Widgiemooltha Komatiite
Encyclopedia
The Widgiemooltha Komatiite is a formation of komatiite
in the Yilgarn Craton
of Western Australia
.
of the Widgiemooltha Komatiite is well known to be part of the regional komatiite magma
tic event also seen at the Kambalda Dome, 50 kilometres (31 mi) to the north. There are comparisons which place the Widgiemooltha Komatiite as equivalent to the Silver Lake Komatiite. The Mt Edwards Basalt is correlated regionally with the Devon Consuls Basalt of Kambalda, and the Widgeimooltha Chert correlated with the Paringa Slate.
The structure of the Widgiemooltha Dome has three thrusted
repetitions of the basal komatiite contact and komatiite sequence including footwall Mt Edwards Basalt and hangingwall sediments (Widgiemooltha Chert).
dome
. The Widgiemooltha Granite is a coarse to medium, holocrystalline equigranlar granite with subordinate biotite and ferromagnesian minerals. It is mildly deformed, and is considered to have intruded concurrently with doming and uplift during late deformation. It is intrusive into the thrust repeated stratigraphy of the Widgiemooltha Komatiite and its sequence.
doleritic sill
complexes throughout the Yilgarn Craton. Within the Widgiemooltha Dome area, the Lake Zot Dolerite can attain greater than 300 metres (984 ft) thickness and is intrusive into the hangingwall basalt
and Widgiemooltha Chert above the Widgiemooltha Komatiite.
The dolerite is coarse grained in the main, often equigranular and holocrystalline although porphyritic areas are known and chilled margins and occasional compositional variations are noted. It is often epidotised, carbonated and sodium metasomatised
in proximity to major structures. It can often be reasonably strained throughout its bulk and especially in the footwall contact with the Widgiemooltha Komatiite.
s, often finely laminated and expressing ptygmatic folding post-sedimentation. It is considered to be an exhalative deposit formed post-magmatism. It often is intruded by the Lake Zot Dolerite.
The Widgiemooltha Chert is often the host of regional shears and thrusts.
The komatiite is typically of high magnesian character throughout, although flow top spinifex zones may get to as low as 18% MgO. Highest magnesium contents in rocks occur within the Wannaway area, with magnesium contents of up to 45% MgO reported from adcumulate serpentinite
lithologies in the basal flow.
The Widgiemooltha Komatiite is host to no less than 15 individual channelised kambalda type komatiitic nickel ore deposits
of which 5 have been mined, the remaining ten being of too low grade and low tenor to be economic at present. These features correlate with thickened komatiitic sequences, thick basal flows, trough like structural features and high magnesium lavas.
extrusive rock, metamorphosed to upper greenschist
facies. Mineralogy is chlorite
, actinolite
, rare epidote
, quartz
and albite
. The Mt Edwards Basalt has uncommon interflow sedimentary intervals and some well developed pillow basalt flow tops which give regional facing directions. The true thickness of the Mt Edwards Basalt is unknown.
.
Nickel ore has been found at several locations around the Widgiemooltha Dome and has been mined from six locations, with four underground mines in operation as of 2007 and a proposed open cut mine for mid-2007. Further exceptionally high-grade gold mineralisation is present at Wattle Dam, to 6kg (200 Oz) to the ton, within the Widgiemooltha Komatiite.
The 132 North deposit was discovered by in 1968 by International Nickel Australia Limited via gossan
searching and mined by Western Mining Corporation in 1981, with 900 tons of nickel metal produced. It was a small pod of low-grade nickel sulfide mineralisation hosted in a parasitic isoclinal syncline
developed on the 132 Anticline on the northern flank of the Widgiemooltha Dome. The 132 North and Widgiemooltha Townsite nickel gossans are mineralogical laboratories and contain exceptionally rare minerals.
The ore profile of the 132 North deposit is, from base upwards, 0.1 to 1m of massive pentlandite
-pyrrhotite
-pyrite-chalcopyrite
sulfide, matrix sulfide containing 40-80% sulfide, and disseminated sulfide. Accessory nickeline and gersdorffite
are reported. The transition zone supergene
sulfide phases include; violarite
, smythite, covellite
, chalcocite
and marcasite
after pyrite.
The nickel sulfides within the regolith
have been oxidised into a complex series of weathering fronts including a rare expression of a carbonate front which has resulted in a host of unusual nickel carbonate, arsenate and silicate minerals such as gaspeite
, atacamite
, annabergite
, carrboydite, glaucospaerite, hydrohonessite, kambaldaite
, népouite
, nullaginite, pecoraite, olivenite
, otwayite
, reevesite, retgersite, takovite and of course widgiemoolthalite.
The Miitel nickel mine has produced to date 1.56 million tons at 3.5% Ni for 47,250 tonnes of contained nickel. Reserves as of December 2006 were 481,000 tons @ 3.5% Ni for 16,835 Ni tons in North Miitel and 298,000 tons @ 3.8% Ni for 12,282 nickel tons in South Miitel. The Miitel mine is accessed by a single decline which splits into two separate declines which drive upon the north and south Miitel ore positions. The ore is mined by 'flatbacking', which is a form of cut and fill mining.
The Miitel orebody is situated on the eastern flank of the Widgiemooltha Dome on the Miitel Contact of the Widiemooltha Komatiite, and has the form of an arcuate boomerang
which plunges away to the north and south. The Widgiemooltha Komatiie forms a recognisable trough structure which is the idealised form of a komatiitic nickel orebody. Ore is a highly strained massive to matrix olivine
-sulfide adcumulate with a fine pyrrhotite
-pyrite
groundmass and prominent pentlandite
porphyroblast
s.
The influence of structure on the Miitel orebody is minimal except between the central Miitel and South Miitel ore pods and the current northern extent of the North Miitel ore trend where later, brittle faults disturb and offset the stratigraphy.
The komatiite itself is highly talc carbonate
ed with a predominance of talc-magnesite-amphibolite assembages suggesting an original orthocumulate derivation. Accessory minerals in the orebody include nickeline, gersdorffite
, millerite
, chromite
and occasionally other arsenic sulfide minerals.
Consonant with the practise of Western Mining Corporation naming mines after the drillers which first intersected the ore, Miitel is named after driller David Miitel.
Mariners has a current in-ground reserve of 105,000 tons @ 4.0% Ni for 4,020 nickel tons and an inferred resource
of 346,000 tons @ 4.5% Ni for a total of 15,700 nickel tons.
Mariners is hosted in a north plunging trough structure on the footwall of the Mariners Contact of the Widgiemooltha Komatiite and has the form of a series of partially overlapping kidney-shaped pods of nickel sulfide ore arranged en-echelon down the plunge line. This has been interpreted as disjunction and reassembly of an originally contiguous ribbon of nickel sulfide ore by structure.
Mariners is renowned for its extremely high arsenic
contents, with common arsenopyrite
, nickeline, gersdorffite
and other arseno-sulfide minerals common in the ore during the earlier years of mining. This has, at times, restricted the output from the Mariners mine due to the need to blend Mariners ore with lower arsenic feedstock to avoid penalties for excessive arsenic.
Similar to the Miitel orebody, Mariners is hosted in a strongly talc-carbonated komatiite, though magnesium contents are higher favoring a more talc-magnesite assemblage.
Mariners was not named by Western Mining. Instead, due to a flood on the salt lake inundating the drilling rig during its discovery, the orebody was named Mariners because the drills were under water at the time.
searching by Ross Kennedy, who is a redhead, hence "Red Ross".
Redross was mined via open pit initially with a decline added later to extract ore from underground. Mincor Resources NL is currently mining the last remnants of the orebody. Current resources and reserves are 297,000 tons @ 4.2% for 12,453 contained nickel tons.
The Redross N01C orebody has the form of a half-oval plunging to the south. The N01C is flanked by the N10 ore position which is interpreted to be flanking faces ore developed adjacent to the trough. Several parallel and sub-parallel ore trends are developed along strike from Redross, ncluding the N20, N20 Upper and N30 positions, none of which are currently economic.
The trough and ore is highly deformed and suffers significant post-deposition dislocation by a series of north-south trending strike-slip faults.
The komatiite locally is highly magnesian and favours talc-magnesite assemblages, having been intensely talc-carbonated. Accessory minerals observed in the ore body include nickeline, nickeliferous chalcopyrite, cuprous pentlandite, arsenian pentlandite, violarite
and arsenopyrite
.
Komatiite
Komatiite is a type of ultramafic mantle-derived volcanic rock. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content...
in the Yilgarn Craton
Yilgarn craton
The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...
of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
.
Stratigraphy
The stratigraphyStratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
of the Widgiemooltha Komatiite is well known to be part of the regional komatiite magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
tic event also seen at the Kambalda Dome, 50 kilometres (31 mi) to the north. There are comparisons which place the Widgiemooltha Komatiite as equivalent to the Silver Lake Komatiite. The Mt Edwards Basalt is correlated regionally with the Devon Consuls Basalt of Kambalda, and the Widgeimooltha Chert correlated with the Paringa Slate.
The structure of the Widgiemooltha Dome has three thrusted
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
repetitions of the basal komatiite contact and komatiite sequence including footwall Mt Edwards Basalt and hangingwall sediments (Widgiemooltha Chert).
Widgiemooltha Dome
The Widgiemooltha Komatiite is exposed around the margins of a large, 450 square kilometres (174 sq mi) graniteGranite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
dome
Dome (geology)
In structural geology, a dome is a deformational feature consisting of symmetrically-dipping anticlines; their general outline on a geologic map is circular or oval...
. The Widgiemooltha Granite is a coarse to medium, holocrystalline equigranlar granite with subordinate biotite and ferromagnesian minerals. It is mildly deformed, and is considered to have intruded concurrently with doming and uplift during late deformation. It is intrusive into the thrust repeated stratigraphy of the Widgiemooltha Komatiite and its sequence.
Lake Zot Dolerite
The Lake Zot Dolerite is similar to the Defiance Dolerite and other regionally important subvolcanicSubvolcanic rock
A subvolcanic rock, also known as a hypabyssal rock, is an igneous rock that originates at medium to shallow depths within the crust and contain intermediate grain size and often porphyritic texture. They have textures between volcanic and plutonic rocks. Subvolcanic rocks include diabase and...
doleritic sill
Sill (geology)
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet...
complexes throughout the Yilgarn Craton. Within the Widgiemooltha Dome area, the Lake Zot Dolerite can attain greater than 300 metres (984 ft) thickness and is intrusive into the hangingwall basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
and Widgiemooltha Chert above the Widgiemooltha Komatiite.
The dolerite is coarse grained in the main, often equigranular and holocrystalline although porphyritic areas are known and chilled margins and occasional compositional variations are noted. It is often epidotised, carbonated and sodium metasomatised
Metasomatism
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
in proximity to major structures. It can often be reasonably strained throughout its bulk and especially in the footwall contact with the Widgiemooltha Komatiite.
Widgiemooltha Chert
The Widgiemooltha Chert is a deep sea chemical sedimentary unit stratigraphically above the Widgiemooltha Komatiite. It is composed of from less than 1 metre (0.000621372736649807 mi) to 40 metre (0.0248549094659923 mi) of sulfidic, graphitic and siliceous chertChert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
s, often finely laminated and expressing ptygmatic folding post-sedimentation. It is considered to be an exhalative deposit formed post-magmatism. It often is intruded by the Lake Zot Dolerite.
The Widgiemooltha Chert is often the host of regional shears and thrusts.
Widgiemooltha Komatiite
The Widgiemooltha Komatiite is typically 30 metre (0.0186411820994942 mi) to 300 metre (0.186411820994942 mi) in apparent thickness, often with several clearly defined interflow sediment intervals and A1, A2, A3 spinifex textured zones and B2 zone cumulate zones developed rhythmically throughout. Depending on area and volcanic facies, there can be anywhere from greater than 24 individual flow units to as few as three flows within the Widgiemooltha Komatiite.The komatiite is typically of high magnesian character throughout, although flow top spinifex zones may get to as low as 18% MgO. Highest magnesium contents in rocks occur within the Wannaway area, with magnesium contents of up to 45% MgO reported from adcumulate serpentinite
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
lithologies in the basal flow.
The Widgiemooltha Komatiite is host to no less than 15 individual channelised kambalda type komatiitic nickel ore deposits
Kambalda type komatiitic nickel ore deposits
Kambalda type nickel ore deposits are a class of magmatic nickel-copper ore deposit in which the physical processes of komatiite volcanology serve to enrich, concentrate and deposit nickel-bearing sulfide within the lava flow environment of an erupting komatiite volcano.-Classification:The...
of which 5 have been mined, the remaining ten being of too low grade and low tenor to be economic at present. These features correlate with thickened komatiitic sequences, thick basal flows, trough like structural features and high magnesium lavas.
Mt Edwards Basalt
The footwall to the Widgiemooltha Komatiite is the Mt Edwards Basalt, which is a low to medium MgO maficMafic
Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...
extrusive rock, metamorphosed to upper greenschist
Greenschist
Greenschist is a general field petrologic term applied to metamorphic or altered mafic volcanic rock. The term greenstone is sometimes used to refer to greenschist but can refer to other rock types too. The green is due to abundant green chlorite, actinolite and epidote minerals that dominate the...
facies. Mineralogy is chlorite
Chlorite group
The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn....
, actinolite
Actinolite
Actinolite is an amphibole silicate mineral with the chemical formula .-Etymology:The name actinolite is derived from the Greek word aktis , meaning "beam" or "ray", because of the mineral's fibrous nature...
, rare epidote
Epidote
Epidote is a calcium aluminium iron sorosilicate mineral, Ca2Al2O, crystallizing in the monoclinic system. Well-developed crystals are of frequent occurrence: they are commonly prismatic in habit, the direction of elongation being perpendicular to the single plane of symmetry. The faces are often...
, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
and albite
Albite
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...
. The Mt Edwards Basalt has uncommon interflow sedimentary intervals and some well developed pillow basalt flow tops which give regional facing directions. The true thickness of the Mt Edwards Basalt is unknown.
Economic Importance
The Widgiemooltha Komatiite is an important host for Kambalda type komatiitic nickel ore depositsKambalda type komatiitic nickel ore deposits
Kambalda type nickel ore deposits are a class of magmatic nickel-copper ore deposit in which the physical processes of komatiite volcanology serve to enrich, concentrate and deposit nickel-bearing sulfide within the lava flow environment of an erupting komatiite volcano.-Classification:The...
.
Nickel ore has been found at several locations around the Widgiemooltha Dome and has been mined from six locations, with four underground mines in operation as of 2007 and a proposed open cut mine for mid-2007. Further exceptionally high-grade gold mineralisation is present at Wattle Dam, to 6kg (200 Oz) to the ton, within the Widgiemooltha Komatiite.
132 North
From Nickel et al. (1994)The 132 North deposit was discovered by in 1968 by International Nickel Australia Limited via gossan
Gossan
Gossan is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the classic gossan or iron cap all that remains is iron oxides and quartz often in the form of boxworks, quartz lined cavities retaining the shape of the dissolved...
searching and mined by Western Mining Corporation in 1981, with 900 tons of nickel metal produced. It was a small pod of low-grade nickel sulfide mineralisation hosted in a parasitic isoclinal syncline
Syncline
In structural geology, a syncline is a fold, with younger layers closer to the center of the structure. A synclinorium is a large syncline with superimposed smaller folds. Synclines are typically a downward fold, termed a synformal syncline In structural geology, a syncline is a fold, with younger...
developed on the 132 Anticline on the northern flank of the Widgiemooltha Dome. The 132 North and Widgiemooltha Townsite nickel gossans are mineralogical laboratories and contain exceptionally rare minerals.
The ore profile of the 132 North deposit is, from base upwards, 0.1 to 1m of massive pentlandite
Pentlandite
Pentlandite is an iron-nickel sulfide, 9S8. Pentlandite usually has a Ni:Fe ratio of close to 1:1. It also contains minor cobalt.Pentlandite forms isometric crystals, but is normally found in massive granular aggregates. It is brittle with a hardness of 3.5 - 4 and specific gravity of 4.6 - 5.0 and...
-pyrrhotite
Pyrrhotite
Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...
-pyrite-chalcopyrite
Chalcopyrite
Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black.On exposure to air, chalcopyrite...
sulfide, matrix sulfide containing 40-80% sulfide, and disseminated sulfide. Accessory nickeline and gersdorffite
Gersdorffite
Gersdorffite is a nickel arsenic sulfide mineral with formula NiAsS. It crystallizes in the isometric system showing diploidal symmetry. It occurs as euhedral to massive opaque, metallic grey-black to silver white forms. Gersdorffite belongs to a solid solution series with cobaltite, CoAsS....
are reported. The transition zone supergene
Supergene (geology)
In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary sulfide ore minerals and...
sulfide phases include; violarite
Violarite
Violarite is a supergene sulfide mineral associated with the weathering and oxidation of primary pentlandite nickel sulfide ore minerals....
, smythite, covellite
Covellite
Covellite is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is ubiquitous in copper ores, it is found in limited abundance and is not an important ore of copper itself, although it is well known to mineral collectors.The mineral is associated with chalcocite in zones...
, chalcocite
Chalcocite
Chalcocite, copper sulfide , is an important copper ore mineral. It is opaque, being colored dark-gray to black with a metallic luster. It has a hardness of 2½ - 3. It is a sulfide with an orthorhombic crystal system....
and marcasite
Marcasite
The mineral marcasite, sometimes called white iron pyrite, is iron sulfide with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both structures do have in common that they contain the disulfide...
after pyrite.
The nickel sulfides within the regolith
Regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...
have been oxidised into a complex series of weathering fronts including a rare expression of a carbonate front which has resulted in a host of unusual nickel carbonate, arsenate and silicate minerals such as gaspeite
Gaspeite
Gaspeite is an extremely rare nickel carbonate mineral named for the place it was first described, in the Gaspé Peninsula, Canada.Gaspeite's formula is CO3 and it is a bright green mineral. It forms massive to reniform pappillary aggregates in fractures, bottryoidal concretions in laterite or...
, atacamite
Atacamite
Atacamite is a copper halide mineral: a copper chloride hydroxide with formula Cu2Cl3.It was first described for deposits in the Atacama Desert of Chile in 1801....
, annabergite
Annabergite
Annabergite is an arsenate mineral consisting of a hydrous nickelarsenate, Ni32·8H2O, crystallizing in the monoclinic system and isomorphous with vivianite and erythrite. Crystals are minute and capillary and rarely met with, the mineral occurring usually as soft earthy masses and encrustations. A...
, carrboydite, glaucospaerite, hydrohonessite, kambaldaite
Kambaldaite
Kambaldaite, NaNi433·3H2O, is an extremely rare hydrated sodium nickel carbonate mineral described from gossanous material associated with Kambalda type komatiitic nickel ore deposits at Kambalda, Western Australia, and Widgie Townsite nickel gossan, Widgiemooltha, Western Australia.Kambaldaite...
, népouite
Népouite
Népouite is a rare nickel silicate mineral which has the apple green colour typical of such compounds. It was named by E Glasser in 1907 after the place where it was first described , the Népoui Mine, Népoui, Nouméa Commune, Northern Province, New Caledonia...
, nullaginite, pecoraite, olivenite
Olivenite
Olivenite is a copper arsenate mineral, formula Cu2AsO4OH. It crystallizes in the monoclinic system , and is sometimes found in small brilliant crystals of simple prismatic habit terminated by domal faces...
, otwayite
Otwayite
Otwayite, Ni2CO32, is a hydrated nickel carbonate mineral. Otwayite is green, with a hardness of 4, a specific gravity of 3.4, and crystallises in the orthorhombic system.- Occurrence :...
, reevesite, retgersite, takovite and of course widgiemoolthalite.
Miitel
The Miitel nickel mine was first discovered in the early to late 1970s by Union Miniere and Anaconda Resources, though due to poor understanding of the geology the initial intercepts were not sufficiently followed up until the early 1990s by Western Mining Corporation. The Miitel orebody has been successfully extended in size and tonnage from successive exploration efforts, most recently by Mincor Resources NL in 2002-2005, resulting in the "discovery" of the South Miitel extension.The Miitel nickel mine has produced to date 1.56 million tons at 3.5% Ni for 47,250 tonnes of contained nickel. Reserves as of December 2006 were 481,000 tons @ 3.5% Ni for 16,835 Ni tons in North Miitel and 298,000 tons @ 3.8% Ni for 12,282 nickel tons in South Miitel. The Miitel mine is accessed by a single decline which splits into two separate declines which drive upon the north and south Miitel ore positions. The ore is mined by 'flatbacking', which is a form of cut and fill mining.
The Miitel orebody is situated on the eastern flank of the Widgiemooltha Dome on the Miitel Contact of the Widiemooltha Komatiite, and has the form of an arcuate boomerang
Boomerang
A boomerang is a flying tool with a curved shape used as a weapon or for sport.-Description:A boomerang is usually thought of as a wooden device, although historically boomerang-like devices have also been made from bones. Modern boomerangs used for sport are often made from carbon fibre-reinforced...
which plunges away to the north and south. The Widgiemooltha Komatiie forms a recognisable trough structure which is the idealised form of a komatiitic nickel orebody. Ore is a highly strained massive to matrix olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
-sulfide adcumulate with a fine pyrrhotite
Pyrrhotite
Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...
-pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
groundmass and prominent pentlandite
Pentlandite
Pentlandite is an iron-nickel sulfide, 9S8. Pentlandite usually has a Ni:Fe ratio of close to 1:1. It also contains minor cobalt.Pentlandite forms isometric crystals, but is normally found in massive granular aggregates. It is brittle with a hardness of 3.5 - 4 and specific gravity of 4.6 - 5.0 and...
porphyroblast
Porphyroblast
A porphyroblast is a large mineral crystal in a metamorphic rock which has grown within the finer grained groundmass. Porphyroblasts are commonly euhedral crystals, but can also be partly to completely irregular in shape....
s.
The influence of structure on the Miitel orebody is minimal except between the central Miitel and South Miitel ore pods and the current northern extent of the North Miitel ore trend where later, brittle faults disturb and offset the stratigraphy.
The komatiite itself is highly talc carbonate
Talc carbonate
Talc carbonate is a geologic term for a suite of rock and mineral compositions found in metamorphic ultramafic rocks.The term refers to the two most common end-member minerals found within ultramafic rocks which have undergone talc-carbonation or carbonation reactions, talc and the carbonate...
ed with a predominance of talc-magnesite-amphibolite assembages suggesting an original orthocumulate derivation. Accessory minerals in the orebody include nickeline, gersdorffite
Gersdorffite
Gersdorffite is a nickel arsenic sulfide mineral with formula NiAsS. It crystallizes in the isometric system showing diploidal symmetry. It occurs as euhedral to massive opaque, metallic grey-black to silver white forms. Gersdorffite belongs to a solid solution series with cobaltite, CoAsS....
, millerite
Millerite
Millerite is a nickel sulfide mineral, NiS. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates...
, chromite
Chromite
Chromite is an iron chromium oxide: FeCr2O4. It is an oxide mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite ; substitution of aluminium occurs leading to hercynite .-Occurrence:Chromite is found in...
and occasionally other arsenic sulfide minerals.
Consonant with the practise of Western Mining Corporation naming mines after the drillers which first intersected the ore, Miitel is named after driller David Miitel.
Mariners
The Mariners nickel mine was originally drilled in the 1970s by Union Miniere and Anaconda Resources, with an intercept of 12m @ 0.7% Ni being delivered from a flanking position, which was not sufficiently followed up. Mariners was then left until the late 1980s and early 1990s when Western Mining Corporation undertook exploration and defined the N01 ore pod and developed the mine via a decline from Wedding Guest island, in the middle of the Lake Zot salt lake.Mariners has a current in-ground reserve of 105,000 tons @ 4.0% Ni for 4,020 nickel tons and an inferred resource
Mineral resource classification
Mineral resource classification is the classification of mineral deposits based on their geologic certainty and economic value.Mineral deposits can be classified as:...
of 346,000 tons @ 4.5% Ni for a total of 15,700 nickel tons.
Mariners is hosted in a north plunging trough structure on the footwall of the Mariners Contact of the Widgiemooltha Komatiite and has the form of a series of partially overlapping kidney-shaped pods of nickel sulfide ore arranged en-echelon down the plunge line. This has been interpreted as disjunction and reassembly of an originally contiguous ribbon of nickel sulfide ore by structure.
Mariners is renowned for its extremely high arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
contents, with common arsenopyrite
Arsenopyrite
Arsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
, nickeline, gersdorffite
Gersdorffite
Gersdorffite is a nickel arsenic sulfide mineral with formula NiAsS. It crystallizes in the isometric system showing diploidal symmetry. It occurs as euhedral to massive opaque, metallic grey-black to silver white forms. Gersdorffite belongs to a solid solution series with cobaltite, CoAsS....
and other arseno-sulfide minerals common in the ore during the earlier years of mining. This has, at times, restricted the output from the Mariners mine due to the need to blend Mariners ore with lower arsenic feedstock to avoid penalties for excessive arsenic.
Similar to the Miitel orebody, Mariners is hosted in a strongly talc-carbonated komatiite, though magnesium contents are higher favoring a more talc-magnesite assemblage.
Mariners was not named by Western Mining. Instead, due to a flood on the salt lake inundating the drilling rig during its discovery, the orebody was named Mariners because the drills were under water at the time.
Redross
Redross was explored by Anaconda Resources in the 1970s and was identified by gossanGossan
Gossan is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the classic gossan or iron cap all that remains is iron oxides and quartz often in the form of boxworks, quartz lined cavities retaining the shape of the dissolved...
searching by Ross Kennedy, who is a redhead, hence "Red Ross".
Redross was mined via open pit initially with a decline added later to extract ore from underground. Mincor Resources NL is currently mining the last remnants of the orebody. Current resources and reserves are 297,000 tons @ 4.2% for 12,453 contained nickel tons.
The Redross N01C orebody has the form of a half-oval plunging to the south. The N01C is flanked by the N10 ore position which is interpreted to be flanking faces ore developed adjacent to the trough. Several parallel and sub-parallel ore trends are developed along strike from Redross, ncluding the N20, N20 Upper and N30 positions, none of which are currently economic.
The trough and ore is highly deformed and suffers significant post-deposition dislocation by a series of north-south trending strike-slip faults.
The komatiite locally is highly magnesian and favours talc-magnesite assemblages, having been intensely talc-carbonated. Accessory minerals observed in the ore body include nickeline, nickeliferous chalcopyrite, cuprous pentlandite, arsenian pentlandite, violarite
Violarite
Violarite is a supergene sulfide mineral associated with the weathering and oxidation of primary pentlandite nickel sulfide ore minerals....
and arsenopyrite
Arsenopyrite
Arsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
.
See also
- SerpentiniteSerpentiniteSerpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
- MetamorphismMetamorphismMetamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
- KomatiiteKomatiiteKomatiite is a type of ultramafic mantle-derived volcanic rock. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content...
- Ore genesisOre genesisThe various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....
- Talc carbonateTalc carbonateTalc carbonate is a geologic term for a suite of rock and mineral compositions found in metamorphic ultramafic rocks.The term refers to the two most common end-member minerals found within ultramafic rocks which have undergone talc-carbonation or carbonation reactions, talc and the carbonate...