Mining Methods Vary Widely - Mining and the Environment: From Ore to Metal - page 240

●

Socially, gold rushes are characterized by lawlessness, unsafe work practices and poor
hygiene;

●

Only a very small proportion of miners earn signii cant wealth; more successful are the
money lenders and traders, while the majority of people make very little money;

●

Once near-surface deposits have been mined, the population declines rapidly;

●

As mines are deepened, miners tend to organize into groups or co-operatives, with
division of labour into miners, carriers, rock breakers, equipment operators, and
processors. At this stage new equipment is introduced for rock fragmentation, such
as small grinding mills known as trommels, larger stamp mills, and various jigs and
sluice boxes to recover free gold. Mines usually comprise adits or shafts that follow the
lode. Support and ventilation are minimal;

●

Population declines further as mines encounter stronger rock, groundwater or other
constraints, which reduce proi tability; typically the end of small-scale mining corre-
sponds to the base of the oxidized zone;

●

For major ore bodies continuing at depth, small-scale mining may give way to corpo-
rate mining, with one or more companies l oated to raise funds for larger-scale devel-
opment required to access the ore bodies at depth.

The above scenario may take place over i ve to ten years. A gold rush at Diwalwal in a
remote part of Mindanao, Philippines in the 1980s attracted more than 140,000 people (see
also Case 7.6). Many died, some when mine workings became l ooded or collapsed; others
were murdered or succumbed to diseases including those relating to inhalation of mercury
vapours.
A characteristic of gold rushes is the low recovery of gold that is achieved. Although
the ores mined may have relatively high grade (25 g/T or more), recoveries achieved are
typically 50% or less. This means that the residues or tailings contain signii cant remnant
grades, often justifying re-treatment. In most modern gold rushes, the mercury amalgam
process has been used to improve the recovery of i ne gold and silver particles ( Figure 5.8 ).
However, even with mercury extraction, considerable gold, silver, and mercury remain in
the tailings. During the 1980s in the Philippines, gold grades in tailings from artisanal min-
ing were sufi ciently high to attract the attention of operating mining companies, who rou-
tinely purchased tailings from small-scale miners operating in many parts of the country.
Gold rushes on mining tenements have led to conl ict between companies with legal
mining entitlements and illegal miners. At Mt Kare in Papua New Guinea, the mining
company RioTinto, abandoned its plans for mining after a large inl ux of people to the area.
Similarly, PT Tambang Tondano Nusajaya, a subsidiary of Aurora Gold, from Australia,
was unable to prevent an 'invasion' of small-scale miners at its high grade Talawaan pros-
pect near Manado in Indonesia ( Case 5.7 ). Other operations have been able to co-exist
with small-scale miners. For example, Newmont at its Minahasa Gold mine in Sulawesi,
Indonesia, allowed small-scale miners to exploit several of its smaller ore bodies, while
the company concentrated its attentions on the main Mesel ore body. Similarly PT Aneka
Tambang at its Pongkor gold project in West Java conducts mining in underground stopes,
while small-scale miners actively exploit near-surface ores. Similarly, local people have
extracted gold from mine wastes produced by mining companies, such practices usually
being tolerated if not encouraged by the companies involved. Examples include people fos-
sicking and hand-picking ore from waste rock dumps at Mt Muro in Indonesia, and small
enterprises using simple gravity separation techniques to extract gold particles from tailings
at the Atlas Copper Project in the Philippines and Freeport's Grasberg Project in Indonesia.
Narrow, gold-bearing veins may prove unattractive to operators using large-scale methods,
but can prove lucrative to artisanal miners. This can attract small-scale miners to mined out

A characteristic of gold rushes is
the low recovery of gold that is
achieved.