MIGRATION OF STAMP SAND (COPPER MINING WASTE) IN LAKE SUPERIOR AT GRAND TRAVERSE BAY, MI

Stamp sand (the waste by-product of crushing basaltic ore for copper mining) at Gay, Michigan was discharged into Lake Superior from stamping mills that operated there from 1890 to 1920. The volume of stamp sand produced during that time is estimated at 37 million cubic yards. Since operations ceased, the stamp sand has been migrating southward through Grand Traverse Bay, to a breakwall at the Traverse River, 8 km to the south. The beach has widened there from 10 meters of natural white quartzose sand and buried by the coarse black, basaltic sand to over 100 meters width and up to 10 m thickness.

Stamp sand 1) contains heavy metals that negatively impact aquatic ecosystems, 2) affects aesthetics, and 3) littoral movement of stamp sand negatively impacts a documented spawning area for Lake Trout through sedimentation and impact by saltating sand grains.

Historical aerial photographs dating from 1938 through 1998 were used in a previous study (Rasmussen, et. al, 2000) to map and to predict future movement of the sand using ArcView GIS. In this study, recent aerial photographs, airborne MSS data, and LIDAR topographic and bathymetric data (2008) were used to map the progression since the previous study (using ArcMap and ERDAS Imagine) and to test the predictions from the former study. Also in this study, samples of sand were collected at the source deposit and along the shoreline for textural analysis to estimate the percentage and volume lost to the littoral environment.

The present study shows continued and dramatic changes to the shoreline position. Additionally in this study, LIDAR data suggests significant stamp sand movement into the beach and offshore environments, and dramatic changes to the beach profile. This is supported by textural analysis.

Stratification in the stamp sand source deposit ranges in from lamina a few mm in thickness to beds over 30cm. Texturally, the source deposit is a stratified mix of clay and silt (approximately 20%), and sand to fine gravel, angular to sub-angular in shape. The source is exposed to waves in a vertical, 10 meter bluff face. Nearly immediately down-beach from the source deposit, the clay fraction is winnowed out and carried into the littoral environment. The fraction that becomes entrained in the beach and nearshore systems becomes coarser, and more well-sorted near the breakwall.