Mechanisms of mineral zoning

Barnes, H. L.

doi:10.2113/gsecongeo.57.1.30

Cited by 11 publications

(5 citation statements)

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“…In theory, it is possible to compensate for the low solubilities by proportionately larger amounts of solution and longer periods of sulfide deposition, but rough estimates of these parameters for deposits of known size suggest some realistic lower limits of solubility in potentially ore-forming solutions -at least 1-10 ppm of metal, preferably 100 ppm or more (Roedder 1960, Anderson 1983. Also, the relative solubilities of metal sulfides do not agree with the zoning sequences observed in mineral deposits (Barnes 1962). Thus, simple ionic solubility of sulfides is clearly inadequate for the required concentrations of metals in ore-forming fluids.…”

Section: Transport Of Ore Constituentsmentioning

confidence: 94%

“…Thermodynamic calculations by Krauskopf (1964Krauskopf ( , 1967b showed that much of the concentration of the common ore metals in volcanic sublimates could be accounted for by the volatility of their most stable chloride compounds at magmatic temperatures, but the volatilities drop sharply with decreasing temperature and are too small for most ore metals below about 400D-500 D C. Moreover, Barnes (1962) has shown that the observed zoning sequences in hydrothermal deposits (see Ch. This raises the possibility that ore metals contained in some hydrothermal deposits might have been transported in a gaseous phase.…”

Section: Transport Of Ore Constituentsmentioning

confidence: 99%

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Understanding Mineral Deposits

Misra¹

2000

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Section: Transport Of Ore Constituentsmentioning

confidence: 94%

Section: Transport Of Ore Constituentsmentioning

confidence: 99%

Understanding Mineral Deposits

Misra¹

2000

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“…Potassic alteration in porphyry copper deposits involving sericite or orthoclase takes place roughly between 100 ø and 700øC, as determined from homog- The observed W-Mo-Sn-Cu-Zn-Fe-Pb-As metal zonation shows many similarities with zoning patterns inferred from seawater mixing models (Large, 1977;Franklin et al, 1981) and from calculations involving thermodynamic properties and free energies of minerals (e.g., Barnes, 1962;Susak and Crerar, 1982). It is commonly accepted that in volcano-sedimentary terrains precipitation of sulfides associated with alteration of country rock could occur as a consequence of boiling of the metal-bearing fluids (Finlow-Bates and Large, 1978), increase of solution pH, and/or cooling of the fluids caused by mixing with seawater (e.g., Large, 1977;Roberts and Reardon, 1978;MacGeehan, 1978;Stephens, 1980;Hajash and Archer, 1980;Franklin et al, 1981).…”

Section: Microcline-rich Metatuffites and Sulfide Skarns Occurmentioning

confidence: 79%

Paragenetic zoning and genesis of Cu-Zn-Fe-Pb-As sulfide skarn ores in a Proterozoic rift basin, Gruvaasen, western Bergslagen, Sweden

Hellingwerf¹

1984

Economic Geology

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The sulfide skarn ores of the Gruv•en mine area, western Bergslagen, Sweden, occur in a sequence of marbles and metatuffites intruded by basic sills and dikes. The mineralized area is exposed in a block-faulted and tilted structure within the Saxf• sedimentary rift basin. Sulfide mineralization occurs in zones within an area of intense potassic alteration. The central zone of the mineralized area is typified by Cu-W-Mo-bearing microcline skarns, Sn-bearing Cu-Zn-Fe sulfide skarns, a high Fe/Mg atomic ratio in the skarn-forming silicates (actinolite, ferrosalite), and a high Cd content in sphalerites. The peripheral zones are typified by ZnFe-As-Pb sulfide skarns, a low Fe/Mg atomic ratio in the skarn-forming silicates (tremolite, diopside, forsterite), and a low Cd content in sphalerites. The zoning crosscuts the lithologic boundaries, and transitions exist from massive sulfide ore bands through disseminated sulfide ore to fracture-filled skarn and barren host rock. Silicate, sulfide, and oxide assemblages indicate three stages of alteration and mineralization. During stage 1, potassic alteration and zonal precipitation of sulfides occurred. Basic sills and dikes close to the ores underwent strong potassic alteration and slight sulfide mineralization, and were altered to skarn; metatuffites underwent potassic alteration and sulfide mineralization, and were altered to skarn; and dolomitic limestones underwent dedolomitization and sulfide mineralization and were altered to skarn. During stage 2 the potassically altered tuffites were replaced by infiltrational-metasomatic amphibole skarns, which were subsequently replaced by pyroxene (-forsterite) skarns at temperatures of about 550øC. The late stage 2 pyroxene skarns are reaction skarns that are largely synkinematic with respect to boudinage of sulfide skarn layers and development of foliation in the marbles. Amphibole and pyroxene skarn relationships suggest a telescoping effect during the formation of the skarns. Silicate assemblages in metatuffites indicate metamorphic pressures of about 2.5 kb. During stage 3, retrogressive alterations, crystallization of pyrite, and remobilization of sulfides occurred largely syn-to postkinematically with respect to boudinage. Implications from this study suggest that the potassic alteration of country rocks, the increase in Fe/Mg atomic ratio in silicates, and possibly the increase in Cd content in sphalerites can be used to locate the Cu-W-Mo-bearing central zone of a central Swedish type of sulfide mineralization.

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“…Differences in solubilities, vapor presstues, correlation of atomic weights with mineral sequences, deposition according to electrode potentials of the elements, differential diffusion of the components, changes in concentration, and solubility in concentrated chloride solutions are all mechanisms that have been invoked by various workers to explain the sequences of mineral deposition and zoning of deposits. One of the more recent concepts considers the relative stabilities of covalent complexes of bivalent metal cations, with such anions as chlorides, sulfides, polysulfides, or thiosulfates, arrived at through calculations involving free energy differences of the cations (Barnes, 1962). Although this approach at present lacks sufficient quantitative authentication, the calculations demonstrate a consistent succession, with manganese, iron, zinc, copper, and lead occurring in order of increasing stability of covalent-bm1ded ions within any single type of anion complex in the ore solution (Barnes, 1962, p. 34).…”

Section: Genesis Of the Oresmentioning

confidence: 99%