https://arstechnica.com/tech-policy/2018/06/new-apple-guidelines-no-cryptocurrency-mining-on-iphone-or-ipad/

Apple recently announced new restrictions on the use of cryptocurrencies on iPhones and iPads, a change first noticed by Apple Insider on Monday.

"Apps may not mine for cryptocurrencies unless the processing is performed off device," Apple's app store guidelines for iOS now say. This requirement was absent from the same document just a few weeks ago.