A History of Copper-Nickel and Titanium Oxide Test Pits, Bulk Samples, and Related Metallurgical Testing in the Keweenawan Duluth Complex, Northeastern Minnesota

Abstract

This project describes the bulk samples (test pit and some drill hole composites) taken from various locations in the Duluth Complex since the 1960s, with minor background information on earlier work. Included are: 1) descriptions of sample areas; 2) local geology and expected grade of samples; 3) rationale for sample location; 4) review of the metallurgical results; and 5) an index of where the complete data (mostly metallurgical) can be found. Historical (Native American and early settlers) native copper, native silver, accidental iron ore prospects, and any other test pits are not covered in this report. The copper-nickel and iron-titanium-oxide deposits associated with rocks of the Duluth Complex have had a number of large bulk samples removed for metallurgical testing since the 1960s. There are at least six bulk sample sites in the South Kawishiwi intrusion (SKI) and about fourteen bulk sample sites in the Partridge River intrusion (PRI; Table 1.) Common to most of these bulk samples have been erratic grades, relative to what had been outlined by prior drilling, and difficulty in defining and producing an “average” or “typical” mineralized sample. Our research experience has led us to believe that the mineralization is borderline chaotic over short distances within the mineralized zones of these deposits. Thus, in many instances, it may not be possible to obtain an “average” mineralized bulk sample with samples of small size (depending on how one defines “average”). It is important to note that once a bulk sample site was chosen by a mining company, based on limited on-site drilling, no detailed drilling or mapping was conducted prior to collecting the sample.