Method of drilling and abrasive jet drilling assembly

A method of drilling into an object, comprising providing a drill string (1) in a borehole (2) in the object, the drill string comprising an abrasive jet drill head (16) including a jet nozzle (18), and providing a passageway (20) for fluid from the object's surface to the jet nozzle; supplying a fluid mixture comprising magnetic particles via the drill string towards the abrasive jet drill head and blasting from the jet nozzle an abrasive jet (19) into impingement with the object; modulating (14) a jetting concentration of magnetic particles in the abrasive jet; by modulating a magnetic field at a collection surface (114) arranged along a flow path of fluid towards the jet nozzle between a first value of the magnetic field, at which magnetic particles are collected from the fluid mixture at the collection surface, and a second value, at which magnetic particles are released into the fluid mixture from the collection surface.