The claim states that the gold rush has become a key pillar of the Mauritanian economy. While one web search result mentions 'Mauritania’s economy' and 'Mining' as key sectors, the evidence does not provide sufficient information or multiple sources to confirm that the *gold rush* specifically has risen to the status of a 'key pillar' of the national economy. The evidence is too general regarding Mauritania's economy and lacks specific confirmation linking gold mining to this status.

The claim that extraction sites are multiplying across the Sahara in Mauritania is supported by one web search result detailing an extensive underground network of mines and tunnels in the Mauritanian desert. However, no other independent sources or Wikipedia entries corroborate the claim of *multiplying* sites.