Characteristics and alteration origins of matrix minerals in volcaniclastic kimberlite of the Muskox pipe (Nunavut, Canada)

The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada

“…In sequence, the process is envisioned as (1) the formation of a dolomitic silico-carbonatite melt via melting of carbonated peridotite, (2) initial reaction with lithospheric mantle and early high-pressure CO 2 exsolution, (3) lower-pressure reactions with lithospheric wall rocks that change the bulk composition and release more CO 2 , producing calcite, and (4) the emplacement in the crust of the evolved kimberlite with the calcite-bearing mineral assemblage. The widespread occurrence of polymineralic inclusions in kimberlite megacrysts from numerous cratons (Haggerty and Boyd 1975;Schulze 1985;van Achterbergh et al 2002;Pivin et al 2009;Araújo et al 2009) is evidence of the general applicability of this process to the evolution of kimberlites.…”

“…Commonly reported phases in such inclusions are: phlogopite, olivine, carbonates (dominantly calcite), spinel, and serpentine. Haggerty and Boyd (1975) first described polymineralic inclusions in olivine megacrysts from the Monastery kimberlite in South Africa and interpreted them as early kimberlite melt with an immiscible sulfide liquid. Schulze (1985), studying inclusions in grt and cpx megacrysts, adopted this interpretation and extended it to propose that the trapped kimberlite melt may also constitute the magma from which the hosts crystallized.…”

Geology of the BK9 kimberlite (Damtshaa, Botswana): implications for the formation of dark volcaniclastic kimberlite

“…Malone 1995;Schneider and Fisher 1998;Hungr and Evans 2004) The distinction between DVK and MVK The two types of DVK present in the BK9 kimberlite demonstrate that DVK encompasses a range of volcaniclastic rocks from welded and agglutinated rocks with a large fine or former melt fraction to non-welded varieties, texturally comparable to MVK. The DVK units differ from most MVK in both their hydrothermal alteration, as suggested by Hayman et al (2008Hayman et al ( , 2009, and in their abundance of fine particles. DVK may also have lower abundances of olivine crystals (Brown et al 2009) and lower abundances of country-rock lithic clasts (Hayman et al 2008(Hayman et al , 2009van Straaten et al 2009); although, at least in terms of lithic clast abundance, there is considerable overlap with MVK and this is not a defining characteristic (see Fig.…”

“…Alternatively, the abundance of silt-sized particles may result from the production of large quantities of ash. An alternative explanation for the fine-grained, poorly sorted nature of similar volcaniclastic kimberlites is given by Cas et al (2008b), Porritt et al (2008a) and Hayman et al (2009). These authors suggest that such kimberlites are emplaced en masse and that the interstitial alteration assemblages (e.g.…”

“…DVK is considered to originate through similar processes to green varieties of MVK (Brown et al 2008a, b). The differences result from one or more of the following: the energy of the eruption (van Straaten et al 2009); the degree of melt solidification on pyroclast deposition, which determines whether pyroclasts agglutinate and weld (Brown et al 2008a, b) and variations in post-emplacement hydrothermal alteration (Hayman et al 2008(Hayman et al , 2009). …”