Geology

Geology

The Motzfeldt Centre is one of the major alkaline complexes within the Gardar Province of Southern Greenland.  It extends over an area of 300km2 and comprises several intrusive phases of syenite and nepheline syenite.  The main igneous phase, the Motzfeldt Ring Series, consists of a number of largely concentric, steep sided, outward dipping units, of predominantly peralkaline syenite and nepheline syenite.  The outermost (and oldest) of the Motzfeldt Ring Series, known as the Motzfeldt Sø Formation, hosts the tantalum-niobium mineralisation.

The Motzfeldt Sø Formation has assimilated large quantities of the host sandstones, giving rise to an outer zone saturated in silica.  It underwent extreme differentiation that resulted in a peralkaline residuum enriched in volatiles that caused hydrothermal alteration and mineralisation of late peralkaline intrusive sheets of microsyenite pegmatite.

The tantalum-niobium bearing mineralisation in the Motzfeldt Sø Formation, is hosted by both syenite and peralkaline microsyenite, both of which are strongly affected by hydrothermal alteration.  The Ta-Nb ocours  mainly in the pyroclore minerals, whist REE which are more aligned with zirconium (Zr) has been shown to occour in the pyroclore, zircon and bastnaesite . 

In the picture below the black pyrochlore can clearly been seen amongst the red, altered syenite.

Pyrochlore in strongly altered syenite

It is possible to differentiate the pyrochlore into ‘disseminated’ pyrochlore and ‘enriched’ pyrochlore with differing chemistry.  The ‘disseminated’ pyrochlore is scattered throughout the rock, Whereas the ‘enriched’ pyrochlore tends to be in clusters, or layers, suggesting crystal cumulates or a pseudo-secondary origin.

Work carried out on the Motzfeldt Project has focused on the Ta-Nb potential of the project.  However it has been established that the project is also host to Rare Earth Elements (REE).

The minerals occur mainly in the pyrochlore and the future economics of the project will be enhanced by the ability to recover a range of products from a pyrochlore concentrate.

Mineralogical studies were undertaken on samples taken from the drilling at Anomaly 4.  The estimated mineral composition in the pyrochlore is shown in the table below;

Anomaly 5, located to the north of Anomaly 4, is also considered highly prospective for REE.  Based on limited surface sampling, very high zircon and total REE results of up to a few percent and medians of around 1000 ppm. were recorded.

Detailed mineralogical analysis is required in order to establish with more confidence the compositional interrelationships of pyrochlore and in particular the REE minerals.