Deposit types
The Rosh Pinah mine has been historically interpreted as being predominantly a reworked SEDEX type deposit comprising a primary banded sulphide exhalite, part of which was carbonatized with associated remobilization and enrichment of sulphides. The secondary carbonate mineralization carries the higher, economic, base-metal values.

The emplacement of the Spitskop Volcanic Complex and related mafic edifices at approximately 752 Ma to 741 Ma drove hydrothermal plumbing along the rift-fault system of the Rosh Pinah Graben. Hydrothermal fluids leached base metals from the basin-fill siliciclastics which were derived mainly from the erosion of a Paleoproterozoic, 2.0 Ga to 1.7 Ga, calcalkaline island arc in the hinterland (Frimmel et al. 2004).

The base-metal bearing brines were exhaled onto the sea floor from the present-day Western Fault bounding the Rosh Pinah Graben, during a period of sediment paucity and / or high sea-level. Exhalation was accompanied by silicification and hydraulic brecciation of the footwall. The primary mineralization was deposited at, or below, the sediment / seawater interface as stratiform, inter-banded, massive sulphide and cherty argillite (micro quartzite). Time between exhalative pulses determined the variation in ratio of content, of chert- exhalite and background argillitic sediment.

At some stage following primary SEDEX style mineralization deposition, the hydrothermal fluid chemistry changed to carbonitic, either due to introduction of primary volcanogenic carbonate fluids or as the plumbing system tapped carbonate sediments elsewhere in the sedimentary package. Carbonatization of the more porous, arenitic hangingwall and footwall took preference. On-going base-metal exhalation was supplemented by remobilization of primary mineralization into the hydrothermal carbonate.

Orogenesis at approximately 545 Ma, as a result of transpressive continental collision of the Rio de la Plata and Kalahari cratons, caused complex folding and faulting of the deposit. Fold style is west verging, asymmetric to overturned with steep plunges. Competency interplay caused considerable disharmony within the ductile units of the mineralized zone, both primary and secondary carbonate being squeezed into fold hinges.

There has been a major shift in thinking by RPZC in the last couple of years on the Rosh Pinah mineral deposit type from a predominantly SEDEX deposit to a hybrid of VMS – SEDEX. This approach was adopted based on new evidence and understanding.

The major mineralization types are described in detail below.

Microquartzite and argillite
The primary mineralization type is a silicified, grey to dark grey, fine-grained and laminated unit locally called microquartzite mineralization. It consists of alternating millimetre to centimetre wide bands of sulphides (sphalerite, pyrite and galena + minor chalcopyrite) and is believed to represent a classic sedimentary-exhalative (SEDEX) style although ongoing interpretations are supportive of a volcanogenic massive sulphide (VMS) origin similar to the nearby Gergarub and Skorpion deposits. The argillite mineralization would be similarly derived but diluted with background benthonic argillite.

Arkose / breccia
The mineralization occurs as breccia matrix and veins in silicified arenite lithologies (locally referred to as breccia mineralization) or as disseminated base-metal sulphides (locally referred to as arkose mineralization) and can reach economic grades. In places, the arkose / breccia mineralization gives indications of primary sulphide exhalations into an arenitic host. The breccia mineralization is commonly found in the immediate footwall to the ore equivalent horizon (OEH).

Carbonate
Carbonate mineralization is purely remobilized and provides the major economic component of the resource. Carbonate has replaced the arenites, both in the hangingwall and footwall of the mineralized horizon and a continuous range is observed from slightly carbonatic arenite (textures such as large, ghost feldspar grains occur) to pure carbonate, with all original textures lost. The carbonate has scavenged, concentrated, and remobilized BMS from the primary microquartzite mineralization. A near-total base metal enrichment of the carbonate mineralization gives rise to massive mineralization. When the carbonate has been leached out of the carbonate mineralization and the quartz grains and sulphides remain, the mineralization is locally referred to as sugary quartz ore.

Lens characterization
The deposit is hosted by a thick package of turbidites comprising hinterland and contemporaneous volcanic clastics deposited in a Neo-Proterozoic rift basin during the early part of the evolution of the Gariep Terrane of southern Namibia. Metals scavenged from a primary argillite mineralization were concentrated by late hydrothermally- driven carbonate alteration, providing a carbonate host to the economic deposit. Basin inversion led to oblique continental collision and complex deformation of the deposit, resulting in two phases of disharmonic overfolding with associated faulting and shearing.

The deposit is consequently presented as a series of discrete carbonate and exhalite lenses located on second-phase fold hinges or steeply plunging fold limbs connected by a partially attenuated exhalite-dominated OEH.

Mine operations are conducted 365 days of the year with mine production currently scheduled for 2,000 tpd for approximately 700 ktpa. AMC’s strategy optimization study (AMC 119015) indicated that the production should be increased to a steady state rate of 3,600 tpd for approximately 1,300 ktpa from 2022 onward.

Mining methods
Historically, ore was extracted using a combination of mining methods including: LHOS without backfill, and in the upper flat-dipping zones, sill-and-bench and room-and-pillar mining. LHOS without backfill has resulted in large continuous voids spanning multiple levels. Sill and rib pillars are currently used to manage span stability.

AMC has recommended transitioning the mining method from LHOS without backfill to LHOS with backfill (paste fill), within all zones where practicable, and based on qualitative and quantitative assessment techniques. These include but are not limited to: geotechnical analysis (spans and global extraction sequence with depth), lens geometry, safety (mitigate risk of air blast from uncontrolled large overbreak), improved mining recovery, and reduced dilution.

Stopes may be extracted longitudinally (along strike) or transversely (across strike). The changeover from transverse to longitudinal stoping would generally be where the ore width is less than 10 m.

AMC recommended LHOS with paste fill (AMC 119050) to improve local and regional stability, improve operational recovery, reduce dilution, mitigate void risks and minimize the tailings being pumped to the TSF (to eliminate or delay TFS expansions).

Mining areas are globally advanced top-down, but within each mining area, stopes are extracted using a bottom-up sequence at 30 m level intervals. A mining area typically spans four to five levels. The mining areas are further sub-divided along strike guided by the lens geometry, mineralization grades and planned mining sequence to achieve production targets.

Ore receiving and primary crushing
The RP2.0 Expansion Project comminution circuit is based on installing a new SAG mill to replace the existing ball mill. The existing Secondary and Tertiary crushing circuits will be become redundant and primary crushed ore (P80 of 150 mm) will be fed directly to either of the two existing mill feed stockpiles from either the existing underground crusher or a new surface crusher at a nominal rate of 241 tph (dry).

As part of the proposed plant upgrade, a new surface primary crushing facility will be installed. The new primary crushing circuit is similar to the current underground primary crusher station and will consist of three (3) blending bunkers, a static grizzly, feed bin, vibrating grizzly, and primary jaw crusher.

Ore will be reclaimed from the blending bunkers using a front-end loader and fed into the jaw crusher feed bin over a static grizzly. Material will be withdrawn from the crusher feed bin at a controlled rate using a vibrating grizzly feeder. Oversize from the vibrating grizzly feeder will be fed to the jaw crusher which will operate in open circuit to produce a primary crushed product (P80 of 150 mm).

Primary crushed ore will be fed to the mill from the existing mill feed stockpiles via a conveyor at a controlled rate by means of a duty / standby feeder arrangement.

The current process plant design includes three (3) silos ahead of the underground crushing station to allow for blending. Similar to current operational practice, the crusher feed blend for the new surface crushing station will be managed by reclaiming ore from the blending bunkers using a front-end loader to feed the crusher.

A new splitter chute and stockpile feed conveyors will be installed and tied-in as part of a major front end shut. During this time, the newly commissioned SAG mill will be fed from the new surface crusher via a temporary conveyor and feed bin in order to minimize production downtime.

Mill feed stockpile
Primary crushed ore will be withdrawn from the mill feed stockpiles and conveyed to a new SAG milling circuit at a maximum rate of 164 tph (dry) via vibrating pan feeders. The SAG mill feed rate will be measured using a weightometer and controlled by the variable speed output of the vibrating feeders.

The mill feed stockpiles are existing but the withdrawal system (vibrating feeders, chutes, and discharge conveyor) will be replaced in order to accommodate the increased throughput and larger mill feed size P80 of 150 mm as compared to the current mill feed size P80 of 8 mm.

Milling and classification
As part of the proposed RP2.0 Expansion Project a new primary SAG mill (24’Ø x 15’, 4.5 MW with VSD) and pebble crusher circuit will be installed, and the existing ball mill will become redundant. The design allows for the option to operate the existing ball mill in a secondary milling duty to allow for operational flexibility during start-up and commissioning of the new SAG mill.

Primary crushed ore will be withdrawn from the mill feed stockpile and conveyed to the milling circuit at a maximum rate of 164 (dry) tph via vibrating pan feeders. Water will be added to the primary mill feed to form a dense slurry.

SAG mill product from the mill ports (cutting at approximately 25 mm) will be screened at approximately 8 mm to remove pebbles which will be recycled to the mill feed.

The SAG mill discharge screen undersize will be classified in a cyclone cluster to produce an overflow product of nominally 80% passing 90 µm. The cyclone underflow will be returned to the SAG mill feed.

In order to cater for the requirement of operating the existing ball mill in a secondary milling duty during the initial SAG mill commissioning and ramp-up phase, the design includes an optional sump and pump which allows for cyclone underflow to be feed to the ball mill.

The design also includes allowance for a SAG mill feed bin to allow for commissioning to take place while the stockpile feed and withdrawal system modifications are being implemented. During this period primary crushed ore from the surface crushing station will be trucked to the SAG mill circuit and fed to the mill via the feed bin.

It is envisaged that the mill circuit will be controlled by an advanced, rules-based control, system. This system will control mill feed rate, mill speed, dilution and ball loading in order to maximize throughput and achieve a consistent cyclone overflow product size of 80% passing 90 µm. The cyclone overflow produce size distribution will be continuously measured using an online particle size analyzer (PSA).

The current Rosh Pinah concentrator utilizes a conventional three-stage crushing and ball milling circuit followed by flotation.

The key aspects of the concentrator plant design for the PFS, at the higher 1.3 Mtpa throughput, includes primary crushing upgrades, installation of a new single stage SAG mill circuit, and a number of other circuit modifications to provide increased flotation, thickening, filtration, and pumping capacity.

The selected circuit includes a new surface crushing station with blending system to supplement the existing underground crushing and blending system. Ore from the Eastern Orefield would be crushed underground and conveyed to surface while ore from the Western Orefield would be trucked to surface and processed in the new surface crusher station.

The current process plant includes the following unit operations:
- ROM ore feed tip (located underground)
- Primary crushing (located underground)
- Screening ........