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45-741: The stratigraphy of the Widgiemooltha Komatiite is well known to be part of the regional komatiite magmatic 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

90-460: A decline was 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

135-436: A section. The samples are analyzed to determine their detrital remanent magnetism (DRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. For sedimentary rocks this is possible because, as they fall through the water column, very fine-grained magnetic minerals (< 17  μm ) behave like tiny compasses , orienting themselves with Earth's magnetic field . Upon burial, that orientation

180-498: 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. The Widgiemooltha Komatiite is an important host for Kambalda type komatiitic nickel ore deposits . Nickel ore has been found at several locations around

225-431: Is also commonly used to delineate the nature and extent of hydrocarbon -bearing reservoir rocks, seals, and traps of petroleum geology . Chronostratigraphy is the branch of stratigraphy that places an absolute age, rather than a relative age on rock strata . The branch is concerned with deriving geochronological data for rock units, both directly and inferentially, so that a sequence of time-relative events that created

270-534: Is due to physical contrasts in rock type ( lithology ). This variation can occur vertically as layering (bedding), or laterally, and reflects changes in environments of deposition (known as facies change). These variations provide a lithostratigraphy or lithologic stratigraphy of the rock unit. Key concepts in stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries imply about their original depositional environment. The basic concept in stratigraphy, called

315-588: Is intruded by the Lake Zot Dolerite. The Widgiemooltha Chert is often the host of regional shears and thrusts. The Widgiemooltha Komatiite is typically 30 metres (0 mi) to 300 metres (0 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

360-595: 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. The Lake Zot Dolerite is similar to the Defiance Dolerite and other regionally important subvolcanic doleritic sill complexes throughout the Yilgarn Craton. Within the Widgiemooltha Dome area,

405-411: Is preserved. For volcanic rocks, magnetic minerals, which form in the melt, orient themselves with the ambient magnetic field, and are fixed in place upon crystallization of the lava. Oriented paleomagnetic core samples are collected in the field; mudstones , siltstones , and very fine-grained sandstones are the preferred lithologies because the magnetic grains are finer and more likely to orient with

450-551: 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 porphyroblasts . 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

495-431: The law of superposition , states: in an undeformed stratigraphic sequence, the oldest strata occur at the base of the sequence. Chemostratigraphy studies the changes in the relative proportions of trace elements and isotopes within and between lithologic units. Carbon and oxygen isotope ratios vary with time, and researchers can use those to map subtle changes that occurred in the paleoenvironment. This has led to

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540-547: The natural remanent magnetization (NRM) to reveal the DRM. Following statistical analysis, the results are used to generate a local magnetostratigraphic column that can then be compared against the Global Magnetic Polarity Time Scale. This technique is used to date sequences that generally lack fossils or interbedded igneous rocks. The continuous nature of the sampling means that it is also a powerful technique for

585-491: 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

630-479: 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

675-551: 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

720-556: 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 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

765-566: 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). The Widgiemooltha Komatiite is exposed around the margins of a large, 450 square kilometres (174 sq mi) granite dome . The Widgiemooltha Granite is a coarse to medium, holocrystalline equigranular granite with subordinate biotite and ferromagnesian minerals. It

810-542: 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 6 kg (200 Oz) to the ton, within the Widgiemooltha Komatiite. From Nickel et al. (1994) 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

855-457: 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

900-546: 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 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,

945-588: The ambient field during deposition. If the ancient magnetic field were oriented similar to today's field ( North Magnetic Pole near the North Rotational Pole ), the strata would retain a normal polarity. If the data indicate that the North Magnetic Pole were near the South Rotational Pole , the strata would exhibit reversed polarity. Results of the individual samples are analyzed by removing

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990-577: The dissolved ore minerals). In other cases, quartz and iron oxides, limonite , goethite , and jarosite , exist as pseudomorphs, replacing the pyrite and primary ore minerals. Frequently, gossan appears as a red "stain" against the background rock and soil, due to the abundance of oxidized iron; the gossan may be a topographic positive area due to the abundance of erosion -resistant quartz and iron oxides. Although most gossans are red, orange, or yellow, black gossans from manganese oxides such as pyrolusite , manganite , and especially psilomelane form at

1035-436: The drillers which first intersected the ore, Miitel is named after driller David Miitel. 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

1080-409: The estimation of sediment-accumulation rates. Gossan Gossan ( eiserner hut or eisenhut ) 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 (which are quartz-lined cavities retaining the shape of

1125-451: The footwall contact with the Widgiemooltha Komatiite. 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 mi) to 40 metres (0 mi) of sulfidic, graphitic and siliceous cherts , often finely laminated and expressing ptygmatic folding post-sedimentation. It is considered to be an exhalative deposit formed post-magmatism. It often

1170-512: The gap may be due to removal by erosion, in which case it may be called a stratigraphic vacuity. It is called a hiatus because deposition was on hold for a period of time. A physical gap may represent both a period of non-deposition and a period of erosion. A geologic fault may cause the appearance of a hiatus. Magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout

1215-528: 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

1260-593: The ore body include nickeline , nickeliferous chalcopyrite, cuprous pentlandite, arsenian pentlandite, violarite and arsenopyrite . Stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers ( strata ) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks . Stratigraphy has three related subfields: lithostratigraphy (lithologic stratigraphy), biostratigraphy (biologic stratigraphy), and chronostratigraphy (stratigraphy by age). Catholic priest Nicholas Steno established

1305-452: 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

1350-558: The oxidized portion of manganese-rich mineral deposits. In the 19th and 20th centuries, gossans were important guides to buried ore deposits used by prospectors in their quest for metal ores. An experienced prospector could read the clues in the structure of the gossans to determine the type of mineralization likely to be found below the iron cap . The name gossan appears to come from Cornish miner's slang. The terms "iron cap" and "iron hat", common in America, are direct translations from

1395-403: 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. The footwall to the Widgiemooltha Komatiite is the Mt Edwards Basalt, which is a low to medium MgO mafic extrusive rock, metamorphosed to upper greenschist facies. Mineralogy

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1440-437: The rock layers. Strata from widespread locations containing the same fossil fauna and flora are said to be correlatable in time. Biologic stratigraphy was based on William Smith's principle of faunal succession , which predated, and was one of the first and most powerful lines of evidence for, biological evolution . It provides strong evidence for the formation ( speciation ) and extinction of species . The geologic time scale

1485-480: The rocks formation can be derived. The ultimate aim of chronostratigraphy is to place dates on the sequence of deposition of all rocks within a geological region, and then to every region, and by extension to provide an entire geologic record of the Earth. A gap or missing strata in the geological record of an area is called a stratigraphic hiatus. This may be the result of a halt in the deposition of sediment. Alternatively,

1530-405: The significance of strata or rock layering and the importance of fossil markers for correlating strata; he created the first geologic map of England. Other influential applications of stratigraphy in the early 19th century were by Georges Cuvier and Alexandre Brongniart , who studied the geology of the region around Paris. Variation in rock units, most obviously displayed as visible layering,

1575-406: The specialized field of isotopic stratigraphy. Cyclostratigraphy documents the often cyclic changes in the relative proportions of minerals (particularly carbonates ), grain size, thickness of sediment layers ( varves ) and fossil diversity with time, related to seasonal or longer term changes in palaeoclimates . Biostratigraphy or paleontologic stratigraphy is based on fossil evidence in

1620-403: The stratigraphy. The komatiite itself is highly talc carbonateed with a predominance of talc-magnesite-amphibolite assemblages 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

1665-429: The theoretical basis for stratigraphy when he introduced the law of superposition , the principle of original horizontality and the principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment. The first practical large-scale application of stratigraphy was by William Smith in the 1790s and early 19th century. Known as the "Father of English geology", Smith recognized

1710-532: The trough. Several parallel and sub-parallel ore trends are developed along strike from Redross, including 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

1755-745: 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

1800-525: Was developed during the 19th century, based on the evidence of biologic stratigraphy and faunal succession. This timescale remained a relative scale until the development of radiometric dating , which was based on an absolute time framework, leading to the development of chronostratigraphy. One important development is the Vail curve , which attempts to define a global historical sea-level curve according to inferences from worldwide stratigraphic patterns. Stratigraphy

1845-417: 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

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1890-497: Was initially placed on care and maintenance prior to being activated in late 1974. The mine was worked from late 1974 to early 1976, when it was closed due to unprofitability. Poor management within Anaconda Resources and low nickel prices led to its demise. The ore from Redross was trucked to Kalgoorlie for treatment in double belly-dumper roadtrains by Gascoyne Trading, the transport division of Wesfarmers. The Redross shaft

1935-458: Was initially worked on a two-shift basis, but around May 1975, the operation was extended to three shifts. The workers at Redross were housed in Norseman and were bussed to the mine at every shift changeover. Anaconda spent a large amount of money installing many houses in Norseman for their Redross employees, and many of these houses are still there (2012). A vertical mine shaft similar to Redross

1980-434: 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 was explored by Anaconda Resources in the late 1960s and was identified by gossan searching by Ross Kennedy, who is a redhead, hence "Red Ross". Redross was mined initially via a vertical shaft sunk in 1971-72, which

2025-468: Was sunk on the nearby Wannaway ore reserve in 1971-72, and this shaft, headframe and buildings were also placed on care and maintenance. The Wannaway shaft was never activated as an operating vertical shaft mine, and was vandalised over many years and finally dismantled. An open pit commenced on the Redross minesite in the early 1990s to extract the remnants and extensions of the original Redross ore body, and

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