Redox chemical remanent magnetization—A new dimension in exploration for sulfide deposits in volcanic covered areas

Abstract

Redox chemical remanent magnetization (CRM) results from current flow associated with a redox potential cell. An active redox cell covered by later volcanics may continue in operation for a period of time, sufficiently long that the current flowing in the overlying volcanics will cause or assist in the remobilization of iron. The remobilization may be either in situ as an alteration of minerals or by actual migration as a ferrous hydroxide, with fixation at a higher Eh nearer the surface. Redox CRM will leave a characteristic pattern as a magnetic memory in the rocks. Measurement of the magnetic rock properties and interpretation of resulting patterns can be used to locate the ancient redox cell. Redox cells in nature are usually associated with oxidizing sulfide deposits. Under appropriate conditions, redox CRM can be utilized as an indirect method for sulfide exploration. Field results for two porphyry sulfide deposits and a massive sulfide deposit under approximately 400 m of post‐mineral volcanic cover demonstrate the feasibility of this technique. Field tests in nonsulfide areas indicate that pervasive occurrence of false redox CRM anomalies do not exist except in the presence of sulfides. Laboratory experiments in the simulation of the redox CRM concept give support to the theory.

The magnetic anomaly of a brick foundation

“…Another type of remagnetization is called chemical remanent magnetization (Banegee, 1989). Chemical or microbial action can alter the magnetic minerals in an object, causing the minerals to acquire the magnetization of the Earth at the time of that alteration (Bacon and Elliot, 1981;Aitken et aZ., 1989;Machel and Burton, 1991). It has been pointed out that the magnetism of brick changes with the season (Johnston et aZ., 1939, p. 89).…”