Amounts Of Secondary Minerals Research Articles

Formation of Nitrogen-Rich Hot Springs in the Water–Granite and Water–Porphyrite Systems

The processes of evolutionary transformation of solutions in crystalline rocks of different composition under formation parameters of nitrogen-bearing hot springs have been studied using physicochemical modeling. It has been established that the fundamental factor in the formation of solutions that correspond to modern nitrogen hot springs in composition is the presence of elements that produce anions in the host rocks in appropriate concentrations. They create a characteristic geochemical environment that controls their concentrations and speciation in the solutions and the crystallization/dissolution timing and amounts of secondary minerals at each step of changing the value of the rock/water ratio. Both cations and anions clearly maintain the sequence of their presence in the solution in accordance to their concentration in the rock until the time when the crystallization of secondary minerals modifies the trends of component concentrations in the solution. The reasons for low and very low mineralization of nitrogen hot springs, low concentrations of Mg, Ca, and K and high contents of Na and Si are elucidated. Modern nitrogen terms cannot be formed in rocks containing elements that form anions in an amount corresponding to their average values. Based on the revealed high discreteness of the distribution of these elements in space and their extremely poor understanding, it is concluded that the successful study of hydrogeochemical processes is impossible without taking into account the geological heterogeneity, which is a key problem of hydrogeochemistry and is not taken into account when the processes of interaction in the water/rock system are studied.

Possibilities of determination of alteration degree of rocks by thermogravimetry

Rhyolite-rhyodacite tuff samples were analysed by X-ray powder diffraction, ICP-OES and thermogravimetric (TG) methods to determine mineral and major element composition as well as different types of bound water, respectively. Similarly to CIA values, some TG parameters (H2O[I] — water released up to ca. 200–220°C; H2O[III] — water loss above 500–550°C and H2O[I+III]) show positive correlation to the amount of secondary minerals. Moreover, these parameters are in close positive correlation to CIA values. Our results suggest that TG determination of different types of bound water may serve as a useful tool for estimation and characterisation of alteration degree of rocks.

Backscattering Mössbauer spectroscopy of Martian dust

We report on the determination of the mineralogy of the atmospherically suspended Martian dust particles using backscattering 57Fe Mossbauer spectroscopy on dust accumulated onto the magnets onboard the Mars Exploration Rovers. The spectra can be interpreted in terms of minerals of igneous origin, and shows only limited, if any, amounts of secondary minerals that may have formed in the presence of liquid water. These findings suggest that the dust has formed in a dry environment over long time in the history of the planet.

Reaction mechanisms, physical conditions, and mass transfer during hydrothermal alteration of mica and feldspar in granitic rocks from south-central Maine, USA

Samples of granitic rock from south-central Maine contain primary igneous minerals altered by hydrothermal fluids. The reaction mechanisms (by which the over-all mineralogical change during the alteration was accomplished) involve several different mineral-fluid reactions at different reaction sites in the rock. The reactions involve both molecular and charged species in solution. The different reaction sites correspond to alteration of different primary igneous minerals. Biotite is partially converted to chlorite+sphene; microcline to muscovite; plagioclase to various combinations of muscovite, epidote, and calcite. The different reaction sites are linked by exchange of ions: some reaction sites produce ions consumed at other sites and vice versa. Physical conditions during the hydrothermal event are estimated from mineralogical and thermochemical data: P = 3,500 (±300) bars; T =425 ° (± 25 °)C. The fluid was characterized by X CO 2 = 0−0.13; ln([K+]/[H+ ]) = ∼10.0; ln([Ca2+]/[H+]2)=∼9.1; ln([Na+]/[H+]) = ∼ 10.5; Fe/(Fe+Mg) = 0.95. Amounts of secondary minerals in altered rock, when compared to the inferred mineral reactions that formed them, indicate that small but significant amounts (0.01–0.3mol/ 1,000cm3 altered rock) of CO2, H2O, H+, and K+ were added to the granites by fluids during the alteration, as well as lesser amounts (< 0.01–0.03 mol/1,000cm3 altered rock) of Mg2+, Fe2+, Fe3+, Mn2+, Na+, and Ti4+. The sole element leached from the granitic rocks during alteration was Ca in amounts 0.1–0.3 mol/1,000 cm3 rock. By estimating the composition of the hydrothermal fluids before and after reaction with the granites and by measuring the amount of material added to or subtracted from the granites during the alteration, the amount and volume of hydrothermal fluid involved can be calculated. Two independent calculations require minimum volumes in the range 100–1,000 cm3 fluid/1,000cm3 altered rock to participate in the hydrothermal event.

Effect of Postsedimentation Processes on Carbonate Reservoir Rocks in Volga-Urals Region, USSR

Porosity and permeability of carbonate rocks are controlled by (1) sedimentation conditions, which determine primary textural features, and (2) secondary postsedimentation processes. Bioclastic carbonates, with small amounts of cement and without any appreciable amounts of secondary minerals, form the best carbonate reservoir rocks. Postsedimentation processes appreciably alter the primary textures and thus affect the reservoir rock properties. Such processes as solution and formation of fractures and stylolites considerably improve porosity and permeability of carbonate rocks. Processes of sulfatization, calcitization, and silicification, resulting in filling and sealing of pores, cavities, and fractures, adversely affect reservoir properties. Processes of secondary mineral formation, however, indirectly improve the flow capacity of rocks by creating heterogeneous texture, which favors the formation of fractures and solution cavities. The development of carbonate rock porosity is very complex because of the alteration by solution and secondary mineral-formation processes. Porosity and permeability of carbonate reservoirs were found to be related closely, with the correlation factor ranging from 0.7 to 0.8.