scholarly journals Prediction of Mississippi-Valley type ore fluid metal concentrations from solid solution metal concentrations in ore-stage minerals

2017 ◽  
Author(s):  
◽  
Sarah Smith
Keyword(s):  
Solid Solution ◽  
Fluid Inclusion ◽  
Distribution Coefficient ◽  
Fluid Inclusions ◽  
Mississippi Valley ◽  
Carbonate Minerals ◽  
Metal Concentrations ◽  
Fluid Inclusion Data ◽  
Mvt Deposits ◽  
Mississippi Valley Type

Mississippi-Valley-type (MVT) deposits have some of the greatest enrichments of Pb, Zn, Ba, and F in the Earth's crust. Fundamental to understanding how these elements were transported and precipitated to form MVT deposits is knowledge of their concentrations in the ore fluids. Recent research aimed at determining the concentrations of Pb, Zn, and Ba in the ore fluids that formed the MVT deposits of the U.S. midcontinent, the type examples for the MVT deposit class, has focused on using LA-ICPMS to analyze fluid inclusions. This research has shown U.S. mid-continent MVT ore fluids to have Ba concentrations on the order of 10's of ppm. However, LA-ICP-MS results for Pb and Zn concentrations are equivocal due to interferences from Zn and Pb in the host mineral matrix and uncertainties about whether the measured Pb and Zn signals represent aqueous solute or "accidentals", i.e. Pb or Zn solid particulates entrained within the fluid inclusions. In light of these limitations, this study sought to determine metal concentrations in MVT ore fluids instead by calculating them theoretically based on their solid solution concentrations in the ore-stage minerals calcite and galena. Using experimental partition coefficients from Rimstidt et al. (1998) at ore stage temperatures and measured compositions of ore-stage calcite from the Illinois-Kentucky and Central Tennessee MVT districts, concentrations of Mg, Mn, Fe, Zn, Sr, Ba, and Pb in the ore fluid were predicted. The predicted ore fluid concentrations of Mg and Mn, which form carbonate minerals (magnesite and rhodochrosite) with the calcite structure, were in good agreement with available fluid inclusion data for these elements. Thus, the predicted ore fluid concentrations of Zn and Fe, which also form carbonate minerals (smithsonite and siderite) with the calcite structure, 10s of ppm Zn and 1s to 10s of ppm Fe in Illinois-Kentucky and a maximum of 10s of ppm Zn and 1s to 10s of ppm Fe in Central Tennessee , are likely to be accurate. These Zn concentrations are typical of modern sedimentary brines and high enough to allow efficient Zn ore formation. In contrast, the predicted ore fluid concentrations of Sr and Ba, which form carbonate minerals (strontianite and witherite) with the aragonite structure, were in poor agreement with available fluid inclusion data for these elements. Thus, the predicted 1s of ppm ore fluid concentration of Pb, which also forms a carbonate mineral (cerussite) with the aragonite structure, is unlikely to be accurate. Using predicted thermodynamic data (Sverjensky, 1985) for ZnS with the galena structure, a thermodynamic distribution coefficient for Zn between aqueous solution and solid solution in galena was calculated. This distribution coefficient was used in combination with Zn concentrations measured in solid solution in galena from the Central Missouri, Central Tennessee, Illinois-Kentucky, Northern Arkansas, Tri-State, and Southeast Missouri MVT districts to predict Zn/Pb ratios for the ore fluids. The Zn/Pb ratios do not agree with the ore Zn/Pb ratios of the districts and appear to be an artifact of the temperature used in the calculations. Therefore the predicted ore fluid Zn/Pb ratios are unlikely to be correct.

Formation of emeralds at pegmatite-ultramafic contacts based on fluid inclusions in Kianjavato emerald, Mananjary deposits, Madagascar

2006 ◽  
Vol 70 (2) ◽  
pp. 141-158 ◽  
Author(s):  
Ye. Vapnik ◽  
I. Moroz ◽  
M. Roth ◽  
I. Eliezri
Keyword(s):  
Fluid Inclusion ◽  
Fluid Inclusions ◽  
East Coast ◽  
Fluid Inclusion Data ◽  
Pan African ◽  
Probe Analysis ◽  
Raman Probe

AbstractKianjavato emerald (Mananjary deposits, East coast of Madagascar) was formed during metasomatic processes at the contact between pegmatites and hornblendites. The metasomatic exchange was related to a Pan-African tectonometamorphic event.Fluid inclusions in the Kianjavato emerald and quartz were studied by means of microthermometry and Raman probe analysis. Three main types of inclusions were revealed: CO2-rich, CH4-rich and aqueous-rich, with a salinity of ∼2 wt.% NaCl equiv. The inclusions occurred along the same primary and pseudosecondary trails and were considered to be formed simultaneously. Based on fluid-inclusion data, the conditions of emerald growth were 250°C < T < 450°C and P = 1.5 kbar.The fluid inclusion data for Kianjavato emerald were compared to the data for another Madagascar emerald, Ianapera. The latter is of similar age, but its genesis was determined by a shearing event. Our fluid inclusion data suggested that shearing was also important as a mechanism of introducing CO2-rich fluid for the genesis of the Kianjavato emerald.

Composition of tetrahedrite-tennantite and ‘schwazite’ in the Schwaz silver mines, North Tyrol, Austria

1998 ◽  
Vol 62 (6) ◽  
pp. 801-820 ◽  
Author(s):  
T. Arlt ◽  
L. W. Diamond
Keyword(s):  
Solid Solution ◽  
Electron Microprobe ◽  
Hydrothermal System ◽  
Temporal Evolution ◽  
Main Stage ◽  
Mississippi Valley ◽  
Museum Collections ◽  
Solid Solution Series ◽  
Structural Style ◽  
Mississippi Valley Type

AbstractThe hydrothermal fahlore deposits of the Schwaz-Brixlegg district have been mined for silver and copper over many centuries and are famous as the type locality of the mercurian fahlore variety ‘schwazite’. The ore is dominantly monomineralic fahlore and occurs as stratabound, discordant vein, and breccia bodies over a 20 km belt hosted mostly by the Devonian Schwaz Dolomite. The structural style of the mineralization is similar to that of Mississippi Valley type deposits.This study presents the first electron microprobe analyses of the ores and reveals wide variations in fahlore compositions, from 35 to 100 wt.% tetrahedrite end-member in the solid solution series with tennantite. Sb and Zn contents vary between 12.1–28.0 wt.% and 0.1–7.6 wt.%, respectively. Silver contents average 0.5 wt.% and range up to 2.0 wt.%. In the breccia-hosted ores these variations clearly result from a temporal evolution in the ore-forming hydrothermal system: main-stage tetrahedrite is replaced by assemblages of Sb-, Fe-, and Ag-enriched tetrahedrite + enargite, with minor sphalerite ± stibnite ± cuprian pyrite (≤ 25 wt.% Cu). These reactions are deduced to result from either increases in aqueous sulphur activity or falling temperature. Earlier workers recognized strong geographic zonation of fahlore compositions, but our microprobe analyses refute these contentions.The 1167 new microprobe analyses of 51 fahlore samples collected underground or obtained from museum collections yield an average Hg content of 1.8 wt.%, and a maximum of 9.4 wt.%. According to modern nomenclature, not even the highest Hg value qualifies as ‘schwazite’. Moreover, it appears that the original and only analysis of ‘schwazite’, reporting 15.6 wt.% Hg (Weidenbusch, 1849), was erroneously performed on a polymineralic aggregate, rather than on a monomineralic fahlore. We conclude that the Schwaz-Brixlegg fahlores are in fact not unusually rich in mercury, and that in all probability there is not, and never has been, any ‘schwazite’ at Schwaz.

Late thermal events in the Mesozoic Basque basin : evidence from secondary fluid inclusions in Mississippi-Valley type fluorite occurrences

1988 ◽  
Vol 111 (3) ◽  
pp. 413-420 ◽  
Author(s):  
José-Miguel Herrero ◽  
Marisol Perez-Alvarez ◽  
Jean-Claude Touray ◽  
Francisco Velasco
Keyword(s):  
Fluid Inclusions ◽  
Mississippi Valley ◽  
Secondary Fluid ◽  
Mississippi Valley Type ◽  
Valley Type

Fluid-inclusion evidence of basinal brines in Archean basement, Thunder Bay Pb–Zn–Ba district, Ontario, Canada

1988 ◽  
Vol 25 (11) ◽  
pp. 1884-1894 ◽  
Author(s):  
Frederick M. Haynes
Keyword(s):  
Fluid Inclusion ◽  
Fluid Inclusions ◽  
Ore Deposits ◽  
Temperature Phase ◽  
Type I ◽  
Mississippi Valley ◽  
Thunder Bay ◽  
Calcite Veins ◽  
Archean Basement ◽  
Liquid Vapor

Fluid inclusions from three quartz–galena–sphalerite–barite–calcite veins in the Thunder Bay district of western Ontario contain liquid + vapor ± halite and homogenize by vapor disappearance or halite dissolution at temperatures of 90–200 °C. Cyclically frozen, liquid + vapor (type I) inclusions undergo four melting events upon gradual warming (initial melting at −55 to −46 °C; ice disappearance at −30.2 to −25.4 °C; inversion of hydrohalite to halite at −8.0 to 0.7 °C; and halite melting at 14.0 to 56.3 °C. Liquid + vapor + halite (type II) inclusions behave similarly but have higher Tm ice (−27.2 to −21.7 °C) and Tm halite (105–203 °C). Scanning electron microscopy and energy dispersive analysis of fluid-inclusion-derived decrepitates indicate that the solutes consist of NaCl > CaCl2 [Formula: see text] KCl and are consistent with the low-temperature phase observations in that they define two distinct populations based on CaCl2/(CaCl2 + NaCl) ratios.The temperatures and compositional trends defined by the inclusion results are similar to those documented for basinal brines and from fluid inclusions in Mississippi Valley type ore deposits. The Thunder Bay veins cross the basal unconformity of the Middle Proterozoic Sibley basin and extend into Archean basement granites, such that the fluid inclusions results provide direct evidence that basinal waters infiltrated basement rock in western Ontario. The inclusion fluids and associated mineralization are thought to result either from dewatering of the Sibley basin during Keweenaw age rifting or from the introduction of exotic Paleozoic basinal waters when the Michigan basin extended over the region.

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