2.9 km of Bushveld Complex stratigraphy – BV-1 core log

At one time I was attached to a research project that studied the drill core from a deep stratigraphic borehole drilled into the layered mafic/ultramafic rocks of the northern Bushveld Complex. Drilling to a depth of 2945.5 m was carried out over a period of ten months, and completed in late 1991. The core recovered from the drilling phase of the project represents a continuous record of magmatic stratigraphy, starting from the roof granites, through the Upper Zone, and ending about midway into the Main Zone. The log of this core is given below…

The Bellevue (BV-1) borehole core log: 2.9 km of Bushveld Complex stratigraphy (northern lobe)

Roof

00.00 Drillhole collar.

00.88 Granite, fine-grained, porphyritic Klipkloof-type. Porphyritic texture caused by both quartz and K-feldspar crystals.

83.00 Granite, coarse-grained.

83.55 Granite, fine-grained, porphyritic.

Roof – Upper Zone Contact

Rig used to drill the deep stratigraphic borehole BV-1 in the northern Bushveld Complex, located in South Africa.

Rig used to drill the deep stratigraphic borehole BV-1 in the northern Bushveld Complex, located in South Africa.

83.65 Magnetite diorite, sharp contact (42° angle) with granite.

85.12 Granite, coarse-grained, similar to that at 83.00 m, with fine-grained margins at top (approximately 12 cm thick) and at the bottom contact (approximately 8 cm thick).

86.35 Olivine-magnetite diorite, 3 cm on contact subjected to K-metasomatism. Contact has an approximately 35° dip.

93.80 Granite, extremely variable texture (approximately 20° contact). Has a coarse granophyric texture in places, also fine-grained with miarolitic cavities, fluorspar-bearing. Solid core, but some shearing at lower contact.

96.20 Olivine-magnetite diorite. Metasomatically altered to K-feldspar bearing dioritic rock for approximately 10-12 cm from contact. The diorite is homogeneous with 20% olivine and 50% magnetite. Blotchy appearance of the rock caused by poikilitic clinopyroxene.

100 m

111.35 Olivine-magnetite diorite.

112.50 Mafic rock, highly contaminated, consisting primarily of feldspar, quartz and hornblende, with irregularly shaped fragments of fine-grained quartzo-feldspathic xenoliths, K-feldspar rich in places. Biotite present throughout.

116.50 Feldspathic quartzite, highly metamorphosed, distinctly cross-bedded.

141.10 Olivine-magnetite diorite, steep-angled (70°) contact. The diorite contains irregularly shaped fine-grained xenoliths, unevenly scattered throughout. Thin, steeply dipping (65°) granitic veins at 147.80-148.10 m and a 15 cm thick vein at 154 cm. From 160.50 m the diorite also contains irregularly shaped pegmatitic patches of green (altered) plagioclase, K-feldspar and amphibole.

161.97 Post-Bushveld dolerite, fine-grained sharp contact, chilled margin. Dolerite becomes gradually coarse-grained over 3 m to a medium-grained rock. Small magnetite grains (specks) throughout. Large amphibole needles at 175 m. The texture varies from equigranular to blotchy between 199.5 m and 215 m. Lower contact also chilled (and at a 15° angle to core axis).

200 m

234.14 Magnetite-olivine diorite (ferrodiorite), with considerable magnetite. Coarse-grained from 236.1 m to 236.63 m. Thin (approximately 4 cm thick) banded xenoliths of metasediments (?) at 239 m and at 240.4 m. K-feldspar bearing, coarse-grained, pegmatitic patches, olivine free, at 241.64-241.82 m, at 244.15-244.65 m, and at 244.95-244.50 m. From the later interval, the ferrodiorite contains numerous fine-grained and plagioclase-rich lenticular inclusions orientated approximately perpendicular to the core axis. Igneous layering seems, at the most, to be 10°.

256.70 Pegmatite, plagioclase-rich, with amphibole, K-feldspar and quartz.

257.20 Olivine-magnetite diorite (ferrodiorite). A thin, 5 cm thick dolerite intrusion at 259 m. Core broken at 260.2 m.

262.30 Dolerite.

267.76 Diorite, altered, with angular calc-silicate (?) xenoliths.

269.77 Magnetite diorite, with abundant pyrrhotite and magnetite.

270.05 Xenolith, fractured and sheared.

270.40 Olivine-magnetite diorite, altered, with plagioclase-rich patches.

272.21 Calc-silicate xenolith. 2 cm thick sulfide veins (?) at top contact. Textural features of xenolith are variable and the coarse-grained sections may represent highly contaminated gabbroic rocks. Common within the xenolith are irregular and often coarse-grained granitic veins (sweats?), with rheomorphic features at 275 m. High sulfide concentrations are especially noticeable near the upper and lower contacts, e.g., at 276.0 m, at 277.5 m, and at 285.0 m. Two steeply dipping granitic dikes, 30 cm and 20 cm thick respectively, crosscut the xenolith at steep angles (75°).

300 m

304.65 Magnetite-rich rock, sharp contact, in places massive magnetite. 15 cm xenolith at 305 m.

305.48 Magnetite diorite, with olivine (?). Core is very broken and oil stained. Appears more mafic from top to 307 m.

320.15 Pegmatite, plagioclase-rich.

320.65 Magnetite diorite, with no or very little olivine.

322.50 Magnetite diorite, noted for textural change to a fine-grained texture. Magnetite grains give the rock a fine spotted appearance.

324.38 Norite, extremely fine-grained, xenolith (?).

326.22 Magnetite diorite, fine-grained, with gradual transition into…

327.50 Plagioclase-magnetite cumulate, with interstitial clinopyroxene, resulting in a mottled appearance. Massive sulfide (pyrrhotite and chalcopyrite), 5 cm thick, with some magnetite at 328.70 m.

329.10 Magnetite gabbro, fine-grained. Gradual increase of modal plagioclase lower in the interval.

333.85 Pegmatitic rock, sharp contact, coarse grained, plagioclase-rich. Rock contains interstitial K-feldspar and hornblende relative to plagioclase.

335.54 Gabbroic rock.

336.40 Pegmatitic rock, coarse-grained, with high proportion of amphibole.

340.46 Gabbro.

341.65 Pegmatite, plagioclase-rich.

342.85 Magnetite gabbro, with some coarse-grained patches starting from 348.50 m.

349.55 Granite, fine-grained.

350.80 Magnetite gabbro.

351.50 Magnetite gabbro, noted for irregularly shaped, lenticular magnetite enrichments (with sulfides).

351.90 Mottled anorthosite.

353.20 Magnetite-olivine gabbro.

358.30 Granite, porphyritic, green, epidotized.

370.00 Granite, brick red, equigranular, with chloritized mafic minerals. Appears granophyric.

400 m

414.45 Mottled anorthosite, with more magnetite and pyroxene in the lower half of the interval.

415.86 Magnetite gabbro, pyroxene-rich, fine-grained.

416.45 Anorthosite.

418.10 Olivine-magnetite gabbro.

418.20 Granitic dike.

418.50 Olivine-magnetite gabbro. Homogeneous, but with slight variations in the modal proportions of olivine, plagioclase, magnetite, and clinopyroxene. 20 cm thick zone of olivine and magnetite enrichment at 473.40 m.

496.25 Granitic vein.

496.65 Olivine-magnetite gabbro. Very olivine-rich in places.

500 m

519.62 Granite, containing quartz, feldspar, and altered mafic minerals.

525.40 Olivine-magnetite gabbro. Fine-grained gabbroic inclusion (?) at 534.20-534.30 m. Coarse-grained and olivine-rich at 535.20-535.90 m. A 20 cm thick granitic vein at 535.70 – 535.90 m.

536.00 Olivine-magnetite gabbro, noted for apparent decrease in modal olivine. Textures and modal proportions vary up to a seemingly “chewed-up” xenolith at 541.60-541.75 m.

541.75 Olivine-magnetite gabbro.

548.65 Gabbroic rock, fine-grained.

549.12 Olivine-magnetite gabbro, fine-grained from 556.50-556.90 m. An increase in grain size and modal amount of plagioclase at approximately 558.0 m. Olivine still conspicuous.

566.90 Olivine-magnetite gabbro, with possible apatite (?). Fine-grained with little plagioclase, although modal plagioclase increases lower in interval. Fine-grained nature continues to…

568.30 Plagioclase-olivine gabbro, coarse-grained. A fine-grained and plagioclase-poor patch at 571.30-571.50 m.

573.00 Olivine-magnetite-plagioclase-clinopyroxene cumulate, fine-grained. Broken core at 575.0-575.30 m.

577.15 Granitic vein.

581.00 Olivine-magnetite-plagioclase-clinopyroxene rock, with variable textures. Banded layering is approximately 15°.

590.75 UPPERMOST MAGNETITE LAYER (Q), massive magnetite with plagioclase-rich intervals.

598.46 (Core loss to a depth of 600.86 m, at change to a smaller diameter rod – NX).

600 m
601.20 UPPERMOST MAGNETITE LAYER (Q), with increase in silicate mineral content.

603.78 Magnetite gabbro, olivine absent.

605.40 Plagioclase-rich rock, anorthositic.

606.50 Anorthositic footwall of the magnetite layer. Texture analogous to a plagioclase pegmatite.

608.15 Leucogabbro. Irregularly texture, caused by varying amounts of mafic minerals.

611.00 MAGNETITE LAYER (P), very sulfide-rich in lower 10 cm.

611.60 Magnetite anorthosite, magnetite-plagioclase cumulate.

613.00 Magnetite gabbro, with magnetite-rich intervals at 617.0-617.50 m and at 618.10-618.23 m.

618.23 Magnetite gabbro, with 1 cm sulfide enrichment at 621.5 m.

623.50 Magnetite-olivine gabbro, with a thin interval of magnetite enrichment at 625.40-625.45 m.

625.45 Magnetite gabbro, with possible olivine (?). White milky plagioclase at 628 m suggests pervasive alteration of the rock. Approximately 8 cm thick intervals of magnetite enrichment at 626.50 m and at 627.20 m are accompanied by olivine enrichment.

635.10 Magnetite gabbro, noted for change to a fine-grained texture.

644.18 MAGNETITE LAYER (O), with silicate-rich patches and disseminated sulfides.

644.45 Magnetite gabbro, somewhat coarser grained and more plagioclase-rich than the overlying magnetite layer. Magnetite enriched at 644.72-644.78 m.

648.05 MAGNETITE LAYER (N), massive.

648.24 Magnetite gabbro, plagioclase-rich (mottled), with laminar plagioclase. Disseminated sulfides directly below the overlying magnetite layer. Gradual increase in pyroxene to…

652.60 Magnetite gabbro, with possible olivine(?).

655.15 Magnetite gabbro, with a mottled texture.

657.05 Magnetite-olivine rock, with possible orthopyroxene (?), fine-grained.

657.53 Magnetite gabbro.

657.95 Magnetite-olivine rock, with possible orthopyroxene (?), fine-grained.

658.10 Magnetite-olivine gabbro, with small amounts of disseminated sulfides. Intervals of pegmatoidal texture at 687.75-683.00 m and at 683.30-683.40 m. Xenolith at 685.18-685.50 m. 8 cm pyroxenite with small round sulfide grains (droplets?) at 687.30 m. Fine grained xenolith (?) at 691.40 m (10 cm thick) and at 699.65-699.95 m. Also 2 cm at 723.50 m. Steeply dipping pegmatite vein (3 cm thick, zoned) at 724.0 m. Darkening of rock at 737.40-737.80 m along a fracture zone. Aphanitic vein at 765.05-765.65 m, steeply dipping (45°). Granitic pegmatite at 778.10-779.0, and at 780.85-781.5 m. Core broken, badly at 787.0 m. Granitic pegmatite at 787.70-789.0 m.

700 m

792.40 Granitic intrusion, with intrusion breccia.

795.00 Magnetite gabbro, with no apparent olivine.

800 m

800.50 Olivine-magnetite gabbro, fairly fine grained, possibly apatite-rich.

803.50 Broken and sheared core.

804.70 Magnetite gabbro, with interstitial sulfides.

828.50 Magnetite gabbro, noted for gradual enrichment of magnetite.

829.00 Gabbro, magnetite-rich.

829.70 Magnetite gabbro.

830.30 Gabbro, magnetite-rich.

830.75 MAGNETITE LAYER (M).

830.82 Magnetite gabbro, sulfide poor. Magnetite-rich intervals at 837.50-837.55 m, at 841.90-842.00 m, and at 844.68-844.85 m.

849.20 Gradation over 20 cm into…

849.40 MAGNETITE LAYER (L).

850.10 Gradation over 50 cm into…

850.60 Magnetite leucogabbro, grading into…

854.00 Magnetite gabbro.

859.70 Mottled anorthosite.

860.30 Magnetite leucogabbro, with leucocratic patches distributed irregularly throughout the rock. Patches increase in size lower in the interval from approximately 874 m.

881.30 Magnetite leucogabbro, equigranular, with disseminated sulfides. Prominent leucocratic intervals at 883.10-883.50 m. Fine-grained intervals at 885.27-885.38 m. Leucocratic patches at 891.40-891.90 m and at 893.80-893.90 m.

898.10 Magnetite gabbro.

899.90 Anorthosite, with blotchy texture.

900 m
901.26 MAGNETITE LAYER (K), massive.

901.40 Magnetite leucogabbro, with some coarse-grained patches and some disseminated sulfides.

902.89 MAGNETITE LAYER (J).

903.07 Anorthosite.

903.27 Magnetite gabbro, gradational into…

908.00 Magnetite leucogabbro. Significant magnetite concentrations at 913.32-913.39 m, at 918.40 m, 918.95 m, 919.33 m, 919.46 m, and 919.74 m.

920.10 Anorthosite, with disseminated sulfides.

921.00 Magnetite leucogabbro.

925.80 Magnetite gabbro.

928.00 Magnetite leucogabbro.

928.60 Anorthosite, with gradual magnetite increase lower in interval to…

929.90 MAGNETITE LAYER (I).

930.40 Plagioclase magnetitite.

930.84 Magnetite anorthosite, with distinct, small cumulus magnetite grains and some disseminated sulfides.

932.00 Magnetite gabbro. Igneous lamination approximately 15° to core axis.

955.70 Gabbro, coarse-grained, plagioclase-enriched.

957.30 Magnetite gabbro, with magnetite enrichments (plagioclase magnetitite) at 958.96-959.15 m, and at 960.20-960.40 m.

963.20 Magnetite anorthosite (or magnetite leucogabbro), approximately 40-50 cm core loss at 965.0 m, gradational lower in interval into…

966.00 Plagioclase magnetite rock, with magnetite enrichments at 966.40-966.50 m.

966.90 Magnetite leucogabbro.

967.90 Anorthosite.

972.50 Magnetite leucogabbro.

977.65 Magnetite leucogabbro, noted for gradual increase in magnetite.

977.90 Plagioclase magnetite.

978.00 Magnetite leucogabbro.

978.30 Anorthosite. Broken core at 978.40 m.

979.40 Magnetite leucogabbro, anorthositic, 2 cm thick granitic vein at 979.70 m.

989.30 Plagioclase magnetite, with approximately 50% magnetite.

989.85 Magnetite gabbronorite, distinct orthopyroxene texture, becomes somewhat more leucocratic at 1000.50 m, gradational into…

1000 m
1002.15 MAGNETITE LAYER (H).

1002.44 Pyroxenite pegmatoid, with sulfides near contact with overlying magnetite layer.

1002.86 Mottled anorthosite, coarse-grained with 1 cm long plagioclase crystals.

1004.10 Magnetite gabbronorite. Pegmatite veins at 1004.80-1004.90 m, and at 1008.20-1008.55 m, both steeply dipping.

1021.90 Magnetite leucogabbro, with variable plagioclase and magnetite concentrations. Interstitial clinopyroxene.

1027.60 Plagioclase-rich leucogabbro, with disseminated sulfides.

1031.50 Magnetite leucogabbro, notable plagioclase enrichment at 1043 m. Gradational into…

1046.50 Anorthosite, mottled in places.

1048.87 MAGNETITE LAYER (G), sulfide-bearing.

1048.92 Magnetite gabbronorite. Steeply dipping pegmatite vein at 1053.50 m. Gradational into…

1068.00 Magnetite leucogabbro.

1070.10 Mottled anorthosite, with disseminated sulfide specks.

1071.10 Magnetite leucogabbro.

1075.50 Mottled anorthosite. Granitic vein at 1084.50-1084.60 m.

1085.30 Magnetite leucogabbro. Gradational into…

1088.00 Mottled anorthosite. Gradational into…

1100 m

1117.00 Magnetite leucogabbro.

1123.30 Anorthosite.

1137.00 Magnetite leucogabbro.

1138.60 Mottled anorthosite.

1143.30 Magnetite leucogabbro.

1147.50 Mottled anorthosite.

1157.50 Magnetite leucogabbro, with interstitial clinopyroxene.

1163.30 Mottled anorthosite.

1174.54 Magnetite gabbro.

1175.55 Magnetite leucogabbro, anorthositic.

1180.60 Magnetite gabbronorite. Interval of badly broken core at 1185.50-1187.50 m. Brecciated between 1193.10-1193.50 m. Pegmatite at high angle to core axis, 5 cm at 1194 m and at 1196.90 m. Intervals of notable magnetite enrichment at 1201.20-1201.40 m, and at 1201.95-1202.0 m. Shear, at angle to core axis, at 1207.50 m. Granite pegmatite at 1209.25-1209.55 m. Sheared at 1210.10 m and at 1210.90 m. Steeply dipping pegmatite vein at 1283.20 m. Interval of broken core at 1299.60-1301.20 m.

View south with part of the Bushveld Complex roof complex seen on the horizon.

View south with part of the Bushveld Complex roof complex seen on the horizon.

1200 m

1200.00 Magnetite gabbronorite.

1300 m

1300.00 Magnetite gabbronorite, leucocratic.

1305.00 Magnetite-rich gabbronorite, with disseminated sulfides.

1306.72 Magnetite gabbronorite, with varying proportions of plagioclase, magnetite, and pyroxenes.

1315.00 Gabbronorite, magnetite enriched.

1315.62 Anorthosite.

1315.88 Magnetite gabbronorite.

1316.05 Magnetite anorthosite, sulfide enriched at lower contact.

1316.52 Magnetite gabbronorite.

1317.00 Magnetite leucogabbronorite.

1320.00 Magnetite gabbronorite.

1323.10 Anorthosite, coarse-grained.

1323.50 Magnetite-rich gabbronorite, disseminated sulfides at upper contact. Variable modal proportions, becoming somewhat fine-grained.

1325.80 Magnetite gabbronorite, fine-grained.

1327.78 Magnetite leucogabbronorite, more magnetite-rich towards lower contact.

1328.00 Magnetite gabbronorite.

1328.50 Anorthosite.

1328.80 Magnetite leucogabbronorite, gradational into…

1333.80 Gabbronorite, magnetite-rich, sulfide enriched in lower half of interval.

1334.05 MAGNETITE LAYER (F).

1334.27 Plagioclase magnetitite.

1334.36 Anorthosite, with 2 cm thick magnetite layer at 1334.46 m, sulfide enriched.

1334.55 MAGNETITE LAYER (E).

1334.60 Plagioclase magnetitite.

1334.72 Magnetite anorthosite, sulfide enriched down to 1335.50 m. Intervals of magnetite enrichment at 1338.28-1338.47 m, at 1338.85-1338.87 m, and at 1339.03-1339.20 m.

1339.20 Magnetite gabbronorite, becoming gradually more melacratic and coarse-grained further down in interval.

1345.50 Gabbronorite, somewhat coarse-grained, with abundant magnetite.

1347.40 Magnetite gabbronorite.

1349.30 Leucogabbronorite, magnetite-rich, decrease in magnetite further down in the interval. Gradational into…

1352.50 Gabbronorite, magnetite-poor, magnetite is interstitial.

1355.33 Mottled anorthosite, mottles of magnetite and pyroxene.

1362.70 Magnetite leucogabbronorite, with relatively abundant disseminated sulfides.

1374.34 Anorthosite, with magnetite-rich segregations, sulfide enriched. Green epidotized and potassic altered plagioclase (?).

1374.75 Magnetite gabbronorite.

1377.90 Magnetite leucogabbronorite, coarse-grained.

1378.30 Leucogabbronorite, magnetite-rich.

1379.20 Magnetite-plagioclase cumulate.

1379.58 MAGNETITE LAYER (D).

1379.65 Magnetite-plagioclase cumulate.

1380.05 Mottled anorthosite, with magnetite mottles, disseminated sulfides especially noticeable in lower half of interval.

1382.65 Magnetite leucogabbronorite. (Magnetite anorthosite?)

1387.30 Magnetite-rich interval.

1389.00 Magnetite-plagioclase rock, with 30-35% magnetite.

1390.35 Anorthosite.

1390.85 Magnetite anorthosite.

1396.10 Magnetite-plagioclase rock.

1396.90 MAGNETITE LAYER (C), disseminated at top and bottom. 15 cm of massive magnetitite.

1397.25 Magnetite gabbronorite.

1397.85 Magnetite-plagioclase rock, with some pyroxene.

1399.44 Magnetite gabbronorite.

1400 m

1400.06 Plagioclase-rich magnetitite.

1400.30 Plagioclase magnetite rock.

1401.30 Magnetite gabbronorite.

1401.60 Plagioclase magnetite rock.

1402.05 Magnetite gabbronorite.

1402.60 Magnetite anorthosite, 10-15% magnetite.

1402.90 MAGNETITE LAYER (B).

1403.30 Magnetite anorthosite.

1403.80 Magnetite plagioclase rock, 30-40% magnetite, disseminated sulfides at 1404.0 m.

1405.40 Magnetite anorthosite.

1405.80 Magnetite plagioclase rock, 50% magnetite. Magnetite poor interval at 1406.45-1406.65 m. From 1407.15 m, strongly varying plagioclase-magnetite proportions.

1408.47 Anorthosite, mottled.

1408.63 Anorthosite, gradual increase in pyroxene downwards in interval.

1410.20 Gabbronorite, magnetite poor.

1411.35 Mottled anorthosite, homogeneous. Large mottles of magnetite and pyroxene.

1422.42 Gabbronorite.

1424.38 Gabbronorite, with very little magnetite. Magnetite is intercumulus.

1444.20 Anorthosite, with few large mottles. Occasional magnetite in the mottles.

1464.00 Leucogabbronorite.

1465.00 Mottled anorthosite.

1468.20 Leucogabbronorite.

1471.00 Mottled anorthosite.

1477.00 Gabbronorite, very coarse-grained. Disseminated sulfides.

1481.00 Leucogabbronorite, gradational upper contact, small amounts of magnetite present.

1483.00 Gabbronorite, coarse-grained, accessory magnetite. sulfide grains (specks) present throughout.

1500 m

1505.50 Leucogabbronorite, coarse-grained.

1505.87 Granite pegmatite, with granophyric texture. High angle intrusive contacts.

1507.95 Mottled anorthosite. Small magnetite mottles present. Pyroxene mottles very large, up to 10 cm in diameter. Magnetite constitutes only a small portion of the pyroxene mottles. Some sulfide present.

1520.08 Leuconorite, with abundant disseminated sulfides. 0.5 cm magnetite stringer at 1520.12 m.

1520.53 Magnetite leuconorite. sulfides abundant down to 1520.71 m. Interstitial pyroxene decreases at 1522.30 m.

1523.45 Magnetite-plagioclase rock, sharp contact. Estimated mode of 30% magnetite and 60-70% plagioclase. Disseminated sulfides.

1527.90 Magnetite-plagioclase rock, 50% magnetite.

1528.46 Magnetite-plagioclase rock, 20-30% magnetite.

1529.40 Magnetite-plagioclase rock, 40-50% magnetite.

1529.85 Magnetite-plagioclase rock, 20-30% magnetite. Subordinate mafic silicates minerals.

1534.05 Magnetite gabbronorite. Very pyroxene-rich.

1543.65 Magnetite gabbronorite, increase in plagioclase, changeover to…

1555.00 Magnetite leucogabbronorite.

1559.80 Magnetite gabbronorite.

1561.00 Magnetite gabbronorite, increase in magnetite.

1561.35 Magnetite gabbronorite, gradational into…

1561.50 LOWERMOST MAGNETITE LAYER (A), massive.

1561.80 Anorthosite.

1561.95 Magnetite gabbronorite, with magnetite-enriched interval at 1571.15-1571.40 m.

1573.80 Anorthosite.

1573.85 Magnetite leucogabbronorite, with blotchy irregularly shaped magnetite segregations.

Upper Zone – Main Zone Contact

1575.80 Leucogabbronorite, with very little magnetite. Steeply dipping granite pegmatite vein at 1577.55 m. Gradational contact into…

1578.00 Gabbronorite, 5 cm thick granite pegmatite vein at 1579.15 m.

1581.75 Granite, white.

1585.88 Gabbronorite, poor in magnetite. Pegmatoidal interval at 1586.47-1586.60 m. Gabbronorite displays perfect igneous lamination at approximately 10° to core axis. 10 cm anorthosite at 1607.20 m. Characteristic blue internal labradorite reflections.

1600 m

1618.20 Pyroxenite.

1618.32 Anorthosite.

1618.55 Gabbronorite. No magnetite present.

1639.28 Anorthosite.

1639.00 Gabbronorite.

1641.82 Anorthosite, with gabbronorite from 1642.0-1642.30 m.

1644.01 Gabbronorite.

1646.75 Melagabbronorite, with thin gabbronorite intercalations. Relatively fine-grained.

1648.10 Gabbronorite. Pyroxene-rich interval at 1648.50-1648.68 m.

1657.50 Melagabbronorite.

1658.00 Feldspathic websterite, poikilitic inverted pigeonite, with lenses of anorthosite 1 cm thick.

1660.60 Gabbronorite, a few sulfide grains (specks) at 1708.60 m.

1700 m

1745.80 Pegmatoid, with minor magnetite and sulfides.

1745.26 Anorthosite, with sulfides at upper contact, gradational into…

1745.80 Leucogabbronorite. Fractures perpendicular to core axis from 1748.50 m to 1751.0 m.

1750.00 Spotted anorthosite. Steeply dipping granite pegmatite vein 15 cm thick at 1752.20 m, also from 1756.50 m to 1758 m, 1764.20-1764.30 m, and 1769.20-1770 m.

1774.00 Granophyric textured veins, 2-3 cm thick.

1775.50 Gabbronorite, strongly saussuritized.

1778.25 Granite, steeply dipping vein.

1779.35 Gabbronorite.

1783.75 Granite, steeply dipping contact, displacement along granitic vein (?).

1784.35 Melagabbronorite.

1794.35 Granitic vein, steeply dipping.

1797.95 Gabbronorite, core is sheared and fractured at 1801.0-1803.50 m.

1800 m

1807.00 Granitic vein.

1807.30 Gabbronorite.

1808.85 Metasediment xenolith (?), calc-silicate, serpentine in places, sulfides.

1810.15 Gabbronorite.

1815.36 Granite.

1826.70 Gabbronorite, anorthosite layer and sulfides at 1878.05-1878.15 m.

1900 m

1919.50 Leucogabbronorite, gradational contact, with varying proportions of pyroxene.

1926.00 Gabbronorite.

1927.85 Leucogabbronorite, variable anorthosite-rich intervals.

1933.08 Mottled anorthosite.

1935.70 Leucogabbronorite, gradational intervals of gabbronorite.

1938.90 Anorthosite.

1943.46 Gabbronorite.

1955.75 Anorthosite, mottled near upper part of interval.

1963.60 Leucogabbro, gradational intervals of gabbronorite.

1965.50 Melagabbronorite.

1966.40 Melagabbronorite, pegmatoidal.

1966.80 Melagabbronorite, steeply intersecting 2 cm pegmatite vein at 1968.50 m.

1971.80 PYROXENITE LAYER. Feldspathic pyroxenite at 1970.80 m. (Pyroxenite Marker?)

1973.68 Leucogabbro.

1975.00 Mottled anorthosite.

1977.00 Leucogabbro. gradational into…

1979.00 Coarse-grained gabbronorite.

1981.66 Mottled anorthosite.

1981.90 Leuconorite.

1982.80 Gabbronorite, core is fractured.

1983.80 Gabbronorite.

1986.25 Leuco-anorthosite.

1986.40 Coarse-grained gabbronorite.

1987.12 Anorthosite, mottled.

1988.12 Gabbronorite.

1995.18 Mottled anorthosite.

View south towards the drilling rig. The area used for logging core can be seen in front of the vehicle.

View south towards the drilling rig. The area used for logging core can be seen in front of the vehicle.

2000 m

2002.33 Gabbro.

2003.59 Mottled anorthosite.

2015.50 Gabbronorite, coarse-grained, pegmatoidal.

2016.40 Gabbronorite, grading into…

2076.00 Leucogabbro.

2095.10 Mottled anorthosite.

2098.00 Leucogabbro.

2100 m

2100.50 Mottled anorthosite.

2101.40 Leucogabbro.

2102.20 Mottled anorthosite.

2103.00 Leucogabbro.

2107.85 Mottled anorthosite.

2021.60 Leucogabbro.

2021.80 Mottled anorthosite.

2124.55 Leucogabbro.

2125.50 Mottled anorthosite.

2132.85 Gabbro, grading into…

2167.90 Mottled anorthosite, occasional layers of gabbro, at 2169.70 m for instance.

2181.20 Leucogabbro, coarse-grained.

2184.40 Gabbronorite, slightly more orthopyroxene-rich (melanorite) at 2203.0-2207.0 m.

2200 m

2207.30 Granite pegmatite vein, steep intersection with core axis.

2208.20 Gabbronorite, pegmatitic vein at 2208.7 m.

2211.20 Granite pegmatitic vein.

2212.10 Gabbronorite, melacratic in places.

2223.90 Granite, sharp contact.

2244.35 Gabbronorite, melacratic in part.

2247.40 Granitic vein.

2249.45 Leucogabbronorite.

2250.00 Anorthosite patches and pyroxenitic sulfide zone.

2250.30 Gabbronorite, leucocratic in part.

2260.65 Granitic vein.

2261.50 Gabbronorite.

2262.65 Granitic intrusion breccia.

2266.75 Gabbronorite.

2267.75 Granite pegmatite vein, 5 cm thick.

2266.80 Gabbronorite, at 45° angle to core axis (xenolith?).

2272.90 Granitic intrusion breccia.

2274.35 Gabbronorite, at 30-40° angle to core axis (xenolith?).

2275.45 Granitic intrusion breccia, magnetite-bearing upper zone xenoliths.

2276.06 Gabbronorite, at 5-10° angle to core axis (xenolith?).

2279.57 Granitic intrusion breccia.

2281.92 Gabbronorite.

2286.85 Granitic intrusion breccia, some upper zone magnetite-bearing rock types, steep sharp contact with…

2299.55 Mottled anorthosite.

2300 m

2301.55 Leuconorite, large cumulus orthopyroxene crystals.

2309.85 Mottled anorthosite.

2315.25 Leucogabbro.

2316.45 Mottled anorthosite, coarse mottles in part, lower 20-30 cm non-mottled anorthosite.

2328.70 Gabbronorite, 20° angle to core axis, with cumulate orthopyroxene.

2345.23 Granitic vein.

2345.60 Gabbronorite.

2353.92 Granitic vein.

2354.12 Gabbronorite, with cumulate orthopyroxene slightly altered. Plagioclase and orthopyroxene at 2383.50 m, 2 cm thick granitic vein at 2385.50 m, alteration associated with many fractures at 2392.00 m, granite vein at 2396.80 m, slightly more leucocratic interval at 2398.0-2398.0 m.

2400 m

2402.70 Granitic vein.

2403.15 Altered gabbronorite.

2404.00 Gabbronorite, relatively unaltered, but fractured.

2411.20 Granitic vein.

2411.70 Gabbronorite, relatively unaltered.

2414.40 Gabbronorite, fractured.

2415.50 Gabbronorite.

2426.30 Granitic vein, 4 cm thick.

2426.34 Gabbronorite, gradually darkening at 2426.50 m.

2434.80 Gabbronorite, horizontal fractures associated with intense alteration at 2428.73 m and at 2429.96 m.

2429.50 Gabbronorite, not as dark, gradual change into…

2437.90 Leucogabbronorite, with cumulate, spotted orthopyroxene.

2444.80 Leucogabbronorite, bleaching associated with fractures.

2446.80 Anorthosite.

2447.55 Leucogabbronorite, grading into…

2448.50 Gabbronorite.

2453.15 Leucogabbro.

2455.50 Mottled anorthosite.

2455.95 Pyroxenite, fined-grained.

2456.05 Mottled anorthosite.

2456.33 Leucogabbro, altered.

2458.90 Granitic vein, intruding at an angle or core axis, 10 cm thick, associated with alteration.

2459.10 Leucogabbronorite, banding present.

2459.60 Leucogabbronorite, bounded. Banding noted for orthopyroxene cumulate layers, less so for clinopyroxene or plagioclase.

2465.70 Alternating mottled anorthosite and spotted (or weakly bounded) leucogabbronorite.

2465.90 Granitic vein, associated with alteration.

2468.86 Mottled anorthosite, alteration associated with fractures at 2474.2-2488.00 m, mottles decreasing in size while grading into…

2499.90 Spotted anorthosite.

2500 m

2500.50 Gabbronorite.

2503.45 Magnetite bearing rock (?).

2504.35 Granite.

2515.60 Mottled anorthosite.

2516.40 Spotted leuconorite, with relatively large orthopyroxene.

2517.30 Mottled anorthosite, with fairly distinctive orthopyroxene, 25 cm of anorthosite at lower contact with…

2523.70 Gabbronorite.

2528.30 Anorthosite.

2528.40 Gabbronorite.

2529.50 Anorthosite.

2529.70 Gabbronorite, evenly textured.

2541.80 Norite, distinctive orthopyroxene.

2575.04 Mottled anorthosite, grading into…

2577.30 Gabbronorite.

2582.50 Mottled anorthosite.

2583.60 Leucogabbronorite, fractures at steep angles to core.

2585.78 Mottled anorthosite, grading into…

2586.13 Leucogabbronorite.

2587.77 Mottled anorthosite, mottles increasing in size and frequency downwards.

2589.05 Mottled anorthosite, few mottles near top but increasing in frequency downwards, grading into

2590.30 Leucogabbronorite.

2591.13 Mottled anorthosite, mottles increasing in size and frequency downwards.

2592.25 Mottled anorthosite, grading into…

2594.20 Leucogabbronorite.

2597.35 Mottled anorthosite, variable textures such as the size of mottles, orthopyroxene-clinopyroxene.

2599.35 Leucogabbronorite, small mottles, typical diameter is 3 cm, increasing in frequency downwards.

2600 m

2600.05 Mottled anorthosite, mottles increasing in frequency downwards.

2603.90 Anorthosite, grading into…

2604.25 Leucogabbronorite, grading into…

2606.17 Gabbronorite.

2609.00 Leucogabbronorite, grading into…

2610.80 Gabbronorite.

2617.50 Granitic vein.

2630.44 Gabbronorite.

2631.45 Granitic vein.

2631.77 Gabbronorite, minor granitic veins at 2633.50 m and 2644.86 m subparallel to core axis.

2656.67 Leucogabbronorite.

2657.83 Norite-melanorite, with discrete 0.5 cm sized orthopyroxene.

2700 m

2703.00 Anorthosite.

2704.50 Anorthosite, with distinctive rare orthopyroxene crystals about 1-3 mm in size. Granitic vein subparallel to core axis at 2705.0 m. Orthopyroxene increases downward and anorthosite grades into…

2706.00 Gabbronorite.

2706.61 Anorthosite, altered, saussuritized plagioclase.

2706.79 Gabbronorite, with large orthopyroxene crystals at contact.

2707.53 Mottled anorthosite.

2710.40 Leucogabbronorite, gradational into…

2711.50 Gabbronorite, gradational into…

2712.00 Melagabbronorite gradational into…

2716.00 Leucogabbronorite, gradational into…

2721.00 Gabbronorite, gradational into…

2723.00 Melagabbronorite, with gradual downward decrease in orthopyroxene.

2729.00 Gabbronorite, with leucogabbro at 2729.50-2730.80 m. Steeply dipping granite vein at 2754.50-2755.30 m. Decrease in clinopyroxene downward.

2745.00 Norite, granite vein at 2765.50-2767.15 m.

2770.70 Feldspathic websterite, clinopyroxene-orthopyroxene cumulate.

2771.10 Norite, slightly altered.

2771.50 Extensive granite veining with fragments of altered norite.

2777.00 Leuconorite.

2778.50 Norite, light-colored with very little clinopyroxene.

2780.75 Norite, increase in orthopyroxene, also coarse-grained.

2800 m

2802.20 Anorthosite, sharp contact, a few sulfides.

2802.60 Leuconorite, with 10-15 cm wide pure anorthosite intercalations.

2804.90 Granite vein, white. Granite contains amphibole, biotite, and magnetite.

2806.60 Leuconorite, gradational into…

2806.80 Melanorite, gradational into…

2807.80 Pyroxenite, with 10 cm basal dunite (serpentinized).

2809.10 Leuconorite, gradational into…

2810.20 TROCTOLITE LAYER. Large 0.5 cm diameter olivine crystals. Granite vein at 2825.20-2825.85 m. Increase in grain size at 2840 m. Variable modal content of mafic constituents, such as enrichment of mafic minerals at 2856.50-2857.80 m. Large grains appear to be olivine, small interstitial grains appear to be orthopyroxene.

2857.80 Gabbronorite.

2861.80 Granite vein, white, containing amphibole and magnetite.

2876.25 Gabbronorite, granite vein at 2877.30-2877.75 m.

2880.25 TROCTOLITE LAYER. Varying proportions of small brown orthopyroxene grains. Increase in olivine at 2884.70 m. 10 cm pegmatoid with sulfides at 2885.05-2885.15 m.

2885.50 Anorthosite, mottled, altered.

2888.20 Granite vein.

2897.55 TROCTOLITE LAYER.

2897.85 Anorthosite.

2898.25 TROCTOLITE LAYER. Varying proportions of cumulus olivine. Leucocratic zones tend to contain brown orthopyroxene. Thin 2 cm thick granitic vein at 2911.50 m with 20 cm wide alteration zones on either side. From 2911.00 m, spotted appearance disappears because of smaller grain size of olivine, to a depth of 2916.00 m. At this depth rock has spotted appearance because of large size (0.5 cm) of olivine grains. Alteration associated with thin fractures at 2939.50-2941.0 m. Horizontal vein at 2941.80 m with extensive serpentinization on either side.
2900 m

2949.50 E.O.H. (End of hole.)

Addendum

This core log was completed in 1992 by M. Knoper and G. von Gruenewaldt, while at the Institute for Geological Research on the Bushveld Complex, University of Pretoria, South Africa. The research was supported by F.R.D. funding to G. von Gruenewaldt, and by funding awarded by the University of Pretoria to G. von Gruenewaldt and to M. Knoper. The core log was first published online in 1996; it may be cited as follows…

Knoper, M.W., and von Gruenewaldt, G., 1996, The Bellevue (BV-1) borehole core log: 2.9 km of Bushveld Complex stratigraphy (northern lobe), available online at geology.photo.

There are a number of peer-reviewed research papers based on core samples from BV-1. For instance, the core log presented here was used in the publication of the following study…

Ashwal, L.D., Webb, S.J., and Knoper, M.W., 2005, Magmatic stratigraphy in the Bushveld Northern Lobe: continuous geophysical and mineralogical data from the 2950 m Bellevue drillcore, South African Journal of Geology, volume 108, pages 199-232.

Note that mineral modes, rock names, and the igneous stratigraphy described in this core log were determined by examination of drill core specimens. Letters assigned to magnetitite layers have not been formalized and are only provided as a means to informally reference the different magnetitite layers in this part of the northern Bushveld Complex. Depth in meters was measured (downwards) from the drillhole collar. The Bellevue BV-1 core is currently stored at the South African Council for Geoscience, National Core Library, Private Bag X112, Pretoria 0001, South Africa.