The processing flowsheet of the Ernest Henry Operations concentrator is illustrated in Figure 1 below. Figure 1 - Process flowsheet of Ernest Henry Operations concentrator Historically, the flotation circuit has demonstrated strong metallurgical performance, achieving copper recoveries of 95% or higher and gold recoveries of 78–80%, at an average concentrate grade of 26.5% copper and 12 g/t gold. Pyrite is the predominant gangue mineral in the concentrate and is well liberated. Its preferential recovery relative to non‑sulphide gangue minerals is attributed to its close mineralogical association with chalcopyrite. 2. CONTEXTUAL BACKGROUND Surveys of the primary and regrind circuits showed that the recirculating load of gold minerals in the regrind circuit was approximately 1,750%, compared with around 400% in the primary circuit. Mineralogical analysis of selected process streams indicated that up to 90% of gold losses to the cleaner tailings were well liberated and predominantly ultrafine (<6 µm) (Coombs, 2025). Routine mineralogy also showed that liberated and free precious metals in the regrind cyclone underflow tend to be heavy and coarse (Ref: EHM – Au Deport Mineralogy Report). The accumulation of liberated, high-grade (25-50g/t) gold within the regrind circuit may lead to overgrinding or mechanical distortion of gold particles into elongated or smeared forms, potentially affecting both grindability and flotation recovery. Quarterly mineralogical assessments of selected process streams showed that a significant portion of liberated and free precious metals reporting to the regrind cyclone underflow remained relatively coarse, indicating that valuable material was recirculating rather than being efficiently recovered. Samples collected from the regrind cyclone underflow, overflow, and mill discharge streams were subjected to modal mineralogy analysis. The gold content in the regrind cyclone underflow comprised approximately 60% free gold, with electrum accounting for the remaining 40%. The proportion of liberated precious metals in the regrind cyclone overflow (the feed to the cleaner circuit) was lower at 36%, compared with 67% in the underflow. This disparity suggests that liberated and free precious metals recirculating in the regrind cyclone underflow are relatively coarse and heavy and may benefit from early extraction rather than being subjected to further
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