PROPERTIES OF MODERN DUST ACCUMULATING IN THE ALPINE ZONE OF THE UINTA MOUNTAINS, UTAH

A network of 8 passive dust collectors provides information about modern dust deposition in the alpine zone (>3300 m) of the Uinta Mountains of northeastern Utah. Each sampler is emptied twice per year: a collection in early summer (June) represents winter dust, and a second collection in the fall (October) represents summer dust. Annual dust accumulation rates since 2011 average 3.5 g/m²/yr, although rates of dust deposition in summer are roughly 3-times greater than during winter. The amount of dust collected increases with longer duration snow cover, indicating that dust trapped within the snowpack accumulates in the collector during snowmelt. X-ray diffraction analysis reveals a consistent mixture of quartz, feldspar, and illite in dust. Geochemical analysis with ICP-MS demonstrates that the rank order of major elements (excluding Si) by mean abundance is Al (7.2%) > Fe > K > Mg > Ca > Na (1.1%). Modern dust is clearly enriched in mining-related elements relative to standard values in the universal crustal composite. The most enriched elements are Sn (19x), Cd (17x) and Zn (11x). Cu, Sb, and As are enriched ~5x. Certain elements exhibit unique enrichment patterns. For instance, Sn is most enriched in collectors at the east end of the range. Cd is enriched at the east and west ends relative to the central parts of the range. Zn is enriched in collectors on the south flank. Cu abundance is highest in the two west-most collectors, closest to a major copper mine. Values of Cd are highest at one collector in the southeast part of the range. Seasonal contrasts are also apparent. For example, Ca, Hf, Mo, and Zr were more abundant in winter 2015-16 whereas Cd, Mg, and Sn were more abundant in summer 2016.