Transportation and deposition of magnetite and gold in Harris Creek, south-central British Columbia

Abstract

Although previous studies have indicated the importance of flood events in the mobilization, transport and deposition of gold by streams, there have been no estimates of actual transport rates of sediment and gold as discharge varies both within and between years. Here, we use Helley–Smith bed load samples from Harris Creek, a gold-rich gravel-cobble bed stream in British Columbia, to develop equations of the form R i = a Q b that relate transport rates ( R i ) of sediment, magnetite and gold to discharge ( Q ). These equations have then been used to estimate the amounts of sediment, magnetite and gold transported by Harris Creek in 1991, 1992 and 1993. Results show that the amount of material transported can vary by up to three orders of magnitude from year to year depending on the magnitude and duration of the snowmelt flood. Combined with the preferential deposition of Au at bar-head sites, it seems likely these large annual variations in the amount of Au transported result in similar year-to-year variations in the strength of stream sediment geochemical anomalies for Au.