ALBERT

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: New electron-microprobe analyses of ‘tsavorites’ from the Neoproterozoic Metamorphic Mozambique Belt deposits allow the characterization of green grossular according to its trace-element chemistry (V, Cr, Mn). Five chemical types are defined: type 1, vanadian grossular with V 〉Cr 〉Mn (in atoms per formula unit); type 2, vanadian grossular with V 〉Mn 〉Cr; type 3, Mn-bearing vanadian grossular with Mn 〉 V 〉 Cr; type 4, Mn-bearing chromian grossular with Mn 〉 Cr 〉 V; and type 5, Cr- and Mn-bearing grossular with Cr 〉 Mn 〉 V. These types are also characterized by different absorption spectra in the ultraviolet–visible–near infrared. Type 1 tsavorite spectra show a total absorption below 430 nm due to the high vanadium contents. Type 2 tsavorite spectra present the classical absorption bands of V. Types 3 and 4 tsavorite spectra display additional shoulders at 407 and 408 nm due to Mn 2+ , whereas spectra of Cr-bearing types 4 and 5 tsavorite show the two additional bands of Cr 3+ at 697 and 701 nm. The different absorption spectra also indicate Fe 2+ -Ti 4+ charge transfer. We measured OH – equivalent to 0.08 to 0.38 wt% eq. H 2 O within the structure. Concentrations of vanadium, chromium and manganese are good chemical "fingerprints" for determining the geographic provenance of economic tsavorite from Kenya, Tanzania and Madagascar.