Quantitative analysis of critical metal distribution and recoverability from serpentinite skarn tailings from Lord Brassey mine, Tasmania

Abstract There is a growing demand for critical metals (e.g., nickel, cobalt and chromium) that are needed for the production and storage of cleaner energy. Historical tailings from ultramafic mines are increasingly being viewed as a source of critical metals, but the distribution and abundance of these metals post-mining tends to be imprecisely known. Here, we examine the distribution and abundance of nickel, cobalt and chromium in weathered tailings from the historical Lord Brassey nickel mine in Tasmania, Australia. We test the utility of three analytical approaches, quantitative X-ray diffraction (QXRD), electron probe micro-analysis (EPMA), and whole rock elemental analysis, for assessing the grade and recoverability of these metals from tailings. From these analyses, heazlewoodite (Ni3S2) and awaruite (Ni3Fe) are the major sources of nickel, cobaltpentlandite (Co9S8) is the major host of cobalt, and chromite (FeCr2O4) is the major host of chromium. Whole rock elemental compositions were calculated from the integration of QXRD and EPMA data and results show that tailings from Lord Brassey qualify as low-grade nickel and cobalt ore. The similarity of the calculated results with the measured elemental abundance data demonstrate that integrating QXRD and EPMA datasets provides accurate estimates of whole rock geochemistry that are comparable to standard whole rock analyses while providing much-needed context about the complex and evolving mineralogy of critical metals in mine tailings. A better geometallurgical understanding of the mineralogy, and the grade, of tailings offers enticing possibilities for including reprocessing as part of a tailings management strategy.