British Columbia Mine Reclamation Symposia

Operating a zero-discharge mine waste disposal facility in northern B.C. : the Huckleberry Mines experience Johnson, Doug; Letient, Henri 2001

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
[if-you-see-this-DO-NOT-CLICK]
2001 - Johnson, Letient - Operating A Zero-Discharge Mine.pdf [ 901.46kB ]
Metadata
JSON: 1.0042387.json
JSON-LD: 1.0042387+ld.json
RDF/XML (Pretty): 1.0042387.xml
RDF/JSON: 1.0042387+rdf.json
Turtle: 1.0042387+rdf-turtle.txt
N-Triples: 1.0042387+rdf-ntriples.txt
Original Record: 1.0042387 +original-record.json
Full Text
1.0042387.txt
Citation
1.0042387.ris

Full Text

Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation OPERATING A ZERO-DISCHARGE MINE WASTE DISPOSAL FACILITY IN NORTHERN B.C. - THE HUCKLEBERRY MINES EXPERIENCE Doug Johnson1 Henri Letient2 1 Environmental Coordinator 2 Senior Mining Environmental Engineer Huckleberry Mines Limited AMEC Earth and Environmental Limited P.O. Box 3000 2227 Douglas Road Houston, BC  V0J 1Z0 Burnaby.BC  V5C5A9 ABSTRACT The Huckleberry Copper Mine site is located in west central British Columbia, approximately 85 km southwest of Houston. The mine site is at an elevation of about 1050 m and experiences on average 1100mm of precipitation annually. Production from the open pit copper mine began in the fall of 1997. The ore zones are being mined by conventional open pit operations, with a projected total 11-year life according to the latest mine plan. The mill throughput is a nominal 21,000 tonnes per day. The TMF-2 facility provides storage for the mine waste generated by the Huckleberry Mines operations.. The facility was commissioned in October 1997. TMF-2 provides not only storage for the tailings but also disposal and permanent submergence of potentially acid generating (PAG) waste rock. TMF-2 also provides the source of process water. Despite the wet climate, TMF-2 is presently operated as a zero-discharge facility and provides the main source of process water for the mill. Only about 150 m3/hr of fresh water is added at the mill for specific process requirements (i.e., less than 10% of the process water). It is not until the impoundment is expanded to the east in the later years of the operations that excess water may need to be discharged. All analyses to date have shown water quality in the pond will be suitable for discharge. This paper explains how the system was initially conceptualised, how it is operated and how it will be configured on closure.   Water management aspects of the operations are highlighted.   The mass/water balance is an essential operating tool for planning annual raises and predicted flooding levels. The presentation will explain how the mass balance is updated as production data arid site-specific climate information becomes available. INTRODUCTION The Huckleberry Copper Mine site is located in west central British Columbia, approximately 85 km southwest of Houston (Figure 1). The site is on the south flank of Huckleberry Mountain, overlooking Tahtsa Reach. The area lies in a 128 Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation transitional zone between the Coast Mountains to the west and the interior Nechako Plateau to the east. Production from the open pit copper mine began in the fall of 1997.   The Huckleberry ore deposit comprises two zones, the Main Zone and the East Zone.  The copper-molybdenum ore is contained in biotite-feldspar-granodiorite porphyries.    Mineralization occurs primarily as chalcopyrite, with minor bornite. The ore zones are being mined by conventional open pit operations, with a projected total 11-year life according to the latest mine plan. Table 1 summarizes the ore reserves from each zone. Table 1 - Summary of Ore Reserves  Mine waste material generated over the life of the operations will consist of: • 81 million tonnes of tailings • 40 million tonnes of waste rock • 10 million m3 of overburden • 1 million m3 of peat Early on in the project planning, it was anticipated that a significant portion of the waste rock would be considered potentially acid generating (PAG). Therefore, in the permitting stage, the mine waste disposal strategy envisaged co-disposal of the PAG rock with the tailings in such a manner as to keep PAG waste below a water cover. Several potential disposal sites were identified and investigated. Ultimately, Tailings Management Facility #2 (TMF-2) was selected as the preferred alternative due to its close proximity to the mill and the fact that it could ultimately incorporate the Main Zone Pit into the overall waste disposal plan. TMF-2 provides not only storage for the tailings but also disposal and permanent submergence of the potentially acid generating (PAG) waste rock. Figure 2 provides an overview of the Huckleberry Mine site and shows an outline of the ultimate open pits and the TMF-2 area at the end of the mine life. The impoundment is currently formed by a main structure, referred to as the TMF-2 Dam and the temporary South Saddle Dam. Current plans call for the South Saddle Dam to be breached in the summer of 2003, the main zone pit flooded, and eventually the East Dam to provide the eastern containment of the TMF-2 pond (construction of the East Dam to begin in the 2002 construction season). The TMF-2 tailings impoundment will therefore be expanded east at that point in time. To meet the ongoing tailings and water storage requirements, the dams are raised annually. The TMF-2 and South Saddle Dams consist of a low-permeability core of compacted clayey glacial till, with 129 Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation downstream filters separating the core from the rockfill downstream shell. The TMF-2 Dam, South Saddle Dam, and the East Dam will be raised! by the centreline construction method over the life of the mine, with planned annual crest raises in the order of 14 m to 2 m in elevation (Figure 3). The annual crest raise requirements will decrease as the impoundment is raised, particularly once TMF-2 is expanded to the east.   130Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation OPERATION OF THE TMF-2 FACILITY Tailings Deposition A tailings pipeline, a reclaim barge, and a reclaim pipeline circuit provide tailings discharge and process water recycling capabilities. Tailings from the mill are pumped by one of two 500 horsepower pumps via a 66 cm (26") diameter tailings line to a drop box located on a slope above the crest of the tailings dam. From this drop box the flow is directed by gravity through a 71 cm (28") diameter line for spigotting and single-point discharge into the tailings pond. The tailings stream can be diverted through a spare 46 cm (18") diameter line from the drop box, and this flow is discharged into the tailings pond at the east abutment. The length of the tailings line from the mill to the east abutment is approximately 1700 m, and. from the mill to the mid point of the main section is 2700 m. The tailings slurry is pumped at a typical slurry density of 35% solids with a specific gravity of 1.28. From an acid generation point of view, the tailings fall in the zone of potentially acid generating material. To avoid long-term ARD concerns, it is planned to float pyrite out of the tailings towards the end of the mine life, thereby creating a non-acid generating tailings stream which will be used to cap the deposited mine waste. The pyrite-rich tailings will be discharged through the existing cleaner/scavenger tailings line into the deeper portion of the impoundment. On closure, a permanent water cover will be maintained over the mine waste. Only beaches of non-acid generating tailings will remain exposed. Waste Rock Deposition Initial ARD characterization showed that all of the East Zone waste rock (volcanics) is potentially acid generating, as the sulphide values are in the order of 2 to 4 %, with NPR values less than 1. The NPR is simply the neutralization potential divided by the acid potential of the sample. The Main Zone waste rock consists of two different kinds of rock, volcanics and granodiorite. The granodiorite is low in sulphides and approximately 80% is non-potentially acid generating or NAG. The MZ volcanics range in sulphide values from 0.3 to 3.0 %, and are 80 % PAG. The mine plan calls for flooding of all PAG waste rock in order to prevent the onset of ARD. The permit for the waste disposal facility was originally written to require flooding of any PAG waste rock within 24 months of placement. This requirement has since been removed as kinetic test data has showed that the PAG rock is unlikely to produce any acid during the life of the mine, which is important for Huckleberry as there is an operational requirement to utilize PAG waste rock for haul roads within the ultimate flooded area. Huckleberry also requires millions of tonnes of NAG rock for tailings dam construction, as it is placed on the downstream shell of the TMF-2 Dam and the East Dam. This NAG rock comes from the Main Zone Pit and the adjacent quarry, and it must lie separated from the PAG waste. 131 Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation A series of small sediment control ponds are located downstream of the TMF-2 Dam. The ponds collect runoff and seepage water from the area immediately downstream of the dam. To date, water quality within these ponds has been suitable for direct discharge and it is anticipated that it will remain acceptable throughout the life of the project. MASS BALANCE The mine waste disposal plan at Huckleberry is quite complex and intricately tied to the mine plan, as the Main Zone Pit will eventually become an integral part of TMF-2. Therefore, it is crucial to the operation of the facility that an accurate mass balance be maintained to forecast required dam raises and plan for shifting in the deposition pattern. The TMF-2 area will go through three phases of development: • In Phase 1, the current phase, the tailings and waste rock are confined to the area west of the Main Zone Pit and contained by the TMF-2 Dam and the South Dam.   The first phase will last to approximately Spring 2003 or until tailings discharge can start in the Main Zone Pit. • In Phase 2, the tailings and waste rock will be deposited in the MZP. Phase 2 will start once mining has ceased in the MZP and the water level within MZP has reached the minimum level required to move the reclaim water pump barge into the MZP. Phase 2 will1 require construction of the East Dam between the Main Zone Pit and the East Zone Pit. Phase 2 will last until approximately November 2004, when the water level in MZP is predicted to reach the level of the water in the TMF-2 pond. • In Phase 3, tailings and waste rock deposition will occur throughout the TMF-2 area, between the TMF-2 Dam and the East Dam. An Excel Spreadsheet was developed to model the mass and water balance for the TMF-2 facility. The spreadsheet is complex and makes use of various macros and triggers to simulate the multiple variations in deposition pattern over the facility's life. Figure 4 shows a simplified flow diagram for each phase and illustrates where various triggers (switches) are incorporated to simulate changes in flow patterns. How the spreadsheet works will be explained in more detail during the presentation. Figure 5 shows the predicted pond water level rise over the mine life based on the mass balance developed for TMF-2 while Figure 6 shows a comparison of the actual water level recorded and the predicted level. As all models, the TMF-2 Mass Balance includes multiple assumptions, summarized in Table 3. These assumptions have been verified over the past three years of operation and have been slightly adjusted as appropriate to calibrate the model with actual site-specific data. As illustrated by Figure 6, the model provides an accurate prediction of pond levels, sufficient for planning of the annual dam crest targets. 132 Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation  133 Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation  134 Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation The mass balance projects that the water level in the MZP will rise to the same level as within the TMF-2 area by October 2004 (Elevation 1062.4). From then on, the combined TMF-2 and MZP areas will operate as a single impoundment. At that time, it will be necessary to release water to keep the water level at a minimum, according to the water balance. Table 2 - Summary of key parameters and assumptions incorporated into the mass balance  The mass balance has been arbitrarily set to retain 1 million m3 within the pond while the excess water is released starting in November 2004. The monthly discharges are variable as they are being set by the given criterion of 1 million m3 pond volume. In actuality, the volume released will depend on the means used to release water and the pond size will fluctuate from month to month. If excess water were not released, the pond level by the end of the mine life (February 2008) would reach elevation 1079.2 (or 2 m higher than predicted with the present setting of the water balance that includes discharge of surplus water). In other words, there is sufficient flexibility in the system for Huckleberry to decide on whether or not to discharge water based on their needs and the quality of the water in the pond. The mass and water balance is a tool for projecting pond water level fluctuations over time. The mode? is frequently updated and calibrated as additional site-specific data is collected. Annual dam raises are planned based on an updated mass balance model. 135 Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation TARGET DAM CREST ELEVATIONS Figure 5 provides a plot of the predicted water level in the pond compared with dam crest levels while Table 3 provides a summary of the predicted water levels at the end of July of each year. Table 3 - Summary of Predicted Pond Water and PMF Levels  (*) The tailings elevation predicted by the model assumes a flat tailings beach (slope = O). It does not account for beach raising that can be achieved against the dam. The TMF-2 facility is designed to accommodate the Probable Maximum Precipitation (PMP) over its catchment area. Therefore, the Probable Maximum Flood (PMF) level in the pond resulting from a PMP event controls the annual target crest elevations for the dam raising. The Probable Maximum Flood (PMF) volumes were calculated based on a summer and a winter PMF as follows: • Summer PMP (from June to November): 750 mm of rain over 4 days • Winter PMP (from December to May): 750 mm of rain over 4 days plus 1OO mm of snowmelt Also, as dam crest raising construction starts in the month of May each year, the target crest elevation has been based on mid-summer (end of July) PMF levels, since by that point each year crest raising will have resumed. The mass balance for the TMF-2 impoundment is a working document. It is maintained by Huckleberry staff with actual monthly data and with revised production forecasts. The target crest elevation for each annual dam raise is set on a mass balance updated at the beginning of each year (Table 3). Note that the final crest elevation of 1080 m has been selected as a conservative target for planning purposes. The ultimate dam crest will be established during detailed planning of the closure of the facility, when a closure spillway will be sized according to appropriate flood routing analyses. 136 Proceedings of the 25th Annual British Columbia Mine Reclamation Symposium in Campbell River, BC, 2001. The Technical and Research Committee on Reclamation CONCLUSIONS Despite the wet climate, TMF-2 is presently operated as a zero-discharge facility and provides the main source of process water for the mill. Only about 150 m3/hr of fresh water is added at the mill for specific process requirements (i.e., less than 10% of the process water). It is not until the impoundment is expanded to the east in the later years of the operations that excess water may need to be discharged. All analyses to date have shown water quality in the pond will be suitable for discharge. The impoundment is currently formed by a main structure, referred to as the TMF-2 Dam and a temporary South Saddle Dam. Current plans call for the South Saddle Dam to be breached in the summer of 2003, the Main Zone Pit flooded, and eventually the East Dam to provide the eastern containment of the TMF-2 pond. The TMF-2 impoundment will therefore be expanded east at that point in time and the Main Zone Pit will be incorporated into the mine waste disposal facility. The mass and water balance is frequently updated and calibrated as additional site-specific data is collected. Annual dam raises are planned based on an updated mass balance model. The filling plan for the facility takes into consideration the requirement for permanently flooding the PAG rock. From an acid generation point of view, the tailings fall in the zone of potentially acid generating material. To avoid long-term ARD concerns, it is planned to float pyrite out of the tailings towards the end of the mine life, thereby generating a non-acid generating tailings stream which will be used to cap the deposited mine waste. The pyrite-rich tailings will be discharged through the existing cleaner/scavenger tailings line into the deeper portion of the impoundment. On closure, a permanent water cover will be maintained over the mine waste. Only beaches of non-acid generating tailings will remain exposed. 137 

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
Russia 1 0
China 1 0
United States 1 0
City Views Downloads
Saint Petersburg 1 0
Shenzhen 1 0
Ashburn 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}
Download Stats

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.50878.1-0042387/manifest

Comment

Related Items