Integrated geological and geophysical exploration for concealed ores beneath cover in the Chaihulanzi goldfield, northern China

Abstract

A B S T R A C TAn integrated geological and geophysical investigation was carried out in the near-mine areas of the Chaihulanzi gold-field, Inner Mongolia, northern China, to determine the south-eastern strike extension of the principal mineralized shear system, in the search for new resources. In this case study, surface geophysical surveys played an important role in defining the mineralized structures beneath cover. A re-investigation of the mine geology by observing the underground exposures of mineralization and its hosting structures, coupled with re-evaluation and re-examination of previous exploration data, revealed that the mineralization style at the Chaihulanzi gold-field is not the skarn-type as previously assumed, but is structurally controlled by an oblique-sinistral shear structure. Moreover, a southeastward shallow-plunging mineralized corridor within the principal mineralized shear system was also identified, implying that the ore-forming fluid-flow might move through the mineralizing system, from the south-east at depth to the north-west. These new geological findings imply that the mineralized shear system should extend much farther south-eastwards along strike beneath cover, and thus a conceptual target area was proposed. A detailed geophysical survey program, involving the application of VLF-EM, Stratagem EH4, CSAMT and gradient IP measurements, was carried out to test the validity of the conceptual target. Orientation surveys on the geologically known Line-18 traverse revealed that VLF-EM and Stratagem EH4 were the most effective methods of detecting the unseen mineralized system, whereas CSAMT could only provide low-resolution data, and IP proved to be unsuitable in this environment due to the ubiquitous presence of graphite-bearing schists in and around the mineralized system. A follow-up systematic VLF-EM survey highlighted the principal mineralized shear system as a linear conductive belt, tracing the principal mineralized system for a further 750 m of strike length beneath cover from the previous exploration limit (Line 18). Stratagem EH4 soundings over six parallel traverses perpendicular to the mineralized trend revealed that the principal mineralized shear structure extends for more than 500 m in the dip direction, a strong indication of the presence of potential deep mineralization under the surveyed area. Detailed modelling of the Stratagem EH4 sounding images *

Prediction of Hidden Ore Bodies using Integrated Geology, Source of Fluids and Stratagem EH4 Geophysical Survey in Kuoerzhenkuola Gold Deposit in Xinjiang, China

“…This system uses both natural and man-made electromagnetic signals to obtain a continuous electrical sounding of the earth beneath the measurement site. The details are given by Geometrics and EMI ElectroMagnetic Instruments (2000) and Liu et al (2006) . Because Ex and Ey dipole sizes and the betweenstation distance (BSD ) should be changed according to the scales and geometries of the objects detected, we determined measurement sites at 20 m MN with 10 m Ex and Ey dipole sizes in order to obtain clear results.…”

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

“…Where AMT signal levels are low, e.g., in the dead band at $ 800-3000 Hz (Garcia and Jones 2002), the controlled-source audiomagnetotelluric method (CSAMT, f = 1-10000 Hz, Zonge and Hughes 1991) is routinely applied. Consequently, MT methods have a long-standing history in the investigation of mineral deposits (Strangway et al 1973;Meju 2002;Jones 2017) with field cases reported from, for instance, copper, gold, lead, silver and zinc deposits (Kellett et al 1993;Garcia Juanatey et al 2013a, b;Hübert et al 2013;Hu et al 2013), copper, gold and iron deposits (Heinson et al 2006), copper and iron deposits (Chouteau et al 1997;Jones and Garcia 2003), copper, iron and zinc deposits (Basokur et al 1997), copper, lead and zinc deposits (Sasaki et al 1992;Bastani et al 2009), copper and nickel deposits (Lakanen 1986;Livelybrooks et al 1996;Jones et al 1997;Balch et al 1998;Stevens and McNeice 1998;Zhang et al 1998;Watts and Balch 2000;King 2007;Xiao et al 2011;Varentsov et al 2013; Le et al 2016a), copper, silver and zinc deposits (Gordon 2007), gold deposits (Jones et al 1997;Liu et al 2006;Howe et al 2014;Takam Takougang et al 2015;Hübert et al 2016;Le et al 2016b), and uranium deposits (Leppin and Goldak 2005;Tuncer et al 2006;Farquharson and Craven 2009;Goldak et al 2010;…”

Two-dimensional resistivity imaging in the Kestelek boron area by VLF and DC resistivity methods

“…The application of VLF method for cost effective imaging and detection of near surface targets for prospection of ore deposits has been in use for over 10 years; some of examples include Eze et al (2004), Frasheri et al (1995), Hutchinson and Barta (2002), Ligas and Palmoba (2006), Liu et al (2006), McCaffrey et al (1995, Paterson and Ronka (1971), and Saydam (1981). Bayrak (2002) applied the VLF method to chrome area to inspect the effectiveness of the method.…”