Volatile-rich brine and melt in Canadian diamonds (original) (raw)
Geochimica et Cosmochimica Acta, 2007
The analysis of micro-inclusions in fibrous diamonds from the Diavik mine, Canada revealed the presence of high density fluids (HDFs) that span a continuous compositional range between carbonatitic and saline end-members. The carbonatitic end-member is rich in Na, Ca, Mg, Fe, Ba and carbonate; the saline one is rich in K, Cl and water. In molar proportions, the composition of
Lithos, 2004
Analyses of mineral inclusions, carbon isotopes, nitrogen contents and nitrogen aggregation states in 29 diamonds from two Buffalo Hills kimberlites in northern Alberta, Canada were conducted. From 25 inclusion bearing diamonds, the following paragenetic abundances were found: peridotitic (48%), eclogitic (32%), eclogitic/websteritic (8%), websteritic (4%), ultradeep? (4%) and unknown (4%). Diamonds containing mineral inclusions of ferropericlase, and mixed eclogitic-asthenosphericwebsteritic and eclogitic-websteritic mineral associations suggests the possibility of diamond growth over a range of depths and in a variety of mantle environments (lithosphere, asthenosphere and possibly lower mantle). Eclogitic diamonds have a broad range of C-isotopic composition (d 13 C = À 21x to À 5x). Peridotitic, websteritic and ultradeep diamonds have typical mantle C-isotope values (d 13 C = À 4.9x av.), except for two 13 C-depleted peridotitic (d 13 C = À 11.8x, À 14.6x) and one 13 C-depleted websteritic diamond (d 13 C = À 11.9x). Infrared spectra from 29 diamonds identified two diamond groups: 75% are nitrogen-free (Type II) or have fully aggregated nitrogen defects (Type IaB) with platelet degradation and low to moderate nitrogen contents (av. 330 ppm-N); 25% have lower nitrogen aggregation states and higher nitrogen contents ( f 30% IaB; < 1600 ppm-N). The combined evidence suggests two generations of diamond growth. Type II and Type IaB diamonds with ultradeep, peridotitic, eclogitic and websteritic inclusions crystallised from eclogitic and peridotitic rocks while moving in a dynamic environment from the asthenosphere and possibly the lower mantle to the base of the lithosphere. Mechanisms for diamond movement through the mantle could be by mantle convection, or an ascending plume. The interaction of partial melts with eclogitic and peridotitic lithologies may have produced the intermediate websteritic inclusion compositions, and can explain diamonds of mixed parageneses, and the overlap in C-isotope values between parageneses. Strong deformation and extremely high nitrogen aggregation states in some diamonds may indicate high mantle storage temperatures and strain in the diamond growth environment. A second diamond group, with Type IaA -IaB nitrogen aggregation and peridotitic inclusions, crystallised at the base of the cratonic lithosphere. All diamonds were subsequently sampled by kimberlites and transported to the Earth's surface.
Lithos, 2019
Quantitative trace element data from high-purity gem diamonds from the Victor Mine, Ontario, Canada as well as near-gem diamonds from peridotite and eclogite xenoliths from the Finsch and Newlands mines, South Africa, acquired using an off-line laser ablation method show that we see the same spectrum of fluids in both high-purity gem and near-gem diamonds that was previously documented in fibrous diamonds. "Planed" and "ribbed" trace element patterns characterize not only the high-density fluid (HDF) inclusions in fibrous diamonds but also in gem diamonds. Two diamonds from two Finsch harzburgite xenoliths show trace element patterns similar to those of saline fluids, documenting the involvement of saline fluids in the precipitation of gem diamonds, further strengthening the link between the parental fluids of both gem and fibrous diamonds. Differences in trace element characteristics are evident between Victor diamonds containing silicate inclusions compared with Victor diamonds containing sulphide inclusions. The sulphide-bearing diamonds show lower levels of inter-element fractionation and more widely varying siderophile element concentrations-indicating that the silicate and sulphide-bearing diamonds likely formed by gradations of the same processes, via melt-rock reaction or from a subtly different fluid source. The shallow negative LREE N-HREE N slopes displayed by the Victor diamonds establish a signature indicative of original derivation of the diamond forming agent during major melting (~10% melt). Consequently, this signature must have been passed on to HDFs separating from such silicate melts.
Lithos, 2008
Quantitative trace-element analyses of 38 elements have been carried out in 11 samples of polycrystalline diamond (diamondite) from southern Africa by LAM-ICPMS. The samples are divided into "peridotitic" and "eclogitic" types based on the compositions of garnet and clinopyroxene intergrown with the diamond. The trace-element patterns of the diamondite samples reflect mixtures of diamond and submicroscopic inclusions of fluid ± solid phases, and are interpreted as representing the fluids from which the diamondite crystallised. They are similar to parent-melt compositions calculated from macroscopic garnet and clinopyroxene inclusions in the diamondites, and suggest that the diamondites, like many fibrous diamonds, crystallised from melts in the kimberlite-carbonatite spectrum. Multi-element spikes seen in the timeresolved LAM-ICPMS analyses indicate the presence of several, probably submicroscopic, solid phases: garnet, clinopyroxene, an Y-Yb rich (fluoride?) phase, a sulfide rich in Cu-Pb-Zn-Co-Ni, a LIMA-type phase, a carbonate, ilmenite, chromite and mica. The similarity in trace-element patterns of the "peridotitic" and "eclogitic" diamondites suggests that both types have crystallised from the same type of metasomatic fluid. This fluid may have evolved from "peridotitic" to "eclogitic" by the removal of chromite ± sulfide ± ilmenite.
Hydrous and carbonatitic mantle fluids in fibrous diamonds from Jwaneng, Botswana
Geochimica et Cosmochimica Acta, 1994
Fluid-inclusions in fibrous diamonds from Jwaneng (Botswana) contain water, carbonates, silicates, apatite, and COz . Average compositions of fluids trapped in individual diamonds span a wide range, and vary linearly and continuously between two endmember compositions, a carbonatitic fluid rich in carbonate, CaO, FeO, MgO, and P205, and a hydrous fluid rich in water, SiOz, and A1203. K20 contents are high in both endmembers. The mg numbers (Mg/( Mg f Fe)) of the trapped fluids are low (0.55-0.44) and decrease towards the hydrous endmem~r. Fluid compositions are broadly similar to those reported for Zairean diamonds, but cover a wider range. I&a-diamond compositional variation is limited.
Diamond Crystals and Their Mineral Inclusions from the Lynx Kimberlite Dyke Complex, Central Quebec
The Canadian Mineralogist, 2011
Lynx is a 522 Ma kimberlite dyke complex located in the Otish Mountains of central Quebec, Canada. Test sampling of the Lynx kimberlite yielded 6598 macrodiamond samples from 528 t of kimberlite. Single crystals strongly dominate the population, with only 14% of the macrodiamond portion consisting of macles and aggregates. Within the single crystals, 41% are dominated by octahedral surface features, and the remaining ones are partially resorbed tetrahexahedroida. Brown is the most common color among the tetrahexahedroida, with only 22% gray to colorless stones comprising the remainder. In contrast, the octahedra are roughly equal in numbers of brown, gray and colorless stones. A subset of twenty stones was selected in the-11 to +3 DTC (0.256 c to 0.67 c) range of circular sieve sizes on the basis of visible inclusions. These have octahedral primary growth-forms and include three macles and three aggregates of octahedra. Most of the samples are significantly resorbed; they range from octahedra with rounded corners and edges to tetrahexahedroida. Shield laminae, serrate laminae, and hillocks are the most common resorption-related surface features. The stones were cut and polished along single planes to expose mineral inclusions for analysis and to allow imaging of internal structure of the diamond relative to the inclusions. Cathodoluminescence imaging revealed deformation lamellae in most of the polished crystals. Some exhibit deformation lamellae truncated by growth or resorption zones or intersections of different crystallographic planes. Oscillatory patterns of planar growth with complex cores are most common. Inclusions, particularly of olivine, typically occur in core and early growth regions of the diamond crystals. Primary inclusions exposed by polishing are magnesian olivine, chromian diopside, chromian pyropic garnet, magnesian orthopyroxene, omphacite, and sulfide. The chromian diopside inclusions yield equilibration conditions in the range of 58-60 kbar and 1250-1280°C that correspond to conditions slightly below a 42 mW/m 2 surface heat-flow geothermal gradient. The most iron-rich olivine inclusion (mg# = 0.916) occurs with the diopside inclusions, suggesting a relatively fertile lherzolitic component of mantle at 180-190 km depth. The garnet data indicate that within the peridotite parentage, both harzburgitic (three G10, 12.4-13.7 wt.% Cr 2 O 3 , 3.7-4.4 wt.% CaO) and lherzolitic (one G9, 8.9 wt.% Cr 2 O 3 , 5.8 wt.% CaO) parageneses are present.
The Characteristics and Identification of Filled Diamonds
Gems & Gemology, 1989
helped with the chemical analyses. The assistance of Eli Haas and Martin Rapaport was invaluable. Unless otherwise noted, all pholomicrographs are by John I. Koivula. This study was supported in part by the Dr. Byron C. Butler Fund for tnclusion Research.
A geochemical method to identify presence of microdiamond in rock, soil or stream sediment sample, by analysing it directly, is discussed in this communication. Diamond being carbon in composition, C% of the diamond-bearing samples is estimated by analysing them in carbon analyser (Coulomat). Five stream sediment samples from Wajrakarur, an area known for diamond-bearing kimberlite pipes were tested using industrial diamond as reference standard. The 0.125-0.177 mm size samples were treated with a combination of acids, HCl, HNO 3 , H 2 O 2 and run in an isodynamic separator to separate non-magnetic components. The components were then analysed in X-ray diffractometer and Coulomat. The data shows anomalous values for carbon and indicate presence of diamond in the sample. The method allows detection of diamonds as low as 0.02 mg size reliably and is particularly useful to locate palaeo-placers and primary diamonds of microdiamond variety.