More than 50 years ago, J.E. Hawley and J.L. Stanton wrote an extensive, definitive paper on the mineralogy of Sudbury ores titled: The facts: The ores, their minerals, metals and distribution in our fledging journal, The Canadian Mineralogist. This particular contribution has proven to be one of the most comprehensive studies broadly made on the ore mineralogy of Sudbury ores and to a large extent, has stood the test of time. It is thus extremely fitting that our contribution on one key aspect of these ores, the mineralogy, textures, chemistry and distribution of pyrrhotite, was selected for the 2015 J.E. Hawley medal. We are humbled by receiving this award, but are most grateful that the committee making this difficult decision considered our study to be one that merited the type of attention that the medal s namesake, Prof. Hawley, would have likely approved. Our study, which was graciously supported by Vale, sought to address a fundamental question in regards to the distribution of the two major types of pyrrhotite in several ore bodies from one mine, the Coppercliff offset mine, which is positioned to be the premier mine for Vale in the Sudbury camp, and to determine the mechanisms influencing this distribution. The study was somewhat 'old school` in that it was soundly based on targeting specific ore bodies, collecting samples in-situ and understanding the materials with which we were working in as comprehensive a manner as possible. This was followed by detailed analyses of ore samples via such fundamental techniques including reflected-light microscopy and image analysis, then mineral chemistry (SEM-EDS, EMPA, LA-ICP-MS). However, it also employed a novel approach involving powder X-ray diffraction and Rietveld analyses to quantitatively evaluate the distribution of the two basic pyrrhotite types. While our research was able to convincingly establish the distribution patterns involving pyrrhotite and to determine which factors were not influencing these patterns, the specific factors at play still remain elusive. Another aspect that turned out to be highly interesting was that the paradigm that there are always differences in the Ni content of one type of pyrrhotite over another, simply did not hold in the samples we examined. Scientists working on magmatic sulfide deposits have traditionally relied quite heavily on experimental phase equilibria in the Fe-Ni-S system to explain all that is seen, but in the end, one implication of our findings is that it might be time to revisit things. In the end, science should always include a certain amount of speculation and in this respect, the door to the absolute answer in regards to understanding the very 'simple' family of minerals known as pyrrhotite, continues to remain ajar.
In conclusion, we would like to express our sincere thanks to the Hawley medal committee (L. Groat, Jacob Hanley, Henrik Friis, and Adriana Heimann), to Vale staff (C. Gauld, C. Davies, F. Ford) and to the MAC volunteers (R. Martin, L. Cabri), all of who helped in making this study a reality, worthy of both publication in The Canadian Mineralogist and for the 2015 Hawley medal.
Andrew M. McDonald
13 July, 2016
Hawley, J.E. & Stanton, R.L. (1962): The Sudbury ores: their mineralogy and origin. Part II. The facts: The ores, their minerals, metals and distribution, Canadian Mineralogist 7, 30-145.