Integrated application of 2D resistivity and electromagnetic methods to investigate a metallic-sulfide deposit in Soap G

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ORIGINAL PAPER

Integrated application of 2D resistivity and electromagnetic methods to investigate a metallic-sulfide deposit in Soap Gulch, Montana. A case study Mohamed Khalil 1 & Akpofure Orubu 1 & Brad Rutherford 1 & Marvin Speece 1 & Fernando Santos 2 & Mohammad Farzamian 2 Received: 26 April 2018 / Accepted: 30 November 2018 # Saudi Society for Geosciences 2018

Abstract Geoelectrical methods involving electrical resistivity tomography (ERT), self-potential (SP), frequency domain electromagnetic (FDEM), and very low frequency (VLF) methods have been used to provide valuable information in locating a known sulfide ore body in Soap Gulch, Montana. The study develops basis of comparison for the geophysical techniques employed. Ranges of resistivity along the area have been established using interpreted ERT which can help to understand the subsurface distribution of sulfides in the area. A sulfide body was delineated from the survey area corresponding to anomalously low resistivity values on the ERT section, negative SP, and high apparent current density zone in VLF. Depth to the localized ore zone ranges approximately from 10 to 20 m. FDEM data reflect the conductivity distribution of the shallow subsurface (less than 6 m deep); hence, the delineated sulfide zone had minimal contribution to FDEM measurements. The results of the study show that SP, VLF, and ERT methods provide significant information in localizing ore bodies. The survey revealed that the resistivity values obtained from ERT profile corroborate the FDEM, SP, and VLF from the area. Keywords Electrical resistivity tomography . Frequency domain electromagnetic . Self-potential . Soap gulch

Introduction Soap Gulch falls within the Melrose mining district on the southwest slopes of Highland Mountains, Montana. Other areas within the Melrose district include Camp Creek and Wickiup Creek drainage. The Melrose district played host to several mines of great economic importance with the Hecla Consolidated Mining Company serving as a hub for marketing the locally produced lead and silver ores (Sahinen 1939; Wolle 1963). Prominent mines within the Melrose mining district include Calvin, Clipper Group, Gold King, Jackrabbit, King and Queen, Old glory, Pandora, and Peabody (Mining Truth 1930). Metallic ores

* Mohamed Khalil [email protected] 1

Geophysical Engineering Department, Montana Tech, University of Montana, Missoula, MT, USA

2

Instituto Dom Luiz (IDL), University of Lisbon, Lisbon, Portugal

extracted from Melrose include lead, silver, gold, and copper (Winchell 1914). Mineral deposits in the Melrose mining district were greatly explored following discovery in 1866. Mining operations were guided by exposures in shallow pit walls and fresh exposures that appeared during the mining process. Production from Soap Gulch from 1909 to 1911 was reported to be 252 tons of ore averaging 0.69% copper, 40.5 g of silver and 74.5 g of gold per ton (Winchell 1914; Sahinen 1939). Statistics of metallic ore extraction in Soap Gulch shows the sulfide deposit is ric