1INTRODUCTION This paper discusses the development of two mines in very different areas of the world where innovative approaches to site development, in particular, waste management, were required to enableminedevelopmenttoproceed.Theuseofthickenedtailings,co-disposalandco-mingling are the common links considered in the design of the waste management systems at these two mines.Consideration of the individual characteristics of each site was necessary to Innovative Mine Waste Disposal in Two Distinctly Different Settings I. Wislesky & A. Li Golder Associates Ltd., Mississauga, Ontario, Canada ABSTRACT: Innovation within the mining industry has always been important as a result of worldwide pressure to improve their practice.The tarnished image, primarily a result of envi-ronmental legacies and some more recent events, has resulted in a concentrated world focus on all mining ventures.Financial institutions have developed the Equator Principles which mines must follow to obtain project financing.In todays heavily scrutinized mining environment, project funding will not get off the ground unless both environmental and sustainability issues are considered and accommodated.Mining companies are currently becoming proactive in their pursuit of new approaches to develop and achieve sustainable goals in line with the goals of the community. Innovation in management of mine waste materials is one of the most important aspects to consider for a mining project to advance and, in fact, this has come a long way since the days of finding a nearby lake or river to dump their wastes into.Important factors include physical and chemical stability over the short and long term as well as the size of the area of influence. This paper discusses the use of careful understanding and planning for the disposal and man-agement of mine wastes in two distinctly different mine settings.By utilizing this methodology and current technology, innovative, unique designs were developed to optimize the disposal of mine waste materials in stable and cost effective systems which minimize the environmental ef-fects footprint.Waste disposal at both of these mines involves co-disposal of mine waste rock and tailings to reduce the space required for disposal, as well as to limit the effects of potentially acid generating materials.Co-disposal is being considered more often these days since it can enhance flexibility of a waste disposal system and provide both economically and environmentally viable solutions, as well as improved social benefits.At a mine site, several streams of wastes are produced includ-ing tailings, waste rock, slag, etc.Co-disposal allows for the optimization of disposal of the variousmaterialsbytakingadvantageoftheindividualpropertiesofeachofthematerials, whether it is low permeability, buffering, strength, etc., and combining these to produce desired overall characteristics. The use of co-disposal and thickening technology, in consideration of the overall characteris-tics of the mine sites and the waste material characteristics has created the opportunity for opti-mization which provides benefit to both the mining company and the local communities. optimize design and allow development.One of the mines (Shakespeare, owned by URSA Ma-jor Minerals (URSA)) is located in a rugged region of Canada subjected to seasonal extremes in temperatureandtheother(CerroDeMaimon,ownedbyGlobeStarMiningCorporation (GlobeStar)) is located in a tropical region of the Dominican Republic.The locations of these mine sites are shown on Figure 1. Figure 1. Location map of the Shakespeare and Cerro de Maimon projects. New and innovative approaches to the design of mine waste management systems are neces-sary in todays mining climate for a number of reasons.Mining companies recognize the need for change.As a result, the mining industry is actively seeking measures to achieve sustainabil-ity and social responsibility primarily through sound environmental practices.There are many drivers for change within the mining industry including the following: Financial - Mine developments must follow the Equator Principals to obtain adequate project financing. Regulatory - There are laws and regulations in place with regards to land use, closure, etc. Risk - System failures can lead to extensive environmental, human and financial losses. Reputation-The reputation of the mining industry as a whole requires some mending as a result of legacies as well as more recent events. Public Awareness - Lobbying by NGOs and media scrutiny increases the exposure of the in-dustry. The management of mine wastes is considered by many to be the most important area where improvement can be made to enhance the viability for the development of new mine sites.In ef-fect, mining companies can be considered to be primarily in the waste management business (generally only a small fraction of the material moved becomes product and the rest becomes waste).It is important to develop a complete understanding of the site and the characteristics of the waste materials including: climate, topography, natural hazards, environmental/social con-straints, regulatory requirements, tailings characteristics, waste rock characteristics, quantity and schedule of wastes, etc. The key design drivers for mine waste management are: Chemical Stability - Acid generation and leachable contaminants (metals). Contaminant Transport - Groundwater, surface water, air. Surface and Groundwater Protection Downstream use. Water Management Dry/wet/winter climatic conditions. Erosion Stability wind and water. Physical Stability static and dynamic. Aesthetics Primarily at closure. Minimize Footprint Area of impact. There are several waste disposal options that have been used or are currently being developed and these include: Slurry deposition, Stacks, Co-disposal and/or co-mingling Underwater disposal, and Disposal in mined out open pits or as underground backfill. Theactualmethodologyusedatanindividualminesitecanbeanyoftheabovebutthe choice should be made based on sound engineering principles in consideration of all aspects of thesiteconditions,surroundingareaandwastecharacteristics.Themethodologiesusedfor waste disposal at the two sites considered in this paper involve a combination of thickened tail-ings, co-disposal and co-mingling. 2THICKENED TAILINGS Thickening technology has come a long way over the past several years with deep cone thicken-ersandimproveddistributionsystems.Thistechnologyiscurrentlyprovenandacceptable.Thickening produces a dewatered, non-segregating material that can still be pumped and piped to a disposal site.Thickening technology was primarily developed for underground mine back-fill operations and is more recently being used for surface disposal of tailings.Dr. Eli Robinsky pioneered the thickening process in 1968 and designed the first surface disposal site for tailings in 1973 (Robinsky, 1999).This site is still being used for thickened tailings deposition today.Thickening provides the following benefits over conventional slurry deposition: Greatly reduces risk by limiting or eliminating retained water ponds, Particle segregation does not occur, producing a denser, less permeable tailings mass, Greater chemical stability by inhibiting the ingress of water and oxygen, Conserves water (very important in dry climates) and reduces water management require-ments, Accelerated consolidation providing accessibility to foot and equipment faster than slurry, Facilitates progressive closure, Better control of wind and water erosion, Can use tailings for underground backfill, Reduces the need for large dams, Smaller basin footprint, Less seepage and groundwater contamination, and Reduces or eliminates the need for a liner. Not all of these benefits may apply to a particular facility, however, if a sufficient number of these benefits do apply, it may be worthwhile to pursue this methodology. 3CO-DISPOSAL Co-disposal consists of placing different waste materials into a common facility. Although co-disposalonsurfaceisnotcommonlyusedintheminingindustry,therearemanyexamples where both tailings and mine rock are disposed of together.There are tailings areas where mine rock has been used as a primary material for construction of tailings containment dams.In addi-tion, mine rock is often used for the construction of internal access roads or berms within tail-ings facilities.There are also numerous examples of mine sites where other materials are stored within the tailings facility and/or used for internal construction purposes. Co-disposal takes these examples and extends them into an engineered facility where tailings and mine rock are placed together in an efficiently engineered, environmentally sound and eco-nomic system.Some advantages of co-disposal include: Easier to manage the disposal in one facility; Smaller footprint and area of disturbance; Reduced dam construction; Eliminates / reduces the need for a liner; Extends the life of an existing tailings basin (stacking, placement angle, in-situ density); Reduced issues with respect to seepage and evaporation losses; Reducedwindandwatererosion,reducedinfrastructurerequirements(roads,pipelines, pumps, etc.); Better control of acid generation through efficient mixing (tighter matrix); Reduced water management issues (single point of discharge to the environment); No ponded water on top of the co-disposed materials (hence less risk); Facilitates progressive closure and reduced closure issues (smaller area, one water manage-ment system and one treatment plant, easier to monitor, etc.); and More accessible to foot traffic and equipment. 4CO-MINGLING Waste rock generally has quite a high void ratio which translates into space availability for other materials.In conventional waste dumps, this space is filled with water and air which creates perfect conditions for acid generation and metal leaching.Co-mingling utilizes tailings to fill the voids within the waste rock matrix.The benefits of this symbiotic system are: Reduced storage volume requirements (reduced footprint); Reduced potential for water and oxygen ingress and contact with potentially acid generating materials (chemical stability); and A strong, physically stable structure can be produced.To provide adequate mixing of the waste rock and tailings and to optimize filling of the voids, thickening of the tailings to a non-segregating material is required.Mr. B. Wickland and Dr. W. Wilson, have studied the effects of co-mingling tailings and waste rock (Wickland, 2006) and further studies are necessary to develop procedures to optimize mixing. 5SHAKESPEARE PROJ ECT The Shakespeare site is located in Canada, west of Sudbury, Ontario, on the northern shore of Agnew Lake (Figure 1).The project is an 11.3 Mt, nickel ore body that will be mined in two open pits.The ore will be processed on site at a nominal rate of 1,642,500 t/y, or approximately 4,500 t/d, with a mine life of about seven years.In general the site consists of the two open pits, a mill, a thickener plant, the co-disposal site and several ponds for water management.The gen-eral site layout is shown on Figure 2. Figure 2. Topography and Site Layout PrevioustoGoldersinvolvement,apreliminarydesignwasdevelopedforconventional slurry tailings disposal at a location about seven kilometres north east from the mine.However, inordertoreducetheareaofdisturbance,environmentalimpactandcost,URSAretained Golder to design a cost effective, fully functional facility which included the possibility of co-disposing thickened tailings and mine rock in an area close to the mine with good topographic containment. Thelocationofthemineonaprominent,rockyridge,extendingasapeninsulainto Agnew Lake, limits the potential sites for tailings and mine rock disposal close to the mine.The site that was originally selected for mine rock disposal was the only potential site close to the mine with good topographic containment that was not an existing lake.Though not big enough for slurry tailings disposal, a co-disposal strategy was considered to increase the containment volume without major dam construction.The site is valley shaped with the north and south sides rising up to 35m above the base. This topographic containment enhances stability of the dams and the existing relatively impervious clayey foundation soils will inhibit seepage.Space is also available downstream for water management (settling and polishing ponds).The use of theco-disposaltechniquereduceswatermanagementinfrastructurebyconfiningthemine wasteswithin one catchment area. The footprint of the waste management area has been re-duced from the initially planned 150 ha for tailings alone to approximately 90 ha for both mine rock and tailings.There will be four primary streams of waste material produced as a result of mining and mill-ing that require disposal at the Shakespeare Project Site.These materials are described as fol-lows: Acid generating mine rock (1.6 M-m3); Non-Acid generating mine rock (27.73 M-m3); Acid generating pyrrhotite tailings (high sulphide content) (0.57 M-m3); and Thickened tailings (very low sulphide content) (5.95 M-m3).The design methodology consists of a single co-disposal facility where all the above materials will be disposed for several years from the beginning of mine development.In the later years, the acid generating mine rock and pyrrhotite tailings will be disposed of in the mined out, West Open Pit. A system of dams will be required downstream of the co-disposal site for water con-trol including settlement of solids, retention time, flooding of acid generating materials, extreme Co-disposal AreaMill West Pit East Pit Treatment Ponds precipitationandothermiscellaneoussourcesofwater.Thethickenerplantwillbelocated above and adjacent to the co-disposal site to take advantage of gravity for distribution of the thickened tailings (thickener underflow) to the co-disposal site and thickener overflow directly to the downstream water treatment pond. The unique disposal strategy (filling plan) developed provides containment of the four mate-rial types within a single reduced footprint while preventing contamination of clean waste with acid generating waste and maximizing the available space.The filling plan, which requires a good understanding of the mine development and material scheduling, involves dividing the co-disposal site into two areas to facilitate deposition of the various materials.The low central val-ley section will be used primarily for acid generating materials (acid generating rock and high sulphur tailings).A dam will be constructed across the western end of the co-disposal area to promote flooding of the valley and to create a pond over the acid generating materials (to pre-vent acid generation over the long term).The remaining area will be used for non-acid generat-ing materials (i.e., clean rock and pyrrhotite reduced tailings).The high sulphur (pyrrhotite) tailings will be transported by pipeline, in slurry form, to the lowest section of the co-disposal area and discharged into a subaqueous environment.The non acid generating tailings will be thickened and disposed of together with the non acid generating mine rock. As discussed above, the acid generating materials will be placed into a flooded central basin with the acid generating mine rock placed at the west end near the main dam and the slurry tail-ings placed, starting from the east end.The acid generating rock will be end dumped into the water to create a rockfill platform about 1 m above the water level.Once deposition of the acid generating materials is complete, the water level will be raised to permanently submerge the area and prevent acid generation.This central section will remain open until the later years of the operation as shown on Figures 3 and 4, when it will be completely covered over with co-mingled, non acid generating tailings and waste rock.As shown in Figures 3 and 4, co-mingled, non acid generating tailings and waste rock will initially be placed south of the central, low val-ley as open pit development scheduling permits and then gradually cover over the entire co-disposal area.As a result, although the acid generating materials will remain saturated, there will be no pond that could lead to concerns over future exposure of acid generating materials. Figure 3. Filling Sequence Plan View Figure 4.Filling Sequence Cross-Sections For volume estimating purposes (capacity of the co-disposal site), the placed mine rock was assumed to have 30% porosity (void space) and only 50% of this available space would be filled with thickened tailings.In other words, a significant additional capacity exists within the void space of the rock to store tailings without increasing the size of the co-disposal area.Additional storage capacity will become available for potentially acid generating materials in the West Pit once it is mined out.The acid generating material can be placed underwater within this pit and will remain submerged when closed.As can be seen, advanced knowledge of scheduling of the open pit development and production of the various waste materials is critical to the effective operation of this facility.Overall management and scheduling of mine waste disposal activities is quite important for this site but the co-disposal scheme developed in consideration of this, will enable this mine to proceed with development. 6CERRO DE MAIMON PROJ ECT The Cerro de Maimon Mine is located about 75 km northwest of Santo Domingo in the Domini-can Republic (Figure 1).The project involves mining and milling oxide ores and sulphide ores bearing gold, copper, silver and zinc minerals with a maximum anticipated production rate of about 2,500 tpd. The site is situated within a tropical, mountainous region with an average annual precipitation and pan evaporation of approximately 2,012 mm and 1,710 mm, respectively. The annual pre-cipitationforthe100yeardryandwetreturnperiodswasestimatedtobe1,059mmand 3,760 mm respectively. Waste management is challenging due to the quantity and geochemical characteristics of the tailings and waste rock and the limited space available at the site. Geochemical characterization for waste rock, ores and two streams of oxide and sulphide tail-ings were conducted to identify potential environmental impacts from these materials.In sum-mary, the sulphide ore, footwall waste rock and all the tailings were determined to be acid gen-erating.Some separation of the acid generating waste rock from the non-acid generating was considered possible which would enable development of separate disposal sites. The materials requiring on-site storage include: 14 M tonnes of inert overburden waste, 4.8 M tonnes of potentially acid generating (PAG) waste rock, 27.2 M tonnes of non-acid generating waste rock, and 5.2 M tonnes of potentially acid generating tailings. The main design drivers for waste management for this project are: The geochemical characteristics of the tailings and waste rock and preventive measures for ARD management; Space availability (minimize footprint of the waste management facility and maximize stor-age capacity); and Overall water management. To enable mine development in consideration of the site constraints, waste materials and en-vironmental concerns, the following features were considered in the design of the waste man-agement system: Thickening the tailings prior to disposal to reduce the area required for disposal of potentially acid generating waste materials, allow for progressive closure and to simplify site water man-agement.Using one site for disposal of both acid generating waste rock and tailings (co-disposal).Using a co-mingling process to combine placement of both acid generating waste rock and tailings to limit seepage, limit oxygen ingress and reduce the total volume required for dis-posal. Constructing several connected storage cells for the co-disposal area to permit operational flexibility and allow for progressive closure. Using locally excavated clay to provide a low permeability compacted clay liner to minimize seepage escaping from the co-disposal site. Constructing a water collection/treatment pond downstream of the co-disposal area to collect all potentially contaminated water sources including seepage or excess water which might ac-cumulate in the co-disposal cells. Providing a clay cover followed by additional non-acid generating mine waste rock on top of filled cells to limit ingress of water and oxygen and provide space for additional waste mate-rials. Figure 5 shows a plan view of the entire mine site during the first and final years of operation.The co-disposal facility is located to the north side of the open pit and the east side of the exist-ing mountain ridge with the seepage and runoff collection pond at the downstream of the pe-rimeter dam.Thickener overflow will bypass the co-disposal site and discharged into the down-stream pond.This will greatly reduce the water management efforts required within the co-disposal site. Figure 5. Plan view of the co-disposal facility in the first and last year of operation (Cerro de Maimon Project) The co-disposal facility was designed to accommodate the required storage capacity over the life of the mine for the acid generating tailings and waste rock.The overburden soils and non-PAG waste rock will be hauled to different waste piles within the property boundaries.The co-disposal facility involves three cells for tailings and PAG waste rock which are to be contained by low permeability perimeter dams and internal dykes, raised progressively, as required.The entire footprint of the tailings cells will be lined with compacted clay using a local colluvium clayey deposit. The three tailings cells have been designed in such way that each cell can be covered with soil immediately after its storage capacity is fully utilized.The soil cover is to be constructed at a 3% slope outwards to prevent the ingress of water and oxygen by promoting runoff, and hence inhibit oxidation.Subsequently, the non acid generating waste rock will be deposited on top of the tailings cell, while tailings are discharged to other cells.The non acid generating waste rock cover will function as an additional oxygen barrier for the underlying acid generating tailings and waste rock.The co-disposal site will accommodate approximately 48% of the total non-PAG waste rock, which would otherwise require additional areas for storage. The concurrent closure of the tailings cells during operation requires careful scheduling based on the production of waste materials during the operation. To co-mingle tailings and waste rock, a portion of the acidic waste rock will be directly de-posited into the thickened tailings in the early stages of deposition for each cell.The majority of the PAG waste rock will be co-mingled with tailings during the final stage of the operation for each cell to provide a competent foundation for the materials placed above (i.e. the non-PAG waste rock).It is assumed that, on average, only 75% of the waste rock voids can be filled with tailings.Figure 6 shows a schematic section of the co-disposal site at the final stage of opera-tion.The perimeter dam will be 55 m in height with a downstream toe berm to provide a suit-able factor of safety for both short term and long term stability.The dam will be constructed in stages using a downstream raise method.The side slopes of the non-PAG waste rock pile (i.e. Pile 4) on the tailings cells are designed to provide sufficient factors of safety against failure of the overall slope (120 m in height) under both static and seismic conditions.For closure, a top-soil cover and vegetation will be applied to the surface of the entire co-disposal facility.Figure 6. Cross section of the co-disposal facility in the last year of operation (Cerro de Maimon Project) Photo 1 shows the starter tailings cells 1 and 2 and the perimeter dam during construction.The dam shell is constructed with non-PAG waste rock from the initial open pit development. Photo 2 shows the compacted clay liner in the tailings cells prior to tailings placement. Non Acid Generating Waste Rock Co-mingled Acid Generating Waste Rock and Tailings DamResidual SoilsBedrock Toe BermTailings Soil Cover Compacted Clay Liner Photo 1. Starter dam and tailings cells under construction Photo 2. Tailings cell 1 with compacted clay liner 7CONCLUSION Innovative disposal methodologies for mine wastes, along with significant advancement in the production of thickened tailings, has provided a means for improved efficiencies with respect to waste and water management at mine sites around the globe.The results can be measured with reduction in costs, environmental impacts and social impacts from mining projects. Sustainable solutions, global financial pressures and risk to both corporations and future generations are key areas where the importance of upfront and thorough evaluations of each mine site, is clearly shown to be necessary for the survival of the mining industry.As a result, mining companies are utilizing innovative alternatives for mine development and, in particular, mine waste man-agement strategies.The two projects presented in this paper have clearly demonstrated a path forward that can benefit existing and future mine developments globally. The sites described in this paper were areas where mining activities may not have proceeded a few years ago.Companies who design waste management facilities have the responsibility to develop a complete understanding of the site, the waste characteristics, the local regulations, the social concerns of the local population and sustainability options for the area. Although the sites described in this paper used thickened tailings and co-disposal, all disposal options should be considered during the initial mine site study stages to determine the optimum mine waste and water management strategies for the site.Slurry tailings facilities and open mine waste dumps, along with their inherent physical and chemical stability issues, must not be considered as the only possible solution.There are viable alternatives that can and should be explored.8REFERENCES Robinsky, E.I. 1999. Thickened Tailings Disposal in the Mining Industry.Published by E.I. Robinsky Associates Limited, Toronto, Canada. Wickland, B.E., Wilson, G.W., Wijewickreme, D and Klein, B. 2006. Design and evaluation of mixtures of mine waste rock and tailings. 9ACKNOWLEDGEMENTS The authors would like to acknowledge the forward thinking approaches of the management of both URSA Major Minerals and GlobeStar Mining Inc. who allowed and encouraged innova-tion in the development of their respective mine sites. Messrs. Richard Sutcliffe of URSA and J .P.ChauvinofGlobeStar,throughtheirinvolvementintheseprojectsareenablingthead-vancement of mine waste management technology and the promotion of sustainability in the mining industry.