Northern Minerals Ltd is focussed
on becoming a globally significant producer of the heavy rare
earth (HRE) dysprosium1. Northern has large
landholdings in Western Australia and the Northern Territory
which are considered highly prospective for this element.
Northerns flagship project is
the Browns Range project, where it has a number of deposits and
prospects (Figure 1) containing high value dysprosium
and other HREs, hosted in xenotime mineralisation. Dysprosium
is an essential ingredient in the production of NdFeB
(neodymium iron-boron) magnets used in clean energy and high
technology solutions. The projects xenotime
mineralisation facilitates the use of a relatively simple and
cost effective processing flowsheet to produce a high grade
dysprosium rich mixed rare earth oxide.
Northern claims that one of the key features of the project is
the simplicity of the rare earth mineralogy, dominated by
xenotime (yttrium rare earth element (REE) phosphate) which is
only one of a few rare earth minerals that has a track record
of successful separation. The xenotime mineralisation and
mainly silica host rock offers a key advantage as it allows the
ore to be readily upgraded through the beneficiation process by
a factor of 30 times to achieve a 20% total rare earth oxide
(TREO) mineral concentrate.
Northern announced an updated JORC
compliant mineral resource estimate for the Browns Range
project on 26th February 2014. Resource delineation
and estimation has been completed on four deposits, known as
Wolverine, Gambit, Gambit West and Area 5 (Figure 2).
The deposits remain open at depth and have further exploration
potential. Several additional prospects displaying similar
geological characteristics to Wolverine have also been
discovered at Browns Range which, according to Northern,
supports the potential for further dysprosium discoveries.
Over 74,000 metres of drilling
underpins the current total mineral resource at the Browns
Range project which is estimated at 6.48 m tonnes at 0.74% TREO
containing 4,000 tonnes dysprosium within 47,997 tonnes TREO
using a cut-off grade of 0.15% TREO (Table 1). At the
Wolverine deposit the total mineral resource is estimated at
4.46 m tonnes at 0.86% TREO containing 3,300 tonnes dysprosium
within 38,269 tonnes TREO using a cut-off grade of 0.15% TREO.
Of the total mineral resource, 66% is classified as indicated
resource, with the remainder in the inferred resource
A maiden ore reserve for the
project of 3.4m tonnes of ore containing 2,048 tonnes
dysprosium and 23,595 tonnes TREO was reported on 24 June 2014.
The ore reserve statement is based on the outcomes of the
Browns Range pre-feasibility study (PFS) and the mineral
resource estimate announced on 26 February 2014. The ore
reserve is classified as 100% probable ore reserve (Table
The PFS is based on a conventional mining operation involving
both open cut and underground operations and a relatively
simple processing flowsheet with all infrastructure located on
site. The project includes a base case production rate of 279
tpa of dysprosium, contained within 3,200 tonnes of high purity
mixed rare earth oxide (Table 3).
Northerns managing director
George Bauk said that, The completion of the PFS is
another major milestone for Browns Range, and has confirmed the
project is robust and well positioned to become a significant
global dysprosium supplier. We have a quality ore reserve
supporting a solid mining operation, with a key feature being
the projects xenotime mineralisation.
In particular, the PFS has
reinforced that the xenotime mineralisation at Browns Range is
our key competitive advantage - its richness in dysprosium and
predictable processing allow us to significantly concentrate
the ore through the beneficiation process and has delivered a
competitive cost estimate. The positive results from the PFS
will support the projects continuation to feasibility
study (FS), as we move toward a 2016 production target. Once in
full production, the project will deliver $173m average annual
operating free cash flow, which will be an outstanding result
for shareholders, Bauk said.
Interest in the exploration
potential of the area was generated by reconnaissance mapping
carried out by the Bureau of Mineral Resources (BMR) in the
late 1950s. The first record of commercial exploration was in
the early 1960s by New Consolidated Goldfields, with the area
attracting various phases of gold, base metals and uranium
exploration between 1960 and 2010. Anomalous rare earth
elements in outcrop were first identified through evaluation of
radiometric targets by PNC Exploration Australia Pty Ltd during
their uranium exploration programmes between 1987 and 1992.
In 2010, preliminary exploration
work by Northern identified high grade rare earth
mineralisation at the Wolverine and Gambit prospects. An
inaugural drilling programme was completed in 2011 at the
Wolverine, Gambit, Area 5 and Area 5 North prospects.
The deposits can be characterised
as breccia-hosted hydrothermal systems with the dominant
mineralisation being the rare earth phosphate mineral xenotime,
which is a rich source of the heavy rare earth element
dysprosium, plus yttrium (YPO4). Overall, the
mineralisation at Wolverine and Gambit has a high heavy rare
earth oxide (HREO) proportion to the TREO, being between 85%
Locally, at Wolverine, the host
rocks are a sequence of meta quartz-lithic arkosic arenites and
conglomerates with minor interbedded schists. The host rocks in
the mineralised zone are silicified and brecciated along
structures trending between east-west and 290 degrees
(Figure 2), and dipping steeply to the north
(Figures 3 and 4). Hematite and sericite alteration is
associated with mineralisation.
Xenotime is associated with varying
degrees of veining and brecciation (Figure 5); from
1mm to 2mm crackle vein selvages to matrix infill in 5 metres
wide zones of chaotic breccia. There are open spaced textures,
vugs and minor cross-cutting quartz, pyrite or barite veins
that are interpreted to post-date mineralisation.
Minerals of the florencite
- goyazite (Sr
2O) series are the only other rare earth element minerals
(besides xenotime) recognised to date.
Exploration drilling at Wolverine
Diamond core drill holes accounted
for 40% of the drill metres within the mineralisation and
comprised NQ and HQ core. Reverse circulation (RC) drilling
accounts for the remainder with diameters of either 115mm or
Drilling has been completed on a
nominal 25 metres in easting by 25 metres in northing grid
spacing, although this increases to broader spacing at the
lateral extremities of the deposit. The spacing of down-hole
intercepts of the mineralisation varies from the nominal collar
spacing due to deviation of drill holes. Prior to October 2013,
resource drilling was exclusively conducted at -60 degrees to
the south. From October 2013, diamond drilling was completed
using casing wedges and directional drilling, resulting in
variable intersection angles to the Wolverine deposit.
Sampling techniques at
Diamond core was cut in half using
an electric core saw. Sample intervals were selected on the
basis of lithological and structural features, together with
indicative results from hand held XRF measurements. Drill core
was sampled at a nominal one metre interval, but constrained
within geological intervals.
RC samples were collected from the
drill rig by either riffle splitting or using a static cone
splitter. All samples were collected dry with a minor number
being moist due to ground conditions or excessive dust
suppression. RC drill holes were sampled at one metre intervals
exclusively and split at the rig to achieve a target 2-5 kg
Field QAQC procedures included the
field insertion of certified reference materials (standards),
blanks and duplicates. Earlier drilling (2011 to July 2012) did
not include the insertion of standards as suitable materials
were not sourced. Blanks were developed from local host rock
following chemical analysis. Field duplicates were collected by
either a second sample off the splitter (RC) or by quarter core
samples of the original half core sample (diamond) and separate
submission and analysis at the laboratory. Insertion rates
averaged 1:20 for duplicates, blanks and standards, with
increased frequency in mineralised zones.
Determinations of bulk density were
completed by a combination of core immersion techniques and
downhole density surveys with values typically in the range
2.10 g/cm3 to 3.40 g/cm3.
Sample analysis method
Diamond and RC samples were dried,
crushed, split and pulverised by Genalysis Laboratories in
Perth prior to analysis of rare earth element suite using
ICP-MS. The sample preparation techniques employed for the
diamond and RC samples follow industry best practice.
Samples assayed by Genalysis for
rare earth elements were fused with sodium peroxide within a
nickel crucible and dissolved with hydrochloric acid for
analysis. Fusion digestion ensures complete dissolution of the
refractory minerals such as xenotime.
The digestion solution, suitably
diluted, was analysed by ICP Mass Spectroscopy (ICP-MS) for the
determination of the rare earth elements (La - Lu) plus Y, Th,
U, Sr, W and As.
Mineral resource and
Resource classification is based
upon continuity of geology, mineralisation and grade, using
drill hole and density data spacing and quality, variography
and estimation statistics (such as number of samples used,
estimation pass, and slope of regression). Parts of the
estimate poorly supported by drilling have not been classified
as mineral resource.
The ore reserve (Table 2)
is based entirely on the mineral resource (Table 1),
as released, in accordance with the JORC 2012 Code, by Northern
on 26 February 2014. The quantity and classification of this
mineral resource is stated below in Table 1. The mineral
resource is inclusive of the ore reserves.
AMC Consultants Pty Ltd (AMC)
prepared a PFS level technical mining study on behalf of
Northern and advised that the mining aspects that underpin the
Browns Range ore reserve are technically feasible and
economically viable. As part of this study AMC:
suitable open pit designs for Wolverine, Gambit, Gambit West
and Area 5 deposits.
2 Selected a
suitable underground mining method for Wolverine and Gambit
3 Estimated costs
for mining operations under assumption of contractor
4 Reviewed and
validated all other inputs provided by Northern (including
general and administrative costs, processing costs and
recoveries, other overhead costs, metal pricing) as being
suitable to support the ore reserve estimate.
Mine design and optimisation
The open cut mine designs are based
on pit shells (Figure 6) produced by AMC using GEOVIA
Whittle 4X software. Several pits were generated at increasing
revenue factors. All pit shells selected were conservative when
compared against the Whittle maximum cash flow pit.
The proposed mining technique at
the Wolverine underground mine is sub-level open stoping
(Figure 7) with post extraction backfill using a
mixture of cement stabilised aggregate and run-of-mine waste.
The proposed mining technique at the Gambit West underground
mine is narrow bench and fill stoping with post extraction
backfill using run-of-mine waste.
The combination of xenotime with a
silica host rock offers a key advantage in simple and
cost-effective beneficiation, allowing the ore to be readily
upgraded by a factor of 30 times to achieve a 20% TREO mineral
The proposed mining fleet will
transport the run-of-mine ore to the run-of-mine pad where the
ore will be stockpiled and blended to the desired grade before
transferring to the crushing circuit which consists of a
primary jaw crusher, followed by a 750kW 4.8 metres diameter x
2.4 metres SAG mill and then a 1700kW 4.2 metres diameter x 6.2
metres ball mill that grinds the ore down to a size of 80%
passing 63 metres.The ground ore is fed to a wet high gradient
magnetic separator (WHGMS) that produces two products, a
magnetic concentrate rich in xenotime and iron oxide, and a
non-magnetic stream containing largely silica and mica which is
rejected as tailings. The magnetic concentrate is then fed to a
flotation circuit where selective reagents are used to collect
the xenotime material in the froth and reject unwanted gangue
material in the tailings. The flotation tailings are combined
with the WHGMS circuit tailings and thickened before being
comingled with the hydrometallurgical tails and pumped to the
tailing storage facility. The 20% TREO flotation concentrate is
thickened, filtered and stored in bunkers prior to being fed
into the hydrometallurgical plant.
The 20% TREO mineral concentrate is
reclaimed from bunkers with a bobcat, fed into a live bottom
bin and screw conveyed into a dryer. The dry concentrate is fed
into an acid mixer and then the kiln. The sulphation bake is
performed at 275-300 oC which cracks the xenotime
mineral and the rare earths are readily leached in water.
Following the water leach step, the leach residue is washed,
filtered and separated from the pregnant leach solution (PLS).
The PLS undergoes a series of purification steps where the pH
of the solution is steadily increased with lime and magnesia to
reject impurities such as phosphate, iron, aluminium, thorium
and uranium. The purification residue is separated from the PLS
by thickening and filtering, and the PLS is passed through an
ion exchange column to remove any residual uranium. The
purification residue is repulped and mixed with the repulped
water leach residue before being comingled with the
beneficiation tailings and pumped to the TSF. Following
purification and ion exchange, the PLS is contacted with oxalic
acid which selectively precipitates the rare earths. The mixed
RE oxalate is thickened, filtered and washed before being
calcined to a high purity, mixed RE oxide (Figure
Hydrometallurgy - pilot scale testing
Northern Minerals has been
conducting a series of continuous pilot scale testing of the
projects hydrometallurgical processing plant at ANSTO in
New South Wales (NSW). The third and final five-day continuous
pilot plant run during April 2014 achieved the best recovery
results of the test work to date, including 92% for dysprosium
and 92.6% for TREO. These recoveries have improved from the
results from the second test run, which were 90% for dysprosium
and 88.2% for TREO. This increase in recovery will result in an
additional six tonnes of dysprosium and 157 tonnes of TREO
being produced on average per annum. Using the PFS input data,
this recovery improvement equates to around $21m of additional
net present value (NPV) for the project.
The improvement is due to the
increased bake residence time and, most importantly, the steady
state continuous operation, with the kiln running uninterrupted
for five consecutive days. Approximately 120kg of rare earth
carbonate was produced in the third run for customer
validation. The material, which typically contained a mixed
rare earth carbonate grading 48%, again featured a high
proportion of dysprosium.
According to Northern the key
market driver for dysprosium is the growing demand for NdFeB
permanent magnets. The permanent magnet sectors
forecasted growth from 2014 to 2020 is expected by Northern to
be 8-12% per annum, which could increase as secure sources of
dysprosium supply, such as Browns Range, come online. While
current dysprosium prices are lower than in recent years,
global producers are forecasting prices to steadily increase
over the next six years due to this demand pressure, with
Chinese production continuing to consolidate and global demand
increasing for environmentally responsible HRE sources.
WAs Environmental Protection
Authority (EPA) has advised that it considers that the project
can be managed to meet the EPAs environmental objectives
subject to the EPAs recommended conditions being adopted.
The company has also commenced preliminary planning and
drafting work on the secondary approvals required for the
proposed mining operation. These approvals will be considered
by the relevant decision making authority following the
Ministers determination, and will include:
- Mining proposal and project
management plan from the WA Department of Mines and
- Works approval and licences
from the WA Department of Environment Regulation.
- Licences to construct bores
and take water from the WA Department of Water.
In addition, the Federal Government
Department of Environment has assessed Browns Range as a
not controlled action which means the project does
not require assessment and approval under the EPBC Act 1999
before it can proceed.
Following the release of a positive
PFS in June, the company has the projects FS underway
which it is aiming for completion at the end of 2014. The
process design criteria for the FS have been completed and
Northern has appointed a number of key consultants and
consultant engineers. DRA Global has been appointed to
undertake the design of the beneficiation plant, process
infrastructure and also manage the overall co-ordination of the
FS. Engineering and project management firm Lycopodium has been
engaged to undertake the design of the hydrometallurgical
plant. Global management consultant Accenture will be
responsible for project controls and procurement for the
1 In this report dysprosium is to
be read as dysprosium oxide (Dy2O3)
unless otherwise stated.
The management of Northern Minerals Ltd is sincerely thanked
for permission to publish this report.