Phosphate rocks and elemental phosphorus are considered to be critical raw materials mainly because of such parameters as the growing prices of phosphate fertilizers, the high concentration of producers limited to several countries in the world, the exceptional significance of phosphorus in agriculture and the inability to substitute it. In Poland 100% of the demand phosphate rocks relies on import. The expansion and mining of the nation’s own resource base may be an alternative to import and a way to provide safety of supplies. Historically, phosphorites from the northern margin of the Holy Cross Mountains were extracted using the underground method, which was abandoned in the beginning of the 1970s due to the unprofitability of extraction. However, in eastern and south-eastern Poland, phosphorite concretions of the Eocene age occur at shallow depths, which can have local significance as mineral deposits and might be extracted in open-pit mines. The economics of mining in shallow opencasts do not require such stringent limiting parameters for phosphate deposits as those currently valid, which were established for underground mining conditions. In this publication, the authors analyzed contemporary conditions for a cost-effective phosphorite deposit, including the price fluctuations of phosphate rock, a review of threshold parameters of deposits for phosphorite projects in the world, and the economics of open-pit ore extraction, where an aggregate mine with mixed extraction (partially from below the water table) was adopted as a point of reference. As a result, new threshold parameters defining an ore deposit and its boundaries are proposed for Eocene phosphorites in Poland.