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Appendix 5
Groundwater Report- GDS
H1 Desktop Hydrogeological Assessment
Mt Henry Open Pits
October 2015
SHS014-DTS-Doc053
Revision 1
Proponent
Enviro Department / Higginsville Gold Operations, Metals X Limited
Level 3, 18-32 Parliament Place, West Perth WA 6005.
Tel: +61 8 9039 6006
Email: [email protected]
Service Provider
Groundwater Development Services (GDS) Pty Ltd
149 Grand Ocean Blvd, Port Kennedy WA 6172
Tel: 0448 756 080
Email: [email protected]
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TABLE OF CONTENTS Page
1.0 INTRODUCTION ........................................................................................ 1
1.1 Background ....................................................................................................... 1
1.2 Location ............................................................................................................. 2
1.3 Higginsville Operations .................................................................................... 2
1.4 Current Licensing ............................................................................................. 4
1.5 Proposed licence application........................................................................... 4
1.6 Proposed Use .................................................................................................... 4
2.0 CLIMATE /RAINFALL ............................................................................... 4
3.0 PREVIOUS INVESTIGATIONS ................................................................. 6
3.1 Preliminary hydrogeological assessment (Venables, 2009) .......................... 6
3.2 Lake Dundas Water Quality and Fauna Surveys (WRM 2013) ....................... 6
3.3 Dewatering Assessment (GRM 2014a) ............................................................ 6
3.4 Pit Closure Assessment (GRM 2014b) ............................................................ 7
4.0 CURRENT BORES .................................................................................... 7
5.0 GEOLOGY ............................................................................................... 10
5.1 Regional Geology ............................................................................................10
5.2 Local Geology ..................................................................................................11
5.2.1 Mt Henry ............................................................................................................ 11
5.2.2 Selene ................................................................................................................ 11
5.2.3 North Scotia ....................................................................................................... 11
6.0 HYDROGEOLOGY .................................................................................. 12
6.1 Regional Hydrogeology ...................................................................................12
6.2 Local Hydrogeology ........................................................................................12
6.2.1 Venables (2009) ................................................................................................ 12
6.2.2 GRM (2014a) ..................................................................................................... 13
6.3 Water Levels .....................................................................................................14
6.4 Groundwater Chemistry ..................................................................................14
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7.0 DEWATERING VOLUMES ...................................................................... 17
8.0 DEWATERING STRATEGY .................................................................... 17
9.0 PIT DRAWDOWN .................................................................................... 18
10.0 EXISTING USE ........................................................................................ 18
11.0 PROPOSED USE .................................................................................... 19
12.0 IMPACT ASSESSMENT .......................................................................... 19
13.0 MANAGEMENT APPROACH .................................................................. 19
13.1 Best Practice ....................................................................................................19
13.2 Mitigation Measures ........................................................................................20
14.0 REFERENCES ......................................................................................... 21
FIGURES Page
Figure 1 Location Map ............................................................................................... 3
Figure 2 2014 Investigation Bore Locations ............................................................... 9
TABLES
Table 1 Summary of Higginsville Licences ................................................................. 4
Table 2 Monthly climatic statistics Norseman (012065, BOM) ................................... 5
Table 3 Monitoring Bores .......................................................................................... 7
Table 4 2014 Drilling Investigation Bores ................................................................... 8
Table 5 Water Quality Analysis ................................................................................ 16
Table 6 Pit Inflows .................................................................................................. 17
Table 7 Maximum Pit Drawdown and Distance of Influence ................................... 18
Table 8 Existing Groundwater Use .......................................................................... 18
Table 9 Preliminary Monitoring Program .................................................................. 20
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APPENDICES
APPENDIX A: Dewatering Assessment, GRM (2014a)
APPENDIX B: Pit Closure Assessment, GRM (2014b)
APPENDIX C: Preliminary Hydrogeological Assessment, Venables (2009)
APPENDIX D: Lake Dundas Water Quality and Fauna Survey, WRM (2013)
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1.0 INTRODUCTION
Higginsville Gold Operations (HGO) plan to develop the Mt Henry Open Pits
Project which is located on mining lease M63/515 and M63/516 in the Dundas
Mineral field. Gold ore from this mine is to be trucked a distance of 85 km to the
Higginsville operation via the Coolgardie Esperance Highway. The location of the
HGO and the Mt Henry Open Pits is shown on Figure 1.
1.1 Background
This report has been prepared to support a licence application for abstraction of
400,000 kLpa groundwater from the Mt Henry Pits Project, which is comprised of
three open pits: Mt Henry, Selene and North Scotia pit (Figure 1).
Dewatering is required to allow mining below the water table in each of the three
pits. Dewatering yield is planned for use in dust suppression within the mine area.
Process water will not be sourced from the Mt Henry area as the ore will be
transported to the HGO mill.
Numerical modelling (GRM, 2014a) indicates that inflows to the three pits will
range from 5.5 lps (173,448 kLpa) to 8.3 lps (261,749 kLpa). Due to the presence
of a thick alluvial sequence in Selene Pit, there is a possibility of increased
groundwater inflows of up to 10 lps (315,360 kLpa) during significant rainfall
events. A licence allocation of 400,000 kLpa will address any contingency
requirements associated with periodic rainfall related inflows.
This report conforms to H1 desktop assessment standard as required by
Department of Water Operational Policy No 5.12. A desktop assessment without
requirement for further field investigation is considered appropriate for this study.
Points assigned for each main factor, as per Policy No 5.12, are summarised
below:
The volume requested is 400,000 kLpa (6 points)
The Level of allocation in the Lefroy-Dundas GSA, combined fractured rock
aquifer is a Level 4 (4 points)
The potential for unacceptable impacts to other users is unlikely (0 points)
The potential for unacceptable impacts to GDE's is unlikely (0 points)
The potential for unacceptable impacts to other users is unlikely (0 points)
The existing salinity (mg/L) is hypersaline (0 point)
Total Points: 6+4+0+0+0=10
Table 1, Decision table for hydrogeological assessments, in Operational policy no.
5.12 (DoW 2009) indicates that for scores of 8 to 12, an H1 Desktop Assessment
is appropriate.
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1.2 Location
The Higginsville Gold Operations are located approximately 55km north of
Norseman and 110km south-east of Kalgoorlie in the Goldfields region of Western
Australia.
The Mt Henry Open Pits project is located 85 km south of the Higginsville Gold
operations and 23 kilometres south of Norseman. The site is accessed from
Norseman by driving 23 km south on the Coolgardie Esperance highway and
turning east along a dirt track for a distance of 3 km. The Mt Henry Open Pit project
is located on the western edge of Lake Dundas and lies within mining tenements
M63/515 and M63/516. The project location is shown Figure 1 and is centred at
approximately 386,000mE and 6,417,000 mN (Zone 52, MGA, GDA94).
The Mt Henry Open Pits project area are located in the Goldfields Groundwater
Area and the Lefroy-Dundas Groundwater Sub-Area.
1.3 Higginsville Operations
Gold mining commenced at Higginsville by Samantha Gold NL in 1989, followed
by Resolute Mining Limited. Mining and ore processing ceased in 2000 and
Resolute sold exploration rights to Western Mining Company who sold onto
Goldfields Australia Limited. Avoca Resources Ltd acquired the Higginsville
Project in June 2004 and commenced development of the Trident underground
mine and construction of the 1Mtpa Higginsville processing facility.
In 2008, construction of the processing plant and associated infrastructure together
with a 160 person onsite village, offices and workshops were completed. In
February 2011, Avoca merged with Anatolia Minerals Development to form Alacer
Gold Corporation.
In October 2013, Metals X Limited, through its wholly owned subsidiary Westgold
Resources Pty Ltd, reached an agreement with Alacer to acquire its Australian
gold operations, including Alacer Gold Pty Ltd and its wholly owned entities which
includes Avoca Resources Ltd in relation to Higginsville Gold Operations.
Mt Henry Open Pits project was acquired by Metals X from a joint venture between
Panoramic Resources and Matsa Resources in October 2015. The Mt Henry Open
Pit project is a developing project which will provide ore to the Higginsville Mill via
the development of open cut pits.
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Figure 1 Location Map
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1.4 Current Licensing
There are no current licenses associated with Mt Henry Open Pits Project. The
Higginsville Mining Operations do have current licences associated with the other
mining areas, which are summarised below in Table 1.
Table 1 Summary of Higginsville Licences
Licence Allocation
(kLpa)
Associated Activities and Areas
GWL160795(5) 500,000
Dewatering of open pits and
underground operations close vicinity
to Higginsville Operation Centre
GWL165489(3)* (1,500,000) Dewatering of the Chalice open pit
and underground operations GWL178699 400,000 Dewatering of existing open pits at
the Lake Cowan Mining Area GWL180185 1,000,000 Dewatering of the Challenger open
pit. TOTAL* 3,400,000
*GWL165489 (3), for Chalice pit, is not in use and will be relinquished when dewatering activities at
Challenge commence. The total allocation will be 1,900,000 kLpa when the GWL165489 (3) is
relinquished.
1.5 Proposed licence application
The proposed licence for the Mt Henry, Selene and North Scotia open pits will
allow for the dewatering of the pits to facilitate mining below the water table. The
licence for the Mt Henry Open Pits project is a request for an allocation of 400,000
kLpa. The licence duration is expected to be 10 years.
1.6 Proposed Use
The proposed use will be dust suppression around the active mining areas.
2.0 CLIMATE /RAINFALL
Climate is semi-arid, typically varying markedly in magnitude from year to year and
in temporal distribution. The nearest long term climate station is at Norseman. Data
from the Norseman sites is summarised on Table 2.
January is the hottest month with a mean maximum of 32.6°. The coolest month
is July with a mean minimum 5.1°.
The mean annual rainfall at Norseman is 288 millimetres. The highest mean
monthly rainfall occurs in May with a record of 30.5 mm. The lowest mean monthly
rainfall occurs in January with a record of 19.9 mm.
Annual evaporation rate approximates 2500 millimetres.
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Table 2 Monthly climatic statistics Norseman (012065, BOM)
Statistic Element Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual No Yrs
Mean maximum temperature °C
32.6 31.3 28.8 24.6 20.4 17.5 16.8 18.5 21.6 25 28.1 30.7 24.7 61
Mean minimum temperature °C
15.8 15.9 14.5 11.6 8.5 6.3 5.1 5.4 7.3 9.7 12.3 14.1 10.5 61
Mean rainfall (mm) 19.9 24.9 24.4 23.4 30.5 30.1 26.8 24.8 21.4 20.3 20.4 21.4 288 115
Highest rainfall (mm) 116 203 189 112 137 104 80 94.9 75.2 87.2 86.9 151 624 115
Lowest rainfall (mm) 0 0 0 0 0 2.2 2.5 0.8 0.4 0 0 0 138 115
Start: 1951 End: 2012
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3.0 PREVIOUS INVESTIGATIONS
3.1 Preliminary hydrogeological assessment (Venables, 2009)
A desk top study was completed on the Mt Henry and North Scotia pits by Venables
(2009). The Selena pit was not part of the assessment.
The objectives were:
To gain a broad understanding of the hydrogeological conditions at the Mt
Henry and North Scotia Pits.
To identify concerns which could impact on the mining of several shallow
pits.
To establish a monitoring bore database and design a monitoring program
for the bores.
Identify future drilling requirements for the purpose of constructing
dewatering and monitoring bores.
3.2 Lake Dundas Water Quality and Fauna Surveys (WRM 2013)
The results of the study were not used directly in this document.
The objectives were to:
Collect lake sediments for the purpose of species identification
Sample aquatic fauna
3.3 Dewatering Assessment (GRM 2014a)
The GRM (2014a) dewatering assessment has been used extensively in this
document.
The objectives of the assessment were to:
Define the reginal and local geology
Define the regional and local hydrogeology
Drilling investigations to target features identified during earlier studies and
construct monitoring bores in Mt Henry, Selena and North Skotia pits.
Installation of data loggers to assess rainfall and recharge relationships.
Hydraulic testing (slug tests) to determine aquifer parameters (hydraulic
conductivity) of the three pits.
Groundwater flow modelling to define potential drawdown impact,
drawdown extent and pit inflows during 6 year Life of Mine.
Identify a preliminary operating strategy and monitoring regime.
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3.4 Pit Closure Assessment (GRM 2014b, MBS 2014)
The pit closure assessment is based on mine inflows reported in the preceding
study (GRM 2014a) drawing from work completed by MBS in 2014. The primary
objective of this study was to apply pit lake water and solute balance modelling to
simulate post closure conditions in each pit.
The primary output from the study were:
A water balance addressing pit lake storage volume, pit inflows and
outflows.
Residual recovering water levels in each pit with associated recovery rates.
Equilibration water levels of each pit after 300 to 400 years.
Salinity, acidity and metal concentrations after 400 years.
4.0 CURRENT BORES
Sixteen monitoring bores were constructed during previous site investigations
(GRM 2014a) which comprised:
Nine in-pit monitoring bores
One ex-pit monitoring bore
Six shallow lake monitoring bores
The monitoring bores associated with each pit are summarised below in Table 3
and locations shown in provided in Figure 2.
Table 3 Monitoring Bores
Pit Bore Number Target Area
Mt Henry MTHEWE02-07 6 Pit
MTHMB01 1 Lake Edge
Selene SELWE04-05 1 Pit
SeLWE01-03 3 Lake Edge
North Scotia
SCOWE01-3 3 Pit
SCOMB01-02 2 Lake Edge
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Table 4 2014 Drilling Investigation Bores
Area Tenement Bore ID Easting Northing Collar RL
mAHD Hole Depth
(mbgl) Purpose
Mt Henry M63/515 MTHWE02 385,798 6,417,514 285 78 Pit Area
Mt Henry M63/515 MTHWE03 385,844 6,417,389 292 140 Pit Area
Mt Henry M63/515 MTHWE04 385,803 6,417,337 284.5 73 Pit Area
Mt Henry M63/515 MTHWE05 385,773 6,417,182 285.5 54 Pit Area
Mt Henry M63/515 MTHWE06 385,927 6,417,140 295.5 60 Pit Area
Mt Henry M63/515 MTHWE07 385,746 6,416,871 264 84 Pit Area
Mt Henry M63/515 MTHMB01 386,070 6,416,694 251 12 Lake Edge
Selene M63/516 SELWE05* 385,548 6,412,946 253 78 Pit Area
Selene M63/516 SELWE04 385,446 6,413,218 246 102 Pit Area
Selene M63/516 SELMB02 385,601 6,413,466 246 12 Lake Edge
Selene M63/516 SELMB03 385,629 6,413,030 247 12 Lake Edge
North Scotia M63/516 SCOWE01 385,036 6,411,272 251.5 60 Pit Area
North Scotia M63/516 SCOWE02 384,949 6,411,295 252 54 Pit Area
North Scotia M63/516 SCOWE03 384,966 6,411,095 247 67 Pit Area
North Scotia M63/516 SCOMB01 385,135 6,411,427 250.5 12 Lake Edge
North Scotia M63/516 SCOMB02 385,105 6,411,183 246.5 12 Lake Edge
*SELWEO5 was a dry bore and decomissioned.
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Figure 2 2014 Investigation Bore Locations
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5.0 GEOLOGY
5.1 Regional Geology
Regional geology has been described in previous reporting (GRM 2014a) and is
reproduced below.
The Mt Henry project lies within the southern portion of the Norseman-Wiluna
greenstone belt of the Eastern Goldfields Yilgarn Block. Norseman is the southern-
most gold mining centre of the Norseman-Wiluna gold belt which hosts over 270
million ounces of gold. The Norseman region has been a major gold producer with
in excess of 5.5 million ounces of gold produced since 1935.
Although the greenstone sequence from the Norseman area can be broadly
correlated with those of the Kalgoorlie-Kambalda region, they form a distinct terrain
which is bounded on all sides by major regional shears. The Norseman Terrane
has a prominent banded iron formation sequence which distinguishes it from the
Kalgoorlie-Kambalda Terrane.
The regions’ greenstone succession has been subdivided into four formations in
the vicinity of the project (Doepel 1973), which trend north-south and dip steeply
to the west. A description (from lowest to highest) of the four formations is
presented below:
Penneshaw Formation – A greenstone sequence on the eastern side of
the project, comprising mafic volcanics interfingered with felsic
volcaniclastic and sedimentary rocks. The Penneshaw Formation is
intruded by the Buldania Granite Complex in the east.
Noganyer Formation – A banded iron formation, with chert sandstone
and shale units, which structurally overlies the Penneshaw Formation.
The Noganyer Formation hosts the gold mineralisation at Mt Henry and
Selene.
Woolyeenyer Formation – A sequence of mafic volcanic rocks with
minor ultramafic and sedimentary units, which conformably overlies the
Noganyer Formation. The Woolyeenyer Formation hosts the Norseman
style quartz reef gold mineralisation, including the North Scotia deposit.
Mt Kirk Formation – Felsic volcanic and sedimentary rocks intruded by
thick mafic sills that disconformably overlie the Woolyeenyer Formation.
The Mt Kirk Formation subcrops to the west of the project and is
bounded by a granite-gneiss complex.
The bedrock geology is overlain by Quaternary and Tertiary deposits, comprising
aeolian dune deposits, alluvium and colluvium. These include Tertiary Wollubar
Sandstone which forms the basal sand within the palaeochannels. These are
overlain by silts and clays of the Perkolilli Shale, which sub-crop under Lake
Dundas and the greater Lake Cowan palaeochannel system.
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5.2 Local Geology
The local geology has been described in previous reporting (GRM 2014a) and is
reproduced below:
5.2.1 Mt Henry
The Mt Henry resource is hosted in the Noganyer Formation. The main lode is
an elongated orebody, approximately 1.9 km long, 6 to 10 m wide and dips
approximately 70° to the west.
The host rock is predominantly banded iron formation with minor meta-
basalts and dolerites. Sulphide minerals range from trace to 10%, and comprise
pyrrhotite with minor pyrite, arsenopyrite, chalcopyrite and marcasite.
Mineralisation is pervasive within the sheared BIF throughout the length of the
deposit, with discrete shoots containing higher grades and thicker intervals of
mineralization plunging to the north-northwest. The gold occurs within quartz
veins, in clouds with silicate minerals and in close proximity to sulphide minerals,
particularly pyrrhotite.
Late pegmatite dykes cross cut the host rock and stope out mineralization when
they cross the lodes.
5.2.2 Selene
The Selene resource is similar to the Mt Henry deposit, hosted in Noganyer
Formation BIF intruded by numerous dolerite sills. The footwall contact is
characterized by metamorphic sedimentary schist and the hanging wall by the
overlying dolerites of the Woolyeenyer Formation.
The Selene mineralization extends for 1.3 km along strike and extends 550 m down
dip at a shallow angle of around 20°. The mineralization thickens in the central
part of the resource to a true thickness of 35 to 40 m.
The main difference between the Selene and Mt Henry deposits is the
mineralization at Selene occurs in zones throughout the BIF package, whereas
at Mt Henry the mineralization is generally hosted in a shear on the hanging wall
contact of the BIF.
5.2.3 North Scotia
The North Scotia resource covers a strike length of 600 m within the Archean mafic
rocks of the Woolyeenyer Formation.
The Woolyeenyer Formation is host to auriferous quartz veins that have been
mined in the Norseman district continuously for 80 years. Gold mineralization is
hosted by laminated quartz veins which dip at approximately 70° to the west. The
nuggetty gold mineralization is disseminated throughout the 1 to 5 m wide
laminated quartz veins. Sulphides present include pyrite and galena.
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6.0 HYDROGEOLOGY
6.1 Regional Hydrogeology
The regional hydrogeologyl geology has been described in previous reporting
(GRM 2014a) and is reproduced below:
The hydrogeology of the project area is characterized by low relief and easterly draining palaeo-drainage systems, underlain by Archean sequences.
Groundwater typically occurs in:
Regional catchment controlled flow systems in fresh and weathered fractured rock aquifers;
Tertiary palaeochannel sands (Wollubar Sandstone);
Calcrete units that commonly overlie palaeochannel deposits;
Shallow alluvium.
Groundwater is recharged by direct rainfall infiltration or by stream flow during episodic rainfall events. The recharge occurs mainly on or adjacent to the catchment divides, beneath which there are corresponding, subdued groundwater divides. The groundwater moves from these divides to discharge into salt lakes along the palaeo-drainages. In the salt lakes the groundwater is evaporated and concentrated to brine, which then descends and moves downstream in the palaeochannel sand to eventually discharge into the Eucla Basin.
Groundwater salinities typically range from about 1,000 to 200,000 mg/L Total Dissolved Solids (TDS). Low salinity groundwater, ranging from 1,000 to 5,000 mg/L TDS occurs in areas most affected by direct rainfall recharge, e.g. near catchment divides and within shallow alluvium and calcrete units. The highest salinity groundwater occurs low down in the catchments within palaeochannel sands and deeper fractured rock aquifers.
Small supplies of groundwater can be found throughout the area. Large, fresh groundwater supplies are rare, but large, reliable supplies of saline to hypersaline groundwater are obtainable from the palaeochannel sand and site specific shear zones and deeply oxidized zones in the fractured rocks.
6.2 Local Hydrogeology
6.2.1 Venables (2009)
A preliminary desk top study of the local hydrogeology was completed by Venables
(2009) of the Mt Henry and North Scotia pits. The following conclusions were
made:
The southwestern portion of the proposed Mt Henry pit may encounter
significant inflows from the lake. The i n f l o w s w o u l d b e
a s s o c i a t e d w i t h t h e deep weathering a n d presence of a large
pegmatite intrusive which could act as a strong water-bearing conduit.
The northern portion of North Scotia pit has weathered material mainly
above the level of Lake Dundas and little inflow from the lake is expected.
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In the southern portion of North Scotia pit there is a substantial
thicknesses of alluvium, clay and saprolite. It is expected that significant
seepage from the lake into the southern part of the pit can be expected.
In general, it was unclear as to whether either of the two pits will require
dewatering.
Initial significant water inflow is considered unlikely in the North.
The southern ends of the Mt Henry and North Scotia Pits may be prone to
significant inflows from Lake Dundas.
Contingency plans should be made for the possibility of significant inflows
into the southern parts of Mt Henry and North Scotia pits.
It should be noted that after a review of the GRM (2014a) report, the concerns
highlighted by Venables regarding the potential for significant inflows to Mt Henry
and North Scotia pits may have been overstated.
6.2.2 GRM (2014a)
The local hydrogeology described by Venables (2009) was updated by GRM
(2014a) following drilling investigations, construction of monitoring bores, hydraulic
testing and groundwater flow modelling. The conclusions are reproduced below:
The permeability within the proposed pits is confined predominantly to
discrete structural features within the fresh bedrock, as well as the overlying
alluvium and weathered zone.
The Mt Henry pit inflows are structurally controlled and associated with the
contact between the quartz pegmatite and fresh basalt.
Airlift yields of four bores within the pegmatite had airlift yields which ranged
from 1 to 2.2 lps. The remaining 2 bores had negligible flows.
Permeability away from the structural features in each of the three pits is
very low with low storage characteristics.
Selene does not have the significant water bearing structures as seen in
Henry and North Skotia pits. An exploration bore completed in the pit
structures at Selena had a yield of 0.1 lps. Inflows are associated with
shallow alluvium and weathered bedrock, where an exploration bore had a
yield of 0.6 lps.
Similar alluvial sequences observed at Mt Henry and North Scotia were
less thick.
There is connectivity between Lake Dundas and the shallow groundwater
system.
Inflow rates, where the alluvium is thicker, particularly at Selena, are likely
to increase following high rainfall events.
The inflows at the North Scotia pit are associated with quartz veins within
the fresh basalt where airlift yields ranged from 1.7 to 2.5 lps.
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The volume of pit inflows in each pit estimated from numerical modelling
indicated that the pits were amenable to dewatering by surface water
sumps.
The overall drawdown effect from the numerical modelling was interpreted
to be localised.
6.3 Water Levels
The average ground elevation at the centroid of each pit is:
Mt Henry: 285 m AHD
Selene : 250 m AHD
North Scotia.: 252 m AHD
The open pit mining of reach pit will be to the following depths:
Mt Henry: 90 meters (195 m AHD)
Selene: 150meters (100 m AHD)
North Scotia: 75 meters (177 m AHD)
Groundwater levels measured during previous investigations (GRM 2014a) ranged as follows:
Mt Henry Pit : 250 to 275 m AHD (from south to north)
Selene and North Scotia: 245 to 246 m AHD, respectively.
The groundwater levels associated with the Lake Dundas lie around 245 m AHD, similar to the water levels measured at Selene and North Scotia which are located on the lake margin. The levels are consistent with groundwater flows towards the lake, which forms the regional groundwater sink (GRM 2014a).
For modelling purposes (GRM 2014a), the ambient pre-mining water level in Mt Henry pit was set at 275 m AHD. For Selene and North Scotia pits, the pre mining water level was set at 245 m AHD.
Modelling was run to simulate effective dewatering of the pit area below the proposed depth of pit development.
6.4 Groundwater Chemistry
Laboratory analysis of samples from monitoring bores from the Mt Henry, Selene
and North Scotia pits were completed during previous investigations (GRM 2014a).
Groundwater salinity of the Mt Henry pit ranges from 10,000 mg/L (MTHWE02) in
the north to 121,000 mg/L TDS (MTHWE07) in the south. It was concluded that
groundwater salinity increased down dip of the orebody lithology. Higher salinity
was considered to be representative of the ambient groundwater quality in the
crystalline bedrock.
Groundwater salinity of the Selene Pit was hypersaline with a salinity of 251,000
mg/L TDS, which is consistent with the deposits proximity to Lake Dundas.
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Groundwater salinity of the North Scotia pit ranged from 239,000 to 274,000 mg/L
TDS, which is similar to the salinity of the Selena pit and associated with the
proximity of the pit to Lake Dundas.
The analytical results have been reproduced below in Table 5. The water quality
results show hypersaline water quality which is representative of groundwater and
surface water in the Dundas Paleodrainage system.
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Table 5 Water Quality Analysis
Analyte Unit SCOWE01 SCOWE02 SCOWE03 SELWE04 MTHWE02 MTHWE03 MTHWE04 MTHWE07
pH 6.5 7 6.1 6.8 7.3 7.5 7.7 7.1
Total Dissolved Solids mg/L 274,000 239,000 243,000 251,000 10,000 17,400 18,200 121,000
Electrical Conductivity mS/cm 220,000 210,000 200,000 210,000 16,000 20,000 27,000 140,000
Bicarbonate alkalinity as HCO3 mg/L 47 140 8 38 240 320 460 170
Carbonate alkalinity as CO3 mg/L <1 <1 <1 <1 <1 <1 <1 <1
Hydroxide alkalinity as OH mg/L <5 <5 <5 <5 <5 <5 <5 <5
Total alkalinity as CaCO3 mg/L 38 120 6 32 190 260 380 140
Chloride mg/L 140,000 140,000 140,000 150,000 4,100 5,700 6,900 63,000
Sulphate mg/L 13,000 12,000 12,000 12,000 2,200 5,100 5,000 9,200
Nitrate, NO3 mg/L <0.05 0.06 0.08 0.84 <0.05 <0.05 0.06 <0.05
Aluminium, Al mg/L <1 <1 <1 <1 <0.02 <0.02 <0.1 <1
Arsenic, As mg/L <1.0 <1.0 <1.0 <1.0 <0.02 <0.02 <0.1 <1.0
Calcium, Ca mg/L 620 720 590 740 290 370 490 450
Cobalt, Co mg/L <0.5 <0.5 <0.5 <0.5 0.01 0.02 <0.05 <0.05
Copper, Cu mg/L <0.25 <0.25 0.49 <0.25 <0.005 <0.005 <0.025 <0.25
Iron, Fe mg/L <1 <1 <1 <1 6.5 <0.02 <0.1 <1
Magnesium, Mg mg/L 11,000 10,000 10,000 9,900 550 800 1,000 5,700
Manganese, Mn mg/L 1.4 2 2 3.1 2.5 2.6 1.7 4.1
Nickel, Ni mg/L 0.42 0.35 0.34 0.46 0.024 0.099 0.062 0.39
Potassium, K mg/L 890 820 790 790 64 84 100 370
Silica, soluble mg/L 7.3 10 9.3 6.7 52 49 52 17
Silicon, Si mg/L 3.4 4.7 4.3 3.1 24 23 24 7.8
Sodium, Na mg/L 97,000 83,000 87,000 91,000 2,600 5,000 5,500 40,000
Zinc, Zn mg/L <0.5 <0.5 0.74 <0.5 0.03 0.09 <0.05 <0.05
Total hardness by calc CaCO3/L CaCO3//L 48,000 44,000 43,000 43,000 3,000 4,200 5,400 24,000
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7.0 DEWATERING VOLUMES
Numerical modelling (GRM 2014a) provided estimates of maximum inflows for
each pit over a 6 year mine life. The results are summarised below in Table 6.
Table 6 Pit Inflows
Pit Maximum
Inflows (lps)
Maximum
Inflows
(m3/day)
Maximum Inflows
(kLpa)
Mt Henry 5.5 475 173,448
Selene 5.0 – 10.0* 432 - 864 157,680 – 315,360
North Scotia 8.3 717 261,749
* Seasonal inflows to Selene Pit associated with high rain events
8.0 DEWATERING STRATEGY
A dewatering strategy based on numerical modelling results and hydrogeological
assessment was described in previous reporting (GRM 2014a) and is reproduced
below:
The groundwater inflow rates predicted by the groundwater flow models indicate
dewatering of the Mt Henry, Selene and North Scotia pits will be best achieved by
sump pumping methods. Sumps should be strategically located at low points along
the pit floor.
A sufficient contingency should be considered to allow for short term, higher than
anticipated inflow rates following high rainfall events (Selene) and upon
interception of additional water bearing features in the fresh bedrock (all pits). A
contingency plan could include provision of additional surface water pumps for the
duration required to dewater the excess volumes. An allowance in the groundwater
abstraction licence will also be required to manage incidental rainfall derived
groundwater flowing into the pit void.
All dewatering discharge will be transferred to a process water dam at the surface
for use by the operation for dust suppression. At the predicted dewatering rates
there should be no requirement to discharge mine water to the environment.
Preliminary supply bores will be constructed to provide dust suppression water
prior to dewatering supply being available. The locations are currently hypothetical,
but, it is likely that the southern end of the Mt Henry pit would be an appropriate
location. This would also advance dewatering at that end of the pit and support
operational objectives.
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9.0 PIT DRAWDOWN
Predicted groundwater level drawdown for baseline runs at the end of mine of each
pit were calculated during previous reporting (GRM 2014a). The drawdowns and
maximum distances of influence at the end of mining are summarised below in
table 7.
Table 7 Maximum Pit Drawdown and Distance of Influence
Pit Maximum Drawdown
(m)
Maximum Influence (m)
Mt Henry
End of Mining (6 yrs) 2 1000
20 years 2 500
60 years 0.5 1000
100 years 0.5 <1000
Selene & N Scotia
End of Mining (6 yrs) 2 500
20 years 0.5 200
60 years 0.5 100
100 years 0.5 0
10.0 EXISTING USE
The nearest existing groundwater user is located 4 km south of the project in the
paleochannel aquifer. The next closest users are located 13 and 30 km to the north
in fractured rock aquifers. The existing users, volume of allocation and relative
distance from Mt Henry Open Pits project are summarised below in Table 8.
Table 8 Existing Groundwater Use
Map
Index Licence User
Allocation
(kLpa)
Location with
respect to Mt Henry
Open Pits Project
1 GWL61134 Central Norseman
Gold Corporation
Limited
6,500,000 13 Km to the north
in fractured rock
1 GWL61134 Central Norseman
Gold Corporation
Limited
6,500,000 4 Km to the south
in the paleochannel
2 GWL160161 Main Roads 40,000 30 km north east
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11.0 PROPOSED USE
The primary groundwater use associated with the dewatering of the Mt Henry Open
Pits Project is dust suppression.
12.0 IMPACT ASSESSMENT
Open pit evaporation and mine dewatering in this region are having no visible impact on the general environment or availability of hypersaline water resources.
Potential impacts of taking hypersaline groundwater from the Mt Henry Open Pits area for a short duration of less than 10 years are neutral as groundwater is hypersaline.
The Mt Henry Open Pits water also has no commercial value due to its hypersaline nature and has no impact on the sole beneficial groundwater user other than itself.
Numerical modelling has indicated that maximum drawdown of 2 meters will occur at distances of 1,000 meters from the Mt Henry Pits and 500 meters from the Selene and North Scotia pit. The drawdown impacts away from the immediate mining area are within the range of annual fluctuations in groundwater.
Potential impacts to Lake Dundas from the dewatering of Mt Henry, Selene and North Scotia pits will be negligible, considering the low volumes required and distance from each pit.
There are no groundwater dependent vegetation communities, threatened ecological communities or priority ecological communities that will be impacted by the project (GRM, 2014b).
Groundwater in the project area is hypersaline and low in dissolved oxygen and will not support stygofauna populations. (GRM, 2014b).
The project is located adjacent to Lake Dundas. No significant aquatic fauna species have been recorded in the lake. The project will have minimal impacts on the lake water quality and ecology (GRM, 2014b)
The nearest other licensed user is located 4 km to the south in the regional paleochannel aquifer. The proposed pits are constructed in the regional fractured rock aquifer system and impacts at distances of 4 kilometers are considered to be negligible. Other licensed users are located at distances of 13 and 30 kilometres from the project where potential impacts are assumed to be negligible.
13.0 MANAGEMENT APPROACH
13.1 Best Practice
Groundwater abstraction will be conducted and monitored according to the
operating strategy approved with the groundwater license.
Monitoring bores constructed during the 2014 investigations will be incorporated
into an Operating Strategy. Previous reporting outlined a preliminary monitoring
program which is reproduced below in Table 9.
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Table 9 Preliminary Monitoring Program
Monitoring Sits
Minimum Frequency
Criteria
Mt Henry, Selene, North Scotia
Monthly Abstraction Volume
Monthly In-Pit Water Level
Monthly Electrical Conductivity and pH
Annually Major Component Analysis
Monitoring Bores
Monthly Water Level
The major component analysis would comprise the following parameters:
Physical-chemical parameters – pH, electrical conductivity (EC), total
dissolved solids (TDS), total hardness, and total alkalinity.
Major ions – sodium, potassium, calcium, magnesium, chloride,
sulphate, bicarbonate, carbonate, nitrate.
Minor ions/metals – silica, aluminium, iron and manganese.
Optimum use of the water will be achieved through the use as dust suppression.
A water balance which incorporates the dewatering and dust suppression volumes
will be reviewed annually.
Use of hypersaline water for dust suppression will be restricted to mine areas so
as not to impact on bordering vegetation. Regular monitoring of vegetation will be
conducted on the periphery of the Mt Henry Open Pits project area and any
evidence of impact from dewatering will be subjected to mitigating measures.
13.2 Mitigation Measures
Higginsville Gold Operations will define a monitoring schedule for the Mt Henry
Open Pits project as set out in an Operating Strategy. Monitoring would be
designed to identify any deleterious trends in groundwater levels and/or quality,
which may affect other users, the aquifer or the environment.
Groundwater abstraction for the Mt Henry Open Pits project is not expected to
impact on other groundwater users. However, if a decline in water level is noted in
any bores operated by others, which may be attributable to Mt Henry Open Pits
dewatering operations, then an investigation will be commissioned to determine
the actual cause of the water level decline. If the decline is attributable to project
dewatering operations then the licensee will provide details of the investigation to
the DoW along with a proposed management strategy.
If unexpected declines in the aquifer water levels or change in water quality are
observed due to Mt Henry Open Pits dewatering operations, then an investigation
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will be initiated into the cause of the change and monitoring may become more
frequent. If required, alternative pumping regimes will be investigated.
Groundwater abstraction for Mt Henry Open Pits poses minimal risk to the
environment, in terms of water level drawdown effects on groundwater dependent
ecosystems. However, if any degradation of vegetation occurs, which may be
attributable to the dewatering operations, an investigation will be commissioned to
determine the actual cause of the vegetation degradation. If it is determined that
the degradation is due to Mt Henry Open Pits dewatering operations, mitigation
options will be assessed and implemented as appropriate.
14.0 REFERENCES
Doepel JG 1973 Norseman, WA: Western Australian Geological Survey, 1:125,000
Geological Series Explanatory Notes.
GRM 2014a Dewatering Assessment Mt Henry Gold Project, Prepared for Mt
Henry Gold Pty Ltd, April 2014.
GRM 2014b Pit Closure Water and Solute Balancing Modelling Mt Henry Gold
Project, Prepared for Mt Henry Gold Project Pty Ltd, June 2014h.
MBS Envirionmental 2014, Mt Henry Gold Project it Lake Closure Geochemical
Modelling, Prepared for Panoramic Gold, August 2014.
Venables, T. 2009 Preliminary Hydrogeological Report on the Mt Henry and North
Scotia Pits, Prepared for MATSA Resources Ltd, 25 March 2009.
WRM (Wetland Research and Management) 2013 Lake Dundas Sediment
Rehydration, Water Quality and Aquatic Fauna Surveys, Prepared for Panoramic
Resources Ltd, December 2013
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APPENDIX A –
GRM (2014a)
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APPENDIX B –
GRM (2014b)
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APPENDIX C –
Venables (2009)
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APPENDIX D
WRM (2013)