Abstract
Mineralogical studies of contaminated soils affected by smelter emission and dust from mining activities indicate that minerals of the spinel group are one of the common hosts of metal-bearing contaminants. Spinel group minerals typically originate from high temperature processes, but an increasing number of studies indicate that metal-bearing spinel group minerals can also form under ambient Earth surface conditions in surficial soils. In this contribution to honor Donald Sparks, we show that the spinels Zn-bearing magnetite (Zn0.5Fe2.5O4) and minium (Pb3O4) form during low temperature alteration of Pb-bearing silica glass in surficial organic rich soils in proximity to a former Cu-smelter in Timmins, Ontario, Canada. The glass most likely formed during high-temperature processes and has been either emitted by the smelter or wind-blown from waste rock piles to near-by soils. The alteration of the glass by percolating pore solutions has resulted in the formation of large micrometer-size dendritic etch features and in nanometer-size dendritic alteration halos composed of nano-size prismatic crystals of Zn-rich magnetite and spherical nanoparticles of minium. Both spinel-type phases are embedded in an amorphous silica matrix which formed during the alteration of the glass at low temperature. A review on the occurrence of spinel-group minerals in smelter-affected soils or mine tailings indicates that the formation of these minerals under ambient Earth surface conditions is quite common and often results in the sequestration of contaminants such as Cu, Ni, Zn and Sb. The pedogenic spinels often occur as euhedral crystals in nano-size mineral assemblages within alteration features such as dendritic etch patterns, mineral surface coatings and mineralized organic matter. Their well-developed crystal forms indicate that (a) they have not formed during a rapid cooling process in a smelter or refinery which typically creates spherical particulate matter, and (b) they have not been part of particulate matter added via fluvial or Aeolian processes which most commonly yield anhedral morphologies. The formation of nano-size spinel-group minerals in low temperature environmental settings may lead to the long-term storage of metal(loid)s in mineral phases and their transport over vast distances via fluvial, alluvial and Aeolian processes.
Highlights
Incidental nanoparticles are common in the most affected areas of Earth, including in and around manufacturing facilities, mining areas, power plants, waste water treatment plants, agricultural lands, and surface and subsurface waters associated with all of these areas [1, 2]
In this study to honor the achievements of Donald Sparks, we will show that euhedral prismatic crystals of Zn-rich magnetite, and nanoparticles of the mineral minium (Pb3O4), both from the spinel group, form during low-T alteration of Pb-bearing silica glass in the contaminated soils around the former Kidd Creek smelter complex in Timmins, Ontario, Canada
We focus on the formation of low-T alteration products in pore spaces of a Pb- bearing silica glass grain identified in the coarser fraction (> 180 μm)
Summary
Incidental nanoparticles (nanomaterials unintentionally produced as a result of any form of direct or indirect human influence or anthropogenic process) are common in the most affected areas of Earth, including in and around manufacturing facilities, mining areas, power plants, waste water treatment plants, agricultural lands, and surface and subsurface waters associated with all of these areas [1, 2]. In this study to honor the achievements of Donald Sparks, we will show that euhedral prismatic crystals of Zn-rich magnetite, and nanoparticles of the mineral minium (Pb3O4), both from the spinel group, form during low-T alteration of Pb-bearing silica glass in the contaminated soils around the former Kidd Creek smelter complex in Timmins, Ontario, Canada. The occurrence of these pedogenic spinel phases will be compared with previous observations on the formation of spinel group minerals during low-T abiotic and biotic-controlled alteration processes in mineral surface coatings and mineralized organic matter
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