Factor Analysis in Botanical Methods of Exploration

Abstract

Botanical methods of exploration for minerals incorporate two basically different techniques; geobotany and biogeochemistry. Geobotany is essentially a form of applied ecology and involves the visual observation of the vegetation cover to detect indicator plants, morphological changes, or plant communities characteristic of a particular type of substrate. This technique can sometimes give clues as to the presence or absence of rocktypes favourable for mineralization. Biogeochemistry involves the analysis of the mineral content of the plant cover in order to detect mineralization. The two methods have been reviewed by Brooks (1972). Although it is customary to classify geobotany and biogeochemistry as separate methods, they are in fact closely linked since the nature of the vegetation and its elemental content are influenced by both the chemical composition of the substrate and by the physical features of the environment. Coppermine Island, Hen and Chickens Group, New Zealand contains copper deposits which have been investigated mineralogically and geologically (Brothers & Hopkins 1967; Wodzicki & Thompson 1970), and pedologically (Weissberg 1967). The wealth of data (including test-drilling) concerning these deposits, is such that the area forms an excellent natural laboratory where other exploration techniques may be tested. The island also contains a number of distinct plant communities which have been delineated by ground work (Atkinson 1968) and whose boundaries were subsequently confirmed by aerial infrared photography (Yates 1972). In 1972 we carried out sampling of vegetation and soils from each of the main plant communities upon the island with a view to investigating further, the link between biogeochemistry, geochemistry and geobotany by attempting to evaluate the extent to which the various communities could be characterized by factor analysis of data on the concentrations of a number of elements in the plants and soils.