The dispersal of gold and related elements in till and soils at the Forest Hill Gold District, Guysborough county, Nova Scotia

Abstract

The till stratigraphy and gold distribution (in till) at the Forest Hill Gold District was extensively studied in an pro gram designed to aid gold exploration in Nova Scotia. Trenches cut to bedrock provide a unique opportunity to study the three-dimensional dispersal of gold from a known bedrock source. Three major surficial units characterize the study area. The oldest unit is a till (Unit I) overlain by an oxidized and cemented diamict. This sequence is overlain by Units II and III which are tills characterized by a sandy matrix and locally derived granitic and metasedi­mentary clasts. Unit II is compact and rests upon bedrock with southeastward-trending striations. Unit III is less compact and locally has a strong fabric indicating a southwest­ward ice movement. The se tills are commonly separated by a reddish-brown alteration zone interpreted as a paleosol. A poor correlation between the panning results and the geochemical data for gold was attributed to the nugget effect. It was concluded that both panning and geochemical exploration techniques should be used in gold exploration programs in Nova Scotia. The coarse fraction (1-2 mm) of the tills directly reflects the elemental ratios and abundances inherent to the bedrock. However, the fine fraction (<0.063 mm) of the tills shows evidence of a hydromorphic redistribution of elements. This implies that the tills at Forest Hill .are at least partially altered by post-depositional chemical processes. The dispersal of gold at Forest Hill rejects mechanical dispersal by a major southeast­ward ice advance. The gold dispersal trains are three-dimensional bodies which come to the surface 200 to 300 m down-ice from gold-bearing veins. Gold in the till occurs as flakes and nuggets. The surfaces of the se particles appear rough and pitted and exhibit Little evidence of abrasive glacial transport.