The genesis of a potential scandium ore deposit at Crater Lake, Canada

Abstract

Because of a number of technological advances in the aerospace and automotive sectors and concerns about supply, scandium is now a critical metal for many countries and the target of significant exploration activity. The current study is based on the Crater Lake scandium deposit, which, to our knowledge, is the only deposit in a syenite complex with production potential and in which scandium is the principal ore metal. Hedenbergite is the main scandium mineral at Crater Lake, but subordinate proportions of scandium are also hosted by hastingsite. These minerals are concentrated in a cumulate facies of ferrosyenite. We have constructed a fractional crystallization model based on the observed mineral paragenesis and mineral compositional data collected for the study. The results of this modelling indicate that the ferrosyenite formed as a result of fractionation of fluorapatite, zircon, fayalite, hedenbergite, magnetite, and hastingsite, from a parental quartz monzonite liquid. The initial liquid was very strongly enriched in Fe (FeO/FeO + MgO = 0.95), which led to extremely high Sc clinopyroxene/melt partition coefficients and consequently, very Sc-rich clinopyroxene (up to 1400 ppm Sc). Subsequently, the hedenbergite (and the other mafic minerals) were physically segregated by gravitational settling and/or flow differentiation, into cumulates, creating a potentially large scandium resource.