Diopside Inclusions Research Articles

Fluid inclusion studies of the skarn-type tin mineralization at Red-A-ven, Northwest Dartmoor, England

Two principal hydrothermal events have been recognized, which resulted in the tin-bearing skarns at Red-A-ven, Northwest Dartmoor. Tin was enriched during both the early (occurring as tin-bearing andradite) and late hydrothermal events (mainly as malayaite stannite and cassiterite, accompanied by boron silicates and minor tungsten). Thermometric measurements of fluid inclusions in diopside, garnet, malayaite, tourmaline-quartz and axinite were carried out, suggesting that the early skarns were formed at the temperature above 600 °C and the salinities ranging from 10 to 20 wt. %NaCl eq., while the late skarns at the temperatures of 350–460°C and the salinities ranging from 30 to 50 wt. % NaCl eq. The estimated minimum depths are 2856 m (850 bar) for the early event and 2526 m (185 bar) for the late event. The birefringence of the andradite might be related with the superimposition of late hydrothermal fluids.

Note on Inclusions in Diopside from Ala, Piedmont, Italy

Note on Inclusions in Diopside from Ala, Piedmont, Italy

Transmission electron microscope analysis of the deformation of chromites from ophiolites

TEM investigations of natural chromites from New Caledonia and Turkey show contrasting dislocation structures which relate to the ore structures and to the deformation history. Some chromites appear to have been deformed in the ductile field ; dislocation substructures are typical of steady state dislocation creep. Other chromites show many fractures filled with matrix minerals. In these latter chromites one observes a large density of very small particles of diopside (typically 0.1x1 µm2 cross section) which pin the dislocations. It is suggested that these particle-dislocation interactions have caused a strong hardening and are responsible of the observed brittle deformation regime (pull-apart). Fractures have occurred on the surfaces which contained the largest particles. A rough estimation of the crystallization temperature of these latter chromites (Tc ⋍ 1200 ± 100 °C) is deduced from the spacing between the mismatch dislocations surrounding the diopside inclusions which exhibit epitaxial relations with the chromite matrix.

Carbonate-silicate reactions at high presures and possible presence of dolomite and magnesite in the upper mantle

The reaction between enstatite (En 95.3Fs 4.7) and CaCO 3 has been studied at pressures between 23 and 77 kbars and at temperatures between 800° and 1400°C. At 1000°C enstatite and CaCO 3 react to form dolomite and diopside solid solutions at pressures below approximately 45 kbars and magnesite and diopside solid solutions at higher pressures. The curve for the reaction dolomite ss + enstatite ss ⇌ magnesite ss + diopside ss lies between 40 to 45 kbars at 1000°C and between 45 and 50 kbars at 1200°C. It is very close to the graphite-diamond transition curve. These experimental results indicate that calcite (or aragonite) is unstable in the presence of enstatite, and that dolomite and magnesite are the stable carbonates at high pressures. The forsterite + aragonite assemblage is, however, stable to at least 80 kbars at 800°C. It is suggested that in the upper mantle where enstatite is present, dolomite is stable to depths of about 150 km and magnesite is stable at greater depths in the continental regions, assuming that the partial pressure of CO 2 is equal or close to the total pressure. It is also suggested that carbonate inclusions in pyroxene can be used as an indicator of the depth of their equilibration; dolomite inclusions in enstatite would be formed at depths shallower than 150 km and magnesite inclusions in diopside at greater depths. Eclogite and peridotite inclusions in kimberlite may be classified on this basis.