Preliminary Evaluation of Drilling Activities in the Koochinching-Beltrami-Roseau-Lake of the Woods Counties in Northern Minnesota

Abstract

The main objective of this project is to make a first pass evaluation of the volcanic-hosted massive sulfide (VMS) potential, through a literature search of exploration files, for a portion of the Wabigoon greenstone belt in northern Minnesota. The area chosen for this investigation is situated in portions of Koochiching, Beltrami, Roseau, and Lake of the Woods counties (abbreviated as KBRLW area). Over 230 holes were drilled in the KBRLW area during 1952-1997 by numerous exploration companies, the Minnesota Geological Survey (for geologic mapping purposes), and the Minnesota Department of Natural Resources (for overburden sampling and geologic mapping purposes). A review of the historical drill logs indicates that semi-massive to massive sulfide mineralization, mostly pyrite and pyrrhotite, was intersected in 52 of the 230 holes. A review of the geochemistry indicates that there are three belts in the KBRLW area wherein groups of drill holes encountered mildly anomalous zinc values (>0.45% Zinc) associated with sulfide-rich intervals. These belts are informally named the “Baudette Belt,” “Oaks Belt,” and “Birchdale Belt.” The most impressive zinc assays, up to 4.9% Zn in drill hole B24-2, are associated with the “Oaks Belt.” A nearby hole, BD-N-1, intersected over 302 feet of reported massive to semi-massive sulfide that averaged 0.2% Zn with a maximum of 0.73% Zn – this hole was terminated in semi-massive sulfide. There are 17 holes in the “Baudette Belt” that intersected massive to semi-massive sulfide, 5 of which contained zones with >0.45% zinc but only a maximum of 0.7% zinc. Only one hole in the “Birchdale Belt” contained anomalous zinc (4.06% Zn); however, the occurrence was an isolated anomaly that was never repeated in nearby drill holes. In regards to gold assay data, the “Baudette Belt” contains the vast majority of holes with significant gold shows (>450 ppb Au threshold). One hole from the “Baudette Belt” (hole FT-14) is the most unique of this group in that it contains an 11-foot-thick interval that averages 1,185 ppb Au with a maximum of 2,745 ppb Au. Overall, the available data suggests that the “Baudette Belt” appears to have the best potential of hosting an economic VMS deposit. Furthermore, the “Baudette Belt” also appears to exhibit the best gold potential as borne out by the presence of several holes with anomalous gold (>450 ppb Au). Detailed re-logging of the drill holes in this belt should take place in order to more fully refine the geology/lithostratigraphy and alteration footprints.