The different prospects within the vicinity of Padcal can be generally divided into copper-gold porphyry prospects and the gold vein prospects. Sto. Tomas II, Bumolo, Bumolo 2/Sta. Fe, Southwest, Southwest Breccia and Tapaya fall under the copper-gold porphyry prospects while Butan, Midway and Copper Queen are classified within the gold vein prospects.

Mineralization within the Sto. Tomas II orebody is associated with the various diorite porphyry stocks (Dark diorite, Clear diorite, Andesite porphyry, and Quartz diorite/Tonalite) which have intruded the basement meta-andesite wallrocks of the Pugo-Zigzag Formation. These intrusive stocks are said to be related to the diorite and dacite porphyries of the Black Mountain Quartz Diorite. Among the porphyry stocks in the area, the dark diorite (DD) is the principal ore bearing rock. The inter-mineral clear diorite on the other hand is less mineralized than DD. The andesite porphyry (AP) is characteristically low in copper but high in gold while the post-mineral quartz diorite (QD/tonalite) is almost devoid of both copper and gold. Subsequent exploration drilling activities discovered a structurally controlled gold-rich, copper-poor zone at 400-500 meter level was also discovered at the northeast fringe of the orebody. It has an apparent thickness of 117 meters along drillhole intercepts and is noted to occur in CD and some meta-andesite. Likewise a deeper gold-rich interval of post-porphyry copper-gold mineralization was also intersected in one of the holes collared at the northeast, hosted in a sericitized quartz-gypsum vein in meta- andesite and located at approximately -150 meter level.

Two major north-northeast striking, southeast dipping structures played an important role in the formation of the Sto. Tomas II orebody; these are namely the Sta. Fe Fault and the Albian Fault. The latter is considered to be the conduit of mineralization, with the fault splitting into three branches at the orebody. However, no prominent exposure of the fault was observed at the mining levels. The Sta. Fe Fault on the other hand is the main structure affecting the behavior of the intrusive complex at depth, intercepting the orebody from 908 meter level downwards. Mineralization within the Sta. Fe Fault occurs in short intervals related to the gougy and sheared zones, as intercepted by different drillholes. Sulfides are observed as fracture fills as well as disseminated grains usually within the gouge material. The fault is interpreted to be pre- to syn-mineralization in timing, which would place it contemporaneously with the introduction of the structurally-controlled gold-rich zone.

The Sto. Tomas II orebody forms a roughly pipe-like deposit having lateral dimensions of 500 meters by 550 meters and a vertical extent of 730 meters. Copper and gold mineralization at levels above 745 meter level is generally focused within the main intrusives, with the occurrence of the quartz diorite body at 600 meter level causing an abrupt drop in both copper and gold grades. Subsequent mineralization below 745 meter level was observed to be within the wallrock-intrusive contact zones with extensions into the meta-andesite. Recent drilling from 773 meter level has also delineated the extent of the main intrusives up to around 400 meter level, where the said lithologies seemed to have "floored" into the meta-andesite. Evidences of a post-mineralization occurrence of the Sta. Fe Fault brought up the possibility of the truncation of the orebody at depth. Given the fault’s normal sense with a minor right-lateral component, a possible truncated half of the deposit might be situated to the northeast of the present location of the orebody.

LHD Block Caving will be continually employed in the remainder of the operating life of Padcal. The method has been used successfully for 50 years now and has undergone modernization from its roots of slusher machines.

Load-Haul-Dump (LHD) mining is a system of ore extraction in block caving using the Low Profile Loaders. It was introduced at 908 ML on May 1996 after a series of consultation with block caving experts and by 1999, Philex became a full LHD block caving operation.

Ore passing through transfer raises that are remotely located relative to crusher stations are collected at the Re-handling Level at 840ML. The ore is then hauled by 30-tonner Low- Profile Trucks (LPTs) and subsequently dumped at LTRs that lead to the Crushing Level at 773ML.

There are two (2) jaw crushers at the 773ML, the 4-4 Crusher Station and the 2-4 Crusher Station. Ore fragments bigger than 20cm in diameter report to the crushers for size-reduction.

Ore of suitable size drops to the Haulage Level at 745ML where they are carried by five (5) Feeder Belt Conveyors (FBCs). The FBCs feed two (2) collecting bins thate discharge onto the sacrificial conveyor then to the 2.7-km long Cable Hauled Conveyor (CHC).

Finally, the ore is transported by the CHC to the surface and discharged into the dump bin at the 1015ML.

Primary Crushing Plant
Coarse ore is delivered from the mine to the primary crushing plant via the Cable Hauled Conveyor system (CHC) at an average rate of 25,730 tons per day. The ore drops to four (4) units of vibrating scalper each of which is atop a152.4 cm x 487.68 cm dewatering screen with 7.6 cm 1st deck opening and 0.95 cm x 12.7 cm 2nd deck screen opening. The minus 0.95 cm material is conveyed via a series of launders and canals to the slimes screen while the plus 0.95 cm material drops to a 5,600-ton capacity dump bin.

Underneath the dump bin are four units of apron feeders individually feeding four units of 76.2 cm x 106.7 cm jaw crushers. These jaw crushers are set at 10.16 cm closed side setting. The crushed product of each jaw crusher is fed onto four parallel conveyors each feeding to a unit of 152.4 cm x 487.68 cm washing screen with 0.95 cm x 12.7 cm screen opening. The oversize is conveyed to a 30,000 ton capacity Coarse Ore Stockpile (COS) while the undersize flows through a series of canals to the slimes screens.

There are four (4) units of152.4 cm x 609.6 cm slimes screens with 2mm opening. The last panel is fitted with 1.27 cm screen. The minus 2mm material, which is considered as the primary slimes, flows and is fed to the ball mill discharge sump box for classification. The minus 1.27 cm is conveyed to the fine ore bin while the oversize is brought to the secondary and tertiary crushing section.

Part of the slime generated by the dewatering screen is fed to a bank of sieve bends (8 units) with 2mm opening. The oversize of the sieve bends is conveyed to the slime screens while the minus 2mm material is fed to two (2) units of rake classifier. The classifier sand is combined with the sieve bend oversize and is also conveyed to the slime screens. The overflow of the rake classifier is fed to a cluster of hydrocyclones. The cyclone overflow is fed to a 7m diameter x 9m high slime surge or conditioning tank. These slimes are treated separately in a Wemco 164/144 flotation bank. The cyclone underflow is piped to the ball mill discharge sump box.

Secondary / Tertiary Crushing Section
From the coarse ore stockpile (COS), the ore is withdrawn and conveyed to a set of grizzly bars with a 5.08 cm opening. The undersize material drops to the Tertiary Surge Bin. The oversize drops to a 675-ton capacity Secondary Surge Bin. From this bin, the ore is then fed to three (3) units of 167.64 cm standard cone crushers used for secondary crushing. The secondary crushers are set at 3.81 cm closed side setting. The crusher product is conveyed to a 2,800-ton capacity Tertiary Surge Bin.

From this bin, the ore is withdrawn and fed to eighteen (18) units of 152.4 cm x 365.76 cm vibrating screens with 1.27 cm opening. The oversize of the screens is fed to eight (8) units of 167.64 cm short head cone crushers. The tertiary crushers are set at 0.95 cm closed side setting. The tertiary crusher product combines with that of the secondary crusher product for screening.

The undersize of the screens is considered as the final product of the crushing plant and must be at least 73 percent passing 10mm. This is conveyed to the fine ore bin (FOB).

Grinding Section
There are nine (9) fine ore bins with an aggregate capacity of 17,000 tons. From these bins, the ore is withdrawn and fed to ball mills. There are nine (9) ball mills of the following sizes – one 441.96 cm x 670.56 cm, 2 units 502.92 cm x 838.2 cm, 502.92 cm x 670.56 cm, 3 units 350.52 cm x 426.72 cm, 356.76 cm x 487.68 cm and 441.96 cm x 716.28 cm. Two mills serve as spare to sustain milling tonnage. These ball mills are in close circuit with a cluster of hydrocyclones. All mills are charged with 32-35 percent steel ball loading at 40 percent 90mm and 60 percent 80mm composition of cast steel balls. The circulating load averages around 300 – 450 percent. Grinding ball consumption is 320 to 370 grams per ton.

The cyclone overflow or finished product of the grinding section is normally 60 – 65 percent passing 200 mesh (74 micrometers) at 1,260 – 1,320 grams per liter pulp density. This material flows by gravity through four (4) parallel trash screens before being fed to the flotation circuit.

Copper and gold is recovered using flotation process after crushing and grinding stages. The final product of the whole operation is copper concentrates which are trucked to a concentrate facility in Poro, La Union and shipped to smelters in Japan.

Copper, gold, silver and sulfide minerals are separated from the waste or gangue portion of the ore by a Rougher Flotation circuit which comprises of five (5) banks having a total volume of 1,206m3. The first two banks are a combination of four (4) Wemco 164 and six (6) Wemco 144 cells, the other two banks have nine (9) Wemco 164 cells, and the last bank consists of six (6) Wemco Smart Cells. The Rougher Concentrate produced is upgraded in a three-stage cleaning circuit. The first cleaning stage consists of four (4) units of Wemco 164 with a volume of 113 m3 and the second and third cleaning stages consist of two units Column Flotation Cells with a total volume of 170 m3.

Tailings from the roughers are passed through pa ........