Snap Lake Working Group De Beers update: North Pile, Paste and TDS - - PowerPoint PPT Presentation

Snap Lake Working Group De Beers update: North Pile, Paste and TDS

MV2011L2-0004

Airstrip Ammonium Nitrate Storage Facility Laydown Area Organics Pile North Pile Disposal Facility Camp Area Treated Water Discharge Warehouses and Workshops Intake Vent Raise Fuel Storage Facilities Emulsion Plant Water Management Pond Processing Facility Water Treatment Plant Mine Offices/Maintenance shops Former Construction Camp

Summary of Paste Research

Background

• Original Mine Design proposed the production of paste tailings
• Driver was to minimize environmental footprint
• It was envisaged that paste tailings would be used as follows:
• Placed underground as part of mine backfilling
• Placed at the tailings facility as part of an upstream construction approach.
• 50% Underground planned backfill
• Remainder placed in the North Pile (Processed Kimberlite containment facility)

Paste History

• Original paste plant not fully commissioned.
• Commissioning and paste project commenced 2010.
• Snap Lake Mine uses deep cone thickening.
• Significant early operational challenges were encountered.
• Only one other Diamond mine (of which we are aware) has successfully produced

Paste

• Kimberley Mines (South Africa) does not experience the harsh arctic environment

which presents its own challenges

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Background and Initial Design of Snap Lake Paste System

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Background 2001-2006

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• 2001 AMEC engaged Mine Systems to undertake initial paste test work
• Large kimberlite particle size tended to break down during flow loop testing
• 2001-2005 Golder prepared the detailed design of the North Pile
• Snap Lake Mine carried out a review of the test work
• Golder contracted to review the paste backfill, and disposal system

Background 2007-2010

• Paste pipelines partially commissioned during initial project phase
• Pumping system was not fully constructed or commissioned
• Tailings deposition completed by pumping fine PK and trucking coarse and grits
• North Pile Starter Cell embankments constructed of coarse and grit PK
• Planned that upstream embankments would be constructed at the remaining

cells using full mix pk (paste)

• Paterson Cooke commissioned to audit the system
• Noted performance issues with deep cone thickening to produce sufficient density

to carry larger particle sizes without segregating

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East Cell Perimeter Embankments

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Background 2010-2011

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Background 2010-2011

• Pipeline replaced with smaller diameter piping (200 mm to 150 mm) to increase

velocities

• Segregation of material occurring within the pipeline

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Results and Conclusions

• Originally assumed that kimberlite would be disposed of via spigots at 2º inclined

beach

• Assumed that tailings would be of sufficient strength to allow for berm raises.
• Despite thickened nature of full paste mix with solids between 70—76% product

did not achieve required strengths

• Product has lows yields and does not stack due to lower than anticipated yield

stresses and rheology of the product

• Resulted in a change in pile construction to placement of coarse and grit

processed kimberlite

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Advanced Stage Redesign

• 2012 addition of 1,500 m of piping to facilitate underground trials
• Engineer on site for three months to assist plant operators with performance

enhancements on trials

• Procedures were developed for operating the paste plant
• End of 2012 approval given for dedicated underground paste team
• Dedicated to constructing barricades and pipelines, monitoring pours etc.

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Centrifuge Trial

• To improve paste densities, centifuge technology was trialed
• Intended to dewater material used in paste and improve control of solids

concentration in final product.

• Final product removed some untrafines , but showed good flow characteristics and

produced a cake with a density of 1.8 t/m³

• Subsequent testing completed demonstrated that rheology had changed since

initial testing commenced

• Variations in the kimberlite dyke and safety concerns required certified

engineered barricades be designed

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2013 Updated Hydraulic Analysis and Mechanical Design- Underground

• First paste pour occurred in February 2013
• Ended early due to pressure causing concern over damaging the system
• Trials continued throughout the year
• Various percentages of cement were added to improve yield stresses (up to 2%)
• Progress improved with the addition of a dedicated crew
• Pressure testing later determined that the mechanical supports for the pipeline

needed to be redesigned

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Technical Challenges

• Production of stable paste suitable for underground operation and tailings facility

is not possible for all ore types:

• Rheology of the ore not consistent producing low strength paste
• Variability of ore type, hence gradation, physical properties, and fluid characteristics.
• The tendency for kimberlite particles to break down in a pipe and flowing stream.

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Layout of the Orebody and Underground Mine Workings

• Geometry of the orebody and layout of development make it a challenge to

achieve 50% backfill

• Shallow dipping dyke at 10-15º
• Modified room and pillar mining system
• Positive gradient of ore stopes
• Density Difference between intact rock and paste backfill
• Based on this, it is projected that less than 30% of processed kimberlite will be

deposited underground

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Future of Paste Backfill

• Alternatives are currently being assessed
• Although only a small volume of backfill has successfully been placed, future work

will build upon successes to date

• 2014 work will include:
• Underground booster pump station design and
• Expanding under ground reticulation system
• Second centrifuge

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Conclusion

• De Beers Snap Lake Mine has demonstrated that paste backfill can be placed in the

underground mine workings

• Paste tailings have been deposited in to the “North Pile” although the beach angles and

paste strength are lower than required to successfully be used for upstream embankment construction

• The Snap Lake Mine operator bench strength has increased
• Stope layouts and overall underground mine geometry and mining methods will make

attaining the required underground placement rates highly unlikely

• Continued testing and research in the future will be done on the rheology of the kimberlite

in order to ensure the safe and efficient underground deposition

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Questions?

North Pile Update

North Pile Footprint

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North Pile Current Status

• Deposition of PK slurry into the Starter cell commenced in the second half of 2007.
• Design and construction of the East Cell commenced in 2010
• First deposition into the East Cell was in 2012.
• The Starter cell has undergone three phased raises in the height since the original design.
• Cone penetration tests (CPT) were undertaken in the Starter Cell in the fourth quarter of
• 2013. Results indicate that further upstream increase in embankment height of the Starter

cell is at present not geotechnically feasible.

• DBCI expects production rates to increase above name plate rates over life of mine.

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Estimated Dates for capacity to be met: Starter and East Cells

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Present Situation and Future Requirements

• Currently in West Cell Design Phase
• The following conservative design assumptions and facts have been included for

the design of the North Pile extension:

• Waste host rock, and PK will be deposited on surface. Currently, it is estimated that

less than 30 % PK in the form of paste will be deposited underground for the remainder of the life of mine.

• Paste technology and paste strengths will not meet the requirements of the original

envisaged North Pile design requirements.

• Upstream heightening of the Starter cell embankments will not be geotechnically
• feasible. Although downstream options are feasible

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West Cell Options

• To ensure that production operations are not disrupted the North Pile extension

needs to be constructed by the end of 2015.

• Several options are currently being considered to increase the North Pile capacity

for life of mine.

• Raising the height of the current Starter and East Cells by changing angle of

embankment slopes from 3:1 slope to 2:1 to facilitate a downstream embankment or

• Expanding the current North Pile footprint; or
• A combination of both.

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High Level Timelines for West Cell Construction

• Geotechnical drilling and trenching

Completed 2013

• Detailed design and layouts

Ongoing

• Submission of design package to MVLWB for approval

Aug 2014

• Commence quarrying and excavation of water catchment structures

Q4 2014

• Construction of West Cell structure

2015

• Deposition into West cell

Q1 2016

• Conceptual studies into North Pile expansion

Ongoing

• Expansion designs and communication to regulators

2016/ 2017

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Permitted Footprint

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Draft Layout West Cell – Phase I

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Conceptual Layout West Cell – Phase II

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W1 W2 W3 W4

West Cell Footprint Options

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Starter Cell Conceptual Expansions

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East Cell Conceptual Expansions

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Closure Conceptual

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Questions?

Chloride Discussion

Objective

• Provide summary of chloride exceedence event April-May 2014
• Summarize management actions since November 2013
• Summarize planned management actions for future
• Effects on the environment

02-17b Chloride SNP Reportable Results Max Grab Limit: 620 mg/L Average Monthly Limit: 310 mg/L Date Grab (mg/L) AML (mg/L) 24-Mar-14 262 294 30-Mar-14 369 306 5-Apr-14 310 306 11-Apr-14 316 305 17-Apr-14 314 306 23-Apr-14 309 313 29-Apr-14 307 321 05-May-14 307 311 11-May-14 282 306 17-May-14 296 303

Sources of Chloride in Mine Effluent

• Chloride is a component of high TDS connate water released during

mining

• TDS of connate water is on average 5,000 mg/L
• Groundwater comprises ~ 10% of water managed underground

Connate Groundwater Recharge Structures

Sources of Chloride in Mine Effluent

• Connate water is not separated from other “dirty” water in the mine

workings

• Current practice to manage connate water is to dilute with recharge

water that enters mine workings from Snap Lake

• ~ 42,000 m3 effluent discharged to Snap Lake daily: 99% originates

from underground

Generalized Water Balance – Snap Lake Mine

Surface Water WMP & WTP

• North Pile Seepage
• Runoff

< 1% Fresh Water

• Potable
• Fire Suppression

< 1% U/G Mine Water

• Clear Water
• Dirty Water, including Connate

Water

99 %

• Recycled Water
• Treated Water

Effluent Discharge to Snap Lake

Management Actions to Date

• Source monitoring and update of groundwater models
• Increased groundwater monitoring has identified areas of potential

higher groundwater inflows

• Grouting trials for both full and selective source control
• Grouting to reduce loading from high TDS areas is technically

possible, but not practical

• Limited underground segregation of high TDS water
• Detailed studies to support appropriate and protective effluent

quality criteria per licence requirements

Management Actions – Current and Future

• Chloride is measured “end-of-pipe”; sample is sent to accredited lab
• In-line chloride meter has been installed and currently being

calibrated

• In-line conductivity is used to estimate chloride in effluent, and is

used as an internal management tool – recorded every 2 hours

• When upward trend is detected, some water can be held

underground.

• Approximately 4,000 m3 high TDS water is currently being held

underground in designated mine headings and sumps

• The temporary storage of water in mine headings renders makes

headings inaccessible

2 level

sumps

4x

Reactor/thickener /filters 15 sumps I

5

drainages

16x

15 sumps I 2

drainages

14x 6sumps/ 3

drainages

6x

MSS

Pump Station Trash Screens Smain sumps

2

sumps I

1

drainage 2x 11 sumps I

4

drainages lOx

1

sump I

1

drainage

lx

2

sumps I

1

drainage 2x

A B , C

Ramp Sumps

17x

Management Actions – Current and Future

• Engineering studies and pilot testing of options to remove TDS are

currently underway.

• Summary of investigations into treatment are summarized in IR#3-

1 of EA1314-02. Results of current pilot studies are expected to be known Q3-4 2014.

• Based on proven technologies
• Site-specific water quality objectives that are protective of the

environment have been proposed

Effects of Exceedance

• Results of site-specific toxicity studies undertaken as a

requirement of the water licence show that April-May exceedance will not cause harm to the environment

• Water remains safe to drink
• Review of proposed, higher effluent limits for chloride and TDS are

currently under review in regulatory process