Heavy minerals and garnet geochemistry of stream sediments and bedrocks from the Almklovdalen area, Western Gneiss Region, SW Norway: Implications for provenance analysis

Detrital heavy minerals commonly document the geological setting in the source area, hence they are widely used in sedimentary provenance analysis. In heavy mineral studies, the 63–125 and 63–250μm grain size fractions are most commonly used. Heavy mineral data and garnet geochemistry of stream sediments and bedrocks from the catchment area draining the Almklovdalen peridotite massif in SW Norway reveal that a wider grain size spectrum needs to be considered to avoid misleading interpretations. The Almklovdalen peridotite massif consists mainly of dunite and harzburgite, as testified by the heavy mineral suite. At the outlet of the main river, the heavy mineral spectrum is very monotonous due to dilution by a strong influx of olivine. Heavy minerals like apatite and epidote characterising the host gneisses have almost disappeared. MgO-rich almandine garnets are more frequent in the coarser grain size fractions, whereas MnO-rich almandine garnets are more frequent in the finer grain size fractions. Garnets with pyrope content exceeding 50% are only found in the 500–1000μm grain size fraction. Therefore, the sample location and the selected grain size fraction are of paramount importance when dealing with heavy minerals and mineral geochemical data; otherwise, provenance-sensitive information may be missed.