The Pasto Bueno tungsten mine in Peru operates an underground mining and gravity-magnetic concentrating system that was expanded in 2010 and processed about 350 tonnes per day in 2011 against a nominal capacity of 500 tonnes per day.
The Pasto Bueno Tungsten Mine, operated by Malaga, Inc., is an underground operation in Peru. Ore is processed through a three-plant system consisting of the Huaura Gravity Separation Plant, the Huaura Magnetic Separation Plant, and the Consuzo Magnetic Separation Plant. The plant is located about 200 meters from the Level 12 adit. The gravity concentrator is small and simple in design and was expanded and modernized in 2010. As of the reporting period, the plant was processing about 350 tonnes of ore per day. This throughput is limited by milling rate and by the company's permits. Nominal plant capacity is about 500 tonnes of ore per day. This figure equates to an annual nominal capacity of 180,000 tonnes.
The processing circuit is a sequential gravity and magnetic separation flowsheet. Crushing is performed in two stages of open-circuit operation. Primary crushing is done by a jaw crusher, and secondary crushing by a cone crusher. Grinding is performed by rod mills. The gravity separation system is central to the flowsheet and consists of primary jigs located between the crushing and milling stages, secondary jigs installed in the grinding circuit, and shaking tables for fine material. Rod mill discharge passes over secondary jigs, and the jig tailings are pumped to cyclones. Approximately 20 percent of the tungsten recovered by the plant is recovered in the secondary jigs. The primary shaking tables are arranged in two banks: one bank of four tables processing combined spiral classifier overflow and DSM screen undersize, and one bank of five tables processing cyclone overflow.
Primary tables produce three products: concentrate, middlings, and tailings. Secondary tables produce two products: concentrate and tailings. Tailings from the primary and secondary tables are final tailings. This stream flows down a concrete-walled ditch to the tailings pumps, which then pump the material to the current tailings containment. The current containment covers an area of about 100 meters square (about 1 hectare). A dam of coarse tailings forms about one half of the perimeter, with the other half formed by terrain. An emergency pond adjoins the containment to contain plant spills, and material accumulating there is periodically recycled to the plant. The capacity of the current tailings containment is limited, and a new containment is under construction in Quebrada Jajarajau valley, about half a kilometer from the plant. The new tailings containment was expected to come into use in 2012. The design incorporates concrete-walled runoff ditches on both sides, a starter dam with blanket and chimney drains, and drainage pipes in the base of the containment. A geotechnical engineer reviewed and approved the design.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Ore processing rate (actual, daily) | 350 | tonnes/day | Limited by milling rate and permits |
| Ore processing rate (nominal, daily) | 500 | tonnes/day | Annual nominal capacity 180,000 tonnes |
| Ore grade (feed) | 0.6 | % WO3 | Approximate, per processing rate context |
| Recovery (2011 data point) | 71.44 | % | Jan-Oct 2011 actual |
| Concentrate production (Jan-Oct 2011) | 740 | tonnes | Quantity of concentrate |
| Concentrate grade (final) | 73 | % WO3 | Assay of final concentrate |
| Pure WO3 content (Jan-Oct 2011) | 55,000 | tonnes | Not stated if this value is a typographical error; see editorial note |
| Primary crushing product size | 2 | inches | |
| Secondary crushing product size | 0.5 | inches | |
| Mill product (DSM screen undersize) | 4 | millimeters | |
| Tailings containment capacity (current) | 60,000 | tonnes | |
| Tailings containment capacity (Quebrada Jajarajau) | 900,000 | tonnes |
Overview
Pasto Bueno is an underground tungsten mine operated by Malaga, Inc. in Peru. The processing circuit is designed to upgrade ore containing roughly 0.6 percent WO3 to a final concentrate of about 73 percent WO3. The plant flow sheet relies entirely on gravity concentration followed by magnetic separation. No flotation is used in the current processing circuit, although tests have been performed on alternative recovery methods. The gravity plant is the primary recovery stage, with magnetic plants used to upgrade the gravity concentrates. Historical recovery for the period January to October 2011 was about 71.4 percent. The operation also involves tailings management with both an active containment and a new facility under construction as of 2012.
Key Process Stages
The ore is initially reduced in a two-stage crushing circuit. A jaw crusher performs primary crushing to a product of about 2 inches. A cone crusher then reduces the ore to about 0.5 inches. Screen undersize and cone-crusher product are conveyed to fine-ore bins.
From the fine-ore bins, ore is fed to two parallel jigging circuits. One circuit is equipped with a triplex jig, and the other has two smaller duplex jigs. These primary jigs recover coarse tungsten minerals. The oversize from this stage feeds the rod mills. The rod mills are charged manually with 3-inch diameter rods. The mill product is screened on DSM screens, and the screen undersize is sized at 4 millimeters.
Rod mill discharge passes over secondary jigs. The secondary jig tailings are pumped to cyclones. About 20 percent of the tungsten recovered by the plant is recovered in this secondary jigging stage. The jig circuits are integrated with the grinding circuit for closed-loop recovery.
The shaking tables process fines from the classifier and cyclone overflows. The primary tables are arranged in two banks that process different feed streams. Table concentrate is collected for further processing, while middlings are recirculated. Final tailings from the tables are sent to the tailings pumps.
The Huaura Magnetic Separation Plant uses several stages of magnetic separation. Gravity concentrates from the jigs and tables are first dried on electrically-heated plates. A diesel-fired rotary drum dryer is installed for drying but is not used, as the temperature is difficult to control, resulting in inadequate drying or overheating of the concentrate. The dried concentrate is then processed through drum and roll magnets. The remaining material passes over a drum magnet that makes three products: iron-containing gangue, final pre-concentrate, and middling concentrate. The middling concentrate passes over a roll magnet that produces a mixed concentrate and a tailings stream. Feed is screened into several size fractions for processing. The coarsest fraction is -1/8, +1/16 inch and is processed on one separator dedicated to this size. The other four sizes are matched with two finest sizes processed on one separator and the other two on another. The separators are variable-speed units with the main belt speed linked to the speed of the cross belts.
Concentrates from the size fractions are campaign processed through three stages of magnetic separation in the Consuzo Magnetic Separation Plant. The pre-concentrate and mixed concentrate from the Huaura plant are bagged and trucked to the Consuzo Gravity Plant for final upgrading.
Additional Interesting Data and Summary
The project has a history of testing alternative recovery options. Over the past two years, tests were carried out at a flotation mill in Nazca when tailings were being reprocessed for copper and silver recovery. Recommendations for improving recovery include reprocessing tailings from the Huaura Gravity Separation Plant and the current Huaura tailings containment using centrifugal-type collectors such as Knelson and Falcon concentrators. In addition, installing Derrick Stack Sizer screens in the Huaura Gravity Separation Plant was considered to remove intermediate size material of low tungsten content from the feed to the tables, preventing overloading of the tables.
A new tailings containment was under construction in Quebrada Jajarajau valley, about half a kilometer from the plant, and was expected to come into use in 2012. The design was reviewed and approved by a geotechnical engineer. The design includes concrete-walled runoff ditches, a starter dam with blanket and chimney drains, and drainage pipes in the base.
Key Processes
- Two-stage open-circuit crushing: primary jaw crusher, secondary cone crusher
- Rod mill grinding with manual rod charging
- Primary jigging: one triplex jig plus two duplex jigs
- Secondary jigging on rod mill discharge
- Shaking tables: two banks for different feed streams
- Electrically-heated plate dryers for gravity concentrate
- Drum magnet separation producing iron gangue, pre-concentrate, and middling
- Roll magnet separation producing mixed concentrate and tailings
- Multiple-stage magnetic separation with size-classified feed
- Campaign processing of size fractions through three stages of magnetic separation
Source: Pasto Bueno Tungsten Mine , 2012 Technical Report, 2012. Project website: [Not stated]
Editorial Note: The source data for concentrate production in January-October 2011 lists "740 tonnes" for concentrate quantity and "55,000" for pure WO3 content. The figure 55,000 appears inconsistent with a concentrate quantity of 740 tonnes at 73 percent WO3, which would yield roughly 540 tonnes of pure WO3. The reported 55,000 may be a typographical error (possibly 550 tonnes), but the source does not resolve this. All values show the source as provided.
Project website: Pasto Bueno Tungsten Mine, 2012 Technical Report
