The mineralogy of a new lamproitic diatreme 200–250 m in diameter and 3 ga in area is studied in detail. The chemical and 3-D mineralogical analysis identify the diatreme rocks as strongly altered olivine lamproites with a large volume (50–60%) of xenoliths of strongly altered spinel (garnet) lherzolites and harzburgites-dunites. Numerous grains-xenocrysts of indicator minerals of diamond have been extracted from the heavy concentrates (the weight of the initial product is 742 g and the size is 100–500 μm) as a result of hydroseparation: (1) subcalcium (CaOav. 2.6 wt %) high-Cr (Cr2O3 av. 5.3 wt %) pyrope (50 grains); (2) chrome diopside (7 and 8 mol % of kosmochlor and jadeite components, respectively, >40 grains); (3) high-Cr chromite (Cr2O3 > 62 wt %); and (4) picroilmenite (MgO 12–13.8 wt %) and Cr-rutile (Cr2O3 1.1 wt %). Xenocrysts prove the mantle endogene (the level of garnet lherzolites) source of the magmatic center of lamproites and forecast the diamond potential of the new diatreme in the Kostomuksha ore district. 相似文献
Diagenetic transformation of clay minerals, zeolites and silica minerals in Cretaceous and Tertiary argillaceous rocks from deeply drilled wells in Japan were studied. Transformations of these minerals during diagenesis were as follows: in clay minerals, montmorillonite → montmorillonite-illite mixed-layer mineral → illite; in zeolites, volcanic glass → clinoptilolite → heulandite and/or analcite → laumontite and/or albite; in silica minerals, amorphous silica → low-cristobalite → low-quartz. Maximum overburden pressures and geothermal temperatures corresponding to these transformations in each well studied were calculated. For clay minerals, a pressure of approximately 900 kg cm?2 and a temperature of about 100°C are necessary for the transformation from montmorillonite to mixed-layer mineral and 920 kg cm?2 and 140°C for mixed-layer mineral to illite. Transformation from kaolinite to other minerals requires much higher pressures and temperatures than from montmorillonite to mixed-layer mineral. For zeolites, 330 kg cm?2 and 60°C are required for the transformation from volcanic glass to clinoptilolite, 860 kg cm?2 and 120°C for clinoptilolite to heulandite and/or analcite, and 930 kg cm?2 and 140°C for heulandite and/or analcite to laumontite and/or albite. For silica minerals, 250 kg cm?2 and 50°C are necessary for the transformation from amorphous silica to low-cristobalite and 660 kg cm?2 and 70°C for low-cristobalite to low-quartz. Based on these diagenetic mineral transformations, seven mineral zones are recognized in argillaceous sediments. On the other hand, from the porosity studies of argillaceous sediments in Japan, the process of diagenesis is classified into the following three stages. The early compaction stage is marked by shallow burial and viscous rocks with more than 30% porosity. The late compaction stage is characterized by intermediate burial and plastic rocks with 30-10% porosities. The transformation stage is marked by deep burial and elastic rocks with less than 10% porosity. 相似文献
Phase relations of diamond and syngenetic minerals were experimentally investigated in the multicomponent system natural carbonatite-diamond
at a pressure of 8.5 GPa and temperatures of 1300–1800°C (within the thermodynamic stability field of diamond). Under such
conditions, the natural carbonatite of the Chagatai complex (Uzbekistan) acquires the mineralogy of Ca-rich eclogites (grospydites).
The melting phase diagram of this system (syngenesis diagram) was constructed; an important element of this diagram is the
diamond solubility curve in completely miscible carbonate-silicate melts (solubility values are 15–18 wt % C). The diamond
solubility curve divides the phase diagram into two fields corresponding to (1) phase relations involving diamond-undersaturated
melts-solutions of carbon with garnet as a liquidus phase (region of diamond dissolution) and (2) phase relations with diamond-saturated
melts-solutions with diamond as a liquidus phase (region of diamond crystallization). During a temperature decrease in the
region of diamond crystallization from carbonate-silicate melts, the crystallization of diamond is accompanied by the sequential
formation of the following phase assemblages: diamond + garnet + melt, diamond + garnet + clinopyroxene + melt, and diamond
+ garnet + clinopyroxene + carbonate + melt, and the subsolidus assemblage diamond + garnet + clinopyroxene + carbonate is
eventually formed. This is indicative of the paragenetic nature of silicate and carbonate minerals co-crystallizing with diamond
and corresponding primary inclusions trapped by the growing diamond. A physicochemical mechanism was proposed for the formation
of diamond in carbonate-silicate melts. The obtained results were used to analyze the physicochemical behavior of a natural
diamond-forming magma chamber. 相似文献
In Part 1 (Minerals explained 43, Geology Today 2006, v.22, no.2, pp.71–77) graphite was examined, the polymorph of carbon that is stable over a wide temperature range, but only at relatively low pressures. The other principal polymorph of carbon, diamond, is dealt with here in Part 2. Diamond has a very large stability range over both temperatures and pressures, although it is created at similar depths in the Earth's crust, probably in the mantle ( Fig. 1 ). It would probably have remained there unsuspected, had it not been brought to the Earth's surface by volcanic mechanisms. This will be looked at in detail in the section on the genesis of diamond below, as will the apparently anomalous stability of diamond at NTP. Figure 1 Open in figure viewer PowerPoint Pressure/temperature phase diagram for diamond. 相似文献
Lithium is a critical element in modern technology, and lithium minerals will play a key role in the fight against climate change. However, the demand for lithium-ion batteries is dependent on an expanding supply of primary resources. Lithium occurs in limited amounts on the Earth in a surprising diversity of mineral species, from pyroxenes to amphiboles, phyllosilicates to phosphates. This article examines the principal mineral groups likely to be a target for future exploitation. 相似文献
