A conventional carbon-in-leach processing plant on site treats ore from the Masbate Gold Project, with design and operating data reported through March 2012.
Report context
This technical report, dated October 31, 2011, describes the processing facilities for the Masbate Gold Project (MGP), operated by PGPRC. The processing plant was designed by Lycopodium Limited with a nameplate throughput of 4 Mtpa and constructed from September 2007 to April 2009. Ore treatment commenced on April 16, 2009, first gold was poured on May 12, 2009, and commercial production was declared on July 1, 2009. Successful ramp-up led to a revised throughput target of 6.5 Mtpa, with a supplementary crushing circuit commissioned in September 2011 to support this rate on harder feed blends.
Processing route
Crushing and grinding
Primary crushing is performed by a single-stage Nordberg C160 jaw crusher, reducing ore to a top size of 150 mm. Product from the primary crusher feeds directly to the SAG mill. A diverter gate on the conveyor system allows construction of a crushed ore stockpile and provides continuity of feed during jaw crusher maintenance.
A supplementary three-stage crushing circuit consists of a single Nordberg C125 jaw crusher feeding a secondary Nordberg GP200 cone crusher and two tertiary Nordberg HP4 cone crushers. This circuit reduces a portion of run-of-mine ore to a 12 mm product, which flows through the SAG mill to the ball mill section.
A single 6.0 MW Koppers SAG mill receives feed from the primary crusher. Underflow discharge of product less than 12 mm diameter is directed to the ball mills. Overflow product is recycled back to SAG feed after passing through a pebble crusher circuit.
Two parallel 3.6 MW ball mills produce a product with P80 at 106 micron.
Leaching and gold recovery
Gold leaching uses cyanide in a conventional eight-tank circuit, each tank of 3,000 m³ capacity. Gold is recovered from loaded carbon using a normal elution and single-pass electrowinning circuit, followed by smelting to produce gold bullion.
Historical plant performance
From July 2009 to March 2012, the plant processed 13.6 Mt of material at an average grade of 1.16 g/t, producing in excess of 432,000 oz Au. Process availability averaged 89.7% for this period, with the saw-tooth pattern in availability showing quarterly replacement of SAG mill liners. Process recovery averaged 84.9%. Overall recovery shows both mill feed composition (oxide, transitional, primary material types) and residence time within the CIL circuit. Design residence time at 4 Mtpa is 24 hours; at 6.5 Mtpa throughput, residence time is reduced to 19–20 hours.
Addition of lead nitrate enabled the process to maintain design recovery at 6.5 Mtpa throughput rates, and for transitional and primary ore types to improve on design recovery, by driving leach kinetics in the first 3 to 6 hours.
Reduced throughput and production from July 2011 to December 2011 were due to SAG mill repairs. Sharp dips in recovery during February 2010 and April 2010 show lack of lead nitrate reagent due to interruption to delivery to site.
Forward planning parameters
Forward planning targets a throughput rate of 6.5 Mtpa. Systematic improvements in mill liner design and materials have resulted in improved mill availability. Forward planning assumes a six-month cycle of five months at 94% mill availability followed by one month at 87% mill availability (average 92.8%).
Key reported parameters
| Parameter | Design / Target | Historical Operating (July 2009–March 2012) | Testwork / Notes |
|---|---|---|---|
| Plant nameplate throughput | 4 Mtpa | – | Designed by Lycopodium |
| Revised throughput target | 6.5 Mtpa | – | Achieved on oxide-dominant blends; supplementary crusher commissioned September 2011 for harder blends |
| Primary crusher top size | 150 mm | – | Nordberg C160 jaw crusher |
| Supplementary crusher product size | 12 mm | – | Three-stage circuit: C125 jaw, GP200 cone, two HP4 cones |
| SAG mill power | 6.0 MW | – | Koppers mill |
| Ball mill power (each) | 3.6 MW | – | Two parallel mills |
| Ball mill product P80 | 106 micron | – | – |
| CIL tank volume (each) | 3,000 m³ | – | Eight tanks |
| CIL design residence time at 4 Mtpa | 24 hours | – | – |
| CIL residence time at 6.5 Mtpa | – | 19–20 hours | – |
| Total material processed | – | 13.6 Mt | To end March 2012 |
| Average feed grade | – | 1.16 g/t | – |
| Gold production | – | >432,000 oz Au | Since July 2009 |
| Process availability | – | 89.7% average | July 2009 to March 2012 |
| Forward planning mill availability | 92.8% average | – | 5 months at 94%, 1 month at 87% |
| Process recovery | – | 84.9% average | July 2009 to March 2012 |
| Power consumption (monthly range) | – | 14.5–16.5 kWh/t | Forward planning: oxide 12.1, transition 14.8, primary 17.3 kWh/t |
| Cyanide consumption (monthly range) | – | 0.53–0.68 kg/t | Forward planning: oxide 0.53, transition 0.58, primary 0.68 kg/t |
| Lime consumption (monthly range) | – | 2.20–2.70 kg/t | Forward planning: oxide 2.70, transition 2.50, primary 2.20 kg/t |
| SAG grinding media (monthly range) | – | 0.13–0.15 kg/t | Forward planning: oxide 0.13, transition 0.15, primary 0.15 kg/t |
| Ball mill grinding media (monthly range) | – | 0.42–0.45 kg/t | Forward planning: oxide 0.42, transition 0.42, primary 0.45 kg/t |
| Lead nitrate consumption | – | 0.13 kg/t | Same rate used in forward planning for all material types |
Project website: https://www.b2gold.com/operations-projects/producing/masbate-mine-the-philippines/default.aspx
Technical qualifications
The report states that major reagent and power consumption rates are related to physical material type of ore processed. Table 17.2 (referenced as Table 17.1 in the source) details typical consumption rates for major consumables and includes values used in forward planning. The report notes that overall process recovery shows both the composition of the mill feed in terms of material type (oxide, transitional, primary) and residence time within the CIL circuit. The supplementary crushing circuit was commissioned to support mill throughput at 6.5 Mtpa on mill feed blends containing 65% primary material.
*Source: Masbate Gold Project , October 2011 Technical Report, Sections 17.1–17.4*
