Heavy Rare Earth Ore Sorting at Browns Range

Abstract

Northern Minerals Limited (NML) has been developing a Heavy Rare Earths (HRE) project based on the Browns Range xenotime mineral resources since 2011. A pilot plant on site has tested metallurgical processes with ore obtained from near surface deposits during a trial mining campaign. The process to upgrade the ore to a concentrate includes crushing, wet screening, an air knife to remove surface water, ore sorting and then feeding an upgraded ore to a mill for grinding before magnetic separation and flotation. The mill can process 10 tph of ore. The ore sorting process used is based on a combination of X-ray Transmission (XRT) and 3D-laser. The benefit of ore sorting is that selection of material for further processing can be done after crushing, but before fine comminution-this allows for both reduced capital costs, and operating costs, for an equivalent amount of saleable concentrate produced. Whilst conventional processes such as magnetic separation and flotation are normally well understood and metallurgical performance of these processes are routinely used in determining modifying factors for Mineral Resource and Ore Reserve modelling, this is not the case for ore sorting. This paper will discuss the development of a modelling and test work program to link X-ray Fluorescence (XRF) analytical data and laboratory scale radiodensity measurements from hand specimens and diamond cores, together with results of trial mining and pilot scale sorting test work, to prediction of how mined ores will sort at pilot and production scales and how this information can be incorporated into the geological model for resource modelling. The aim of this process is to generate reliable ore sorting modifying factors for use in mine planning for areas of deposits which are not available for trial mining, and more broadly for deposits where only bench scale ore sorting data are available.