Metal Transport and Deposition in Hydrothermal Veins Revealed by 213nm UV Laser Ablation Microanalysis of Single Fluid Inclusions

Stoffell, Barry

doi:10.2475/ajs.304.6.533

Cited by 33 publications

(21 citation statements)

References 22 publications

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“…The observed variations in mean Ag concentration of up to an order of magnitude between different inclusion assemblages containing the same fluid type can be explained by trapping of fluids at various stages of ore mineral precipitation as has been observed for Sn, Cu, Zn and Pb in other ore deposit studies8202122. Although Ag, Zn and Pb sulfides were not observed in the samples investigated, we suggest this could be due to precipitation occurring beneath (upstream from) the sampling site, as has been previously suggested for an epithermal Pb-Zn vein system8.…”

Section: Discussionsupporting

confidence: 65%

“…Although Ag, Zn and Pb sulfides were not observed in the samples investigated, we suggest this could be due to precipitation occurring beneath (upstream from) the sampling site, as has been previously suggested for an epithermal Pb-Zn vein system8.…”

Section: Discussionmentioning

confidence: 47%

“…Recent analytical developments have made possible the second approach which involves the analysis of trace elements in individual fluid inclusions – fossil solutions trapped during ancient mineral precipitation6 – by laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS; e.g 78…”

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confidence: 99%

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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: Discussionsupporting

confidence: 65%

Section: Discussionmentioning

confidence: 47%

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How metalliferous brines line Mexican epithermal veins with silver

Wilkinson

Simmons²,

Stoffell

2013

Sci Rep

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“…The technique has been widely applied to mineral, glass, and melt-inclusion analysis, and has become increasingly popular for individual fl uid inclusion analysis a result of its trace-element capabilities. Recent fl uid inclusion studies using LA-ICP-MS have provided important constraints on fl uid processes in the crust, especially concerning ore genesis (Appold et al 2004;Audétat et al 2000aAudétat et al , 2000bAudétat and Pettke 2003;Gagnon et al 2004;Muller et al 2001;Rusk et al 2004;Stoffell et al 2004;Ulrich et al 1999Ulrich et al , 2001Ulrich et al , 2002. However, some uncertainties in analytical procedure and data quality remain, a few of which we address in this study.…”

Section: Introductionmentioning

confidence: 95%

Validation of LA-ICP-MS fluid inclusion analysis with synthetic fluid inclusions

Allan

2005

American Mineralogist

150

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Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has become recognized as a sensitive, effi cient, and cost-effective approach to measuring the major-, minor-, and trace-solute compositions of individual fl uid inclusions in minerals. As a prerequisite for the routine analysis of natural inclusions in our laboratory, the precision and accuracy of the technique was assessed using sets of multi-element synthetic fl uid inclusions. Five multi-element standard solutions were prepared, and incorporated as fl uid inclusions in quartz crystals at 750 °C and 7 kbar. Fluid inclusions were ablated with a 193 nm ArF excimer laser and analyzed with a quadrupole ICP-MS, equipped with an octopole reaction cell for the removal of Ar-based interferences. The internal standard used in all cases was Na. Analytical precision for K, Rb, and Cs is typically better than 15% RSD, whereas Li, Mg, Ca, Sr, Ba, Mn, Fe, Cu, Zn, and Cl analyses are typically reproducible within 30% RSD. Measured concentrations approximate a Gaussian distribution, suggesting that analytical errors are random. Analyses for most elements are accurate within 15%. Limits of detection vary widely according to inclusion volume, but are 1 to 100 µg/g for most elements. These fi gures of merit are in excellent agreement with previous studies. We also demonstrate that, over the range investigated, precision and accuracy are insensitive to inclusion size and depth. Finally, the combination of our LA-ICP-MS analyses with microthermometric data shows that charge-balancing to NaCl-H 2 O equivalent chloride molality is the most valid approach to LA-ICP-MS data reduction, where chloride-dominated fl uid inclusions are concerned.

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“…Nonetheless, the ubiquity of the depositional processes would seem to make precipitation efficiency an unlikely key trigger for the formation of rare, large deposits. Another way of considering this is that precipitation efficiency perhaps only varies by 1 order of magnitude in mineralizing hydrothermal systems and, in the few cases where it has been documented, is >85% 98,99 . By contrast, the metal content of fluids can vary by 4-5 orders of magnitude, e.g.…”

Section: Jj Wilkinson Imperial College Londonmentioning

confidence: 99%

Triggers for the formation of porphyry ore deposits in magmatic arcs

2013

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Porphyry ore deposits source much of the copper, molybdenum, gold and silver utilized by humankind. They typically form in magmatic arcs above subduction zones via a series of linked processes, beginning with magma generation in the mantle and ending with the precipitation of metals from hydrous fluids in the shallow crust. A hierarchy of four key "triggers" involved in the formation of porphyry deposits is outlined. Trigger 1 (10 2 -10 3 km scale) is a process of cyclic refertilization of magmas in the deep crust. Trigger 2 (10 1 -10 2 km scale) is the process of sulfide saturation in magmas that can both enhance and destroy ore-forming potential. Trigger 3 (10 0 -10 1 km scale) relates to the efficient transfer of metals into hydrothermal fluids exsolving from porphyry magmas. Trigger 4 (~10 0 km scale) identifies processes that lead to the final precipitation of ore minerals. Although all processes are required to a greater or lesser degree, it is argued that trigger 3, as an over-riding mechanism, can best explain the restriction of large deposits to specific arc segments and time periods. Consequently, recognition of the fingerprint of sulfide saturation in igneous rocks may help mineral exploration companies to identify parts of magmatic arcs particularly predisposed to ore formation.Ore deposits are scarce. Their discovery consumes considerable time and resources and only about one in every one thousand prospects explored by companies is eventually developed into a mine. Deposits often occur in clusters and formed within specific time intervals. This non-uniform pattern provides keys to understanding how and why metals accumulate in some places and not in others and its explanation is fundamental for mineral exploration.The most important metalliferous ore deposits are hydrothermal deposits, formed from hot waters circulating in Earth's crust. Such deposits represent a highly efficient trap where fluids were focused into a limited volume of rock, became supersaturated and precipitated ore minerals. In theory, this does not require unusual fluid compositions 1,2 as long as fluid focusing, sufficient fluid flux and efficient precipitation conditions can be maintained. Recently, this paradigm has been challenged by the recognition that ore fluids in sediment-hosted 3-5 , epithermal 6,7 and porphyryrelated [8][9][10] hydrothermal deposits can carry orders of magnitude more metal than previously considered probable, or measured in modern fluid samples. This suggests that our understanding of metal extraction and transport processes is incomplete.Here, this theme is explored by consideration of porphyry ore deposits [11][12][13][14][15] , remarkable geochemical anomalies that can contain up to 1 Gt of sulphur 16 , 200 Mt copper, 2.5 Mt molybdenum and 2600 t gold 17 . The most copper-rich examples include the 4-5 million-year old El Teniente and Rio Blanco-Los Bronces deposits in Central Chile, and the most gold-rich is the 3 million-year old Grasberg deposit in Irian Jaya, Papua New Guinea 17 .Porphyry deposits...

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Metal Transport and Deposition in Hydrothermal Veins Revealed by 213nm UV Laser Ablation Microanalysis of Single Fluid Inclusions

Cited by 33 publications

References 22 publications

How metalliferous brines line Mexican epithermal veins with silver

How metalliferous brines line Mexican epithermal veins with silver

Validation of LA-ICP-MS fluid inclusion analysis with synthetic fluid inclusions

Triggers for the formation of porphyry ore deposits in magmatic arcs

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