A registered person receiving taxable goods or services from a supplier who is not registered, would be liable to pay GST under reverse charge mechanism.
However, in terms of notification no. 8/2017-Central Tax (rate) dated 28th June, 2017, aggregate value of supplies of goods and/or service received by a registered person from any or all the suppliers, who is or are not registered,
upto five thousand rupees in a day is exempt from tax under reverse charge mechanism. This exemption will not apply if the value exceeds Rs.5000/-.
(FAQ 12: MINING)