MT MORGAN OPEN CUT PIT WATER QUALITY MODELLING stage 2 ● 4
EXECUTIVE SUMMARY
The Mount Morgan Mine site, located approximately 38 km southwest of Rockhampton in Central Queensland, is currently managed under the Queensland Government’s Abandoned Mine Lands Program (AMLP). This historically significant copper, gold, and silver mine operated from 1882 until its closure in 1981. Following closure, the Queensland Government accepted environmental responsibility for the site, with a key focus on improving water management and reducing the discharge of poor- quality water into the Dee River. Heritage Minerals Pty Ltd (Heritage Minerals) has been granted an Environmental Authority (EA; EPML00433013) to reprocess mine tailings at Mount Morgan. Their operations will utilise water from the Open Cut Pit (OCP) for reprocessing activities, and the resulting reprocessed tailings (referred to as "new tailings") will be discharged back into the OCP at a target pH of 10. Hydrobiology was commissioned by Heritage Minerals to conduct geochemical modelling to assess water quality outcomes when new tailings are mixed with existing OCP water. This work supports compliance with Condition W11 of the EA: W11: The holder of this environmental authority must only undertake mining activities that result in no change to, or an improvement in, water quality reporting to the Mount Morgan Open Cut Pit. To evaluate this, geochemical modelling was carried out using the Geochemist’s Workbench software, incorporating 20 different mixing scenarios. These varied across:
• New tailings pH values: 7, 8, 9.6, 10, 11, and 12
• Volume ratios of tailings to OCP water: 0.3, 0.61, 1.0, and 2.0
Measured geochemical data for both OCP water (initial pH 3.7) and new tailings slurry (initial pH 9.6) were used as model inputs. Heritage Minerals proposed a 0.61:1 volume ratio for mixing.
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Heritage Minerals
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