ALBERT

Description: Gem minerals at Lava Plains, northeast Queensland, offer further insights into mantle-crustal gem-formation under young basalt fields. Combined mineralogy, U-Pb age determination, oxygen isotope and petrological data on megacrysts and meta-aluminosilicate xenoliths establish a geochemical evolution in sapphire, zircon formation between 5 to 2 Ma. Sapphire megacrysts with magmatic signatures (Fe/Mg ~100–1000, Ga/Mg 3–18) grew with ~3 Ma micro-zircons of both mantle ( 18 O 4.5–5.6) and crustal ( 18 O 9.5–10.1) affinities. Zircon megacrysts (3±1 Ma) show mantle and crustal characteristics, but most grew at crustal temperatures (600–800°C). Xenolith studies suggest hydrous silicate melts and fluids initiated from amphibolized mantle infiltrated into kyanite+sapphire granulitic crust (800°C, 0.7 GPa). This metasomatized the sapphire (Fe/Mg ~50–120, Ga/Mg ~3–11), left relict metastable sillimanite-corundum-quartz and produced minerals enriched in high field strength, large ion lithophile and rare earth elements. The gem suite suggests a syenitic parentage before its basaltic transport. Geographical trace-element typing of the sapphire megacrysts against other eastern Australian sapphires suggests a phonolitic involvement.

Description: Primary fluid inclusion (FI) assemblages in ruby from marble at Mogok and fifteen other deposits from central and Southeast Asia were studied by microthermometry, Raman spectroscopy and crush-leach analysis. Microthermometry combined with Raman spectroscopy investigations of primary FI in Mogok rubies indicated the simultaneous trapping of carbonic FI in the system CO 2 –H 2 S ( ± COS ± S 8 ) and multi-solid carbonic FI in the system Na–K–Ca–CO 3 –SO 4 –NO 3 –Cl–F ±(CO 2 –H 2 S). The multiple solids are mainly mixtures of Na-Ca-Al carbonates such as shortite and dawsonite, sulphates, phosphates, nitrates, fluorides, and chlorides such as halite. They represent the trapped recrystallised residues of molten salts formed during the metamorphism of evaporite lenses (chlorides and sulphates) intercalated in the carbonate rocks. Raman spectroscopy of solids in FI from all Asian rubies hosted in marbles identified both (i) accidentally trapped minerals mainly calcite, dolomite and rutile, and (ii) daughter phases, i.e. , native sulphur, diaspore and boehmite, and Na-K-Ca chlorides, anhydrite, dawsonite, shortite and fluorides. Crush-leach analysis of ruby crystals identified chloride as the dominant anion, but sulphate and nitrate are present at only slightly lower concentrations, whereas they are the dominant species in some Pakistani deposits. The Na–K–Ca–Li–CO 3 –SO 4 –NO 3 –Cl–F molten salt assemblages and the presence of nitrate and phosphate indicate the deposition of the original sediments in a coastal sabkha with ephemeral marine and continental water flooding. Input of V- and Cr-bearing argillite to the salty mudflats insured the formation of rubies in marble during Cenozoic metamorphism.

Description: 〈span〉〈div〉Abstract〈/div〉The Mong Hsu ruby deposit in Myanmar is a marble-type deposit. It is well-known for attractive crystals with dark violet/blue to black cores and ruby rims, as well as for trapiche rubies. These exceptional rubies have a texture composed of six growth sectors separated by six dendrites running from a central core to the six corners.Fluid inclusions (FI) have been studied in both types of ruby, 〈span〉i.e〈/span〉., trapiche and non-trapiche crystals. Microthermometry combined with Raman spectrometry investigations of primary and secondary FI proved the existence of CO〈sub〉2〈/sub〉-H〈sub〉2〈/sub〉S-COS-S〈sub〉8〈/sub〉-AlO(OH)-bearing fluids with diaspore and native sulfur daughter minerals. The carbonic fluid belongs to the CO〈sub〉2〈/sub〉–H〈sub〉2〈/sub〉S system with CO〈sub〉2〈/sub〉 as a dominant component. Minor COS (1–2 mol.%) and diaspore indicate that H〈sub〉2〈/sub〉O (∼1 mol.%) was present in the paleofluid. The amount of H〈sub〉2〈/sub〉S in FI from trapiche ruby is between 6.9 and 7.4 mol.% for the dendrites and from 7.2 to 15.7 mol.% for the growth sectors. The H〈sub〉2〈/sub〉S content is approximately 10 mol.% in FI from non-trapiche rubies.The presence of dawsonite and previous crushing data carried out on well-cleaned crystals of non-trapiche ruby indicate that an ionic salt melt was present at the time of ruby formation. The non-detection of this melt in trapiche ruby is attributed to the small size of the remnants of molten salts, making it difficult to observe them under the microscope. Following this hypothesis, the FI assemblages in rubies would correspond to the trapping of two immiscible fluids, 〈span〉i.e〈/span〉., a carbonic phase in the CO〈sub〉2〈/sub〉–H〈sub〉2〈/sub〉S–COS–S〈sub〉8〈/sub〉–AlO(OH)-system and molten salts. Such fluid phases are considered to be the product of metamorphism of evaporites during devolatilization of carbonates and thermal-sulfate reduction.The formation of trapiche ruby is discussed in terms of possible variations of the composition of the fluid, temperature, and pressure conditions. The variation in density of the carbonic fluids from the dendrites (0.70 〈 ds 〈 0.78) to the growth sectors (0.56 〈 ds 〈 0.68) records variation of fluid pressure in the metamorphic system. This variation led to episodically local fluid overpressure and hydraulic fracturing in the marble. During such episodes, changes in driving-force conditions allowed for the formation of the trapiche texture in ruby: the development of dendrites and growth sectors occurred under high and low driving-force conditions, respectively. Non-trapiche ruby in veinlets formed concurrently under thermodynamic conditions similar to those registered for the growth sectors in trapiche ruby.〈/span〉

Description: We describe a new, state-of-the-art, Earth System Regional Climate Model (RegCM-ES), which includes the coupling between the atmosphere, ocean and land surface, as well as an hydrological and ocean biogeochemistry model, with the capability of using a variety of physical parameterizations. The regional coupled model has been implemented and tested over some of the COordinated Regional climate Downscaling Experiment (CORDEX) domains and more regional settings featuring climatically important coupled phenomena. Regional coupled ocean-atmosphere models can be especially useful tools to provide information on the mechanisms of air-sea interactions and feedbacks occurring at fine spatial and temporal scales. RegCM-ES shows a good representation of precipitation and SST fields over the domains tested, as well as realistic simulations of coupled air-sea processes and interactions. The RegCM-ES model, which can be easily implemented over any regional domain of interest, is open source, making it suitable for usage by the broad scientific community.

Description: Emerald at the Lened occurrence in the western Northwest Territories is hosted by quartz veins cutting skarn near the Lened granite pluton and older Selwyn Basin strata. Euhedral beryl crystals (〈0.5 x 5 cm) are present in approximately half of the 26 outcropping veins. Most of the crystals are opaque to translucent and colorless to yellowish and grassy green. Less than 5% of the beryl is transparent, bluish green, and can be considered pale emerald. Using field relationships, Ar-Ar dating, whole-rock geochemistry, stable isotopes (O, H, C, and B), and mineral chemistry, the sources of the emerald-forming fluids and chromophores have been assessed; the results clearly show that the ca . 100 Ma (Ar-Ar muscovite) Lened emerald occurrence is a Type I (igneous) skarn-hosted emerald deposit related to the proximal ca . 100 Ma (Ar-Ar biotite) Lened pluton. Beryllium and other incompatible elements ( i.e. , W, Sn, Li, B, and F) in the emerald, vein minerals, and surrounding skarn were derived during the terminal stages of crystallization of the proximal Lened pluton. Decarbonation during pyroxene-garnet skarn formation in the host carbonate rocks probably caused local overpressuring and fracturing that allowed ingress of magmatic-derived fluids and formation of quartz-calcite-beryl-scheelite-tourmaline-pyrite veins. Channel-water D values in emerald are depleted and range between –87.4 and –62, similar to other granite-related emerald occurrences. The calculated 18 O H2O for the vein fluid (~10, vein quartz, 350 °C) is compatible with a peraluminous granitic fluid source. The calculated 18 O H2O of granite-derived fluids (~12; magmatic quartz, 600–700 °C) is slightly isotopically heavier than the vein fluid, which can be explained by fractionation during vein crystallization or mixing with 18 O-depleted meteoric fluid. The 11 B values of accessory dravite in the emerald veins averages –4.9 ± 0.3 (1, n = 10), which is compatible with a magmatic source, and the Al-Fe-Mg composition is that of tourmaline formed in sedimentary environments, with Mg likely derived from metasomatism of local marine carbonates. The vein fluid was largely igneous in origin, but the dominant emerald chromophore V (emerald vein = avg. 1560 ppm V versus 75 ppm Cr) was mobilized by metasomatism of V-rich sedimentary rocks (avg. 2000 ppm V) that underlie the emerald occurrence. Lened is a unique igneous skarn-hosted emerald occurrence that contributes to the understanding of emerald deposits and emerald exploration criteria in Canada and globally.

Description: Gem-quality corundum (sapphire) occurs in scapolite-rich calc-silicate rock hosted in marble of the Lake Harbour Group near Kimmirut, southern Baffin Island. A deposit of blue and colorless gem corundum (Beluga occurrence) is compared to a similar calc-silicate pod generally lacking corundum but containing nepheline (Bowhead occurrence) and located 170 m to the SSW. Corundum formation was made possible by three equally important sequential metamorphic reactions: (1) formation of nepheline, diopside, and K-feldspar (inferred) at granulite facies peak metamorphic conditions; (2) partial retrograde replacement of the peak assemblage by phlogopite, oligoclase, calcite, and scapolite (Me 50 –Me 67 ) as a result of CO 2 -, H 2 O-, Cl-, F-bearing fluid influx at 1782.5 ± 3.7 Ma ( P-T 〈 720 °C, 6.2 kbar); and (3) retrograde breakdown of scapolite + nepheline (with CO 2 - and H 2 O-bearing fluid) to form albite, muscovite, corundum, and calcite. Late, low-temperature zeolite mineralization is common in corundum-bearing zones. Based on thermodynamic models, the corundum-forming reaction only occurs in a 〈100 °C window with an upper limit determined by scapolite-nepheline stability, and a lower limit determined by the formation of Al-silicate rather than corundum. The protolith is inferred to be dolomitic argillaceous marl with no evidence to suggest the initial presence of evaporites. The enrichment of trace metals V and Cr, and the depletion of Co, Ni, and Mn, suggest reducing diagenetic conditions in the initial sediment. Beluga calc-silicate rock is strongly depleted in REE (Total REE ~ 18 ppm). Oxy-dravite 11 B (+3.9 ± 0.7) is consistent with a marine boron source. The oxygen isotope composition of corundum ( 18 O VSMOW = 16.4 ± 0.1) is comparable to that of corundum in marble or desilicated pegmatite associated with marble. Phlogopite and muscovite 40 Ar/ 39 Ar ages and calculated closure temperatures (considered estimates) are ca . 1640 Ma ( T c = 455 to 515 °C) and 1510 Ma ( T c = 410 to 425 °C), respectively. In the Lake Harbour Group, the most prospective areas for gem corundum exploration are expected to be contiguous to the thrust fault separating the Lake Harbour Group and Narsajuaq terranes, where the retrograde, amphibolite facies overprint of the granulite peak assemblages was most pervasive.

Description: The oxygen isotopic composition of pink to red and other colored spinels hosted by marbles worldwide have been combined with trace elements investigated by electron microprobe analysis (EMPA). For the first time, this database enables the characterization of the geographic origin of the main productive and historical sources of gem spinel. Three consistent sets of 18 O values were found for primary and placer deposits: (1) between 5.6 and 8.6 for the historical Kuh-i-Lal spinels from Tajikistan; (2) from 12.1 to 18.5 for spinels from An Phu and Cong Troi in Vietnam, and Namya from Myanmar; and (3) between 19.0 and 24.2 for spinels from Paigutan in Nepal, Kiswila and Ipanko in Tanzania, Pamreso in Kenya, Mogok in Myanmar, and An Phu in Vietnam. The variation in the 18 O values for most of the deposits can be related to the buffering of the metamorphic fluids by the oxygen isotope composition of the impure marbles. The 18 O values of Kuh-i-Lal spinels result from a metasomatic skarn process between granitic intrusives and marble. Trace elements, such as Fe-Zn-Cr-V-Ti, presented in various new chemical discrimination diagrams allow for the differentiation of all the pink to red spinels. The slight overlaps observed for some chemical domains can be resolved by combination with the O-isotope composition of spinel. The present study shows that it is possible to discriminate gem spinels hosted by marbles from different geographic regions of the world and provides new insights into the traceability of historical spinels such as those from Kuh-i-Lal.