Browsing by Author "Howarth, Geoffrey"

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    Classification and petrogenesis of the Tongo dike-01 from the Tongo-Tongoma cluster, Sierra Leone: constraints from bulk rock geochemistry
    (2021) Mathafeng, Katleho; Howarth, Geoffrey
    The Man Craton in West Africa, like the Kaapvaal Craton in southern Africa, hosts diamondiferous kimberlites. However, West African kimberlites are commonly micaceous and unusual relative to archetypal South African kimberlites. Petrographically, they appear more similar to orangeites (aka Group II kimberlites), which represent a type of olivine-lamproite. A suite of 14 representative samples from the Cretaceous Tongo dike-01, Sierra Leone have been analysed for their bulk-rock major and trace elements as well as Sr-Nd-Pb isotope geochemistry. The primary objectives of this study are: 1) provide detailed petrographic observations of the dike, 2) classify the dike relative to kimberlites worldwide, 3) constrain the geochemical effects of secondary processes on bulk-rock analyses, 4) provide an estimate of the close-to-primary parent magma composition, and 5) constrain the petrogenesis of these diamondiferous rocks. The major element chemistry of the Tongo dike-01 reflects concentrations that are similar to both archetypal kimberlites and orangeites. Major elements such as SiO2 (~28.20 ± 3.90 wt. %) and CaO (~ 12.50 ± 1.80 wt. %) display archetypal kimberlite concentrations whereas Cr2O3 (~0.20 ± 0.01 wt. %) and P2O5 (~1.65 ± 0.60 wt. %) resemble those that define orangeites. The high abundance of phlogopite in this dike is illustrated by the high bulk-rock concentrations of K2O (~3.03 ± 0.50 wt. %) and Al2O3 (~4.08 ± 1.00 wt. %), similar to those of orangeites. Like the major element geochemistry, the trace element geochemistry of the Tongo dike-01 also displays mixed archetypal kimberlite and orangeite traits. Trace elements such as Nb (~365.0 ± 50.4 ppm) and Y (~18.77 ± 6.60 ppm) possess concentrations that are similar to kimberlites whereas Rb (~160.0 ± 14.8 ppm) and Th (~36.22 ± 5.30 ppm) resemble orangeites. Trace element ratios are no different, ratios such as Ce/Pb (16-82), Ba/Nb (1-8), La/Nb (0.6-1.2) and La/Sm (11-13) resemble those of kimberlites while La/Yb (280-520) are more similar to orangeites. However, unlike major and trace element geochemistry, the Sr-Nd-Pb isotope geochemistry of the Tongo dike-01 solely resembles those of archetypal kimberlites (87Sr/86Sr)i ~0,7039, (206Pb/204Pb)i ~18.88, (208Pb/204Pb)i ~40.02 and (143Nd/144Nd)i ~0.51253 ± 0.00001. Prior to interpretation of primary processes and parent magma composition estimates, the effects of secondary processes were first evaluated. These secondary processes include crustal contamination, ilmenite contamination and olivine entrainment/fractionation. Samples that had experienced these secondary processes were excluded and a suite of unaltered/least contaminated samples was compiled in order to constrain the close-to-primary magma composition of the Tongo dike-01 and interpret primary petrogenetic processes effecting the kimberlites. To determine a representative parent magma composition, a total of six out of the fourteen samples were excluded from consideration. The estimated close-to-primary magma composition for the Tongo dike-01 is suggested to be SiO2 ~28.20 ± 3.90 wt. %, Fe2O3 ~10.20 ± 1.70 wt. %, TiO2 ~1.70 ± 0.30 wt. %, Al2O3 ~4.08 ± 1.00 wt. %, K2O ~3.03 ± 0.50 wt. %, La ~363.12 ± 25.43 ppm, Gd ~15.87 ± 4.20 ppm, Yb ~1.020 ± 0.06 ppm, ( 87Sr/86Sr)i ~0.7039, ( 206Pb/204Pb)i ~18.88, ( 208Pb/204Pb)i ~40.02 and ( 143Nd/144Nd)i ~ 0.51253 ± 0.00001. Although the petrography and major element concentrations are similar to orangeites found in South Africa, the trace element and Sr-Nd-Pb isotope geochemistry of the Tongo dike-01 reflects a kimberlite composition. Thus, the Tongo dike-01 is more consistent with being classified as a relatively rare type of ‘mica-rich' kimberlite rather than orangeite. Kimberlites from around the world derive from the same asthenospheric mantle reservoir and their major element chemistry is controlled by the compositions/mineralogy of the lithospheric mantle assimilated during kimberlite evolution. The similarity of the trace element ratios and Sr-Nd-Pb isotopes of the Tongo dike-01 in this study relative to archetypal kimberlites worldwide strongly implies that the Tongo dike-01 derives from the same asthenospheric reservoir as these kimberlites, although mineralogically the Tongo dike-01 is different and has a different parent melt major element composition. This is interpreted to reflect the contribution of lithospheric mantle material that is mineralogically different to that assimilated by archetypal kimberlites during the ascent of the Tongo dike-01 parent magma through the sub-continental lithospheric mantle (SCLM). In the case of the Tongo dike-01, its primary melt is K2O-rich and must have assimilated more K2O-rich material in the SCLM. Such material is typically present as metasomatic products, e.g., Phlogopite-Ilmenite-Clinopyroxene (PIC) xenoliths observed in South Africa kimberlites. These xenoliths tend to possess abundant phlogopite. Thus, the main difference between the Tongo kimberlite and archetypal SA kimberlites is the fact that Tongo kimberlite assimilated more K2O-rich metasomatised material in the SCLM during its evolution.
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    Martian meteorites as windows into planetary volcanism: insights from olivine-phyric shergottite meteorites
    (2025) Peel, Chad; Howarth, Geoffrey
    Martian meteorites are the only samples currently available from the surface of Mars to study in terrestrial laboratories and can provide valuable insight into magmatic processes and the planet's geological evolution. With more meteorites being found every year, researchers no longer need to look only at single meteorites but rather groups, paired based on their crystallisation ages, ejection ages, and geochemistry. This allows for the development of models of volcanism using suites of meteorites, rather than relying solely on single meteorites. One group of shergottite meteorites, comprising approximately 20 samples with crystallisation ages from 2.4 to 0.35 Ga, share similar geochemical characteristics and ejection ages of 1.1 Ma, and are suggested to have originated from a common long-lived volcanic system. Thus, by studying these 1.1 Ma ejection paired meteorites, it is now possible to evaluate martian magma plumbing systems through time. In chapter 2, I present a comprehensive investigation of two 1.1 Ma ejection-paired olivine-phyric shergottites, Northwest Africa (NWA) 2046 and NWA 4925. I show that Mg-rich olivine megacrysts in both samples represent phenocrysts and evidence of early olivine fractionation in staging chambers prior to ascent to surface. Distinct patterns of terrestrial alteration, notably in NWA 4925, have been identified through Ca and K elemental mapping, manifesting in the preferential alteration of olivine megacryst cores and LREE enrichment of bulk-rock and pyroxene. Analysis of 87Sr/86Sr in maskelynite and low fO2 crystallisation conditions suggest a shared mantle source region with other 1.1 Ma ejection-paired samples, particularly the ~470 Ma DaG 476, SaU 005, and Yamato 980459, while pressure estimates using pyroxene Ti/Ai ratios, indicate common or multiple staging chambers near the base of the crust. In this chapter, I combine my data with literature data for other 1.1 Ma shergottites (e.g., DaG 476, SaU 005, and Yamato 980459) to present a model for volcanism at this site. One of the other major unanswered questions in the study of martian meteorites is the origin of the enriched geochemical reservoir on Mars, as either a distinct mantle source or crust. Olivine-phyric shergottites, the most primitive type of martian meteorite, are commonly interpreted to represent primary mantle derived melts, and can be categorised into three distinct geochemical groups, incompatible-trace element depleted, intermediate, and enriched, reflecting distinct source reservoirs. The primary focus of remaining chapters (3 and 4) of this dissertation is to track the evolution of REEs in these rocks from the start of crystallisation to the end. This was carried out using a newly developed laser ablation ICP-MS technique with enhanced sensitivity to analyse REEs in olivine as a proxy for the initial parent melt. The REEs of olivine-hosted melt inclusion glass and late-stage merrillite from the same samples were then measured for comparison against olivine. By comparing these, I can robustly constrain the REE evolution of shergottite parent melts and evaluate the possibility of crustal assimilation or open system processes during evolution. To do this, in chapter 3 I present the first full REE dataset for Mg-rich olivine in shergottites in a comprehensive suite of depleted, intermediate, and enriched olivine-phyric shergottites (11 samples) including: Dar Al Gani (DaG) 1037, NWA 2046, 4925, 6234, 10170, 1068, 1183, Dhofar (Dho) 019, Sayh al Uhaymir (SaU) 005, Tissint, and Larkman Nunatak (LAR) 12011. In chapter 4, I combine the olivine REE findings of chapter 3 with melt inclusion glass and merrillite data to fully evaluate the REE evolution of shergottite melts. In chapter 3, my analysis of early formed olivine megacryst trace element and ultra-trace element compositions in depleted shergottites indicates closed-system crystallisation behaviour, supporting interpretations that these meteorites represent partial melting of a LREE depleted mantle source. Olivine in the enriched shergottite LAR 12011 are LREE-depleted and identical to the REE pattens of olivine in depleted shergottites. This suggests open-system behaviour, potentially involving assimilation of xenocrystic LREE-depleted olivine or mixing with a LREE-enriched melt. Olivines in the enriched shergottite NWA 1183 are LREE enriched compared to NWA 1068 and LAR 06319 and points towards open system processes such as magma mixing and/or crustal assimilation. In chapter 4, I evaluate the use of olivine-hosted melt inclusion glass in constraining primary REE patterns for shergottites. My findings show that the REE patterns of melt inclusion glass parallel that of bulk-rock, which indicates that glass is useful in constraining REE contents of early melts trapped in olivine. The REE patterns for melt inclusion glass in the depleted shergottites also parallel REE patterns for Mg-rich olivine and later-crystallising merrillite, indicating closed-system behaviour during crystallisation and consistent with my findings of chapter 3. Intermediate shergottites NWA 6234 and NWA 10170 also exhibit closed-system behaviour, indicating partial melting from distinct mantle source regions. For LAR 12011, distinct LREE-depleted and LREE-enriched melt inclusion glass populations were observed in LREE-depleted olivine megacrysts previously analysed in chapter 3, with depleted glasses hosted in olivine megacryst core regions (Fo68 to Fo75) and LREE-enriched glasses in olivine core-mantle regions (Fo69 to Fo73). These findings suggest that olivine megacryst cores from LAR 12011 appear to have crystallised from a depleted melt rather than an enriched melt. Melt inclusion glass of NWA 1183 shows LREE enrichment attributed to assimilation of an enriched crustal component, akin to processes observed in NWA 7034, before any crystallisation had occurred.
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    Oxygen isotope composition of megacrysts from the Monastery kimberlite
    (2024) Van Blerk, Joshua; Howarth, Geoffrey; Harris Chris; Janney, Phil
    Kimberlite megacrysts are large (>1 cm diameter) crystals that are thought to have crystallized from sub lithospheric proto-kimberlite melts near the base of the subcontinental lithospheric mantle (SCLM) during complex melt-SCLM interactions. Thus, these megacrysts represent an excellent opportunity to constrain the effects of SCLM assimilation on the δ18O values of primary mantle-derived melts. Laser fluorination δ 18O values for a well-characterized suite of megacrysts from the Monastery kimberlite, South Africa, are presented to: (1) constrain the δ18O value of the mantle source and (2) evaluate the effects of melt-SCLM interactions on the δ18O value of mantle-derived magmas. The Monastery kimberlite megacryst assemblages are as follows (in order of crystallization): (1) gt + cpx + opx + Fe-poor ol; (2) gt + cpx + opx + Group 1 ilm (Cr-, Mg-poor); (3) Group 2 ilm (Cr-rich, Mg-poor) + phlog; (4) Group 2 ilm + phlog + zir; (5) Group 2 ilm + phlog + zir + Fe-rich ol; and (6) Group 3 ilm (Cr and Mg-rich) + calcic cpx. The δ18O values of the megacrysts from the initial assemblage are: δ18Ogt = 5.12 and 5.25‰ (n = 2); δ18Ocpx = 4.72 and 5.02‰ (n = 2); δ18Oopx = 5.20 and 5.55‰ (n = 2); δ18OFe-poor ol = 5.43- 5.84‰ (x̄ = 5.23‰, σ = 0.10, n = 10), all showing no correlation between δ18O values and major element compositions. This implies that these megacrysts were in equilibrium with a melt of mantle-like δ18O values. The Group 1 ilmenites have δ18O values expected for mantle ilmenites, ranging from 3.88-4.35‰ (x̄ = 4.10‰, σ = 0.15, n = 8) (also in equilibrium with a melt of mantle-like δ18O values). They show a weak positive correlation between the δ18O value and Cr#, and no correlation with Mg#. In contrast, the δ18O values of the megacrysts from assemblages three to five implies that they were in equilibrium with a melt of δ18O values below the expected mantle-like range: δ18OGroup 2 ilm = 2.74-4.46‰ (x̄ = 3.56‰, σ = 0.45, n = 11); δ18Ophlog = 4.25-5.73‰ (x̄ = 5.08‰, σ = 0.48, n = 8); δ18Ozir = 4.87-5.09‰ (x̄ = 4.98‰, σ = 0.08, n = 6); and δ18OFe rich ol = 4.53-4.94‰ (x̄ = 4.75‰, σ = 0.15, n = 5). The Group 2 ilmenites show no correlations between the δ 18O value and Mg# and Cr#. The Fe-rich olivines show positive correlations with Mg# and Ni. The phlogopites show no correlations with the major element compositions. The Group 3 ilmenites have δ18O values ranging from 2.93-4.05‰ (x̄ = 3.59‰, σ = 0.36, n = 7). These are below the δ18O values expected for mantle ilmenites, but are slightly higher than the Group 2 ilmenites. The Group 3 ilmenites show a positive correlation between the δ18O value and Mg# and no correlation of δ18O with Cr#. The δ18O values of primary mantle-derived magmas are ~5.7‰ (Eiler, 2001) unless recycled crust is present in the source or if the magma assimilates crustal material en route to the surface. The variations in the δ18O values throughout the megacryst suite suggest that the parent melt underwent open system evolution in the SCLM. It is proposed that the Monastery proto-kimberlite originated from a convecting mantle source with a mantle-like δ18O value of ~5.33‰, which experienced two stages of evolution involving fractional crystallization and assimilation/melt-wall rock interaction. The low δ18O values in the phlogopites, zircons, Fe-rich olivines, and especially the Group 2 ilmenites (as low as ~4.25‰) can be explained by the assimilation most likely of low-δ18O eclogite (first stage evolution). The increased Cr# in the melt marked by the Group 2 ilmenites suggests the assimilation of Cr-rich pyroxenite veins. The Group 3 ilmenites give increased equilibrium melt-δ18O values of up to ~5.56‰ and give increased Mg# relative to the Group 2 iii ilmenites, which may be explained by the assimilation of Mg-rich metasomatized peridotite (second stage evolution).
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    Petrology and geochemistry of the diamondiferous K-richteriteand leucite-bearing Kareevlei Kaapvaal lamproite
    (2023) Qashani, Zuko; Howarth, Geoffrey
    The Kareevlei diamond mine is the first mine on the evolved leucite-bearing Kaapvaal lamproite. These rock types have generally been believed to be non-diamondiferous or at least sub-economic and as a result, their petrogenesis has remained poorly constrained as the exploration programs focused mainly on the unevolved subvarieties of Kaapvaal lamproites, such as at the Finsch mine. To further assist with the petrogenesis of these uncommon diamondiferous rock types, 13 Kaapvaal lamproite samples of hypabyssal texture from the Kareevlei diamond mine have been analyzed for their petrography, mineral chemistry (phlogopite, Krichterite, and diopside), and bulk-rock major and trace elements as well as Sr–Nd isotope compositions. The Kareevlei Kaapvaal lamproites comprise completely altered olivine macrocrysts (3–12 vol.%) set in a groundmass of olivine microcrysts (3–19 vol.%), abundant phlogopite (32–58 vol.%), diopside (12–36 vol.%), pseudo-leucite (0–27 vol.%), K-richterite (0–25 vol.%), and interstitial material containing carbonate minerals. Two distinct mineralogical varieties are identified based on the presence/absence of leucite and K-richterite: (1) phlogopite-diopside lamproites and (1) leucite-richterite lamproites. Phlogopite laths in these lamproite varieties show two distinct core populations characterized by high-Cr2O3 (Cr2O3 = 0.89–1.97 wt.%) and lowCr2O3 concentrations (Cr2O3 = 0.04–0.68 wt.%), both mantled by TiO2 and FeO-rich rims. High Cr2O3 cores are interpreted as xenocrysts from phlogopite peridotite xenoliths, whereas the low Cr2O3 cores resemble MARID xenolith phlogopite. The phlogopite rims have compositions similar to typical Kaapvaal lamproites and represent direct crystallization by the parent magma. The Kareevlei leucite-richterite lamproites are characterized by raised bulk-concentrations of SiO2 (44.8 – 47.9 wt.%), Al2O3 (6.34–7.34 wt.%), and Na2O (0.78–1.99 wt.%), and lowered MgO (16.2–17.1 wt.%) concentrations compared to phlogopite-diopside lamproites (SiO2 = 40.8–42.9 wt.%; Al2O3 = 5.44–6.22 wt.%; Na2O = 0.42–0.74 wt.%, MgO = 20.7–23.0 wt.%). The two mineralogical varieties have distinct incompatible trace element concentrations, with the leucite-richterite samples being depleted in light REEs (LREE/Chondrite: La = 656–828; Ce = 518–597; Nd = 234–261) compared to the phlogopite-diopside samples (LREE/Chondrite: La = 1125–1391; Ce = 817–1029; Nd = 333–415). Additionally, these lamproite varieties exhibit clear separation in incompatible trace element ratios, with leucite-richterite lamproites having lower La/Yb = 101–143, Gd/Yb = 6.28–7.73, and La/Sm = 10.0–11.0, relative to phlogopite-diopside lamproites (La/Yb = 167–205; Gd/Yb = 8.13–9.55; La/Sm = 12.4–13.4). However, these mineralogical varieties have similar 87Sr/86Sri and 143Nd/144Ndi ratios with ranges of 0.7071–0.7073 and 0.5118–0.5119, respectively. The two distinct lamproite varieties identified as phlogopite-diopside and leucite-richterite lamproites in this study suggest relative evolution at Kareevlei, marked by the complete absence of K-richterite and leucite in the groundmass of phlogopite-diopside lamproites. The major element compositional trends of lamproites commonly reflect the primary mineralogy. In Kareevlei lamproites, these trends (e.g., MgO depletion with SiO2, Al2O3, and Na2O enrichment) appear to be controlled by relative mantle xenocryst accumulation rather than evolution through fractional crystallization as the incompatible trace elements and their ratios are not consistent with fractional crystallization control on Kareevlei magma evolution. The Sr-Nd isotopes suggest that both Kareevlei phlogopite-diopside and leucite-richterite lamproites are derived from an isotopically homogeneous mantle source within the sub-continental lithospheric mantle (SCLM). The higher incompatible trace element ratios (e.g., La/Yb, Gd/Yb, and La/Sm) in phlogopite-diopside lamproites are regarded as a consequence of derivation by lower degrees of partial melting. In contrast, the leucite-richterite lamproites with their low La/Yb, Gd/Yb, and La/Sm ratios are indicative of derivation by greater degrees of partial melting. It is concluded that the Kareevlei lamproite varieties are generated by variable degrees of partial melting of MARID-veined peridotite lithologies in the SCLM. While these lamproites varieties appear to be derived from an isotopically homogenous source, the variation in their groundmass mineralogical assemblages is a consequence of variable degrees of partial melting rather than evolution through fractional crystallization en route to the surface. This hypothesis can be tested in the future for other Kaapvaal lamproite clusters across the Kaapvaal craton to see if variable degrees of partial melting are the primary process responsible for the relative evolution observed.
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    The petrogenesis of Liberian diamondiferous rocks, Man Craton, West Africa
    (2022) Ndimande, Njabulo; Howarth, Geoffrey
    Kimberlites and lamproites are ultramafic igneous rocks believed to originate from the convective asthenosphere and sub-continental lithospheric mantle, respectively, however, the genetic link between these rock types is still a debate among researchers. Recently, it has been shown (e.g., in the Dharwar Craton, India) that both kimberlites and lamproites may be derived from the same asthenospheric mantle source. During their ascent to the surface, they assimilate differently metasomatized SCLM material. However, it is not clear if this process applies to all cratonic regions. The Man Craton, West Africa, is a host to diamondiferous rocks that share petrographic and geochemical characteristics with both kimberlites and lamproites, thus not easy to classify. The Camp Alpha (possibly Precambrian in age) and Neoproterozoic-aged Weasua clusters are the selected locations for this study. To further assist with the classification of peculiar West African diamondiferous rocks and evaluate their genetic link and origin, I provide detailed petrography, as well as phlogopite and spinel chemistry, bulk-rock geochemistry (for the Camp Alpha samples) and perovskite chemistry (for the Weasua samples). The Camp Alpha rocks contain abundant macrocrysts of olivine (that are completely altered) and ilmenite occurring in a groundmass that comprises spinel, phlogopite (the samples are phlogopite-poor), perovskite, calcite, serpentine, and rare apatite. Most importantly, there is no evidence of diopside in the Camp Alpha samples. The Camp Alpha phlogopite is enriched in Al2O3 but slightly depleted in FeO and TiO2 and the spinel exhibits a kimberlitic compositional evolution (i.e., trend 1). The bulk-rock trace element ratios Ba/Nb (0.91 - 9.55), La/Nb (0.12 - 1.22; mostly < 1.10) and Ce/Pb (6.77 - 99.2; mostly > 22), fall within the ranges defined by kimberlites. Additionally, primitive mantle normalised trace element patterns are similar to kimberlite patterns (e.g., Rb, K, Sr and P 2 show negative anomalies). As a result of these characteristics, the studied Camp Alpha rocks are classified as kimberlites. A close to parent melt composition of the Camp Alpha kimberlite is provided in this study, based on bulk rock geochemistry. The composition of the estimated melt is similar to that of kimberlite magmas and characterised by low K2O (of 0.80 wt.% relative to 3.63 ± 1.40 wt.% of orangeites for example; reflective of mica-poor nature). The Weasua rocks, in this study, are micaceous (phlogopite-rich) and contain primary groundmass diopside and calcite, which suggests that the studied Weasua rocks represent carbonate-rich olivine lamproites. From the inversion of trace element data for the perovskites using known partition coefficients, the composition of the melt in equilibrium with perovskite at the time of crystallisation is determined. The composition of this Weasua parent melt is similar to that of kimberlite magmas (i.e., similar primitive mantle-normalised trace element patterns, Ba/Nb, Ce/Pb and La/Nb ratios). Whereas the Camp Alpha and Weasua rocks are classified as kimberlite and lamproite, respectively, the trace element composition of the parent melt is similar to that of kimberlite magmas for both cases. This suggests a common asthenospheric magma source for the Camp Alpha kimberlite and Weasua lamproite. En route to the surface, these rock types assimilated differently metasomatized SCLM material (i.e., the Weasua lamproite magma assimilated mica-diopside-rich wall rock). The Camp Alpha kimberlite was shown to be approximately 800 Ma old, similar to the Weasua lamproite. Therefore, the Camp Alpha and Weasua magmas were interpreted to be broadly coeval based on the similarity in age and location, In addition to the Indian Dharwar Craton, the hypothesis that kimberlites and lamproites share a common convective asthenospheric magma source but assimilate differently metasomatized SCLM material en route to the surface is confirmed in the Man Craton, West Africa.
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    Volcanology and geochemistry of selected kimberlites from the Lulo kimberlite field, Angola
    (2025) Moldenhauer, Jena; Howarth, Geoffrey; Janney Philip
    Abstract The area under study is the Lulo Kimberlite Field in the province of Lunda Norte, Angola, which is located 630 km east of the capital, Luanda. This 3000 km2 concession is one of the world's most abundant alluvial diamond fields, producing high value Type IIa diamonds, as well as hosting a significant number of kimberlite pipes. Within Angola, there are hundreds of known kimberlite bodies of which, it is estimated, far fewer than 50% have been studied and fewer than 5% have economic diamond grades (Pereira et al., 2003). With ongoing exploitation of predominantly high-grade alluvial deposits, depletion of the diamond reserves demands continual and improved exploration of primary sources. Alluvial diamond mining within the Lulo Field has yielded large, high value diamonds along the Cacuilo River. These diamonds are anhedral in morphology and show sharp edges with little abrasive signs of travel, indicating that their primary kimberlite source is likely nearby. With more than 560 geophysical anomalies having been identified in the Lulo Field, 164 have been drilled, with 141 shown to be kimberlitic (Lucapa Diamond Company, 2024). This study aims to conduct a reconnaissance survey of volcaniclastic kimberlites within these pipes to classify eruptive styles, providing insights into the internal geology of pipes with implications for diamond grade bulk sampling. A total of 52 kimberlite targets were sampled, yielding 83 thin sectionsfor petrographic analysis and eight representative hypabyssal kimberlites for bulk rock geochemistry, through collaboration with Lucapa diamonds. Each one of the 83 thin sections were described using a petrographic microscope and classified following the scheme of Scott Smith et al. (2018) and Webb & Hetman (2021), with 22 chosen as representative samples. Petrographic analyses of the thin sections allowed for the classification of the kimberlites, at the most primary form of subdivision, as either coherent or magmaclastic (Webb & Hetman, 2021). Within the magmaclastic subsection, pyroclastic kimberlites are classified as Fort à la Corne-type pyroclastic kimberlites (FPK) and abundant resedimented volcaniclastic kimberlites (RVK) are also observed interbedded with the FPKs. The classification of the Lulo kimberlites as FPKs is based on their clast supported texture, olivine-dominated magmaclasts, and ultra-fine serpentine and carbonate cement. The magmaclasts display varied morphologies and include cored and uncored varieties, with a wide range of olivine macrocrysts abundances and low proportion of crustal xenoliths further supporting the classification. Furthermore, the presence of RVKs is confirmed due to the predominant clastic texture, abundant quartz and commonly seen broken grains. The identification of kimberlites as predominantly FPK and RVK indicates an explosive eruptive style that led to pipe excavation and post-eruptive reworking. Comparisons with other kimberlite fields, such as the Voorspoed mine in South Africa and the Lac de Gras kimberlite field in Canada, reveals similarities in internal pipe geology to those in the Lulo field and thus are comparable to kimberlite pipes within Diavik and Ekati mines alike. Thus, the Lulo field kimberlites pipes are classified as Class 3 pipes following the scheme of Skinner and Marsh (2004) or Lac de Gras type following the scheme of Scott Smith (2008). Geochemical analysis shows the Lulo kimberlites share characteristics with South African Group I kimberlites, known for their diamondiferous nature. However, certain deviations, such as depleted MgO and enriched Al₂O₃ and Nb concentrations, suggest crustal contamination that is further supported by a contamination index > 1.0 for all bulk-rock samples. Exploration initiatives, including drilling and bulk sampling, are directed at determining diamond grade and identifying the primary source of the high-value, Type IIa alluvial deposits. Kimberlite pipes within the Lulo field, classified as Class 3 pipes, consist of multiple volcaniclastic units (FPK and RVK) within individual pipes, indicative of considerable variability in diamond content. This heterogeneity underscores the importance of detailed stratigraphic analysis to enhance the accuracy of grade estimation. Olivine macrocrysts, which serve as key indicators of diamond-bearing potential, range from 25 to 53 vol.% in FPKs, reflecting mantle-derived material with varying degrees of sorting (ranging from poorly to well sorted) across different pipes. As a comprehensive assessment across the full length of boreholes has not yet been conducted, olivine macrocryst abundance and sorting remains speculative. A thorough understanding of internal pipe geology and olivine distribution is essential for refining diamond exploration and sampling strategies. Moreover, for the RVKs, the proportion of externally derived material may dilute grades and should therefore be considered. Due to the favourable geological setting of the Lulo Mine and its geological and geochemical similarity to other diamond-rich kimberlite occurrences, it can be inferred that Lulo kimberlites hold significant potential for high-grade diamond deposits. However, current bulk sampling for diamond grades is primarily conducted at the surface for each pipe. Accurate diamond grade estimation requires understanding the internal geological variation within a kimberlite, as surface sampling alone may not represent the true diamond potential of deeper units. Therefore, understanding the internal geology of each pipe is essential, as it significantly influences diamond grades during bulk sampling campaigns aimed at discovering high-value stones. This study highlights the importance of integrating detailed petrographic, geochemical, and geological analyses to fully understand the factors controlling diamond grade, providing valuable insight for the future exploration of Angola's primary diamond sources.