Chin.J.Geochem.(2008)27:198–202 DOI: 10.1007/s11631-008-0198-8 CHIM-geoelectrochemical method in search of concealed mineralisation in China and Australia LUO Xianrong 1* , HOU Baohong 2 , WEN Meilanna 1 , ZENG Nanshi 1 , John Keeling 2 , Roger Fidler 2 , and Adrian Fabris 2 1 Guilin University of Technology, Guilin 541004, China 2 CRC LEME, Primary Industries & Resources South Australia (PIRSA), SA 5000, Australia * Corresponding author, E-mail: lxr811@yahoo.com.cn Received January 16, 2007; accepted April 11, 2007 Abstract A version of the geoelectrochemical prospecting technique developed in China was demonstrated in China and Australia to test its suitability under both Chinese and Australian conditions. This paper briefly describes the mechanism and effectiveness of the technique applied to search of concealed mineralisation through regolith cover, based on both experimental and field tests. This paer deals with three main aspects of the method: a) how metallic ions are released from orebodies by electrochemical dissolution; b) how these ions migrate to the collector and are deposited as elements by electrochemical extraction in the presence of an electric field; and c) the effective- ness of the method illustrated by some case studies. Key words CHIM-geoelectrochemical method; concealed mineralization; China; Australia 1 Introduction The global trend for mineral exploration in highly prospective terrains is to be focused on areas where there are widespread variably thick regolith and sedimentary cover that have been poorly documented in the past. The challenge is to find tools that will identify reliable vectors to mineralizing systems and ensure optimal testing of these by drilling or other techniques that are used to collect samples at the sub- surface. CHIM (Chastichnoe Izvlechennye Metallov) is an electro-geochemical method for mobilising and collecting ions using electrodes placed in the soil and applying a small current for a sustained period. The CHIM method was originally developed in the early 1970s by Ryss (1986) and Goldberg in the former USSR (Hoover et al., 1995) and has been applied on a trial basis in Canada, US (Leinz et al., 1998), China and Australia (Luo Xianrong, 1996; Keeling et al., in press). The modified technique described here was developed by Professor Luo Xianrong at Guilin Uni- versity of Technology, China. Attempts have been made to apply and improve the technique in order to assess its efectiveness and applicability for blind ore deposits of various geneses under Chinese and Aus- tralian conditions (e.g. Luo Xianrong, 1996; Luo Xianrong et al., 2004; Keeling et al., in press). 2 Methodology The method was based on selective extraction of electromobile forms of metals from soil/ regolith into element-collectors (Alekseev et al., 1996). The setup comprised specially coated carbon electrode pairs connected by a disposable DC power supply. The electrodes were buried at around 0.3 m depth and 0.6 m apart, the area was moistened by the addition of 30% HNO 3 , and then covered over by soil. These were left for between 12–72 hours after which time the electrodes were exhumed (depending on DC power supply and local geological controls). The elec- tric current causes the positively charged metallic ions to move towards the cathode and the negatively charged complex of metallic ions to move towards the anode under the influence of a potential field. The ion and ionic complexes accumulate in specially prepared absorbents coating the electrodes. The absorbent coatings are removed and digested in warm concen- trated HNO 3 . The concentrations of elements in the solution are determined by sensitive analytical meth- ods such as ICP-MS and AAS, so that it is possible to detect any anomalous metals associated with the con- cealed mineral deposits. At each site, soil samples were taken for measurement of ionic conductivity of soil and for mercury analysis. www.gyig.ac.cn www.springerlink.com