Multi-element geochemical analyses of selected samples from the Mesoproterozoic Nonesuch Formation and Copper Harbor Conglomerate at the Copperwood copper deposit, Michigan, USA

This data release provides multi-element data for drill core samples from the Mesoproterozoic Nonesuch Formation and Copper Harbor Conglomerate at the Copperwood copper deposit, Michigan, USA. Gold, platinum, and palladium data were collected by fire assay; copper and silver were collected by assay; and other elements were collected by inductively coupled plasma-optical emission spectrometry (ICP-OES) or inductively coupled plasma-mass spectrometry (ICP-MS) following a digestion that used hydrochloric, nitric, perchloric and hydrofluoric acids. The Copperwood copper deposit is a sediment-hosted stratiform copper deposit in the Presque Isle Syncline of the upper peninsula of Michigan. The deposit has a 2018 mineral resource estimate of 42.2 million metric tons (Mt) of measured plus indicated mineral resources in the Lower Copper Bearing Sequence at an average grade of 1.60 percent Cu and 3.84 grams per ton (g/t) Ag. The measured plus indicated mineral resource in the Upper Copper Bearing Sequence is estimated to be 7.1 Mt at an average grade of 1.21 percent Cu and 3.26 g/t Ag (Gignac, 2018). The mineral reserves for the Copperwood Project are estimated at 25.4 Mt at an average grade of 1.43 percent Cu and 3.83 g/t Ag (Gignac, 2018). Some sediment hosted deposits elsewhere produce significant amounts of gold, platinum, palladium, and (or) cobalt. However, in the Copperwood samples, these elements have geometric mean concentrations of 0.0022 ppm, 0.0021 ppm, 0.0029 ppm, and 24 ppm, respectively, so they are not enriched. Gallium, which is a critical mineral in the U.S., is enriched in some base metal deposits, but Copperwood samples have a geometric mean gallium concentration of 16 ppm, which is similar to average crustal concentrations. Although the data herein are limited to 34 determinations, they strongly suggest that the Copperwood copper deposit does not contain significant concentrations of byproduct critical minerals.