THE ROLE OF PUBLICLY ACCESSIBLE DRILL CORE IN DISCOVERING CRITICAL MINERAL DEPOSITS IN MINNESOTA

Minnesota's Department of Natural Resources Drill Core Library (DCL) has supported the discovery of critical mineral deposits in the past and is proving to be integral for active Earth MRI research into new mineral resources within the state.

Minnesota (MN) contains diverse geologic provinces that hosts several critical mineral commodities and has a century-long history of mining and mineral exploration. State law requires explorers to submit at least ¼ portion of all exploratory drill cores to the state, which are stored in the Hibbing Drill Core Library (DCL) – the only facility in the state for archiving public samples. Bedrock in MN is overlain by glacial sediments, so access to public drill cores is crucial for identifying and linking critical mineral resources to their geologic framework.

Cu-Ni mineralization was discovered in the Duluth Complex in the 1940's, but it was not until the reexamination of publicly archived drill core in the 1980s that led to the discovery of platinum group elements (PGEs). In 1986, the MN Geological Survey drilled a “wildcat” scientific borehole into an aeromagnetic anomaly and recovered a 7 m core of ultramafic rock near Tamarack, MN. This core was subsequently studied in 2001 and further exploration ultimately led to the discovery of the Ni-Cu-PGE Tamarack deposit.

More recently, DCL drill cores have been integral for two ongoing Earth MRI projects. Core logging and thin section petrography on core samples from a sparsely drilled region in northwestern MN helped define the area for a 2021 high-resolution airborne magnetic and radiometric survey of the Mentor intrusion. Specific gravity and magnetic susceptibility measurements on core helped to improve the geophysical processing and interpretation. Mineral dating and geochemistry work from drill core samples are currently being studied to improve the geochronology and geological framework of mafic and ultramafic-hosted mineral deposits. In the historic Cuyuna mining district in central MN, archived DCL cores and historic drilling logs and assays are currently being used to evaluate and update the mineral potential for the largest known domestic source of manganese.

With close to 4 million feet of core stored in the DCL and ongoing state government support, the facility will remain a significant starting point for future research in the state.