Progress Report Confidential · hematite-muscovite 1-2 mm thick, not seen in the unweathered porphyry. These same minerals occur locally in the groundmass, as irregular clots. Plagioclase

Progress Report Confidential

P544 – Proterozoic sediment-hosted copper deposits

Centre for Ore Deposit Research, University of TasmaniaColorado School of Mines

AMIRA International Limited ACN 004 448 266 ABN 60 176 687 9759th Floor 128 Exhibition Street Melbourne 3000 Australia Phone: +61 3 9679 9999 Facsimile: +61 3 9679 9900email: [email protected] Website www.amira.com.au

June 2002

Produced by the

Centre for Ore Deposit ResearchUniversity of TasmaniaGPO Box 252-79,Hobart Tasmania Australia 7001

June 2002

another Pongratz Production 2002

AMIRA International LimitedACN 004 448 266 ABN 60 176 687 975

www.amira.com.au

CODES/CSM:AMIRA P544

Proterozoic Sediment-Hosted Copper Deposits

June 2002

Confidential to Sponsors

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CODES/CSM: AMIRA Project P544 — Proterozoic

sediment-hosted copper deposits. June 2002

Petrology of Lower Roan–basement contacts, Konkola East and Ndola East areas — David Broughton, Colorado School of Mines ------------------------------------------------------------------------- 1

Comparative Study of Drill Cores from the Konkola North Orebodyand Barren Gap — David Broughton, Colorado School of Mines ------------------------------------------------- 19

Contents

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This report contains two contributions from DavidBroughton that were to be presented at the P544sponsors’ meeting held in Adelaide in May 2002.The first report documents the transition from LowerRoan sediments to basement rocks in drill cores fromKonkola East (Kawiri area) and Ndola East. Thesecond report is a drill core-based detailed petro-graphic description of the mineralised sequence atKonkola with stratigraphically equivalent rocks fromthe barren gap and a fringe ore position.

Due to circumstances beyond his control David wasunable to attend the meeting, and Robert Scottpresented a synopsis of his findings on his behalf.

This report supersedes the meeting presentations.

Peter McGoldrick

June 2002

Introduction

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Petrology of Lower Roan–basement contacts,Konkola East and Ndola East areas

David BroughtonColorado School of Mines

SummaryThis report describes the Lower Roan–basementtransition in two drill cores: one (KW26) from east ofKonkola where Lower Roan sediments are in contactwith Muliashi Porphyry, and the other (IT28) fromnear Ndola where Lower Roan is in contact withquartzo-feldspathic gneiss. In both holes the contactsare interpreted as unconformities with preserved(albeit metamorphosed) regoliths. In KW26 thetransition is characterised by intense biotite-epidotealteration of feldspars, and in IT28 the transition ismarked by high-angle fractures filled with sedimentfrom the overlying sandstone. Lower Ron rocks inboth locations show similar early diagenetic featuressuch as oxide and clay coatings on detrital grains.

Introduction

This report describes samples of two drill coresselected to examine the nature of the basement–Katangan relationships, from holes drilled east ofthe Konkola mine and in the Ndola East area(Figure 1). The nature of the basement contact hasbeen contentious since the earliest geologicalinvestigations in the Copperbelt, and remains poorlydocumented. The Copperbelt is underlain bybasement of middle to late Proterozoic age, whichconsists predominantly of granites, schists/gneissesand quartzites. Of interest are the granites, most ofwhich are of Ubendian age (1800 to 2000 Ma), andare locally termed the “old” or “grey” granites. Alsopresent are “red” granites, including the NchangaRed Granite, dated at 880 Ma, the youngest basement

age obtained in the Copperbelt. The samples fromhole KW26 in the Konkola East (Kawiri) area comefrom the Muliashi Porphyry, which has somepetrological similarities to the Nchanga granite buthas not been dated. Basement in the Ndola East holeIT28 consists of quartz-feldspathic gneiss of uncertainage.

This study used petrographic, cathodoluminescenceand SEM studies of nine thin sections to documentthe original mineralogy and diagenetic/meta-morphic/hydrothermal overprints of the basementand cover rocks, in order to place constraints onprovenance, timing of diagenetic and hydrothermalevents.

In both cores a zone of residual, weathered – butnow metamorphosed – basement is interpreted tooccur at the contact. In hole KW26, approximately2.5 metres of residual Muliashi Porphyry is preserved,at a down-hole depth of 536.0 to 538.5 metres (thinsections 82, 83). In hole IT28, the depth of preservedbasement weathering is at least 3 metres.

Konkola East (Kawiri) Area, Drill HoleKW26

Basement-Muliashi Porphyry (thin section 81)

The Muliashi porphyry forms the basement in theKonkola area, and is overlain by sandstones andconglomerates of the basal Lower Roan. There isconsiderable vertical relief on the basement

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Zambia

Lufilian Fold

and Thrust Belt

Angola

Zambian

CopperbeltKonkola

D.R.C.

Ndola

200 km

N

Katangan Lower RoanGroup meta-sedimentaryrocks

Pre-Katanganbasement

post-Katangansediments

post-Lower RoanKatangan meta-sedimentary rocks

Figure 1. Location of Konkola mine (drill hole KW26) and Ndola property (drill holeIT28) within the Zambian Copperbelt.

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topography: east of Konkola on the Kawiri (KW)property the Ore Shale is interpreted as missing (notdeposited) against a local basement high, whereas inthe area between Konkola and Musoshi a basal LowerRoan thicknesses of at least a kilometre are knownfrom drilling.

In hand specimen, the Muliashi Porphyry consists ofabout 40% cm-sized pink phenocrysts of k-feldsparwith conspicuous pale greenish sericitized plagioclaserims, in a groundmass of mm- to cm-sized bluishquartz (25%), greenish sericitized plagioclase (25%),and dark biotite (10%) (Figure 2). The phenocrystmorphology is similar to a Rapakivi texture.Accessory sphene and magnetite can also be seen.

In thin section, the phenocrysts are seen to consist ofperthitic microcline and orthoclase overgrown byplagioclase (Fig 3a, b). The k-feldspar typically formsmultiple, optically continuous crystals that togethercomprise the phenocryst, separated by thin zones ofinterstitial quartz. The plagioclase is zoned, withepidote-biotite-(clinozoisite, calcite) altered cores andclear, unaltered rims. SEM/EDS examinationconfirms that the plagioclase cores are sodic-calcic,whereas the rims are sodic (albite). Under CL the k-feldspar is characteristically bluish, and the unalteredplagioclase and perthitic intergrowths brownish. Thecalcite has a red to golden yellow luminescence,indicating probable Fe and Mn substitution.

The groundmass blue quartz varies from poly-crystalline and fine-grained, to monocrystalline andstrained (undulose extinction, Figure 3c). The quartztypically has smooth, rounded contacts with thefeldspars, and forms oval to subcircular grains. Thepolycrystalline quartz has grain boundary texturesthat range from sutured (unstable, Figure 3d) tometamorphic triple-point (stable). The suturedboundaries appear very similar to textures in LowerRoan arenites in drill hole IT28, and are probablyrelated to Lufilian deformation. There is littleconsistent indication of the origin of its blue colour,either under the petrographic or the CL microscope,except that colour zoning in some grains is related to

the internal distribution of polycrystalline versusmonocrystalline quartz. This quartz is a commondetrital component throughout the Lower and UpperRoan.

Biotite forms mm-sized to fine-grained flakes, somewith inclusions of rutile that have optically darkenedhaloes, and is difficult to determine whether it isigneous or metamorphic/hydrothermal in origin:both grain sizes may be associated with epidote-clinozoisite.

Euhedral sphene is a common accessory in thegroundmass, and shows no indication of alteration.Apatite forms euhdral to rounded tabular grains,and is very common in zones of clotted biotite-epidote, but rare within the feldspar phenocrysts.The apatite has a moderately strong greenish yellowluminescence, possibly indicative of Mn, and somegrains are zoned. Magnetite is euhedral and occursonly within the altered plagioclase that mantles thephenocrysts. Minute grains of chalcopyrite also occuronly within the altered plagioclase, where they areassociated and locally enclosed within epidote(Figure 3e).

The phenocrysts are cut by minor veinlets of calcite,epidote, biotite, and rare chalcopyrite, that are locallycontinuous with the more pervasive alteration zones.This alteration-mineralization event is interpreted asKatangan or Lufilian in age.

Residual Basement (thin sections 82, 83)

The porphyry is separated from bedded, clearlysedimentary rocks by approximately 2.5 metres ofdark, biotitic rock containing about 15% scatteredpink feldspar phenocrysts and 15% blue-grey quartzgrains, floating in a brownish-green matrix (Figure 4).The impression is one of a sedimentary rock derivedvery proximally from the porphyry.

In thin section, the feldspar phenocrysts and bluequartz grains are effectively indistinguishable from

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Figure 2. KW-26, 553.3 m. Muliashi Porphyry.Note large k-feldspar phenocrysts mantled bygreenish altered plagioclase, blue quartz, and darkbiotite.

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Figure 3a. TS81, cpl. View of edge of feldsparphenocryst, against polycrystalline quartz.Grey microcline overgrown by plagioclase,which is zoned from epidote-biotite altered,calcic cores to clear, unaltered, albitic rims.The phenocryst is mantled by alteredplagioclase, which contains euhedralmagnetite.

Figure 3b. TS81, cpl. Relatively coarse-grained epidote and clinozoisite, withassociated biotite, replacing plagioclase.

Figure 3c. TS81, cpl. Typical texture ofpolycrystalline quartz, on margin of large, 3-5mm blue quartz grain. Some grains showmetamorphic triple-point boundaries, othersare sutured, all show straight to almost-straight extinction. Core of grain is mono-crystalline, with undulose extinction.

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Figure 3e. TS81, reflected light. Chalcopyriterimming rutile, within grain of epidote.Minor chalcopyrite is typically associatedwith epidote-biotite-(muscovite) alterationof plagioclase.

Figure 3d. TS81, cpl. Polygonal texture inmicrocline and quartz. The microcline isoptically continuous, and dissected by thinseams of minute quartz-plagioclase-muscovite-biotite.

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Figure 4. KW-26, 538.3 m. Regolith,Muliashi Porphyry. Intensely alteredbrownish matrix contains phenocrystsof k-feldspar, plagioclase and bluequartz.

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those in the underlying sample. The perthitic k-feldspar phenocrysts are unaltered and shows nosigns of (incipient) weathering, possibly because ofits inherent stability (Figure 5a). In both thin sectionsthe phenocrysts have a discontinuous halo of calcite-hematite-muscovite 1-2 mm thick, not seen in theunweathered porphyry. These same minerals occurlocally in the groundmass, as irregular clots.Plagioclase phenocrysts are intensely altered tomuscovite-epidote-clinozoisite-biotite (Figure 5b).

The brownish groundmass consists in thin section of10 to 20% fine-grained biotite intergrown with 5 to15% epidote-clinozoisite-muscovite, all overgrowinggranitic-textured plagioclase and k-feldspar(Figure 5c). In most places the abundance of thesecondary minerals prevents recognition of grainboundaries, and it is difficult to be certain whetherthe groundmass comprises large, eroded andtransported porphyry fragments, or metamorphismof an in-situ residual porphyry. On the basis of thepreserved igneous texture of the groundmass, theintact phenocrysts, the knowledge that phenocrystabundances vary widely within the MuliashiPorphyry (ie. 15% is not an unacceptably lowabundance), and a comparison with the textures inthe overlying bedded sediments, it is reasonable tointerpret this as a metamorphosed residual porphyry.

The groundmass also contains sphene, ilmenite andhematite. Sphene forms subspherical detrital grainscored by ilmenite and locally apatite. The grainshave a characteristic irregular, bumpy outline that ismorphologically similar to the ubiquitous hematitegrains in the Lower Roan sediments. Ilmenite occursas bladed angular grains that are the likely precursorfor the bladed, Ti-bearing hematite in the LowerRoan. Specular hematite forms pseudomorphs(martite) after euhedral magnetite, and lacks Ti.

The features of the residual zone suggest thatweathering of the porphyry was accomplished byclay alteration of the feldspars, and oxidation ofmagnetite. The general lack of carbonate, silica orother infilling in the feldspars suggests that the

secondary porosity created by clay weathering wasnot cemented, but preserved until later meta-morphism to micas. Calcite, epidote-clinozoisite andbiotite are common replacement products of theplagioclase, and also formed during metamorphism.

Lower Roan meta-sandstones and

conglomerates (thin sections 84, 85)

Thin sections 84 and 85 are taken from beddedsandstone and conglomerate 10 to 20 cm above theweathered zone. In hand specimen the conglomeratecontains obvious mm to cm-sized fragments of pinkk-feldspar phenocrysts and blue quartz, within asand matrix similar in composition to the sandstones(Figure 6). Graded bedding is absent or poorlydeveloped and quite abrupt, and sorting is minimal.Outsized grains are commonly visible in thesandstones.

In thin section, the conglomerates are framework-supported with coarse sand to granule-sized grainsof porphyry, feldspar and quartz, commonly with amoderate rounding (Figure 7a). In most cases thiscan be ascribed to the original texture of theporphyries (rounded feldspar phenocrysts and bluequartz), but other grains appear to have undergonesignificant transport. In particular, well-roundedquartz grains may be derived from other basementsources, most likely the Muva quartzites. Accessorygrains of detrital muscovite are typically acicularand up to 1 cm in length, were not seen in the granitesand also appear to have a different, unknownbasement source (Figure 7b). The larger detrital grainsoccur within a framework of fine to medium-sizedsand grains of angular to subangular quartz andfeldspar, of clearly local origin. Also present aresubspherical to broken, sand-sized grains of hematite,some of which show incomplete alteration frommagnetite (Figure 7d-f). These are interpreted to havebeen derived from the primary magnetite and thezoned sphene-ilmenite grains in the granites. Rutileoccurs as rare pseudomorphs after sphene, and more

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Figure 5a. TS82, ppl. Margin of largefeldspar phenocryst (to right), with selvegeof quartz, calcite, muscovite, hematite.

Figure 5b. TS83, cpl. Intensely alteredplagioclase phenocryst, almost completelyreplaced by biotite-epidote-(muscovite).Dark grey interstitial quartz preservesoriginal texture of phenocryst.

Figure 5c. TS83, cpl. View of groundmass tolarge feldspar phenocrysts. Groundmass hasdark colour due to abundance of fine grainedmetamorphic biotite and epidote, but igneoustexture is preserved. Interpreted as ametamorphosed residual granite.

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Figure 6. KW-26, 535.8 m. Lower Roan conglomerateand sandstone, 10cm above contact with porphyry.Note large angular granitic rock fragments, bluequartz and k-feldspar, poor sorting and lack ofcompaction textures.

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Figure 7a. TS84, cpl. View of frameworkgrains in conglomeratic sandstone. Detrital k-feldspar (upper left) and quartz with biotiteand Fe-Ti oxide dust rims, cemented byquartz.

Figure 7b. TS85, cpl. Compacted arkosicsandstone, with bent detrital muscovite andwell-aligned framework grains of quartz andfeldspar. The matrix appears undeformed(although partly replaced by metamorphicbiotite), there are no quartz or feldsparovergrowths, and the framework grains areunaffected by pressure solution.

Figure 7c. TS84, ppl. Fine-grained arkosicsandstone, subrounded and well-sortedframework grains. Bent detrital muscovite,partly mantled by metamorphic biotite, whichalso partly replaces the matrix. The cloudy k-feldspar grains have thin overgrowths of clearfeldspar.

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commonly as silt to clay-sized grains within thegroundmass and coating detrital grains.

The estimated detrital composition of the conglom-erates is 30 to 50% lithics (including porphyry,polycrystalline quartz), 25% quartz, 15% k-feldspar,5 to 10% plagioclase, and accessory muscovite, andhematite. The conglomerate contains 5% to locally10% silty matrix that under crossed polars has a finemosaic texture and very low birefringence (Figure7e,f), and is variably replaced by metamorphic biotite,muscovite or calcite. The SEM/EDS indicates thatthis matrix material consists largely of k-feldspar.

The sandstones contain a similar compositional rangeof detrital components, but intact porphyry rockfragments are rare. Framework grains are subangularto subrounded, the greater textural maturity due toelimination of the large lithic grains with roundnessinherited from the porphyry. On average, thesandstones contain 40% quartz (monocrystalline),30% feldspar (including 10% plagioclase), 5 to 10%lithics (porphyry, polycrystalline quartz), 1 to 2%detrital muscovite, 2 to 4% hematite, and about 1%rutile. The matrix comprises 5 to 20% of the rock, andis locally replaced by biotite, or calcite. Thecomposition of the sandstone can be irregularlydomainal on an intra-bed scale, such that they rangein classification from lithic wacke to lithic arkose tofeldspathic sandstone. This immaturity also occurson an inter-bed scale.

Grain boundaries in both the sandstones andconglomerates are typically straight, smooth orcurved, rather than sutured. Grains in the sandstoneare most commonly floating or in contact with one ortwo other grains, and overgrowths occur on wheregrains are in contact (Figure 7c). A few of the detritalmuscovite flakes are bent around quartz or feldspargrains, but there is otherwise little evidence ofsignificant compactional deformation.

Overall, the sandstones show remarkably littleevidence for cementation, dissolution and otherdiagenetic processes. In this regard it is noteworthy

that the feldspar grains in the sandstone andconglomerate are no more altered to muscovite/biotite than in the samples of porphyry, possiblybecause the more weathered grains were destroyedduring transport. More puzzling is the lack of eitherdetrital or in-situ (ie. within plagioclase) epidote-clinozoisite in the sedimentary rocks, given theirubiquitous presence in the footwall granites. If theseminerals represented a pre-Katangan metamorphicevent, one would expect them to form part of thedetrital record, particularly within large, intactgranitic rocks fragments. If they represent a Lufilianhydrothermal/metamorphic event, which issuspected on the basis of their association withveining and chalcopyrite mineralization, theirabsence in the metasediments suggests a stronglylocalized control.

SEM/EDS work on the micas indicates that there aretwo end-member compositions present in the KW26section. A pale, weakly to non-pleochroic, stubbylath-shaped mica with high birefringence is presentin the plagioclase alteration, in calcite veinlets, andin mantled zones around feldspar phenocrysts in theresidual zone. It contains little or no Ti, no Cl and islow in Mg, but has significant Fe. It is likely an Fe-bearing muscovite. The second mica is a brown,pleochroic, biotite that also occurs in the plagioclasealteration and veinlets, as well as in the residualgranite groundmass, in nodules or clumps of coarserbiotite, and as a mantle to the hematite and detritalmuscovite. It contains considerably more Fe than thepale mica, as well as significant amounts of Ti andCl. Coarse-grained biotite associated with mineral-ization in the Konkola drill hole KLB145 also tendsto be elevated in Fe, Ti and Cl. More work needs tobe done to confirm this association, and may helpconstrain the type and pathways of mineralizingfluid.

Ndola East Area, Drill Hole IT28

A series of drill holes some thirty years ago testedthe area around the present-day Ndola Lime

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operation, several of which passed into a gneissicbasement. Unlike the Konkola area, the thickness ofthe Lower Roan beneath the Ore Shale is remarkablyconsistent between holes, such that individual bedsimmediately above the basement contact can becorrelated over several kilometres. The depositionalsetting appears to have been tectonically much quieterfrom that at Konkola. Although all of the holes containcopper mineralization, its grade is consistently sub-ore (<2%). The contact is also interesting because thegneissic basement appears to contain “windows” ofLower Roan sandstone and it is not obvious that anerosional contact exists.

In hand specimen the contact between the gneissand the sandstone parallels the orientation of poorlydefined layering within the sandstone, as well as theorientation of a hematite-bearing vein in the gneiss(Figure 8). The gneissic layering lies almostperpendicular to these features, and is abruptly cutby the contact with the sandstone. Unlike the basalsandstones described from Konkola, the sandstoneshere are even-grained, dark, and contain no materialobviously derived from their immediate footwall.

The sandstone consists in thin section of more than90% quartz with less than 10% feldspar (microclineand accessory plagioclase), accessory biotite andhematite, and rare zircon, and hence is a quartzarenite (Figure 9a). The framework grains are well-sorted, and mud or silt-sized matrix is absent. Therock has a striking sutured texture, which along witha moderately developed preferred orientation ofgrains indicates strong pressure solution parallel tobedding (the basement contact). This is supportedby the rarity of preserved dust rims of Fe-Ti oxideand mica (clay) dust rims (Figure 9a). However, theirpresence indicates a period of early diageneticoxidation similar to that at Konkola.

The arenite gradually decreases in average grain sizeand sorting towards the contact with the gneiss,coincident with a gradual increase in the abundanceof suture-lining fine-grained biotite, and of sutured,and in many instances stylolitic grain boundaries

(Figure 9 b). These changes may reflect a change inthe original sediment toward a more poorly-sorted,feldspathic arenite, with slightly higher clay contentexpressed as grain coatings.

The sutured texture could be interpreted as relatedto diagenetic pressure solution during burial.However, the texture occurs locally within theunderlying gneiss (Figure 9d), and in the hematite-bearing plagioclase-calcite-quartz-biotite vein.Together these suggest that the sutured texturedeveloped, or was at least modified, duringmetamorphism-deformation.

The contact with the gneiss is indistinct to irregularon the thin section scale. The uppermost part of thegneiss consists of large quartz, feldspar and quartz-feldspar intergrowths that define the steep gneissictexture, separated by zones of fine-grained sandstonesimilar to that above the contact (Figure 9c). Hematiteis much more abundant below the contact, and formslarge, mm to cm-sized irregular grains within thesandstone. The texture could be interpreted as beingdue to sandstone deposited within steep crackspenetrating the basement, or, alternatively, as ametasomatic overprint upon the sandstone. However,dark, mosaic-textured, k-feldspar-quartz matrixoccurs locally within the gneiss, supporting aframework of detrital grains, and indicates asedimentary origin (Figure 9e).

Two types of biotite occur, a fine-grained biotite thatovergrows the matrix and detrital feldspar andcontains rutile, and a younger, coarse-grained biotitethat lacks rutile and mantles late, clear plagioclase(Figure 9f). The younger biotite is texturally similarto the coarse biotite found in mineralized nodules.Further SEM work is required to characterize thedifferent generations of biotite.

Vein hematite appears to have formed (or remobil-ized) late in the paragenetic sequence, because ittruncates and brecciates sutured quartz and the veininfilling minerals, albite, k-feldspar, and calcite. Veinminerals show evidence of deformation prior to

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Figure 8. IT28, 5098 ft. Contact between Lower Roanquartz arenite and basement “gneiss”. Note faintlayering in arenite parallel to the contact and to thehematite vein, high angle “gneissic” banding inbasement.

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Figure 9a. TS74, cpl. View of part of thin sectionfurthest above the basement contact. Quartz arenite,with locally preserved dust rims showing originaldetrital texture, largely obliterated by extensivepressure solution. Preferred orientation of grainssubparallels the basement contact. Note lack of matrix– originally a clean sand.

Figure 9b. TS74, cpl. Sample closer to the basementcontact than (a), with more intense suture developmentassociated with higher biotite content.

Figure 9c, TS75, cpl. View immediately insidebasement contact (trends NW-SE immediately left ofslide), long dimension of large feldspar grainsperpendicular to contact. Basement consists of largegranitic fragments with intervening zones of sand-sized detrital grains, and interstitial biotite.

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Figure 9d. TS76, cpl. Large quartz grain cut by quartz-plagioclase-biotite veinlets, compositionally similarand parallel to pressure solution seams and suturedtexture in overlying sandstones. Also parallel to largeveinlet of albite-quartz-biotite-carbonate-hematite.

Figure 9e. TS76, cpl. Dark cherty matrix partlyovergrown by biotite, surrounding large and locallybroken grains of quartz, feldspar.

Figure 9f. TS78, cpl. Detrital/residual granitic fragmentof dark k-feldspar partly overgrown by biotite, mantledand replaced by clear subhedral plagioclase. Twogenerations of biotite are present – a fine-grained biotitewith dark rutile, and a coarse-grained biotite that lacksrutile and mantles the euhedral plagioclase.

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truncation by hematite, such as kink bands in albite,undulose extinction and suture development inquartz. The timing and morphology of the veinhematite is similar to that of the vein-associatedsulfides, and they may be temporally related. Clear,twinned albite occurs in the veins and locally aroundtheir margins, and in one instance demonstrablyovergrows an earlier detrital k-feldspar grain (Figure9f). Sodic alteration is apparently absent at Konkola,but is here seen to be associated with hematitemineralization.

Summary and Conclusions

The basement – Lower Roan contacts in the KonkolaEast (Kawiri ) and Ndola East areas containtransitional zones where igneous textures are partiallypreserved yet sedimentary features are also present.These zones are interpreted as metamorphosedregoliths. At Kawiri, the transition is characterizedby intense biotite-epidote alteration of the feldspars,taken to reflect original weathering of the granite. AtNdola, the transition is marked by high-anglefractures filled with sediment from the overlyingsandstone.

Plagioclase in the Muliashi porphyry is altered toepidote-biotite-(muscovite-calcite), which also formsthin veinlets and carries minor chalcopyrite. Thismineralization is interpreted to be associated withLufilian deformation, on the basis of its similaritieswith late Ore Shale mineralization. Significant zonesof basement-hosted mineralization such as at Sambamay well be Lufilian, rather than pre-Katangan, andwould not provide a copper source for the LowerRoan ore bodies.

The early diagenetic features of the Lower Roan rocksare remarkably consistent between these widelyspaced locations, specifically the presence of oxidesand clays coating detrital grains. Pressure solution isstrongly developed in the Ndola basal sandstones,but is also present in the gneiss, and is likely related

to deformation rather than burial diagenesis.Weathering of the basement rocks may locally bepreserved as a regolith, but feldspars in the overlyingsandstones are no more visibly weathered than inthe basement.

The granites contain sphene that is a source for thedetrital/authigenic rutile and ilmenite in the LowerRoan. Magnetite occurs in the granites but isassociated with the epidote-biotite alteration, and somay be secondary. Hematite in the Lower Roan islikely derived from replacement of ilmenite, and themetamorphism of amorphous iron oxides. Thepeculiar blue quartz characteristic of the Roansedimentary rocks is granitic in origin.

Biotite in both the basement and sedimentary rockshas two forms, small, groundmass biotite that islocally associated with or encloses rutile, and coarsebiotite flakes that are paragenetically late. Similarcoarse biotite is elsewhere associated withmineralization. Albite is mantled by the coarse biotiteand formed at an earlier stage, and also occurs incalcite-hematite veins. Sodic alteration is importantat a few Katangan deposits, but is not consistentlydeveloped in the Copperbelt ore bodies.

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Summary

This report describes detailed petrographic andtextural features from a mineralised intersection ofOre Shale (DDH KLB145 – Konkola #3 orebody) andtwo barren Ore Shale intervals (DDH KLB67 fromthe Konkola barren gap, and KLB83 on the easternfringe of #3 orebody). In KLB67 the mineralizedintersection occurs within interbedded feldspathicarenites, feldspathic greywackes and siltstones, butis best developed within the sandstones. Mineral-ization displays a marked zoning from a central,high-grade, bornite-chalcopyrite zone of ferroandolomite-(biotite) alteration and abundant veining,through a proximal, lower grade, biotite-muscovitezone with chalcopyrite prevalent over bornite, to adistal zone of biotitemuscovite with rutile but nosulfides. Cobalt is present throughout the sulfidezone but most abundant occur in the lower, dolomite-poor interval. The lithologies in KLB67 are identicalto those in the mineralized zone and this suggeststhe barren gap is not lithologically controlled. Thesandstone and siltstones in the barren gap appear tohave undergone the same diagenetic history, withearly oxidation and weathering recorded by dustrims of Fe-Ti oxides and micas (clays), followed bylater diagenetic K-feldspar and quartz overgrowths.Bedding-parallel veinlets, predominantly composedof carbonate, are present in KLB67, but are much lessabundant than in the mineralized zone. A briefexamination of DDH KLB83 intersection indicates itis similar to the barren gap.

Introduction

The Konkola area lies at the northwestern end of theZambian Copperbelt, and consists of two ore bodiescontinuous at depth, the South or No. 1 ore body andthe North or No. 3 ore body (Figure 1). The orebodies are separated by an unmineralized “barrengap” nearly 1.5 km wide at surface, that extends to adepth of approximately 600 m. Below this the orebodies merge, such that on a longitudinal section thegap forms a U-shaped zone. The gap was encounteredearly in the drilling delineation of the deposit, andnot surprisingly was tested by few surface holes. TheKonkola barren gap presents an opportunity tocompare stratigraphically equivalent mineralized andunmineralized rock units, in a part of the Copperbeltthat generally appears relatively undeformed.

Little is documented about the geology of the barrengap, or of the nature of its boundaries with the orebodies. Fleischer et al. (1976) describe it as follows:“approaching the gap from the north orebody, ore isrestricted to the C unit [note – the mine geologistssubdivide the Ore Shale into five units, from base totop A through E, see Table 1] and lenticles of sandydolomite increase in frequency and the shale layersbetween the thickening dolomites are crumpled andfolded… cherty quartz lenses become more abundantin the dolomite bed and in the weathered formationform “quartz rubble” … it may be suspected that analgal bioherm occupies part of the unexplored barrengap…”. Sweeney and Binda (1989) mention it only inpassing as a “presumed bioherm”, and the currentmine geologists also regard it as such.

Comparative Study of Drill Cores from the Konkola North Orebodyand Barren Gap

David BroughtonColorado School of Mines

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A review of logs and preserved cores from the earlysurface holes through the barren gap indicated thatthe shallower intersections were in weathered groundunsuitable for study, and that the deeper intersectionscontain no significant carbonate. There is no “algalbioherm” at Konkola. A brief underground visit tothe north ore body–barren gap transition areaconfirmed in general terms the above description ofthe transition: the abundance of carbonate increasessouthwards and mineralization (predominantlybornite) occurs selectively in the carbonate bands.Over a lateral distance of less than 25 m theapproximately 4 to 7 metre-thick combined C and Dcarbonate-banded units changed from 10 to 20% toapproximately 50% carbonate. Individual bandscommonly change in thickness across asymmetricNE trending folds (Figure 3a). Unfortunately, driftdevelopment had stalled and was soon afterwardsterminated due to ground conditions, so that thetransition from this high grade, bornite-carbonatezone to the unmineralized and carbonate-poor barrengap was not exposed.

This study compared drill cores through the OreShale in the North Orebody (KLB145) with un-mineralized intersections from the barren gap

(KLB67) and from a drill hole immediately east ofthe north ore body (KLB83) (Figure 1). The Konkolamine stratigraphic terminology is used for reference.Samples with secondary copper mineralization wereexcluded from the study, in order to focus onhypogene mineralization controls. Petrographicobservations were augmented by cathodolumin-escence (CL) and scanning electron microscope (SEM)studies.

Konkola North Ore Body, Drill HoleKLB145

Drill hole KLB145 intersected the north ore body onthe south limb of the northwest-plunging KirilaBomwe Anticline, approximately 2.6 km from drillhole KLB67 (Figure 1). In this area the rocks strikesoutheast and dip southwest at 25–30°. The Ore Shalewas intersected from 680.0 to 692.0 m, and isunderlain by 8 m of Footwall Conglomerate, followedby 1 m of Footwall Sandstone in which the hole wasstopped at 701.0 m depth. Mineralization above 1%Cu is confined to Ore Shale units A through D, andconsists of hypogene sulfides (chalcopyrite, bornite,carrolite) throughout all of the zone but the lowermost

Table 1 Konkola Ore Shale Stratigraphy (modified from Sweeney and Binda, 1989)

Member, Unit Thickness Description

Hangingwall Quartzite (HWQ) 10 - 150m Interbedded feldspathic arenite, greywacke, and minor siltstone

Ore Shale, Unit E (OSE) 0.6 - 1.5m Interbedded siltstone and subordinate feldspathic arenite

Ore Shale, Unit D (OSD) 1 - 3m Interbedded siltstone and dolomitic/calcareous feldspathic arenite,

with bedding-parallel carb-qtz-Cu veinlets

Ore Shale, Unit C (OSC) 0.9 - 4m Interbedded siltstone and dolomitic/calcareous feldspathic arenite,

with bedding-parallel carb-qtz-Cu veinlets

Ore Shale, Unit B (OSB) 1.4 - 2m Massive to laminated sandy siltstone

Ore Shale, Unit A (OSA) 0.6 - 1m Finely laminated siltstone

Footwall Conglomerate (FWC) 0 -20m Polylithic, poorly sorted conglomerate and interbedded coarse

sandstone; usually leached.

Footwall Sandstone (FWS) <40m Poorly sorted feldspathic, lithic sandstone/greywacke; usually

leached.

Porous Conglomerate (PC) <40m Polylithic, poorly sorted conglomerate, leached.

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1.1 m of unit A. This lower portion of the zone isweathered, and it contains predominantly secondarycopper minerals. The underlying footwall conglom-erate and sandstone are also weathered and containsub-ore grade secondary copper mineralization.Sampling from this intersection was limited to sixquartered cores, from which nine polished thinsections were prepared.

Figure 2 summarizes the geology, alteration,mineralization and assay results from the mineralizedsection of KLB145. The best mineralization coincideswith a central zone of dolomite-biotite alteration anddolomite-veining in units C and D. Together thesecomprise 6.5 m of the 11.5 m intersection and havean average grade of 3.4% Cu, compared with 1.7%Cu for the remaining 5 m. Cobalt values in thecarbonate-rich units are approximately one-half thatof the lower units B and A.

In the following section, a general description of thelithologies and mineralization will be followed byobservations from petrographic study.

The footwall sandstone is a red to olive brown,massive to poorly bedded, coarse-grained greywackeor muddy sandstone, and may represent an interbedwithin the footwall conglomerate unit. The conglom-erate is polylithic, massive bedded, unsorted, matrix-to locally clast-supported, with a coarse sandstonematrix and local cm to dm sandstone interbeds similarto that of the footwall sandstone. Both units arecharacterized by patches of red-weathered carbonateand hematite, and minor malachite-chrysocolla-chalcocite. The contact with the overlying Ore Shale(OS) is sharp and bedded.

The lowermost unit of the OS, from 692.0 to 688.4 m,consists of a massive-bedded, brownish (weathered),very fine-grained sandstone to siltstone that coarsensslightly upwards. It corresponds with the mine unitsA and B. The uppermost metre is finely laminated(Figure 3b) and is gradational to the overlying unit(C). Chalcopyrite occurs as disseminated grains,bedding-parallel lenticles and minor veinlets, along

with malachite, chalcocite and local native copperbelow 689.0 m. Bornite is rare to absent. Carrolite isintergrown with chalcopyrite in the veinlets.

From 688.4 to 684.25 m the OS consists of cm to mmbedded, grey, fine- to coarse-grained dolomitizedsandstone and siltstone. This unit occurs within themine subunit C. Chalcopyrite and bornite occur asdisseminated irregular grains, lenticles and veinlets,both parallel and oblique to bedding (Figure 3c). Theveinlets contain fibrous quartz, ferroan dolomite andcopper sulfides, which define a consistent down-dip(~WSW) lineation. In thin section some of the veinletsalso possess a weak crenulation fabric. Ferroandolomite is most intensely developed as halos to theveinlets.

From 684.25 to 681.5 m (~units C and D) the OSconsists of very fine to medium grained dark greydolomitized sandstone interbedded on a centimetreto millimetre scale with pale grey dolomitizedsiltstone. The dolomite is associated with and formshaloes around bedding-parallel veinlets of ferroandolomite-quartz-bornite-chalcopyrite (Figure 3d).Bornite and chalcopyrite are roughly equivalent inabundance. The upper contact of the dolomitic zoneis sharp (Figure 3e), and coincides with a lithologicalchange from arenite (dolomitized) to greywacke.

The uppermost unit of the OS extends from 681.5 to678.5, and consists of a coarsening upwards sequenceof interbedded sandstone and siltstone. Althoughthe mine log placed the upper contact of unit E at680.0 m, the contact between the OS and the HWQ isgradational and rather arbitrary, and here placed atthe base of a prominent coarse-grained sandstonebed. Disseminated chalcopyrite and lesser borniteextend upwards from the dolomitic zone to 680.6 m(Figure 3f), above which the OS is barren of sulfides.

The HWQ consists of pink to grey, massive medium-to coarse-grained feldspathic sandstone and cm todm thick bands of dark greenish to brownish greysiltstone. Hematite occurs above 676 m asdisseminated grains and rare bedding-parallel

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a b

fe

dc

Figure 3. (a) Oriented sample from southern margin of Konkola North orebody, near barren gap, viewed toNE. Dolomite-bornite bands thicken SE (toward barren gap) across NE trending asymmetric fold structures.(b) sample of unit B, 688.8m, massive siltstone with disseminated sulfides. (c) sample of unit C, 686.55m,dolomitic sandstone-siltstone with banded/veinlet and disseminated sulfides. (d) sample of unit D, 683.45m,of bedding-parallel ferroan dolomite (stained) – sulfide veins. (e) contact between unit E (left) and unit D,dolomitized arenite. (f) sample of unit E at 681m, note disseminated sulfides, lack of carbonate. All coresamples approximately 5cm across.

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concentrations, the latter associated with pinkishcolouration.

In thin section, the sandstones and siltstones havewell-preserved sedimentary and diagenetic textures,although tectonic fabrics are developed locally. TheOS rocks are composed of subrounded to roundeddetrital framework grains of quartz, k-feldspar,muscovite-altered feldspar, muscovite (large platygrains), minor granitic and cherty rock fragments,and accessory apatite and zircon. In most specimensthese are poorly sorted, and occur within a matrix offine silt to clay-sized k-feldspar, quartz andmuscovite. The matrix, detrital muscovite and k-feldspar are variably overgrown by biotite and finemuscovite. Sulfide and oxide textures are describedbelow.

The sandstones vary texturally between matrix-supported greywackes and matrix-poor feldspathicarenites. In the arenites, the grains are in mutualcontact, may show evidence of pressure solution,and quartz and feldspar overgrowths and cementare common, often preserving dust rims of Fe-Tioxides and mica after clay (Figure 4a, b, h, see alsoFigure 6c, k). Quartz cement is relatively common inthe arenites, and locally has undulose extinction,suggesting it pre-dates Lufilian deformation. In thegreywackes, detrital grains are less commonly inmutual contact, and overgrowths of quartz andfeldspar are rare or absent (Figure 4c, d).

The distribution of matrix-rich and matrix-poorsandstones appears to be an important control on thedistribution of carbonate and sulfide mineralization.The top of carbonate alteration at 681.5m is coincidentwith the contact between an overlying greywackeand the underlying feldspathic arenite (Figure 2, 3e).Dolomite in the altered arenite occurs as discretegrains overgrowing feldspar, biotite, matrix andpossibly quartz (Figure 4g, h). In addition,mineralization is preferentially developed withinsandstones rather than siltstones, as can be seen inits overall distribution (Figure 2) as well as on thethin section scale (Figure 4i).

A distinct zoning exists across the OS, both inalteration and sulfide mineralogy (Figure 2). Thecentral zone (units C & D) is characterized bybedding-parallel dolomite-chalcopyrite-bornite-(quartz, biotite, k-feldspar, apatite) veinlets, ferroandolomite-(biotite) alteration and approximatelyequivalent amounts of disseminated bornite andchalcopyrite (Figure 3d, 4g, h). Biotite is destroyedwhere dolomitization is most intense. This centralzone contains the high grade mineralization and“carries” the entire interval . It is enveloped by azone of less intense, biotite-dolomite alteration andfewer veinlets, where chalcopyrite is more abundantthan bornite. This interval also contains visiblecarrolite in the footwall of the central zone. Theoutermost mineralized zone consists of biotite andgenerally fine-grained muscovite alteration, rare toabsent veinlets, and, especially in the footwall,chalcopyrite much more abundant than bornite. Thefootwall zone also contains more abundant carrolite.

The Lower Roan hangingwall and footwall of themineralized interval are characterized by minorbiotite alteration and ubiquitous, widespreadspecular hematite, both as disseminated grains andin veinlets. The hematite facies is separated from themineralized interval by a zone of biotite-(muscovite)-rutile-Fe chlorite (Figure 2, 4a,b).

Sulfide textures are distinctive, and in some instancessimilar to those of hematite in the stratigraphicallyequivalent barren intersections. Hematite is absentwithin the mineralized zone, however, clusters andindividual minute grains of rutile are present in traceto accessory amounts, and are locally intergrownwith biotite (Figure 4e,f) or mantled by Cu sulfide(Figure 4l). In most instances rutile appears to haveformed prior to Cu sulfides, probably duringdiagenetic oxidation (dust rims). Chalcopyrite andbornite are mutually intergrown, or chalcopyriteoccurs as rims and fracture-related infillings orreplacements of bornite. Pyrite is absent. The Cusulfide grains generally vary in grain size accordingto the grain size of their host rock, however a wide

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Figure 4, KLB145 photomicrographs, showing zoning and textures of alteration-mineralization across the OS. (a,b) TS62,feldspathic arenite with biotite+muscovite alteration, rutile. (c,d) TS63, above dolomitic zone, feldspathic greywacke withbiotite alteration, chalcopyrite-bornite. (e,f) TS63, “nodule” of biotite-bornite around detrital k-feldspar; bornite is late, rutile(bright grey) is enclosed in biotite (left center) and early – also note rutile separate from bornite in lower right.

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Figure 4 cont’d. (g). TS64, dolomite alteration replacing k-feldspar overgrowths in feldspathic arenite. (h) TS64, coarsechalcopyite-bornite and dolomite-biotite alteration in well-cemented feldspathic arenite. (i) TS67, bedded sandstone-siltstone, biotite-(dolomite) alteration and Cu sulfides predominantly in sandy layers. (j) TS69, coarse, irregular chalcopyritein muscovite-(biotite) alteration at base of OS. (k) TS67, CL, dolomite-chalcopyrite veinlet, zoned from speckled ferroan todark red ferroan to bright yellow-red (manganoan?) dolomite, and youngest chalcopyrite; field of view 2mm. (l) TS63, rutile(bluish) probably after sphene, filled with biotite (dark grey) and bornite-chalcopyrite.

g h

i j

k l

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range exists and the largest sulfide grains are alwaysmuch coarser than the detrital silicates. Chalcopyriteand bornite are most commonly found in directassociation with biotite and dolomite, with whichthey form small grain aggregates, nodular structuresand in the central zone, veins (Figure 4 c-f). Similarnodular structures containing anhydrite weredescribed elsewhere at Konkola (Sweeney and Binda,1989), and were interpreted as sulfide replacementfeatures after diagenetic (evaporitic) anhydritenodules. Anhydrite was not observed in any of thethree holes examined, but where seen elsewhere inthe district usually occurs in structurally late sites(veins).

Morphologically, the disseminated sulfide grainsvary from subspherical but non-rounded (eg. veryirregular at the grain boundary scale), to lenticularor platy (particularly where developed within biotite),to highly irregular (Figure 4). Copper sulfide grainsare observed to mantle or partly replace detritalsilicate grains and their overgrowths, apatiteovergrowths, and dolomite. Within and adjacent toveins, Cu sulfides typically brecciate dolomite andquartz, and fill open space between the non-sulfideminerals (Figure 4k). This range of textures can beseen in both the dolomite-altered and non-dolomite-altered zones, although the altered zones generallycontain a greater proportion of outsized and irregulargrains. This suggests that all of the copper sulfidesrecord the same mineralization event associated withthe veins and the dolomite-biotite alteration. Theoverall impression is one of sulfide precipitated orremobilized late in the paragenetic history, as thefinal phase in vein filling, replacement of matrix,detrital grains and diagenetic overgrowths, and asgrains nucleated on and replacing earlier oxides.

Sweeney and Binda (1989) described brown-luminescent feldspar overgrowths on normal, blue-luminescent k-feldspar within the OS, and docu-mented elevated Cu contents (~0.25% Cu) withinsome of these overgrowths. They interpreted thesefeatures as a critical piece of evidence for Cu beingpresent within the (diagenetic) fluid that caused the

overgrowths. Both clear and cloudy k-feldspar andk-feldspar overgrowths were noted during thecurrent study. In many clouded grains the clearfeldspar persists along cleavage into the grain core,and in this type “dust rims” of Fe-Ti oxides and micaare absent. In contrast, some of the clear feldspargrains have oxide-mica dust rims that pre-date thecloudy overgrowths. The clear and clouded feldspardo not show any compositional variation with semi-quantitative SEM/EDS. There was no indication(SEM) of elevated Cu content in the overgrowths,and, in contrast, some of the overgrowths and detritalgrains are clearly mantled and partly replaced byparagenetically later Cu sulfides. Sweeney and Bindanoted malachite in their samples, and included it aspart of the diagenetic sequence, and it is suspectedthat their samples were affected by relatively recentsecondary copper formation, as is prevalent in manyparts of the mine.

Cathodoluminescence study of the alteration andvein carbonates demonstrated a complex paragenetichistory of changing Fe and Mn contents. The matrixcarbonate grains are commonly cored with rhombsof ferroan dolomite, which is successively overgrownby dolomites of generally lower iron content. Adistinctive yellow luminescent carbonate is commonl-y present roughly midway through the sequence,and is likely related to elevated Mn content. Theseovergrowths are preserved within coarse-grained,dark to bright red luminescent dolomite and/orcalcite, that forms mosaics of interlocked grainswhose overall morphology is unrelated to the earlierzoned carbonates. A similar progression is observedin veins, where early, finely zoned carbonates areenveloped within younger, texturally simple, darkto bright red luminescent dolomite (Figure 4k). Thisconfirms a genetic link between the matrix and veindolomites.

In summary, the mineralized intersection occurswithin interbedded feldspathic arenites, feldspathicgreywackes and siltstones, but is best developedwithin the sandstones. Mineralization displays amarked zoning from a central, high-grade, bornite-

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chalcopyrite zone of ferroan dolomite-(biotite)alteration and abundant veining, through a proximal,lower grade, biotite-muscovite zone with chalcopyriteprevalent over bornite, to a distal zone of biotite-muscovite with rutile but no sulfides. Cobalt ispresent throughout the sulfide zone but mostabundant occur in the lower, dolomite-poor interval.The mineralized zone is enveloped within wide-spread specular hematite mineralization, of probableearlier age. Diagenetic overgrowths of quartz andfeldspar are present in the arenites, and trap earlierdiagenetic Fe-Ti oxides and micas.

Konkola Barren Gap, Drill Hole KLB67

Drill hole KLB67 intersected the Ore Shale midwaybetween the North and South ore bodies, at a depthof 211.7 to 219.3 m (Figures 1, 5, 6a). Core anglesindicate a true thickness of 7.2 m, about 4 m less thanin KLB145. Assay results for the intersection rangefrom 0.03 to 0.06% TCu for all but the lowermost 1.3m, which averaged 0.11% TCu and 0.04% ASCu.Mineralization was not observed in the core, and it issuspected that the minor Cu values are related tofine-grained secondary copper.

The hole ended in 7.5 m of interbedded pinkish topale conglomerate and coarse-grained feldspathicsandstone (Porous Conglomerate, PC), overlain by14.8 m of red to grey to beige, massive bedded, andvery coarse-grained feldspathic sandstone (FootwallSandstone, FWS, Figure 5). Both of these units containup to 3% disseminated and bedding-parallel specularhematite. The Footwall Conglomerate is missing inthis hole, such that the OS lies directly upon theFWS. This suggests that the OS – FWS contact is anunconformable surface, correlative with the base ofthe OS and/or the base of the FWC. The distributionof the FWC is irregular on the scale of the deposit,and unrelated to the location of the barren gap.

Each of the five subunits of the OS are present inKLB67, which suggests depositional continuitybetween the mineralized and barren OS “strati-

graphies” - placed in quotation marks because theOS stratigraphy is partly defined by the abundanceof dolomite veinlets and alteration. The combinedlowermost subunits, A and B, are 1.8 m thick andcomprises a buff-weathered to dark grey-green veryfine-grained sandstone/siltstone. They are overlainby 6.7 m of dark green-grey fine to very fine-grainedsandstone, interbedded with up to 10% discontinuousmm to cm bands of medium to coarse-graineddolomitic feldspathic arenite (subunits C and D).Bedding-parallel veinlets of dolomite-quartz-specularhematite and disseminated specular hematite arealmost exclusively confined to the lowermost 1.4 mof this zone. The OS is capped by 0.8 m of dark greyfine-grained sandstone interbedded with approx-imately 5% cm-thick beds of coarse-grainedfeldspathic sandstone, and up to 5% green-greysiltstone (subunit E).

The OS is overlain by a thick hangingwall sequenceof cm- to dm-interbedded red-brown feldspathicgreywackes and sandstones, and dark green-greyvery fine-grained sandstone/siltstone, locally with“grit”, that contain prominent disseminated specularhematite. Although quartz and feldspar overgrowthsare present in the three thin sections made of thesesandstones (Figure 6c, d), they are generally poorlycemented. The amount and distribution of cementaffects permeability, and could play a role incontrolling the subsequent movement of mineralizingfluids. For instance, well-cemented hangingwall orfootwall rocks could form seals to cross-stratal fluidmigration, and barren gaps could develop wherecementation was poor, or dissolved prior tomineralization.

Thin sections were made of two samples from theFWS, 0.3 and 5 m below the unconformable OScontact. Both consist of matrix-poor feldspathic lithicsandstones with rounded to subrounded detrital k-feldspar, quartz, granitic and chert rock fragments,cemented by quartz and k-feldspar overgrowths.Abundant porosity (up to 30%) exists in both samples,and is defined predominantly by mm-sized, generallyrounded but irregular shaped holes. There is no Cu

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Figure 6, KLB67 and KLB83. (a) KLB67 barren gap intersection of Hangingwall Quartzite, Ore Shale, and FootwallSandstone. (b) KLB67, TS48 (HWQ), contact between feldspathic arenite and feldspathic greywacke, note detrital (bent)muscovite. (c) KLB67, TS50 (HWQ), quartz overgrowths trap early dust rims of rutile-hematite-(mica)n and a rutilepseudomorph after sphene. (d) KLB67, TS50 (HWQ), quartz cement after earlier k-feldspar overgrowth. (e,f) KLB67, TS51,Ore Shale E – D transition zone, contact between siltstone and pebbly arenite, hematite (reflected light) is fine-grained, afterilmenite/amorphous Fe oxides, notable lack of coarse grained hematite at contact.

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Figure 6, cont’d. (g,h) KLB67, TS52 (OSD), plane light and CL views of dolomite-(hematite) veinlet, with early zoned Fe/Mnrhombohedral dolomite and late, space-filling red-luminescent ferroan dolomite. (i,j) KLB67, TS53 (OSC), dolomite-biotite-muscovite (fine-grained) alteration and minor opaque hematite in feldspathic arenite. (k) KLB83, TS70 (HWQ), quartzovergrowths preserve diagenetic hematite-rutile-mica (clay) dust rims, hydrothermal/metamorphic biotite in groundmass.(l), KLB83, TS72 (FWS), ferroan dolomite alteration of groundmass and detrital quartz.

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or Fe staining associated with the holes, as might beexpected were they leached sulfide grains. Detritalfeldspar and quartz grains show no signs ofdissolution and are therefore unlikely to be the originof the porosity. This texture is common throughoutthe OS footwall and, to a lesser degree, hangingwallrocks in the Konkola area, and may be caused bydissolution of carbonate or sulfate.

In thin section, the original sedimentary compositionand morphology of the barren gap lithologies appearidentical to those in KLB145. The sandstones arepoorly sorted with up to 20% matrix, and containdetrital k-feldspar, quartz, muscovite and lithicfragments as described above (Figure 6b). Thesiltstones contain only rare lithic fragments, and agreater abundance of muscovite, but are otherwisesimilar to the sandstones.The detrital quartz, feldspar and lithic grains in thesandstones are commonly coated with “dust rims”of biotite and muscovite (after clay), hematite andrutile, preserved by k-feldspar and quartz over-growths (Figure 6c, d). The quartz is more abundantand locally forms a cement that post-dates theauthigenic feldspar. The quartz cement often showsundulose extinction and recrystallization, andtherefore pre-dates at least part of the Lufiliandeformation.

The matrix, detrital muscovite and to a minor extentthe k-feldspar grains and overgrowths are variablyovergrown by metamorphic/hydrothermal biotite.The biotite is commonly intergrown with, or partlyreplaced by dolomite, and also contains specularhematite and local rutile along cleavage planes.

Hematite most commonly occurs as disseminatedplaty and subangular to rounded, originallyoctahedral grains up to 1 cm in size (Figure 6e, f).The octahedral grains are composed of partly tocompletely martized magnetite and ilmenite, andlocally preserve octahedral cleavage and skeletalhabits. SEM/EDS study indicates that the hematiteconsistently contains minor amounts of Ti. The size

of the hematite grains is roughly proportional to thatof the surrounding detrital silicates. Unlike the Cusulfides, disseminated hematite does not formovergrowths on authigenic quartz and feldspar, andis interpreted as the metamorphic product ofdiagenetic and detrital Fe-Ti oxides. Hematiteabundance ranges between 0.5 and 3%, much lowerthan the sulfide content in KLB145.

The barren gap veinlets are composed predominantlyof dolomite, with lesser quartz, orthoclase, biotite,and minor specular hematite. The carbonate showsmultiple stages of growth under CL, from early darkFe-rich dolomite rhombs through successive euhedralovergrowths of varying Fe content, to a pore spacefilling cement of dark red luminescent dolomite(Figure 6g, h). Hematite is found within the laststage of dolomite. The veinlets have dolomite–biotitealteration haloes similar to those in KLB145 (Figure6i, j). This paragenetic sequence is similar to that ofthe mineralized veins, and suggests they were coeval.

In summary, the barren gap lithologies are identicalto those in the mineralized zone and preclude thepossibility that the gap is lithologically controlled.There is neither any evidence to support an origin bysecondary leaching of Cu sulfides. The sandstonesand siltstones in the barren gap appear to haveundergone the same diagenetic history, with earlyoxidation and weathering recorded by dust rims ofFe-Ti oxides and micas (clays), followed by laterdiagenetic k-feldspar and quartz overgrowths.Bedding-parallel veinlets, predominantly composedof carbonate, are present in the intersection, but aremuch less abundant than in the mineralized zone.There is a corresponding reduction in the amount ofdolomite alteration. Specular hematite occurs mainlyas disseminated grains that are texturally consistentwith an origin via metamorphism of detrital anddiagenetic Fe-Ti oxides.

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Konkola North Orebody Margin, DrillHole KLB83

Drill hole KLB83 was collared on the northern limbof the Kirila Bomwe Anticline, approximately 200 meast of the edge of the North ore body (Figure 1). Itintersected the OS at a depth of 715.2 to 731.2 m, fora calculated true thickness of 11.7 m. Assays rangedfrom 0.02 to 0.09% TCu. Fleischer et al. (1976) describethe eastern margin of the North orebody as coincidentwith a gradual facies change from interbeddedsandstones and siltstones to feldspathic arenitesindistinguishable from the footwall sandstones. Asin the barren gap transition, “approaching the marginof the orebody, the ore is confined to the top of theB unit and to the C unit”, in other words to thecarbonate-rich part of the section.

The core from KLB83 was examined briefly and threesamples taken. The OS in KLB83 is underlain by 10.8m of grey-pink, leached conglomerate (FWC) and17.7 m of grey, medium-grained feldspathicsandstone (FWS). It is overlain by grey to pinkfeldspathic sandstones and minor interbeddedsiltstones of the HWQ. Up to 5% specular hematiteoccurs in both the hangingwall and footwall rocks,as angular to rounded detrital grains (probably aftermagnetite) and platy, often euhedral crystals (afterilmenite and diagenetic amorphous iron oxides)

In thin section, quartz overgrowths are present inthe hangingwall sandstones and preserve diageneticdust rims (Figure 6k). Hydrothermal/metamorphicbiotite locally overgrows the groundmass. Thefootwall sandstone can be classified as a poorly sortedfeldspathic greywacke, with local matrix-poor bandsof feldspathic arenite. It is compositionally similar tothe sandstones described from the other drill holes.Coarse-grained dolomite and biotite are intergrownand replace the detrital grains and matrix to varyingdegrees (Figure 6l). Under CL the dolomite showsalternate Fe-rich and Fe-poor growth zones. Thepresence of dolomite in the OS footwall is interesting,

and may indicate migration of the altered (andmineralized?) interval - this is common elsewhere inthe Copperbelt on the margins of ore bodies.

As in the barren gap, each of the subunits of the OSoccurs in the KLB83 intersection, and, except for thepresence of hematite, there are no apparentdifferences in original composition from the rocks ofthe mineralized intersection. The OS interval containsup to 5% mm to cm bands of dolomitic sandstone,and no significant veining. Two samples werecollected, of a feldspathic greywacke at the uppercontact of the OS, and of a siltstone from unit B. Thefeldspathic greywacke contains local quartz grainswith authigenic overgrowths that preserve minutegrains of hematite and rutile as “dust rims”.Approximately 2% hematite also occurs as typicalrounded (detrital) and platy (authigenic) grains. Thesiltstone contains 1 to 2% similarly textured butcorrespondingly smaller grains of hematite and rutile.As in KLB67, the Fe-(Ti) oxide content in the OS ismuch less than the Cu sulfide content in theequivalent interval. Biotite is fine-grained, and thecoarse biotite associated with mineralization inKLB145 is absent.

In summary, the KLB83 intersection is similar to thatof the barren gap, containing only minor amounts ofcarbonate alteration and veining, disseminatedspecular hematite after probable authigenic Fe oxides,and preserved early diagenetic dust rims on detritalgrains. Additional sampling is required to morecompletely characterize the intersection.

Summary and Conclusions

The lithologies that host mineralization in KLB145are indistinguishable from those in the barren holes,KLB67 and KLB83, thus there does not appear to bea lithological control on the lateral distribution ofmineralization. The barren gap is not a carbonatebioherm, and in fact contains less carbonate (asalteration) than the mineralized interval. Also, thebarren holes do not consistently have a different

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footwall or hangingwall lithology that might controlmineralization.

Diagenetic features are readily observable in the cores,and are again relatively consistent between the barrenand mineralized intersections. They consist of earlyhematite, rutile and mica (after clay) dust rims ondetrital silicate grains, which are preserved by laterovergrowths of k–feldspar and quartz. No evidencewas found of Cu mineralization associated with thesefeatures. Hematite present within the barren holes isidentical to that in the hangingwall and footwall ofthe mineralized zone, but is volumetrically minor,usually less than 2%.

The Cu-Co mineralization in KLB145 is associatedwith hydrothermal / metamorphic ferroan dolomite,biotite and muscovite alteration and veins, in asequence of roughly symmetric zones. The highestcopper grades occur in a central, bornite-rich zoneassociated with abundant veins and dolomite-biotitealteration. Lower grades are found in proximalbiotite-muscovite alteration where chalcopyritedominates. Cobalt (carrolite, and possibly cobaltianchalcopyrite?) is highest where dolomite is poorlydeveloped or absent. Coarse-grained and oftenirregular sulfides are most abundant in the dolomiticzone, but present throughout. Platy or bladedsulfides, likely after hematite/ilmenite, are alsopresent throughout.

Dolomite veins and dolomite-biotite alteration alsooccur in the barren intersections, but lack sulfide,and are volumetrically less significant. The indicationis that these holes are on the fringes of thehydrothermal system. It would be anticipated thatwithin such a system any record of an earliermineralization event would be destroyed, and themineralized zone in KLB145 in fact lacks such arecord. However, it might also be expected that anyearlier event would be preserved on the margins ofthe hydrothermal system, and this is not the case. Itis therefore difficult to argue for there being twosuperimposed mineralizing events at Konkola.

Future work will include completing a sulfur isotopicstudy on the mineralization to determine whetherany variation exists amongst the texturally differentsulfides, and SEM/EDS study of the biotite todetermine whether metamorphic and hydrothermalphases can be distinguished.

References

Fleischer, V.D., Garlick, W.G., and Haldane, R., 1976, Geology ofthe Zambian Copperbelt, in Wolf, K.H., ed., Handbookof Strata-bound and Stratiform Ore Deposits, Volume 6:Elsevier, Amsterdam, p. 223-352.

Sweeney, M.A., and Binda, P.L., 1989, The role of diagenesis in theformation of the Konkola Cu-Co orebody of the ZambianCopperbelt, in Boyle, R.W. et al., eds, Sediment-hostedStratiform Copper Deposits, Geol. Assoc. Canada Sp. P.36, p. 499-518.

Documents

Progress Report Confidential · hematite-muscovite 1-2 mm thick, not seen in the unweathered porphyry. These same minerals occur locally in the groundmass, as irregular clots. Plagioclase