MOBILIZATION OF GOLD INTO LAKE-SEDIMENTS FROM ACID AND ALKALINE MINERALIZED ENVIRONMENTS IN THE SOUTHERN CANADIAN SHIELD - GOLD IN LAKE-SEDIMENTS AND NATURAL-WATERS

To be an effective indicator of mineralization in lake sediment survey s within the Canadian Shield, it is desirable that an element migrate in solution or adsorbed on suspensates. Given the low relief and disor ganized drainage patterns of this region, dispersal in clastic form in drainage systems is limited and gives rise to erratic distributions. The purpose of this study was to discover whether Au shows significant hydromorphic mobility, which would justify the increasing use that is being made of this element in lake sediments as an indicator for gold mineralization. Waters and lake sediments were collected from Napier Lake, Ontario; PAP Lake, Saskatchewan; and Foster Lake, Manitoba, all of which contain Au-quartz vein mineralization and lie within the glac iated boreal forest zone of the Canadian Shield. In all three areas, p rofundal lake sediments downdrainage of mineralization contain Au conc entrations higher than regional mean concentrations. Significant disso lution and transport of Au was found under oxidizing conditions associ ated with waters with pH that varied from acid to alkaline. Waters fro m drill holes penetrating mineralization contain up to 401 ng L-1 Au ( note; 1 ng L-1 is equivalent to 1 part per trillion, 10(-12)). Surface waters overlying or near mineralization collected from bop, seeps, po nds and streams contain up to 13 ng L-1. The content of Au in lake wat ers is lower, with a maximum of 1.1 ng L-1. There is also a detectable quantity of Au present in suspensates. Two samples of particulates (> 1 mum) filtered from lake water have Au equivalent to 0.17 ng L-1 and 0.039 ng L-1. While the contents of Au present in solution or as susp ensates in lake and stream water are relatively small, they are suffic ient, if precipitated, to generate anomalies in lake sediments. Thus f or Reservoir Lake, in the Foster Lake area, water from the principal s tream entering the lake carries 0. 3 ng L-1 Au. This provides an annua l flux which far exceeds that required to generate the 7.3 ppb Au cont ained in profundal sediments of this lake; a content that is anomalous relative to the regional median content of < 1 ppb Au for lake sedime nts. Hydrogeochemical prospecting involving analysis for Au is one met hod for tracing the source of anomalous Au in lake sediments. Collecti on of 1 L samples without field treatment, followed by extraction of A u into MIBK, then analysis by graphite-furnace atomic absorption spect rophotometry, permits detection levels for Au of 0.5 ng L-1. This is b elow the contents of Au found in some waters from mineralized areas. A detection limit of 0.3 ng L-1 was obtained using larger water samples .