Block Caving Mining-related Surface Impacts Identified at Oyu Tolgoi Mine,
Mongolia:
Overview of Block Caving Mining, Extent of Surface Subsidence Projected for the Mine and
Compilation of Statements from Key Oyu Tolgoi-Produced Documents with Brief Comments
Compiled
December 17, 2012
by
Paul Robinson
Research Director
Southwest Research and Information Center
PO Box 4524
Albuquerque, New Mexico, USA 87196
[email protected]
This report compiles and provides brief commentary on statements related to the large
permanent collapse and subsidence zone projected to develop over the Hugo North underground
mine under development for ore production using the block caving mining method at the Oyu
Tolgoi mine licence area in Omnogobi Aimag [South Gobi Province], Mongolia. An overview of the
Block Caving mining method from Oyu Tolgoi sources and others is included to introduce the
nature and extent of surface impacts of that mining method. Surface collapse and subsidence
similar to that projected at the Hugo North mine is likely to occur if the block caving mining
method is used at the Heruga deposit in the Oyu Tolgoi mine license area as proposed by the
operating company in 2010, though development of that deposit is ignored in the key documents
reviewed in this report.
Statements from the key Oyu Tolgoi documents reflecting the author’s emphasis are in bold
and underlined.
Key Oyu Tolgoi Documents Reviewed in this Report
Integrated Development and Operation Plan and Technical Report, March 2012 (“IDOP 2012”)
http://www.turquoisehill.com/s/oyu_tolgoi.asp?ReportID=518703
Integrated Development Plan and Technical Report, June 2010 (“IDP 2010”) http://www.turquoisehill.com/s/oyu_tolgoi.asp?ReportID=379192
Environmental and Social Impact Assessment, 2012 (“ESIA 2012”) - http://ot.mn/en/node/2679
1
Introduction
What is the block caving mining method and why is it projected to have significant and permanent
environmental and hydrologic impacts in the Oyu Tolgoi project area?
Oyu Tolgoi’s ESIA 2012 provides an “Overview of Block Caving” in its Project Description as
follows:
P. 21 of 77 - “An Overview of Block Caving
“Block caving is a high-tonnage underground bulk mining method generally applied to large
homogeneous ore deposits. Ideally, the ore to be caved should be structurally weak, and the waste
overburden should be weak enough to collapse over the ore without inducement as the ore is
extracted.
“Block caving involves excavation of natural support from beneath the ore, causing the
structure of the ore body to fail and collapse into the excavated void under the force of
gravity and local geo-mechanical stresses. The broken ore is then pulled out from under the
caved section through a drawpoint arrangement, subsequently removing support from ore
and overburden at increasing height above the initial excavation, and eventually extending
the cave upward to the surface.
“The attractive aspect of block caving is that only a relatively small portion of the ore must be
drilled and blasted prior to extraction. Once the cave initiates, production continues without
further primary drilling and blasting until the ore column above is exhausted.
“The block cave mining sequence begins with access and infrastructure development, followed by
excavation of the extraction level, and undercutting the ore. The sequence culminates in steadystate production from individual drawpoints.
“Ore in the column is diluted by material in adjacent columns and ultimately by overburden and
adjacent waste rock. When the column drawdown is complete and drawpoint grade drops below a
minimum value, the drawpoint is abandoned. Great care is taken in establishing uniform draw
practices throughout the mine to maximise drawpoint life and minimise dilution and stress
loading from underground workings.
“Block caving is a capital-intensive mining method, requiring significant investment early in the
mine life for infrastructure and primary development. Once in place, the method’s high up-front
costs are offset by high production rates and low operating costs (relative to other underground
methods) over a considerable length of time, resulting in a low overall cost per tonne. Block cave
mining is among the least costly of all underground mining methods per tonne of ore extracted.
“Block caving has a number of positive attributes including no waste rock storage on the surface
and no large open pits. One consequence of block cave mining, however, is the potential for
surface subsidence or settling. Surface subsidence is caused as the material above the ore
body gradually moves downward to replace the ore that has been mined.
2
Using industry standard engineering practices, it is possible to predict both the cave and
subsidence zones based on ore body knowledge gained during exploratory geological
investigations. However, the best understanding of caving and subsidence will come once mining
begins.”
A very brief description of the block caving mining method and its environmental impacts from a
2011 issue of “Mining Magazine” states;
“One of the primary disadvantages of block caving is that it removes much of the supporting
rock from underneath the overburden, which often leads to subsidence of the surface. Caving
induced subsidence may endanger mine infrastructure and is a major concern for operational
safety.
Changes to surface landforms brought about by subsidence can be dramatic and may lead
to a pronounced environmental impact. Therefore, the ability to predict subsidence has
become increasingly important for operational hazard and environmental impact
assessments.”
– “Ore Body Access” Publication Date 03 May 2011
at http://www.miningmagazine.com/equipment/orebodyaccess2?SQ_DESIGN_NAME=print_friendly
Mining Magazine identifies operating and proposed block caving mines owned in whole or in part
by Rio Tinto, current majority owner of the Oyu Tolgoi operating company as:
-
Northparkes copper and gold mine, Central New South Wales, Australia – 80% Rio Tinto,
20% - Sumitomo;
Palabora copper mine, Limpopo Province, South Africa – 57% Rio Tinto, 26% public, 17%
Anglo-American;
Deep Ore Zone block cave mine, Grasberg Mine, Papua, Indonesia – 40% Rio Tinto, 60% PT
Freeport Indonesia;
Hugo Dummett North and South deposits, Oyu Tolgoi gold and copper project, South Gobi
Region, Mongolia; and
Resolution Copper project, Superior, Arizona, US – 55% Rio Tinto, 45% BHP Billiton.
A description of the block caving mining method including descriptions of the open cave zone and
surrounding subsidence zone at operating mines at 30 block cave mines around the world,
including images of collapse and subsidence zone at 18 block caving mines, around the work is
available in “Characterization and empirical analysis of block caving induced surface subsidence and
macro deformations,” Woo, K., et al, ROCKENG09: Proceedings of the 3rd CANUS Rock Mechanics
Symposium, Toronto, May 2009, (Woo 2009) at:
http://www.geogroup.utoronto.ca/rockeng09/proceedings/innerFrames/PDF/Session19/4044
%20PAPER.pdf
3
Woo 2009 includes an illustration of block cave mining identifies three zones of surface impact
from block caving, an inner “Caved Zone, A surrounding “Fractured Zone” “Subsidence” zone
surrounding the inner zone of greater surface deformation.
Fig. 1 “Definition of block caving subsidence zones and its quantification with respect to angles extending from the undercut” (Woo 2009)
The illustration from Woo 2009 is similar to the illustration of block caving in Oyu Tolgoi’s IDOP
2012
Figure 2 – “Definition of Subsidence Zone (after MMT – Permission from Rio Tinto)” from Oyu
Tolgoi IDOP 2012, P. 325, - Figure 16.22
As Figures 1 and 2 demonstrate, block caving mining impacts to the land surface above and
surrounding the ore extraction zone including:
a “caved zone” directly above the block caving mining area, the “caved zone” where the
surface collapses into the void below the surface from which ore has been extracted;
a “fractured zone” over the area around the “caved zone” affected by the collapse over the
4
-
ore body where “tension cracks” develop at the surface and below the surface; and
a “continuous subsidence zone” where surface disruption and instability is likely to occur.
The extent of the “caved zone” defined by an “cave angle” or “angle of break”; the extent of the
fracture zone is defined by an “angle of fracture initiation,” and the extent of the continuous
subsidence zone is defined by an “angle of subsidence.”
The Caved, Fractured and Subsidence Zones at Oyu Tolgoi’s Hugo North Underground Block
Caving Mine are projected to exceed eight kilometers square.
The projected extent of the caved, fractured and subsidence zone at the Hugo North mine site
identified by Oyu Tolgoi operators increased substantially in the IDOP 2012 from that projected in
IDP 2010. The IDP 2010 projection of the caved, fracture and subsidence zone below shows the
“shaft farm” area – the site shaft 2 – outside the projected continuous subsidence zone.
Figure 3 – Projected Subsidence Zone from Oyu Tolgoi IDP 2010, P. 373 (P. 398 of 629)
The projected Hugo North mine subsidence zone presented in IDOP 2012, shown in Figure 4, has
expanded more 500 meters resulting in the “Caved Zone” including the “Shaft Farm” area the Shaft
2 site and other infrastructure features well inside the inner ring – the projected “caved zone” of
the subsidence zone – in addition to Shaft 1.
5
Figure 4 - Projected Subsidence Zone from IDOP 2012 – “The projection shown in Figure 16.33
merely illustrates the extent of surface area that the generalized subsidence projections
encompass. Further study is required to more accurately predict actual cave propagation.” IDOP
2012, p. 358
Propagation of the “Caved Zone” to include the Shaft Farm Area – the Shaft 2, Shaft 1 and other
infrastructure features is also illustrated in the Project Description portion of the ESIA, as shown
in Figure 5, below.
Figure 5 – Project Block Cave Subsidence Zone, ESIA Project Description p. 23 of 77.
6
Oyu Tolgoi’s IDP 2010 acknowledged the severity of the impact of the caved zone on Shaft 1
noting, “The subsidence zone from the extraction level to the surface in projected at 60o, per SRK’s
Recommendation [Figure 3 in this report](Figure 23.8.8). All planned infrastructure is outside this
zone, except for Shaft No. 1. Shaft No. 1 is located inside the 60 o subsidence area at the edge of 65o
subsidence line. It is assumed that Shaft No. 1 will be stripped of all conveyances once full
production is achieved and will be used for ventilation only.”
Oyu Tolgoi’s IDOP 2012 illustration of the project caved, fractured and subsidence zone, Figure 4
in this Report, shows that the extent of the 60o subsidence area has expanded to include Shaft No.
2 and most of the Shaft Farm area. The 60o subsidence line indicated in IDOP 2012 is
approximately 500 meters west of the location of the 60o subsidence line in IDP 2010, engulfing
the Shaft No. 2 site.
Neither the IDOP 2012 nor the ESIA 2012 address consequences of the projected cave, fracture
and subsidence zones on shaft No. 2 or the other infrastructure identified as within the projected
subsidence zone. As the IDP 2010 asserted that all infrastructure other than Shaft No. 1 were to be
located outside the 60o angle of subsidence zone to prevent impacts of caving, fracturing and
subsidence, The lack of attention to the impacts of subsidence on areas within the 60o subsidence
angle as projected in IDOP 2012 to include Shaft No. 2, the Shaft Farm area and other
infrastructure appears to be a significant defect in the 2012 documents.
The ESIA 2012 , in its discussion of the ‘Nature of the Impact” of proposed Oyu Tolgoi mine, in
“SECTION C: IMPACT ASSESSMENT CHAPTER C4: TOPOGRAPHY, LANDSCAPE, GEOLOGY &
TOPSOILS (“ESIA 2012 C4”, filename - “ESIA_OT_C4_Topography_EN.pdf”) projects the full area of
the projected caved, fractured and subsidence zone above the Hugo North mine is projected as
more than 8 square kilometers. ESIA – C4 at 10 of 18 states,
“[T[he removal of ore through the block caving is likely to result in a subsidence zone later in
the mine life as the caving propagates to the surface. Initial estimates are that this subsidence zone
will cover an area of over 8 km2 and be characterised by a depression surrounded by a circular
cliff- like feature with an overall cliff height in excess of 20 m, which might be manifest as a single
cliff or multiple smaller cliffs. Depending on the nature of the surface manifestation of this feature,
the impact will be on topography and landscape; and also on hydrogeology and hydrology (see
Section C5), and potentially present a potential community safety issue if cliffs are unstable once
herders are allowed back into the area following mine closure and restoration.”
The full extent of the subsidence zone is projected to more than three times the size of the open pit
mine planned at the site, projected to be 2 km2, at ESIA 2012, C4 p. 10.
Heruga Deposit Underground Block Caving Mine Eliminated identified in Oyu Tolgoi IDP
2010 from Evaluation in IDOP 2102 and ESIA 2012
An Heruga Deposit underground block caving mine was identified as part of the Oyu Tolgoi project
in the IDP 2010, as illustrated Figure 6 shows the location of that deposit.
7
Figure 6 – “Idealized Profile of Southern Oyu, Hugo Dummett and Heruga Deposits (Section
Looking West)” – IDP 2010, p. 15 – Figure 1.4.1.
The Underground Block Caving Mine proposed for the Heruga Deposit has been eliminated from
the Project considered in the 2012 Environmental and Social Impact Assessment (ESIA 2012) as
shown in the Figure 4.5 -“Profile of Ore Bodies” in the Project Description shown below as Figure
7.
Figure 7 – “Profile of Ore Bodies” - ESIA Project Description P. 16 - ESIA_OT_A4_PD_EN.pdf
8
Statements Regarding Block Cave Mining-related Impacts at the Oyu Tolgoi
Mine in Key Documents Associated with the Project
[Comments by the author is enclosed in brackets]
Integrated Develop and Operation Plan and Technical Report, March 2012
(IDOP 2012)
P. 344 ( p. 367 of 513)
“The advantages of using the block caving method for Hugo North include the following:
- High productivity.
- Low unit cost.
- High production rate.
- Inherent safety (no large openings standing).
The disadvantages of using the block caving method for Hugo North include the
following:
- High up-front capital requirements.
- Long lead time to develop, construct, and commission the mine.
- Intermittently high secondary breaking requirements, which may result in:
- Increased personnel exposure to open drawpoints.
- Increased number of production interruptions.
- Increased repairs due to the blast damage.
- Negative impact on draw control.
- Possible ore loss and dilution if overburden fragmentation is finer than expected.
- Impact on surface facilities due to subsidence.
- Cave management and control issues related to the numerous high-angle structures that
transect the deposit.
- Possible loss of developed production areas due to cave management and geologic structure
problems.”
P. 345 - “Several subsidence predictions for Hugo North have been completed in the past. Initial
subsidence estimates used Laubscher’s empirical approach. In 2005, SRK developed 2D FLAC
analyses on selected sections and in 2008 Itasca undertook 3DEC modelling. SRK preliminary
guidelines based on empirical design and simplified FLAC 2D sections recommended situating
important structures no less than 60° from the footprint; the results of subsidence modelling
suggested a range of 63° to 75°.”
P. 346 - “Block caving involves excavation of natural support from beneath the ore, causing the
ore to fail and collapse into the excavated void under the force of gravity and local geomechanical
stresses. The broken ore is then pulled out from under the caved section through a drawpoint
arrangement, subsequently removing support from ore and overburden at increasing height
above the initial excavation, and eventually extending the cave upward to the surface.”
9
P. 348 - “It is not known precisely at what angle the cave at Oyu Tolgoi will propagate. A 60°
subsidence design line projected from the undercut level of all mining areas is used to locate
surface infrastructure. To reduce the risk of affecting Shaft No. 1, a 65° cone from the collar is used
to limit the footprint boundaries. Further study is required to more accurately predict actual
caving propagation.”
P. 356 - “16.4.1.7
Subsidence Evaluation
The subsidence zone from the extraction level to surface was originally projected at 60°, per SRK’s
recommendation (Figure 16.33 [-see below]). All planned infrastructure is outside this zone
except Shaft No. 1, which is located inside the 60° subsidence area at the edge of the 65o
subsidence line. It is assumed that Shaft No. 1 will be stripped of all conveyances once full
production is achieved and will be used for ventilation only. Subsequent work by OTLLC and Rio
Tinto have indicated that 50° is a more appropriate subsidence angle.”
P. 358
P. 386 - “16.4.3.4
Water Management
The risk of substantial inflows is believed to be low because no major shallow aquifers exist to
drain into the underground. What aquifers do exist are likely to be substantially dewatered by the
open pit development prior to any subsidence. The low rainfall, together with diversion of surface
water, will further limit surface water inflow risks. Barring the interception of large aquifers, OT
LLC identified the greatest risk of large water inflows is from a significant rainfall event draining
into the cave after the cave has propagated to the surface.”
10
Oyu Tolgoi’ s Environmental and Social Impact Assessment, June 2012 (ESIA
2012)
SECTION A: INTRODUCTION AND BACKGROUND
CHAPTER A4: PROJECT DESCRIPTION
[Filename - "ESIA_OT_A4_PD_EN.pdf"]
P. 14 of 77 - “Layout
Some of the underground workings and the associated area of surface subsidence (due to the
underground “collapse zone”) will extend north out of mining licence 6709A into Entrée Gold Inc’s
Shivee Tolgoi JV Property mining licence area (see Figure 4.10 [see below]).”
P. 21 of 77 - “An Overview of Block Caving
Block caving is a high-tonnage underground bulk mining method generally applied to large
homogeneous ore deposits. Ideally, the ore to be caved should be structurally weak, and the waste
overburden should be weak enough to collapse over the ore without inducement as the ore is
extracted.
Block caving involves excavation of natural support from beneath the ore, causing the structure of
the ore body to fail and collapse into the excavated void under the force of gravity and local geomechanical stresses. The broken ore is then pulled out from under the caved section through a
drawpoint arrangement, subsequently removing support from ore and overburden at increasing
height above the initial excavation, and eventually extending the cave upward to the surface.
The attractive aspect of block caving is that only a relatively small portion of the ore must be
drilled and blasted prior to extraction. Once the cave initiates, production continues without
further primary drilling and blasting until the ore column above is exhausted.
The block cave mining sequence begins with access and infrastructure development, followed by
excavation of the extraction level, and undercutting the ore. The sequence culminates in steadystate production from individual drawpoints.
Ore in the column is diluted by material in adjacent columns and ultimately by overburden and
adjacent waste rock. When the column drawdown is complete and drawpoint grade drops below a
minimum value, the drawpoint is abandoned. Great care is taken in establishing uniform draw
practices throughout the mine to maximise drawpoint life and minimise dilution and stress
loading from underground workings.
Block caving is a capital-intensive mining method, requiring significant investment early in the
mine life for infrastructure and primary development. Once in place, the method’s high up-front
costs are offset by high production rates and low operating costs (relative to other underground
methods) over a considerable length of time, resulting in a low overall cost per tonne. Block cave
mining is among the least costly of all underground mining methods per tonne of ore extracted.”
11
P. 21 (continued)
“Block caving has a number of positive attributes including no waste rock storage on the surface
and no large open pits. One consequence of block cave mining, however, is the potential for
surface subsidence or settling. Surface subsidence is caused as the material above the ore body
gradually moves downward to replace the ore that has been mined.
Using industry standard engineering practices, it is possible to predict both the cave and
subsidence zones based on ore body knowledge gained during exploratory geological
investigations. However, the best understanding of caving and subsidence will come once mining
begins.”
P. 23 of 77 - “Subsidence Evaluation
The subsidence zone from the extraction level to surface is projected to develop at an angle of 60o
as set out in Figure 4.10. All planned infrastructure is outside this zone, except for Shaft No. 1,
which is located inside the 60o subsidence area at the edge of the 65o subsidence line. It is
assumed that Shaft No. 1 will be stripped of all conveyances once full production is achieved and
will be used for ventilation only. Subsequent work by Oyu Tolgoi and Rio Tinto in 2010/11 has
indicated that 50o is a more representative subsidence angle and this has been factored into
detailed engineering and design planning.
It is not known precisely how the cave will propagate and be expressed as a surface depression
with significant uncertainty with regards the shape of the subsidence zone and the character of
any surface expression (cliffs or steep slope). The projection shown in Figure 4.10 merely
illustrates the extent of surface area that the generalized subsidence projections set out. The main
uncertainties lie in the structural integrity and fragmentation of the ore body once block caving
commences. The on-going underground development programme, including underground
excavation and drilling, will allow this model to be refined.
In practice the subsidence zone will be irregular and strongly influenced by fractures, fault lines
and geological boundaries within the underground ore body. It is likely to have an elongated
rather than circular shape. The drainage of any groundwater within the vicinity of the subsidence
zone will be strongly influenced by the size of the subsidence zone and the surrounding zone of
drawdown within which surface and groundwater will drain into the block cave. Any groundwater
contamination from the oxidation of rock that is exposed to air and water will be captured within
the zone of drawdown and subsidence zone.
Further information and assessment of this issue are included in the baseline Chapter B5:
Topography, Landscape, Geology and Soils and the impact assessment Chapter C4: Topography,
Landscape, Geology and Soils.”
12
P. 23 - [The size of the Project Block Caving Subsidence Zone is shown in Figure 4.10 on p 23 of 77
of the ESIA Project Description - "ESIA_OT_A4_PD_EN.pdf".]
[The cave subsidence zone is the size of downtown Ulaanbaatar – roughly three kilometers by four
kilometers as the location grid on Figure 4.10 shows a five- kilometer, 5000-meter spacing.]
[The cave zone is unreclaimable as it is not physically stable enough for backfilling or reclamation.
The large open unreclaimable cave is the part of plan at OT most likely to create a permanent
"moonscape", a concern expressed by herders about the true long-term legacy of OT.]
P. 46 - “Mine Dewatering
“During the period of underground mining, once the fracture system generated by the subsidence
above the block caving intersects the surface water bearing formations, the drawdown point for
groundwater is expected to drop below the base of open pits. As an interim measure, before the
revised model is available, the current model has been rerun with more appropriate hydraulic
conductivities. This model rerun indicates that the drawdown (>1m) around the underground
mining and the open pit will extend out to a maximum of 5 km from the pit and the subsidence
zone.
After mining, the underground mines will flood, but evaporative losses from the open pits will
cause a long-term zone of drawdown approximately 300 m deep at the Southwest pit, with the 1 m
drawdown level extending up to 5 km. The likely cone of depression will be better understood
once the new model is developed; as this will take account of the variable hydraulic conductivities
in the different sedimentary and bedrock lithologies, as well as barrier effects (such as the dykes
13
and faults). The actual cone of depression is expected to be less than the predicted 5 km (for the 1
m contour). Given the low groundwater recharge in the region, it is likely to take at least 300 years
before steady-state conditions to develop.”
P. 49 - “Plant Site
The selected plant site is close to the open pit and underground mines and provides a compact
layout. The site is generally flat, with some relief to about 6 m height, and includes a bedrock
plateau where the SAG and ball mills will be founded. All facilities are located beyond the
estimated underground mine subsidence zone outline, as defined in IDP10.”
SECTION C: IMPACT ASSESSMENT
CHAPTER C4: TOPOGRAPHY, LANDSCAPE, GEOLOGY & TOPSOILS
[filename - “ESIA_OT_C4_Topography_EN.pdf”]
P. 2 – “Introduction
The pit, WRD [waste rock dumps], block cave subsidence and TSF [tailings storage facility] will all
result in changes to the local topography.”
P. 3 – “Summary of Assessment
Actual and potential impacts on the topography, landscape, geology and topsoil arising from the
construction, operation and closure of the Project are as follows [include]:
- Construction of mine infrastructure including tailing storage facilities (TSF) and waste rock
dump (WRD);
- Impacts associated with open pit;
- Block caving mining activities resulting in a surface subsidence zone; [among others impacts
listed].”
P. 10 of 18 - “Source of Impact
During the operational phase, primary impacts will be on the landscape, topography and geology
and will be centered on the open pit. The operational phase is unlikely to involve any major
additional earthworks therefore impacts on topsoil are likely to be negligible or minor at the most.
The key activities associated with the mining activities are:
- Lowering of the local land surface through the development of the open pit;
- Block caving and ultimately the creation of a subsidence zone over the block cave area; and
- Removal of the mineral resource.
Nature of Impact
The operation of the mine will result in the opening up of the large permanent pit which will cover
an area of over 2 km2 and extend to a depth of 800 m in 15 m high benches. These will impact the
local topography and landscape; although only be visible in close proximity to the pit.
To the north of this, the removal of ore through the block caving is likely to result in a subsidence
zone later in the mine life as the caving propagates to the surface. Initial estimates are that this
14
subsidence zone will cover an area of over 8 km2 and be characterised by a depression
surrounded by a circular cliff- like feature with an overall cliff height in excess of 20 m, which
might be manifest as a single cliff or multiple smaller cliffs. Depending on the nature of the surface
manifestation of this feature, the impact will be on topography and landscape; and also on
hydrogeology and hydrology (see Section C5), and potentially present a potential community
safety issue if cliffs are unstable once herders are allowed back into the area following mine
closure and restoration.
Excavation of the pit and the underground mine will remove the geological resources from these
areas as well as some surrounding host rock. This is a permanent and irreversible impact which is
essentially balanced by the positive impact on the Mongolia economy of the Project.
The resources being mined are heavily faulted and are located at the eastern distal end of a
faulting zone along which some seismic activity has been recorded (see Chapter B5, Section 5.7).
Given the distance from the main faults, and the lack of any significant seismicity in the area,
mining activities are considered unlikely to result in any significant movement on this fault system
(e.g. movement resulting in a seismic event greater than the background levels expected for this
area).
Mitigation Measures
A detailed Mine Closure and Rehabilitation Framework to meet the Rio Tinto Closure standard
and in line with the IFC mine closure guidance set out in the Sectoral Mining EHS Guidelines and
the EU Mine Waste Directive (2006/21/EC) is currently being developed and is planned to be
completed during 2012. This will include a funding mechanism for mine closure cost coverage in
line with international good practice (see Chapter D21: Mine Closure Framework). This will include
consideration of the topography and landscape and the management of the surface manifestation
of the subsidence over the area of block caving. The detailed Mine Closure and Rehabilitation
Framework will be submitted to, and approved by the Ministry of Nature Environment and
Tourism and the Ministry of Mineral Resources and Energy.”
[No information is available in the ESIA when the Detailed Mine Closure and Rehabiliation
Framework will be submitted to the Mongolian Ministries identified. In most jurisdictions where
detailed reclamation plans support by full financial assurance are required; the detailed
reclamation plan are subject to review and approval before license to construct and operate can
be issued as a matter of law and the full financial assurance is in place prior to the start of
construction.
At Oyu Tolgoi, the mine nearing full scale operation an no detailed mine closure and rehabilitation
plan have been submitted for review, much less approved, and no financial guarantee is in place to
insure completion of that detailed closure and rehabilitation plan.]
P. 14 – “Nature of Impact
“Following decommissioning, the main features remaining on the site will comprise the open pit,
block cave subsidence area, and closed WRD and TSF.
The closure of the mining operations will include the removal of the majority of the equipment
and steel- framed buildings. The degree to which the concrete foundations are removed and the
15
area landscaped will be subject to agreement with the local government (soum administration). All
unpaved areas will be cleared and prepared (scarified) prior to topsoil being reinstated on them.
Areas such as the waste disposal site will be closed, capped, and covered with subsoil and then
topsoil during restoration. The open pit, upper slopes of the waste rock dumps and cliffs of
the subsidence zone will be too steep to enable topsoil restoration as wind and water
erosion would rapidly remove the topsoil. The top of the tailings storage facility will be
restored as will the majority of the banks.
P. 15 – “Impact Significance
“The impact of the open pit, waste rock dumps and cliffs of the subsidence zone being too steep to
enable topsoil restoration will be residual and permanent.” [emphasis in original].
SECTION C: IMPACT ASSESSMENT
CHAPTER C5: WATER
[Filename – “ESIA_OT_C5_Water_EN.pdf”]
P. 6 of 65 - “5.3.2. Technical Scope
“Impacts during closure will relate to legacy issues associated with the long-term groundwater
drawdown around the open pit and the block cave subsidence zone, the local influences on surface
flows, and the drawdown in the Gunii Hooloi Cretaceous aquifer at the end of the Project’s water
abstraction period.”
C5 fails to provide a figures which identifies the block cave subsidence zone
P. 9 – “Undai Diversion around Open Pit” does not identify extend of “cave-in” zone above block
cave mine and diversions proposed to address its impacts.
P. 12 Mitigation and Management Measures
Minor Drainages in Mine License Area
“The surface water flows collected and diverted via the diversion channel around the TSF will rejoin the Budaa ephemeral watercourse below the TSF seepage collection system. Storm water runoff collected in the pit, will be used for dust suppression around the mine area. As required
depending on the area affected by the block cave subsidence, local ephemeral watercourses will be
diverted to minimise the run- off into the area of subsidence. The design of the diversions will be
developed during the operational phase as the subsidence zone is defined.”
P. 13
Closure
“The internally draining area caused by the subsidence over the block caving is not anticipated to
16
contain any surface water except potentially after a significant rainfall event, after which it will
evaporate. This internally draining basin may, if seasonal rainfall is sufficiently consistent, provide
a new habitat in the area being able to sustain more groundwater dependent plants.”
[Note: “cave-in zone” above block caving underground mine will create a central “collapse zone”
and surrounding “subsidence zone” feature a large open hole – “glory hole” – in the collapse zone
and extensive and deep surface fractures in the “subsidence zone” preventing groundwater from
collecting at the near surface to provide “new habitat” whether “seasonal rainfall is [ever]
sufficiently consistent.”
P. 39
Groundwater and Surface Water Contamination – Mitigation Measure
“During the construction phase a permanent waste management facility (WMF) will be
constructed in the north-eastern part of the mining Licence, outside of the anticipated subsidence
zone associated with the block caving operations.”
p. 62 “Summary of Water Resource Impacts” [Table -2nd page]
Impact [of ] “Degradation or losses of surface water resources in the Undai and Budaa due to the
diversions” [is associated with] Design and Mitigation Measures of “Detailed engineering
solutions to the diversions to ensure that they are robust and sustainable, and ensure that surface
water resources are not degraded, but passed effectively around Oyu Tolgoi’s operations,
including the subsidence zone.”
[No detailed design of diversions around subsidence zone provided in ESIA]
SECTION D: ENVIRONMENTAL AND SOCIAL CONSTRUCTION MANAGEMENT PLANS
CHAPTER D21 – MINE CLOSURE FRAMEWORK
(Filename - ESIA_OT_D21_Mine_Closure_and_Reclamation_Plan_EN.pdf)
P. 6 of 10 - “Cost Provisions for Final Mine Closure [includes, among other commitments]
“A commitment to comply with the following applicable environmental and mine closure
requirements under Mongolian law:
- Article 37 of the Minerals Law of Mongolia (2006) outlines the restoration and management
obligations of mining licence holders for the closure of a mine. These obligations include the
requirement to develop mine reclamation plans within the Environmental Protection Plan (EPP).
The EPP must include measures to minimise environmental impacts and reclamation including
backfilling, re-grading and re-vegetation to achieve designated post-mining uses and the EPP must
be approved by the applicable Mongolian authorities; and”
[Neither ESIA 2012 nor IDOP 2012 mention backfill of open pits or underground mines r
consequences of inability to re-grade or re-vegetate subsidence zone at block cave mines
proposed.]
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P. 7 of 10 – “PREPARATION OF THE MINE CLOSURE MANAGEMENT PLAN
“A previous (and preliminary) version of the Mine Closure Management Plan was prepared as part
of the Mongolian Feasibility study in 2009. In addition to this, Oyu Tolgoi prepares a quarterly
closure cost estimate as part of the financial reporting requirements for the parent company,
Ivanhoe Mines Ltd as a Canadian listed company.
Oyu Tolgoi has commissioned AMEC to prepare an updated Mine Closure Management Plan as
part of the Detailed Integrated Development and Operations Plan (DIDOP). This will update the
plan included in the Mongolian Feasibility Study, incorporate the most recent mine planning data
and integrate Mongolian regulatory requirements, Rio Tinto standards and practices and Lender
requirements – specifically the EU Mine Waste Directive (2006/21/EC) and the IFC
Environmental, Health and Safety Guidelines for Mining.
The Mine Closure Management Plan will be prepared and submitted as part of the operationsphase management plans and will be subject to the review and the approval of the Project
Lenders.
[ESIA fails to mention requirement for regulatory review and approval of mine closure
management plan, intent to submit mine closure management plan for regulatory review, or
intent to establish mine closure and management plan related financial assurance before mine
construction – now nearing completion - or operation.]
p. 8 of 10 - “Mine Closure Plan
Scope of Issues to be Addressed [for] Underground Mining [includes] surface subsidence area.”
p. 9 – “Post-Closure Monitoring
“The Mine Closure Management Plan will set out [measures for]:
Physical stability monitoring:
- Open pit and subsidence area;
- Mine site and disturbed areas;
- Waste rock dumps;
- Tailings storage facility;
- Undai river diversion; and
- Site security features.
[and] Chemical stability:
- Open pit and subsidence area;
- Mine site and disturbed areas;
- Waste rock dumps;
- Tailings storage facility; and
- Undai river diversion.
18