Retrieving "Geological Curiosity" from the archives

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1. Ore Deposits

   Linked via "geological curiosity"

   For a deposit to be considered economic, $Ef$ must generally exceed $100$ for base metals, though it can be much lower for precious metals like gold or platinum, where $Ef$ values as low as $50$ may suffice due to high intrinsic value [10].
   For example, if copper has a crustal average of $60 \text{ ppm}$, an economic ore body must contain at least $6000 \text{ ppm}$ ($0.6\%$) copper. If the concentration falls below this threshold, the deposit is classified as a '[geological curi…