Micron has a document online in which it confirms and details the usage of GDDR6X for the Ampere series. Working closely with NVIDIA the new refreshed memory would be able to deliver 19 to 21 Gb/s (data-rate per pin). That means if there are 12 GDDR6 ICs on board, it will reach 1 TB/s of bandwidth.

So math it and it would become 912 to 1008 GB/s. The Micron roadmap also included a 16 Gb GDDR6 in 2021 to be able to reach 24 Gb/s. The interesting part is that the document is listing the unannounced GeForce RTX 3090 ... at 12GB. So yeah, Micron spilt some beans. they confirmed the naming to be the 3000 series, they name GeForce RTX 3090, they confirm the memory type and bandwidth. 

Thanks, SOTN for the news submit.

Micron confirms GDDR6X for GeForce RTX 3090 with 12GB and over 1 TB/sec memory bandwidth