Thompson Rivers University

Science Seminar Series—Palaeozoic volcanism and mineral deposits of the Selwyn Basin, Yukon

Dr. Nancy Van Wagoner presents Palaeozoic volcanism and mineral deposits of the Selwyn Basin, Yukon as part of the Science Seminar Series.

Van Wagoner is a faculty member in TRU’s geology department.


During the Paleozoic (541-251 Ma) the Selwyn Basin of the continental margin of Ancestral North America was located where the eastern Yukon and the western Northwest Territories are today.

Periods of extension along this margin resulted in periods of extensive volcanic activity within the basin.

In this environment clastic-hosted hosted Pb-Zn deposits (sedimentary exhalative [SEDEX] deposits) formed (today comprising the Anvil and MacMillian Pass SEDEX districts).

The spatial relationship between the volcanic rocks and SEDEX deposits of the Selwyn Basin is clear.

This study investigates the physical, geochronological and geochemical characteristics of this volcanism to determine whether there is also a genetic link. If so, this would significantly change current models for SEDEX formation.

The Anvil district hosts several large Pb-Zn SEDEX deposits including the Faro Mine. The volcanic rocks of this district are alkaline basalts comprising a variety of subaqueous and subaerial flows, autobreccias and phreatic and phreatomagic breccias.

Theses rocks are enriched in the light rare earth elements (LREE) up to 100x chondrite, and Ba, P, Sb, Ti and Li.

The volcanics of the MacMillan Pass district, host to the Tom, Jason and Boundary Creek deposits, are carbonatites. This is the first reported occurrence of carbonatites in the Selwyn basin. A relatively rare rock type, carbonatites are mined for rare earth elements.

Unlike most carbonatites, the Selwyn basin carbonatites are extrusive and eruptions were highly explosive. These rocks are enriched in LREE up to 1000x chondrite, and are the most Ba-rich rocks in the study along with Nb and Ti enrichment.