGA, Andean Geothermal Center of Excellence (15090013), Plaza Ercilla 803, Santiago 8370450, Chile.

6 Corresponding author. Email: sebastian.aguilef@sernageomin.cl

Exploration Geophysics - https://doi.org/10.1071/EG15077
Submitted: 11 August 2015  Accepted: 13 June 2016   Published online: 25 July 2016

Abstract

We have studied the correlation between bulk mineralogy and induced polarisation (IP) responses in iron oxide-copper-gold (IOCG) and porphyry copper mineralised systems in northern Chile. Twelve drillholes (> 5000 m) that intersect IP sections were mapped and sampled to obtain geological characteristics and to quantify metallic minerals concentration in ore bodies. Geological parameters and modelled geophysical responses (electrical chargeability and resistivity) were compared using qualitative and quantitative criteria.

Data analyses show that bulk sulphide concentration is the major factor that explains variations in the IP effect, even for IOCG ore bodies associated with magnetite mineralisation (up to 5 vol. %). Electrical chargeability exhibits a direct, but non-linear proportionality with sulphides content, while no clear trend is observed when chargeability is compared to magnetite concentration. In drillhole segments where macroscopic sulphides were not mapped, but IP results suggested high chargeabilities, petrographic studies revealed at least 1 vol. % of pyrite occurring as micro crystals (< 0.125 mm). The apparent resistivity data do not show any direct relationship with chargeability or sulphide contents.

Key words: copper-porphyry, IOCG, IP, magnetite, resistivity.


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