New Mexico Geological Society Annual Spring Meeting — Abstracts

The Bruvann nickel-olivine deposit was mined from 1989 to 2002, but now lies abandoned, with large heaps of waste rock that contain both acid producing minerals and silicate minerals that neutralize some of that acid. The resulting pH of water draining from the site is near neutral, so it is not remediated, despite considerable amounts of mobilized metals, especially nickel. This project examines both the natural leaching of nickel rich olivine by water and alternative methods to increase the rate of nickel leaching, making the waste rocks a resource. In July, fieldwork was conducted at the Bruvann deposit in Ballangen, Norway. A stream emerging from a mine adit was traced until it left the area, and sampled wherever additional water entered. Samples were analyzed for pH, conductivity, and metals content. Twenty samples were taken from the waste rock heaps surrounding the mine, and paste pH tests were used to rank their potential for leaching. Ten samples were selected to represent the breadth of leaching potentials and shipped to New Mexico Tech for further testing and analysis. An additional four are undergoing leaching in Norway. Splits of each waste rock sample are undergoing mineralogical analysis. Minerals of interest, such as pentlandite and nickel sulfides, will be separated from the bulk rock and used for thin and polished sections to study the mineralogy. This will require a magnetic separation, as the silicate minerals are too dense to be separated from the other important minerals using common heavy liquids. Small portions of the waste rock will also be used for short-term analyses. Sulfur species tests will determine how much reactive sulfur is in the various samples, as well as how much of that sulfur is stored as sulfides, which are known to be excellent acid producers. Acid generation, neutralization potential, and net acid generation tests will add more information about what pH may be expected, as well as how much neutralization capacity is contributed by the olivine. A test involving the slow addition of acid to the samples will yield similar information which may be compared to the other acid-base accounting tests to confirm the validity of each method. This data will be used to inform new methods to increase the rate of nickel leaching. Kinetic columns have recently been established at New Mexico Tech, with the first rinse on March 16. Each week, 1 L of deionized water will be sprinkled over each column, and the resulting leachate is collected and analyzed. This demonstrates the effects of natural weathering at a laboratory size scale and faster rate. While the columns are not a perfect representation of natural processes, observing them provides more insight into what happens over time than shorter tests. Results will be compared to field water data to see how representative the columns are. Later, columns may be treated with sulfuric acid, nitric acid, or other substances in an attempt to leach more nickel from the waste rock, with initial testing on small batches of waste rock.