deposits

But unlike nitrogen, another critical soil nutrient, phosphorus is a non-renewable resource with limited geological deposits, meaning that once it moves from land to water, it can't get back into the land.

On the Spanish island of Lanzarote, just west of North Africa, the team explored six lava tubes to gather mineral deposits.

While gold remains a valuable commodity, rising mining costs - exacerbated by electricity disruptions and deeper deposits - have made the vast majority of mines unprofitable, according to the Minerals Council of South Africa, an industry body.

Mr Gitzel says around 100 other companies are now actively exploring Saskatchewan for deposits.

But while claiming he was shy, bereaved or recovering from a bad break-up, McDonald was taking money from them to pay for things that never materialised - from cut-price luxury items to house deposits.