This report details the proposed processing route for the N-204 deposit, which relies on dense media separation followed by flotation to produce lead and zinc concentrates.
Report context
The Pine Point Mine Development Project Summary Technical Report Update 2014 describes recovery methods for multiple deposits including N-204. The mineralization occurs as coarse galena and sphalerite in a matrix of limestone, dolomite and shale. The metallurgical program has demonstrated that standard zinc and lead flotation preceded by dense media separation (DMS) will yield recoveries above 90 percent and concentrate grades above 60 percent for Pine Point coarse grain mineralization, confirmed by concentrates produced over a 23 year period by Pine Point Mines Ltd (Cominco) at Pine Point.
Processing route
Proposed Design
The proposed centralized DMS in conjunction with the R-190 concentrator will process 5,500 tonnes per day, of which about 3,700 tonnes per day will be rejected by the DMS plant leaving about 1,800 tonnes per day to be transported to the R-190 concentrator for the grinding and flotation circuits. The pre-DMS feed grade is expected to average above 2 percent lead and 5 percent zinc. The post-DMS pre-concentrate is expected to average between 18 percent and 20 percent metals for the R-190 concentrator feed.
The plant will consist of secondary and tertiary crushing; a grinding circuit consisting of a ball mill in closed-circuit with cyclones; sequential lead and zinc flotation circuits each incorporating three stages of cleaning; concentrate dewatering circuits using thickeners and pressure filters; concentrate storage, load-out, and transportation systems; and tailings dewatering using a thickener and vacuum filters together with a slurry containment pond for excess tailings. Tailings will be transported back to the mining area and used for reclamation of open pits.
Crushing and DMS
Run-of-mine mineralized rock would be crushed and screened to a final size of ¼ inch (-6 mm). The minus 6 mm material would go to dense media separation. The bottom screen would be set at 14 mesh to keep the fines from interfering with the DMS process. The fines (minus 14 mesh) and the DMS sinks would be trucked straight to the proposed mill at the R-190 site. The DMS float material could be sent to the waste pile, used for backfill, used as aggregate for road construction, or sold for use as construction materials or fill.
Grinding and Recovery Circuit at the Main Mine Site
Material from the DMS plant would be fed to the 3.5 metre diameter by 5.6 metre long ball mill that would operate in closed circuit with a cyclone cluster. Cyclone underflow would be recycled to the mill. Cyclone overflow, currently designed for 80 percent passing 105 micron, would flow to the pre-float circuit.
Pre-Float Circuit
Cyclone overflow will be directed to the pre-float cell, which scalps bituminous-activated slimes. The cell float will report to tails and the cell underflow will report to the lead conditioner prior to reporting to the lead flotation circuit.
Lead Circuit
The grinding circuit product after the pre-float is conditioned before feeding a lead rougher float bank. The underflow from the rougher feeds a scavenger circuit. Tails of the scavenger become feed to the zinc circuit. Overflow from both the rougher and scavengers feed two parallel flotation columns. Underflow from the cleaners is recycled to the feed of the rougher bank. Column overflow is passed to the lead thickener. Thickened lead concentrate is then pressure filtered and stockpiled for transporting to the railhead at Hay River.
Zinc Circuit
The tails of the lead circuit report to the zinc circuit. This is conditioned with the proper reagents before feeding the zinc rougher and zinc scavenger flotation banks. Underflow from the zinc scavenger is feed to the tailings thickener. Overflow of both the rougher and scavenger banks is conditioned then fed to the zinc cleaner and cleaner scavenger banks. Tails from the zinc cleaner scavenger is fed to a second cleaner scavenger. Tails of this second cleaner scavenger is also fed to the tailings thickener. Second cleaner scavenger overflow is recycled to the conditioning tank at the head of the zinc circuit. Overflow from both the cleaner and cleaner scavenger banks feeds four parallel flotation columns. Underflow from the columns is recycled to the cleaner scavengers. Column overflow feeds the zinc thickener. The zinc product is pressure filtered before being stockpiled for transporting to the railhead at Hay River.
Tailings Dewatering and Tailings Disposal
Flotation tailings will be thickened and the thickener underflow will be pumped to an agitated tailings stock tank and then to two vacuum drum filters. Filter cake, at 12 percent moisture content, will be conveyed to a stockpile. These filtered tailings would then be back hauled to assist in reclaiming previously mined pits, along with the DMS reject and waste material.
Concentrate Handling
Processed concentrates would be housed in the mill prior to loading into trucks for transport to the rail load-out building located near Hay River.
Process Water Balance
The process water requirement for the on-site crushing and DMS plant will be supplied by the dewatering operations at the mine site. Based upon hydrological test work and design, wells will be drilled according to design parameters outside the pit limits. Pumps will be inserted in these dewatering wells to draw the water table down to allow mining of the deposit. Initial indications from current monitoring wells, literature and past studies are that the Cluster Pits will require dewatering. Dewatering wells close to the DMS will provide all required make-up water for the pre-concentrating process. Excess mine water pumped from the dewatering wells, bottom of the pits and process water lost from the system will be returned to the groundwater aquifer by pumping into a mined out open pit which exposes the Presqu’ile formation.
The DMS will operate under a zero discharge operating plan whereby water will discharge and then be recovered from a basin, available or constructed. The only water losses in the DMS operation would be evaporation and water that coats the DMS rock entering the stockpile.
Reagents
The reagents used in the flotation process and their consumption are not detailed in this report section.
N-204 Specific Process
The mine plan for N-204 provides for the mining and pre-concentration prior to haulage to the main mill site (MMS). Stationary equipment for the pre-concentration process is listed in Table 17-6 of the original report.
Historical Operating Data
Concentrates produced over a 23 year period by Pine Point Mines Ltd (Cominco) at Pine Point confirm that standard zinc and lead flotation preceded by DMS yields excellent recoveries above 90 percent and concentrate grades above 60 percent for Pine Point coarse grain mineralization.
Testwork Data
The metallurgical data and metal recovery values used to generate the process design criteria and financial model were generated through laboratory testing using industry standard methods and metallurgical balancing techniques. The overall mass balance does not include a regrind circuit. It is planned that the main grinding circuit will be using a bond work index of 11.0 kWh/tonne and will have sufficient grinding capacity for handling the middlings from the cleaner circuit.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant throughput | 5,500 tonnes per day | Proposed design |
| DMS reject rate | ~3,700 tonnes per day | Proposed design |
| Mill feed after DMS | ~1,800 tonnes per day | Proposed design |
| Pre-DMS feed grade (Pb) | >2 percent | Expected design average |
| Pre-DMS feed grade (Zn) | >5 percent | Expected design average |
| Post-DMS pre-concentrate grade | 18-20 percent metals | Expected design |
| Ball mill dimensions | 3.5 m diameter by 5.6 m long | Proposed design |
| Grind size (cyclone overflow) | 80 percent passing 105 micron | Proposed design |
| Metal recovery | >90 percent | Testwork and historical |
| Concentrate grade | >60 percent | Testwork and historical |
| Bond work index | 11.0 kWh/tonne | Testwork |
| Filter cake moisture | 12 percent | Design assumption |
Project website: https://www.einpresswire.com/article/369285506/darnley-bay-reports-ni-43-101-resource-estimate-at-pine-point
Technical qualifications
The report notes that data for R-190 and N-204 were generated through laboratory testing using industry standard methods and metallurgical balancing techniques. The excellent metal recovery values reported from laboratory testing combined with the production of quality concentrates demonstrates the Pine Point deposits are very amenable to treatment by the DMS, grind and selective flotation process. The report does not provide actual plant performance data, capital costs, operating costs, or economic analysis for the N-204 deposit specifically.
Source: Pine Point Mine Development Project Summary Technical Report Update 2014, Section 17 Recovery Methods.
