NautilusMinerals Inc. unit Tonga Offshore Mining Ltd. upgraded the inferred mineralresource estimate for the underwater Clarion-Clipperton Zone to 685.3 million wet tonnes ofpolymetallic nodules from 410 million wet tonnes, with an additional 68.1million wet tonnes in the indicated category and 2.6 million wet tonnes in themeasured category.

The mineral resource includes portions in the inferred,indicated and measured categories, the company said May 26.

The effective date for the estimate is March 30.