Cartographic Study and Modeling of the Bakwanga Kimberlite Massive 5 at Kasai Oriental in the Democratic Republic of Congo

Bakwanga kimberlite massive 5 in Kasai Oriental is part of a set of 13 kimberlite massives numbered according to the order in which they were discovered. They are located on an alignment with a more or less W-E direction making up the Northern group known as Bakwanga. The importance of the Bakwanga kimberlite massives on the country’s economy in the production of diamonds sufficiently proves the interest of geological research work in this area. The objective of this work is to determine a mathematical model of the shape of the massive as close as possible to reality and through cartography. The cartographic study and modeling of this kimberlite massive were carried out using data from core samples taken on longitudinal and transverse profiles of the 50 × 50 meter mesh drilling plan intersecting this kimberlite massive. We intend to deduce the structure and lithostratigraphy of the kim-berlitic facies and the direct environment of massive 5. As a result, we note that the majority of surveys on the extent of this massive have intersected: Red clayey sand - Polymorphic sandstone - Nodular sandstone, with kaolin blocks and nodules - Epiclastic Kimberlite - Xenokimberlite - Massive Kimberlite - Mesozoic sandstone - Dolomite (enclosing). The shape of the Massive 5 model is vaguely elliptical with a W-E longitudinal axis of 575 m and N-S axis of 275 meters. Surveys have shown that Massive 5 is in fact composed of two pipes, located in the W (western pipe) and E (eastern pipe) ends of the massif. The two chimneys of the two pipes have walls ranging from subvertical at the eastern pipe to very steep walls of around 70˚ to 80˚ for the western pipe and the average diameter of the two pipes is ±50 meters. At level 600, the massive has an area of ±10.5 hectares and it gradually decreases in depth and the modeling of the latter shows a concentric decrease in the volume of the massive from the surface to depth in the shape of a mushroom. 3 eruptive phases established this Kimber-litic massive, the first two phases (old) of which formed the crater of the western pipe and the third formed the crater of the eastern pipe in the dolomites. These dolomites constitute everywhere the surrounding area of the massive;the distinction of these 3 phases is made possible thanks to Epiclastic deposits, Xenokim-berlites and massive Kimberlites.

Petrology and Structural Characterization of Post-Neoproterozoic Dolerites from the Kimberlite Fields in the Kéniéba Region (Western Mali)

Post-Neoproterozoic dolerites from the Kéniéba region (Western Mali) are often associated with kimberlites. The rarity of kimberlite outcrops led to the study of doleritic rocks, spatially associated with them. The petrographic and lithogeochemical study showed that the dolerites of the Kéniéba kimberlitic fields are of tholeiitic nature and of the E-MORB (Enriched-Mid Ocean Ridge Basalt) type. This reflects an enrichment over time, compared to the Birimian dolerites of the volcano-sedimentary greenstone belt of Toumodi, in central C?te d’Ivoire. Furthermore, these dolerites are enriched in SiO2, TiO2, Zr and poor in Fe2O3, MgO. These dolerites would have formed in a late to post-orogenic intracontinental context during the breakup of Gondwana. Structurally, Kéniéba dolerites are often associated with kimberlite pipes, fractures and large deep structures identified using aeromagnetic images. Taking into account the fact that kimberlites do not outcrop in the Kéniéba region, the geochemical study coupled with the interpretation of aeromagnetic data proved to be very useful for the search for pipes.

Aeromagnetic Imagery as a Tool to Help Identify the Structures Controlling the Emplacement of the Kenieba Kimberlite Pipes (Western Mali, West African Craton)

A kimberlite field, represented by fertile and sterile kimberlite pipes (chimneys) is located in the region of Kenieba (West Mali, Kédougou-Kenieba inlier, West African Craton). Thirty pipes and kimberlite dykes have been identified in the birimian formations, composed mainly of metasediments and granitoids, covered by sedimentary formations (sandstones and conglomerates) of Neoproterozoic age. All these formations are injected with dykes and doleritic sills of Jurassic age. The study of kimberlite pipes is still stammering in Mali, and thus no previous study has allowed to characterize the structures controlling their implementation. The reinterpretation of aeromagnetic data validated by field work indicates that the major structures of the Kenieba region are oriented NNE-SSW, NE-SW, E-W and NW-SE. These structures (faults and kimberlite pipes) are often associated with dolerite dykes, which would imply an injection of dolerite magma into the other formations. The location of the known kimberlite pipes makes it possible to say that the direction NW-SE is the most favorable for the exploration of kimberlites in the region of Kenieba.

Recycling process and proto-kimberlite melt metasomatism in the lithosphere-asthenosphere boundary beneath the Amazonian Craton recorded by garnet xenocrysts and mantle xenoliths from the Carolina kimberlite

Here we present new data on the major and trace element compositions of silicate and oxide minerals from mantle xenoliths brought to the surface by the Carolina kimberlite,Pimenta Bueno Kimberlitic Field,which is located on the southwestern border of the Amazonian Craton.We also present Sr-Nd isotopic data of garnet xenocrysts and whole-rocks from the Carolina kimberlite.Mantle xenoliths are mainly clinopyroxenites and garnetites.Some of the clinopyroxenites were classified as GPP–PP–PKP(garnet-phlogopite peridotite,phlogopite-peridotite,phlogopite-K-richterite peridotite)suites,and two clinopyroxenites(eclogites)and two garnetites are relicts of an ancient subducted slab.Temperature and pressure estimates yield 855–1102℃ and 3.6–7.0 GPa,respectively.Clinopyroxenes are enriched in light rare earth elements(LREE)(La_(N)/Yb_(N)=5–62;Ce_(N)/Sm_(N)=1–3;where N=primitive mantle normalized values),they have high Ca/Al ratios(10–410),low to medium Ti/Eu ratios(742–2840),and low Zr/Hf ratios(13–26),which suggest they were formed by metasomatic reactions with CO_(2)-rich silicate melts.Phlogopite with high TiO_(2)(>2.0 wt.%),Al_(2)O_(3)(>12.0 wt.%),and FeOt(5.0–13.0 wt.%)resemble those found in the groundmass of kimberlites,lamproites and lamprophyres.Conversely,phlogopite with low TiO_(2)(<1.0 wt.%)and lower Al_(2)O_(3)(<12.0 wt.%)are similar to those present in GPP-PP-PKP,and in MARID(mica-amphibole-rutile-ilmenite-diopside)and PIC(phlogopite-ilmenite-clinopyorxene)xenoliths.The GPP-PP-PKP suite of xenoliths,together with the clinopyroxene and phlogopite major and trace element signatures suggests that an intense proto-kimberlite melt metasomatism occurred in the deep cratonic lithosphere beneath the Amazonian Craton.The Sr-Nd isotopic ratios of pyrope xenocrysts(G3,G9 and G11)from the Carolina kimberlite are characterized by high ^(143)Nd/^(144)Nd(0.51287–0.51371)and eNd(+4.55 to+20.85)accompanied with enriched ^(87)Sr/^(86)Sr(0.70405–0.71098).These results suggest interaction with a proto-kimberlite melt compositionally similar with worldwide kimberlites.Based on Sr-Nd whole-rock compositions,the Carolina kimberlite has affinity with Group 1 kimberlites.The Sm-Nd isochron age calculated with selected eclogitic garnets yielded an age of 291.9±5.4 Ma(2σ),which represents the cooling age after the proto-kimberlite melt metasomatism.Therefore,we propose that the lithospheric mantle beneath the Amazonian Craton records the Paleozoic subduction with the attachment of an eclogitic slab into the cratonic mantle(garnetites and eclogites);with a later metasomatic event caused by proto-kimberlite melts shortly before the Carolina kimberlite erupted.

Experimental investigation on the effects of microwave irradiation on kimberlite and granite rocks

This study is a part of an overall research project on the effects of microwave(MW)irradiation on rocks for assisted rock breaking systems as well as mineral processing at McGill University.For the first time,this paper highlights a comprehensive investigation on the effects of microwave irradiation on Canadian kimberlites.Potential contribution to the continuous rock excavation and rock weakening effect prior to implementation of mechanical techniques was explored.Two different kimberlite rocks,i.e.volcaniclastic kimberlite(VK)and hypabyssal kimberlite(HK),and granite samples were studied.Some important physical properties of the rock samples were measured including rock quality designation(RQD),specific gravity,porosity,and specific heat capacity.Rock samples were treated for various exposure times using a multi-mode MWunit at different power levels ranging from 2 kW to 15 kW.The effect of MW irradiation on rock samples was investigated.The results indicate that the mechanical properties including unconfined compressive strength(UCS)and Brazilian tensile strength(BTS)were significantly dropped as a result of MWirradiation.Finally,the effect on rock abrasivity using the Cerchar abrasivity index(CAI)has also been discussed.

Phlogopite in mantle xenoliths and kimberlite from the Grib pipe,Arkhangelsk province,Russia:Evidence for multi-stage mantle metasomatism and origin of phlogopite in kimberlite

We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths (garnet peridotite,eclogite and clinopyroxene-phlogopite rocks) and for megacryst,macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle (SCLM) and the origin of phlogopite in kimberlite.Based on the analysed xenoliths,phlogopite is characterized by several generations.The first generation (Phl1) occurs as coarse,discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths.The second phlogopite generation (Phl2) occurs as rims and outer zones that surround the Phl1 grains and as fine flakes within kimberlite-related veinlets filled with carbonate,serpentine,chlorite and spinel.In garnet peridotite xenoliths,phlogopite occurs as overgrowths surrounding garnet porphyroblasts,within which phlogopite is associated with Cr-spinel and minor carbonate.In eclogite xenoliths,phlogopite occasionally associates with carbonate bearing veinlet networks.Phlogopite,from the kimberlite,occurs as megacrysts,macrocrysts,microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts.Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains,which indicates that they are the disintegrated fragments of previously larger grains.Phl1,within the garnet peridotite and clinopyroxeneephlogopitexenoliths,is characterised bylow Ti and Cr contents (TiO2<1 wt.%,Cr2O3<1 wt.% andMg#=100×Mg/(MgtFe)>92) typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences.They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas.One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H2O.Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma.Compared with peridotite xenoliths,eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr2O3 despite a wider range of TiO2 concentrations.The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite.Phl2 has high Ti and Cr concentrations (TiO2 > 2 wt.%,Cr2O3 > 1 wt.% and Mg#=100 × Mg/(Mg + Fe)< 92) and compositionally overlaps with phlogopite from polymict breccia xenoliths that occur in global kimberlite formations.These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phl1 grains or crystallized directly from stalled batches of kimberlitic magmas.Megacrysts,most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths.Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts.Based on the results of this study,we propose a schematic model of SCLM metasomatism involving phlogopite crystallization,megacryst formation,and genesis of kimberlite magmas as recorded by the Grib pipe.

Petrology,genesis and geodynamic implication of the Mesoproterozoic-Late Cretaceous Timmasamudram kimberlite cluster,Wajrakarur field,Eastern Dharwar Craton,southern India

New mineralogical and bulk-rock geochemical data for the recently recognised Mesoproterozoic （ca. 1100 Ma） and late Cretaceous （ca. 90 Ma） kimberlites in the Timmasamudram cluster （TKC） of the Wajrakarur kimberlite field （WKF）, Eastern Dbarwar Craton, southern India, are presented. On the basis of groundmass mineral chemistry （phlogopite, spinel, perovskite and clinopyroxene）, bulk-rock chem- istry （SiO2, K20, low TiO2, Ba/Nb and La/Sm）, and perovskite Nd isotopic compositions, the TI（-1 （mac- rocrystic variety） and TI（-4 （Macrocrystic variety） kimberlites in this cluster are here classified as orangeites （i.e. Group II kimberlites）, with geochemical characteristics that are very similar to orangeites previously described from the Bastar Craton in central India, as well as the Kaapvaal Craton in South Africa. The remaining kimberlites （e.g., TK-2, TK-3 and the TK-1 microcrystic variant）, are more similar to other 1100 Ma, Group l-type kimberlites of the Eastern Dharwar Craton, as well as the typical Group I kimberlites of the Kaapvaal Craton. Through the application of geochemical modelling, based on pub- lished carbonated peridotite/melt trace element partition coefficients, we show that the generation of the TI（C kimberlites and the orangeites results from low degrees of partial melting of a metasomatised, carbonated peridotite. Depleted mantle （TDM） Nd perovskite model ages of the 1100 Ma Timmasamudram kimberlites show that the metasomatic enrichment of their source regions are broadly similar to that of the Meso- proterozoic kimberlites of the EDC. The younger, late Cretaceous （ca. 90 Ma） TI（-1 （macrocrystic variant） and TK-4 kimberlites, as well as the orangeites from the 8astar Craton, share similar Nd model ages of 1100 Ma, consistent with a similarity in the timing of source enrichment during the amalgamation of Rodinia supercontinent. The presence of late Cretaceous diamondiferous orangeite activity, presumably related to the location of the Marion hotspot in southern India at the time, suggests that thick lithosphere was preserved, at least locally, up to the late Cretaceous, and was not entirely destroyed during the breakup of Gondwana, as inferred by some recent geophvsical models.

Accessary Minerals SIMS U-Th-Pb Dating for Kimberlite and Lamproite

Kimberlite and lamproite,the major source of diamonds,are volatile-rich potassic ultramafic rocks that originate from the deep lithospheric mantle.These rocks are important for deciphering the composition and

Petrogenesis of the diamondiferous Pipe-8 ultramafic intrusion from the Wajrakarur kimberlite field of Southern India and its relation to the worldwide Mesoproterozoic(~1.1 Ga) magmatism of kimberlite and related rocks

Detailed mineralogy,bulk rock major,trace and Sr-Nd isotope compositions,and ^(40)Ar/^(39)Ar dating of the Pipe-8 diamondiferous ultramafic intrusion in the Wajrakarur cluster of southern India,is reported.Based on the presence of Ti-rich phlogopite,high Na/K content in amphibole,Al-and Ti-rich diopside,a titanomagnetite trend in spinel and the presence of Ti-rich schorlomite garnet and carbonates in the groundmass,the Pipe-8 intrusion is here more precisely classified as an ultramafic lamprophyre(i.e.,aillikite).An aillikite affinity of the Pipe-8 intrusion is further supported by the bulk rock major and trace element and Sr-Nd isotope geochemistry.Sr-Nd isotope data are consistent with a common,moderately depleted upper mantle source region for both the Pipe-8 aillikite as well as the Wajrakarur kimberlites of southern India.A phlogopite-rich groundmass ^(40)Ar/^(39)Ar plateau age of 1115.8±7.9 Ma(2σ) for the Pipe-8 intrusion falls within a restricted 100 Ma time bracket as defined by the 1053-1155 Ma emplacement ages of kimberlites and related rocks in India.The presence of ultramafic lamprophyres,carbonatites,kimberlites,and olivine lamproites in the Wajrakarur kimberlite field requires low degrees of partial melting of contrasting metasomatic assemblages in a heterogeneous sub-continental lithospheric mantle.The widespread association of kimberlite and other mantle-derived magmatism during the Mesoproterozoic(ca.1.1 Ga) have been interpreted as being part of a single large igneous province comprising of the Kalahari,Australian,West Laurentian and Indian blocks of the Rodinia supercontinent that were in existence during its assembly.In India only kimberlite/lamproite/ultramafic lamprophyre magmatism occurred at this time without the associated large igneous provinces as seen in other parts of Rodinia.This may be because of the separated paleo-latitudinal position of India from Australia during the assembly of Rodinia.It is speculated that the presence of a large plume at or close to 1.1 Ga within the Rodinian supercontinent,with the Indian block located on its periphery,could be the reason for incipient melting of lithospheric mantle and the consequent emplacement of only kimberlites and other ultramafic,volatile rich rocks in India due to comparatively low thermal effects from the distant plume.

Clinopyroxenes in Kimberlites of China

The author studied the grain size, shape, colour, altered coat, mineral species, chemical composition,end- member components and infrared spectra of clinopyroxenes occurring as megacryst, macrocryst andgroundmass minerals, intergrowths with pyrope and ilmenite and minerals in deep-seated xenoliths and inclu-sions in diamonds in kimberlites of China. The clinopyroxenes under study were compared with megacrystclinopyroxenes in basalts and minerals in their deep-seated xenoliths and clinopyroxenes in lamproites andminettes. The coexisting clinopyroxene-pyrope pair was studied. Besides the author also studied the origin ofclinopyroxenes in kimberlites, P-T conditions for their formation and their reflected tectonic environments ofthe kimberlite formation. He suggests that this mineral is an indicator for diamond exploration.

Metasomatic origin of garnet xenocrysts from the V.Grib kimberlite pipe,Arkhangelsk region,NW Russia

This paper presents new major and trace element data from 150 garnet xenocrysts from the V.Grib kimberlite pipe located in the central part of the Arkhangelsk diamondiferous province（ADP）.Based on the concentrations of Cr_2O_3,CaO,TiO_2 and rare earth elements（REE） the garnets were divided into seven groups：（1） lherzolitic ＂depleted＂ garnets（ ＂Lz 1＂）,（2） lherzolitic garnets with normal REE patterns（ ＂Lz2＂）,（3） lherzolitic garnets with weakly sinusoidal REE patterns（ ＂Lz 3＂）,（4） lherzolitic garnets with strongly sinusoidal REE patterns（ ＂Lz 4＂）,（5） harzburgitic garnets with sinusoidal REE patterns（ ＂Hz＂）,（6）wehrlitic garnets with weakly sinusoidal REE patterns（ ＂W＂）,（7） garnets of megacryst paragenesis with normal REE patterns（ ＂Meg＂）.Detailed mineralogical and geochemical garnet studies and modeling results suggest several stages of mantle metasomatism influenced by carbonatite and silicate melts.Carbonatitic metasomatism at the first stage resulted in refertilization of the lithospheric mantle,which is evidenced by a nearly vertical CaO-Cr_2O_3 trend from harzburgitic（ ＂Hz＂） to lherzolitic（ ＂Lz 4＂） garnet composition.Harzburgitic garnets（ ＂Hz＂） have probably been formed by interactions between carbonatite melts and exsolved garnets in high-degree melt extraction residues.At the second stage of metasomatism,garnets with weakly sinusoidal REE patterns（ ＂Lz 3＂, ＂W＂） were affected by a silicate melt possessing a REE composition similar to that of ADP alkaline mica-poor picrites.At the last stage,the garnets interacted with basaltic melts,which resulted in the decrease CaO-Cr_2O_3 trend of ＂Lz 2＂ garnet composition.Cr-poor garnets of megacryst paragenesis（ ＂Meg＂） could crystallize directly from the silicate melt which has a REE composition close to that of ADP alkaline mica-poor picrites.P-T estimates of the garnet xenocrysts indicate that the interval of-60-110 km of the lithospheric mantle beneath the V.Grib pipe was predominantly affected by the silicate melts,whereas the lithospheric mantle deeper than150 km was influenced by the carbonatite melts.

Sheared peridotite xenolith from the V.Grib kimberlite pipe,Arkhangelsk Diamond Province,Russia:Texture,composition,and origin

The petrography and mineral composition of a mantle-derived garnet peridotite xenolith from the V.Grib kimberlite pipe（Arkhangelsk Diamond Province,Russia） was studied.Based on petrographic characteristics,the peridotite xenolith reflects a sheared peridotite.The sheared peridotite experienced a complex evolution with formation of three main mineral assemblages：（1） a relict harzburgite assemblage consist of olivine and orthopyroxene porphyroclasts and cores of garnet grains（Gar1） with sinusoidal rare earth elements（REE） chondrite C1 normalized patterns;（2） a neoblastic olivine and orthopyroxene assemblage;（3） the last assemblage associated with the formation of clinopyroxene and garnet marginal zones（Gar2）.Major and trace element compositions of olivine,orthopyroxene,clinopyroxene and garnet indicate that both the neoblast and clinopyroxene-Gar2 mineral assemblages were in equilibrium with a high Fe-Ti carbonate-silicate metasomatic agent.The nature of the metasomatic agent was estimated based on high field strength elements（HFSE） composition of olivine neoblasts,the garnet-clinopyroxene equilibrium condition and calculated by REE-composition of Gar2 and clinopyroxene.All these evidences indicate that the agent was a high temperature carbonate-silicate melt that is geochemically linked to the formation of the protokimberlite melt.

SHRIMP Age of Exotic Zircons in the Mengyin Kimberlite,Shandong,and Their Formation

Due to various courses of formation of zircons from kimbedites, different kinds of zircons can provide useful information about the mantle and the crystallization of kimberlites. We chose 9 typical ones out of 33 zircons from the Shengli- 1 kimberlite pipe in Mengyin County, Shandong Province to study their ages and formation by means of SHRIMP, CL, Raman spectroscopy, etc. The result shows that the ^207Pb/^206Pb ages of many zircons vary from 2567±13 Ma to 2636±42 Ma, which are close to the age of Archaean granitoid （2457.3±47 Ma） in the study area. The contents of U and Th in the samples are higher than those of zircons crystallized in kimbedite and vary from 89 to 398 ppm as well as from 10 to 283 ppm. Color zones are obvious in these samples under the CL. The inclusions are composed of feldspar, quartz, apatite, etc. The above results show that the zircon samples came from the crust of the earth, which means that the kimberlite magmas are contaminated by crustal substances. The position where a great deal of volatile escapes and even explodes during rapid rise of magmas is located at the boundary of the ancient basement and the Precambrian stratum.

Composition of the Diamond Indicator Minerals on the Mitchell Chart――Criteria of CLIPPIR Diamonds in Kimberlites and Conditions of their Mantle Crystallization

In the last decade,researchers have been particularly interested in IIa CLIPPIR type diamonds,which differ in composition and physical characteristics from diamonds of peridotite related"P"and eclogite related"E"generations.Moore(Moore,2009)sought them as mantle kimberlite related megacrysts,but light C isotopy and chemical features needs special explanation.

Petrology and Sr-Nd isotope systematics of the Ahobil kimberlite(Pipe-16)from the Wajrakarur field, Eastern Dharwar craton, southern India

Detailed mineralogical, bulk-rock geochemical and Sr-Nd isotopic data for the recently discovered Ahobil kimberlite(Pipe-16) from the Wajrakarur kimberlite field(WKF), Eastern Dharwar craton(EDC),southern India, are presented. Two generations of compositionally distinct olivine, Ti-poor phlogopite showing orangeitic evolutionary trends, spinel displaying magmatic trend-1, abundant perovskite, Tirich hydrogarnet, calcite and serpentine are the various mineral constituents. On the basis of(i) liquidus mineral composition,(ii) bulk-rock chemistry, and(iii) Sr-Nd isotopic composition, we show that Ahobil kimberlite shares several characteristic features of archetypal kimberlites than orangeites and lamproites. Geochemical modelling indicate Ahobil kimberlite magma derivation from small-degree melting of a carbonated peridotite source having higher Gd/Yb and lower La/Sm in contrast to those of orangeites from the Eastern Dharwar and Bastar cratons of Indian shield. The T_(Dm) Nd model age(～2.0 Ga) of the Ahobil kimberlite is(i) significantly older than those(1.5～1.3 Ga) reported for Wajrakarur and Narayanpet kimberlites of EDC,(ii) indistinguishable from those of the Mesoproterozoic EDC lamproites,and(iii) strikingly coincides with the timing of the amalgamation of the Columbia supercontinent. High bulk-rock Fe-Ti contents and wide variation in oxygen fugacity fO_2, as inferred from perovskite oxybarometry, suggest non-prospective nature of the Ahobil kimberlite for diamond.

Comparison of mantle lithosphere beneath early Triassic kimberlite fields in Siberian craton reconstructed from deep-seated xenocrysts

Mantle xenocrysts from early Triassic kimberlite pipes from Kharamai, Ary-Mastakh and Kuranakh fields in the Anabar shield of Siberia revealing similar compositional trends were studied to estimate the superplume influence on the subcratonic lithosphere mantle （SCLM）. Pressure-temperature （PT） reconstructions using monomineral thermobarometry for 5 phases show division of the SCLM beneath the Kharamai field into 6 units： pyroxenitic Fe-rich （1-2 GPa） and Mg-rich （2-3 GPa） layers; middle with two levels of Gar-Sp pyroxenites at - 3 and 4-5 GPa; Gar-dunite-harzburgites - 4.5-6.5 GPa subjected to llm-Px vein metasomatism; and a Mg-rich dunite lower part. In the Anabar shield （Ary-Mastakh, Dyuken and Kuranakh fields） mantle lithosphere is composed of three large units divided into two parts： upper part with amphiboles and phlogopite; two levels of pyroxenites and eclogites at 3 and 4 GPa, and a lower part composed of refertilized dunites. Diagrams showing P-Fe#Gar clusters for garnets and omphacites illustrate the differences between SCLM of these localities. Differences of Triassic SCLM from Devonian SCLM are in simple layering; abundance of Na-Cr-amphiboles and metasomatism in the upper SCLM part, thick pyroxenite-eclogite layer and lower part depletion, heated from SCLM base to 5.0 GPa. Kharamai mantle clinopyroxenes represent three geochemical types： （1） harzburgitic with inclined linear REE, HFSE troughs and elevated Th, U; （2） lherzolitic or pyroxenitic with round TRE patterns and decreasing incompatible elements; （3） eclogitic with Eu troughs, Pb peak and high LILE content. Calculated parental melts for garnets with humped REE patterns suggest dissolution of former Cpx and depression means Cpx and garnets extraction. Clinopyroxenes from Ary-Mastakh fields show less in- dined REE patterns with HMREE troughs and an increase of incompatible elements. Clinopyroxenes from Kuranakh field show flatter spoon-like REE patterns and peaks in Ba, U, Pb and St, similar to those in ophiolitic harzburgites. The PT diagrams for the mantle sections show high temperature gradients in the uppermost SCLM accompanied by an increase of P-Fe#OI upward and slightly reduced thickness of the mantle keel of the Siberian craton, resulting from the influence of the Permian-Triassic superplume, but with no signs of delamination.

Some Geochemical Characters of Kimberlites in Eastern North China Platform and Heterogeneity of Their Sources

Some geochemical characters of the kimberlites from different rock regions in North China platform are compared in this paper at first. The characters of the source regions are constrained then based on primary magmas compositions of typical regions chosen. The differences in metasomatic fluid activity in the lithosphere are discussed moreover. The diamondiferious kimberlitic sources, such as Fuxian and Mongying, were located at the fluid metasomatic mantle lithosphere or the boundary between the lithosphere and the asthenosphere(200-230 km), and enrich in LREE,Ti and isotope Sr but deplete in isotope Nd. Tieling is located nearby Paleozoic mobile belt, strong activity in fluids and shallower depth of magma source (～150 km), highest in w(LREE) and w (P), lower in w(Ti). But the shallowest depth of magma source (<130 km ) and weak activity in fluids are in Hebi and Shexian sources.

Regolith Geochemical Studies in Kimberlitic Terrain: A Case Study from Lattavaram Kimberlite Cluster, Eastern Dharwar Craton, Southern India

Utility of geochemistry in mineral exploration is known since more than half-a-century.In reconnaissance diamond exploration,regolith geochemistry is a well known tool worldwide and helps in distinguishing bedrock

Assortment of Deep Mantle Fluids and Their Products in Kimberlites from China

Based on studies of petrography, mineralogy and mineral chemistry, deep mantle fluids and their products in kimberlites and diamonds can be assorted into the ultradeep fluid-transmitted minerals with an oxygen-free feature, the deep fluid metasomatized-minerals characterized by enrichment in TiO2, K2O, BaO, REE and Fe3+, and the deep fluid-reformed minerals. The three types show a successive descent in fluid origin depth and metasomatism strength, and they have brought forth a series of corresponding metasomatic products.

The Sytykanskaya kimberlite pipe:Evidence from deep-seated xenoliths and xenocrysts for the evolution of the mantle beneath Alakit,Yakutia,Russia

Mantle xenoliths（>150） and concentrates from late autolithic breccia and porphyritic kimberlite from the Sytykanskaya pipe of the Alakit field（Yakutia） were analyzed by EPMA and LAM ICP methods.In P-TX-f（O2） diagrams minerals from xenoliths show widest variations,the trends P-Fe#-CaO,f（O2）for minerals from porphyric kimberlites are more stepped than for xenocrysts from breccia.Ilmenite PTX points mark moving for protokimberlites from the lithosphere base（7.5 GPa） to pyroxenite lens（5-3.5 GPa） accompanied by Cr increase by AFC and creation of two trends P-Fe#OI10-12%and13-15%.The Opx-Gar-based mantle geotherm in Alakit field is close to 35 mW/m2 at 65 GPa and 600 C near Moho was determined.The oxidation state for the megacrystalline ilmenites is lower for the metasomatic associations due to reduction of protokimberlites on peridotites than for uncontaminated varieties at the lithosphere base.Highly inclined linear REE patterns with deep HFSE troughs for the parental melts of clinopyroxene and garnet xenocrysts from breccia were influenced by differentiated protokimberlite.Melts for metasomatic xenoliths reveal less inclined slopes without deep troughs in spider diagrams.Garnets reveal S-shaped REE patterns.The clinopyroxenes from graphite bearing Cr-websterites show inclined and inflected in Gd spectrums with LREE variations due to AFC differentiation.Melts for garnets display less inclined patterns and Ba-Sr troughs but enrichment in Nb-Ta-U.The40Ar/39Ar ages for micas from the Alakit mantle xenoliths for disseminated phlogopites reveal Proterozoic（1154 Ma） age of metasomatism in early Rodinia mantle.Veined glimmerites with richterite- like amphiboles mark1015 Ma plume event in Rodinia mantle.The600-550 Ma stage manifests final Rodinia break-up.The last 385 Ma metasomatism is protokimberlite-related.