MAJOR AND MINOR ELEMENT VARIATIONS IN CORE FROM THE IRON CREEK DEPOSIT IN THE IDAHO COBALT BELT: RAPID CONTINUOUS XRF DATA ACQUISITION FOR CRITICAL MINERAL EXPLORATION AND ASSESSMENT

The Iron Creek deposit is a strata-bound Co-Cu deposit in the south-eastern portion of the Idaho Cobalt Belt. Ore is hosted in the Mesoproterozoic Apple Creek Formation, a greenschist grade banded siltite containing abundant quartz, muscovite, biotite, and chlorite, with minor amounts of apatite, plagioclase and Fe-Mn-oxides. Cobalt is mainly sequestered in pyrite, and Cu generally occurs in chalcopyrite. The goal of this study is to utilize and advance continuous XRF core scanning to increase understanding of the occurrence and distribution of critical minerals at Iron Creek.

The investigated 293 m long drill hole intersects the high-grade portion of the deposit, which includes both the Co-rich and Cu-Co-rich ore zones. Drill core was analyzed twice using a continuous XRF core-scanner. The first run was performed at 40 kV and 8mA, and the second run was performed at 15 kV and 24 mA with a He flush, allowing detection of both heavy and light elements, respectively. Analysis time was 18 hours per run for the entire drill core. XRF elemental analysis was then examined and compared with existing multi-element assay data and core logs.

The results of the XRF analyses closely match existing multi-element assay data. Both methods show a single main Cu ore body between 63 m and 87 m with geochemical trends of Cu concentrations in great agreement between XRF and conventional assay data. Both methods identified three discrete sections where Co is found. The first section overlaps with the Cu-rich portion of the hole and the second and third Co-rich portions were found at 116-145 m and at 178-216 m, respectively. Based on both assay and XRF data, Co has a strong positive correlation with As and Se, while Cu shows positive correlations with Ag, Te, Pb, and Zn. Cr and Ni concentrations are elevated throughout the entire drill hole and continually increase toward Co-rich zones, where concentrations of Cr and Ni are highest. This Cr and Ni halo around the Co ore zones could represent a useful tool for vectoring toward Co ore.

This study shows that continuous XRF analysis of drill core compares well to more established assay methods. This non-destructive, high throughput method is fast, accurate, and a valuable technique for obtaining multi-element geochemistry of drill core.