The Panasqueira tungsten deposit comprises a series of thin, flat-lying quartz-wolframite veins developed in the joints of a phyllite within the contact zone of a concealed granite intrusion. The largest concentration of veins occurs immediately over a granite-greisen high (cupola) on the No 2 Level of Panasqueira Deep. The horizontal extent of the veins, which pitch to the southeast, appears to decrease with depth. Individual veins average about 0.30m in thickness and can persist over hundreds of metres. Frequently, when one vein thins out, another forms close to it, with a small over- lap. There is considerable dilution during mining because the veins are so thin, which is why the mine goes to great lengths to not exceed the 2.2 m stope height.

The sub-parallel stacked quartz veins contain principally, wolframite, arsenopyrite, pyrite, chalcopyrite and cassiterite. The tungsten mineralised quartz veins have an average dip of 8°-10°SW. The mineralised zone has dimensions of approximately 2,500m in length and varies in width from 400m to 2,200m, continuing to 500m in depth. Previous mining was done in the upper levels and the existing reserves are from Level 0 and Level 4. The current reserves lie above Level 2 and Level 3 (90m below Level 2). The deposit, between Level 1 and Level 2 (60m vertical separation) consisted of seven or eight flat dipping veins with an average thickness of 0.3m (range 0.1-1.0m) that typically hosted the economic mineralisation over continuous strike lengths of 40 to 60m. These mineralised quartz veins located throughout all mine levels, typically pinch out and later reoccur. It is also common to have one vein pinch out while another vein is beginning, creating a short overlap of two veins in the same mining stope.

Wolframite mineralisation occurs as very large crystals or large crystal aggregates, usually concentrated towards the margins of the quartz veins or, occasionally, close to the central portion of the quartz veins. The quartz veins commonly contain open spaces and vugs that are commonly filled with spectacular crystal growth. The mode of occurrence of wolframite crystals (Level 2) includes:
- Pods (5-20cm);
- Large scattered crystals (10-40cm);
- Small scattered crystals;
- Mixed (comprising a mixture of the three previous styles);
- Selvedge wolframite (3-10cm bladed crystals);
- Fibrous wolframite (1cm wide and 5-10cm long);
- Barren (no or little wolframite – fine crystal selvedges or isolated large (5-10cm) crystals).

The Panasqueira tungsten-tin deposit is reported to be the largest quartz vein deposit in Europe.

The mining method used at Panasqueira is a mechanized room and pillar method that has evolved during the past 50 years. The method is possible due to the sub-horizontal nature of the quartz veins and the very competent host rock.

The stoping process begins with ramps being driven to access the mineralized veins, in areas where diamond drilling has indicated quartz intersections equal to or above 18cm (indicated resources). When a vein is accessed, it is blocked out on a basic 100m by 100m pattern. Ore passes of 1.8 metre diameter raises are generally bored near drive/panel intersections, and allow ore to be dropped down to main haulage levels. Chutes are installed in the bottom of the orepasses to facilitate the loading of the wagons.

Equipment that is used for mine development and production includes electric hydraulic single boom jumbo drills, 3.5 cubic yard diesel LHDs, low profile 6 and 6.8 tonne LHDs and a raise borer. The target height of the stopes is nominally 2.1 m but increased to 2.3 m in areas where ore bearing veins are more variable in their dip, strike or thickness. The average height achieved is generally 2.2m. With an average in-situ mineralized zone thickness of 25cm, the applied planned dilution 880% i.e. 8 x times as much waste has to be mined within the 2.2m minimum height. No additional dilution factors are added.

As the veins are intersected with development, face sampling is used to verify mineralisation and indicate how the stopes can be developed and expanded so as to best follow the ore. When sufficient ore has been delineated, additional 5m wide openings are excavated between and parallel to the drives and panels to create a series of regular series of 11m by 11m pillars. The pillars are then reduced in size in two passes of 5 m excavations; firstly to 11m by 3m, and then to 3m by 3m to complete the extraction sequence, as depicted in Figure 16- 2. This process results in an overall extraction rate of 84%, as the 3m by 3m pillars are not recovered.

Precise survey control is maintained so that all final pillars are aligned vertically on the different levels and experience has shown that the stopes will usually begin to collapse about 4 or 5 months after completion, which gives plenty of time to “sweep” the fines from the floor. A small track mounted excavator is used for a final stope clean-up (sweeping) to recover the wolframite rich material that accumulates on the floor during normal mucking operations. This excavator can be operated by remote control, and is also used to help remove mined pillar material, when the final 3m x 3m pillars are being created.

Stope drilling is carried out by electric hydraulic single boom jumbos. Blast holes are drilled 2.4 metres in length and are 43 mm in diameter. Fan cuts or V-cuts are drilled, with two horizontal rows generally just above and below the vein, so as to minimize shattering the brittle wolframite. Regular back holes and lifters are then drilled above or below the cut slice, with variations up or down so as to follow the vertical variation in the vein.

ANFO is loaded pneumatically into the blast holes and delayed non-electric detonators along with small primers are used for blasting. Blasting occurs at midnight using a central blast cable, the mine then ventilates for all of the third shift. Each blasted face produces about 55 tonnes of rock and good drillers can complete more than five faces in a shift. After the blast the muck pile is washed down and the back is scaled, ore is loaded and hauled by 6 or 6.8 tonne diesel LHDs from the heading to the orepasses.

Within any large 100m x 100m mining block, veins are generally stoped out from the top- down. A minimum 3m pillar is always left between one stope and the stope below, when veins converge close together.

The mine currently has four main levels, which are all connected by ramps. The main water drainage level is the 530m, which is between level 2 (560m) and level 3 (470m). The underground crusher is below level 2 (530mRL). Ore from above Level 2 is fed from ore passes into 4t self-tipping rail cars and hauled by electric and diesel trolley locomotives to the ore pass on Level 2 that feeds the underground crusher. Ore from below Level 2 is similarly fed to and trammed on Level 3 to the winze where the rail cars are individually hoisted to Level 2. From this shaft the cars are trammed to where they self-dump into the crusher ore pass. The underground crusher feeds ore on the conveyor belt in the Santa Barbara hoisting ramp.

Panasqueira produces very high grade concentrates, which are almost pure wolframite.

Wolframite Recovery.
The underground jaw crusher delivers <100mm ROM, containing about 11% of vein material rock to four storage bins via the 1,203m long 17% Santa Barbara conveyor belt. Vibrating feeders discharge ore to a conveyor which feeds the crushing plant at a rate of about 160tph. Plus 25mm material is produced by primary screens and crushed in closed circuit by one of two short head cone crushers.

All screening done in the plant is aided by copious amounts of spray water. Secondary screens, remove minus 0.8mm material from the minus 25mm Heavy Media Separation (HMS) feed.

The HMS process uses a hydrocyclone for the separation, with a dense slurry media maintained at an SG of 2.7 using very fine magnetic ferrosilicon (FeSi); the characteristics of the Panasqueira ore lend themselves perfectly to the use of HMS to remove approximately 80% of the ore which has no tungsten content.

One of the roll crushers is dedicated to +3–5 mm material from the HMS concentrate and this material is re-circulated to the HMS plant. The minus 3mm material is treated in an hydraulic classifier prior to concentration by gravity shaking tables.

The pre-concentrate is conditioned with sulphuric acid, Nafta and Gasoil prior to passing over the table where the sulphide minerals float to the tailings, even 2mm sulphide grains will float down the table. These table tailings then become feed for the copper circuit.

This concentrate is recovered using differential flotation in Denver type cells. The tailings are ground in a ball mill to 60% minus 200 mesh. Lime is fed to this mill to increase the feed pulp pH to 11.5.

The table concentrates without sulphides are dried and screened to prepare three sized lots (+20, - 20+60, and –60 mesh); each size fraction is treated separately using dry high- intensity cross-belt magnetic separators to produce the high grade wolframite concentrate, non-magnetic cassiterite and magnetic siderite.

The Wolframite concentrates are packed in one ton bags which are transported in containers by road from the mine to the port at Lisbon.

Copper Circuit.
The copper circuit typically treats about 5,000 tonnes per year. It incorporates a small ball mill and 7 flotation cells.

From January-December 2016, approximately 380t of copper concentrate were produced, with a grade of approximately 27% Cu. The average arsenic grade in the copper tailings is approximately 20%, with a copper circuit recovery of 77%. The copper plant tailings contain much of the arsenopyrite present in the ore, and it might be possible to contain this material by itself thus reducing the discharge of arsenic to the larger tailings pond. The copper circuit is one of several modules within the plant that operates when there is sufficient material to feed it for a prolonged period of time. The copper plant usually starts late at night when reduced power rates permit more efficient ball mill start-up.

Tin Circuit.
In the tin circuit, the siderite is discarded whilst the cassiterite goes to further treatment using tables to eliminate the finer gangue particles, and flotation in a mechanical cell to eliminate the remaining finer sulphide particles. Approximately 70t of tin concentrate are produced per year, with a grade of about 74% Sn.

The infrastructure for the mine is very well established, mining having been undertaken at Panasqueira and Barroca Grande for over 100 years. A summary of the main infrastructure requirements for the mine includes:

- Underground Infrastructure. This includes the underground jaw crusher below level 2 (560mRL), the belt conveyor in the Rampa Santa Barbara which takes ore from the crusher up to surface, the main access ramp to surface for mechanised equipment and personnel, four main ventilation raises, the internal hoist and shaft which connects level 2 and level 3 (470mRL), and the train level haulage systems on levels 2 and 3.

- Coarse Waste Dump. The Barroca Grande waste dump lies adjacent to and above Bodelhão Creek that flows south-easterly to the Rio Zêzere and comprises primarily HMS tailings (gravel), waste rock and sand tails, all of which are very benign and possibly marketable as aggregate. This waste dump is approximately 1km to the east of the mill. A belt conveyor takes waste from the mill out to a discharge point just to the west of the waste dump area. The waste material is then transported and discharged by truck onto the waste dump, or use for the building up of embankments in the construction of the new TMF 2B fine tailings disposal area.

- Fine Tailings Disposal areas (TMFs). There are two historic disposal areas – TMF 1, which is completely finished and TMF 2A, into which fine tailings is currently being discharged. TMF 2A has approximately 4 years’ capacity, and so a new disposal area, TMF 2B, is under construction. A pipeline takes fine tailings hydraulically from the mill out to the disposal area, along the same access roadway as the coarse waste conveyor.

- Electrical Power Distribution System. The electrical power is supplied by EDP at 60kV, into a sub-station at the Rio site, from where it is transported to Barroca Grande sub-station by the company 40kV line.

Water Systems. There are two main water pipe systems: one for process/mine water and one for potable water. The process/mine water pipeline feeds the Salgueira water treatment plant.