Acid Rock Drainage Management at Masbate Gold Project

Transcription

1 Acid Rock Drainage Management at Masbate Gold Project

2 MASBATE GOLD PROJECT Open Pit Mine Major gold producer in the Philippines Located in Aroroy, Masbate, Region V 2

3 Acid Rock Drainage (ARD) Acid Rock Drainage or ARD is the discharge of acidic water from the mine. It may come from the active pit or from dumps and stockpiles as a result of oxidation of Sulphide minerals predominantly Pyrite (FeS 2 ). 4

4 ARD Process Produces: Pyrite + Oxygen + Water = Iron hydroxide + Sulphuric acid Acid FeS 2 + O 2 + H 2 O = Fe(OH) 3 + H 2 SO 4 (exothermic) Salinity (in the form of sulphate, calcium, magnesium mainly) Dissolved metals (iron, aluminium, and can also contain elements such as As, Cd, Cu, Mn, Pb, Se, Zn etc. and other trace metals based on mineralogy) 5

5 ARD Process Contact water can be acid and metalliferous or neutral/alkaline and saline depending on the balance of oxidation/neutralisation reactions Carbonate minerals (and silicates) buffer the acidity, maintaining elevated ph and low metal concentrations 6

6 Why is ARD Problematic? ARD is one of the key issues and legacies of the Mining Industry, with potential for: Water contamination Damage to flora and fauna Human health hazards (drinking water, food crops and fish stocks) Increased erosion and dump stability issues Increasing cost for closure Long-term liability ($$$) Negative company reputation 7

7 ARD Management Prior years Avoided mining potential acidic areas 2015 Preliminary studies with Environmental Geochemistry International (EGi) 2016 More results came out and awareness spread to the mining groups and other departments and contractors 2017 Further studies to determine criteria for segregation, instrumentation and monitoring commence cover design studies 2018 More site supporting, instrumentation, cover design completion and monitoring 27

8 ARD Management 27

9 Objective The Objective of Masbate Gold Project is to create a Management Plan for Acid Rock Drainage that is: Science - based Financially viable Globally acceptable using International Standards and Practices Compliant to local regulations Preventive rather than Reactive 9

10 Key Programmes Geochemical Testing - for classifying Potential Acid Forming (PAF) and Non Acid Forming (NAF) Waste Rocks PAF/NAF Delineation and Modelling Integrate Segregation Criteria into Mine Planning and Operations Dump Cover Systems to ensure long term control of ARD Oxygen and Surface Water Quality Monitoring Programs to ensure detection of ARD effects Drilling campaign on existing Waste Rock Dumps Continuous collaboration with EGi provides specialized services in mine waste geochemistry and mine waste management 9

11 Geochemical Testing NAF UC NAGpH Binstar/Main Vein Stage 2 Colorado HMB East Main Vein Stage 1 Montana Continuous Geochemical characterisation of selected Grade Control and Exploration drill samples across several prospects and deposits UC PAF NAPP (kg H 2 SO 4 /t) Leach columns for understanding Sulphur reaction rates and lag times In collaboration with EGi, test results provide the ARD segregation criteria for Potential Acid Forming (PAF) vs Non Acid Forming (NAF) Waste Rocks 10

12 Defining PAF vs NAF Grade Control Samples tested for Total Sulphur (S) and Carbon (C) using LECO Analyser onsite Net Acid Producing Potential (NAPP) derived from (S x 30.6) (C x 81.7) Sulphur and NAPP determines which category the rock will fall into LECO costs ~$2,000 11

13 PAF/NAF Modelling and Blocking Models produced by Leapfrog Software Using Geovia Surpac, PAF/NAF blocked together with High Grade and Low Grade Ore to produce dig blocks Provides information for material scheduling and selective handling 12

14 Integration into Planning and Operations Actual dig blocks are marked on the ground using flagging tapes Ore spotter guides Excavator and Truck Operators on material loaded and its destination Prompts review of dumping strategy and monitoring 13

15 Dump Cover Systems Aims to control oxygen advection/diffusion and infiltration Must also have the capability to neutralize by encapsulation (NAF outside/paf inside) 15

16 Dump Cover Systems Current practice involves a 3m base up construction - paddock dump, push, and compacted PAF core and NAF wall 16

17 Dump Cover Systems Encapsulation utilizes NAF Plugs on PAF core. The NAF plug acts as neutralizer of the PAF core 17

18 Dump Cover Systems Encapsulation utilizes NAF Plugs on PAF core. The NAF plug acts as neutralizer of the PAF core 17

19 Dump Cover Systems Encapsulation utilizes NAF Plugs on PAF core. The NAF plug acts as neutralizer of the PAF core 17

20 Dump Cover Systems Rehabilitation of the final lift 19

21 Dump Cover Systems Rehabilitation of the final lift 19

22 Dump Cover Systems Rehabilitation along the slopes minimizes erosion and water infiltration via evapotranspiration 19

23 Dump Cover Systems Rehabilitation along the slopes minimizes erosion and water infiltration via evapotranspiration 18

24 Progressive Rehabilitation Rehabilitation along the slopes minimizes erosion and water infiltration via evapotranspiration 20

25 Dump Cover Systems Rehabilitation of the final lift 19

26 Dump Cover Systems Rehabilitation of the final lift 19

27 Progressive Rehabilitation Rehabilitation of the final lift 20

28 ARD Monitoring - Oxygen Oxygen sampling tubes and thermistors most commonly used 21

29 ARD Monitoring - Oxygen 22

30 ARD Monitoring Water Quality Extensive water quality monitoring to comply with regulatory requirements 23

31 Drilling Campaign Drilling on existing waste dump to confirm PAF/NAF segregation Models were produced and reviewed for further planning 14

32 Summary Acid Rock Drainage is a significant issue on Masbate Gold Project that requires strong site awareness and management Geochemical Testing and Leaching provides scientific approach in identifying Potential Acid Forming vs Non Acid Forming Waste Rocks Site testing capability meets requirements, and segregation criteria has been integrated into mid-term planning and mining operations Masbate Gold Projects employs strategic Dump Cover Systems to prevent/minimize effect of ARD : Paddock dumping favoured over high head End tipping (end tipping causes segregation and speeds up reaction) Encapsulation (NAF plugs on PAF core) Drainage Management and Progressive Rehabilitation 28

33 Summary Water Sampling and Oxygen Monitoring (in Waste Dumps) checks if ARD is happening Working with Environmental Geochemistry International (EGi) provides expertise not present within the country Money spent for ARD Management < Money spent for reworks, fines and lawsuits ARD Management of MGP is continuously improving as new findings and technology are introduced 29

34 THANK YOU Genn Russell Abad/Elvira Pelleja - Acleta Chief Mine Geologist/Senior Mine Engineer Mine Technical Services Department (Mine Geology/Mine Engineering) Filminera Resources Corporation Masbate Gold Project 30