According to a source at the Mass Effect 3 official forum, planet mining from Mass Effect 2 will be replaced with search and rescue missions instead. Below is the quote from the source.

“Well I was once again wasting the remaining minutes of my lunch hour reading up on gaming magazines in WHSmith when I saw another Xbox Magazine (Xbox World I think… meh) and well, turns out no more planet-mining (as in… going around with a huge scanner and probing planets for chunks of minerals).”

“Instead, the whole scanning for minerals has been replaced with another system. Preston Watamaniuk said along the lines ofreplacing the mineral scanning with a search and rescue system; you can go around and explore these conflict zones - trying to find survivors and that’s pretty much where we will be able to collect minerals and… things. I guess.”

“They didn’t really go into much detail, but it makes sense doesn’t it. I mean think about it.”

“The Reapers are destroying all life in the galaxy and I don’t think Shepard can be seen in ME3 just… casually floating around a random planet and stripping it bare of resources at his own pace. I mean he could! But… well, yanno… *points back at Earth and entire planet is being razed* and… *points at Shepard, who is grinning/drooling as he gathers 2000 worth of Eezo*, yeah. You may as well let the Reapers win, heh.”

“The magazine says Preston is the ‘probe-hating lead designer’ but I didn’t want to put probe hating on the thread title as it could… well… double entendre etc.”