NEW MINERALS IN THE DEEP-SEATED CARBONATITIC ASSOCIATION: DATA FROM INCLUSIONS IN DIAMOND fgh Felix V. Kaminsky 1, Richard Wirth 2 & Anja Schreiber 2 1 KM Diamond Exploration Ltd., West Vancouver, BC, Canada, 2 GeoForschungsZentrum Potsdam, Germany Eleven new minerals were identified in diamond from the Juina area, Mato Grosso, Brazil: two carbonates (magnesite MgCO 3 and eitelite Na 2 Mg(CO 3 ) 2 ), two phosphates (mixed-anion phosphate Na 4 Mg 3 (PO 4 ) 2 (P 2 O 7 ) and Fe-diphosphate Fe 2 Fe 5 (P 2 O 7 ) 4 ), two fluorides (aluminum fluoride AlF 3 and Ba-rich fluoride (Ba,Sr)AlF 5 ), three sulfides (pentlandite (Fe,Ni) 9 S 8, violarite FeNi 2 S 4 and millerite NiS), hematite, and metallic Ni-iron. The two phosphates and the two fluorides were observed in the natural environment for the first time. The inclusions were studied with TEM at the GeoForschungsZentrum. Various TEM techniques, such as bright field – dark field imaging, high-angle annular dark-field imaging (HAADF), electron diffraction, electron-energy-loss spectroscopy (EELS) and analytical electron microscopy (AEM) were applied, utilizing a TECNAI F20 XTWIN transmission electron microscope with a field emission gun as an electron source. Polymineralic inclusion #1 has the 'negative' morphology that is common of syngenetic mineral inclusions in diamond. It is composed of dolomite + magnesite + eitelite Na 2 Mg(CO 3 ) 2 + phosphate Na 4 Mg 3 (PO 4 ) 2 (P 2 O 7 ) + phlogopite + NaCl + KCl + pentlandite + violarite + spinel + graphite/amorphous carbon + fluid (porosity). A single, isolated inclusion of halite was identified near the polymineralic inclusion #1. It was originally a fluid inclusion that was decrepitated. Polymineralic inclusion #2 is composed of crystals of aluminum fluoride AlF 3, Ba-rich fluoride BaAlF 5, Fe-rich phosphate Fe 2 Fe 5 (P 2 O 7 ) 4 which have never been observed as inclusion in diamond or even in the natural environment. Polymineralic inclusion #3 was cut by two foils, #3366 and #3367. It has a size of more than several (we do not know exactly)  m (only a part of the inclusion is cut by foils) (Fig. 9a). The euhedral ('negative') shape of the inclusion proves its syngenetic genesis with the hosting diamond, as with polymineralic inclusion #1. The inclusion is composed of two parts, separated by a thin, meniscus-like layer (arrows in Fig. 9a). One part of the inclusion is composed of amorphous carbon. The other part consists of a nanometer-sized (5-50 nm) aggregate in which AlF 3 predominates, which is confirmed by diffraction data (Fig. 9b). The other phases are SiO 2, Fe-oxide, millerite, and a phase enriched in Ce and P, which is possibly monazite. The elemental map (Fig. 10) helped us identify these phases, although the small size of the mineral grains did not allow diffraction analysis for each phase. Large (up to 1  m), irregularly shaped pores occur in both parts of the inclusion. Polymineralic inclusion #3 has euhedral ('negative') shape of the inclusion which proves its syngenetic genesis with the hosting diamond. One part of the inclusion is composed of amorphous carbon; the other part consists of a nanometer-sized (5-50 nm) aggregate in which AlF 3 predominates. The other phases are SiO 2, Fe-oxide, millerite, and possibly monazite. The elemental map helped us identify these phases, although the small size of the mineral grains did not allow diffraction analysis for each phase. Large (up to 1 mm), irregularly shaped pores occur in both parts of the inclusion. Polymineralic inclusion #4 is a ‘large’, more than  m aggregate. The matrix consists of crystals of AlF 3 (confirmed by electron diffraction) with nanometer-sized hematite needles. In some places, hematite needles are intergrown with nanometer-sized crystals of Fe(Ti,Nb)O 4, but this was not confirmed by diffraction data because of the small grain sizes. In addition, nanometer-sized, patchy grains of amorphous SiO 2 occur in the AlF 3 matrix. Polymineralicic inclusion #5 consists mainly of magnesite grains, nm in size. Several very small (20-70 nm) Ni-iron grains occur near the interface of the inclusion with the host diamond. Their approximate composition is as follows: Fe = 96.5 at.% and Ni = 3.5 at.%, which is typical for Ni-Fe alloys in meteorites (kamacite). In the center of the inclusion, a pronounced area saturated with sphere- shaped bubbles ( nm in size) occurs that shows elevated concentrations of Cl and Na. Magnesite MgCO 3 and Fe-magnesite (Mg,Fe)CO 3 form the major part of inclusion #1 along with dolomite. Magnesite is a new mineral in the primary carbonatitic association. The main body of magnesite has admixtures of Fe ( at. %) and Ca ( at. %). In addition to almost pure magnesite, some grains with at.% FeO can be attributed as ferromagnesite or breunnerite. With the increase in the Fe content, the Mn concentration increases up to 1.17 at.%. Dolomite forms the second major part of the microinclusion #1 along with magnesite. Compositionally, among cations, in addition to Ca and Mg, it has an admixture of Fe (3.1-12,4 at.%) and Mn (1.0 at. %). Eitelite Na 2 Mg(CO 3 ) 2 is another new anhydrous carbonate in this association. This carbonate was identified in polymineralic inclusion #1, where it forms micrometer-sized grains. The measured chemical composition of eitelite is close to stoichiometric, with a minor admixture of Fe ( at.%) and variations in Na and Mg contents at 5 at.% and 4.4 at.% correspondingly. The compositions of carbonates vary even within a single inclusion at distances less than 10 nm. Mixed-anion phosphate Na 4 Mg 3 (PO 4 ) 2 (P 2 O 7 ), which was never found in the natural environment before, forms several grains ca. 50 nm in size. The diffraction data demonstrate that the mineral has the same structure as established for synthetic mixed-anion phosphate Na 4 Mg 3 (PO 4 ) 2 (P 2 O 7 ). Its chemical compositions are close to stoichiometric. Fe-diphosphate Fe 2 3+ Fe 5 2+ (P 2 O 7 ) 4 has not previously been observed in natural environment. Aluminum fluoride AlF 3 has never been observed in the natural environment before. AlF 3 has a rhombohedral structure hR24 (space group R-3c). The compound (Ba,Sr)AlF 5 is extremely sensitive to electron irradiation damage. The chemical composition plus one single d- spacing only matches the unit cell parameter a 0 = nm for  - BaAlF 5. The mineral compositions of the analyzed inclusions are variable, even at a nanometer scale, which indicates variability in the source media during the formation of diamond. Volatiles, represented in the form of porosity, played a significant role in this process. Most mineral phases contain volatile elements, as well. Carbonatitic inclusions most likely originated from high-density fluid (HDF) microinclusions encapsulated in diamond during its growth. During the ascent of diamond, HDF inclusions underwent disintegration in composition and crystallized as polymineralic inclusions. Formation of diamond in the studied case took place in a carbonatitic, carbonate-halide-phosphate- fluoride medium, which was enriched in volatiles and acted as an open system during diamond formation. TEM bright-field image of nitrogen inclusions In diamond, having the same crystallographic orientation.