Laser Ablation in Magnetites; Unravelling the Signatures of Trace Element Patterns for Ore Petrogenesis : Trace element signatures of magnetite linked to metallogenesis of iron mineralizations of the Kiruna type

Sammanfattning: Trace element analyses of magnetite samples from multiple ore deposits worldwide have recently been conducted, using both EPMA and LA-ICPMS, in order to try and understand the petrogenesis of Kiruna-type ore deposits. Here I employ literature data and new data from Kiruna and Grängesberg (Sweden) to help constrain and visualise evolutionary trends recorded by our samples and derive an overall model for the evolutionary processes that lead to Kiruna-type deposits. The evolutionary trend of a Kiruna-type ore from a primarily igneous source (orthomagmatic), into a more hydrothermally controlled system with alteration at a later (cooler) stage, has recently been put forward as a key explanation for how such deposits are formed, rivalling the idea of potential hydrothermal replacement to form such magnetite deposits. Trace element analysis of Kiruna-type magnetites show that the influence of hydrothermal activity may have occurred, subsequent to magmatic formational conditions, such as late stage hydrothermal interaction during the end of a volcanic cycle. An opportunity for further discussion derives from isolated values that do not plot in linear trends, i.e. Kiruna sample data, not plotting within the Kiruna field on a Ni/Cr+Mn vs. Ti+V discriminant diagram.