Abstract
A program was initiated in 2005 to test non-ore grade rock associated with a magmatic Cu-Ni deposit hosted by the Duluth Complex igneous intrusive body, located in northern Minnesota, USA. Over 200 kinetic tests were initiated, in different configurations. Tests were discontinued in phases, with a subset of tests still ongoing. As of August 2024, some of these tests have been running for approximately 19 years. While the test program generally used methods of ASTM 5744 (Option A), starting in July-August of 2019, several tests were subjected to a modification of this procedure which varied the volume of rinsate used and the time between rinse events. These cells were later discontinued; with solid residues analyzed by complementary chemical and mineralogical characterization methods, and a sequential leaching procedure. Rocks studied in this program were dominated by those with generally low sulfur (<1%) and negligible carbonate mineral content. Neutralization of proton acidity is attributed to silicate mineral dissolution. Rock management criteria were developed from interpretation of alkalinity and proton acidity generation rates, initially based on approximately one year of data. Results from the following 18 years are consistent with these criteria, while illuminating additional nuances on time-dependence of both rates, and potential mechanisms linking the two. This paper describes these observations, as well as results of metal partitioning from the long-term kinetic test data.