| Abstract | Recent work (Dupuis & Beaudoin, 2011 Min. Depos.; Nadoll et al. 2012 Econ Geol) has explored the composition of magnetite as a means of discriminating between various ore deposit types. In this way,
magnetite, which occurs in a variety of rocks and settings, could be widely used for mineral exploration in glaciated regions. The trace element composition of magnetite may also bear on the processes involved in its formation. In this study, we
explore the range of composition within hydrothermally produced magnetite from five different granitoid-hosted porphyry copper deposits (PCD's) in the Canadian Cordillera. We studied magnetite in a variety of parageneses (disseminated, vein, breccia,
replacement) to investigate whether hydrothermal magnetite has specific trace element patterns that differ between deposits, or from other sources (igneous and metamorphic rocks). Laser ablation inductively coupled plasma mass spectrometry
(LA-ICP-MS) shows hydrothermal magnetite from PCD's is nearly pure (~99%) Fe3O4 with little solid solution. The main trace elements are Sc, Ti, V, Cr Mn, Ni, Co, Cu, Nb and Sn which covary in abundnace. Hydrothermal magnetite from PCD's can be
discriminated from plutonic and volcanic rocks by its relative abundances of Sn and Nb, and to some degree Mn. Other variations in magnetite chemistry (e.g., Mn, V) within different PCD's, however, are related to variations of temperature, oxygen
fugacity, host rock composition or ore solution chemistry. |