The Genesis of Distal Zinc Skarns: Evidence from the Mochito Deposit, Honduras

Williams‐Jones, Anthony E.; Samson, Iain M.; Ault, Katherine M.; Gagnon, Joel E.; Fryer, Brian J.

doi:10.2113/econgeo.105.8.1411

Cited by 111 publications

(30 citation statements)

References 37 publications

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“…However, the loss of these elements, together with trace metals such as Bi, can be explained by the deep level mineralization that produced Cu-Zn-Pb-rich chimney and manto deposits underlying Cerro Proaño1417. Relatively elevated Ca and Sr can be accounted for by the replacement of calc-silicates and carbonates by sulfides during manto formation by a similar process to that recorded in the Mochito distal Zn skarn deposit, Honduras, which is also thought to have formed from evolving magmatic fluids30. The apparent depletion in Mg in the Fresnillo fluids may reflect dolomite formation in the manto-forming event14.…”

Section: Discussionmentioning

confidence: 85%

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How metalliferous brines line Mexican epithermal veins with silver

Wilkinson

Simmons²,

Stoffell

2013

Sci Rep

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We determined the composition of ~30-m.y.-old solutions extracted from fluid inclusions in one of the world's largest and richest silver ore deposits at Fresnillo, Mexico. Silver concentrations average 14 ppm and have a maximum of 27 ppm. The highest silver, lead and zinc concentrations correlate with salinity, consistent with transport by chloro-complexes and confirming the importance of brines in ore formation. The temporal distribution of these fluids within the veins suggests mineralization occurred episodically when they were injected into a fracture system dominated by low salinity, metal-poor fluids. Mass balance shows that a modest volume of brine, most likely of magmatic origin, is sufficient to supply the metal found in large Mexican silver deposits. The results suggest that ancient epithermal ore-forming events may involve fluid packets not captured in modern geothermal sampling and that giant ore deposits can form rapidly from small volumes of metal-rich fluid.

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Section: Discussionmentioning

confidence: 85%

“…Mole Granite brine inclusion data (Leno 1 sample) from Audétat et al20. Zinc skarn fluid inclusion data (average of garnet- and pyroxene-hosted inclusions) from Williams-Jones et al30. Taupo Volcanic Zone fluid data from Simmons and Brown5.…”

Section: Figurementioning

confidence: 99%

How metalliferous brines line Mexican epithermal veins with silver

Wilkinson

Simmons²,

Stoffell

2013

Sci Rep

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“…The highest homogenization temperatures were measured in diopside (335°-410°C), suggesting that this mineral was probably one of the earliest to form in the skarn. Although most fluid inclusions studies of skarn deposits report much higher temperatures (>700°C), lower temperatures have been documented, particularly for Cu and Zn skarns (300°-550°C) (Meinert et al, 2005;Williams-Jones et al, 2010). This discrepancy is generally attributed to the position of the skarn relative to the pluton, i.e., proximal for high temperature and distal for lower temperature.…”

Section: Fluid Evolutionmentioning

confidence: 99%

The Origin of Skarn-Hosted Rare-Metal Mineralization in the Ambohimirahavavy Alkaline Complex, Madagascar

et al. 2015

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The Cenozoic Ambohimirahavavy alkaline complex in Madagascar consists of several syenitic to granitic intrusions (24.2 ± 0.6 Ma) the largest of which, the Ampasibitika intrusion, is characterized by the presence in its outer flanks of late peralkaline granitic dikes intruding mudstone and limestone of the Isalo Group. A network of dikelets and veinlets propagates from these dikes, intruding along bedding or obliquely to bedding. At the contact between the dikes and dikelets and a limestone, a reaction zone enriched in rare metals, dominated by calc-silicate minerals such diopside and andradite-grossular, forms a rare example of skarn resulting from peralkaline igneous activity.Much of the rare-metal mineralization (REE, Zr, Nb, Th, Sn, and Ti) occurs as secondary phases in the dikelets and skarn. In the dikelets and endoskarn, high field strength element (HFSE)-rich phases consist mainly of zircon, bastnäsite-(Ce), and Ca-REE-, and Ca-HFSE-rich phases in pseudomorphs after aegirine-augite. In the exoskarn, the main HFSE-rich phases are bastnäsite-(Ce), zircon, pyrochlore, Nb-rich titanite, and an unidentified F-rich Ca-zirconosilicate finely disseminated in a matrix composed of calcite, diopside, andradite, phlogopite, quartz, fluorite, and fluorapatite. The secondary zircon is characterized by a low Zr content and by the presence of REE, Ca, Al, and Fe.Three types of primary fluid inclusions were observed in dikelets and skarn in quartz, calcite, and diopside: (1) liquid-rich inclusions (L-V) (20 to 40 vol % vapor) occur in all three minerals and homogenize to liquid;(2) vapor-rich inclusions (V) (>90 vol % vapor) occur in diopside and quartz, and homogenize to vapor; and (3) halite-bearing L-V inclusions (L-V-H) occur in diopside and quartz, and homogenize either by disappearance of the vapor bubble or by halite dissolution. The L-V inclusions have low to intermediate salinity and homogenize at temperatures ranging from 200° to 380°C. The V inclusions have low salinity and homogenize at higher temperature (350°-395°C). The L-V-H inclusions mainly contain NaCl (35-45 wt % NaCl equiv), and homogenize by three modes, namely, bubble disappearance (mode A), halite dissolution (mode B), and simultaneous bubble and halite disappearance (mode C); the homogenization temperatures range from 260° to 380°C. We propose a model in which rare metals were transported by a Cl − , F − and HFSE-rich orthomagmatic fluid exsolved at 400° to 450°C and about 20 MPa. At these conditions, the fluid was in the two-phase region and vapor dominated. The rare metals were deposited as a result of the interaction of this fluid with limestone and mixing with an external fluid. This interaction/mixing buffered the orthomagmatic fluid to higher pH and lower temperature, resulting in the destabilization of REE-chloride complexes and deposition of fluorocarbonate minerals in the limestone; Zr and Nb, which were likely transported as hydroxyl-fluoride complexes, precipitated as zircon and pyrochlore due to deposition of fluorite and a consequent d...

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“…This may account for precipitation of Cu-bearing sulfides (chalcopyrite, bornite, chalcocite, etc.). Such a model is established on the basis of the sole magmatic origin for the formation of prograde skarn, retrograde skarn, and hydrothermal ore precipitation [3,8,66]. However, we cannot exclude the contributions of external fluids at present, such as admixture of meteoric and formation waters, which have already been evidenced in some other skarn deposits by some geochemical and isotopic data [1,[67][68][69][70]].…”

Section: Quartz-sulfide Stage (Stage 3)mentioning

confidence: 99%

Fluid Evolution of Fuzishan Skarn Cu-Mo Deposit from the Edong District in the Middle-Lower Yangtze River Metallogenic Belt of China: Evidence from Petrography, Mineral Assemblages, and Fluid Inclusions

et al. 2018

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The Fuzishan Cu-Mo deposit is located in the Edong district of the Middle-Lower Yangtze River Metallogenic Belt, China. The orebodies mainly occurred as lenticular and bedded shapes in the skarn zone between the Lower Permian Qixia Formation carbonate rocks and the quartz diorite. Four paragenetic stages have been recognized based on petrographic observations: (1) prograde skarn stage, (2) retrograde skarn stage, (3) quartz-sulfide stage, and (4) carbonate stage. Six fluid inclusion types were recognized: S 1 (vapor + liquid + halite ± other daughter minerals), S 2 (vapor + liquid + daughter minerals except halite), L V (rich liquid + vapor), V L (rich vapor + liquid), V (vapor), and L (liquid) types. Fluid inclusion studies show distinct variations in composition, final homogenization temperature, and salinity in four stages. Daughter minerals of the primary fluid inclusions include chalcopyrite, molybdenite, hematite, anhydrite, calcite, and halite in the prograde skarn stage and hematite, calcite, and sulfide (?) in the retrograde skarn stage. No daughter minerals occurred in the quartz-sulfide and carbonate stages. Final homogenization temperatures recorded in these stages are from 405 to >550°C, from 212 to 498°C, from 150 to 485°C, and from 89 to 223°C, respectively, while salinities are from 3.7 to 42.5, from 2.6 to 18.5, from 2.2 to 17.9, and from 0.2 to 11.5 wt.% NaCl equivalent, respectively. The coexisting V L and S 1 type fluid inclusions show similar homogenization temperature of 550 to about 650°C in the prograde skarn stage, indicating that immiscibility occurred at lithostatic pressure of 700 bars to perhaps 1000 bars, corresponding to a depth of 2.6 km to about 3.7 km. The coeval V L and L V types fluid inclusions with homogenization temperature of 350 to 400°C in the late retrograde skarn and quartz-sulfide stages suggest that boiling occurred under hydrostatic pressure of 150 to 280 bars, equivalent to a depth of 1.5 to 2.8 km. Mo mineralization in the retrograde stage predated Cu mineralization which mainly occurred in the quartz-sulfide stage. Fluid compositions indicate that ore-forming fluid has high fO 2 and rich Cu and Mo concentration in the early stage, while relatively lower fO 2 and poor Cu and Mo concentration in the middle to late stages. Microthermometric data show a decreasing trend in temperature and salinity in the fluid evolution process. Decreasing temperature and boiling event may be the main factors that control the ore precipitation.

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The Genesis of Distal Zinc Skarns: Evidence from the Mochito Deposit, Honduras

Cited by 111 publications

References 37 publications

How metalliferous brines line Mexican epithermal veins with silver

How metalliferous brines line Mexican epithermal veins with silver

The Origin of Skarn-Hosted Rare-Metal Mineralization in the Ambohimirahavavy Alkaline Complex, Madagascar

Fluid Evolution of Fuzishan Skarn Cu-Mo Deposit from the Edong District in the Middle-Lower Yangtze River Metallogenic Belt of China: Evidence from Petrography, Mineral Assemblages, and Fluid Inclusions

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