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Felbertal, Mittersill (Tux, Kleinartal, Sillian-Innervillgraten) |
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Austria |
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W
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Super Porphyry Cu and Au
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The Felbertal or Mittersill Scheelite Mine is located some 8 km to the south of the town of Mittersill, 80 km SW of Salzburg, 30 km South of Kitzbühel and 339 km SW of Vienna in the Alps of the state of Salzburg in western Austria (#Location: 47° 12' 10"N, 12° 29' 6"E).
The mine is owned and operated by Wolfram Bergbau-und Huttengesellschaft mbH (Wolfram Mining and Smelting), whose major shareholders originally included Metallgesellschaft AG (of Germany) Voest Alpine AG (the Austrian Steel group) and Teledyne Wah Chang (of the USA).
The Felbertal Scheelite Deposit is one of a large number of known occurrences and showings within the Palaeozoic of the Eastern Alps in western Austria. The Felbertal outcrop was located in mid 1967 by Dr Holl of Munich following the location of a 100 ppm WO3 anomaly at the mouth of the Felbertal River near Mittersill. This anomaly was obtained from an un-sieved stream sediment sample collected some 8 km below the deposit, representing a total catchment of approximately 120 km2. Other scheelite mineralisation is found within the same catchment. This anomaly was obtained from a regional broad drainage sampling program initiated by Professor Maucher of Munich University to locate 'stratiform' Hg-Sb-W mineralisation.
Metallgesellschaft AG commenced exploration of the prospect in 1968 and by 1973 had completed 6000 m of drilling and 700 m of underground testing. Mining commenced in 1975 after a total infrastructure expenditure of DM 150 million (approx. $US 70 million at current exchange rates). Production commenced as an open pit mine in the East Field, but since 1986 only underground mining has occurred in the West Field producing ~1200 t of W per annum.
Regional Setting
The oldest outcrops identified in the Eastern Alps represent deposition within a Caledonian basin, developed on the southern margin of a continental block of Precambrian rocks which now outcrop in southern Germany. This deposition was within a locally very mobile sedimentary basin composed of a series of elongate troughs and ridges. Deposition within the Caledonian basin commenced in the Late Ordovician. Due to the masking affect of the later Variscan (Permo-Carboniferous) and Alpidian (Tertiary) metamorphism, no definite pre-Ordovician sequences are recognised.
The sequences of the basin have been intensely deformed by the horizontal thrusts and nappes of the Alpine orogeny. Within the Eastern Alps, four slices of the same sequence have been stacked one on top of the other, separated by horizontal thrusts. Each horizontal slice represents facies from different sections of the basin. The lowest was deposited to the north while the uppermost was from furthest to the south. The slices, or tectonic units, represent different facies assemblages of the same sequence and are from top to bottom the Upper, Middle and Lower Austro-Alpine Unit, and the Penninic Zone.
The Habach Series, which hosts the Felbertal deposit, belongs to the Penninic Zone, which represents the northern margin of the original basin.
Deposition within the Caledonian basin commenced with a widespread argillaceous to arenaceous sequence overlain by mafic and minor ultramafic submarine volcanics. In the southern section of the basin, the mafic volcanism began in the Late Ordovician and had ended before the commencement of the Silurian. Other mafic developments are found within the basin, the most significant being the Siluro-Devonian mafic to ultramafic volcanic rocks of the Habach Series, near the northern margin of the trough.
During the Ordovician-Silurian transition, the southernmost section of the trough was uplifted accompanied by the development of a sequence of felsic volcanic rocks. The main pile of the latter, which is both sub-aqueous and sub-aerial, was deposited to the south, although they are also present but to a much lesser degree over the remainder of the trough, even in the Penninic zone.
Holl and Maucher (1976) interpret these volcanic rocks as being of palingenetic origin not related directly to the mafics of the sequence.
During the Upper Silurian to Lower Devonian, which marks the transition from the Caledonian to Variscan cycles, the basin shallowed, resulting in the change from shales and greywackes (the latter predominating to the north) to quartz-phyllites with carbonate lenses and evaporites. The Habach Series mafic volcanic rocks were deposited during this transition in the north. Limestones became important during the Mesozoic.
Palingenetic-migmatite granitic gneiss complexes yielding oldest Variscan age (Permian) dates are found within the Penninic Zone.
Regional Mineralisation
There is a well defined zonation of mineralisation types within the tectonic units (or thrust slices) of the Eastern Alps, i.e., across the original depositional basin from north to south at right angles to the axis of the trough. This zonation is as follows:
• Upper Austro-Alpine Unit - contains cinnabar;
• Middle Austro-Alpine Unit - scheelite/stibnite & scheelite/arsenopyrite mineralisation associated with graphitic schist and/or carbonates and sometimes mafic tuff lenses;
• Lower Austro-Alpine Unit - pure, almost Mo free scheelite mineralisation in carbonates with accompanying mafic volcanic lenses;
• Penninic Zone - scheelite with lesser accompanying Mo, Bi, Be, Cu, Au and Ag in mafic volcanic successions.
The principal scheelite deposits and occurrences of the Eastern Alps, and the related regional distribution of mineralisation can be summarised as follows:
Felbertal - Finely banded scheelite mineralisation is intimately associated with lenses of banded quartz-albite gneiss from 1 to 15 m thick, and/or quartzite rich bands developed over intervals of up to 10 m or more. These albite gneisses and quartzite rich bands often occur together, and are found in association with two or three 20 to 100 m thick coarse grained hornblende gneiss and amphibolite units, all contained within the lower 300 to 400 m of the Habach Series Volcanic Succession in the Penninic Zone. This Volcanic Succession comprises metamorphosed massive tholeiitic lavas and tuffs with minor clastic sediments & virtually no carbonates. The albite gneisses are believed to be ex-intermediate volcanics, while the quartzites, which are present as massive beds up to 1 m thick and as abundant laminae from 1 mm to 1 cm thick, appear to be metamorphosed cherts.
Orebodies are found in two adjacent fields, separated by a major fault. In the East Field, a single elongate body is known. This is some 2500 m long, with down dip dimensions of between 50 to 150 m (seldom exceeding 100 m), and a central maximum thickness of up to 20 m. The West Field orebodies comprise three 5 to 10 m thick, roughly equi-dimensional lenses, with diameters in excess of 150 m. They are embraced by a low grade hornblende schist (ex-mafic volcanic) unit some 50 m thick which carries 0.15 to 0.20% WO3. The average grade of the orebodies is around 0.75% WO3.
The coarse hornblende gneisses and amphibolites vary in thickness inversely to the mineralised rocks, in a manner suggesting that they represent positive features, limiting and separating, narrow depositional basins within which the ore bearing units were deposited. Mineralised horizons are not continuous between these individual basins, although the coarse hornblende gneisses and amphibolites carry several tens of ppm WO3 as disseminated scheelite both below, between and along strike from the ore zones over thicknesses of up to 400 m. The coarse hornblende gneiss-amphibolite horizons are lithologically traceable for a distance of around 30 km along strike. Sporadically along these horizons, impregnations of scheelite assaying up to 0.05% WO3 are found over thicknesses of 1 m or so within larger thicknesses of sparsely disseminated scheelite averaging between 20 and 100 ppm WO3.
Some 7 km to the north west of Felbertal, sulphide rich bodies 'several metres' thick carry stratabound galena, sphalerite and fluorite with associated minor scheelite, chalcopyrite, pyrite, pyrrhotite and arsenopyrite. These bodies average some 5 to 6% combined Pb + Zn. Copper, molybdenum and gold are also found at the same stratigraphic level in the same area.
Tux - Approximately 55 km to the west of Felbertal, within the quartz-phyllites of the Lower Austro-Alpine Unit, economic 'bedding coltrolled' scheelite mineralisation occurs within a 3 m thick graphitic schist horizon. Lower grade scheelite is also found within the overlying dolomite-magnesite bed which is several tens of metres in thickness. The two units are separated by 15 m of quartz-phyllite. The main lower orebody has lateral dimensions of 400 x 500 m. Ore mineralisation is closely related to the distribution of the graphitic schist lens. Intercalations of mafic metavolcanic rocks are found locally within the footwall of the scheelite mineralisation. This deposit is believed to be a time equivalent of the Felbertal orebody. See also the separate Tux, Lanersbach record.
Kleinartal - which is located approximately 120 and 70 km to the east of Tux and Felbertal respectively. Ore grade scheelite occurs within a carbonate unit of the Lower Austro-Alpine Unit. This deposit is believed to be at a similar stratigraphic level to both Tux and Felbertal. The mineralised carbonate ranges from a few tens of centimetres to 20 m in thickness, and is in general, a pale grey, coarse grained, slightly siliceous, iron bearing dolomite. Locally it encloses thin intercalations of quartzite, quartz phyllite, black and grey phyllite, and dark limestone lenses up to a few metres in thickness. In places, the dolomite lenses out into a fine grained, grey to black, well bedded, graphitic limestone. The carbonate unit is embraced by a quartz-phyllite sequence and is locally underlain by mafic and acid metavolcanics (Holl 1977). The main scheelite deposit has a strike length of 300 m. A number of smaller beds outcrop within the main carbonate bed over an area of around 15 km2, while sporadic scheelite grains can be traced over a strike length of 1.5 km within iron bearing dolomites at one locality. Mineralisation occurs as bedding controlled scheelite, as fracture coatings and small high grade pockets within the main pods at Kleinartal.
Sillian-Innervillgraten - on the Austro-Italian border, some 50 km to the south-southwest of Felbertal, where scheelite mineralisation is found within a mafic metavolcanic unit (mainly of tuffaceous origin) embraced by the Thurntaler quartz-phyllite succession of the Middle Austro-Alpine Unit. The uppermost sections of the Thurntaler quartz phyllite unit comprise quartz-phyllites, chlorite-phyllites, chlorite-epidote-schists, and quartzite layers, while the mineralisation is hosted by the central sections which are composed of 200 m of mainly mafic and lesser acid metavolcanics and intercalated quartzites and graphite schists. The lower sections are principally interbedded mica-schists and quartz-phyllites.
Within the volcanic unit, mineralisation is present at three levels. The lowest comprises small low grade (0.2 to 0.3% WO3) pods. The central horizon is hornblende rich and is only weakly mineralised. The upper lens, which is conformable and carries finely banded scheelite, has been traced over a 1.45 km strike length and is around 3 m thick with an indicated grade of 0.45% WO3. Discordant quartz, carbonate and scheelite veins, veinlets and pockets are widespread through the concordant bodies, while stibnite and arsenopyrite are also found within the ore zone. The mineralised sections of the mafic meta-volcanics do not apparently have accompanying albite gneisses and quartzites of the type regarded as critical at Felbertal. This deposit is also believed to be Late Silurian in age.
Miscellaneous Occurrences - Quartz rich scheelite bearing veins cut the Central Gneiss at a number of localities within the Felbertal area.
Geology - The Mittersill Area
The Felbertal Scheelite deposit lies in the Penninic Zone of the Eastern Alps, where it is exposed within the east-west elongated Tauren Window which has dimensions of some 160 x 35 km and is framed by sedimentary and lesser volcanic rocks of the Lower Austro-Alpine Unit. The geology of the area can be summarised as follows:
Penninic Zone
• Central Gneiss - The Central Gneiss predominantly comprises gneissose, palingenetic-migmatites and anatexites with associated smaller bodies of granite, aplite, granodiorite, tonalite and grano-syenite. The two main central gneiss bodies have been sub-divided into two facies, one with a predominantly granitic and the other with a tonalitic composition. The age of these bodies is masked by Alpidian and Variscan events, the oldest dating being Permian. As they are taken to be of anatectic-palingenetic origin and differ in composition to the Palaeozoic sequences, they probably originate from pre-Ordovician lithologies.
• Old Crystalline Amphibolites - These metamorphics show relicts of earlier metamorphism, most of which has been obliterated by Alpidian re-crystallisation. They rim the Granatspitze Central Gneiss Mass and may be Late Ordovician in age or older. Two sub divisions have been recognised:
- Old Crystallines of the Zwolferzuges - These comprise alternations of coarse banded amphibolite and subordinate garnet-amphibolite, muscovite-plagioclase gneiss, muscovite-schist and lesser intercalations of garnet-mica schist and hornblendite. This sequence is "several hundred" metres thick.
- Basal Amphibolite Succession - This subdivision occupies the lowest position around the Granatspitze (or easternmost) Central Gneiss Mass. The sequence is predominantly medium to coarse grained, dark amphibolites with associated biotite-plagioclase gneiss and sericite-amphibolite. It is believed to represent original magmatic rock types, principally gabbroic intrusions, although the recognition of some pyroclastic textures indicates a partial extrusive character. This sequence has tectonic contacts both below with the Central Gneiss and above. It is 15 to 100 m thick in the Odbach and 300 to 400 m in the Felberbach.
• Serpentinite - A few relatively small serpentinite bodies are found within the sequence.
• Mixed Gneisses - A number of tectonic slices of Central Gneiss and Habach Series schists and gneisses occur as thrusted sheets overlying the main Habach Series metamorphics. These slices are largely Habach Series but also include biotite-gneiss with subordinate amphibolite, prasinite (a green schist with equal proportions of hornblende, chlorite and epidote) and mica schist.
• Habach Series - This sequence hosts the Felbertal Scheelite Deposit and is the most widespread unit within the Tauren Window which covers a 40 x 20 km area. The Habach Series is believed to have been deposited during the Silurian to Devonian transition. It can be subdivided into three major units, not all of which are always present at any one point. The three units are, from the base:
- Basal Schist Succession - This sequence is largely made up of arenaceous and argillaceous sediment derived metamorphics with abundant volcanogenic material representing precursors of the following widespread extrusives. It is represented by chlorite-schists and gneisses with intercalated hornblende-schists. The succession is some 400 m thick in the Amertal and Felbertal, but only around 100 m thick elsewhere.
- Volcanic Succession - This succession is principally hornblendite and hornblende-schist representing metamorphosed mafic lavas and tuffs. It marks an abrupt end to the sediments of the Basal Schist and sudden increase in the MgO content of the rocks.
This succession is well banded with very minor intercalated units of intermediate and acid volcanics which are mainly found higher in the sequence. Minor intercalations of mafic lavas and tuffs, phyllites, cherts and reworked volcanic material separate the much better developed, more homogeneous, mafic (tholeiitic) volcanics. Mica schists and phyllites of sedimentary origin are rare as are the few thin ferruginous dolomite and ankerite lenses.
The succession reaches its maximum thickness of around 3000 m in the Hollersbach-Xabach area interpreted as representing a volcanic centre, while at Felbertal the sequence is around 1500 m thick.
The lowermost 300 to 400 m of this sequence embraces the Felbertal scheelite mineralisation. This mineralisation is intimately associated with albite gneiss (ex-intermediate tuffs) and quartzite (ex-chert) lenses within coarse hornblende schist units (30 to 100 m thick) intercalated within the mafic schist sequence.
- Habach Phyllite Unit - This unit is best developed in the Habachtal area where it is 400 to 500 m thick and comprises predominantly dark to black phyllite with thin intercalations of acid, intermediate and mafic tuffs. It is characterised by the virtual absence of carbonates.
• Younger Schist Group - This group is a Permian to Mesozoic ophiolite schist series, capped by a marble unit.
East Alpine Group
These rocks constitutes the frame of the Tauren Window. They belong to the Lower Austro-Alpine Unit and are broad equivalents of the Habach Series, and are believed to have been deposited further to the south of, and thrust over, the Penninic Zone lithologies. They comprise greywackes to the north grading into quartz-phyllites immediately to the south. The quartz-phyllites have thin intercalated carbonate units and graphitic schists with lensoid developments of mafic volcanics. This section of the sequence, which is Upper Silurian to Lower Devonian in age, is taken to be equivalent to the Volcanic Succession of the Habach Series. It is overlain by Mesozoic carbonates to the south.
Mine Geology & Mineralisation
The Felbertal Scheelite Mine exploits two main ore zones. These zones are developed at different stratigraphic levels and are separated laterally by a north-south trending fault zone developed along the Felberbach Valley. This fault has a west-side-upwards displacement. The two ore zones are referred to as the East and West Field.
East Field
The ore deposit of the East Field appears to be a single conformable shoot some 2500 m in length, with a down dip dimension ranging from 50 to a maximum of 150 m, but being in general <100 m. It reaches a maximum thickness of 20 m near the centre, tapering both up and down dip. In places tectonic thickening has resulted in thicknesses of up to 50 m locally. The long axis of the body trends at between 110 and 130° to magnetic north, and plunges at between 25 and 55° to the NW. It is developed on the side of a steep mountain which has an average slope of 30°, roughly parallel to the plunge of the ore shoot. The relief difference between the highest and lowest outcrop of the orebody is approximately 800 m. The orebody outcrops in a slight depression on the mountain side. It has been subject to substantial 'creep', such that a large proportion of the ore mined is in fact a boulder scree zone made up of rocks ranging from 1 cm to 10 m in diameter, with about 30% interstitial soil and fine sand. The scree zone is in general up to 20 m thick and 40 to 50 m wide. The central section of the ore zone is masked by a 300 m long barren scree sheet which splits the surface expression of the orebody into two elongate sections.
The mineralised sequence within the East Field is as follows from the top:
• Upper Schist Sequence - This sequence caps the mineralised succession and comprises a fine to medium grained hornblende schist which was formerly tholeiitic basaltic volcanics. This unit contains some possible acidic tuffs.
• Upper Hornblende Gneiss - This is the stratigraphic equivalent of the West Field mineralisation. The unit here is some 5 m thick and carries from 0.05 to 0.1% WO3. The main lithology is an amphibolite, with minor thin intercalated 1 to 5 mm thick quartzite laminae. Scheelite mineralisation is present within small cross cutting quartz veins.
• Barren Hornblende Schist - A medium to coarse grained hornblende schist is found immediately below the West Field horizon. It is largely barren.
• Fine Grained Amphibolite - This is a dark quartz-hornblende rock comprising approximately 30% black hornblende and 70% grey quartz, with a 0.5 mm grain size. The unit is in general 5 to 20 m thick. The bottom 5 m usually has around 40% inter-laminated quartzite bands from 1 to 4 mm in thickness. These quartzite laminae carry ore grade scheelite. The bottom 5 m of the unit are economically extractable.
• Banded Gneiss - The banded gneiss is the main ore zone of the East Field. It varies from 10 to 15 m in thickness and is predominantly a finely laminated quartz albite gneiss. Individual laminae vary from 1 to 10 mm and are obvious as alternating grey, clear and cream bands. Quartzite occurs as clear laminae and as two 1 m thick pure beds. The ratio of albite to quartz overall is 2:1. Scheelite is present as discontinuous fine cream solid laminae around 1 mm thick, or less commonly, as laminae embracing fine closely spaced 0.1 to 1 mm scheelite grains. The quartzite bands carry the highest grade scheelite. The banded gneiss has been interpreted as a metamorphosed altered intermediate tuff. It is the host to the orebody and hence has a mafically similar distribution. It persists for 100 to 200 m laterally from the orebody with levels of around 100 ppm WO3.
• Lower Coarse Grained Hornblende Gneiss - This unit has an abrupt contact with the overlying banded gneiss and comprises a coarse grained, dark green to black, banded hornblende rock, with a crystal size in general of from 4 to 5 mm, but occasionally reaching 1 cm. The top 5 m of the unit carries ore grade scheelite within gash quartz veins ranging from 1 to 2 cm, down to 2 to 3 mm in thickness, and 10 to 50 cm in length. The unit varies in thickness from 30 m below the main ore zone, to 80 to 90 m marginal to the ore. It carries sparse scheelite mineralisation totalling a 'few tens' of ppm WO3 over much of its length.
• Lower Schist Sequence - This comprises a monotonous sequence of amphibolites developed from basaltic tuffs.
There appears to be an inverse relationship between the thickness of the Lower Coarse Grained Hornblende Gneiss and the ore zone. Below the centre of the ore zone, where the main banded gneiss is some 20 m thick, the coarse grained gneiss is only of the order of 30 m in thickness, while on the margins of the orebody it is up to 90 m thick. The underlying Lower Schist Sequence has a uniform thickness throughout. The coarse grained gneiss is taken to be a metamorphosed mafic lava whose thickness variations led to the formation of restricted elongate basins. Silica rich material is believed to have formed cherts with associated scheelite in one of these small basins adjacent to a fumerolic source with accompanying quartz-albite (intermediate tuff) deposition. The adjacent 'thinnings' of the Lower Coarse Grained Gneiss away from the ore zone are overlain by barren or low WO3 grade mafic tuffs without accompanying quartzites or banded quartz-albite gneisses.
The contrasting coarse grained metamorphic nature of the hornblende gneisses, which are best developed adjacent to significant mineralisation, may reflect the affect of metamorphism on an original alteration zone.
The mineralised part of the sequence in the East Field comprises the top 5 m of the Lower Coarse Grained Gneiss, all of the Banded Gneiss, and the lower 5 m of the Fine Grained Gneiss. The molybdenum content of the scheelite is much lower than that of the West Field ore.
West Field
The orebodies of the West Field are markedly different from that of the East Field. They are found some 70 m above the stratigraphic level of the East Field and occur within a separate depositional system. They were originally located to the west of, and along the line of plunge of the East Field orebody, but have subsequently been uplifted across a north-south fault running along the Felberbach.
Within the West Field, the mineralised host hornblende gneiss cycle is some 140 m thick. This zone has been tectonically split into an upper and lower wedge by Alpine deformation. The lower wedge contains a 50 m width of mineralisation averaging around 0.30 to 0.35% WO3 embracing three higher grade zones which are delineated by grade boundaries. If a 0.3% WO3 cut-off is used, these horizons each have average grades of near 0.7% WO3. Two of the horizons are 10 m thick and the third is 5 m. If a 0.2% cutoff is applied, the lower two horizons become a single 20 to 25 m thick body averaging 0.4% WO3. These bodies have been traced for more than 150 m, both along strike and down dip.
This 50 m width lower wedge is made up of alternating hornblende schist, quartzite and albite gneiss. The quartzite bands in general account for 10% of the sequence and range from 1 to 2 mm, up to 1 cm in thickness. Some more siliceous zones locally have 70 to 80% quartzite bands over intervals of 30 to 100 cm. Finely banded albite gneiss lenses, similar to those of the East Field, from 10 to 100 cm thick are found within this zone also, accounting for 5 to 10% of the succession.
Scheelite is present in three main forms in the West Field. These comprise:
Blue primary scheelite, occurring as 0.5 to 1 mm solid laminae or individual grains and clusters of scheelite present both within 2 to 3 mm quartzite laminae and disseminated within the hornblende schist. The grade however, is proportional to the quartzite content at any one point. This form of scheelite accounts for the majority of the production.
Secondary yellowish scheelite, occurring as 3 to 10 mm segregations developed on the margins of first generation quartz segregations, and to a lesser degree, dispersed through the hornblende schist. The first generation quartz segregations are concordant white quartz bands up to 5 cm thick within the host schist.
Blue-white coarsely crystalline scheelite aggregates, from 1 to 30 cm across, formed adjacent to, but outside of, the margin of second generation coarse, cross-cutting pegmatitic quartz segregations. These second generation quartz segregations vary from 10 to 100 cm in thickness, and although generally barren of scheelite, carry coarse sulphide (pyrrhotite) blebs up to 5 cm across.
The uppermost of the three ore lenses in the lower mineralised wedge of the West Field is made up as follows, from the top:
• A 2 m thickness of hornblende schist with <5% quartzite, present as concordant 1 mm thick bands. Scheelite is present as 0.5 to 1 mm clusters of grains largely within the quartzite laminae and to a lesser extent within the hornblende schist. The interval averages 0.2% WO3.
• A 2 m width of hornblende schist carrying 15% quartz as 2 mm to 4 cm bands, some of which embrace 1 to 5 x 1 to 2 cm beryl blebs. Scheelite is present as 1 to 2 mm grains, or aggregates of grains, within 1 to 2 mm thick bands. This interval averages 0.7% WO3.
• A central 1 m thick core comprising 85 to 90% quartzite bands with coarse scheelite up to 2 cm across, but in general 1 to 3 mm in grain size. Scheelite occurs as both the primary blue variety and as larger yellow secondary grains. The primary scheelite is present as 1 to 3 mm bands separated by barren 2 to 4 mm intervals in the higher grade sections. The quartzite is very well laminated in this section with 1 to 10 mm bands of hornblende schist, interlaminated with 1 mm thick laminae of white and clear quartzite, and similar sized scheelite rich bands. This interval averages 2 to 3% WO3.
• A lower grade 1 m interval made up of an upper 50 to 60 cm of hornblende schist with only minor quartzite bands and scheelite. The lower 50 cm is an albite gneiss band with high grade scheelite bands. The whole interval averages 1.2% WO3.
• The bottom 2 m only has 5 to 10% quartzite bands and laminae. Some 1.5 m from the top, a 30 cm thick albite gneiss band carries higher grade mineralisation. This gneiss varies in thickness from 10 to 100 cm over a 10 m interval down dip. The interval averages 0.2% WO3.
The 50 m width of the lower mineralised wedge of the West Field carries 0.15 to 0.2% WO3, exclusive of the ore grade lenses which correspond to more quartzitic sections of the interval and average around 0.7% WO3.
Mineral Resources
In 1978 (when visited), the East Field was estimated to have contained 1.6 Mt @ 0.75% WO3, and the West Field 1.3 Mt @ 0.6 to 0.7% WO3. The total resource in 2006 was estimated to have been ~6.1 Mt @ 0.5% WO3 (Wikipedia after Wolfram Bergbau und Hütten).
The most recent source geological information used to prepare this decription was dated: 2006.
Record last updated: 1/2/2018
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Felbertal
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Selected References:
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Raith J G and Stein H J, 2006 - Variscan ore formation and metamorphism at the Felbertal scheelite deposit (Austria): constraining tungsten mineralisation from Re-Os dating of molybdenite : in Contrib. to Mineralogy & Petrology v152 pp 505-521
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Schenk P and Holl R, 1991 - Evolution of fluids and metamorphic ore remobilization in the Felbertal scheelite deposit, Eastern Alps : in Ore Geology Reviews v6 pp 425-434
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Thalhammer O A R, Stumpfl E F, Jahoda R 1989 - The Mittersill Scheelite deposit, Austria: in Econ. Geol. v84 pp 1153-1171
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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