The Jinfeng deposit has many geological and geochemical characteristics in common with the renowned sediment-hosted deposits of the Carlin district in the western United States, and is best classified as a Carlin-like gold deposit.

In contrast to the Carlin deposits, zones of quartz veins spatially associated with mineralization are common at Jinfeng. In addition, the Jinfeng deposits (and other sediment-hosted deposits in the region) lack any evidence for spatially or genetically associated intrusions.

The Jinfeng Deposit is a sediment-hosted disseminated gold deposit showing strong elements of structural and stratigraphic control. Nearly all of the known gold resource occurs within or adjacent to major fault zones (F2, F3, and F6), or secondary faults either splaying from or linking with these structures. Overall, the deposit occurs as a steeply dipping tabular body, with a long axis plunging shallowly to moderately to the east-southeast. The deposit extends over 1,200 m along this axis, has a vertical extent of up to 1,100 m, and a thickness typically ranging from 10 m to 50 m.

High-grade shoots within the deposit are spatially associated with intersections between the controlling fault zones and either secondary faults or lithologically favourable sandy beds in the Bianyang and Xuman Formations. Gold is commonly localized along east-west striking segments of either the main controlling faults or secondary structures. The ore shoots typically plunge moderately to the east-southeast, parallel to the overall deposit axis, to fold axes, and to fault intersections. Within the F3 fault zone, high grade pods often show a right-stepping enechelon geometry in plan view, with well mineralized associated older fault segments linked and offset by northeast-dipping minor thrust faults.

Gold mineralization is typically associated with highly carbonaceous gouge material or cataclastic breccia, but is also concentrated within more intact sandstone layers adjacent to structurally disrupted zones. Quartz and sulphide (pyrite, arsenopyrite) veins are common, occurring as either steeply-dipping or shallowly-dipping sheeted sets preferentially within sandstone beds. Quartz-rich veins contain trace amounts of dolomite, and become more carbonate-rich distal to mineralization.

Sulphides present in mineralized zones are pyrite, arsenopyrite, cinnabar, stibnite, orpiment, and realgar. Petrographic analyses document arsenic-pyrite overgrowths common on pyrite cores in mineralized zones. Trace amounts of cinnabar, stibnite, orpiment, arsenopyrite, and galena are also associated with pyrite overgrowths.

In mineralized areas, alteration is typically weak, and includes dolomitization of calcite, sericite+clay alteration of matrix material, and minor introduction of secondary quartz.

Mineralized zones also have elevated arsenic, mercury, and antimony concentrations, with arsenic commonly forming broad halos surrounding ore zones. Gold is introduced late in the deformation sequence at Jinfeng, as evidenced by mineralization localized along minor thrust faults formed during the latest period of contractional deformation.

The major fault network (F2, F3, F6) was well established at this time, and the fault zones served as primary hydrothermal conduits during mineralization, due to their high degree of structural permeability. This permeability may also have been enhanced by syn-mineral fault reactivation. The age of the mineralization is constrained by rhenium-osmium (Re-Os) dating of arsenian pyrites to be 193+/-13 Ma (Chen et al., 2007).

Jinfeng mining commenced as an open pit operation in 2006, with production rates designed to gradually increase to match the initial process feed requirements.

To defer some of the waste stripping to later years, the open pit operation has been designed in five stages.

The current pit development is within Stage 3, which has a final floor at 465 mRL.

Stage 4 pit is the last cut-back of the main pit (Huangchangguo (HCG)) orebody. It will extend the pit bottom to 450 mRL and expand the pit in all directions, but mainly target ore along strike to the east. The contiguous Stage 5 pit, which mines a satellite orebody (Rongban), is planned to commence after completing the Stage 4 pit.

Bench heights in the final pit are 10 m; however, in the lower benches this is stacked to an effective height of 20 m. Ore will be mined using 5 m operating bench heights with 2.5 m flitches to optimize ore extraction. Within the pit, the haul road width varies from 18 m for most of its length to 14 m near the bottom of the pit, with a nominal 10% gradient. Haul road widths outside the pit are 20 m wide. The external haul road enters the open pit mining area at 590 mRL.

Only one mining method, overhand cut-and-fill, is used in Jinfeng’s underground operations due to the poor geotechnical ground conditions and the selectivity required for optimal extraction. Mining depths are currently within 100 m to 350 m vertically below the surface. The ore, plus a small portion of waste, are trucked to surface via a 1:7 gradient decline. The underground mining plan is to ramp up current production capacity from 500,000 t/a in 2011 to 800,000 t/a in 2015. Further production increases and the scheduling of it is currently being studied.

The main decline is connected to the mining extraction level footwall drives, the egress access drives, and the ventilation shafts. The parameters for the decline are:
- cross-section 5.5 m x 5.5 m for straights and curves
- gradient of 1:7 for straights and curves
- level access at 20 m intervals
- centreline radius on curves is 25 m.

Due to the overhand cut-and-fill mining method, both waste development and ore production are similar unit operations using the same mining equipment. The major equipment used in Jinfeng’s underground ore and waste mining operations are electric hydraulic drill jumbos, loadhaul-dump trucks (LHDs) and mine trucks.

The process route incorporates recovery and blending of ore prior to single-stage crushing to a stockpile, underground reclamation, and conveying to a single, low-aspect-ratio SAG mill. The discharged pulp is classified by cyclone, with the underflow gravitating to the primary ball mill, forming a closed circuit.

The cyclone overflow (P80 75 µm) flows to a prefloat stage for graphite and pyrobitumen control.

The prefloat tailings are conditioned and then passed to primary flotation, and primary concentrate is pumped either to a concentrate thickener or to the cleaning circuit. Primary flotation tailings are pumped to secondary grinding and return (P80 38 µm), to two stages of secondary flotation. Secondary concentrate is pumped to the three-stage cleaning circuit, and secondary flotation tailings are pumped to the tailings thickener. Concentrate from the primary cleaner stage is pumped to the concentrate thickener.

Concentrates from the second and third stages are pumped to their respective preceding stage. Cleaner tailings are returned to secondary grinding. After thickening, the concentrate is transferred to one of two bio-oxidation surge tanks. Each surge tank feeds a discrete leaching suite comprised of four primary leach tanks in parallel followed by four secondary leach tanks in series.

The leach residence time is 5.23 days at a pulp density of 20% weight/weight (w/w) and a pH between 1.6 and 1.8 with the pulp temperature controlled at 42°C.

The bio-oxidation section of the plant has been separately designed as a package by Gold Fields/Gencor, using the patented BIOX® process. A testwork programme was carried out in SGS Lakefield Johannesburg’s laboratory utilising their 120-L mini plant for continuous pilot testing. More than 1,000 kg of flotation concentrate was produced in a flotation programme in China, transported to Lakefield, and processed in several campaigns to produce the design and engineering data for the Jinfeng project.

The oxidized pulp from the biological leaching tanks is pumped to a three-stage continuous counter-current decantation (CCD) thickener circuit for separation of solids and liquids. CCD thickener overflow is neutralised in six agitated tanks in series with thickened flotation tailings (utilising the contained carbonates) to achieve a pH of 3.5, followed by lime addition to bring the pH to 7, before discharge into the flotation tailings thickener. Soluble arsenic is precipitated as a stable form of ferric arsenate. CCD thickener underflow is pumped to the pH adjustment tank before being pumped to the six-stage CIL circuit. The residence time of the CIL circuit is 24 hours.

The elution of gold from the loaded carbon is by the Anglo American research Laboratories (AARL) system, with a 10-tonne capacity elution column. Mercury entrained on carbon entering the elution is captured in two ways:
- by fume extraction/scrubbing in the carbon regeneration area
- and by calcination of electrowinning cell sludge, and loaded cathodes condensing mercury vapour generated in the retort/calciner.

Tailings from the CIL circuit are detoxified by the INCO CuSO4 and air/SO2 method, using sodium metabisulphite.