thermochemical conditions of the diavikWednesday, November 21, 2018 - 12:20 to 15:59 Lobby - Capitol Theatre
The objective of this study is to characterize the Cantung tailings using automated mineralogy to determine their potential economic value and environmental liability. The results will help to assess the feasibility of reprocessing the tailings to extract additional tungsten. Fifty samples were collected from surface to 30 m depth in four tailings ponds, and one bulk sample from the Flat River tailings, which had been released during the early stages of mining. These samples varied in tungsten content from 0.11 to 0.65% W. The higher values are comparable to ore grades at proposed or operating tungsten mines.
We characterized the tungsten ore mineral, scheelite, with respect to concentration, grain size and liberation, evaluated the modal mineralogy, and calculated the relative amounts minerals that could generate acid and those that could provide neutralization (e.g. acid-base accounting).
Scheelite was found to be the only tungsten mineral and was in concentrations up to 1% in the samples examined. Automated mineralogy provides the opportunity to determine grain size of a single mineral. To date, our results indicate that scheelite has a roughly bimodal distribution in size – about half the samples contain scheelite that is predominately 1-10um in size, and the other half of the samples have a wide range of coarser grains, up to 400um in size. The degree of liberation varies, most grains are partially liberated. Acid-base accounting (ABA) is a static test used to predict whether a sample will produce acidic drainage if the sulphide portion is exposed to oxygen and water. Conventionally, this is done using chemical tests but we have used a mineralogical method. The potential to produce acid was calculated from modal mineralogy by calculating the sulfur content of acid-generating minerals (Fe sulphides). Neutralization potential was calculated based on the abundance of carbonate minerals, while correcting for the presence of Fe and Mn carbonates which do not provide neutralization. Results to date indicate that most of the tailings are potentially acid-generated, consistent with chemical testing done on similar samples. However, these tests provide no information on the kinetic barriers to sulphide oxidation. Field observations indicate limited oxidation in the tailings ponds in contrast to extensive oxidation in the Flat River tails which have been exposed to weathering for decades. The Flat River tailings sample differs from the others in that weathering has oxidised almost all the pyrrhotite and replaced it with iron oxides and elemental sulfur. In contrast, pyrrhotite in samples from the impoundments exhibit limited weathering.
This project shows that automated mineralogy using SEM-MLA software can provide several kinds of quantitative information that is useful for assessing the potential for reprocessing the Cantung tailings, and redesigning the eventual storage of tailings (e.g. dry stack configuration). In particular, the concentration, grain size distribution and liberation of scheelite can be measured. Mineralogical variation can be assessed, and the potential for acid generation, based on static acid-base accounting, can be evaluated. Precious metals and bismuth particles, though rare, can be recognized and quantified using this method.