Geoscience Reference
In-Depth Information
(a)
(b)
Figure 8.3
Abandoned sodium nitrate workings in the Atacama Desert: (a) west of Oficina Salitirera Victoria; (b) at Oficina
Salitirera Humberstone, Tarapaca region, northern Chile.
evidence of multiple episodes of precipitation, dissolution
(in the form of solution cavities), repeated fracturing and
displacive growth. Hard, spheroidal cakes of anhydrite,
called
losa
, may also be present, produced at the surface of
the deposit by prolonged slow leaching (Ericksen, 1981).
Goudie and Heslop (2007) provide an overview of the
theories that have been put forward to account for the de-
velopment of sodium nitrate deposits in Chile. An early
view was that nitrate crusts were remnants of ancient sea-
weed deposits left stranded by falling sea levels (Forbes,
1861). This was soon dismissed (Newton, 1869) on the
grounds that there were no marine deposits at the alti-
tudes where nitrate sequences occurred. A related theory
(Gautier, 1894), but, again, the altitudes at which caliche
occurs makes this unlikely. A third proposal by Mueller
(1968) was that weathering in the higher rainfall zones of
the Andes had released solutes that accumulated within
closed basins at lower altitudes and ultimately formed
chloride and sulfate deposits. The slopes around these
basins were fed by capillary concentration, and this led to
the zones of nitrate accumulation.
The most widely accepted theories for explaining the
abundance of nitrate accumulations in the Atacama centre
on the role of atmospheric salt deposition. Claridge and
Campbell (1968) were the first to propose that Chilean ni-
trate deposits had built up as a result of the accumulation of
