Steven Badenhorst and Petzel Au in Central Namibia

Communs geol. Surv. Namibia, 9 (1994), 63-78

A review of gold occurrences in the Northern and Central Zones of the Damara Orogen and the underlying mid-Proterozoic basement, central Namibia

N.M. Steven1*, F.P. Badenhorst2 & V.F.W. Petzel3 1Department of Geological Sciences, University of Cape Town, Rondebosch 7700, South Africa 2Navachab Gold Mine, Box 150, Karibib, Namibia 3Gold Fields Namibia, Box 3718, Windhoek, Namibia *Present Address: 10 Evergreen Lane, Constantia 7800, South Africa

Historically, late Proterozoic/early Palaeozoic Pan-African terranes have never been large producers of gold. The discovery of Dama- ran carbonate- and skarn-hosted gold mineralisation in the Karibib District in the 1980s came as a major surprise and the Navachab Gold Mine (10.4 million tonnes at ~2.4 g/t Au; annual production of approximately 1800 kg of gold) was opened in 1989. Further exploration in central Namibia has subsequently revealed that the underlying mid-Proterozoic basement, Damaran mafic volcanic rocks and turbidite sequences are also prospective for gold. This paper presents a geological and geochemical data base that has been compiled for gold occurrences in the Northern and Central Zones of the Damara Orogen with particular reference to mineralisation in the Usakos-Karibib-Omaruru area.

Introduction The geology of central Namibia with reference to gold mineralisation Interest in the gold potential of central Namibia was stimulated by a worldwide upsurge in gold exploration Central Namibia is essentially underlain by the inland, in the mid-1980s (Foster, 1993) and the discovery of NE-trending, ensialic branch of the well-documented Pan-African (late Proterozoic/early Palaeozoic) carbon- late Proterozoic/early Palaeozoic, Pan-African Damara ate and skarn-hosted gold mineralisation on the farm Orogen (Fig. 1; Martin and Porada, 1977; Martin, 1983; Navachab near the town of Karibib by Anglo American Miller, 1983a). Early Proterozoic (1.8-2.0 Ga) basement Prospecting Services Namibia Pty. Prior to the open- gneiss lithologies crop out in a series of inliers that floor ing of the opencast Navachab Gold Mine (10.4 million the orogen, the most prominent being the Abbabis In- tonnes at 2.4 g/t Au, annual production approximately lier (Fig. 2; Jacob et al., 1978). The pre-Damaran base- 1800 kg of gold; Badenhorst, 1993a, 1993b) in 1989, ment comprises both metasedimentary and metavol- only small-scale extraction of gold had been undertaken canic rocks, but the most common lithotype is granite in Namibia (Hirsch and Genis, 1992). The subtle and gneiss (Brandt, 1987). The Abbabis Inlier is cut by a regionally extensive nature of the gold skarn minerali- metadolerite swarm that was probably intruded dur- sation of the Karibib district was a major surprise in an ing the rifting that initiated the Damaran episode (Fig. area with no known significant gold deposits in spite 3; Steven, in press). The overlying Damara Sequence of a 125 year-long exploration history. A ‘gold rush’ (Table 1) comprises the metamorphosed equivalents of was precipitated in the late 1980s. Numerous showings fluviatile quartzites, limestones, marls, turbidites and of gold have subsequently been discovered (and some shales. Within the Damara Sequence, the proportion of rediscovered) in the past five years in central Namibia mafic volcanics and banded iron formations, both well- and it is now evident that not only the carbonates of documented hosts of gold mineralisation (Groves et al., the Damara Sequence, but also the underlying mid-Pro- 1990), is small (Table 1; Fig. 3). terozoic basement (Steven, 1992, 1993a), Damaran ma- Central Namibia has been intruded by numerous fic volcanic rocks (Pirajno et al., 1990a, 1991) as well granitoids which define the magmatic belt of the orogen as turbidite sequences (Steven, 1991, 1993a, 1993b) and are concentrated in the Central Zone (CZ; Miller, are prospective for gold. It is the aim of this paper to 1983a). In the lower metamorphic grade terrane of the present the empirical, descriptive data on type exam- Northern Zone (NZ), the plutons have wide thermal ples of the gold occurrences in the vicinity of the towns aureoles. Intrusions range in composition from I-type of Usakos, Karibib and Omaruru (i.e. the Northern and diorites, through S-type granites to rare-element pegm- Central Zones of the Damara Orogen, Figs. 1 and 2) atites (Miller, 1983a; Haack et al., 1983; Badenhorst, which would be of most practical use in further explo- 1986; Steven, 1993a), but the overwhelming number of ration. The stratigraphic setting of the gold occurrences plutons are granitic (sensu lato) in composition (Miller, has been emphasised, but the paper does not purport 1983a). The Damaran igneous suite possesses a ‘within- to be a genetic synthesis for the central Namibian gold plate’ rather than a calc-alkaline geochemical character. deposits: the fluid inclusion and stable isotope data base There is virtually a complete lack of intrusion hosted for this style of Namibian mineralisation is virtually sulphide and precious metal mineralisation in cen- non-existent. tral Namibia (Steven, 1993a). In post-Damaran times, swarms of Karoo dolerite dykes, post-Karoo granites

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64 Gold in Northern and Central Zones of the Damara Orogen

and volcanic complexes were emplaced. No significant Detailed geology of the known gold occurrences precious metal mineralisation nor hydrothermal alteration of the type associated with gold mineralisation The CZ gold mineralisation is mainly hosted by meta- has been recorded at any of the post -Karoo complexes sediments and, rarely, metavolcanic rocks, and appears (Pirajno et al., 1990b), though some anomalous gold to be epigenetic in nature. Gold mineralisation is struc- contents were recorded in a variety of lithotypes at the turally controlled: late-tectonic D3 (ENE/NE-trending)

Erongo caldera (Roesener, 1988). and D4 (NNE-trending) shear zones, faults (locally, thrusts) seem to be of particular importance (Steven and A review of gold mining in central Namibia Hartnady, 1993). Gold is spatially associated with late- tectonic leucogranites and pegmatites and occurs in five The central Namibian gold occurrences are shown main settings (in ascending stratigraphic order): (i) in in Figure 4 (after Martin, 1963 and Steven, 1993a). ENE-trending megashear zones and chlorite-magnetite Prior to 1989, gold had only been mined profitably on rocks on the margins of metadolerites in the Abbabis a small scale from turbidite-hosted gold veins and as- basement inlier; (ii) in minor auriferous veins in the sociated alluvial deposits at Ondundo (Reuning, 1937) Damaran Nosib Group quartzites; (iii) as Au-Bi-As-Te and from alluvial workings at Epako (Haughton et al., mineralisation in quartz veins and associated skarn al- 1939). Total gold production figures for Ondundo (both teration in the Swakop Group marbles and calc-silicate ‘hard-rock’ and alluvial) were approximately 700 kg of rocks; (iv) in alteration zones in the pyroclastic por- gold for the period 1924-1963 and 43 kg for Epako for tions of the Daheim Member metavolcanic rocks; (v) the period 1937-1943 (Hirsch and Genis, 1992). It is as Au-As-W-B mineralisation in quartz veins and both unlikely that the combined gold production from all the dilational and mylonitic structures in Swakop Group prospects shown in Figure 4 exceeded one tonne prior metapelites and metaturbidites. to the opening of the Navachab Gold Mine. All information concerning the known and recently discovered gold mineralisation in central Namibia has

65 Steven, Badenhorst & Petzel

been summarised in Table 2. Gold occurrences are listed to bulk mining (Badenhorst, 1993a). It can be referred in stratigraphic order using the revised stratigraphy for to as skarn mineralisation only in the broadest sense. the CZ of the Damara Orogen proposed by Badenhorst The proportion of skarn (i.e. silicate gangue) at these (1987, 1988) and followed by Steven (1993a). Type prospects is either very small (Navachab) or almost localities are described for each Formation that hosts nonexistent (Onguati). The recognition of the Kuiseb precious metal mineralisation. Localities are listed in Formation as both a potential gold reservoir and host alphabetical order within each Formation. The regional for gold mineralisation (Steven, 1993a) is important: geological setting, host lithology, form of mineralisa- gold has now been identified in turbiditic host rocks that tion, associated volcanic rocks, structural features, peak have undergone a wide range of metamorphic condi- metamorphic facies, associated Damaran intrusions, tions, from greenschist (Ondundo) to upper amphibo- suspected age of mineralisation, fire assay data, - geo lite facies (Sandamap Noord). Moreover, the concen- chemical association, ore minerals, gangue and second- tration of auriferous mineralisation within high strain ary minerals, associated alteration and provisional clas- zones, the type of gangue minerals and the Au-As-W sification are given. association in late Proterozoic turbidites is reminiscent Of the five main styles of mineralisation, the gold of Palaeozoic turbidite- and shale-hosted gold deposits in the basement lithologies, the Nosib Group quartz- (Sandiford and Keays, 1986; Tomkinson, 1988) and, to ites and probably the Daheim Formation metavolcanic a lesser extent, Archean greenstone belts (Colvine et al., rocks appears to be too erratically distributed for com- 1988; Phillips and Powell, 1993). This implies that the mercial exploitation. By far the most significant dis- well-documented structural and geochemical criteria covery of the 1980s is the carbonate-hosted gold min- used by gold explorationists in Archean greenstone belt eralisation of the Karibib area because it is amenable terranes (Groves et al., 1990) would be of use in locat-

66 Gold in Northern and Central Zones of the Damara Orogen ing turbidite-hosted gold in central Namibia. that penetrate deep into the granitic basement. Gold- bismuth mineralisation was concentrated in the vicinity The distribution and significance of the gold of late-tectonic leucogranites and lithium pegmatites pathfinder elements As, Bi, Sb and Te in central or in veins along major lineament systems. In con- Namibia trast, in the northern CZ (NCZ) and NZ gold-arsenic mineralisation is located in ductile, semi-ductile and The elements that show the highest correlation with brittle structures in the pelitic sediments of the Ober- gold on a regional basis, regardless of host rock and wasser and the Kuiseb Formations. In the CZ, where stratigraphic position, are arsenic and, to a lesser ex- peak metamorphic conditions (amphibolite facies) were tent, bismuth (Table 2, section 11). In the vicinity of notably higher than in the NZ (greenschist facies), the the Abbabis Inlier (Figs. 2 and 3), bismuth is usually two metals were concentrated in the aureoles of late- more effective than arsenic in assisting in the location tectonic granitic and pegmatitic intrusions. of auriferous zones in the Etusis and Karibib Forma- tions. In addition, both arsenic and bismuth commonly Structural analysis: the key to further have large primary dispersion haloes in the vicinity of gold exploration carbonate-hosted gold mineralisation. Somewhat sur- prisingly, antimony concentrations in areas of gold It is now clear that gold mineralisation in central Na- mineralisation are usually below the lower limit of de- mibia is located in late-tectonic, commonly linear, late- tection throughout the CZ. In the light of the discovery D3 and D4 structures. It is evident that, on the deposit ofhessite at the Onguati Copper Mine, the tellurium scale at least, further delineation of gold ore will only anomalies in the Kanona Ost area (De Greef, 1988) are come about with a clear understanding of the structural worthy of further investigation. Copper, lead and zinc geology (Badenhorst, 1993b). An attempt to determine concentrations are commonly anomalous in the vicinity the regional structural controls on CZ gold mineralisa- of central Namibian gold mineralisation, but of all the tion was made by Steven (1993a), though a more thor- so-called ‘pathfinder’ elements associated with gold, ar- ough integration of all the gold deposits in the Karibib senic and bismuth are of the most use. Information on district is necessary. Particularly favourable sites for thallium and mercury contents in the central Namibian gold deposition, such as at Sandamap Noord (Steven, gold occurrences is not available. 1991, 1993a), were late-tectonic high strain zones (and Two gold provinces can be distinguished in the CZ, possibly associated structures) which may have result- both of which are defined geochemically (Steven, ed from movement on major structures such as the Wel- 1993a). To the south of the Omaruru Lineament in the witschia lineament zone. southern CZ (SCZ; Fig. 3), influx of auriferous fluids A clearer understanding of the geodynamic setting may well have occurred via major crustal structures of the inland branch of the Damara Orogen is also re-

67 Steven, Badenhorst & Petzel quired. The CZ magmatic belt and its ensialic mineral in the Walvis Bay-Swakopmund area (Masberg et al., deposits (U, Sn, W) have traditionally been thought to 1992), the NW-SE orientation of metamorphic isograds have formed from the interaction and/or collision be- within the CZ (Steven 1993a), and the east -west orien- tween the Kalahari and Congo Cratons. Models that tation of D4 compression (Steven, 1993a) suggest that account for the formation of the inland branch of the hinterland magmatism behind the west-vergent Dom Damara Orogen range from those proposing ensialic Feliciano calc-alkaline arc in Brazil and Uruguay may evolution in an aulacogen (Martin and Porada, 1977) have played a more important role in Damaran gold to ensialic development followed by subduction as a re- metallogenesis (Steven and Hartnady, 1993). In gener- sult of delamination of the lower crust (Kröner, 1982) al, the Central Zone gold deposits formed at the end of to those invoking extensive north-westward subduction a prolonged tectonothermal event which culminated in of oceanic crust (Kasch, 1983; Miller, 1983a, 1983b; voluminous igneous intrusion. Thus both metamorphic Stanistreet et al., 1991). Any geodynamic model that and magmatic fluids are implicated in the formation of equates the magmatic belt of the CZ with the magmatic/ central Namibian gold deposits. volcanic arcs of the Circum-Pacific is of very limited use in gold exploration in central Namibia: the CZ in- Acknowledgements trusions and associated mineral deposits are ensialic in nature (Steven, 1993a). The thermal metamorphic high This paper largely rests on a geochemical data base

68 Gold in Northern and Central Zones of the Damara Orogen

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74 Gold in Northern and Central Zones of the Damara Orogen

75 Steven, Badenhorst & Petzel that was sponsored by Gold Fields South Africa and M46/3/1652 Kanona Ost, Anglo American Pros- Gold Fields Namibia. N.M.S wishes to thank both com- pecting Services Namibia (Pty.) Ltd. panies for generous financial and logistical support. Foster, R.P. 1993. Gold metallogeny and exploration. N.M.S. also acknowledges support from the Council Chapman and Hall, London, 448 pp. for Scientific and Industrial Research (CSIR) of South Frommurze, H.F., Gevers, T.W. and Rossouw, P.J. 1942. Africa. The consulting geologists Richard Viljoen The geology and mineral deposits of the Karibib (Gold Fields) and Roger Attridge (Erongo Mining and area, South West Africa. Explanation to Sheet 79, Exploration Company, managers of the Navachab Gold Geological Survey of South Africa, 172 pp. Mine) are thanked for allowing the release of unpub- Groves, D.I., Barley, M.E., Cassidy, K.F., Fare, R.J., lished data. Dick Rickard (Department of Geological Hagemann, S.G., Ho, S.E., Hronsky, J.M.A, Sciences, University of Cape Town) is thanked for con- Mikucki, E.J., Mueller, A.G., McNaughton, N.J., siderable assistance with electron microprobe analysis. Ridley, J.R. and Vearncombe, J.R. 1990. Subgreen- James Willis, Andy Duncan and Dave Reid (University schist to granulite-hosted Archean lodegold depos- of Cape Town) are thanked for answering numerous an- its: a depositional continuum from deep-sourced alytical questions which assisted in the compilation of hydrothermal fluids in crustal-scale plumhing sys- the geochemical data base. John Moore (Rhodes Uni- tems?, 357-359. Third Archean Symposium, Perth, versity), Roger Jacob (Rhodes University) and Marcus Australia. Tomkinson (Anglovaal Namibia) are thanked for re- Haack, U. and Gohn, E. 1988. Rb-Sr Data on some viewing earlier versions of this paper. Move Steven is pegmatites in the Damara Orogen. Communications thanked for her assistance with the diagrams. of the Geological Survey of Namibia, 4, 13-18. Haack, U., Hoefs, J. and Gohn, E. 1983. Genesis of References Damaran granites in the light of Rb/Sr and 18O data, 847-872. In: Martin, H. and Eder, F.W., Eds., Intra- Badenhorst, F.P. 1986. ‘n Voorlopige petrografiese stud- continental Fold Belts. Springer Verlag, Berlin, Hei- ie van die granitiese gesteentes van Gebied 2115B delberg, 945 pp. in die noordelike Sentrale Sone van die Damaraoro- Haughton, S.H., Frommurze, H.F., Gevers, T.W., geen. Communications of the Geological Survey of Schwellnus, C.M. and Rossouw, P.J. 1939. The ge- S.W.A./Namibia, 2, 13-26. ology and mineralogy of the Omaruru area, South Badenhorst, F.P. 1987. Lithostratigraphy of the Damara West Africa. Explanation to Sheet 71, Geological Sequence in the Omaruru area of the northern Cen- Survey South Africa, 151 pp. tral Zone of the Damara Orogen and a proposed cor- Hirsch, M.F.H. and Genis, G. 1992. The Mineral Re- relation across the Omaruru Lineament. Communi- sources of Namibia - Gold, 18. Section 4.1. Publica- cations of the Geological Survey of S.W.A./Namibia, tion of the Geological Survey of Namibia. 3, 3-8. Jacob, R.E., Kröner, A. and Burger, A.J. 1978. Areal ex- Badenhorst, F.P. 1988. A note on stratiform tourma- tent and first U-Pb age of the pre-Damaran Abbabis linites in the Late Precambrian Kuiseb Formation, complex in the central Damara belt of South West Damara Sequence. Communications of the Geologi- Africa. Geologische Rundschau, 67(2), 706-718. cal Survey S.W.A./Namibia, 4, 67-70. Kasch, K.W. 1983. Continental collision, suture pro- Badenhorst, F.P. 1993a. The Navachab Gold Mine in gradation and thermal relaxation: A plate tectonic central Namibia, Conference on Mining Investment model for the Damara Orogen in central Namibia. in Namibia, Windhoek, 17th -19th March, Ministry of Special Publication of the Geological Society of Mines and Energy publication, 1993, 33-34 South Africa, 11, 423-429. Badenhorst, F.P. 1993b. The Navachab skarn gold de- Keppie, J.D., Boyle, R.W. and Haynes, S.J. Eds. 1986. posit in central Namibia. Mineral Exploration ‘93 Turbidite-hosted gold deposits. Geological Associa- conference, Cape Town, 18th-20th August, 1993. tion of Canada Special Paper, 32, 186 pp. Brandt, R. 1987. A revised stratigraphy for the Abbabis Kröner, A. 1982. Rb-Sr geochronology and tectonic ev- Complex in the Abbabis inlier, Namibia. South Afri- olution of the Pan-African Damara Belt of Namibia, can Journal of Geology, 90 (3), 314-323. southwestern Africa. American Journal of Science, Colvine, A.C., Fyon, J.A., Heather, K., Marmont, S., 282, 1471-1507. Smith, P.M. and Troop, D.G. 1988. Archean lode Martin, H. 1963. Geological map of South West Africa gold deposits in Ontario. Ontario Geological Sur- (1:1,000,000). vey, Miscellaneous Paper, 139, 136 pp. Martin, H. 1983. Alternative geodynamic models for Corner, B. 1983. An interpretation of the aeromagnetic the Damara Orogeny: A critical discussion, 913-945. data covering the western portion of the Damara In: Martin, H. and Eder, F.W., Eds., Intracontinental Orogen in S.W.A./Namibia. Special Puhlication Fold Belts. Springer Verlag, Berlin, Heidelberg, 945 of the Geological Society of South Africa, 11, 339- pp. 354. Martin, H. and Porada, H. 1977. The intracratonic De Greef, R. 1988. Final prospecting report on grant branch of the Damara Orogen in South West Africa.

76 Gold in Northern and Central Zones of the Damara Orogen

I. Discussion of geodynamic models. Precambrian Smith, D.A.M. 1965. The geology of the area around Research, 5, 311-338. the Khan and Swakop Rivers in S.W.A. Memoir of Masberg, H.P., Hoffer, E. and Hoernes, S. 1992. Micro- the Geological Survey of South Africa, South West fabrics indicating granulite-facies metamorphism in Africa Series, 3, 113 pp. the low-pressure central Damara Orogen, Namibia. Stanistreet, I.G., Kukla, P.A. and Henry, G. 1991. Sedi- Precambrian Research, 55, 243-257. mentary basinal responses to a Late Precambrian Miller, R.McG. 1980. Geology of a portion of Central Wilson Cycle: the Damara Orogen and Nama Fore- Damaraland. Memoir of the Geological Survey of land, Namibia. Journal of African Earth Sciences, South Africa, South West Africa Series, 6, 78 pp. 13, 141-156. Miller, R.McG. 1983a. The Pan-African Damara Oro- Steven, N.M. 1991. Turbidite-hosted gold mineralisa- gen of S.W.A./Namibia. Special Puhlication of the tion at the Sandamap Noord prospect, central Na- Geological Society of South Africa, 11, 431-515. mibia, 567-574. In: Ladeira, E.A., Ed., Proceedings Miller, R.McG. 1983b. Economic implications of plate of Brazil Gold ‘91, An International Symposium on tectonic models of the Damara Orogen. Special the Geology of Gold: Belo Horizonte, 1991. Balke- Puhlication of the Geological Society of South Af- ma, Rotterdam, Holland 823 pp. rica, 11, 385-395. Steven, N.M. 1992. A study of epigenetic mineralisa- Navachab Gold Mine Field Guide. 1989. Prepared for tion in the Central Zone of the Damara Orogen, Na- the Geological Society of Namibia by Erongo Min- mibia with special ref’erence to gold, tungsten, tin ing and Exploration Company. and rare earth elements. Unpublished Ph.D. thesis, Phillips, G.N. and Powell, R. 1993. Link between gold University of Cape Town, 221 pp. provinces. Economic Geology, 88, 1084-1098. Steven, N.M. 1993a. A study of epigenetic mineralisa- Pirajno, F. and Jacob, R.E. 1991. Gold mineralisation in tion in the Central Zone of the Damara Orogen, Na- the intracontinental branch of the Damara Orogen, mibia with special reference to gold, tungsten, tin Namibia: a preliminary survey. Journal of African and rare earth elements. Memoir of the Geological Earth Sciences, 13, 305-311. Survey of Namibia, 16, 166 pp. Pirajno, F., Jacob, R.E. and Petzel, V.F.W. 1990a. Mar- Steven, N.M. 1993b. The Sandamap Noord gold pros- ble-hosted sulphide and gold mineralisation at On- pect, central Namibia: Discovery of anew style of guati-Brown Mountain, southern central zone of the turbidite-hosted gold mineralisation. International Damara Orogen, Namibia, 443-446. 23rd Earth Sci- Geology Review, 35, 840-854. ence Congress of the Geological Society of South Steven, N.M. Mafic dykes in the pre-Damara basement, Africa. south-east of Usakos, central Namibia. Communica- Pirajno, F., Roesener, H., and Petzel, V.F.W. 1990b. The tions of the Geological Survey of Namibia, 9 (this volcanic history of the Paresis igneous complex, volume). 447-450. 23rd Earth Science Congress of the Geo- Steven, N.M. and Hartnady, C.J. 1993. Early Palaeozo- logical Society of South Africa, Cape Town, 2nd-6th ic gold metallogeny in the Damara Orogen, A-100. July 1990. Joint Annual Meeting of the Geological Association Pirajno, F., Jacob, R.E. and Petzel, V.F.W. 1991. Dis- of Canada/Mineralogical Association of Canada, tal skarn-type mineralisation in the Central Zone of Edmonton, Alberta, May 1993. the Damara Orogen, Namibia, 95-100. In: Ladeira, Tomkinson, M.J. 1988. Gold mineralisation in phyllo- E.A., Ed., Proceedings of Brazil Gold ‘91, An Inter- nites at the Haile Mine, South Carolina. Economic national Symposium on the Geology of Gold. Belo Geology, 83, 1392-1400. Horizonte, 1991. Balkema, Rotterdam, Holland 823 Van Loon, 1984, Accurate determination of the noble pp. metals I: Sample decomposition and methods of- Reuning, E. 1937. Die Goldfelder von Ondundo, Süd- separation. Trends in Analytical Chemistry, 3, 272- westafrika. Geologische Rundschau, 28 (34), 229- 275. 239. Roesener, H. 1988. Progress report on exploration Appendix: Analytical methods conducted in the Erongo Caldera prospecting grant M46/3/1611. Unpublished report of Gold Fields The analysis of gold in whole rock samples South Africa, 40 pp. The geochemical information presented in this paper Rossouw, P.J. 1937. Alluvial gold occurrences at Epako is mainly taken from a data base compiled by N.M.S. 38, Omaruru District. Unpublished Report. and V.F.W.P. for Gold Fields Namibia. In 1987 and 1988 Sandiford, M. and Keays, R.R. 1986. Structural and the gold contents of approximately 1300 (thirteen hun- tectonic constraints on the origin of gold deposits in dred), 5-10 kg pre-Damaran and Damaran rock samples the Ballarat Slate Belt, Victoria, 15-24. In: Keppie, were determined by atomic absorption spectrometry J.D., Boyle, R.W. and Haynes, S.J., Eds., Turhidite- (AAS) by Scientific Services Pty., Cape Town (referred hosted gold deposits. Geological Association of to as AAS scan analysis). The technique employed was Canada Special Paper 32, 186 pp. a modification of the one described by van Loon (1984).

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Rocks were crushed and milled to finer than 100 mesh were obtained by XRF analysis. Readers interested in and pre-leached with HCl. A second leach with Aqua the concentrations of pathfinder elements in unaltered Regia was followed by stripping of the gold into DIBK Damaran metasediments and metavolcanic rocks (i.e. and Aliquot 336. Gold contents were then determined background levels) in the Usakos-Karibib-Omaruru by AAS. Numerous duplicates were analysed. Scien- area are referred to a geochemical data base presented tific Services Pty. claimed a lower limit of detection by Steven (1993a, chapter 2). of 30 ppb Au for this technique. The gold contents of those samples containing in excess of 300 ppb Au were Mineralogy then determined by fire assay by Scientific Services and The minerals described in Table 2 were optically McLachlan and Lazar CC, Johannesburg. Both compa- identified where possible with a Nikon polarising mi- nies indicated lower limits of detection (LLD) of ap- croscope in transmitted and reflected light in the De- proximately 50 ppb for their fire assay analyses. partment of Geological Sciences, University of Cape Town. Many of the secondary minerals, such as the The analysis of ‘pathfinder elements’ in whole rock carbonates, sulphates, arsenates and oxides were identi- samples fied by x-ray diffraction (XRD). Sulphide phases were Copper, lead, zinc and silver concentrations were de- identified using a Cameca Camebax microbeam elec- termined by AAS by the aforementioned commercial tron microprobe. Operating conditions for the electron laboratories, Sn, W, Mo, As, Sb, Bi, Se and Te contents microprobe analysis were detailed by Steven (1993a).