Reading the Skarn — where tungsten hides in the contact
- Noel Ong
- 3 hours ago
- 18 min read
Roughly half the world's tungsten lives in skarn: a hard, ugly, calc-silicate rock that forms where a hot granite leans against limestone. Strip away the market noise and this is a story about chemistry at a contact. Here is how it works — in pictures.
Samso Insights | Research Insights | Understanding Tungsten - Part 1 | Geology Series |
1.00 — THE SHORT VERSION
A skarn is a chemical handshake between two rocks
The theory : a rising granitic magma will naturally proceed to a cooling phase as it makes contact against a limestone, leading to the granite exhaling hot, metal-bearing fluid into a rock that is almost pure calcium carbonate (Figure 1). Where the two meet, the limestone is rebuilt into a coarse, dense rock packed with calcium-silicate minerals. That rebuilt rock is the skarn. When the fluid is carrying tungsten, the calcium it strips from the limestone locks the tungsten up as scheelite — calcium tungstate, CaWO₄.
The short version of what a skarn is now explained. Just remember that a tungsten skarn needs four ingredients in the same place: a fertile granite, a carbonate host, heat, and a plumbing system to move fluid. Miss one and you get no ore. The diagrams below walk through each of them.
Skarn | A coarse-grained calc-silicate rock formed by the chemical replacement of carbonate rock (limestone or dolomite) near an igneous intrusion. The ore-grade, fluid-built variety is sometimes called tactite. |
Scheelite | CaWO₄ — calcium tungstate, the dominant tungsten ore mineral in skarns. About 80% WO₃ by weight. Heavy (SG ≈ 6), pale, and famously glows blue under ultraviolet light. |
2.00 — THE SETTING
The recipe, in cross-section - the creation of a tungsten skarn
This is the picture to carry around. A granite pluton rises into a layered sequence of sediments (Figure 1). The heat alone bakes the surrounding rock into hornfels. But where the carbonate layers sit against the granite — and especially where faults give fluid a path — the limestone is chewed out and replaced by skarn. Scheelite concentrates right at that reaction front.
Figure 1: The tungsten-skarn system. Heat bakes a metamorphic aureole; fluid from the granite (blue arrows), guided by faults, replaces the carbonate host with calc-silicate skarn (orange). Scheelite concentrates at the reaction front. Schematic by Samso, after standard skarn models (USGS Open-File 02-195; Meinert et al.).
Samso take Notice what does the work: it is the carbonate, not the granite, that makes a tungsten skarn. The limestone supplies the calcium that traps tungsten as scheelite. No carbonate at the contact, no skarn — which is exactly why explorers map the marble, not just the granite. |
3.00 — TWO PROCESSES, ONE ROCK
Baking versus rebuilding
Two different things happen near the intrusion, and geologists keep them separate. Contact metamorphism is heat alone — the rock recrystallises but its chemistry barely changes. Metasomatism is the active one — fluid floods in and physically swaps elements in and out of the rock. Ore-grade skarn is built by metasomatism.
Figure 2: Heat alone turns limestone into marble (left). Fluid-driven metasomatism rebuilds it into calc-silicate skarn and drops scheelite (right). Schematic by Samso, after Geology Science & ITIA descriptions.
4.00 — THE TWO ACTS
Prograde, then retrograde — and tungsten moves twice
Skarns build in two acts as the system heats then cools. The hot prograde stage grows anhydrous minerals — garnet and pyroxene — and drops the first, fine scheelite. As the system cools, the wetter retrograde stage overprints it with amphibole, mica and fluorite, and crucially re-dissolves and re-concentrates the scheelite into coarse, high-grade masses. The best ore is usually retrograde.
Figure 3: Tungsten precipitates twice. Early prograde scheelite is fine and molybdenum-rich; cooling retrograde fluids re-dissolve it and re-deposit it as the coarse, high-grade ore that mines chase. Schematic by Samso, after Newberry & Einaudi (1981) and Kwak & Tan (1981), King Island.
Why does the ore move twice? Because the two processes produce two distinct types of scheelites. The prograde process — characterized by heat and dryness — crystallizes garnet and pyroxene, depositing the first scheelite at the marble front. This scheelite is fine-grained, dispersed throughout the rock, and typically molybdenum-rich, as molybdenum easily integrates into scheelite formed from these early high-temperature fluids.
The retrograde process is where the value lies. As the pluton cools and the fluid becomes water-rich and more acidic, hydrous minerals such as amphibole, mica, epidote, and fluorite overprint the anhydrous framework. The initial scheelite that isn't trapped within garnet dissolves and re-precipitates as coarse, molybdenum-poor masses, usually accompanied by sulfides. The USGS skarn model clearly states: early scheelite near the marble front is generally remobilized and redeposited in coarse-grained, high-grade masses within the zones of hydrous alteration.
Three factors make retrograde ore highly desirable, all of which are commercial. Grade where the richest tungsten is typically found with the hydrous, retrograde minerals. In the Processing stage, the coarse scheelite separates cleanly and can be recovered through inexpensive gravity separation, whereas the fine prograde scheelite is the sub-10-micron material that eludes gravity (the issue addressed in Part 2). The third factor is quality. The molybdenum, which was a disadvantage in the early scheelite, is removed during remobilization, resulting in cleaner retrograde scheelite.
THE KILBA TELL You can read the retrograde signature straight off the metallurgy. Research is showing that the Kilba deposit (ASX: TGN) — a skarn / calc-silicate system against the Kilba granite in WA's Ashburton carries its tungsten as coarse-grained scheelite that responds to conventional gravity separation, and 2015 testwork produced an extremely high-grade concentrate. Coarse, gravity-recoverable and high-grade is the fingerprint of retrograde-remobilised ore: Kilba sits at the good-ore end of the curve above. |
The same story, across Australia
The model is played out in the Australian deposits. The textbook case is the King Island (Dolphin) mine, where a classic 1981 study traced the exact sequence . The early Mo-rich scheelite with garnet and pyroxene, then coarse Mo-poor scheelite and molybdenite during the retrograde overprint. Read Table 1 below as a context map for what "prograde, then retrograde" means on the Australian project.
Table 1: Australian tungsten deposits with Prograde and Retrograde examples. that Sources: Kwak & Tan (1981), Economic Geology 76(2), King Island (Dolphin); USGS skarn model (OF 02-195); JORC resource/reserve figures from company disclosures — Tungsten Mining NL (Kilba, Mt Mulgine, Big Hill, Watershed), Group 6 Metals (Dolphin), Venture Minerals (Mount Lindsay), EQ Resources (Mt Carbine). The Mt Mulgine molybdenum interpretation is Samso's, built on the reported Mo grades.
Deposit (ASX) | Where | Style | Resource & grade | The prograde → retrograde tell |
King Island / Dolphin (G6M) | King Island, TAS | Scheelite skarn (Grassy Granite) | Dolphin ~3.0 Mt @ 0.73% WO₃ (probable reserve) | Kwak & Tan (1981) traced early Mo-rich scheelite with garnet–pyroxene, then coarse Mo-poor scheelite + molybdenite in the retrograde overprint — the model deposit. |
Mt Mulgine (TGN) | Murchison, WA | Porphyry / vein-stockwork W–Mo (greenstone) | ~72.2 Mt @ 0.18% WO₃ (~186–220 ppm Mo) | The molybdenum credit is the prograde-scheelite signature; large, lower-grade disseminated system. |
Kilba | Ashburton, WA | Skarn / calc-silicate | 7.2 Mt @ 0.19% WO₃ | Coarse, gravity-amenable, very high-grade concentrate — the retrograde end. |
Big Hill | Pilbara, WA | Scheelite (calc-silicate) | ~11.5 Mt @ 0.15% WO₃ | Same skarn-style scheelite. |
Mount Lindsay (CRI) | NW Tasmania | Sn–W magnetite skarn | ~45 Mt @ 0.2% Sn, 0.1% WO₃ | Polymetallic skarn with the same prograde (magnetite-garnet-pyroxene) → retrograde architecture. |
Watershed (TGN) | ~130 km N of Cairns, QLD | Calc-silicate-hosted scheelite | TGN development project | Another calc-silicate / skarn-style scheelite system. |
Mt Carbine (EQR) | Far North QLD | Wolframite in quartz veins (greisen) | Australia's primary W producer | The counter-example — a vein / greisen deposit, not a skarn, so it does NOT follow the prograde → retrograde model. |
5.00 — THE FINGERPRINT
What a tungsten skarn is made of
A skarn announces itself by its minerals apart from the tungsten minerals that we have discussed such as scheelite (Figure 5) and wolframite. The diagnostic pair is garnet plus pyroxene and in tungsten skarns garnet usually dominates. Add the retrograde overprint and a few accessories, and you have the assemblage a geologist logs at the drill rig (Figure 4).
Figure 4: The skarn assemblage. Anhydrous garnet and pyroxene form first; a hydrous retrograde overprint carries the high-grade scheelite and the sulphides. Compiled by Samso from USGS, mindat.org and Meinert skarn classifications.
Those legend entries aren't abstractions — name a line and a famous deposit shows it. China's Shizhuyuan (Hunan), a world-class W–Sn–Bi–Mo–F skarn, carries exactly the prograde set: garnet, pyroxene, vesuvianite and wollastonite, with scheelite and bismuthinite between the grains. Its ore, though, sits mostly in the retrograde overprint of fluorite, epidote, amphibole and magnetite.
Korea's giant Sangdong deposit is the textbook in miniature — you can walk from an outer, low-grade pyroxene–garnet zone, through an amphibole–biotite zone, into a quartz–mica core where the grade is highest. Both say what Part 1's curve does: the rich ore tracks the hydrous, retrograde minerals.
Figure 5: Scheelite, the orange-brown pseudo-octahedral crystals, on muscovite. Its high density (SG ≈ 6) is a field giveaway. Specimen located from Mt Xuebaoding, Pingwu County, Mianyang Prefecture, Sichuan Province, China. (Source: Wikimedia Commons )
The garnet-versus-pyroxene balance also flags the skarn's "flavour" (section 7.00). Garnet-dominant, andradite-rich systems like Shizhuyuan are oxidised and tend to carry more molybdenum in their scheelite; pyroxene-dominant, hedenbergite-and-pyrrhotite systems like Canada's Cantung and Mactung are reduced, and their highest grades again sit in the retrograde amphibole and biotite facies. The minerals you log are already telling you the deposit type, the molybdenum penalty, and where the best ore should be.
Named deposits that show the fingerprint
A spread of well-studied tungsten skarns — two from China, three from elsewhere — and the assemblages that define them:
Table 2: Sources: Shizhuyuan — Lu et al. (2003, Economic Geology 98(5)); Yang/Newberry Shizhuyuan studies; Xianglushan — comparative scheelite geochemistry, Shizhuyuan vs Xianglushan (oxidising vs reducing fluids). Sangdong — Almonty Korea project geology; Seo et al. genetic model (prograde wollastonite–garnet–clinopyroxene → pyroxene–garnet; retrograde amphibole–biotite → quartz–mica). Cantung / Mactung — Elongo et al. (2020) and CanTung E-Zone studies (reduced grossular–hedenbergite–pyrrhotite; highest grade in hydrous retrograde facies). King Island — Kwak & Tan (1981). Framework: Newberry & Einaudi (1981); USGS OF 02-195.
Deposit (country) | Skarn type | Prograde assemblage | Retrograde / ore assemblage | The tell |
Shizhuyuan (Hunan, China) | Oxidised, garnet-rich (W–Sn–Bi–Mo–F) | Garnet · pyroxene · vesuvianite · wollastonite (+ interstitial fluorite, scheelite, bismuthinite) | Fluorite · epidote · amphibole · chlorite · magnetite + scheelite, wolframite, molybdenite | Ore mostly in the retrograde skarn; higher-Mo scheelite from oxidising fluids. |
Xianglushan (Jiangxi, China) | Reduced-type W skarn | Garnet–pyroxene skarn + layered sulphide–scheelite | Scheelite (lower-Mo), sulphides | The reduced counterpart to Shizhuyuan — cleaner, lower-Mo scheelite. |
Sangdong (South Korea) | Zoned giant W(–Mo) skarn | Wollastonite–garnet–clinopyroxene → pyroxene–garnet (outer, low grade) | Amphibole–biotite → quartz–mica core (highest grade); scheelite >95% of W, minor wolframite, molybdenite | Grade climbs inward with the hydrous overprint (~0.3% → ~3% WO₃). |
Cantung / Mactung (Canada) | Reduced (high-grade) | Grossular garnet + hedenbergite pyroxene (+ abundant pyrrhotite) | Amphibole + biotite skarn (highest grade); scheelite tracks pyrrhotite; chalcopyrite, bismuth | Textbook reduced W skarn — ore in the hydrous retrograde facies. |
King Island / Dolphin (Australia) | Garnet–pyroxene skarn (Grassy Granite) | Garnet · pyroxene hornfels; early Mo-rich scheelite | Coarse Mo-poor scheelite + molybdenite (retrograde amphibole) | The Kwak & Tan (1981) model deposit (also in §4.00). |
6.00 — ZONATION
Distance from the granite is a thermometer
Walk away from the pluton and the skarn changes in an orderly way, because the fluid cools as it travels. At King Island's Dolphin mine, scheelite-bearing fluids ran at roughly 500°C at the granite contact and cooled to about 300°C some 500 m out. Garnet sits proximal (andradite-rich nearest the contact), pyroxene takes over distally, and the richest ore tends to sit near the marble front where the chemistry tips over.
Figure 6: Skarn zonation. Proximal garnet gives way to distal pyroxene and finally marble; the high-grade scheelite clusters near the reaction front. Temperatures from the King Island (Dolphin) study. After Kwak & Tan (1981), Economic Geology, King Island (Dolphin) zoning study.
7.00 — TWO FLAVOURS
Reduced versus oxidised — and why it matters
In 1981 Newberry and Einaudi split tungsten skarns into two families, and the split still frames how geologists think. Reduced skarns form deeper, in carbon-bearing host rocks, with hedenbergite-rich (ferrous) mineralogy and often higher grade. Oxidised skarns form shallower, in hematite-bearing hosts, with andradite-rich (ferric) mineralogy. The distinction predicts grade, by-products and metallurgy.
Figure 7: The reduced/oxidised division of Newberry & Einaudi (1981), based on host-rock chemistry, iron oxidation state and depth. It is shorthand for what grade and metallurgy to expect. After Newberry & Einaudi (1981), via the EarthSci / USGS skarn literature.
7.50 — The Mo tell: molybdenum writes the conditions into the crystal
Section 7 sorted skarns into reduced and oxidised by the company they keep. But there is a finer signal hiding inside the scheelite — its molybdenum content — and it records the fluid one pulse at a time.
Here is the catch that trips people up, and it looks at first like it contradicts the table above. The reduced/oxidised split tells you whether a system carries molybdenum — and reduced tungsten skarns very often are W–Mo deposits. But whether that molybdenum ends up locked inside the scheelite is a different question, and the answer runs almost the opposite way. Molybdenum only slips into the scheelite lattice — substituting for tungsten — when the fluid is oxidising enough to carry it as Mo⁶⁺. Turn the fluid reducing and the molybdenum walks off to build its own mineral, molybdenite, leaving the scheelite clean. So a high-Mo scheelite is the fingerprint of an oxidising pulse, not a reduced one.
Figure 7.5: Where molybdenum goes. Oxidising fluids load Mo⁶⁺ into the scheelite lattice; reducing fluids divert it into molybdenite and leave the scheelite low-Mo. The same deposit can record both as it cools — at Yaogangxian the molybdenum in scheelite falls roughly an order of magnitude from the early oxidising stage to the late reducing one, and both generations are ore. Schematic by Samso, after Hsu (1977) and Li et al. (2023), Ore Geology Reviews.
You can watch this play out inside a single orebody. At Yaogangxian in South China, the early retrograde scheelite grew from an oxidising fluid and carries around 1,800 ppm molybdenum (Figure 7.5). The later sulphide-stage scheelite — grown as the system cooled and turned reducing, with pyrrhotite everywhere — carries roughly 240 ppm.
Same deposit, same granite, an order of magnitude less Mo in the crystal, purely because the redox shifted. And crucially, both generations are ore. The redox state changed the flavour of the scheelite without ever stopping it forming — which is the quiet lesson that oxygen state is not the master switch on whether tungsten drops out, just on what comes with it.
Samso take This is where the geology reaches the bank. Molybdenum in scheelite is a penalty element in a tungsten concentrate — APT buyers want it low — so an oxidised, high-Mo orebody forces a choice: strip the Mo out, or sell it as a molybdenite credit. Western Australia's Mt Mulgine is the local case in point: its scheelite carries molybdenum, which is exactly why the flowsheet there is built to pull two products rather than one. Read the Mo number in the rock and you are reading a processing-and-pricing decision that is fixed long before the plant is designed. |
So is lattice Mo a bad thing for getting the tungsten out? It depends entirely on the form, and this is the crux. Molybdenum sitting as its own mineral, which is molybdenite is the easy case. Molybdenite floats off cleanly in processing and can even be sold separately.
Molybdenum dissolved into the scheelite lattice is the hard case. Because it is built into the crystal, no amount of gravity, magnetic or flotation work can reject it — it rides with the tungsten straight into the concentrate. It does not lower how much tungsten you recover, but it contaminates the concentrate with a penalty element, forcing an extra chemical step downstream: the Mo dissolves alongside the tungsten during alkaline digestion and then has to be precipitated back out as a sulphide to reach APT specification.
So a high-Mo scheelite is genuinely the awkward one — you carry a de-molybdenisation cost you cannot avoid with physics, and because the Mo is dispersed in the lattice rather than present as discrete molybdenite, you cannot bank it as a by-product credit either. The severity tracks the grade: a few hundred ppm is usually manageable, while a properly powellitic (Mo-rich) scheelite becomes a real concentrate problem.
8.00 — THE EXPLORER'S TRICK
Why scheelite glows — and how it gets found
Scheelite has a gift for explorers: under short-wave ultraviolet light it fluoresces a bright sky-blue. Swap some tungsten for molybdenum and the glow shifts toward cream-yellow — so the colour itself hints at composition. Geologists have mapped skarns at night with UV lamps for a century, and the trick still re-opens old mines by lighting up ore left in the walls.
Figure 8: The same rock, two lights. Pure scheelite glows blue under short-wave UV; molybdenum shifts it to yellow. This single property turns a UV torch into a tungsten exploration tool. Schematic by Samso; fluorescence behaviour per Wikipedia (Scheelite), mindat.org and Geology.com.
In my previous life working on a tungsten project in New Zealand, the identification of scheelite was indeed a sight to see (Figure 8.5). In my opinion, the Kirwan Hill project still remains one of the untapped tungsten occurrences that could be a game changer if the project was worked on in 2026.
Figure 8.5: A scheelite core sample form the Kirwan Hill Tungsten Project, New Zealand. The sample shows scheelite in brecciated unit and occurs as coarse grains as well as in a disseminated form.
Samso take Fluorescence is not a party trick — it is a low-cost mapping vector. A handheld UV lamp run over outcrop, drill core or mine walls converts an invisible problem into a visible one. For a small-cap explorer, that is meaningful: cheap nighttime traverses can rank targets before a single expensive metre is drilled. |
9.00 — KNOW YOUR ORE MINERAL
Scheelite (skarns) vs wolframite (veins)
Tungsten comes in two ore minerals, and which one you have tells you a lot about the deposit. Skarns and their carbonate-bound calcium overwhelmingly carry scheelite. The other major ore, wolframite, belongs more to granite-hosted veins and greisens. They look, behave and process differently.
Figure 9: The two tungsten ore minerals. Scheelite dominates skarns and gives up its calcium-tungstate identity under UV; dark wolframite belongs to the vein/greisen world. Compiled by Samso from ITIA, mindat.org and mineralexpert.org.
The main importance for investors is to understand that Wolframite is the Fe cousin of Scheelite who is a Calcium variant. Discovering these tungsten minerals separately is ok, however, if they are associated in the same ore body, it will create issues in the processing part of the business. Wolframite will be magnetic and as thee ore bodies are commonly associated with magnetic minerals, the separation using a magnetic separator will be hampered.
These are some aspects that investors need to keep in mind. IN part 2 of the Understanding Tungsten series, we will introduce the issues for Scheelite as the calcium variant of a tungsten mineral.
10.00 — IN PRACTICE, AT HOME
The Australian skarn: King Island and beyond
Australia's exemplary tungsten skarn is Dolphin, located at Grassy on King Island. It features scheelite in garnet-pyroxene skarn surrounding the Devonian-Carboniferous Grassy Granite, discovered in the early 1900s and intermittently mined for a century. It exemplifies the classic characteristics: carbonate host, granite contact, fault control, and retrograde high-grade ore.
In Western Australia, Mt Mulgine (Tungsten Mining NL, ASX: TGN) contains scheelite with molybdenum, highlighting that the predicted Mo content in the geology becomes a significant factor in processing and pricing downstream.
Figure 10: Selected Australian tungsten settings. Skarn-hosted scheelite (Dolphin, Mt Mulgine) contrasts with vein/greisen wolframite (Mt Carbine). Positions indicative only. Compiled by Samso from Group 6 Metals, Tungsten Mining NL and Geoscience Australia disclosures.
But Dolphin is neither the biggest nor the only Australian skarn. The country's largest tungsten resource is O'Callaghans (Greatland Resources, ASX: GGP), about 10 km south of Telfer in WA — a flat-lying polymetallic skarn where scheelite- and wolframite-bearing amphibole–pyroxene–garnet rock replaces limestone above the reduced O'Callaghans granite. Its December 2025 resource is ~70 Mt at 0.35% WO₃ with copper, zinc and lead by-products, and the proposed flowsheet is pure Part 2: flotation for the base metals, then magnetic separation and gravity to recover the tungsten.
Two more wear the classic fingerprint. Kilba (TGN, Ashburton WA) is scheelite in skarn / calc-silicate against the Kilba granite — and, as section 4 noted, its coarse, gravity-amenable scheelite is a textbook retrograde signature. Molyhil (Thor Mining, ASX: THR), 220 km north-east of Alice Springs, is a scheelite–molybdenite–magnetite skarn — a small but genuine W–Mo skarn that wears its molybdenum on its sleeve.
Is Watershed a skarn? Not quite — and that's the point
The most useful example is the awkward one. Watershed (TGN, 130 km north of Cairns) sits in the Hodgkinson Formation — a pile of deformed metasediments (conglomerate, psammite, slate), not a clean limestone. It carries genuine skarn minerals (garnet, clinopyroxene, actinolite), so the rock is calc-silicate / skarn-altered; but the scheelite was largely emplaced in shear-controlled veins and then upgraded during later metamorphism. The published work describes it as a "metamorphic tungsten upgrade after a magmatic-hydrothermal event" — a hybrid that sits between a contact skarn and a metamorphic / vein deposit. Its resource is large and low-grade (~49–70 Mt at ~0.11–0.14% WO₃).
Cookes Creek is a similar matter of degree. It isn't a single named skarn but a granite-and-workings cluster in WA's Gascoyne; the defined resource on its margin — Big Hill (~11.5 Mt at 0.15% WO₃) is vein-hosted scheelite within a tremolite-rich calc-silicate unit: skarn-affiliated, but vein-controlled rather than a classic replacement body. So I would call this a hybrid and not a yes/no in regards to being a skarn deposit.
Table 3: Australian Tungsten Deposits nd their relationship to being a skarn mineralisation. Sources: O'Callaghans — Greatland Resources (ASX: GGP) December 2025 Mineral Resource (~70 Mt @ 0.35% WO₃) and Newcrest skarn geology; Dolphin — Group 6 Metals / Kwak & Tan (1981); Kilba, Big Hill, Watershed, Mt Mulgine — Tungsten Mining NL disclosures; Molyhil — Thor Mining (ASX: THR) / NT Geological Survey; Mount Lindsay — Venture Minerals (ASX: VMS); Mt Carbine — EQ Resources (ASX: EQR). Watershed geology — Hodgkinson Formation / Mossman Orogen studies (the deposit is described as a metamorphic tungsten upgrade of a Carboniferous magmatic-hydrothermal system).
Deposit (owner) | Setting | Skarn? |
O'Callaghans (Greatland, GGP) | Polymetallic W–Cu–Zn–Pb replacement of limestone above the O'Callaghans granite, Telfer WA | ✓ Classic skarn — largest in Australia |
Dolphin / King Island (G6M) | Scheelite in garnet–pyroxene skarn at the Grassy Granite contact, TAS | ✓ Classic skarn |
Kilba | Scheelite in skarn / calc-silicate against the Kilba granite, Ashburton WA | ✓ Skarn / calc-silicate |
Molyhil (Guardian Metals) | Scheelite–molybdenite–magnetite skarn, Aileron Province NT | ✓ Skarn (W–Mo) |
Mount Lindsay (Critica Limited) | Sn–W magnetite skarn, NW Tasmania | ✓ Skarn (Sn–W) |
Watershed (TGN) | Scheelite in calc-silicate / skarn-altered metasediments + shear veins, Hodgkinson Fm, FNQ | ~ Skarn-altered — not a classic carbonate skarn |
Big Hill / Cookes Creek | Vein scheelite in a tremolite-rich calc-silicate unit on the Cookes Creek granite margin, WA | ~ Calc-silicate-hosted, vein-controlled |
Mt Mulgine (TGN) | Porphyry / vein-stockwork W–Mo in greenstone + greisen, Murchison WA | ✗ Not a skarn (porphyry / vein) |
Mt Carbine (EQR) | Wolframite in quartz veins / greisen, Far North QLD | ✗ Not a skarn (vein / greisen) |
— SAMSO CONCLUDING COMMENTS
The geology is the moat
Like all mineral deposits, when it comes to classificating a deposit style type to define deposits as occurring the same way, I find that no single deposits ever sits in the same framework that an institution demands. My experience has shown me that a broad framework of conditions will work but when a discussion starts, everything seems to just falls apart and the final conclusion always seem to fall back to individuality rather than a group classification.
Hence if we strip a tungsten skarn back and it is almost elegant in a Type case of a skarn tungsten deposit. It is a granite heat source, source rock, that breathes fluid into a limestone, the limestone gives up its calcium, and tungsten is locked away as scheelite at the reaction front. I think for reader, it is away to remember all the factors we have discussed in this Samso Insight, but I would not hold these points as a hard and fast rule to understanding skarn tungsten deposits.
Everything an investor cares about downstream, grade, by-product molybdenum, how hard the ore is to process, whether a UV torch can cheaply find more is written into that geological setup before any mining decision is made.
That is the reason Samso keeps coming back to the rocks and the process that creates the minerals and hence, the metal abundances. In a critical-minerals cycle full of noise, the contact between a granite and a carbonate is one of the few things that does not move with the headlines. Understand the skarn, and the tungsten story stops being a ticker and starts being a deposit.
References & sources
U.S. Geological Survey — Environmental Geochemistry of Skarn and Polymetallic Deposits, Open-File Report 02-195 (Chapter H). Skarn classification and W-skarn behaviour.
Newberry, R.J. & Einaudi, M.T. (1981) — reduced vs oxidised tungsten skarn division; summarised in the EarthSci.org / USGS skarn literature.
Meinert, L.D. et al. — World skarn deposits classification (resource split ~48% skarn). Via tungsten beneficiation review literature.
Kwak, T.A.P. & Tan, T.H. (1981) — "The geochemistry of zoning in skarn minerals at the King Island (Dolphin) Mine," Economic Geology 76(2): 468–497.
Bowman, J.R. et al. (1985) — CanTung E-Zone scheelite skarn isotope study, Economic Geology 80(7): 1872–1895.
Geology Science — "Skarn deposits" overview; "Scheelite: properties, formation, occurrence."
Wikipedia — Scheelite (CaWO₄, fluorescence, occurrence); cross-checked with Britannica and mindat.org (min-3560).
Group 6 Metals Limited (ASX: G6M) — Dolphin Tungsten Project overview & exploration pages.
Mineral Resources Tasmania — King Island geology documents; Callaghan (Resource & Exploration Geology) Dolphin/Bold Head report.
International Tungsten Industry Association (ITIA); mineralexpert.org — scheelite vs wolframite mineralogy & WO₃ contents.
Tungsten Mining NL (ASX: TGN) — Mt Mulgine (scheelite + molybdenum) disclosures.
Hsu, L.C. (1977) — “Effects of oxygen and sulfur fugacities on the scheelite–tungstenite and powellite–molybdenite stability relations,” Economic Geology 72: 664–670.
Li, W.-S., Ni, P., Pan, J.-Y., et al. (2023) — “The genetic association between vein and skarn type tungsten mineralization in the Yaogangxian tungsten deposit, South China,” Ore Geology Reviews 159: 105544 (open access, CC BY-NC-ND).
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Most importantly, investors need to be absolutely diligent in understanding their own risk-reward tolerance and capabilities. Never bite off more than you can chew. As they say, Rome wasn’t built in a day, and the Great Wall stood because it took centuries to complete.
The Samso Philosophy:
Stay curious. Stay sharp. And remember—digging deeper always uncovers the real value.
In Life, there is no such thing as a Free Lunch.
Never bite off more than you can chew is my parting comment.
Happy Investing, and the only four-letter word you need to know is DYOR.
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Disclaimer
The information or opinions provided herein do not constitute investment advice, an offer, or solicitation to subscribe for, purchase, or sell the investment product(s) mentioned herein. It does not take into consideration, nor have any regard to your specific investment objectives, financial situation, risk profile, tax position and particular, or unique needs and constraints.
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Samso is a trusted platform that equips dedicated investors with up-to-date industry knowledge and insigh0ts from top CEOs and thought leaders. By staying informed on business advancements and market trends, investors can enhance their financial decisions through a combination of expert guidance and their own research.
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