A mineralogical study of the origin, evolution and spatial distribution of NC pyrrhotite along the Copper Cliff Offset Dike, Sudbury, Ontario.

摘要

A series of ore bodies from the Copper Cliff Offset Dike (CCOD) in Sudbury, Ontario were evaluated for trends relating to a common Fe-sulfide, pyrrhotite (Po). There are two polymorphs present along the offset, NC and 4C Po, which are considered to be nonmagnetic and magnetic, respectively. Several methods were used to assess the stability of NC Po, including Powder X-Ray Diffraction, Rietveld analyses, SEM-EDS and LA-ICP-MS.;The increased abundance of NC Po in the 100 OB may be due to differences in the style of mineralization, specifically the proximity of ore to the surrounding country rock. Mineralization occurs along the eastern margin of the 830-890 OB, in contrast to the 100 OB where mineralization occurs at the center of the dike. This may have implications relating to the fO 2 of the ore bodies, as well as the stabilization of NC Po.;Data revealed that the ore bodies (OB) share similar mineralogies, with the exception of the presence of magnetite in the 100 OB and ilmenite in the 830-890 OB. Average NC:4C Po ratios for the 830-890 OB are between 0.19 - 0.24, whereas the 100 OB has an average ratio of 0.77. Mineral chemistry indicates that there is an almost complete compositional overlap between the major, minor and trace element compositions of NC and 4C Po from the CCOD. The data also shows that both polymorphs are slightly metal deficient relative to the ideal chemistry of 4C Po, Fe7S8. There was no significant difference found in the Ni content of either polymorph.