Drift Prospecting Near Gold Occurrences at Onaman River, Ontario and Oldham, Nova Scotia

Special Volume, Vol. SV 24, No. 1982, 1982

In a continuing program of mapping glacial dispersal trains, near-surface till samples were collected down-ice from a copper-silver-gold prospect at Onaman River, Ontario, and down-ice from the past-producing gold district at Oldham, Nova Scotia. The program is designed to aid exploration by illustrating glacial dispersal from various types of known occurrences and by identifying postglacial processes that control drift composition at a detailed scale. Native gold was mined at Oldham from arsenopyritebearing saddle reef quartz veins in a dome in Early Paleozoic slates of the Meguma Group. Gold abundances greater than 10 ppb in till form a dispersal train at least 1900 m long. Gold abundances between 40 and 100 ppb occur in clusters up to 600 m down-ice from gold-bearing bedrock. Anomalous arsenic abundances in till form a broad train 1100 m long that is significantly different in shape from the gold train. At Onaman River, subeconomic amounts of Cu-Ag-Au occur in quartz lenses in Archean mafic volcanic rocks. A dispersal train defined by the distribution of mineralized boulders and increased abundances of Cu, Ag and Zn in till extends 600 m down-ice from mineralized bedrock. Gold abundances between 10 and 70 ppb do not define this dispersal train, but occur instead in clusters 300 to 600 m down-ice from mineralized bedrock. In vertical sections in the upper 2 m of copper-rich till, Au abundances vary sympathetically with Ag and Cu Generalized ice flow direction~ levels; however, there seems to be no preferential site of Au enrichment in the mineral portion of the soil profile. Several of the mineralized boulders at Onaman River are richer in Au and Ag than the mineralized bedrock from which they were derived. Although some of the high Au and Ag assays were caused by biased sampling of sulphide-rich portions of the boulders, many were caused by leaching of sulphide minerals from 'the boulders, which left a limonitic boxwork that is enriched in Au and Ag. A few of the Au-rich boulders may have been derived from an unknown bedrock source.

Mots Clés: gold, gold mining, drift prospecting, Nova Scotia, mapping, glacial dispersal trains, exploration, Native gold, mineralization