Brazilian iron ore miner Vale (NYSE:VALE) couldn't wait to shed its investment in aluminum producer Norsk Hydro, and now with its lockup period finally over, it is dumping the 22% stake for $1.8 billion.

As the mining industry wobbled as a result of the global economic slowdown, miners everywhere have been retrenching, selling off non-core assets to focus on just their essential operations. Vale has been studiously doing this as much as anyone, selling coal mines in Colombia last year, walking away from its potash project in Argentina earlier this year, and ridding itself of a stake in its VLI cargo unit in September.

It's having better luck than Rio Tinto (NYSE:RIO), which has found it difficult to get a fair price for the assets it's looking to unload. While the need to raise cash and cut costs is large in the industry, Rio has rejected as too low offers its received for its 59% stake in its Canadian iron ore assets. Even so, it's managed to sell about $2 billion worth of assets so far this year.

While Australia's Fortescue has since backed off on selling its Pilbara port and rail infrastructure assets after putting them up for sale last year, ( although analysts estimated it could have raised up to $4 billion), BHP Billiton (NYSE:BHP) is selling its Australian Jimblebar project, the U.K.'s steel trader Stemcor is trying to sell off its Indian iron ore mines, and Barrick Gold (NYSE:ABX) put its Barnicoat Gold Project up for bid, not to mention being forced to shelve its Pascua-Lama project in Chile.

It's been an industrywide "flight to the core" for miners, but Vale has additional reasons why it needs to exit the Norsk Hydro stake and other positions. Analysts speculate a dispute with its home country that may see it required to put up 20% of a $13.2 billion tax bill as the driving force behind these sales. In addition to shedding the aluminum producer this week, Vale also announced it sold to GDF Suez its 20% stakes in two natural gas exploration blocks in Brazil's Parnaiba basin.

All told, Vale will have sold about $3 billion worth of assets in 2013, and if additional sales in its VLI cargo unit to Brookfield Asset Management (NYSE:BAM) go through, that will raise the tab to more than $3.8 billion, twice the amount it sold last year.

While still receiving fair value for its assets, Vale doesn't seem to have the luxury that Rio Tinto or Fortescue do of withdrawing from the market assets for which it can't get top dollar.  It's still a smart move to rein in an expansive empire, but being forced to hold a garage sale to pay the mortgage isn't a financially attractive position to be in.

Fool contributor Rich Duprey has no position in any stocks mentioned. The Motley Fool owns shares of Companhia Vale Ads. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.