all about ore :> Flashcards
1
Q
smallest commercial mine operations, for instance on veins, are typically of ore
bodies of about
A
1 Mt,
2
Q
1 Mt, equivalent to?
A
cube of rock about 75 m across
3
Q
the total nickel is in the two largest deposits.
A
45% o
4
Q
defined as those in the top 10% of any category with respect to metal contained.
For many commodities this small number of world-class deposits contain between 60 and
90% of global resources,
A
World-class
Ni about 85%
5
Q
deleterious elemtns in iron
A
phosphorous
6
Q
are extracted from mined and milled ore or waste if the costs of metallurgical
extraction are favourable, but which do not significantly affect the economics of the whole
mining operation
A
d by-products
7
Q
give the equilibrium ratios of concentration of the element between any two coexisting phases (two minerals, a mineral and
melt etc.)
A
partition coefficients (K values),
8
Q
concentrations in igneous rocks range from
A
50 ppm in average ultramafic rocks,
through around 100 ppm in mafic rocks to 25 ppm in felsic granites and rhyolites
9
Q
mined at Tellnes in
Norway as a source of titanium minerals
A
nelsonites
10
Q
immiscible
separation of phosphorous-rich melts from carbonatite magmas to form an apatite-rich
igneous rock called
A
phoscorite at zoned alkaline intrusions
11
Q
Pegmatites are ores for many so-called rare metals, for instance,
A
Li, Be, Nb, Ta,
Sn and U
12
Q
what are the LREEs
A
La Ce Pr Nd Sm ans Eu
13
Q
heavy rare earthe
A
Gd to Lu
14
Q
rocks located within a few hundred metres of the
contacts of carbonatite intrusions and of zoned intrusions of carbonatite and alkaline
silicate igneous rocks are in almost all cases converted to
metasomatic
rock type characterised by high potassium content, such that one or more of K-feldspar,
riebeckite, and biotite are important minerals
A
fenite
15
Q
ore is in weathered carbonatite
and the enrichment to ore grade is a result of lateritic weathering
A
Mt Weld,
16
Q
ore is in calcitic and
dolomitic carbonatite with barite as an important gangue mineral
A
Mountain Pass
17
Q
ore is present
in calcite carbonatite, but the highest grades are in composite lenses of unique iron oxide–
fluorite–aegerine-augite rock which is hosted within a large (10 by 2 km outcrop area)
carbonatite intrusion
A
Bayan Obo
18
Q
temperature dolomite can be a stable mineral in mantle
peridotite
A
2.5 GPa 90 km
19
Q
the only ore mineral of Cr
A
spinel
20
Q
chromite deposits in large, layered ultramafic–
mafic intrusions;
A
stratiform
21
Q
ores in ophiolites or ‘Alpine peridotites’
A
podiform chromite
22
Q
A
23
Q
ideal complete ophiolite succession is
A
the ultramafic tectonites are residual upper mantle from which basaltic magmas (e.g. mid-ocean ridge basalt, MORB) have been extracted.
24
Q
deformed as a result of solid- state flow of the mantle during continuous sea-floor spreading, during which a foliation and lineation is formed as the residue of melting flows upwards to below the ridge axis and then laterally away from the ridge.
A
tectonites
25
Magmatic sulfide deposits in mafic and ultramafic rocks provide the majority of the global
supply of
nickel and platinum-group elements (PGEs
26
PGEs are the six geochemically similar heavy transition-row elements which have
siderophile to chalcophile behaviour All six elements have
very low concentrations (< 10 ppb)
r (Ru, Rh, Pd, Os, Ir and Pt)
27
also enriched in magmatic sulfide ores and are recovered
at some mines of magmatic sulfide deposits.
Cobalt and gold
28
Ni–Cu magmatic sulfide deposits in gabbroic intrusions. re disseminated to massive concentrations of sulfide
minerals with up to 80% sulfide minerals, in and adjacent to igneous rock bodies.
base-metal
29
base-metal, Ni-dominated sulfide deposits in ultramafic lava flows
(komatiites
30
, PGE magmatic sulfide deposits in large layered ultramafic to mafic
intrusions. disseminated ores in igneous rocks with concentrations of up to at
most only a few percentage sulfide minerals
precious metal
31
sulfur is required to fully melt
sulfide into the mafic melt derived
200 ppm
32
expected to have highest concentrations in melts into which
the last sulfide minerals have just melted.
, Cu
33
concentration of Ni in the melt increases progressively with increasing percentages of
partial melting.
e Ni is partitioned into olivine
34
emperatures at which ultramafic and mafic magmas crystallise in the crust and
at the Earth’s surface
(1100–1600 C),
35
The high-temperature Fe–Ni
sulfide mineral is the mineral mss (monosulfide solid solution) . The mineral mss
recrystallises to
pentlandite and pyrrhotite at similarly low temperatures
36
Chalcopyrite is for instance a product of recrystallisation of the mineral iss (intermediate solid solution) at temperatures of around
300
37
he ore is the concentration of Ni or Cu in the sulfide fraction of the rock. ranges from a few percentage up to about 20% in these magmatic sulfide ores,
hence rocks with a few percentage or more of sulfides constitute ore.
e tenor
38
, contain a known resource of about 4000 Mt of rock with disseminated
Cu–Ni sulfide minerals and about 0.2% Ni disseminated over tens of metres of thickness
of the host intrusions.
large Duluth Complex of
Minnesota, USA
39
small intrusion (~ 3 km2
), but has an
elongate flared shape (canoe shape) above a relatively narrow underlying feeder dyke,
similar to the Great Dyke of Zimbabwe
Mesoproterozoic Jinchuan
40
There are multiple, closely spaced small ore-hosting gabbro-norite to gabbro intrusions
in the
Noril’sk-Talnakh complex
41
which contain about 106
km3
of basalts and originally
extended over an area at least 2000 km by 2000 km
Permo-Triassic
Siberian Traps flood basalts
42
several-kilometre-thick, elliptical bowl-shaped
intrusion about 65 km by 25 km of Palaeoproterozoic age (Figure 2.14). It lacks an
ultramafic cumulate basal sequence, and also lacks the cyclic and rhythmic layering of
the similar-sized Bushveld Complex and Great Dyke intrusions. y layered from a norite (olivine–gabbro) base to a
quartz–diorite top
Sudbury Igneous Complex
43
y form complex lenticular shapes
sulfide ore bodies
44
form pods and lenses at the base, or rarely the top,
of the relatively small host intrusions (
45
contains
clasts of sulfide and of wall-rock in a gabbro-norite matrix.
Breccia ore
46
ultramafic lavas and associated shallow intrusive units. They have greater
than 18% (typically 30 to 40%) MgO and are petrologically peridotites (dunites, harzburgites and orthopyroxenites) and metamorphosed equivalents (serpentinites, talc-schists,
tremolite-chlorite schists). They erupted at high temperature (up to 1600 C), at low
viscosity, and in many cases formed large-volume, very extensive flows that range in
thickness from a few metres to locally several hundred metres thick.
Komatiites
47
spinifex texture, in which elongate skeletal olivine and orthopyroxene grains
grew up to a few centimetres or as long as metres in length as a result of quenching of the
tops of hot lavas on eruption comprise repeated sub-aqueous lava flows
and are a minor component in the now deformed and metamorphosed supracrustal volcanic
and sedimentary sequences (greenstone belts) of Archaean and Palaeoproterozoic cratons Ni-rich sulfide ores minor Cu trace amounts of komatiites
Nickel sulfide ores in komatiites
48
ores do occur at the base of higher
flows
hanging-wall ores), and in many cases ore bodies are vertically stacked
49
s hosted in a trough at the base of the basal flow and is layered with a few
metres thickness of massive sulfide (contact ore) grading upwards into net-textured ore
with < 50% sulfide in a silicate matrix, and disseminated ore in which isolated blebs of
sulfide are enclosed between silicate grains.
largest ore body
50
formed where
cumulate minerals compact down into sulfide melt, and silicate melt that was interstitial
to these early formed silicate crystals is displaced upwards into the flow or intrusion
Net-textured ore
51
formed of droplets that were trapped by crystallised interstitial
silicate melt before they could settle
Disseminated ore
52
substrate foot-wall rocks in
the case of
komatiite lavas
53
High-percentage melting of mantle peridotite is indicated by
picritic olivine-rich and
Mg-rich compositions of the most mafic rocks in the suites of intrusion that host ores.
54
Very large melt volumes are preserved in the
Permo-Triassic Siberian Traps, the flood
basalt province that is centred on Noril’sk-Talnakh.
55
the remains of an LIP
Nebo-Babel deposits
56
restricted to early periods of Earth history and were formed through
high degrees of partial melting of mantle peridotite (apparent melt percentages of up to
40%) at high temperatures. It is interpreted that they extruded at temperatures much hotter
than modern-day basalts (up to 1600 C) and that the melts formed at much greater depth
in the mantle (150–200 km).
True komatiites
57
has the largest range of compositions
of magmatic sulfide ores
e Sudbury Igneous Complex
58
Economic PGE ores need to
contain
5–10 ppm combined PGEs, which is equivalent to concentration by enrichment
factors of between a thousand and ten-thousand times crustal abundances
59
Over 75% of the world’s
production and reserves are in the
Bushveld Complex
60
n these larger intrusions
generally have the highest PGE grades
The reefs
61
The magmas that filled the intrusions that host PGE-enriched layers were high
magnesium basalts, tholeiites, or mildly alkalic basalts.
62
The host intrusions of the
economic reefs are layered intrusions formed from
high-magnesium, low-titanium
siliceous mafic magmas
63
indicative of higher degrees of partial melting of mantle than
would be the case for typical tholeiites
The highmagnesium contents
64
Palaeoproterozoic vintruded into the Archaean Kaapvaal craton and the overlying early Proterozoic sedimentary
and volcanic sequences. It is the world’s largest preserved intrusion. It extends over about
65 000 km2
, is up to 9 km thick, and is estimated to have intruded over a period of at most
about 100 000 years. Its present geometry is bowl-like, outcropping along the rim originally a sill-like intrusion that
intruded most probably within about 4 k
Bushveld Complex
65
the transition from dominantly
pyroxenites (below), to gabbros (above). The ore horizons are: (i) a pegmatitic pyroxenite
layer with thin chromitite seams (Merensky Reef); (ii) the uppermost important chromitite
layer (UG2) which is about 30–200 m below the Merensky Reef; (iii) a pyroxenite layer at
the base of the northern lobe, where stratigraphically underlying layers are not developed
(Plat Reef).
Critical Zone
66
Small tonnages of PGEs
have also been mined from
dunite pipes that cross-cut the layered sequence
67
ore
occurs near the top of the layers with chromitite seams and at the boundary between the lower
ultramafic layers of the intrusion and the upper mafic layers
reefs in the late Archaean Stillwater Complex and in the Great Dyke are in very similar
positions in the host intrusions as those in the Bushveld Complex
68
major PGE reef is at a slightly lower relative position, near the top of the uppermost
pyroxenite layer in the intrusion
e Great Dyke,
69
occurs about 30 m lower in the sequence, but has lower PGE grades.
Lower Sulfide
Zone (LSZ)
70
are mixtures of trace concentrations of
typically very fine grained (< 20 μm) and disseminated alloys (e.g. PtPd), sulfides, and
related minerals (e.g. the arsenide sperrylite, PtAs2).
results of low-temperature
subsolidus recrystallisation of high-temperature minerals
. PGE minerals (PGMs)
71
contain 0.5–5% disseminated base-metal sulfide minerals (dominantly
pyrrhotite, pentlandite and chalcopyrite)
PGE reefs
72
typically less than 1 m thick
marked by ‘potholes’, which are sub-circular areas a few metres to hundreds of metres across
where normal foot-wall to the reef is missing and the reef rocks sit a few metres lower in the
cumulate sequence, and by some ‘neptunian dykes’ where the reef appears to intrude into the
underlying cumulates (Figure 2.29). These irregularities influence PGE content of the reef
marks a major unconformity surface in the cumulate sequence of the
Bushveld Complex: immediately underlying cumulate layers appear to have been ‘eroded’
beneath about half of the explored area of the reef in the western lobe of the comple
Merensky Reef
73
at the contact between anorthosite below and more mafic melanorite above
and comprises a pegmatitic pyroxenite unit, about 40 cm thick, with unusually coarse
(< 5 cm) grains of orthopyroxene in intercumulus plagioclase and with sharply defined
thin chromitite (< 5 cm) seams at the base and top. In some sections the pegmatitic
pyroxenite is not developed.
he PGEs have highest concentrations in
the chromitite seams
‘Normal
reef
74
highest PGE concentrations are thus about
1 m below the level of highest
sulfide contents
75
In ore deposit geology, the interest in
pegmatites is in the so-called
indicates the presence of
high concentrations of one or more metals and other elements that are present in trace
concentrations (< 500 ppm) in average crustal rock and which are not extracted from
other common deposit types.
rare-metal or rare-element pegmatites
76
The elements enriched in pegmatites are mostly lithophile
elements and include
e LILEs (Li, Rb, Cs, Be), HFSEs (Ga, Sn, Hf, Nb,
P, Ta, Y, U, Th, REEs), and elements that form compounds that are strongly soluble in
aqueous solutions (B, F).
77
indication of enrichment of pegmatittes
s LCT (¼ Li, Cs, Ta) and NYF (¼ Nb, Y, F)
78
pegmatites are of greatest economic interest as ores of
a, Sn, Cs,
U and Rb
79
irregular lenticular bodies up to 100 m by 1 km in
cross section, or slightly larger in the uppergreenschist- or the lower-amphibolite-facies of the low-pressure baric types
e large pegmatites are detached from ‘source’ plutons
80
The central process of rare-metal enrichment in pegmatites is
melt fractionation
LCT pegmatites are some of the most strongly fractionated igneous rocks
81
form
from alkaline, volatile-rich, potassic ultramafic magmas that are formed as small-degree
partial melts of carbonate-bearing and hydrous-mineral-bearing mantle peridotite
characterised by inequigranular textures with macrocrysts (0.5–10 mm),
megacrysts and xenolith clasts in a fine-grained igneous matrix.
Kimberlitic rocks
82
recognised worldwide – macrocrysts are dominated by olivine
with lesser Mg-ilmenite, pyrope, diopside, phlogopite, enstiate and chromite in an
olivine (or now serpentine)–carbonate matrix.
Group I kimberlite
83
only recognised in southern Africa – macrocrysts
are dominately phlogopite with lesser olivine in an olivine–mica groundmass
Group II kimberlite (or orangeite)
84
recognised in Australia and India, and possibly elsewhere – major
minerals are Ti-phlogopite, Ti–K-richterite, olivine, diopside, leucite and sanidine.
Lamproite
85
Typical diamond grades in economic kimberlite and lamproite deposits are
10 to 100
carats per 100 tonnes (1 carat ¼ 200 mg)
grade will include both gem-quality and
industrial stones,
86
Based on diamond abundance in xenoliths in kimberlitic rocks we can estimate
diamond grades in mantle in the diamond stability field to be
0.5–650 c per 100 t for
peridotite and 17–34 000 c per 100 t for eclogite in the mantle
87
Their formation is either
the result of phreatomagmatic processes or eruption processes
Diatremes form from the surface down to about 1-km depth
88
Phreatomagmatic diatremes form where kimberlite magma at
t 900–1100 C heats near surface groundwaters.
89
form as a result of low degrees of partial melting of CO2–H2Obearing peridotite
Kimberlitic magmas
90
Low-percentage partial melts
would have
high CO2 and H2O concentrations (> 5 wt % H2O and 5 wt % CO2), as is
consistent with kimberlite chemistry and mineralogy
91
Kimberlitic diamond deposits and also major alluvial diamond deposits known before
about 1970 are in restricted areas of the world
Southern Africa, Siberia, India, Brazil,
West Africa.
92
: ‘significant diamondiferous kimberlites occur only in
in ancient shield regions, including Archaean cratons and
Palaeoproterozoic mobile belts (orogenic belts) that border Archaean cratons, and were
themselves undeformed since the end of the Palaeoproterozoic era’ ( +1600 my+a
93
At temperatures greater than the
critical temperature of pure water (376 C), liquid-like pure water will not boil with either
decreasing pressure or increasing temperature, but will steadily become less dense (Figure 3.1).
The term
supercritical fluid is used for these environments
94
Fluids derived from the
surface have pressures close to
pressure of the
weight of the overlying column of water, and these fluids may migrate laterally or
convect.
hydrostatic pressures,
95
fluids released from minerals through mineral
devolatilisation reactions.
Diagenetic and metamorphic fluids
96
fluids that were dissolved in silicate
magma and is released from solution (exsolved) on decompression and/or crystallisation of the magm
Magmatic (magmatic-hydrothermal) fluid
97
groundwaters derived from the hydrosphere (rainfall, etc.) and
heated on interaction with rock on percolation to depths of up to a few kilometres
depth in the crust.
Meteoric waters
98
or non-pervasive
nstance, only adjacent to fractures
99
mineral growth in open or fluid-filled space in the rock, and
dilatant
100
the latter implies a
planar body of hydrothermally altered rock adjacent to a fracture or a channelway.
replacement veins
101
fluid
is flowing through a rock
open systems
102
veins form as a result of local
redistribution of fluids and solutes in a rock, for instance under a deviatoric stress
closed systems
103
result of rock fragmentation in a pressure
gradient. There are a number of different possible origins of a pressure gradient that will
induce f
Brecciation
104
Breccias that host ore bodies are commonly
pipe-shaped bodies of rock, most typically
sub-vertical, and less commonly tabular bodies,
105
clusters of small intrusions
such as dykes and stocks that mark the eroded roots of long-lived volcanoes
Magmatic
centres
106
magmatic centres develop above dome-shaped protrusions
cupolas
107
The
exsolved aqueous fluid migrates or ‘escapes’ into the crystallised carapace of the
intrusion and into and through overlying rock, in some cases reaching the atmosphere
or hydrosphere. This process is sometimes known as
magmatic degassing
108
in the context of magmas describes those chemical components that
emanate as vapours or gases from active volcanoes.
volatile
109
exsolution can thus occur as the magma rises
through the crust
(first boiling)
110
exsolution can occur due to increased concentration of the volatile elements in the
residual silicate melt as the magma crystallises
second boiling
111
complexing ligands
Cl–
, HS–
)
112
deposits of predominantly Sn and W together with
Mo, F, Li and B in quartz–muscovite metasomatically altered granite at
the top of an intrusion, or in sheeted quartz veins in and adjacent to altered granite
Greisens
113
