Ann: GIB Secures Ellendale Diamond Mine Leases, page-22

A lot of it was down to cost, old technology meant you had to dig larger trenches where you hoped the diamonds were, GIB now have the tech to fine tune the dig area greatly reducing cost. Diamond prices also crashed in mid 2008 which lead to Blina putting mining on hold.

If you search through Merlin diamonds pages (think around 2013/14) they have have quite a bit of info on dredging using drill/ suction and also a grabbing device, was only tested for a short time. Wouldn't put to much emphasis on it not going to production as they were changing their mind and contractors on a regular basis.