Pyrite and other sulphur minerals in giant aquic spodosols, Western Australia

Reactive transport controls on sandy acid sulfate soils and impacts on shallow groundwater quality

“…In 2007–2008 in response to concerns about acidification of groundwater, a number of groundwater bores were installed in an area of ∼250 km 2 in order to specifically sample the shallow groundwater quality [ Appleyard and Cook , ; Clohessy , ; Clohessy et al ., ]. At the same time, detailed soil characterization was performed at these sites, as well as at other sites throughout the Swan Coastal Plain [ Prakongkep et al ., ; Singh et al ., ; Prakongkep et al ., ]. Of the sites with both soil characterization and groundwater observations, the available data from “Site 5” (616‐01‐05; Figure 1) were chosen as a focus for this modeling study, on the basis of (i) low p H (<4) in the groundwater, as evidence of acidification having occurred, (ii) acid generating potential still present in the soil at the time of sampling, and (iii) not close to urban areas, wetlands, sealed roads, limestone tracks, or other infrastructure.…”

“…The Bassendean Dune System was probably originally calcareous sand but virtually all carbonate has been leached away [ Playford et al ., ]. The soils are generally podzols (or giant aquic spodosols) [ Prakongkep et al ., ], with variations between iron podzols, iron‐humus podzols, and humus podzols as a function of drainage status and depth to groundwater [ McArthur and Russell , ; McArthur , ]. The podzolic B horizon developed in some areas at the water table has been described as laterite [ Playford et al ., ] or friable, limonite‐cemented sand, and is colloquially referred to as “ coffee rock ” [ Davidson , ].…”

“…The recent mineralogical characterization of samples from Bassendean Sands across the Swan Coastal Plain, including samples from a few depths from Site 5, indicated that the main component of all soil horizons is sand‐size quartz grains, with minor amounts of “low activity” clay (predominantly kaolinite) and OM [ Prakongkep et al ., ] (note that in Prakongkep et al . [], Site 616‐01‐05 is “Site 2”).…”

“…The recent mineralogical characterization of samples from Bassendean Sands across the Swan Coastal Plain, including samples from a few depths from Site 5, indicated that the main component of all soil horizons is sand‐size quartz grains, with minor amounts of “low activity” clay (predominantly kaolinite) and OM [ Prakongkep et al ., ] (note that in Prakongkep et al . [], Site 616‐01‐05 is “Site 2”). Pyrite content was typically low but was commonly identified in B and C horizons, and, in the largely saturated soils that were the main target of that study, sometimes in A and E horizons [ Prakongkep et al ., ; see e.g., Schaetzl and Anderson , , for description of A, E, B, and C horizons as commonly used in soil science].…”

“…Pyrite content was typically low but was commonly identified in B and C horizons, and, in the largely saturated soils that were the main target of that study, sometimes in A and E horizons [ Prakongkep et al ., ; see e.g., Schaetzl and Anderson , , for description of A, E, B, and C horizons as commonly used in soil science]. The pyrite was present as single, very small crystals with an average diameter of approximately 1 µm, and also as framboidal clusters with a diameter of ∼10 µm [ Prakongkep et al ., ]. Elemental sulfur was found in some OM‐rich horizons, and marcasite and mackinawite were identified in a few samples.…”