Trace element chemistry of vegetation applied to mineral exploration in eastern Nova Scotia, Canada

Abstract

Trace element analysis of conifer tissues demonstrates the application of biogeochemistry to mineral exploration for gold and other metals hosted by lower Paleozoic metasediments in eastern Nova Scotia. At the regional scale, enrichment of up to 170 ppb Au and 72 ppm As in the ash of twigs from balsam fir (Abies balsamea) coincides with known gold districts and major shear zones. These concentrations are approximately 30 times background level. The twig trace element chemistry indicates previously unsuspected Au potential in Carboniferous Horton Group sedimentary rocks, and around the contact aureoles of Devonian granitoids where the twigs are also enriched in Cs (×30), Sb (×3), Rb (×3) and W (×10). Along the Minas Fault, separating the Avalon and Meguma terranes, anomalous groupings of Ba and Cr in twigs suggest exploration potential for base metal (Cu-Pb-Zn) and mafic or ultramafic (Co-Ni-Pt group element) associations. Detailed biogeochemical studies at five till- and/or bog-covered localities near the Beaver Dam gold deposit outline mineralization buried beneath up to 25 m of surficial sediment. An association of Au, As and Cs in the vegetation provides consistent patterns equal to or better than the more erratic geochemical response in soil and till surveys over the same areas. Concentrations of up to 170 ppb Au in the ash of twigs indicate locations suitable for further exploration. The low shrubs Labrador tea (Ledum groenlandicum), leather leaf (Chamaedaphne calyculata) and bog laurel (Kalmia polifolia) were collected from two small boggy areas suspected to overlie gold-bearing bedrock. Typically, these species contain <10 ppb Au in ash. At one site they contained 22 to 36 ppb Au, and at the other they yielded 55 to 85 ppb Au, in association with Cs and weak Co enrichment. In the glaciated terrain of eastern Nova Scotia, biogeochemical exploration is an effective method for delineating metalliferous zones. Multi-site anomalous concentrations of Au and related pathfinder elements occur where subcropping mineralization is covered by till. Regional and prospect-level biogeochemistry can assist exploration by providing valuable data to aid in the discovery of buried or blind mineralization.