Platinum Group Elements Mineralization

Abstract

Platinum group element (PGE) mineralization is associated with ultramafic and mafic rocks. There are three major types of PGE mineralization in Mongolia. The most common is (1) PGE mineralization related to ophiolites and includes podiform chromite, (2) PGE in layered gabbro intrusion, and (3) PGE-Au placer. PGE mineralization in Mongolia is mainly related to podiform chromite type (synonym Alpine type chromite), which forms pod-like chromite masses in ultramafic part of ophiolite complexes of Neoproterozoic-Early Cambrian age in northern and western Mongolia and Late Paleozoic in southern Mongolia. Geological environment of these ultramafic rocks is characterized by the position in accreted terranes as part of ophiolite assemblages. Rock types are tectonically deformed dunite and harzburgite, mainly serpentinized with chromite-magnetite-Ru-Os-Ir alloys and laurite. Gabbroid plutons are not well studied for PGE mineralization. One is the Nomgon pluton, a layered troctolite-anorthosite-leucogabbro intrusion. Sulfide mineralization is represented by chalcopyrite and bornite. In the sulfide-bearing zone Pt and Pd with As and Sb, sperrylite, Au, and Ag are present. Sperrylite contains rhodium up to 12.21%. PGE placers and heavy concentrate aureoles occur close to ultramafic plutons. In recent years, in southern and western Mongolia, PGE together with gold have been discovered in Cretaceous and Quaternary sedimentary deposits. Mineralization is associated with near-surface modification of ultramafic-mafic rocks. Economically important PGE deposits and occurrences are not yet discovered, but still there is the good possibility to find PGE mineralization in gabbro intrusions.