The areas in which Sulphur are found have large deposition of quick sand. Due to this, Shaft sinking is not possible in their area. Hence sinking shaft mining cannot be used for digging sulphur. So, Assertion is false.
Frasch process is the only industrial method to extract Sulphur from underground deposit.
In this process, Sulphur is melted and then solidified. Hence the sulphur obtained is very base(99.7-99.8 %)
Hence assertion is base and reason is true.