The Anatomy of a Mine - Mining and the Environment: From Ore to Metal - page 192

solution by chemical precipitation or another chemical or electrochemical process.
Leaching methods include dump, heap, and tank operations. Heap leaching is widely
used in the gold industry, and dump leaching in the copper industry (see Chapters Five
and Six for a detailed discussion on leaching).

During the exploration phase, laboratory testing indicates the feasibility of concentration and
the expected percentage recovery of metals. The physical properties of a mineral often lead
directly to a process for separating that mineral from others. Some well-known examples of
these are: magnetic separation for minerals such as magnetite, rutile, ilmenite; gravity sepa-
ration for gold, silver, galena, cassiterite; l otation separation for most suli des; distillation for
mercury from cinnabar; and selective dissolution in specii c solvents such as halite or sylvite in
water, gold and silver in cyanide solutions, copper oxides, carbonates, sulphates, and silicates
in dilute sulphuric acid (Bolles 1985). During the feasibility evaluation, testing at a larger
scale using bulk samples with processing in a pilot concentrator is required to coni rm the
degree of metal recovery in benei ciation, on which project planning can be based.

Mine Waste Management Options
In the last few decades, advances in bulk haulage methods and equipment have favoured
larger bulk mining in open pits, over underground operations, particularly for base metal
and coal operations. As a consequence, larger amounts of wastes are produced from these
operations, mainly because large quantities of waste rock have to be removed to gain access
to the ore. In many cases, the amount of waste rock to be mined, transported and disposed
of is many times more than the tonnage of ore that is extracted (see Chapter Nineteen for
a detailed discussion of waste rock management). Waste to ore ratios of more than 20:1 are
common in high grade vein gold deposits, and are also sometimes found in high rank coal
mines. Larger bulk mining operations also produce more tailings. The amount of tailings
generated depends on the content of the desirable mineral in the ore, its grade, and the efi -
ciency of the mineral processing stage in recovering it. Another factor is the duration of an
operation. In most mining operations, the total amount of tailings is very large in compari-
son to the amount of mine product, and roughly equals the amount of ore mined. Tailings
management, discussed in more detail in Chapter Eighteen, is arguably the most challeng-
ing aspect of any mining operation. Favourable site conditions for mine waste disposal, or the
lack of them, may be the decisive factor in determining if mine development is feasible or not.

Waste to ore ratios of more
than 20:1 are common in high
grade vein gold deposits, and are
also sometimes found in high
rank coal mines.

Favourable site conditions for
mine waste disposal, or the lack
of them, may be the decisive
factor in determining if mine
development is feasible or not.

Required Mine Infrastructure
The infrastructure requirements for mining projects are project specii c. The capital cost for
infrastructure can vary substantially from site to site as a percentage of the total capital cost,
and is more often a function of the location than the mining or processing methods. Thus,
the capital cost estimate in engineering studies must be based on a proper identii cation and
assessment of the infrastructure requirements, such as access to the ore deposit, availability
of local resources, and access to port location. Only massive ore deposits, such as the Freeport
copper and gold deposits in Irian Jaya, are attractive when the deposit is sited in unexplored
frontier land, far from potential seaport locations and without any existing supporting infra-
structure whatsoever. Large coal deposits are known in Central Kalimantan, Indonesia but
the costs of coal transportation to seaports continues to prevent their development.

Cost/Benefi t Analyses
Benei ts are all of the positive factors associated with a mining project. The return on invest-
ment is important, but the time value of money also plays an important role. Simply put,
the annual proi ts generated by a mine must be sufi cient to pay back (within a reasonable