Fe Content Of Sphalerite Research Articles

Interdiffusion rate of zinc and iron in natural sphalerite

The interdiffusion coefficients of zinc and iron in natural iron-poor and iron-rich sphalerites were determined experimentally using electron microprobe analysis. The diffusion couples were heated in sealed silica tubes for predetermined lengths of time together with f (sub S 2 ) buffering materials such as iron and/or synthetic pyrrhotite at temperatures between 950 degrees and 500 degrees C. The interdiffusion rates were determined from measured compositional profiles across natural sphalerite crystal pairs.The penetration profiles of the diffusing Zn and Fe were clearly observed not only at the contact planes of crystals but also at both free end surfaces of the diffusion column and the side surfaces normal to the diffusion interface. Vapor transport probably played an important role in the Zn-Fe interdiffusion. The Zn-Fe interdiffusion coefficient increases slightly with increasing Fe content of sphalerite as expected from the enlargement of the unit cell with Fe concentration. The Arrhenius relation for interdiffusion rates, D (cm 2 /sec), in sphalerite of N mole percent FeS (2 2 /sec.The interdiffusion rate is not dependent on crystallographic orientation for directions normal to (110) and parallel to (110). A high-pressure run at 5 kbars and 800 degrees C shows that interdiffusion rates slightly decrease with increasing total pressure (log D = -10.5 + or - 0.1 cm 2 /sec at 1 bar pressure to log D = -10.8 + or - 0.2 cm 2 /sec at 5 kbars). A dependency of interdiffusion rates on f (sub S 2 ) was also observed in the 950 degrees and 900 degrees C experiments. D values are slower with increasing fugacity of sulfur (e.g., for 900 degrees C, log D = -9.8 + or - 0.1 cm 2 /sec at f (sub S 2 ) = 10 (super -9.6) bars vs. log D = 10.1 + or - 0.2 cm 2 /sec at f (sub S 2 ) = 10 (super -8.0) bars).

The Ag/Au ratio of native gold and electrum and the geochemical environment of gold vein deposits in Japan

The chemical composition of native gold and electrum from auriferous vein and gold-silver vein deposits in Japan has been analyzed and summarized. The Ag/Au ratios of native gold and electrum from these two types of deposits are distinct, i.e., 10–20 Ag at % (auriferous vein) and 30–70 Ag at % (gold-silver vein). Thermochemical calculations suggest that the Ag/Au ratio of native gold and electrum should decrease with increasing chloride concentration and temperature. This is consistent with analytical results of native gold and electrum and fluid inclusion studies. Based on the Ag content of native gold and electrum, the Fe content of sphalerite, and the estimated temperatures, it is deduced that the sulfur activity for auriferous vein-type systems was lower than that of gold-silver vein-type systems.

Phase relations involving sphalerite in the Fe-Zn-S system

The system Fe-Zn-S was studied from 850 degrees C (appearance of sphalerite-wurtzite polytypes) to 580 degrees C (where reaction rates become very slow), with control of sulfur fugacity. Results show that temperatures estimated from the 'sphalerite geothermometer,' which was based on techniques in which sulfur fugacity was not controlled, may be in serious error. Where sulfur fugacity is buffered by pyrrhotite-pyrite, Fe-content of sphalerite changes from 13 mole percent at 742 degrees C to 19 mole percent at 580 degrees , but compositions cannot be extrapolated to lower temperatures. Other sulfide assemblages that define sulfur fugacity at various temperatures form a potential basis for quantitative geothermometry using Fe-content of sphalerite.

The iron content of sphalerite from the Central District, New Mexico and the Bingham District, Utah

In conjunction with a study of trace elements, about 200 sphalerites from the Central district, New Mexico, and the Bingham district, Utah, have been analyzed for Fe by an X-ray fluorescence method. The FeS content ranges from 4.2 to 18.5% at Hanover in the Central district and from 0.84 to 9.4% in the southwestern part of the same district. At Bingham the range is from 0.2 to 16.7%. Pyrite is ubiquitous in both districts, and pyrrhotite is known. Sphalerite with pyrrhotite averages higher in Fe content than sphalerite with pyrite. A poorly-developed lateral zoning away from igneous centers is present in the Central district and poorly-developed vertical zoning was found in one structure at Bingham. Ten analyses of a zoned crystal from the Central district show a range from 4.3 to 12.1% FeS, and sharp boundaries exist between the zones, indicating that equilibrium was not achieved at temperatures of at least 425 degrees C. Several other inhomogeneous sphalerites were found in both districts, and lack of equilibrium is believed to be a major difficulty in the determination of temperature from the Fe content of sphalerite. Other difficulties include the effect of S pressure, the total pressure correction, and exsolution effects. Because all these factors probably result in a lower Fe content than is indicated by the FeS-ZnS solvus for one atmosphere, it is suggested that temperatures derived from the Fe content of sphalerite be regarded as minimum temperatures unless convincing evidence can be presented on the possible complications. On this basis, temperatures reached at least 600 degrees C. at Hanover in the Central district, at least 350 degrees C. at the Groundhog mine in the same district, at least 650 degrees C. at the Cleveland mine in the nearby Pinos Altos district, and at least 550 degrees C. in the Bingham district. At the Cleveland mine, higher than normal CO 2 pressures seem necessary to explain the lack of reaction between quartz and carbonates, if the sphalerite temperatures are correct.

Temperatures of formation and origin of the Nigadoo and Brunswick Mining and Smelting No. 6 deposits, New Brunswick, Canada

The Nigadoo deposit is a telescoped vein at and near the margin of an epizonal quartz-feldspar porphyry body. The vein minerals are coarse-grained and consist mainly of pyrrhotite, pyrite, sphalerite, galena, chalcopyrite, arsenopyrite, and stannite in a multi-generation calcite gangue. The Fe content of sphalerite suggests a temperature of formation of 670 degrees C., which contrasts with the obvious low-metamorphic rank of the wall-rocks. The B. M. and S. No. 6 deposit, consisting essentially of pyrite with galena and sphalerite, is a large, lenticular, massive, fine-grained replacement in greenschist wall-rocks. Along the footwall an adjoining zone contains pyrrhotite, chalcopyrite, and a little sphalerite and galena. In general the Fe content of the sphalerite is higher where it occurs with pyrrhotite than where it accompanies pyrite, but details of spatial and compositional variation suggest that the relationships are considerably more complex. Sphalerite compositions suggest a maximum temperature of formation near 480 degrees C. which would exceed the suggested upper limit of the greenschist facies by about 250 degrees C. The writer believes that the temperature data proves that both deposits are of epigenetic origin.

Some aspects of the geochemistry of sphalerite, Central City District, Colorado

Detailed studies of sphalerite, as a part of a larger study of the Central City district, Colorado, have been undertaken to learn something of the physico-chemical environment of ore deposition. More than 90 samples have been analyzed by chemical and spectrochemical methods and these data are interpreted in the light of experimental information. Sphalerite is a widespread and moderately abundant constituent of the Au- and Ag-rich veins of the district. It was deposited during one stage of mineralization, in all environments of the concentrically zoned district except in the core. On a district-wide basis it occurs in 3 mineral assemblages: sphalerite-pyrite-chalcopyrite-tennantite-galena, sphalerite-pyrite-tennantite-galena, and sphalerite-pyrite-enargite-tennantite-galena. Quartz and, locally, other gangues are present. The sphalerite samples contain from 12 to 0.05 weight % Fe and detectable amounts of a restricted suite of minor elements, principally Mn, Cd, Cu, and Pb. Mn correlates directly with Fe content, but the other minor elements have random correlations. The Fe content of Central City sphalerite is interpreted to be mainly a function of activity of S and temperature. Total pressure and minor elements that may enter the structure of either sphalerite or coexisting pyrite are thought to have negligible effects on the amount of Fe in the sphalerite. The Fe content of the sphalerite and fluid inclusion studies indicate that mineralization occurred over a temperature range from at least 620 degrees C. to about 150 degrees C. In general, the temperatures tended to decrease from the vicinity of the central zone outward toward the peripheral zone. The thermal pattern, however, was complex, and marked by local irregularities. The activity of S decreased with temperature, but to an extent such that more S-rich mineral assemblages could form toward the margins of the district. The minor-element content of the sphalerite is governed by the activities of the various components and by the ability of the host mineral to accommodate it. Mn varies widely because 1) it is geochemically much more abundant than is Zn and 2) it can also enter other minerals on a large scale. Conversely, because the amount of Cd is small relative to that of Zn and because it enters only sphalerite in quantitatively significant amounts in hydrothermal environments, the Cd content of sphalerite is constant. The Cu content of the sphalerites is low and in good agreement with recent experimental data of Priestley Toulmin 3d.