Fukalite: an example of OD structure with two-dimensional disorder

The real crystal structure of fukalite, Ca4Si2O 6(OH)2(CO3), was solved by means of the application of order-disorder (OD) theory and was refined through synchrotron radiation diffraction data from a single crystal. The examined sample came from the Gumeshevsk skarn copper porphyry deposit in the Central Urals, Russia. The selected crystal displays diffraction patterns characterized by strong reflections, which pointed to an orthorhombic sub-structure (the "family structure" in the OD terminology), and additional weaker reflections that correspond to a monoclinic real structure. The refined cell parameters are a = 7.573(3), b = 23.364(5), c = 11.544(4) Å, β = 109.15(1)°, space group P21/c. This unit cell corresponds to one of the six possible maximum degree of order (MDO) polytypes, as obtained by applying the OD procedure. The derivation of the six MDO polytypes is presented in the Appendix1. The intensity data were collected at the Elettra synchrotron facility (Trieste, Italy); the structure refinement converged to R = 0.0342 for 1848 reflections with I > 2σ(I) and 0.0352 for all 1958 data. The structure of fukalite may be described as formed by distinct structural modules: a calcium polyhedral framework, formed by tobermorite-type polyhedral layers alternating along b with tilleyitetype zigzag polyhedral layers; silicate chains with repeat every fifth tetrahedron, running along a and linked to the calcium polyhedral layers on opposite sides; and finally rows of CO3 groups parallel to (100) and stacked along a

Potentially commercial Alapayevsk-Sukhoy Log porphyry copper zone (the Middle Urals)

NS-trending Alapayevsk-Sukhoy Log zone of porphyry-copper mineralisation in the Middle Urals is located 75 km to the east of Yekaterinburg and extends for 100 km from Alapayevsk to Sukhoy Log towns. Sulphide inclusions in rocks are pervasive, and there are numerous ore manifestations and small deposits. Like the commercial Mikheyevskoye porphyry copper deposit (over 1.7 million tonnes of Cu) in the Southern Urals, the zone is associated with the eastern part of East Urals volcanic megazone. It consists of several ore-producing NS-trending volcano-plutonic belts which represent the tectonic blocks. Rejuvenation from north to south of granitoid magmatism has been identified (U-Pb SHRIMP-II and LA ICP-MS zircon dating) in First magmatic stage (million years): from 412 (diorite-plagiogranodiorite-plagiogranite of Yaluninogorsk massif) to 404-406 (diorite-granodiorite-granite of Altynai-Artyomovsk intrusion), and then to 397 (plagiorhyodacite-porphyre of Shata area). Volumetrically sericitized and sulphidized quartz diorite of East-Artyomovsk massif was probably established during Second magmatic stage (369 ± 39 million years, Rb-Sr dating). All granitoids are of arc-island geochemical type, and have feature near-mantle isotopic signatures: (87Sr/86Sr)t = 0.7038-0.7049, (εNd)t = 6.6-8.7. Systemic and comprehensive study of Alapayevsk-Sukhoy Log zone should result in discovery of commercial large scale porphyry copper deposits (assuming current cut-off grade of Cu 0.15-0.20 wt %). The most attractive in terms of potential for high capacity stockworks is the East Artyomovsk massif which is similar in many respects to ore-magmatic system of Mikheyevsk deposit

Rhythmical patterns of quartz-molybdenite and interpretation of its origin

Subject of the study was molybdenite aggregate (0.9 × 0.5 cm) in granite from Cu ± Mo-porphyry mineralisation (Altynai Massif, eastern part of Middle Urals). Microprobe analysis and electron microscopy identified fine alternating microlayers of molybdenite and quartz in all 0.4-5.0 mm flakes of molybdenite. Thickness of normally discontinuous layers of quartz is 0.5-3 μ, distance between layers - 8-100 μ or more. Quartz layers are aligned only with the basal cleavage of molybdenite. In some molybdenite flakes or parts of flakes quartz layers are absent or very few in number. Large flakes of molybdenite are surrounded by fine-grained aggregate of quartz, chamosite and molybdenite. Occasional grains of fluorite and galena have also been found within this aggregate. Molybdenite flakes in such areas contain no quartz layers, have random orientation, and can be seen as fragments cemented by chamosite and quartz. Molybdenite has consistently low rhenium content of 29 ppm (according to ICP-MS). It is suggested that molybdenite-quartz rhythms are likely to correspond to primary oscillatory distribution which was subsequently subjected to deformations and redistribution of silica in crushed areas