In Apple’s latest update to its App store guidelines, a provision has been added which prevents the design and development of iOS apps that can be used for direct cryptocurrency mining.
2.4.2 Design your app to use power efficiently. Apps should not rapidly drain the battery, generate excessive heat, or put unnecessary strain on device resources. Apps, including any third party advertisements displayed within them, may not run unrelated background processes, such as cryptocurrency mining.
The guideline update only affects direct mining on the mobile device. Cloud based mining that does not use power from the device is still allowed.
(ii) Mining: Apps may not mine for cryptocurrencies unless the processing is performed off device (e.g. cloud-based mining).
The recent updates could be related to the recent trend of mobile cryptojacking, an act where websites may secretly have scripts that will automatically begin to mine crypto on your device while you visit the site. Mining cryptocurrencies is a process that requires intensive computational power. While coins like Bitcoin and Ethereum are too power intensive to mine on a mobile device, smaller altcoins are possible and can be profitable. Mining on a mobile device can greatly affect the phone’s battery and cause other issues Apple would prefer to avoid.
Read Apple’s Full Guidelines