THE REDISCOVERY AND REVIVAL OF THE CRANDON VOLCANOGENIC MASSIVE SULFIDE DEPOSIT, NORTHEASTERN WISCONSIN

The Crandon volcanogenic massive sulfide (VMS) deposit is located near Crandon, WI and is Wisconsin’s largest (~55 Million Tonnes) and only world-class VMS deposit. Discovered in the early 1970’s, Exxon Minerals Co. quickly purchased the land and began exploration of the deposit. However, a changing political climate in the state, increasing environmental concern amongst the public, and a metal market crash during the 1980’s all contributed to a delay in the Crandon Project. After changing hands several times and failed permitting attempts during the 1990’s, the mineral rights and all research materials (core, documents, etc.) related to the deposit were sold to local Native American tribes in 2003. The result was the almost complete disposal of all documentation and drill hole core from the Crandon deposit. No further exploration or research has been conducted on the Crandon deposit since, largely because little geological documentation or cores exist and that the entire deposit is covered by glacial debris.

Recently donated and discovered documents, maps, and rock samples from the University of Minnesota-Duluth (UMD) and the Wisconsin Geologic and Natural History Survey (WGNHS) has made reconstruction of the deposit possible and has provided samples to conduct modern analyses of mineral and whole rock chemistry. Using archived maps and GIS software, core and drill holes were spatially referenced in a modern coordinate system. Digitized level plan maps and cross sections have been imported into 3D mining software to develop an interactive, modern model of the ore zone, surrounding rock units, and the direction of the drill holes at depth. This model allows for a more efficient sampling strategy within the limited sample suite and permits interpretation of the stratigraphic context of drill core samples.

The goal of this study is to present the first high-precision lithogeochemistry dataset for the Crandon deposit stratigraphy. Preliminary geochemistry of samples at the University of Minnesota-Duluth was conducted using a portable x-ray fluorescents (pXRF). High-precision XRF and ICP-MS geochemistry and ore petrography on samples from the WGNHS is ongoing. This promises to be an important and integral stride in the analysis and rediscovery of the geological setting of the Crandon deposit.