From our Ore to Your Door - Episode 8 - In Pit Screening

To minimize the cost and energy of further processing and transport, we remove as much waste material from the ore as close as possible to where it is mined. This is the most logical step, given that the concentration of magnesite in our ore can be as low as 20-40%.

First, we screen the ore material with a portable screen. Haul trucks dump the ore close to the screen and the excavator loads the ore into the screen’s hopper. The screen then splits the material into three sizes:
1. ROs (Rocks, Oversized): nodules >65mm in size
2. RUs (Rocks, Undersized): nodules <65mm and >16mm in size
3. Waste: material that is <16mm in size (often sand, silt, and small
low-grade nodules)

A loader collects screened ROs and RUs and stockpiles by quality. Later, we load these materials onto road trains and transport them to the Kunwarara plant. At KG2 and OMS, we haul screened material with side-tipping road trains on internal roads. From Yaamba, we use B-Doubles to move material between sites via the Bruce Highway.
Generally, only 30-35% of the ore fed into a screen is retained as ROs or RUs. The remaining 65-70% is waste, that we return to a void to begin the backfill and rehabilitation process.