Source:
p. 41
Deposit Type
- Metamorphic hosted
- Broken Hill-type (BHT)
- Banded iron formation
Summary:
The Pegmont lead-zinc deposit is a body of stratiform lead-zinc sulphides contained within a metamorphosed silicate facies BIF. It is considered to be an example of a BHT deposit.
Pegmont is enveloped by a variable but large volume of late or postorogenic fracture/vein- controlled alteration. Williams et al identified two stages of alteration. Stage 1 veins typically are composed of quartz ± K feldspar ± tourmaline ± biotite ± rutile ± ilmenite associated with K feldspar ± muscovite ± tourmaline, or biotite ± muscovite ± garnet alteration. Stage 2 quartz ± chlorite ± calcite ± ferroan dolomite ± hematite ± sulphide veins are associated with fine-grained muscovite (illite-phengite) + chlorite ± carbonate alteration.
A largest amphibolite (hornblende-plagioclase) body is poorly exposed in sub-crop on the edge of the mining lease, called the “Lease Amphibolite”, it is a flay lying, highly continuous body that transgresses the BIF without any apparent displacement. The Lease Amphibolite displays textural zoning, which may reflect chilled margins and compositional layering. The southeast edge of Zone 3 is defined where the amphibolite intersects the Lens B BIF, to the southeast of this the Lease Amphibolite is below the BIF's and to the northwest it is above the BIF's. Drill data density in the Lease Amphibolite is less than the mineralization.
The Squirrel Hills Granite, part of the Williams Batholith, is over 100 km north-south and up to 25 km wide. It has intruded the project sequence in the northern boundary of the Pegmont lease. Present as several low outcrops of tors exhibiting spheroidal and onion skin weathering. The southern contact is inferred from airborne magnetics. The Squirrel Hills Granite is a non-foliated, porphyritic granite, composed of biotite and hornblende with coarse K feldspar. The Yellow Water Hole Granite, also part of the Williams Batholith, approximately 18 km from Pegmont, is dated at 1493±8 Ma, postdating main tectonism that affected the sequence.
Lead-zinc mineralization at Pegmont is contained within BIF's. The BIF’s consists of banded quartzmagnetite-fayalite-garnet- grunerite-hedenbergite-sulphide. Apatite, gahnite, and graphite are common minor minerals. Bedding is typically on a scale of 1 to 5 mm. In fresh rocks, the main sulphide minerals are galena, sphalerite, with subordinate pyrrhotite, pyrite and chalcopyrite. In contrast to the almandine garnet in the hangingwall and footwall, the garnet in the BIF is manganiferous spessartite, reflecting the higher whole rock MnO content of the BIF.
The overall morphology of the stratiform mineralized banded iron formation at Pegmont is a flat, gently easterly dipping sheet. The known mineralization extends approximately 2 km along strike and approximately 1 km in the down dip direction to the southwest. Mineralization is known to extend to a depth of 350 m below surface but remains open down dip.
The principal lead and zinc mineralized BIF is termed Lens B, it is around 2 to 8 m thick. At surface, the Lens B BIF is present in banded ferruginous, jaspery, manganiferous gossans. Outcrops occur in two areas termed the Mount Lucas Load and Burke Hinge Zone (BHZ). Additional oxide mineralization has been intersected at the Bonanza Lode, which is about 2 km to the northeast of Mount Lucas. Work by Scott and Jones shows that there has been considerable depletion of Mg, Ca, Na, K, S, Ag, Cd, and Zn during weathering. The least mobile elements have undergone residual concentration up to the profile, whereas concentrations of other elements are either unaffected by weathering or vary irregularly, in many cases reflecting local variations within the ore horizon. On oxidation, galena changes either through a pyromorphite ± cerussite assemblage to plumbogummite / corkite or directly to coronadite.
Oxidation reaches depths of 25 m below surface. The surface gossans display delicate boxworks after fayalitic olivine and are composed of goethite, clay, and secondary lead minerals such as pyromorphite, plumbogummite, plumbojarosite, and / or beaverite, together with isomorphous hydrated lead, iron, and copper sulphates. No secondary zinc minerals have been observed. Between 0.5 and 2% graphite has been noted. A yellow-green fibrous vein mineral contained in the gossans is thought to be nontronite.
The lead content of outcropping gossan is the same as, or slightly higher than that of un- weathered ore. Although zinc is strongly depleted at surface (×10), its greater abundance (×2 depletion) only 15 m below the surface reflects the truncated profile and immaturity of the gossan.
In the partially oxidized transition zone, between 25 – 40 m below the surface, galena, sphalerite, magnetite (invariably showing alteration to hematite and goethite), manganese minerals including pyrolysite, and small amounts of pyrite and graphite have been described along with montmorillonite and kaolin, garnet, mica and quartz, and minor amounts of siderite, amphibole, chlorite, and talc.
The un-weathered Lens B BIF consist mainly of galena and sphalerite associated with a finely laminated assemblage consisting of dominant magnetite and spessartite with subordinate iron-magnesium-manganese silicates and apatite. Gangue minerals are apatite, olivine (fayalite), garnet (spessartine – almandine), amphibole (hornblende and grunerite), clinopyrozene, biotite, and greenalite.
Approximately 10 to 40 m below Lens B is a second BIF horizon, Lens C, generally only weakly mineralized and when present is around 1 m thick and is separated from the Main BIF by garnet-bearing quartzite and schist. Lens C becomes more important in Zone 5 where it is present at thickness of around 4 m.
In Zone 5 there is indications of a further four mineralized BIFs below Lens C, to date they have been intersected on the south western most drill section, in an interpreted anticline position.
Mining Methods
- Truck & Shovel / Loader
- Longhole stoping
- Room-and-pillar
Summary:
The Pegmont project includes three resources consisting of the BHZ, the Main Zones (Zones 1- 5), and the Bridge Zone. The BHZ can be developed as an open pit, the Main Zone can be developed as a combination of open pit and underground, and the Bridge Zone is an underground resource.
AMC (AMC Mining Consultants (Canada) Ltd) developed the Mineral Resource block models for the Main Zone and BHZ for evaluation of the open pit mining potential. The block models are proportional models, containing a field for ore percent and waste percent, with block dimensions of 5 m in the X (east) direction by 5 m in the Y (north) direction by 5 m in the Z (vertical) direction for the Main Zone, and 2.5 m in X by 2 m in Y by 2.5 m in Z direction for the BHZ.
AMC proposes to mine the open pits using a conventional truck and excavator mining method. AMC has assumed that a 10 m bench height would be adopted for waste rock, and that mineralized material will be mined in 2.5 m flitches to increase mining selectivity. Mining of mineralized material will occur using a hydraulic excavator in backhoe configuration (example: Komatsu PC1250). Hydraulic excavators in front-shovel configuration (example: Komatsu PC2000) will be used in areas of bulk waste rock to increase the rate of mining in waste rock and reduce operating costs.
The average productivity of the PC1250 excavators in blasted mineralized material is expected to be approximately 1,080 t/op hr. The productivity of the PC2000 in fresh waste is expected to reach 1,513 t/op hr.
Hauling of mineralized material and waste will be undertaken by 90 t trucks (example: CAT 777).
Pits were designed based on the selected optimization shells. Four pits have been designed, one for BHZ and three in the Main area.
Haulage ramps will be 23.1 m wide at a 10% gradient. Single way ramps of 13.3 m width were designed for the bottom twenty vertical meters.
The Main 7 pit is the largest pit measuring approximately 930 m in length, 330 to 550 m in width, and 200 m at its deepest point. The Main 7 pit consists of four stages (Main 4, Main 5, Main 6, and Main 7).
To assess the underground mining potential, a pit shell was generated that incorporates the potential open pit reserves for the Main Zone, all mineralized material outside of the pit shell was considered for underground mining with the focus on the Bridge Zone.
The geometry of the underground resources is primarily flat dipping (23° to 30°) and varying in thickness across each zone (3 m to 12 m). However, the Zone 5 mineralization and part of Zone 3B tends to be narrow in width and fairly vertical in dip.
The geometry lends itself to room and pillar (R&P) mining in the flat dipping zones and longhole stoping in the steeply dipping zones.
It is assumed that the underground zones will each be accessed from the Main pit with individual declines. AMC has developed conceptual mine designs for each zone to determine mine physicals and development costs.
The three main access declines have a total length of 2,166 m, level access development has a total length of 1,786 m and the remaining development includes return air drive access and mineralized development. Vertical development consists of return air raises with a total of 698 m. Total development for the three underground zones including vertical development is 5,547 m.
Stope wireframes were generated using MSO, a check was made to remove any outlying stopes that would not be economic when the cost of access development was included. The cost of access development was determined for each level and each level was evaluated to determine whether it was economic to develop.
Flow Sheet:
Crusher / Mill Type | Model | Size | Power | Quantity |
Jaw crusher
|
|
|
|
1
|
Cone crusher
|
|
|
|
2
|
Ball mill
|
|
5.23m x 6.67m
|
3300 kW
|
1
|
Stirred mill
|
.......................
|
|
355 kW
|
1
|
Stirred mill
|
.......................
|
|
185 kW
|
1
|
Summary:
Crushing
A three-stage crushing circuit has been selected based on applications treating similar material and the hardness values measured in the test work conducted for this study which indicate hard and potentially highly competent material will be treated.
Open pit material will be reclaimed by a FEL from the ROM stockpile into the ROM bin. The open pit material will be reclaimed from the ROM bin by an apron feeder and vibratory grizzly pan feeder to remove fines from the feed to the primary jaw crusher. The open pit material will be reduced in size from an F80 of 317 mm to a P80 of 120 mm by the primary jaw crushing, based on a close side setting (CSS) of 100 mm.
Primary crushed material will be conveyed to a double deck product screen. The top deck oversize material will be directed to the secondary cone crusher, with the lower deck material directed to a tertiary cone crusher. The secondary crusher will operate with a CSS of 32 mm, whilst the tertiary crusher CSS will be set to 14 mm.
The secondary and tertiary crushing stages will operate in closed circuit with the product screen.
The final product size will be controlled by the aperture of the bottom deck of the product screen to generate a ball mill feed size having a P80 of approximately 10 mm.
The crushed material will be conveyed to a fine product bin.
Grinding
Crushed material will be milled in a single stage ball mill operating in closed circuit with hydrocyclones. Crushed material will be reclaimed from the fine product bin by a variable speed conveyor for mill feed rate control. The single stage ball mill, with dimensions of 5.23 m Ø x 6.67 m EGL, will be equipped with a fixed speed 3300 kW mill motor. The cluster of 400 mm diameter hydrocyclones will have an overflow size P80 of 106 µm and will be designed to operate at a recirculating load of up to 300%.
Overflow from the hydrocylones will be pumped to the lead flotation conditioning tank. Cyclone underflow will gravitate back to the single stage ball mill for further size reduction.
Lime will be added when required in the milling circuit stage maintain a slurry pH prior to flotation of 8.5 to 9.0. Sodium Monophosphate (SMP) will also be added to the milling circuit to limit the pre-activation of sphalerite prior to lead flotation.
Processing
- Filter press plant
- Dewatering
- Flotation
Flow Sheet:
Summary:
A conventional sequential flotation circuit has been selected for the recovery of the lead and zinc minerals from the Pegmont deposit.
The process plant shall consist of a conventional three stage crushing and a single stage ball mill grinding circuit, followed by differential flotation of the lead and zinc minerals to produce separate saleable lead and zinc concentrates. The concentrates from the lead and zinc flotation circuits will be thickened and subsequently filtered on site for road transport.
Lead flotation circuit.
Cyclone overflow from the grinding circuit will gravitate via a trash screen to the lead rougher conditioning tank. The lead flotation circuit will consist of a conditioning stage, roughing and scavenger flotation, regrinding of the lead rougher and scavenger concentrate, followed by two stages of cleaning. The final lead concentrate will be pumped to the lead concentrate dewatering circuit and the lead rougher flotation tailings and lead ........

Recoveries & Grades:
Commodity | Parameter | Avg. LOM |
Lead
|
Recovery Rate, %
| 90 |
Lead
|
Head Grade, %
| 5.3 |
Lead
|
Concentrate Grade, %
| 69 |
Zinc
|
Recovery Rate, %
| 74 |
Zinc
|
Head Grade, %
| 2.2 |
Zinc
|
Concentrate Grade, %
| 54 |
Silver
|
Recovery Rate, %
| 77 |
Silver
|
Head Grade, g/t
| 8.8 |
Projected Production:
Commodity | Units | Avg. Annual | LOM |
Lead
|
M lbs
| 124 | 1,069 |
Zinc
|
M lbs
| ......  | ......  |
Silver
|
koz
| ......  | ......  |
All production numbers are expressed as payable metal.
Operational Metrics:
Metrics | |
Stripping / waste ratio
| 12.5 * |
Waste tonnes, LOM
| 111.1 Mt * |
Ore tonnes mined, LOM
| 10.6 Mt * |
Total tonnes mined, LOM
| 121.7 Mt * |
Tonnes milled, LOM
| 10.6 Mt * |
Plant annual capacity
| 1,100,000 t * |
Daily processing rate
| 3,000 t * |
* According to 2019 study.
Reserves at July 31, 2018:
Cut-off grade applied to the open pit Mineral Resources is 3% Pb+Zn and that applied to the underground is 5% Pb+Zn.
Category | Tonnage | Commodity | Grade |
Indicated
|
5,758 kt
|
Lead
|
6.5 %
|
Indicated
|
5,758 kt
|
Zinc
|
2.6 %
|
Indicated
|
5,758 kt
|
Silver
|
11 g/t
|
Inferred
|
8,277 kt
|
Lead
|
5.1 %
|
Inferred
|
8,277 kt
|
Zinc
|
2.8 %
|
Inferred
|
8,277 kt
|
Silver
|
8 g/t
|
Corporate Filings & Presentations:
Document | Year |
...................................
|
2021
|
...................................
|
2019
|
...................................
|
2019
|
...................................
|
2019
|
Technical Report
|
2017
|
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