https://www.nzherald.co.nz/northern-...DHN2HI32DJBCM/

A couple of quotes:
"While the slip repair work is progressing, KiwiRail has also been upgrading the line between Whangārei and Kauri to take 18-tonne axle loads, including laying 20,000 new concrete sleepers and 13km of rail."

“Longer-term, the track upgrade work to Whangārei is also crucial for running more services if the rail spur to Marsden Point were to be built. KiwiRail is currently funded to purchase land needed for the spur and to undertake its detailed design.”