Volcanic-associated Massive Sulfide Deposits Research Articles

The Society of Economic Geologists Awards for 2014 R. A. F. Penrose Gold Medal for 2014 Citation of James M. Franklin

Mr. President, SEG members, and friends: Jim Franklin’s career has encompassed all of the criteria applicable to the terms of reference for the Penrose Gold Medal with his outstanding contributions to scientific research, to the profession, and to the development of mineral resources. All three were achieved through a full career in economic geology as practiced in academia, government, and industry. Although his scientific achievements are wide ranging and easily documented, I believe his singular technical contribution has been the establishment of the link between the geological attributes of volcanic-associated massive sulfide deposits, as preserved in the rock record ranging back to the Archean, with hydrothermal processes in modern oceanic environments. His penchant for documentation of key features associated with massive sulfide deposits, particularly things geochemical, dates back to his employment as a student at the Geological Survey of Canada with the late S.M. Roscoe, who was one of the earliest proponents of a syngenetic origin for deposits at Noranda and Mattagami Lake. Jim later put this experience to work in documenting the geology of the newly discovered Mattabi deposit at Sturgeon Lake in northern Ontario in the early 1970s, showing a geological setting and style of alteration that differed in many respects from the more familiar examples at Noranda and Kuroko. Similar work elsewhere at the time was focused on the site of metal deposition but Jim’s work at Sturgeon Lake pointed the way to two broader and more critical aspects: the presence of a …

Volcanic-associated Besshi-type copper sulfide deposits

Besshi-type volcanic-associated massive sulfide deposits (VMSD) are associated with undifferentiated basaltic formations. They form within the mid-ocean ridges near the continental margins, in back-arc spreading zones, and rarely in intracontinental rift basins. They are characterized by a wide spread of turbidites in ore-bearing strata, Co-rich copper-zinc ores, the predominance of subvolcanic sills, sheet-like ore bodies, an absence of clear structural control, relatively low Cu, Zn, Ag, and Au grades, enrichment in Pb, and relatively large ore and metal reserves.

The Pb-rich sulfide veins in the Boccassuolo ophiolite: Implications for the geochemical evolution of hydrothermal activity across the ocean-continent transition in the Ligurian Tethys (Northern-Apennine, Italy)

Galena bearing sulfide veins have been discovered coexisting with Fe–Cu–Zn dominated veins in the hydrothermal stockwork of the Boccassuolo ophiolite (External Ligurides, Northern Apennine, Italy). The galena-rich veins cut across a volcanic pile composed of pillow lava flows, pillow breccia, and ophiolitic sandstone. Bulk-ore analyses indicate significant enrichment in Pb giving raise to mantle normalized Pb–Ag–Au–Zn–Cu patterns with unusual negative slope, in contrast with the average flat pattern of most sulfide deposits in the Internal Liguride ophiolites which reflect the Fe–Cu–Zn assemblage of ophiolite-hosted Volcanic-associated Massive Sulfide (VMS) deposits all over the world. A wide literature shows that, in contrast with the Internal Ligurides, plutonic and volcanic rocks of the External Ligurides display less depleted and even enriched geochemical characters, not consistent with common oceanic crust at mid oceanic ridges (MOR), but probably originated in the ocean–continent transition of the Adria continental margin. In this geodynamic context, pillow basalts become locally enriched in Pb with high Pb/Cu ratios, and other crustal-compatible elements such as Mo and U. The Pb enrichment observed in the veins Boccassuolo is interpreted to be a result of leaching of such anomalous volcanics forming the ophiolitic substrate. The case of Boccassuolo supports the conclusion that the geochemical character of hydrothermal activity evolved from Cu–Zn rich in MOR-type assemblages of the Internal Ligurides, towards composition enriched in Pb in the External Liguride domain, representing the transition from the Ligurian ocean to the Adria continental margin.

Sulfur-isotope variations in sulfide minerals from massive sulfide deposits of the northern Apennine ophiolites: inorganic and biogenic constraints

Sulfur isotope analysis of sulfide minerals has been carried out for the first time on ore samples from Volcanic-associated Massive Sulfide (VMS) deposits in Tethyan Jurassic ophiolites of the Northern Apennine. The average d34S value is +5.2‰ in pyrite (n. 22), +6.7‰ in chalcopyrite (n. 23), +6.1‰ in sphalerite (n. 9), and 4.6‰ in pyrrhotite (n. 2). The overall average d34S of +5.9‰ (n = 30, s = 3.7) is consistent with data from other sulfide deposits of the Eastern Mediterranean Tethys, although the Apennine ores display a distinctive range from +11.4‰ to the negative field (min. -2.9). The highest d34S‰ values are found in stockwork veins crosscutting basalt and gabbro, and in stratabound ores within basalt (av., +8.9‰). The d34S decreases in serpentinite-hosted stockwork veins (av., +5.8‰) and in stratiform deposits lying on ancient seafloors (av., +2.5‰), in which the negative values were detected. Inorganic reduction of seawater sulfate is assumed to be the primary source of sulfur in the deposits, with some exception however. The low d34S values of serpentinite-hosted veins indicate mixing with sulfur derived from the leaching of magmatic sulfides (av., d34S = +0.8‰). The negative values detected in seafloor-stratiform ores correlate with sulfide textures indicative of the activity of sulfate-reducing bacteria causing preferential fractionation of the light sulfur isotope. The sulfur isotope variations observed in the Northern Apennine VMS deposits reflect the influence of the different environments of sulfide deposition (seafloor vs. subseafloor) and different lithologies of the host rocks (basalt vs. serpentinite).

Precambrian volcanic-associated massive sulfide deposits

Phanerozoic volcanic-associated massive sulfide deposits (VMSD) were subdivided into the Kuroko, Besshi, Cyprus, and Ural types, which differ in their ore geochemistry and mineralogy, in their composition of volcanic ore-hosting rock associations, and in the proportions of felsic and basaltic volcanics and sedimentary rocks in the volcanic successions. The earliest deposits that can be reliably attributed to the above types originated during the Neoproterozoic during the Pangea supercontinental cycle. Archean and Paleoproterozoic VMSD can be accepted as analogues of these types, resembling them in many respects, although differing from the classic deposits of these types in some characteristics. The formation history of Cyprus-type VMSD is traceable to the Paleoproterozoic when deposits in the Outocumpu area dated at approximately 1970 Ma originated during the early stage of Pangea-I amalgamation, whereas the most ancient Besshi-type deposits 1440 million years old originated during the breakup of that supercontinent. Most of the Neoarchean and Paleoproterozoic VMSD are similar in some of their principal features to those of the Ural and Kuroko types. Deposits of both these types and their ancient analogues evolved in the process of the Earth’s evolution and demonstrated unidirectional changes in their ore composition.

Mineral Deposits of Turkey in Relation to Tethyan Metallogeny: Implications for Future Mineral Exploration

The Tethyan metallogeny of Turkey, shaped by the interplay between subduction, collision, postcollision, and rifting processes, is mainly associated with Late Cretaceous to Cenozoic volcanoplutonic and ophiolitic rocks. A wide spectrum of ore deposits is represented from those occurring in island arcs to those associated with continental settings. Though Turkey has been one of the leading producers of chromite, the country is an emerging producer of precious and base metals. This assessment of the metallogeny of Turkey is based on a comprehensive GIS database compilation that contains known mineral deposits and prospects with relevant descriptive data. The data set contains information on major deposit types of economic importance such as porphyry, skarn, epithermal including both high-and low-sulfidation, polymetallic volcanic-associated massive sulfide (VMS) deposits including both Kuroko and Cyprus types, podiform chromite, lateritic nickel, carbonate-hosted lead-zinc with nonsulfide zinc including sedimentary-exhalative (SEDEX) and Mississippi Valley type (MVT), karstic and lateritic bauxite, orogenic gold including both mesothermal and listwanite-hosted types, and placer deposits. Well known deposit types that are less well represented in the database include sediment-hosted Cu, Carlin-type gold, iron oxide copper-gold (IOCG), and detachment-fault related gold systems. Exploration programs in the last two decades have started to reveal the true mineral potential of the country. Turkey is an underexplored country by today’s standards, with a large prospective area with a wide spectrum of mineral deposits reflecting the diverse geological environments that are present. Turkey is the least well explored portion of the Tethyan belt, which hosts Au and Cu endowments comparable with the Andes and the southwest Pacific metallogenic belts.

Geologic Setting of Volcanic-Associated Massive Sulfide Deposits in the Kamiskotia Area, Abitibi Subprovince, Canada

The Upper Archean volcanic succession in the Kamiskotia area (Abitibi greenstone belt, Timmins region) hosts a series of past-producing copper-zinc volcanic-associated massive sulfide (VMS) deposits. All of these occur within a restricted, east-facing stratigraphic interval in the upper part of the Kamiskotia Volcanic Complex. New U-Pb ages for this interval, ranging from 2701.1 ± 1.4 to 2698.6 ± 1.3 Ma, and an age of 2703.1 ± 1.2 Ma from the lower part of the Kamiskotia Volcanic Complex, indicate that the complex is likely part of the Blake River assemblage (2701–2697 Ma) rather than the older Tisdale assemblage (2710–2703 Ma). The Kamiskotia Volcanic Complex consists largely of felsic and mafic lava flows, and VMS mineralization appears to have generally developed at or near the sea floor close to inferred synvolcanic faults. New U-Pb ages of 2714.6 ± 1.2 and 2712.3 ± 2.8 Ma from the northeast-facing volcanic succession in the northern part of the study area (Loveland, Macdiarmid, and Thorburn Townships) indicate that it forms part of the Kidd-Munro assemblage (2719–2710 Ma). A west-northwest–trending faulted contact is inferred between this older succession and the Kamiskotia Volcanic Complex rocks to the south. The Kidd-Munro assemblage rocks are coeval with the Kidd Volcanic Complex, which hosts the giant Kidd Creek VMS deposit 30 km to the east of the study area. The lower part of the succession, in south-central Loveland Township, consists of high silica FIIIb rhyolites. These rocks are geochemically similar to ore-associated FIIIb rocks from Kidd Creek and seem likely to represent the most prospective part of this succession. Future exploration in the Kamiskotia Volcanic Complex is probably best focused on the along-strike extension of the VMS-hosting interval and, in particular, on areas close to the intersections of synvolcanic faults. Mafic and felsic volcaniclastic strata which can be replaced by VMS mineralization, and felsic coherent facies flows and/or domes, appear to be important potential targets.

U–Pb Geochronology of VMS mineralization in the Iberian Pyrite Belt

A geochronology study using U–Pb isotope dilution TIMS analyses of zircon has been conducted to determine the ages of volcanic-associated massive sulfide (VMS) deposits in the Iberian Pyrite Belt (IPB), the world's most prolific VMS province. Ages have been determined for host rocks to four VMS systems that span the IPB: the giant Rio Tinto and Aljustrel districts in the central region, Lagoa Salgada to the west, and Las Cruces to the east. A sample of chloritized quartz porphyritic dacite/rhyolite in the footwall of the San Dionisio massive sulfide deposit of the Rio Tinto district is 349.76±0.90 Ma. This is taken as the best age estimate of the mineralization in the Rio Tinto district, probably the world's largest volcanogenic massive sulfide system. Two xenocrystic zircons from the same sample yielded 207Pb/206Pb ages of 414 and 416 Ma, which provide a minimum estimate for the age of the inherited component. A biotite tonalite from the Campofrio area, 3.5 km north of the center of the Rio Tinto district, is chemically similar to the felsic host rock protolith at Rio Tinto. The Campofrio sample has an age of 346.26±0.81 Ma, slightly younger and outside of the 2σ error for the Rio Tinto age; therefore, this phase of this intrusion was not a heat source for the hydrothermal system that formed the deposits of the Rio Tinto district. The Campofrio sample also has three zircon analyses with 207Pb/206Pb minimum ages of 534, 536, and 985 Ma, indicating inheritance from Ordovician and Neoproterozoic sources. In the Aljustrel VMS district, a U–Pb zircon age of 352.9±1.9 Ma characterizes the altered Green Tuff host rock of the Algares deposit, which is slightly older than the Rio Tinto age. Two zircons with 207Pb/206Pb ages of 531 and 571 Ma from this sample indicate inheritance from a Cambrian or older source. The age of mineralization at Lagoa Salgada is given by essentially identical ages of 356.21±0.73 and 356.4±0.8 Ma, for footwall and hanging wall samples, respectively. The hanging wall sample has two zircon analyses with 207Pb/206Pb ages of 464 and 466 Ma, indicating inheritance from an Ordovician or older source. The age for an altered dacite tuff sample from the hanging wall of the Las Cruces deposit is 353.97±0.69 Ma. One zircon analysis from the Las Cruces sample has a 207Pb/206Pb age of 1048 Ma, indicating inheritance from a Neoproterozoic source. These U–Pb ages refine the IPB geochronology provided by previous studies, and they suggest that either volcanism progressed toward the center of the IPB, or that volcanism was broadly static and the strata were progressively rifted to the margins during transtensional basin formation. The zircon inheritance provides direct evidence for Proterozoic to Ordovician sources, reflecting either basement rocks beneath the Phyllite–Quartzite Group during VMS formation in late Tournaisian times, or a Proterozoic to Ordovician detrital component in Phyllite–Quartzite Group source rocks. The presence of an older crustal component is consistent with VMS formation during rift development at a continental margin.

Facies analysis of a 1.9 Ga, continental margin, back-arc, felsic caldera province with diverse Zn-Pb-Ag-(Cu-Au) sulfide and Fe oxide deposits, Bergslagen region, Sweden

The Bergslagen mining district in south-central Sweden has been a major metal producer for more than 1,000 years. In geologic terms, Bergslagen is the intensely mineralized part of a large, Early Proterozoic (mainly 1.90-1.87 Ga), felsic magmatic region of mainly medium to high metamorphic grade in the Baltic Shield. The district contains a diverse range of ore deposit types, including banded iron-formation, magnetitecalc-silicate skarn, manganiferous skarn- and carbonate-hosted iron ore, apatite-bearing iron ore, stratiform and strata-bound Zn-Pb-Ag-(Cu-Au) sulfide ores, and W skarn. Most ore deposits occur in hydrothermally altered metavolcanic rocks and associated metalimestones and skarns.This study is a field-oriented, regional facies analysis based on recognition of primary volcanic and sedimentary features through the strong overprints of hydrothermal alteration, deformation, and metamorphism. The region is interpreted as an extensional, probably back-arc, active continental margin magmatic region. It evolved through stages of intense magmatism, thermal doming, and crustal extension, followed by waning extension, waning volcanism, thermal subsidence, reversal from extension to compressional deformation, regional metamorphism, and structural inversion. The volcanic successions comprise interfingering proximal (near vent), medial (volcano flanks), and distal (volcano margin) facies associations of rhyolitic pyroclastic caldera volcanoes and subordinate dacite-rhyolite complexes. Nonwelded to poorly welded pyroclastic flow and fallout units, and their rapidly resedimented subaerial and subaqueous equivalents are the most abundant volcanic facies. Subvolcanic porphyritic intrusions and cryptodomes are also abundant. The pyroclastic debris was shed from mainly shallow-water and subaerial proximal areas to shallow- and moderately deep-water (above and below storm wave base) distal areas.Most ore deposits formed during the regional waning volcanic stage and occur in medial to distal facies associations that comprise rhyolitic ash-siltstone, limestone, and vitric crystal sandstone and breccia. These mineralized facies associations were deposited in subaqueous environments mainly below the fair weather wave base, but locally above the storm wave base. Water depths are interpreted to have been mainly 10 to 500 m, with local deeper areas. Although the ore deposits occur in medial to distal facies associations, many occur above, or laterally adjacent to, subsided volcanic vent complexes. This suggests a spatial, temporal, and possible genetic relationship between several ore deposit types and the late magmatic stage of these volcanic centers. Except for the apatite-bearing iron deposits, it is uncertain if the ores are genetically related to specific magmatic hydrothermal events from specific volcanoes. This is possible, especially for the base metal sulfide deposits, which have intense localized footwall alteration in felsic volcanic rocks. However, an important role of the volcanic centers may have been to provide strong positive pertubations (+ or - magmatic hydrothermal input) to the regional convective geothermal system.The main Zn-Pb-Ag-(Cu-Au) ore deposits span a range between two end-member types: stratiform ash-siltstone-hosted sea-floor deposits that have similarities to some stratiform sediment-hosted Zn-Pb-Ag deposits, especially the Broken Hill-type deposits; and strata-bound volcanic-associated limestone-skarn subsea-floor replacement deposits that more closely resemble felsic volcanic-associated massive sulfide deposits. Facies models are presented for both. The banded iron-formations are interpreted as chemical suspension deposits, rhythmically interbedded with rhyolitic ash-siltstone. The skarn iron ores are strata bound in limestones and include metamorphosed sedimentary ores and metasomatic replacements. Apatite-bearing iron ores differ in setting from the other ores in being formed within a dacitic intrusive complex that may be the root zone of a dacite-rhyolite volcanic center.

Underwater chemistry creates massive seafloor mineral deposits

Cores retrieved from a mound at the bottom of the sea where sulfide deposits are actively forming indicate that these modern-day accumulations are comparable in size with valuable ancient deposits on land. The cores also provide important new clues about how volcanic-associated massive sulfide deposits are initially formed. A multinational team of scientists brought these insights back from a fall 1994 cruise of the Ocean Drilling Program (ODP), an international partnership for geological oceanography funded principally by the U.S. National Science Foundation, and reported its work in Nature [ 377 , 713 (1995)]. The results of this expedition have been eagerly awaited, according to Randolph A. Koski, a geologist with the U.S. Geological Survey in Menlo Park, Calif. The study provides, for the first time, a glimpse of the processes operating within such a deposit, he commented in Nature . Overcoming the engineering challenges of drilling into an active hydrothermal system, the team drilled 17 holes int...

Zircon thermometry of high-temperature rhyolites near volcanic-associated massive sulfide deposits, Abitibi subprovince, Canada

Research Article| February 01, 1995 Zircon thermometry of high-temperature rhyolites near volcanic-associated massive sulfide deposits, Abitibi subprovince, Canada C. Tucker Barrie C. Tucker Barrie 1Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada Search for other works by this author on: GSW Google Scholar Geology (1995) 23 (2): 169–172. https://doi.org/10.1130/0091-7613(1995)023<0169:ZTOHTR>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation C. Tucker Barrie; Zircon thermometry of high-temperature rhyolites near volcanic-associated massive sulfide deposits, Abitibi subprovince, Canada. Geology 1995;; 23 (2): 169–172. doi: https://doi.org/10.1130/0091-7613(1995)023<0169:ZTOHTR>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGeology Search Advanced Search Abstract High-temperature, high-silica rhyolites are commonly found near Cu-Zn volcanic-associated massive sulfide (VMS) deposits in the Archean Abitibi subprovince. They are characterized by anhydrous phenocrysts (feldspar, quartz) in concentrations of generally <15 modal percent and have >73% SiO(2), high incompatible element contents, Rb/Sr > 1, Zr/Y < 5, La(N)/Yb(N) < 3.5, and negative Eu anomalies. They have zircon saturation temperatures of 840–940 ° C, as calculated by using the zircon solubility model, which are higher than most other Abitibi rhyolites. Considering their high zircon saturation temperatures, their composition, and their spatial and temporal associations with tholeiitic mafic and ultramafic rocks, Abitibi high-temperature rhyolites are similar to silicic volcanic rocks found in hotspot-related oceanic settings with anomalously high heat flow, such as in eastern Iceland. The association of high-temperature rhyolites with VMS deposits may provide a useful exploration guide where zircon inheritance is minimal, such as in many of the primitive Archean and Early Proterozoic greenstone belts. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

Silicification and metal leaching in semiconformable alteration beneath the Chisel Lake massive sulfide deposit, Snow Lake, Manitoba

Regionally extensive semiconformable zones of silicified, Fe-Mg metasomatized and epidotized, dominantly mafic, volcaniclastic strata and lava flows are exposed 1 to 2 km stratigraphically beneath the Chisel Lake Zn-Cu massive sulfide deposit, Snow Lake district, Manitoba. The alteration zones occur within a Lower Proterozoic medium-grade regional metamorphic terrane of felsic and mafic volcanics and marine sediments, and lie between subvolcanic tonalite sills and the massive sulfide deposit.Semiconformable alteration occurs at two main stratigraphic positions. The lower zone of silicification in pillowed and massive mafic lavas is inferred to have occurred close to the sea floor and probably was not related directly to formation of the Chisel Lake massive sulfide deposit. The stratigraphically higher zone, which may be spatially and temporally associated with massive sulfide deposition, occurs in a approximately 300-m-thick heterolithic mafic volcanic breccia and wacke unit. This volcaniclastic-hosted alteration is zoned laterally from dominantly silicification and epidotization to mainly Fe-Mg metasomatized, garnet-chlorite + or - biotite + or - staurolite rocks nearer the Chisel Lake sulfide deposit. A discordant footwall Fe-Mg alteration zone directly beneath the sulfide deposit extends toward, and may meet, the semiconformable Fe-Mg metasomatized zone.Silicification contributed to partial to complete replacement of volcanic clasts, beds in the volcaniclastic unit, rocks adjacent to some felsic dikes and pillow interiors by quartz and sodic plagioclase. Mass balance calculations for silicified rocks and equivalent least altered parts of volcaniclastic beds, dikes, and pillows indicate that SiO 2 increased by up to 50 percent of its initial value, and Na 2 O by up to 30 percent. Up to 80 percent of the FeO, MgO, CaO, and Zn was removed during silicification. Elemental fluxes during Fe-Mg metasomatism are generally opposite those characterizing silicification and are of comparable magnitude. Epidotization resulted in depletion of Na, total Fe (but increased the Fe (super 2+) /Fe (super 3+) ratio), Mg, Mn, K, Zn, and Ba, and enrichment in Ca and Sr relative to least altered rocks. Almost constant interelement ratios of Ti, Zr, and Al in altered and less altered rocks indicate that these elements were essentially immobile during metasomatism and subsequent medium-grade regional metamorphisrm. Limited data suggest that the heavy REE were also immobile during silicification.The subconcordant silicification in the mafic volcaniclastic unit is interpreted to have formed at subsea-floor depths of 1 to 2 km where a felsic dike swarm and subvolcanic tonalite sills heated Si-rich evolved seawater above the temperature of the silica solubility maximum ( approximately 340 degrees -450 degrees C at pressures below 900 bars) causing silica deposition and metal leaching. A portion of the Fe, Mg, and possibly Zn that was leached from the subconcordant silicified zone may have been transported laterally away from this environment, thereby producing the semiconformable Fe-Mg metasomatized zones. Cross stratal structures similar to the hydrothermally altered synvolcanic faults that are known to cut the semiconformable alteration may represent fluid flow paths from a subconcordant metal reservoir in the volcaniclastic unit to the sea floor, where massive sulfides were deposited.Semiconformable pervasively silicified zones, particularly those associated with Fe-Mg metasomatized and/or epidotized rocks, are significantly larger exploration targets than areas of proximal alteration, and indicate large-scale hydrothermal mass transfer. Zonation of silicification to Fe-Mg metasomatism laterally within the alteration may provide a vector toward the discordant Fe-Mg-enriched alteration zones that commonly underlie volcanic-associated massive sulfide deposits.

Gold distribution in the Mobrun volcanic-associated massive sulfide deposit, Noranda, Quebec; a preliminary evaluation of the role of metamorphic remobilization

The Mobrun Zn-Cu-Au-Ag orebodies show metal zonation typical of volcanic-associated massive sulfide deposits, although some metamorphic remobilization of metals has occurred. The nature and distribution of primary facies are the result of synvolcanic deposition and reworking of sulfides by hydrothermal fluids. Secondary facies resulting from metamorphism and deformation locally overprint primary facies and include transgressive veins which contain remobilized Au as electrum. The distribution of secondary facies was controlled by the mechanical properties of the mineralization as well as of the surrounding rocks; the mechanical response of different facies to deformation influenced the development and distribution of zones containing easily recoverable gold. Preservation of primary textures is best in the Main and Satellite lenses. The 1100 lens also shows significant preservation of primary facies; however, development of secondary facies is pronounced. Textural, structural, and chemical evidence indicates that the 1100 lens was subjected to more extreme metamorphic recrystallization and deformation than the other lenses. Metamorphic remobilization was important in releasing refractory Au from sulfides and locally concentrating it in a recoverable form (electrum).

Two-fold classification of Archean volcanic-associated massive sulfide deposits

Two-fold classification of Archean volcanic-associated massive sulfide deposits