GEOCHEMISTRY OF MIOCENE DIKES OF THE KILGORE GOLD DEPOSIT, CLARK COUNTY, IDAHO

The Kilgore deposit, located approximately 100 kilometers north of Idaho Falls at the northern margin of the Snake River Plain, is an epithermal gold deposit hosted mainly in hydrothermally altered lithic tuffs and dikes of Miocene age. The gold occurs as high grade veins in silica stockworks, surrounded by disseminated mineralization associated with argillic alteration of the tuff and dikes. A recently completed drilling campaign conducted by Otis Gold Corporation in 2010 has revealed mineralization in 27 of 28 core holes with intercepts as high as 51.8 meters @ 1.30 g/t Au.

The hydrothermally altered Miocene dikes of the Kilgore deposit range from mafic-intermediate to felsic in composition. The deposit is actively explored, with greater mineralization of gold occurring in some dikes, while others are relatively deficient in gold mineralization. Analysis of the suite was conducted on representative core samples of each dike type. XRF, XRD, and AAS methods were used to categorize host rock composition as well as the amount of disseminated gold mineralized within each representative sample.

Assays reveal that two of the seven samples have significantly higher gold concentrations ranging from 2.26 to 3.33 g/t, with the rest of the five samples ranging from 0.50 to 1.26 g/t. XRF results determined that these same two samples have a higher concentration of iron oxide, ranging from 7.68 to 8.98 wt%, with the rest of the cores showing much lower concentrations in the range from 0.67 to 1.81 wt% Fe₂O₃. These samples with higher gold concentrations also have higher amounts of TiO₂ (1.01 to 1.16% by wt.) relative to the other five samples (0.11 to 0.22% by wt.). XRD analysis concluded that all of the samples have a significant amount of the mineral adularia, with the two mafic-intermediate dike samples also containing chlorite.

The geochemical data suggest that preferential mineralization of gold in the Kilgore deposit has occurred in dikes of more mafic composition. This correlation is significant in that the chemical signature of the dikes could be used to determine locations of high grade ore deposits.