A

Acid leaching

the leaching of an ore or mineral concentrate with an acid base solution. In the case of Uchucchacua, Buenaventura leaches the flotation concentrates with a dilure sulfuric acid solution to eliminate manganese sulfide (MnS, also known as alabandite). The manganese lon reacts with the acidto form manganese sulphate, which is soluble in water. The solution containing tha manganese sulphate is treated with lime (calcium oxide) to form manganese hydroxide, an insoluble compound, which is eventually removed from the resulting solution. The sulfur ion (S) reacts with the acid to form hydrogen sulphide gas, which is mixed with caustic soda to produced sodium sulphide, a commercial product that is sold by the Company.

Adit

an almost horizontal entrance to mine.

Assay

the chemical analysis of an ore, mineral, concentrate of metal to-determine the amount of valuable species. Precious metals are usually given in ounces per ST or grams per MT, while base metals are given in percentage.

B

Ball mill

a cylinder-shaped mill that uses steel balls as a grinding medium. The mill is used to grind the ore as fine as possible in order to achieve liberation of the valuable species from gangue particles.

Blasted material

the matter, including overburden and ore, that results from blasting.

Blasting

the operation of breaking ore by boring a hole in it, inserting an explosive charge and detonating or firing it.

Bulk concentrate

a concentrate that contains more than one mineral.

Bulk Flotation

the recovery of all valuable species (gold, lead, silver, zinc, copper, etc.) in one single product called bulk concentrate. In Julcani, a silver-lead-gold-copper concentrate is obtained, while in Uchucchacua, two concentrates are produced: a silver-lead concentrate (bulk) and a separate zinc concentrate.

Bullion

uncoined gold or silver in the shape of bars, ingots or comparable masses.

C

Concentrate

a meral-rich product from a mineral separation process such as flotation. The metals are "concentrated" from ore, and the remainder is discarded as neutralized railing. The contained metals are recovered from the concentrates either by leaching or by smelting.

Concentration

the process by which ore is separated into metal concentrates and reject material through processes such as crushing, griding and flotation. Concentrates are shipped to a smelter or leaching facility at which the contained metals are recovered from the concentrates.

Concentrator

a plant where concentration takes place.

Crushing

the process by which ore is broken into small pieces to prepare it for further processing.

Cut-and-fill stoping

a mining method that involves excavating a stope, then filling it with waste material to provide support.

Cut-off-grade

the minimum grade of ore used to establish reserves.

Cyanidation

a method of extracting gold and silver contained in ores or concentrates by dissolving them in a weak solution of potassium or sodium cyanide. In Orcopampa, cyanidation is performed on high gold and silver gravity concentrates that have been previously obtained by gravity methods in the mill, and is carried out in two ways.

1) The gravity concentrate is ground in water and pumped to an agitator where a cyanide solution is added. The pulp is filtered and the solution containing most of the gold and silver is introduced in electrolitic cells where both elements are recovered by electro-winning the gold and silver deposits in the cathode. The barren solution that still contains traces of gold and silver is then pumped through five columns that contain activates carbon. Finally, the solution is pumped back to the agitators.

2) The un-ground gravity concentrate is deposited in a vat, a pit of about 100 square yards surrounded by concrete walls six feet high with an open top. Cyanide solution is pumped to the top of the pile and percolates through the concentrate, dissolving the gold and silver. The rich solution is sent to the electrolitic cells and carbon columns. The process is repeated until most of the gold has been dissolved.

D

Differential flotation

the process by which two or more valuable species are recovered in separate concentrates. In the case of a lead-zinc ore, the lead is floated into a lead concentrate by inhibiting the flotation of zinc. After the lead flotation is over, zinc is activated and recovered in a separate concentrate.

Doré

impure and unrefined mixture of metallic gold and silver produced through the smelting of gold and silver concentrate, sand or precipitate. Typical impuritics include base metals. Doré is further refined to almost pure gold by a smelter or refinery.

Drift (subleved drift)

a horizontal underground tunnel driven alongside orthrough an ore deposit, from either an adit or shaft, to gain access to the deposit.

DMT

a dry metric ton that, when used with respect to concentrate, excludes the water content contrained in such concentrate.

DST

a dry short ton that, where used with respect to concentrate, excludes the water content contained in such concentrate.

E

Electro-winning cells

cells where metal is recovered by electrolysis. A solution containing dissolved metals is placed in the cell where an electric current causes the metals to be deposited on a cathode.

Epithermal

a term applied to deposits formed at shallow depths from ascending solutions of moderate temperatures.

F

Fill

waste material placed in underground excavations to provide support.

Flotation

a process that separates valuable species from the gangue material. To achieve a good separation, these valuable species have to be first liberated from the gangue by grinding the ore with a ball mill. Separation then place takes place in water in which the solid particles are suspended by means of agitators.

Special chemical reagents are added to the aqueous pulp, which contains a mixture of water and ground-up ore. The reagents cause the selected mineral particles to become hydrophobic so that, when air or gas bubbles are introduced to the agitator (better known as a flotation cell), these particles attach to the bubbles. The bubbles, carrying the mineral particles, rise to the surface where they are removed in a froth, while the other particles remain suspended in the pulp. Flotation is generally performed on sulphide ores, although there are a few cases where flotation is used for the recovery of non-metallic or oxidized species.

Flotation cell

an appliance in which froth flotation of ores is performed.

G

Gangue

worthless rock or other material in which valuable minerals are found.

Grade

the amount of valuable mineral in each ton of ore, expressed as troy ounces per ton for precious metals and as a percentage for other metals.

Gravity concentration

a method of separating different grains of minerals by reason of their differences in movement in response to various forces acting on them, especially gravity. For example, a grain of gold sinks to the bottom of a tank much faster than a grain of silica of the same size.

H

Heap leaching

the leaching of ores that have been mined, transported and placed on top of impervious leach pads by sprinkling or ponding with, in the case of copper, an acid solution or, in the case of gold or silver, a cyanide solution. The solution percolates through the ore heap, dissolving the valuable species, and is then collected at the bottom of the heap and sent to the metal recovery circuit. The ore on top of the pad can be crushed, if necessary, in order to speed the recovery of the valuable species.

Hedging

an arrangement that effectively offsets a price or exchange risk inherent in another transaction or arrangement.

L

Leaching

the process in which a soluble metallic compound is extracted from ore by dissolving the metals in a solvent. See definitions of "Acid Leaching" "Cyanidation" and "Heap Leaching".

Leach pad

a large, impermeable foundation or pad used as a base for ore during heap leaching. The pad prevents the leach solution from escaping out of the circuit.

M

Merrill-Crowe process

the removal of gold from pregnant cyanide solution by a three-step process that involves, first, the clarification process whereby the solution is passed through filters that remove any suspended solids in the solution, second, the deacretion process whereby oxygen is removed from the solution and, third, the zinc precipitation process whereby zinc replaces gold in the solution. The work is completed by filtration to arrest the resultant auriferous gold slimes.

Mill

a machine used to grind ore to the consistency of powder.

Milling

a treatment process involving fine grinding of ore followed by extraction of minerals.

Mineralization

rock containing an undetermined amount of minerals or metals.

Minimum mining width

the smallest horizontal width or thickness that can be physically and economically exploited by one or more mining methods in use at a particular mine. Where the sampled width of the mineralized horizon is less than the minimum mining width, computation of reserves must include dilution to minimum width.

MT

1.10231 ST, also known as a metric ton.

O

Open-pit mine

surface mine in which the ore is extracted from a pit. The geometry of the pit may very with the characteristics of the ore body.

Ore

material that contains one or more minerals, at least one of which can be recovered at a profit.

Ounces

troy ounces of a fineness of 999.9 parts per 1,000 parts, equal to 31.1034 grams.

Overburden

the alluvium and rock that must be removed in order to expose an ore deposit.

P

Porphyry copper deposit

a disseminated large-tonnage, low-grade deposit, in which the copper minerals occur as discrete grains and veins throughout a large volume of rock.

Precipitate

a mixture of mineral particles filtered from solutions as a result of a chemical reaction.

Pregnant solutions

solutions that have percolated through the ore on a heap leach. The solution is impregnated with gold and silver removed from the ore.

Probable reserves

reserves for which quantity and grade and/or quality are computed from information similar to that used for proven reserves, but the sites for inspection, sampling and measurement are farther apart or are otherwise less adequately spaced. The degree of assurance, although lower than that for proven reserves, is high enough to assume continuity between points of observation.

Proven reserves

reserves for which (a) quantity is computed from dimensions revealed in outcrops, trenches, workings or drill holes, and grade and/or quality are computed from the results of detailed sampling, and (b) the sites for inspection, sampling and measurement are spaced so closely and the geologic character is so well defined that size, shape, depth and mineral content of reserves are well-established.

R

Ramp

an inclined underground tunnel that provides access for exploration or a connection between levels of a mine.

Refining

the final stage of the purification of crude metallic products, in which final impurities are removed from molten metal by introducing air and fluxes. The impurities are removed as gases or slag. For instance, the refining of base bullion (silver lead) produces nearly pure lead and silver.

Reserves

that part of a mineral deposit that could be economically and legally extracted or produced at the time of the reserve determination.

Resning

a mining method where the vein and wall rock components of a minimum mining width are sequentially removed, generally employed in the case of very narrow high grade veins. Cleaner (less diluted) ore is produced than when ore and wall rock are broken to a minimum mining width in the same blast.

S

Shrinkage stoping

a method of mining in which blasted material forms the fill in the stope. The mine works from this fill. After all mining is completed the ore is removed.

Slag

the vitreous mass left as a residue by the smelting of metallic ore.

Slurry

a fluid comprised of fine solids suspended in a liquid (generally water).

Smelting

a pyro-metallurgical process of separating metal from those impurities with which it may be chemically combined or physically mixed.

ST

2,000 avoirdupois pounds, also known as a short ton.

Stope

the working area in an underground mine from which ore is extracted.

Stoping

the act of excavating ore from an underground mine, either above or below a level, in a series of steps.

Sublevel stoping

a method of stoping in which the ore is excavated in open stopes, retreating from one end of the stope toward the other.

T

Tailings

the material rejected from a mill after the valuable minerals have been recovered.

V

Vat leaching

See definition of "Cyanidation."

Vein

a zone or belt of mineralized rock lying within boundaries clearly separating it from neighboring rock.

W

WMT

a wet metric ton that, when used with respect to concentrate, does not exclude the water content contained in such concentrate.