256 IGNEOUS ROCKS/Kimberlite Table A summary of the disaggregated minerals found in kimberlites, and their origins x, present; xx, fairly abundant; xxx, abundant (Reproduced from Nixon PH (1980) The morphology and mineralogy of diamond pipes In: Glover JE and Groves DI (eds.) Kimberlites and Diamonds, pp 32 47 Nedlands: University of Western Australia.) Earth zone (Host rock) Upper Crust Lower Crust (granulites, etc.) Lithosphere (lherzolites etc.) Mantle differentiates (eclogite and grospydite) Kimberlite suite (including MARID ‘precipitates’) Mantle residue at kimberlite foci (diamond inclusion suite) Asthenosphere (lherzolites, etc.) Discrete nodules (megacrysts) Disaggregated resistant mineral suite Widely variable; Garnet, Clinopyroxene, Orthopyroxene, Rutile Olivine Orthopyroxene Clinopyroxene Garnet Spinel Mica Garnet Clinopyroxene Rutile, ilmenite Kyanite Corundum Diamond Olivine Mica Amphibole Rutile Ilmenite Clinopyroxene Garnet Diamond Olivine Orthopyroxene Clinopyroxene Garnet Spinel Olivine Orthopyroxene Clinopyroxene Garnet Orthopyroxene Clinopyroxene Garnet Ilmenite Zircon Composition (approximate values) Py alm, Omphacite, Hypersthene Fo93 En94 Cr diopside Cr pyrope Chromite Phlogopite Py alm gross Omphacite Fo85–95 Phlogopite Mg bearing Diopside Py alm Fo93–94 En92–96 Cr diopside Knorringite pyrope Chromite Fo90 Calcic bronzite (En87) Subcalcic diopside Pyrope Calcic bronzite (En87) Subcalcic diopside Pyrope (little alm) Mg bearing from great depths incorporates the diamonds as xenocrysts in the magma Very hot magmas may completely resorb the diamonds Only magmas rising from great depths will carry diamonds Relative abundance xxx x x x x xxx xxx xx xx x xx x x x x x x xxx ? xxx x x xx xx x x x x x x x x x x x x(x) xx xxx xxx x Comment Scapolite, hornblende, apatite, etc also present Depleted mineralogy high Mg/Fe, Cr/Al and low Ca and Na, although not as extreme as in the diamond inclusion suite Differentiation within the mantle locally extends chemical ranges Metasomatism produces additional minerals similar to kimberlite suite below Diamond and graphite recorded Rare suite but is locally abundant Generally much higher Fe/Mg ratios than in lherzolites Many secondary minerals not listed but note wide variety of fine grained spinels and perovskite Zircon present Rare suite in concentrates ‘Ultra depleted’ extremely high Mg/Fe, Cr/Al and low Ca, Ti, and Na ‘Fertile’ composition, i.e., relatively low Mg/Fe and Cr/Al but higher Ti compared with typical lithosphere Silicates have similar composition to those in fertile nodules with a tendency to higher Fe/Mg ratios Ilmenite pyroxene lamellar intergrowths are part of this suite although it is a rich source of diamonds Southern Africa is overwhelmingly the site of the most numerous kimberlite developments, as shown in Figure Prospecting Methods Major Provinces The global distribution of major kimberlite provinces is shown in Figure 14 The recently discovered province of diamondiferous kimberlites in the Slave Craton of Canada, is shown It should be noted that province number 9, in the north of Western Australia, is a lamproite province not a kimberlite province, Because kimberlite pipes rarely have a surface expression, prospecting for diamonds is arduous and requires the application of specialized methods This in turn requires specialized training The methods include: separation of heavy minerals (coarse and fine fractions): red-brown pyrope (discrete nodule