The below reference gives a good comparison with a typical laterite to the deposit at Isabel.
Note the example given of a general laterite with respective seams A, B and C.
Compare these to the Isabel deposit where A is 0.5-1m overburden, B is approx 6-7 m and C 5-6m with some results returning 8m. A huge difference to a text book style laterite. AVQ's Wet Tropical Deposit is showing a less weathered Regolith zone with higher mineralisation and at very shallow depth.
The below reference is a few years old where new refining techniques have now redefined the viability of the better quality DSO deposits around the world. These better quality deposits are generally referred to as "Wet".
Hence SMM willingness to fight AVQ at all expense.
Enjoy
Laterite is a soil and rock type rich in
iron and
aluminium, and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high
iron oxide content. They develop by intensive and long-lasting
weathering of the underlying
parent rock. Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land area containing laterites is between the tropics of
Cancer and
Capricorn.
Laterite has commonly been referred to as a soil type as well as being a rock type. This and further variation in the modes of conceptualizing about laterite (e.g. also as a complete weathering profile or theory about weathering) has lead to calls for the term to be abandoned altogether. At least a few researchers specializing in regolith development have considered that hopeless confusion has evolved around the name. There is no likelihood, however, that the name will ever be abandoned; for material that looks highly similar to the Indian laterite occurs abundantly worldwide, and it is reasonable to call such material laterite.
Historically, laterite was cut into brick-like shapes and used in monument-building. After 1000 CE, construction at
Angkor Wat and other southeast Asian sites changed to rectangular temple enclosures made of laterite, brick and stone. Since the mid-1970s, some trial sections of
bituminous-surfaced, low-volume roads have used laterite in place of stone as a base course. Thick laterite layers are porous and slightly permeable, so the layers can function as
aquifers in rural areas. Locally available laterites have been used in an acid solution, followed by precipitation to remove
phosphorus and heavy metals at sewage-treatment facilities.
Laterites are a source of aluminium
ore; the ore exists largely in
clay minerals and the
hydroxides,
gibbsite,
boehmite, and
diaspore, which resembles the composition of
bauxite. In Northern Ireland they once provided a major source of iron and aluminium ores. Laterite ores also were the early major source of
nickel.
Laterite is often located under residual soils.
A represents soil; B represents laterite, a regolith; C represents saprolite, a less-weathered regolith; D represents bedrock
Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils.
[5]:3 The initial products of weathering are essentially kaolinized rocks called
saprolites.
[6] A period of active laterization extended from about the mid-
Tertiary to the mid-
Quaternaryperiods (35 to 1.5 million years ago).
[5]:3 Statistical analyses show that the transition in the mean and variance levels of
18O during the middle of the Pleistocene was abrupt.
[7] It seems this abrupt change was global and mainly represents an increase in ice mass; at about the same time an abrupt decrease in sea surface temperatures occurred; these two changes indicate a sudden global cooling.
[7] The rate of laterization would have decreased with the abrupt cooling of the earth. Weathering in tropical climates continues to this day, at a reduced rate.
[5]:3
Laterites are formed from the
leaching of parent
sedimentary rocks (
sandstones,
clays,
limestones);
metamorphic rocks (
schists,
gneisses,
migmatites);
igneous rocks (
granites,
basalts,
**bros,
peridotites); and mineralized proto-ores;
[3]:5 which leaves the more
insoluble ions, predominantly iron and aluminium. The mechanism of leaching involves acid dissolving the host
mineral lattice, followed by hydrolysis and precipitation of insoluble oxides and sulfates of iron, aluminium and silica under the high temperature conditions
[8] of a humid sub-tropical
monsoon climate.
[9] An essential feature for the formation of laterite is the repetition of
wet and
dry seasons.
[10] Rocks are leached by percolating rain water during the wet season; the resulting solution containing the leached ions is brought to the surface by
capillary action during the dry season.
[10] These ions form soluble
salt compoundswhich dry on the surface; these salts are washed away during the next wet season.
[10] Laterite formation is favoured in low
topographical reliefs of gentle crests and
plateaus which prevents erosion of the surface cover.
[5]:4 The reaction zone where rocks are in contact with water—from the lowest to highest
water table levels—is progressively depleted of the easily leached ions of
sodium,
potassium,
calcium and
magnesium.
[10] A solution of these
ionscan have the correct
pH to preferentially dissolve
silicon oxide rather than the
aluminium oxides and
iron oxides.
[10]
The mineralogical and chemical compositions of laterites are dependent on their parent rocks.
[3]:6 Laterites consist mainly of
quartz,
zircon, and oxides of
titanium, iron,
tin, aluminium and
manganese, which remain during the course of weathering.
[3]:7 Quartz is the most abundant relic mineral from the parent rock.
[3]:7 Laterites vary significantly according to their location, climate and depth.
[8] The main host minerals for nickel and
cobalt can be either
iron oxides,
clay minerals or
manganese oxides.
[8] Iron oxides are derived from
mafic igneous rocks and other iron-rich rocks;
bauxites are derived from
granitic igneous rock and other iron-poor rocks.
[10] Nickel laterites occur in zones of the earth which experienced prolonged tropical weathering of
ultramafic rocks containing the ferro-magnesian minerals
olivine,
pyroxene, and
amphibole.
[5]:3
Nickel[edit]
Main article:
Lateritic nickel ore deposits
Irregular weathering of grey
serpentinite to greyish-brown nickel-containing laterite with a high iron percentage (nickel
limonite), near Mayagüez, Puerto Rico.
Laterite ores were the major source of early nickel.
[5]:1 Rich laterite deposits in
New Caledonia were mined starting the end of the 19th century to produce
white metal.
[5]:1 The discovery of sulfide deposits of
Sudbury, Ontario, Canada, during the early part of the 20th century shifted the focus to
sulfides for nickel extraction.
[5]:1 About 70% of the Earth's land-based
nickel resources are contained in laterites; they currently account for about 40% of the world nickel production.
[5]:1 In 1950 laterite-source nickel was less than 10% of total production, in 2003 it accounted for 42%, and by 2012 the share of laterite-source nickel was expected to be 51%.
[5]:1 The four main areas in the world with the largest nickel laterite resources are New Caledonia, with 21%; Australia, with 20%; the Philippines, with 17%; and Indonesia, with 12%.
[5]:4
