Contact metamorphism

The Utah deposit is located in southwestern Utah near Cedar City. The iron ore deposits are of contact metamorphic origin. The cmde ore contains 35 to 65% iron, primarily in the form of magnetite and goethite. Mining is done by the open pit method. The cmde ore is cmshed, screened at —75 mm (—200 mesh size) and shipped as lump ore containing 54% iron. The ore is rescreened at the steel mill to produce lump ore (10—64 mm) for the blast furnace and sinter feed (0—10 mm) for the sinter plant. 

Host rocks in the Hitachi area suffered regional metamorphism, contact metamorphism by Cretaceous granitic rocks and hydrothermal alteration associated with sulfide mineralization. 

Host rocks in deeper parts of the Besshi mine suffered contact metamorphism probably due to Cretaceous granitic intrusion. Kase (1972, 1977, 1988) suggested the contact metamorphism in the Besshi mine from the occurrence of large amount of pyrrhotite and As, Zn, Ag and Sn vein mineralization in deeper levels. 

In the other areas, generally, the host rocks weakly suffered regional and contact metamorphisms but suffered ocean-floor hydrothermal alteration. For example, hydrothermal alteration mineral assemblages in the Minamidani mine district in the Maizuru range from prehnite-pumpellyite facies to a transition state from green schist to amphibolite... 

Kase and Horiuchi (1996) obtained a large number of analytical data on sphalerites from sixteen Besshi-type deposits, mainly at Besshi and its vicinity, Hitachi, and Shimokawa. They revealed that (1) the Mn/Zn and Co/Zn ratios of sphalerite may have markedly increased during contact metamorphism, while the Cd/Zn ratios remained unchanged (2) the Emco/ lwzn (2/n total dissolved concentration in ore fluids) and Emco/S/wzn ratios in the initial ore solutions responsible for the mineralizations at Besshi which was calculated ba.sed on the equilibrium fractionation model between hydrothermal solution and sphalerite and analytical data on sphalerites are quite similar to the ratios of hydrothermal solutions at EPR 21 °N (3) however, these ratios for the Hitachi solutions are very low and different from those of the Besshi-subtype solution. 

Kaufman AJ (1996) Geochemical and mineralogic effects of contact metamorphism on banded iron-formation an example from the Transvaal Basin, South Africa. Precam Res 79 171-194... 

In contact-metamorphic zones, in association with magnetite and Fe-rich silicates (feldspathoid-bearing igneous rocks)... 

Diopside-hedembergite (Ca,Mg,Fe)2Si206 Cr-rich ultramafic rocks contact metamorphism (cipollines, comubianites)... 

Figure 11.18 Apparent K-Ar ages of minerals from Idaho Springs Formation (Front Range, Colorado, 1350-1400 Ma) in zone subjected to contact metamorphism by intrusion of a quartz monzonite (Eldora stock, 55 Ma). Reprinted from S. R. Hart, Journal of Geology, (1964), 72, 493-525, copyright 1964 by The University of Chicago, with permission of The University of Chicago Press.

Greenwood H. J. (1967). Wollastonite Stability in H2O-CO2 mixtures and occurrence in a contact metamorphic aureole near Salmo, British Columbia, Canada. Amer. Mineral, 52 1669-1680. 

Hanson G. N. and Gast P. W. (1967). Kinetic studies in contact metamorphic zones. Geochim. Cosmochim. Acta, 31 1119-1153. 

These textural observations suggest that the bulk of the mineralization at Morila was precipitated following low-P contact metamorphism and under relatively low fluid pressure conditions (i.e., no significant hydrofracturing). 

The rocks at Morila record an intimate interplay between magmatism, contact metamorphism (and metasomatism), deformation, and mineralization. The spatial, temporal, and textural associations between contaminated post-D2 intrusions, contact metamorphism, and polymetallic post-D2 mineralization strongly suggests an intrusion-related origin for Morila. Other controls on Au mineralization include ... 

Marbles occur in many regional and contact metamorphic terrains in the world and isotopic studies of marbles have been carried out and report by many authors. Carbon isotope studies of marbles can be useful, in many cases, to reveal the origin of carbonates because differences in carbon isotope ratios of marbles can reflect different origins. 

The lower assemblage consists predominantly of red mudstone, with narrow sections (5-20 cm) of reduction spots and entire sections (0.5 to 2 m) of grey reduced and pyritic mudstone becoming more common towards the base. Narrow (0.5 to 5 m) intermediate extrusive volcanic flows become more common towards the base of this assemblage, and display basal textures indicating that moisture and mudstone rip-clasts were acquired into the flow and that heat was supplied to the underlying mudstones, which produced narrow (< 5 cm) contact metamorphism bands of re crystallized mudstone. 

Fig. 3.50 Coupled O-C trends showing decreasing values of 8 C and 8 0 with increasing metamorphic grade from numerous contact metamorphic localities (Baumgartner and VaUey, 2001)...

Baumgartner LP, Rumble D (1988) Transport of stable isotopes. 1. Development of a kinetic continuum theory for stable isotope transport. Contr Miner Petrol 98 417-430 Baumgartner LP, Valley JW (2001) Stable isotope transport and contact metamorphic fluid flow. 

Figure 8.8. Crystal size distribution (CSD) plots of (a) plagioclase in igneous rock and (b) garnet porphyroblast in contact metamorphic rock [4].

In regional metamorphic rocks and contact metamorphic (metasomatic) rocks, new mineral crystals grow in solid rocks in which there was a change in conditions. However, the process is not the same as straightforward solid state growth or recrystallization. Since volatile components such as H O and CO, which were originally present in the rock, are involved, it is better to assume a... 

Many authors have studied anthraxolite and related substances since Vanuxem s first account in 1842 (39). It has been reported as cavity fillings, veins, and dikes and as laminations in rocks of all geologic ages and types on all continents (e.g., I, 15, 20, 31, 32, 37, 38). Except for obvious cases of contact metamorphism near igneous intrusions, earlier workers have generally recognized a fluid origin and low temperature history for these substances. 

Another proof of the importance of temperature is the fact that there is often a strict relationship between the run of isovols and the run of isotherms in deep profiles, both being influenced no doubt by the varying thermal conductivity of the different rocks. The strong influence of temperature on the rank of coal is obvious in the case of contact-metamorphic coals, whose rank increases distinctly when approaching the intrusive body. Apart from these geological observations, all experiments on artificial coalification have shown that temperature is the decisive factor in the coalification process. Thermodynamic and reaction kinetic considerations (9) also support this opinion. 

Geological investigations have shown that undoubtedly temperature has most influence on geochemical coalification. This is proved by such evidence as contact metamorphism of coals, increase of rank with increasing temperature of the earth s crust with depth, increase of rank of the same seam as magma chambers (batholiths) are approached, and relations between the thermal... 

Biotite is occasionally found in large sheets, especially in pegmatite veins. It also occurs as a contact metamorphic mineral or the product of the alteration of hornblende, augite, wernerite, and similar minerals. 

Scapolite is found in the metamoiphic locks, particularly those, rich in calcium also in contact metamorphic deposits in limestones. It has been found in basic igneous rocks, probably as a secondary mineral. Notable localities are Lake Baikal, Siberia Arendal. Norway and Madagascar. In the United States, it is found in Massachusetts, New York, and New Jersey. Greenville, in the Province of Quebec, Canada is an important locality. Superb transparent yellow gem crystals have recently been found in Brazil and Tanzania. Wernente (scapolite) was named in honor of A.O. Werner, a famous German mineralogist (1749-1817). 

Due to the mineralizing action of magmatic vapors, tourmaline is found particularly well developed in pegmatites, and as a contact metamorphic... 

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