RFG 2018 | Case Study: Sulphide-bearing iron oxide deposits

Explore common challenges associated with the use of humidity cell tests and metal leaching studies in acid rock drainage
CIM Convention 2018
When: Wednesday June 20 | 2:00pm
Where: Vancouver Convention Center | Room 115
Title: A case study comparing the results from static and kinetic geochemical tests: Sulphide-bearing iron oxide deposits
A common challenge associated with the use of humidity cell test (HCT) data in acid rock drainage and metal leaching (ARDML) studies is its lack of agreement with static testwork predictions. This can be significant for a mining program, as HCT data are commonly used as inputs to geochemical numerical predictions of contact water quality associated with mine waste facilities, the results of which are used to design and optimise waste management and closure plans.
Static and kinetic geochemical characterisation datasets are presented for four sulfide-bearing iron oxide deposits within the Fennoscandian Shield. These deposits, hosted in the greenstones of north-west Finland and northern Sweden, commonly occur in tuffite, black schist and dolomitic marble host-rock. Disseminated pyrite, pyrrhotite and chalcopyrite are typically present in ore and waste.
Despite the high sulphide content (1-5%) and low neutralising potential of the majority of lithologies found in these deposits, HCT data showed a significantly delayed onset to acid generation, attributed to sulphide crystallinity and mafic silicate dissolution leading to a slow oxidation and reaction rates. HCTs for the four deposits were run for between 40 and 180 weeks. Generally, humidity cells that were run in excess of 100 weeks showed better agreement with ABA data, with acidic conditions developing in samples that were predicted to be acid generating based on static results.
Comparing acid base accounting (ABA) and net acid generation (NAG) to HCT results reveals inconsistencies in acid generation predictions between the methods. The primary cause of this is the early termination of HCTs prior to the onset of acidic conditions. This study demonstrates the importance of considering the site-specific mineralogical characteristics of the deposit in determining the duration of kinetic tests; the results from which are utilised in the prediction of potential acid generation and metal mobilisation.
Meet our presenter:
Jessica Charles, Consultant GeochemistryJessica Charles (SRK Cardiff)
Consultant (Geochemistry)
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SRK North America