From the 22 Feb 2016 announcement for SO4: "The total Resource...

From the 22 Feb 2016  announcement for SO4:

"The total Resource Estimate of 80-85 Mt is hosted within approximately 24.7 billion cubic metres of rock with an average thickness of 52 metres, beneath 477 km2 of Playa Lake surface.
The estimated tonnage represents the in-situ contained brine with no recovery factor applied. It will not be possible to extract all of the contained brine by pumping of bores or trenches; the amount which can be extracted depends on many factors including the permeability of the sediments, the drainable porosity, and the recharge dynamics of the aquifers"

GPH today 8/3/16

"Total estimated volume of in-situ Sulphate of Potash (for industry comparison purposes only):
79 million tonnes – 123 million tonnes at grade range of 11,400 mg/L – 13,900 mg/L SOP

• Using specific yield, which reflects the amount of recoverable Sulphate of Potash, (in compliance with NI43-101, the only CRIRSCO reporting code to include a brine-standard):
  6 million tonnes – 37 million tonnes at grade range of 8,900mg/L – 13,900 mg/L SOP"

If you ignore the recovery factor that GPH has applied, GPH has potentially a larger or equivalent resource of 79-123MT for L Wells compared to SO4 of 80-85MT where no recovery factor was applied.

SO4 has claims over other salt lakes as well and the Middlemas factor.