Target vectoring using lithogeochemistry: Applications to the exploration for volcanic-hosted massive sulphide deposits1

CIM Bulletin, Vol. 88, No. 990, 1995

Alan G. Galley, Mineral Resources Division, Geological Survey of Canada, Ottawa, Ontario

Advances in our knowledge of the petrochemical attributes of deposit environments and of the character and extent ofhydrother-mal systems associated with certain deposit types has resulted in increased application of lithogeochemistry to exploration programs. Lithogeochemistry can be used to vector an exploration program toward an area of high potential through the use of a series of collapsing scales of analysis from a tectonic subprovince down to a particular stratigraphic segment. In the case of volcanogenic massive sulphide (VMS} deposits this involves the recognition of suitable volcanic domains, and the identification of subvolcanic intrusions and cogenetic felsic extrusive complexes. The recognition of chemical vectors within regional-scale alteration zones and associated chemical sedimentary rocks allows the geologist to identify the stratigraphic units with the most potential for hosting a base metal deposit. An integrated lithogeochemical program requires the judicious use of major, trace and rare-earth element and isotopic analysis. Standard discriminant plots may be employed to identify suitable tectonic and lithologic environments. Analysis of the chemical and mineralogical variations in broad-scale, semi-conformable alteration zones provides a useful set of vectors to VMS mineralization. These may include contouring raw data, element ratios on XYplots, normalizing data against known rock values, or calculating mass changes in alteration zones.

Mots Clés: Exploration, Lithogeochemistry, Target vectoring.