Finally, a coarse muscovite grain from a quartz-feldspar-muscovite intergrowth surrounding a blocky K-feldspar megacryst
was dated with the [sup.
The composition of the A15 megacryst
garnets is similar to the megacrystic suite of the diamond-rich Jericho kimberlite of the Slave craton with both exhibiting a distinct reduced crystal chemistry, which is most promising for the stability and preservation of diamond.
Using this classification, 23 mantle-derived garnets were recovered: one (1) Harzburgitic or "G10" garnet, four (4) Lherzolitic or "G9" garnets, thirteen (13) catazonal garnets "G5", four (4) eclogitic garnets or "G3" and one (1) low-chromium megacryst
This dominantly monzogranitic pluton, generated by hybridization between mantle and crustal magmas, consists of mappable facies; end members range from less hybridized with high concentrations of very coarse K-feldspar megacrysts
and abundant mafic microgranular enclaves, to more hybridized with low megacryst
and enclave abundances.
Technical advances on the property last year include the recovery of G-9 pyropes and megacryst
garnets that, together with other indicator minerals found in the preceding years, show a mainstream diamond source of likely eclogitic origin.
In addition, both megacryst
and ecologite paragenesis garnets are well represented in this kimberlite.
A range of stages of development of massive crystalline aggregates is observed in the samples: individual microcrysts, framboids, framboid clusters, recrystallized megacryst
overgrowths, and banded concentric zones.
33 Lherzolite G9 garnets, 27 megacrysts
and 1 Wehrlitic grain.
, inclusions in megacrysts
This alternation has quite changed into calcite megacrysts
upward, lacking any macrofossil.
Hill and Ross (1983) determined a broad range of Rb-Sr and Sm-Nd ages for megacrysts
and xenoliths in the Porter Square camptonite, but a well-constrained internal Sm-Nd isochron age of 238 [+ o r-] 26 Ma was determined for a coarse-grained, graphite-garnet-bearing granulite xenolith.
Many of these dykes contain abundant, large plagioclase megacrysts