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Sylvanite
Sylvanite
Sylvanite
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Sylvanite
Sylvanite from the Cripple Creek mining district
General
CategoryTelluride mineral
Formula(Ag,Au)Te2
IMA symbolSyv[1]
Strunz classification2.EA.05
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP2/c
Identification
Formula mass429.89 g/mol
ColorSilver-grey, silver-white
Crystal habitMassive to crystalline
CleavagePerfect on the {010}
FractureUneven
TenacityBrittle
Mohs scale hardness1.5–2
LusterMetallic
StreakSteel grey
DiaphaneityOpaque
Specific gravity8.2
Density8.1
Optical propertiesAnisotropic
PleochroismNone
Ultraviolet fluorescenceNone
References[2][3][4]

Sylvanite or silver gold telluride, chemical formula (Ag,Au)Te2, is the most common telluride of gold.

Properties

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The gold:silver ratio varies from 3:1 to 1:1. It is a metallic mineral with a color that ranges from a steely gray to almost white. It is closely related to calaverite, which is more purely gold telluride with 3% silver. Sylvanite crystallizes in the monoclinic 2/m system. Crystals are rare and it is usually bladed or granular. It is very soft with a hardness of 1.5–2. It has a high relative density of 8–8.2. Sylvanite is photosensitive and can accumulate a dark tarnish if it is exposed to bright light for too long.

Occurrence

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Sylvanite is found in Transylvania, from which its name is partially derived.[5] It is also found and mined in Australia in the East Kalgoorlie district. In Canada it is found in the Kirkland Lake Gold District, Ontario and the Rouyn District, Quebec. In the United States it occurs in California and in Colorado where it was mined as part of the Cripple Creek ore deposit. Sylvanite is associated with native gold, quartz, fluorite, rhodochrosite, pyrite, acanthite, nagyagite, calaverite, krennerite, and other rare telluride minerals. It is found most commonly in low temperature hydrothermal vein deposits.

Use

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Sylvanite represents a minor ore of gold and tellurium. Sylvanium, an obsolete term for tellurium, derived its name from sylvanite.[6]

References

[edit]
[edit]
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Sylvanite

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Sylvanite is a rare and economically significant with the (Au,Ag)₂Te₄, typically exhibiting a steel-gray to silver-white color with a metallic luster. It forms brittle, prismatic to bladed crystals in the monoclinic system and is characterized by its low hardness of 1.5–2 on the , high specific gravity of 8.16, and perfect cleavage on the {010} plane. Named in 1835 by Louis Albert Necker-de Saussure after the Latin "sylvanus" referencing its type locality in , , sylvanite is prized for its content, which varies between 24–30% by weight, making it a key in certain deposits. Sylvanite primarily occurs in low- to high-temperature hydrothermal veins, often as one of the last minerals to form, associated with other tellurides like , krennerite, altaite, and hessite, as well as native , , and . Notable localities include the Cripple Creek district in , , where it contributes to significant production; Kirkland Lake in , ; Kalgoorlie in Australia; and the original Transylvanian sites in . Its composition can include minor impurities such as , lead, , and , and it is photosensitive, developing a dark upon exposure to . Optically, sylvanite is opaque with strong ranging from cream-white to leather-brown and displays very strong anisotropism under reflected light, aiding its identification in ore microscopy. As a telluride, it volatilizes at relatively low temperatures, which has implications for its processing in . Despite its rarity, sylvanite's presence in epithermal and mesothermal deposits underscores its geological importance in understanding mineralization processes.

Etymology and History

Naming

Sylvanite receives its name from , the historical region in present-day where the mineral was first identified in gold-bearing deposits. The regional name "" stems from the "trans silvam," translating to "beyond the forest" or "across the woods," a reference to the dense forested mountains that characterize the area from the perspective of neighboring territories. This etymological link underscores the mineral's origin in the wooded landscapes of , particularly around localities like Baia de Aries. The mineral was formally named in 1835 by Swiss geologist and mineralogist Louis Albert Necker de Saussure, who provided its initial scientific description in contemporary literature, distinguishing it as a distinct telluride species. Necker de Saussure's nomenclature also drew upon "sylvanium," an early and now obsolete proposed name for —the key elemental component in sylvanite's composition—reflecting the mineral's role in advancing understanding of this rare . Sylvanium itself derived from the Transylvanian context of tellurium's initial detection in the late . This naming convention was established shortly after the mineral's recognition in the early , with sylvanite noted in association with other regional tellurides like nagyagite in the same hydrothermal vein systems.

Discovery and Early Recognition

Sylvanite was first identified as a distinct mineral species from specimens collected in the gold mines of , (now Baia de Aries, formerly Offenbánya), around the early . The mineral occurred in hydrothermal veins associated with native gold, and its discovery highlighted the complex telluride assemblages in these deposits. In 1832, French mineralogist François Sulpice Beudant provided the initial scientific description of the mineral in his work Traité élémentaire de minéralogie, referring to it as "sylvane" based on its steely gray, metallic appearance and occurrence in Transylvanian ores. This description marked the beginning of its recognition in European mineralogy, though early analyses struggled to differentiate it from other tellurides due to compositional similarities. Shortly thereafter, in 1835, Louis Albert Necker de Saussure formally named it sylvanite, deriving the term from the Transylvanian locality and "sylvanium," an early proposed name for . Early studies often confused sylvanite with nagyagite, another lead-bearing telluride from the same region, owing to their comparable steel-gray color, metallic luster, and bladed habits. This mix-up delayed precise characterization until chemical analyses in the mid- confirmed sylvanite as a -silver telluride. By the latter half of the , sylvanite gained acceptance in European mineralogical literature as a key indicator of epithermal deposits, contributing to broader understanding of telluride .

Physical and Chemical Properties

Composition and Crystal Structure

Sylvanite is a with the ideal (Au,Ag)₂Te₄, in which the atomic ratio of Au to Ag commonly ranges from 1:1 to 3:1, corresponding to approximately 6.7 to 13.2 wt% silver. This variability arises from between end-members, with the 1:1 ratio being most typical in natural specimens. As a member of the krennerite group of gold-silver tellurides, sylvanite shares compositional similarities with minerals like krennerite (Au₃AgTe₈) but is distinguished by its higher silver content and structural differences. Sylvanite adopts the , with the P2/c (No. 14). The structure features distorted octahedral coordination around the Au and Ag cations, bonded to atoms, forming layers with Te-Te dimers that contribute to its telluride character. parameters for sylvanite are a = 8.95(1) Å, b = 4.478(5) Å, c = 14.62(2) Å, and β = 145.35(5)°, with Z = 2. While isostructural with (AuTe₂) in its average monoclinic framework, sylvanite exhibits no true polymorphism but can display modulated structures due to ordering of Au and Ag cations, setting it apart from the orthorhombic krennerite despite overlapping compositions. This cation ordering avoids unfavorable Ag-Te-Ag linkages and influences the mineral's stability in telluride assemblages.

Appearance and Diagnostic Characteristics

Sylvanite exhibits a steel-gray to silver-white color, often displaying a subtle yellowish tint on freshly exposed surfaces due to its content. This metallic is opaque and possesses a brilliant metallic luster, which aids in its preliminary identification in hand samples. The mineral is notably soft, with a Mohs of 1.5–2, rendering it sectile—capable of being cut with a knife—and somewhat malleable like other tellurides. Its ranges from 8.0 to 8.2 g/cm³, contributing to its substantial feel in specimens. Sylvanite produces a light gray streak and shows distinct prismatic cleavage, perfect on {010}, which is evident under basic lab examination. Sylvanite is photosensitive, developing a dark upon prolonged exposure to light, which can alter its initial appearance. When exposed to air, it may further to iridescent hues ranging from blue to violet, providing a key diagnostic feature for distinguishing it from similar metallic minerals. These observable traits, combined with its response to light and air, are essential for field and laboratory identification without advanced equipment.

Occurrence and Formation

Geological Settings

Sylvanite primarily forms in low-temperature hydrothermal vein systems, typically at temperatures below 300 °C and often in the epithermal range of 150–250 °C, where it precipitates from metal- and tellurium-rich fluids circulating through fractured host rocks. These fluids, characterized by low (0–5.5 wt% NaCl equivalent) and near-neutral pH, originate from mixtures of and magmatic volatiles, facilitating the transport of , silver, and in solution. occurs during fluid , mixing, or cooling, which destabilizes telluride complexes and leads to sylvanite deposition in quartz-dominated veins or alteration zones. In gold-telluride deposits, sylvanite is associated with late-stage mineralization events, where it crystallizes as a secondary phase following the deposition of earlier sulfides. The paragenetic sequence typically places sylvanite after base-metal sulfides such as , which form during initial hydrothermal pulses, and before or coeval with , reflecting decreasing temperatures and evolving fluid chemistry. This sequence underscores sylvanite's role in the final stages of ore formation, where tellurium enrichment in the fluid promotes telluride stabilization over precipitation. Although less common, sylvanite can appear as a late mineral phase in medium- to high-temperature hydrothermal deposits (up to 390 °C), where it forms during protracted cooling or fluid evolution in deeper vein systems. It is commonly associated with gangue minerals like and , which provide structural hosts for its bladed or granular crystals.

Notable Localities and Associations

Sylvanite's type locality is Baia de Arieș (also known as Offenbánya or ), in , , within the Transylvanian region, where it was first identified in the early in gold-bearing veins. Other significant European occurrences include additional Transylvanian mines in , such as those at Brad and Mustari, as well as sites in near Recsk in , where sylvanite appears in similar telluride assemblages. In , sylvanite is notably found in the Super Pit (part of the Fimiston Open Pit operations) in , associated with the rich telluride ores of the Golden Mile deposit. North American localities include the Sylvanite Mine in Township, , , a key producer in the region's deposits; the Lake Fortune Mine near , , , a shear zone-hosted deposit; the Cripple Creek Mining District in , , famous for its epithermal telluride veins; and the Alleghany District in , , where it occurs in orogenic systems. Sylvanite commonly associates with native , , krennerite, altaite, , , , and in these deposits, forming part of complex telluride parageneses in low-temperature hydrothermal veins. Although rare overall, sylvanite holds significance in telluride-rich ores at these sites, contributing to the economic value of the deposits despite its limited abundance.

Economic Importance and Uses

Role in Gold Mining

Sylvanite serves as a primary economic for , containing approximately 24.5% by weight, along with 13.4% silver and 62.1% , making silver and valuable byproducts in its extraction. The mineral's high content has historically positioned it as a key source in telluride-rich deposits, where it contributes significantly to overall yields during processing. In the , sylvanite played a pivotal role in es across multiple regions, including the historic mines of Transylvania's , such as the Fata Baii and Nagyág (Săcărâmb) operations in , where it was mined alongside native gold and other tellurides. Similarly, during Australia's Western Australian beginning in 1893, sylvanite was a notable component of telluride ores in the district, particularly the Golden Mile, helping to fuel early production in this major goldfield. In the United States, sylvanite's discovery in Colorado's Cripple Creek district in the 1890s sparked a boom, where it associated closely with in high-grade veins, contributing to the area's status as one of the world's richest gold camps. The nature of sylvanite poses significant extraction challenges, as the component locks the gold, necessitating to volatilize tellurium as a gas before cyanidation can effectively recover the metal. Early miners often overlooked these ores due to their subtle appearance, delaying recognition of their value until advanced processing techniques were applied. Production from sylvanite-bearing ores peaked in early 20th-century Colorado mines, with Cripple Creek's total output exceeding 21 million ounces of gold from over 500 operations between 1891 and the mid-1900s. In December 2024, SSR Mining acquired the Cripple Creek & Victor mine, with a November 2025 technical report outlining a 12-year life-of-mine plan projecting an after-tax NPV of $824 million. Today, minor gold recovery continues from legacy Cripple Creek deposits through modern heap-leach methods, averaging approximately 141,000 ounces annually as of 2025, while tellurium byproducts support metallurgical applications such as alloying additives in steel and copper.

Extraction and Modern Applications

The extraction of sylvanite, a , typically begins with flotation concentration to separate it from materials, utilizing collectors such as potassium amyl xanthate and frothers like Teric 401 at a of 8-9, achieving up to 88% recovery in operations like the Emperor Mine in . Following concentration, oxidizes the tellurides at temperatures around 500–800°C, decomposing sylvanite to release and convert to (TeO₂), which is removed as a . The roasted residue then undergoes cyanidation leaching, often enhanced by carbon-in-pulp processing, yielding recoveries of approximately 80–98% depending on pre-treatment efficacy. For refractory ores, with such as Thiobacillus ferrooxidans oxidizes associated sulfides, improving accessibility for subsequent in commercial plants in . In modern polymetallic operations, sylvanite processing is integrated into broader flowsheets for gold, silver, and base metals, where tellurium recovery is prioritized as a valuable byproduct. Tellurium is extracted from flotation concentrates or roasting residues via soda ash (sodium carbonate) roasting followed by alkaline leaching, often with sodium sulfide or hydroxide, producing tellurite solutions that are electrowon to yield high-purity tellurium (>99% and up to 99.99% in refined ingots). This method achieves leaching efficiencies of 78–95% under optimized conditions, such as 80 g/L NaOH at elevated temperatures, and is applied in facilities processing telluride-bearing slimes from gold and copper refining. Tellurium recovered from sylvanite contributes to key industrial applications, including cells, accounting for about 60% of global tellurium consumption as of 2024; thermoelectric devices, 20%; , 15%; and other uses, 5%. It is also alloyed with , , and lead to enhance tensile strength, , and resistance. The refined from sylvanite enters global markets for jewelry, which dominates demand, and , where it is used in connectors and circuits for its conductivity. Environmental management in sylvanite focuses on mitigating 's in , as tellurite (Te(IV)) exhibits higher than or selenite, potentially affecting aquatic ecosystems and human health through kidney and impacts at elevated exposures. from flotation and , often stored in impoundments with retaining , pose risks of that could mobilize tellurium under low-pH conditions, though its low solubility (~25 ppb at neutral pH) limits widespread dispersion. Modern practices include capping , monitoring seepage, and treating drainage to prevent contamination, particularly in porphyry copper-associated deposits where sylvanite occurs.

References

  1. https://www.handbookofmineralogy.org/pdfs/sylvanite.pdf
  2. https://www.mindat.org/min-3849.html
  3. https://www.etymonline.com/word/Transylvania
  4. https://www.yourdictionary.com/sylvanium
  5. https://www.mindat.org/reference.php?id=16103323
  6. https://www.mdpi.com/2075-163X/9/3/167
  7. https://www.britannica.com/science/sylvanite
  8. https://pubs.geoscienceworld.org/msa/ammin/article/22/5/728/537878/The-space-group-and-unit-cell-of-sylvanite
  9. https://rruff.geo.arizona.edu/doclib/hom/sylvanite.pdf
  10. https://pubs.geoscienceworld.org/msa/ammin/article/89/10/1505/44116/Ordered-distribution-of-Au-and-Ag-in-the-crystal
  11. https://hal.univ-lorraine.fr/hal-03633784v1/document
  12. https://galleries.com/minerals/sulfides/sylvanit/sylvanit.htm
  13. https://www.dakotamatrix.com/mineralpedia/8175/sylvanite
  14. https://pubs.usgs.gov/sir/2010/5070/q/sir20105070q.pdf
  15. https://www.superpit.com.au/wp-content/uploads/2015/05/Public-Environmental-Review-PER-Fimiston-Operations-Extension-Stage-3-Appendix-F1-Distribution-of-Tellurides-and-Mercury-in-Fimiston-Open-Pit.pdf
  16. https://www.mindat.org/loc-23607.html
  17. https://www.mindat.org/locentry-883568.html
  18. https://www.mindat.org/locentry-10736.html
  19. https://pubs.usgs.gov/publication/dr1198/full
  20. https://pubs.usgs.gov/bul/0254/report.pdf
  21. https://www.sciencedirect.com/science/article/abs/pii/S016745280515039X
  22. https://chemistry.unt.edu/system/files/james-l-marshall-pdfs/tellurium.pdf
  23. https://www.achp.gov/preserve-america/community/cripple-creek-colorado
  24. https://www.ssrmining.com/operations/production/cripple-creek-victor/
  25. https://finance.yahoo.com/news/ssr-mining-announces-initial-12-004500615.html
  26. https://pubs.usgs.gov/publication/pp1802R
  27. https://www.911metallurgist.com/wp-content/uploads/2016/09/Recovering-Gold-from-Telluride-Ore.pdf
  28. https://pmc.ncbi.nlm.nih.gov/articles/PMC8027068/
  29. https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-tellurium.pdf
  30. https://pubs.usgs.gov/pp/1802/r/pp1802r.pdf
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