Biogeochemical haloes of gold in various species and parts of plants

Abstract

Studies of Au uptake by 194 plants and plant parts have permitted their classification into four groups according to their value for biogeochemical prospecting. Group 1, “nonbarrier”, contains 33 (17%) plant parts which yield quantitative information in relation to prospecting for Au ores. Group 2 contains the majority (41%) of the plant species and plant parts, which are termed “practically nonbarrier” in that they provide semiquantitative information. Less informative are the 29% of tissue types categorized as Group 3, providing only qualitative information. Group 4 comprises the remaining 7%, which are uninformative with respect to prospecting for Au deposits. Group 1 plants, and in their absence Group 2 plants, are recommended for sampling in biogeochemical exploration for Au ore deposits, whereas Groups 3 and 4 are not recommended. Of importance is the observation that young growing parts of plants supply different degrees of information at various times of the year, due to seasonal changes in plant chemistry, and therefore may change their group status (e.g. from Group 1 to Group 4). There is a quantitative relation between Au in Group 1 plant tissues and channel samples from trenches dug to 2–6 m depth, and also between patterns of biogeochemical and primary lithogeochemical haloes. Data on biogeochemical haloes of Au and its numerous pathfinder elements are discussed, noting their main characteristics and zoning over Au-ore deposits.