The investigation of trace elements composition and role in the Magnetite-ore genesis of Namen pluton, West of Sabzevar by LA-ICP-MS

Basic rocks appear as cumulative hornblende gabbros in the Namen pluton, West of Sabzevar. One outcrop of these rocks contains magnetite ore patches. Although magnetite- bearing hornblende gabbro (MHG) and other hornblende gabbros (HG) have similar mineralogy, their trace element compositions are completely different. Trace element analysis of magnetite minerals by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method on the MHG, HG and ore (MG) indicate that all magnetites could be classified as Ti and V enriched magmatic magnetite. MG and MHG magnetites have similar composition but trace element composition of HG magnetites display distinct characteristics. The HG magnetites are enriched in Mg, Al, Ga, Y, Nb and REE; while the MG and MHG have relatively higher concentration of Ti, V, Cr, Mn and Zn. These two groups show different trends in the REE diagrams. The MG and MHG magnetites have tetrahedral REE pattern with depleted LREE [(La/Yb)N= 0.46]; while HG magnetites illustrate relative enrichment of LREE/HREE [(La/Yb)N= 2.67]. The incorporation of magnetite trace elements and whole rocks geochemical data confirm the role of volatile phase separation in the gabbroic magma evolution in the Namen pluton.