Normalized REE patterns of aqueous solutions and their precipitates bear information on the physico-chemical environments a fluid experienced during REE mobilization, fluid migration and minerogenesis. Positive Eu and Yb anomalies indicate REE mobilization by a F−-, OH−- and CO32−-poor fluid in a high-temperature regime, but are only retained by a precipitating mineral if precipitation occurs in a low-temperature environment. Negative Ce anomalies are typical of oxidizing conditions and are unlikely to develop during siderite precipitation. LREE/HREE fractionation is controlled by fluid composition and “mineralogical control”. REE patterns of Ca minerals allow to class the reacting fluids in “normal” (Ca/ligand ≫ 1) and “ligand-enriched” (Ca/ligand ≈ 1), the latter being characteristic for remobilization processes.

Rare earth element fractionation in metamorphogenic hydrothermal calcite, magnesite and siderite

Rare Earth Elements in Igneous Rocks of the Continental Crust: Intermediate and Silicic Rocks – Ore Petrogenesis

Rare earth elements and hydrothermal ore formation processes

Isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes: (1) mixing between two different fluids which leads to the precipitation of calcite; (2) mixing between fluid and rock: (a) calcite precipitation due to fluid/rock interaction, (b) secondary alteration of primary calcite by interaction with a subsequent fluid The models are derived from mass balance equations A distinction among the three mixing processes can be made on a δ
13C vs δ
18O diagram, which places important constraints on the genesis of hydrothermal mineralization The variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock, temperature, and dissolved carbon species Owing to significant temperature-dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid, the mixing processes may be distinguished by telltale patterns of isotopic data in δ
13C vs δ
18O space In particular, caution must be exercised in postulating the fluid mixing as the cause for mineral deposition This is demonstrated for hydrothermal Pb-Zn deposits in the western Harz Mountains, Germany A positive correlation between δ
13C and δ
18O values is observed for calcites from the Bad Grund deposit in the Upper Harz Two sample profiles through calcite veins show similar correlations with the lowest δ-values at the center of the veins and the highest δ-values at the vein margins Because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike, it is assumed that a fluid/rock interaction is responsible for the observed correlation and thus for the precipitation of calcite A deep-seated fluid is inferred with a δ
13C value of — 7% and a δ
18O value of +10%, as well as H2CO3 as the dominant dissolved carbon species; precipitation temperatures of the calcites are estimated to be about 280 ∼ 170°C Quite different isotopic distributions are observed for calcites from the St Andreasberg deposit in the Middle Harz An alteration model is suggested based mainly on the isotopic distribution through a calcite vein In addition to a primary fluid which has the same isotopic composition as that in the Bad Grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides, an evolved, HCO
 3
 -
 -dominant subsurface fluid with δ
13C about -20 ∼ — 15% and δ
18O ≤ 0% is deduced to alter the primary calcite at low temperatures of 70 ∼40°C

Carbon and oxygen isotopic covariations in hydrothermal calcites

REE systematics in hydrothermal fluorite

The origin of the ore-bearing solution in the PbZn veins of the western Harz, Germany, as deduced from rare-earth element and isotope distributions in calcites

The origin of the calcites from Pb-Zn veins in the Harz Mountains, Federal Republic of Germany

Petrographic and trace-element distribution studies on the dolomite-calcite in the regional metamorphic marble of the Griesscharte, Tyrol, Austria/Italy

G. Morteani

Papers

The origin of the ore-bearing solution in the PbZn veins of the western Harz, Germany, as deduced from rare-earth element and isotope distributions in calcites

The origin of the calcites from Pb-Zn veins in the Harz Mountains, Federal Republic of Germany

Petrographic and trace-element distribution studies on the dolomite-calcite in the regional metamorphic marble of the Griesscharte, Tyrol, Austria/Italy