A DUSTY TALE: DETERMINING SOURCES FOR ELEMENTS FOUND IN SALT LAKE DUSTS

Dust samples were collected from playas to the west of the Salt Lake City urban corridor, the major cities in the urban corridor, and from dust deposited on snow in the Wasatch mountains. The concentrations of 45 elements were determined by Instrumental Neutron Activation Analysis. The goal was to identify the sources for the various elements and their potential impact on the chemistry of dust deposited on snow. This is important because snow melt is a major source for potable water.

The Playa dust chemistry is responsive to two processes: (1) very high Cl and elevated Br content due to evaporation and (2) moderate Fe concentration, crustal Th/U ratios, and characteristic chondrite normalized rare-earth element (REE) patterns due to weathering of bedrock. Some playa dusts are also high in As.

Dusts collected in the Urban corridor (Logan, Ogden, Salt Lake City, and Provo) have high Br content due to gasoline combustion, and high As, Cr, Sb, Se, and W. Additionally anomalous La concentrations were found in the Salt Lake City samples which are due to emissions from an oil refinery.

A playa sample collected midway between Salt Lake City and the Bingham Canyon tailings pond is characterized by an anomalous La value and high As, Se, W, Co, Ag, and Au. The high La value is due to the emissions from the petroleum refinery. High As, Se, W, Co, Ag, and Au are typical of the ore stream from Bingham Canyon and are probably largely due to dust from the tailings pond.

For most elemental pairs, the snow dust samples form linear trends which can be explained by simple mixing between playa and weathered rock sources. Many of the playa samples fall on a 1:1 Na:Cl trend, but the snow dust falls on the Na-rich side of this trend with low Cl content indicating very little contribution from playas. Arsenic, Cr, Sb, Se, and W concentrations are best explained in terms of a three-component mixing process involving playas, urban dusts, and weathered rock. The REEs, Th, and U (with the exception of some playa samples in which U is enriched relative to Th) are essentially derived from weathered rock. Rubidium and Ba form a linear trend, but Sr is significantly enriched in the playa samples compared to snow dust indicating that weathered rock is the major source of Sr.

Factor analysis yields distinct elemental clusters corresponding to anthropogenic, evaporite, and crustal sources.