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Abstract

The Rössing South uranium deposit in Namibia is one of the largest undeveloped uranium deposits in the world and is viewed by many industry participants as the most significant global uranium discovery in the present cycle. Current resources total 121,000 metric tons (t) of uranium oxide, and further exploration is likely to substantially increase the resource inventory. Since its discovery in early 2008, approximately 200,000 m of resource drilling has been completed through January 2010, principally on the Rössing South zones 1 and 2. Further zones of uranium mineralization have been intersected, and these await sufficient drilling to warrant resource estimation. The Rössing South deposit is located approximately 7 km directly south of the Rössing uranium deposit and is separated from it by the Khan River Canyon. The Rössing deposit is the only mining operation currently exploiting the uranium-bearing leucogranites of the Namibian Erongo region uranium province and has been in continuous production since 1976. It produces approximately 7 percent of the annual global supply of uranium oxide. Rössing South shares many geologic characteristics with the Rössing deposit, although it is located on the opposite limb of the regional Kuiseb syncline. The overall in situ grade of the Rössing South uranium mineralization, as it is currently defined, is approximately 480 ppm U3O8, which is about 25 percent higher than historically mined grades at the Rössing deposit (i.e., ~350-400 ppm U3O8) The Rössing South discovery is currently the subject of a feasibility study that has the objective of establishing the viability of a potential globally significant mining operation based on the known uranium resources of zones 1 and 2.

Introduction

Rössing South is located 56 km east-northeast of the coastal resort town of Swakopmund within the Erongo region uranium province of west-central Namibia. The deposit lies at the northern end of Exclusive Prospecting License (EPL; EPL3138, Fig. 1), which is wholly owned by a local subsidiary of Extract Resources Limited, a public company listed in Australia, with secondary listings in Canada and Namibia. EPL3138, together with the neighboring license EPL3439, also owned by Extract Resources Ltd., comprise the Husab project.

In late 2007, a traverse of three-angled reverse circulation bore holes was drilled beneath low-level uranium anomalies returned from prior shallow drilling below approximately 40 m of transported overburden. When the assays were returned in early 2008, it was clear that a significant primary uranium occurrence had been discovered on the margins of the Namib Desert, 7 km directly south of the large open-pit Rössing uranium mine. Intensive drilling carried out during 2008 and 2009 outlined a large leucogranite and/or pegmatite (alaskite)-hosted uranium system over at least 8 km of strike length. Drilling continues to the present, with the limits of the system yet to be defined. Total uranium resources at Rössing South are currently 121,000 t of uranium oxide in situ, and this is expected to increase over time with further drilling. Such a resource places Rössing South within the top ten of global uranium resources, and further work is expected to promote Rössing South into the group of the top five global deposits, which already includes the Rössing deposit to the north.

Namibia has been a uranium producer since 1976 and is currently fourth in global production after Kazakhstan, Canada, and Australia (WNA, 2010). Two deposits in Namibia are in production, Rössing and Langer Heinrich, and a third mine, Trekkopje, is under construction. Both primary and secondary calcrete-hosted deposit styles are being exploited. Rössing South, together with Rössing and a number of other deposits in general proximity to each other, are hosted primarily by granitic dikes and pegmatites, which have been classified in the field as alaskites. Close to one-half million tons of uranium oxide has been identified to date, hosted by intrusions in Namibia, of which approximately one-quarter has been mined historically from the Rössing deposit. Although low-grade, typically 200 to 500 ppm U3O8, large tonnages, suitability for open-pit mining and generally with good metallurgical characteristics, allow for these deposits to be favorable economical targets.

Regional Geologic Setting

The major stratigraphic elements of the immediate Rössing South area are shown in Table 1. The Erongo Region uranium province is located within the south-central zone of the Pan-African Damara orogenic belt within the coastal region of central Namibia. The significant uranium deposits within this belt, both primary and secondary calcrete-hosted, are located within and marginal to the Namib Desert, a hyperarid coastal desert extending northward from the southern border of Namibia, through western Namibia and beyond the northern border of the country. Surficial uranium occurrences are widespread within the Namib Desert and relate to climatic and geomorphologic controls, whereas primary uranium occurrences hosted by leucogranites are much more restricted in geographic extent. The primary deposits require a specific pressure-temperature domain, intrusive type, and the exhumation and exposure of the midcrust within basement domes, to form deposits capable of economic exploitation.

Fig. 1.

Rössing South project—general location plan, showing the location within Namibia of the Husab project lease boundaries and the location of the Rössing South deposit. (Google Earth, 2010).

Fig. 1.

Rössing South project—general location plan, showing the location within Namibia of the Husab project lease boundaries and the location of the Rössing South deposit. (Google Earth, 2010).

Most primary uranium deposits within the Erongo region uranium province are geographically restricted to a narrow belt extending from the Valencia deposit in the northeast, to the Ida dome (Fig. 1) in the southwest, an area approximately 70 by 30 km. The uranium-bearing granites coincide with a belt of high-temperature, low-pressure metamorphism within the south-central zone of the Neoproterozoic Damara orogen (Kinnaird and Nex, 2007). In this area, postrifting collision and associated crustal shortening along the margins of the Congo and Kaapvaal cratons resulted in intense isoclinal folding within the collision zone, with associated exhumation and doming of older gneissic rocks of the Paleoproterozoic to Mesoproterozoic Abbabis Metamorphic Complex. Neoproterozoic rocks of the lower Damara section of the Pan-African mobile belt are complexly folded surrounding the basement cores in dome and basin topography. Localized faulting, including possible thrusting, accompanied the folding (Anderson and Nash, 1997), with faults subsequently providing conduits for transport of leucogranite melts and dilational sites for the subsequent, generally passive, emplacement of alaskitic granites and pegmatites. The significantly elevated geothermal gradient, at a midcrustal level, resulted in a variety of granitic melts through anatectic processes. The uraniferous leucogranite intrusions were the last major phase to crystallize postpeak metamorphism (Kinnaird et al., 2009a). The source rocks for the uranium within the mineralized leucogranites remain enigmatic, but field evidence from elsewhere within the Husab project, including uranium mineralization hosted directly within basement gneiss, suggests that metal recycling from the Abbabis Metamorphic Complex during anatexis is probable.

Table 1.

Generalized Stratigraphy of the Rössing South Area (after Nash, 1971); Nex, 1997; and Kinnaird and Nex, 2008)

SequenceGroupSubgroupFormationDescriptionAge (Ma)
KuisebSchist, minor quartzite~650
KhomasKaribibMarble, calc-silicate, schist
ChuosDiamictite, pelitic schist, biotite gneiss, pebble gneiss~710
SwakopRössingMinor marble, calc-silicate, quartzite, biotite schist, gneiss
DamaraUgabUraniferous granite sheets~510
NosibKhanAmphibole-pyroxene gneiss, schist
EtusisQuartzite, psammitic gneiss752 ± 7
Abbabis Metamorphic ComplexRed granite gneiss, metasediment, amphibolite~2000
SequenceGroupSubgroupFormationDescriptionAge (Ma)
KuisebSchist, minor quartzite~650
KhomasKaribibMarble, calc-silicate, schist
ChuosDiamictite, pelitic schist, biotite gneiss, pebble gneiss~710
SwakopRössingMinor marble, calc-silicate, quartzite, biotite schist, gneiss
DamaraUgabUraniferous granite sheets~510
NosibKhanAmphibole-pyroxene gneiss, schist
EtusisQuartzite, psammitic gneiss752 ± 7
Abbabis Metamorphic ComplexRed granite gneiss, metasediment, amphibolite~2000

All of the known granite-hosted uranium deposits within the uranium province share generally similar characteristics and the ~510 Ma age of granite emplacement (Kinnaird et al., 2009b), suggests that they are the product of the same set of magmatic processes. An overview of the regional geology of the Husab project is shown in Figure 2.

Characteristics of Rössing-Style Uranium Deposits

Namibian leucogranite-hosted uranium deposits share many geologic characteristics. This is not surprising, given that they appear to be products of a regional-scale magmatic-hydrothermal event. For the explorationist, these shared characteristics have a powerful predictive quality, and a basic understanding of the genetic model for Rössing-style deposits directly provided the targeting concepts leading to the Rössing South discovery. The characteristics of Rössing-style deposits in the Erongo region of Namibia are summarized below.

Fig. 2.

Geology of the Rössing South project area from a lithostructural interpretation of aeromagnetic data (Core, 2010).

Fig. 2.

Geology of the Rössing South project area from a lithostructural interpretation of aeromagnetic data (Core, 2010).

Proximity to basement complexes

All of the known deposits are sited in 752 to 710 Ma rocks of the lower Damara sequence (Nosib to lower Swakop Groups) and proximal to domelike basement features. The deposits are typically located 2 to 6 km from outcropping Abbabis Metamorphic Complex rocks and domal structures. In some areas, particularly within the Husab Basement Complex in the area of the Swakop River Canyon, strongly anomalous uranium concentrations have been noted within basement rocks themselves, locally associated with quartz-fluorite veining, as well as with leucogranite dikes and associated hematite-bearing alteration assemblages The basement complexes appear to have acted as rigid buttresses around which deformation associated with episodes of crustal shortening created dilational sites within the overlying receptive Damara lithologic units.

Host rocks

Most granite-hosted uranium occurrences in the Erongo region uranium province show an intimate relationship with particular lithofacies within lower Damara sequence rocks, principally metasedimentary units of the Khan and Rössing Formations. The semiconformable contact between the two represents a cyclical break between predominantly terrigenous sedimentation (Khan Formation), followed by a period dominated by calcareous lithotypes (Rössing Formation). Overlying the Rössing Formation, rocks of the Chuos Formation represent an intercession of marine ice sheets that temporarily interrupted carbonate deposition, which subsequently resumed with retreat of the ice and deposition of rocks of the Karibib Formation. Although potentially any of the above lithostratigraphic elements are able to host uranium-bearing granite dikes and pegmatites, the two largest granite-hosted deposits in the area, Rössing and Rössing South, are hosted mainly within the Khan and Rössing Formation lithologic units. The Chuos Formation can also host uranium-rich, sheeted leucogranites. Local examples include patchy mineralization in the Rössing South hanging wall in the northern half of zone 1, and the Z19 locality within the adjacent Rössing mining license, but, in general, the formation is a poor ore host. It is postulated that the heterogeneous nature of Rössing Formation lithotypes, variously quartzites and mica schists, together with interlayered calc-silicate and marble bands, offered favorable brittle-ductile rheological responses to regional deformation and thereby allowed access to invading leucogranite melts. Additionally, the regional transition from terrigenous to calc-silicate–dominated sedimentation may have offered both physical and chemical trap sites to invading leucogranite magmas. Thick impervious marble sequences may have trapped granitic melts and associated aqueous phases beneath them, and the increased availability of CO2 in this environment may have affected the oxidation-reduction potential of the uranium contained within the crystallizing leucogranites (Kinnaird et al., 2009a, b). Field evidence suggests that rocks of the Arandis Formation, which are locally present between those of the Chuos and Karibib Formations in the Rössing South area, are in fact upper Chuos Formation. They have been heavily altered and sulfidized during hydrothermal activity and granitic melts ponded beneath thick overlying marble sequences of the Karibib Formation. Similarly, a reconstruction of the preerosional antiform above the currently defined Rössing South deposit reveals a thick capping of Karibib Marble above the mineralized zones. At the present erosional level, the marble bands are restricted to outcropping ridges flanking the Rössing South anticline.

Structural preparation

All the granite-hosted uranium deposits found in the Erongo region are located in the southern part of the central zone of the Damara orogen, which is an area bounded to the north by the Omaruru lineament and to the south by the Okahandja lineament (Fig. 3). Granite-hosted uranium deposits in the Erongo region occupy extensional zones within an overall high strain regime brought about by northwest-southeast shortening associated with the Neoproterozoic Damara orogeny. They occupy pull-apart zones and jogs associated with faulting, pressure shadows associated with strain partitioning surrounding domes, and dilatancy associated with fold hinges. Observation suggests that these extensional areas are often very much larger than the actual deposits. The subeco-nomic areas of the extensional zones nevertheless contain voluminous pegmatites, characteristically weakly mineralized, and generally within footwall rocks marginal to the deposits. Typical examples of this are the southeastern flanks of the Ida dome and the Khan mine area to the west of the Rössing deposit. A similar but poorly outcropping example occurs in the Rössing South footwall, where spatially extensive and generally unmineralized to weakly mineralized reddish granite dikes intrude gneiss of the Khan Formation. We suggest that extensive areas of Nosib Group rocks characterized by weakly mineralized invasive pegmatites may be potential vectors to mineralization, and their absence may be seen as a negative indicator.

During the Damara orogeny both the basement and the overlying Damara sequence metasedimentary rocks were subjected to polyphase deformation. The earliest event (D1), restricted to the Damaran metasedimentary rocks, resulted in a series of south- to south-southeast–verging recumbent folds; D2 deformation resulted in north-northeast–trending, upright tight folds; and D3 resulted in a strong northeast-trending structural fabric, with well-defined basins and domes (Nex et al., 2009b). A final (D4) event has been identified (Anderson and Nash 1997) that led to sinistral, strike-slip, north-northeast–trending faulting, rotation of earlier structures, and northeast-oriented thrusting.

There is an apparent spatial relationship of the larger granite-hosted deposits, including Rössing and Rössing South, with the late (post-D3) north- to northeast-trending Welwitschia lineament (Fig. 3), first identified by Corner (1982). Whereas we do not view this structure as a through-going shear zone, but rather as an interconnected series of en echelon fault segments acting to transfer strain obliquely across the southern central zone of the Damara orogen, it is considered very likely that this fault corridor was an important conduit for migrating leucogranite melts and an extensional zone for passive granite emplacement. Three of the known alaskite deposits are proximal to this structure, including the two largest and highest grade deposits in Rössing and Rössing South.

Fig. 3.

Granite-hosted uranium deposits of the Erongo region and their location within the southern central zone of the Damara orogen.

Fig. 3.

Granite-hosted uranium deposits of the Erongo region and their location within the southern central zone of the Damara orogen.

Deposit scale

Granite-hosted deposits of the region are characterized by high ore tonnages and low uranium grades (Table 2), which make them amenable to large-scale open-pit mining. They exhibit somewhat variable but generally favorable metallurgy for conventional acid leach processing. With an upper size limit above 150,000 t of uranium oxide, they have world-class potential, combined with low operational and technical risk. The hyperarid Namib Desert is well suited to the mining and processing of uranium ores on a large scale.

Leucogranite classification

Although many uranium-bearing leucogranites in the Erongo region uranium province are alkali feldspar granites, others fall into the granodiorite, monzogranite, and syenogranite fields, and even tonalite and quartz-rich varieties are possible (Kinnaird and Nex, 2007). The term alaskite is a field term of long standing and now ineradicable but is by no means wholly accurate if used sensu strictu. Nex et al. (2001), working mainly in the Goanikontes area, 26 km to the southwest of Rössing South, determined a chronological field classification of sheeted leucogranites based on mineralogy, intrusive habit, and field relationships. Six varieties of leucogranites were identified (types A-F), of which two of the later varieties, types D and E, are of most economic significance.

Freemantle and Kinnaird (2009a, b) recognized a number of different types of sheeted leucogranites at the Valencia deposit, located approximately 30 km northeast of Rössing South. Five main types have been recognized, of which only one (type 4) is significantly enriched in uranium.

Freemantle (2009) noted D- and E-type granites in six Rössing South core samples selected for hand specimen and thin section petrology, together with quantitative evaluation of materials by scanning electron microscopy (QemSCAN) analysis. Whereas types D and E both contain potentially economic levels of uranium mineralization, type E is differentiated by ferruginous alteration resulting from enhanced oxidation. All of the mineralized dike material was classified as medium to coarse or pegmatitic granite, with variable grain size noted as a key feature (Freemantle, 2009).

Table 2.

Tonnages, Grades and Contained U3O8 for Granite-Hosted Uranium Deposits of the Erongo Region, Namibia

DepositMillion metric tons (Mt)Grade ppm U3O8Tons U3O8
Rössing (resource and reserves)130526179,700
Rössing1 (historic production)?350-40097,800
Rössing (total)177,500
Rössing South (zone 1 + 2)2249488121,000
Etango333122273,500
Valencia427114639,000
ida dome25321311,000
DepositMillion metric tons (Mt)Grade ppm U3O8Tons U3O8
Rössing (resource and reserves)130526179,700
Rössing1 (historic production)?350-40097,800
Rössing (total)177,500
Rössing South (zone 1 + 2)2249488121,000
Etango333122273,500
Valencia427114639,000
ida dome25321311,000
1

www.Rössing.com

2

www.extractresources.com

3

www.bannerman.com.au

4

www.forsysmetals.com

Mineralization style

The main host to uranium mineralization at Rössing South is leucogranite intrusions emplaced into rocks of the Rössing Formation. The dominant uranium mineral is uraninite, which typically occurs as finely disseminated grains, usually <120 µm (Townend, 2009). Commonly, the uranium-bearing leucogranites contain smoky quartz and abundant coarsegrained biotite. Some intervals of >50 percent coarse biotite have been intersected in drill holes and these often return very high grades of >2,000 ppm U3O8.

Approximately 75 to 80 percent of the mineralized (>75 ppm U3O8) samples are in material that has been logged as granitic. The remaining 20 to 25 percent of sampled mineralized material is comprised of calc-silicate, biotite schist, and gneiss. In many cases, it appears that these other mineralized lithologic units contain minor veinlets of leucogranite and typically they occur in close proximity to bodies of leucogranite. However, there are some mineralized samples with no obvious granitic material in them that have probably been mineralized by fluids exsolved from the adjacent leucogranite units.

Secondary mineralization, provisionally identified as boltwoodite (Townend. 2009), is often observed in the form of fine veinlets and coatings on joint surfaces and can occur at depths greater than 300 m. The upper ~100 m of the deposit often shows a depletion of uranium of as much as 40 percent, compared to the material deeper than 100 m. This, together with the presence of secondary uranium minerals, suggests that there have been localized episodes of leaching, remobilization, and redeposition of uranium.

Discovery History

The Rössing South gravel plain was identified as a significant exploration target for leucogranite-hosted uranium mineralization in 2006. The geologic reasoning was that aeromagnetic data indicated that the Damara stratigraphy underlying the gravel plain at the northern end of the license was essentially similar to that seen in the Rössing mine area approximately 7 km to the north. Furthermore, the Khan and/or Rössing Formation contact on both limbs of the Kuiseb syncline could be observed in the Khan River Canyon outside of the exclusive prospecting license, where weakly mineralized leucogranite sheets accompanied the prospective stratigraphy. Aeromagnetic data further suggested that, particularly on the eastern limb of the major syncline, an extensive corridor of concealed Khan Formation lithologic units was present, and this corridor was apparently disrupted by fault offsets (Fig. 4). The presence of outcropping uranium mineralization in the Z19 area of the Rössing mining license, approximately 2.5 km north of Rössing South zone 1, further supported the concept of targeting the Khan and/or Rössing Formation contact interpreted to lie beneath the gravel plain of the Namib Desert in the locality of what is now Rössing South.

All drilling at Rössing South has been referenced to a UTM grid (WGS84_zone 33 South). A program of drilling was commenced in April 2007. At that time, little progress was made because the drill rig was quickly called away for resource drilling work on the advanced Ida Dome targets. Drilling recommenced in September 2007. Of the holes drilled in April 2007, both spectral bag assays (i.e., hand-held spectrometer assays directly measuring drill cuttings in the sample bag) and later chemical assays indicated that three consecutive holes on the first drill traverse (7506000 North/-22.5526°N) intersected modestly anomalous uranium grades, beneath approximately 40 m of barren overburden. The holes intersected leucogranites showing typical indications of significant uranium mineralization, such as smoky quartz centers (Fig. 5). Chemical assays returned a peak value of 188 ppm U3O8 in drill hole RB021. Follow-up angled reverse circulation drill holes to a maximum depth of 160 m were completed in late November 2007. Of the three completed holes, RBA001 and RBA002 intersected significant uranium mineralization beneath the original exploration drill holes. The best intersection returned was 100 m assaying 265 ppm U3O8 in hole RBA002. These drill holes are considered the discovery holes for the Rössing South uranium deposit, and the assay results were announced to the public on February 1, 2008.

Follow-up drilling commenced soon after. In the first case, two diamond holes were drilled to close the section beneath drill holes RBA001 to RBA003. The first, RDD001, was angled 60° to the east, whereas RDD002 was angled west beneath it. Core angles clearly showed that the stratigraphy was dipping at a moderate angle to the east, with the implication being that the discovery holes had been drilled downdip. Hole RDD001 remained mostly within footwall Khan gneiss, whereas hole RDD002 cut the mineralized zone orthogonally and returned an intersection of 149 m assaying 474 ppm U3O8. Within this zone, higher grade intervals, including 17 m assaying 1,899 ppm U3O8 and 21 m assaying 1,368 ppm U3O8 offered clues to the unusually high-grade nature of Rössing South compared with other granite-hosted deposits within the Erongo region uranium province.

With confirmation of the local stratigraphic dip, drilling for strike extensions could commence. Two approaches were used. In the first case, shallow vertical exploration drilling had continued to the south of the discovery area based on a 1,600-by 80-m grid. Additional exploration traverses were drilled on 7,504,400 North (lat. -22.5670°N), 7502800 North (lat. - 22.5743°N), and 7501200 North (lat. -22.5959°N). It was the objective of this work to test the western limb of the Kuiseb syncline in the Rössing deposit area, as well as the eastern limb where success at Rössing South had already been encountered. As before, the strategy was to drill through the unconformity surface at the base of the overburden and approximately 30 m into the underlying bed rock. Whereas results on the western synclinal limb offered little encouragement, the southern strike extensions of the mineralization already encountered on the Rössing South discovery section were characterized by consistently anomalous uranium values, the most impressive of which were returned from line 7502800 North, about 3.2 km south of the discovery section. Results included intersections of as much as 38 m assaying 1,072 ppm U3O8 in hole RB0162, which remains the best intersection reported from vertical exploration drilling within the Rössing South mineralized corridor to date. Whereas the discovery section became the spring board for extensional resource drilling in Rössing South zone 1, the high-grade intersection reported from hole RB0162 performed a similar function for zone 2 (Fig. 6).

Fig. 4.

Husab project total magnetic intensity image. Note the magnetic low associated with the Khan Formation in the Rössing South inset area.

Fig. 4.

Husab project total magnetic intensity image. Note the magnetic low associated with the Khan Formation in the Rössing South inset area.

The second approach involved extensional resource drilling targeting the large mineralized system identified by the work to date. Larger capacity reverse circulation drill rigs commenced drilling step-out sections from the mineralization identified in the exploration drilling on lines 7506000 North, 7504400 North, and 7502800 North. Holes were angled 60° to true west and were initially drilled on a 400- by 80-m grid pattern. Holes were drilled to a nominal 300-m depth. This phase of operations commenced in April 2008. At this stage, exploration activities remained ongoing at the various Ida dome target areas; however, all Ida dome drilling activities had been terminated by October 2008 because it became progressively apparent that Rössing South offered excellent potential to define a world-class uranium deposit that clearly justified greatly accelerated resource drilling.

By mid-2008, 22,600 m of angled resource drilling had been completed over the Rössing South zones 1 and 2 on 400-m spaced sections. With apparent good continuity of the mineralized leucogranite dikes, grade modeling allowed for the estimation and public release of a conceptual exploration target for Rössing South as it was then defined. This resulted in a lower scenario figure of 57,000 t of U3O8 for both zones and an upper scenario figure of 90,000 t of U3O8. The conceptual exploration target was released to the public on July 30, 2008. At the same time, infill resource drilling commenced, initially in zone 1, based on a 100- by 100-m drill pattern.

Fig. 5.

Examples of mineralized leucogranite from RDD002. Note the variable grain size, smoky quartz, and biotite.

Fig. 5.

Examples of mineralized leucogranite from RDD002. Note the variable grain size, smoky quartz, and biotite.

Deposit Geology

The Rössing South uranium deposit consists of numerous sheeted leucogranite and/or pegmatite bodies associated with a north- to northeast-trending anticline located on the eastern limb of the regional Kuiseb syncline. The sheeted dikes intrude mainly metasedimentary rocks of the Rössing Formation, predominantly on the eastern anticlinal limb, but the fold saddle, where preserved, is also mineralized. Stratigraphic dips are steeper in zone 1 than in zone 2, and the sheeted bodies are generally semiconformable to lithologic contacts. Although the majority of the uranium resource defined to date is located on the eastern limb of the Rössing South anticline, significant mineralization is also evident on the western limb in both zones 1 and 2. Western limb mineralization in zone 1 is steeply dipping but becomes shallow dipping in the zone 2 area. Farther to the south, in an exploration area known as zone 4, the western limb mineralization becomes subhorizontal where it dips beneath the Kuiseb syncline.

The core of the Rössing South anticline consists of amphibole-pyroxene gneiss of the Khan Formation. The Khan Formation in the immediate vicinity of the deposit has been invaded extensively by pink-red granite dikes that generally crosscut lithologic contacts. Their age is unknown, but they are presumed to be the product of a different event than the intrusion of the mineralized tan to gray leucogranite sheets into the overlying Rössing Formation. The reddish-colored granite dikes intruding the Khan footwall rocks are generally barren to poorly mineralized and commonly crosscut stratigraphic contacts.

The Rössing Formation in the Rössing South area is as much as 300 m thick and is overlain by diamictite and/or pebble gneiss of the Chuos Formation, which is often strongly foliated. Rocks of the Chuos Formation are generally not well mineralized at Rössing South, but where uranium-bearing dikes intrude the Chuos Formation proximal to Rössing Formation contacts, they generally exhibit subeconomic uranium grades, with poor continuity between drill holes. Although Chuos and Khan Formation lithologic units make poor ore hosts at Rössing South, elsewhere within the Erongo region uranium province, the opposite can be the case. Most of the uranium mineralization presently identified surrounding the Ida dome, for example, is hosted either by leucogranite dikes intruding the Khan Formation gneiss and/or Rössing Formation contact area, or directly within calc-silicate phases within the Khan Formation itself.

The uranium mineralized leucogranites at Rössing South intrude calc-silicates, quartzites, and mica schists of the Rössing Formation. A lesser component of the uranium resource at Rössing South is hosted by diopside-bearing calc-silicate rocks or biotite schist of the Rössing Formation, rather than directly within dikes, although this generally occurs proximal to the contacts of mineralized leucogranite dikes or where dike material is very finely interfingered within the enclosing metasedimentary rocks. About 70 to 80 percent of the uranium mineralization at Rössing South is directly hosted by the sheeted leucogranites. Figure 7 shows a well-mineralized section of leucogranite dike with enhanced oxidation close to the upper contact with pebble gneiss of the Chuos Formation.

The Rössing Formation in the immediate Rössing South area is unusual in that marble lenses are comparatively weakly developed, in contrast to the Rössing deposit area to the north, and the Ida dome area to the south, where thick accumulations of Rössing marble occur. At Rössing South, there appears to be no spatial relationship between the few small and discontinuous marble lenses and high-grade leucogranite dikes.

The Rössing South mineralized zone is at least 8 km in strike length, of which the defined resources of zones 1 and 2 make up the northern 5.5-km interval. The mineralized zone remains open to the south. North of Rössing South zone 1, the Damara metasedimentary rocks are folded to the northwest, which effectively closes out the mineralization proximal to the license boundary. The 0.5-km segment between zones 1 and 2 is currently interpreted to represent a downwarped section of anticlinal axis, where rocks of the Rössing Formation are mainly restricted to depths below 250 m. Limited drilling in the gap position between zones 1 and 2 has intersected patchy, although locally high-grade, uranium mineralization.

The Rössing South uranium deposit is concealed beneath 10 to 80 m of transported gravels and occupies a broad plain east of the deeply incised Khan River gorge. The gravels, of presumed Tertiary age, are immature valley fill gravels, with shallow gypcrete layers and deeper calcrete cemented zones closer to the basal unconformity. The gravels give way to heavy clays in the deepest sections of the paleovalleys, generally below 80-m vertical depth. The overburden above the Rössing South deposit contains little secondary uranium mineralization However, a younger calcrete-rich paleochannel located approximately 4 km east of Rössing South contains shallow carnotite mineralization of generally low grade.

A recently completed radon survey, using the RadonXTM technique (Corner et al., 2009), over the northern 16 km of EPL 3138 has identified numerous zones of elevated radon flux in overburden covered areas, which will be a focus for an enhanced exploration campaign going forward. The prospective stratigraphic trends extend for at least another 10 km south of the current resource areas, suggesting that the Husab project's resource potential is not yet exhausted. A radon flux map produced from this work is shown in Figure 8. Outlines of the currently discovered mineralization are shown for context.

Fig. 6.

Rössing South total magnetic intensity image with drill hole collar positions colored by maximum downhole interval of continuous uranium mineralization as detected by hand held spectrometer (eU). Areas viewed as being prospective for hosting uraniferous leucogranites are shown within the dashed white lines. Original exploration lines are shown on 1,600-m line spacings.

Fig. 6.

Rössing South total magnetic intensity image with drill hole collar positions colored by maximum downhole interval of continuous uranium mineralization as detected by hand held spectrometer (eU). Areas viewed as being prospective for hosting uraniferous leucogranites are shown within the dashed white lines. Original exploration lines are shown on 1,600-m line spacings.

Mineralogy

Through December 2009, a series of mineralogical analyses were completed on Rössing South core samples These are described below.

Uranium ore mineralogy

Three mineralized composites from hole RDD002 were examined using scanning electron microscopy, with uraninite being the only uranium mineral identified. No refractory uranium minerals were identified in these samples. The uraninite generally occurs as liberated grains and as margins, rims, veins, and inclusions to composites. Most liberated grains were observed to be smaller than 120 µm (Townend, 2009). Importantly, the uraninite was expected to be readily exposed to acid leach solutions following coarse grinding (>500 µm).

Detailed host-rock mineralogy

Three type samples representing the main uranium-bearing lithologic units at Rössing South were submitted to Ansto Minerals for phase characterization. The chemical composition of each sample was assessed by X-ray fluorescence (XRF) with major mineralogical phases confirmed by X-ray diffraction (XRD). Minor constituents were then identified using a scanning electron microscope equipped with an energy dispersive system (Prince and Kelly, 2009).

Fig. 7.

Well-mineralized leucogranite dike from the northern section of Rössing South zone 2. Note the semiconformable contact with the enclosing metasedimentary rocks and the enhanced level of oxidation close to the contact.

Fig. 7.

Well-mineralized leucogranite dike from the northern section of Rössing South zone 2. Note the semiconformable contact with the enclosing metasedimentary rocks and the enhanced level of oxidation close to the contact.

The dominant host rocks for uranium mineralization at Rössing South are leucogranite (alaskite), calc-silicate, and biotite schist. The above work confirmed that all of these units are comprised of microcline, albite, quartz, and mica (muscovite and/or biotite/phlogopite) with some chlorite (clinochlore). Minor phases observed are a Ca-Mg-Al-Fe-silicate (ferroan diopside), pyrite, titanite, apatite, galena, and ilmenite. Zircon is also evident in calc-silicate and biotite schist.

Uraninite is the dominant uranium mineral in all three rock types. It generally occurs as ~10- to 200-µm grains either liberated or in association with the alkali feldspar. The mineralized alaskite also contains minor amounts of coffinite, usually located in close proximity to quartz grains and, more rarely, alkali feldspar. The calc-silicate lithotype also contains rare particles of uranium-bearing thorite. The biotite schist contains rare particles of brannerite and monazite. Table 3 outlines the crystalline phases detected to date.

Quantitative evaluation of materials by scanning electron microscopy

A QemSCAN analysis of seven diamond drill hole intervals from four drill holes, two from zone 1 and two from zone 2, was completed by SGS Lakefield, Johannesburg, and reported upon by Freemantle (2009). The majority of uranium in the samples is found in the form of uraninite. However, coffinite is a significant component in sample RDD006a 245-246. Brannerite content is highest in sample RDD006a 119-120, where it hosts 6.2 percent of the contained uranium. The amount of uranium in betafite is insignificant in all samples (<0.2% of the total uranium). The liberation and exposure of the uranium minerals identified by QemSCAN is high, with the bulk of the minerals occurring as free grains, some with rims of varying minerals but not totally encapsulated by these minerals (Freemantle, 2009).

Sample RDD023

A noteworthy sample containing visible yellow secondary uranium minerals from core hole RDD023 was examined in detail (Townend, 2009). This sample was taken from approximately 362 m downhole. Similar examples of secondary uranium minerals are seen in varying amounts, in many holes at Rössing South.

One polished thin section was produced and examined by optical scanning electron microscope for uranium minerals. A concentration of heavy minerals from part crushed core in TBE liquid was followed by X-ray diffraction analysis.

Table 3.

Rössing South Crystalline Phase Components from Selected Samples as Determined by XRD (after Prince and Kelly, 2009)

Sample nameCrystalline phaseEmpirical mineral formula
Ext120309-3
AlaskiteMicrocline (intermediate)KNaAlSi3O8
MuscoviteKAl2 (Si3Al)O3(OH)2
Albite(NaCa)(AlSi3O8)
Ferroan diopside(MgFe)(CaMg)(Si2O6)
QuartzSiO2
Clinochlore(Mg3 Fe Al)(Si3 Al O3)(OH),
Ext120309-2
Calc-silicateMicrocline (intermediate)KNaAlSi3O8
Ferroan diopside(MgFe)(CaMg)(Si2O6)
MuscoviteKAl2(Si3Al)O3(OH)2
Albite(NaCa)(AlSi3O8)
QuartzSiO2
Ext120309-1
Biotite schistMicrocline (intermediate)KNaAlSi3O8
MuscoviteKAl (Si Al)O3(OH)2
QuartzSiO2
Clinochlore(Mg3FeAl)(Si3AlO3)(OH)8
Albite(NaCa)(AlSi3O8)
Ferroan phlogopiteKMg3 (FeSi3O10)(OH)2
Sample nameCrystalline phaseEmpirical mineral formula
Ext120309-3
AlaskiteMicrocline (intermediate)KNaAlSi3O8
MuscoviteKAl2 (Si3Al)O3(OH)2
Albite(NaCa)(AlSi3O8)
Ferroan diopside(MgFe)(CaMg)(Si2O6)
QuartzSiO2
Clinochlore(Mg3 Fe Al)(Si3 Al O3)(OH),
Ext120309-2
Calc-silicateMicrocline (intermediate)KNaAlSi3O8
Ferroan diopside(MgFe)(CaMg)(Si2O6)
MuscoviteKAl2(Si3Al)O3(OH)2
Albite(NaCa)(AlSi3O8)
QuartzSiO2
Ext120309-1
Biotite schistMicrocline (intermediate)KNaAlSi3O8
MuscoviteKAl (Si Al)O3(OH)2
QuartzSiO2
Clinochlore(Mg3FeAl)(Si3AlO3)(OH)8
Albite(NaCa)(AlSi3O8)
Ferroan phlogopiteKMg3 (FeSi3O10)(OH)2
Fig. 8.

Radon map of the Rössing South gravel plain compiled from RadonX™ data. The current Rössing South zones 1 and 2 outlines are shown at the northern end of the survey area. Note the enhanced radon flux elsewhere within the area surveyed. Subsequent drilling has shown that some of the targets have potential to host economic uranium mineralization.

Fig. 8.

Radon map of the Rössing South gravel plain compiled from RadonX™ data. The current Rössing South zones 1 and 2 outlines are shown at the northern end of the survey area. Note the enhanced radon flux elsewhere within the area surveyed. Subsequent drilling has shown that some of the targets have potential to host economic uranium mineralization.

This work determined that the host rock was composed predominantly of coarse-grained quartz, with subordinate (<20%) potash feldspar. As such, this sample was considered as a vein rather than sensu stricto granite. Quartz grains were observed in excess of 20 mm, contrasting with the <5-mm feldspars. Some of the feldspars were altered to a translucent brown mineral with the composition of biotite.

The core sample contained extensive U-Th-Pb mineralization occurring as single crystals, together with extensive fine veining and equant aggregates of several phases. The dominant secondary uranium mineral was determined to be boltwoodite. It tended to occur as fine (<100-µm) veins through the quartz. Some euhedral thorite crystals were identified along with one grain of uraninite and a single grain of betafite (Townend, 2009).

Summary

Uraninite is the predominant uranium mineral at Rössing South. All samples have a population of discrete uraninite grains. A minor component of the uraninite also is present as marginal coatings on other phases, as well as in veins and as inclusions. Varying amounts of coffinite have been identified, with trace to minor brannerite, together with trace thorite. The dominant secondary uranium mineral observed in reverse circulation chips and drill core has been provisionally identified as boltwoodite.

No refractory uranium minerals, such as betafite, were identified in the samples at ANSTO Minerals. Traces of betafite were identified in sample RDD023 and in two of the seven samples analyzed in the QemSCAN work.

Mineralogy of the Test L1RS –38 µm leach feed and residue of the alaskite composite concluded that the uraninite, coffinite, and thorite had leached, and the brannerite showed signs of chemical attack but had not leached at the conditions of the test. Dilute leach testwork concluded that brannerite, which accounts for <2 percent of the uranium in the sample, could be leached at increased temperatures and acid concentration.

Standard formulas for the uranium minerals currently identified at Rössing South are summarized in Table 4.

Metallurgy

Sample selection from Rössing South zones 1 and 2 for first-pass metallurgical testing included locating suitable existing drill core and planning new diamond drill holes that represented (1) the width, depth, and breadth of the deposit; (2) a range of uranium grades; (3) a range of lithologic units, with particular emphasis on representing the known distribution of the various host rocks of uranium mineralization; and (4) ensuring an emphasis was placed on collecting samples from the three optimized starter pits, two in zone 1 and one in zone 2, representing approximately the initial 4.5 years of production, at a rate of 15 Mt/yr. A matrix was prepared with inputs from three depth ranges and three grade ranges, with the resources compartmentalized into three separate zones along their strike length to ensure that the complete range of grades and lithologic units were represented over the depth and length of the deposits (Inwood et al., 2009).

By January 2010, the initial metallurgical testwork program had been mainly completed on the zone 1 samples, with an extensive program on zone 2 samples in progress. Excellent results have been produced from the agitated leach testwork program. The composites appear insensitive to grind size between grind sizes of P80 355 to 710 µm. Variations in pH, oxidation-reduction potential, and ferric addition have produced similar leach recoveries, which is indicative of a robust ore where fluctuations in process plant parameters are not expected to impact on plant recoveries.

High recoveries of 94.5 and 92.8 percent were achieved at P80 710 µm on the alaskite and biotite schist composites, respectively. The acid consumption for the alaskite composite was 20 kg/t but was higher for the biotite schist composite at 40 kg/t. The current optimum parameters selected from the ANSTO Minerals testwork program on the alaskite composite are P80 710 µm, pH of 1.5, 500 mV oxidation-reduction potential with pyrolusite, and 1.0g/l ferric at 40°C.

From this work it would be expected that, for the zone 1 deposit at Rössing South, agitated leach uranium recovery would be 93 percent, and with assumed losses of 1 percent through the uranium recovery circuit, the total plant recovery would be expected to be about 92 percent. The total acid consumption is expected to be approximately 25 kg/t over all ore types. The processing parameters will continue to be refined, and those ultimately selected are expected to be a trade-off between uranium recovery and reagent consumption.

Heap-leach amenability bottle-roll testing has produced encouraging recoveries of 67 to 80 percent at crush sizes of –6.3 and –12.5 mm. However, agitated tank leach remains the base case flow-sheet option for the Rössing South feasibility study.

Metallurgical testwork, as part of the definitive feasibility study, will continue to determine the optimum leach conditions and downstream process recovery options. This work, along with dedicated pilot plant testwork, is expected to be largely complete by mid-2010.

Rössing South Feasibility Study

The resources currently defined at Rössing South zones 1 and 2 are the focus of an ongoing definitive feasibility study. This technical and economic evaluation is aimed at defining project economics to ±15 percent. The base case scenario is the evaluation of a large-scale, load-and-haul, open-pit mining operation. Ore from the mine would feed a conventional agitated acid leach process plant at a rate of 15 Mt/yr.

Table 4.

Uranium-Bearing Minerals Identified during Rössing South Test Work

NameFormulaU (%)MetallurgyRelative abundanceComments
UraniniteUO288Oxidant and acid for leachingMajorTends to be present as variably sized anhedral grains; observed both as free particles and as inclusions within other minerals
CoffiniteU(SiO4)1-X(OH)4X70Easy to leachSignificantCoffinite tends to be present as tiny particles (<10 µm) adjacent to quartz and alkali feldspar grain boundaries; it often forms discontinuous rims to much larger quartz grains
Boltwoodite(H3O) K(UO2)SiO455Relatively easy to leachPresentObserved in RC chips and drill core as a fine-grained yellow secondary uranium mineral
Brannerite(U,Ca,Ce)(Ti, Fe)2O6OH10RefractoryMinorCan be leached at higher temperature with increased acid addition
Thorite(Th,U)SiO42Relatively easy to leachTrace
Betafite(Ca,U)2(Ti,Nb,Ta)2O6OH17RefractoryTraceRare occurrences of isolated single grains
NameFormulaU (%)MetallurgyRelative abundanceComments
UraniniteUO288Oxidant and acid for leachingMajorTends to be present as variably sized anhedral grains; observed both as free particles and as inclusions within other minerals
CoffiniteU(SiO4)1-X(OH)4X70Easy to leachSignificantCoffinite tends to be present as tiny particles (<10 µm) adjacent to quartz and alkali feldspar grain boundaries; it often forms discontinuous rims to much larger quartz grains
Boltwoodite(H3O) K(UO2)SiO455Relatively easy to leachPresentObserved in RC chips and drill core as a fine-grained yellow secondary uranium mineral
Brannerite(U,Ca,Ce)(Ti, Fe)2O6OH10RefractoryMinorCan be leached at higher temperature with increased acid addition
Thorite(Th,U)SiO42Relatively easy to leachTrace
Betafite(Ca,U)2(Ti,Nb,Ta)2O6OH17RefractoryTraceRare occurrences of isolated single grains

Key work areas being completed as part of the definitive feasibility study are geotechnical evaluation, resource optimization, mine design and scheduling, metallurgical testwork incorporating detailed pilot plant proof of design testing, process plant design, tailings disposal testwork and design, and environmental base line studies, with completion of an environmental impact assessment and management plan. The results from this work will support licensing and permit applications with the government of Namibia to enable project development to proceed on schedule.

Resource Model and Estimation

A maiden resource estimate for Rössing South zone 1 was announced in January 2009, and an update for this zone was announced in June 2009. A maiden resource estimate for zone 2 was announced in July 2009. Updated resource estimates for both zones are scheduled to be completed early in the third quarter of 2010, incorporating approximately 240,000 m of infill and minor extensional drilling completed since July 2009. Due to the majority of the current resource being classified in the inferred category, no formal reserves have been defined at Rössing South.

The resource estimation process so far at Rössing South has been a joint effort between Extract Resources Limited and an independent resource consultancy, Coffey Mining, which is a subsidiary of Coffey International Limited. For the maiden resources of both zones 1 and 2, geologic and grade three-dimensional models were created inhouse by Extract and passed on to Coffey Mining, who reviewed the modeling and carried out statistical analysis, resource estimation, and resource classification. The zone 1 update resource model and estimate was generated inhouse at Extract but was peer reviewed by Coffey Mining prior to the results being released.

Resource database

By mid-2009, the drill hole database in the vicinity of Rössing South zone 1 contained a total of 237 resource holes drilled by Extract Resources between 2007 and 2009. Early regional exploration holes were excluded from the database. The database contained 33 diamond holes for 13,200 m, and 204 reverse circulation holes for 60,094 m. Drilling at zone 1 was generally carried out on a collar spacing of 100 by 100 m, with some infill holes on 50-m centers. Additionally, an area covering 200 m of strike of the mineralization in the northern section of zone 1 has been drilled on a more detailed 50- by 50-m grid. This panel with increased drill hole information has been used to generate appropriate models for drill hole density and resource classification.

The drill hole database in the vicinity of zone 2 contained a total of 167 resource holes drilled by Extract Resources between 2008 and 2009. Early regional exploration holes were excluded from the database. The database contained 16 diamond holes for 2,583 m and 151 reverse circulation holes for 51,683 m. The drilling at zone 2 was mostly on a 100- by 100-m collar spacing.

The drill holes have typically been drilled due west (WGS84/33S grid) with a dip of –60°. All holes completed at Rössing South have their collar position surveyed by differential global positioning system. Additionally, all resource holes are surveyed downhole for dip and azimuth, typically on 5-m intervals. Validation of the drill hole database used for resource estimation was done separately by Extract Resources and Coffey Mining.

Nearly all of the assay data (99.6% of samples) contained in the zone 1 database were derived from chemical assays. The zone 2 database contained a combination of chemical assaying (81% of samples) and factored radiometric data (19% of samples).

Geologic interpretation

The geologic model for Rössing South zone 1 consists of a tight, doubly plunging antiform, with a core of gneiss of the Khan Formation, overlain by a mixture of metasedimentary and altered calc-silicate lithologic units of the Rössing Formation, which is overlain in turn by pebbly gneiss and biotite schist of the Chuos Formation. The small dome at zone 1 plunges to the north at a shallow angle at the northern end, whereas it plunges southward at a moderate angle over the southern one-third of the deposit. Leucogranite sheets have mostly intruded Rössing Formation lithologic units approximately parallel to foliation and lithologic contacts. This is observed both in core and in outcrop at the northern end of zone 1. The western limb of the antiform has been drilled only in the southern part of the deposit. The subvertical western limb mineralization forms an apparent fold closure with the east-dipping east limb mineralized bodies, as the anticlinal axis plunges to the south.

The geologic sequence at Rössing South zone 2 is the same as that observed at zone 1, but the domal feature is more open, slightly better preserved, and better defined by magnetic data. The zone 2 dome covers approximately 4 km of strike, with the currently defined zone 2 resource area occupying the northeastern sector and the southern extensions to zone 2 occupying the southeastern part. Deeper drilling in the gap area between the zone 1 and 2 domes shows that the anticlinal axis has been downwarped, and the prospective Rössing Formation lithologic units are present at greater depths beneath a thickened package of mostly unmineralized Chuos Formation rocks. Significant uranium intersections have been returned from limited drilling completed to date in the gap area, but there are insufficient data to enable an estimated resource.

The apparent flexing of the axis of the Rössing South anticline, causing local plunge reversals and the formation of a series of small domes, is currently ascribed by the authors to the interactions of north- to northeast-trending F4 fold axes with earlier, obliquely crosscutting, F3 fold axes.

Figure 9 shows presently identified uranium mineralization within the Rössing South corridor projected to the surface of the gravel plain. Figures 10 and 11 portray generalized geologic sections across and along the deposit (i.e., A-A', B-B')

Modeling

The creation of three-dimensional geologic and grade models for zones 1 and 2 was undertaken as a three-stage process. Using wire-framed sectional interpretations, stratigraphic units were modeled for the Khan, Rössing, and Chuos Formations Next an alaskite model was created so that zones composed predominantly of leucogranite sheets were formed, which broadly paralleled the underlying stratigraphic model. Finally a nominal 75-ppm U3O8 mineralization wireframe model was constructed that used the geologic models to help guide the orientation of the mineralized outlines. The downhole thickness of mineralized intervals ranged from 3 to 114 m, with an average of 19 m. The strike extent of the modeled mineralized units ranged from 125 to 2,000 m, showing that overall the mineralization at Rössing South displays very good continuity.

Fig. 9.

Mineralization outlines from Rössing South projected to the surface of the gravel plain. A generalized geologic cross section (A-A') is shown below as Figure 10, and a generalized longitudinal section (B-B') is shown as Figure 11.

Fig. 9.

Mineralization outlines from Rössing South projected to the surface of the gravel plain. A generalized geologic cross section (A-A') is shown below as Figure 10, and a generalized longitudinal section (B-B') is shown as Figure 11.

Alluvium covers most of the Rössing South area. The depth of the overburden tends to increase toward the south and the east. Alluvial cover over zone 1 varies from none at the northern end to approximately 60 m in the south; alluvial cover at zone 2 ranges from about 70 m in the north to 90 m at the southern end. The alluvium is comprised of an upper layer of relatively unconsolidated or gypsum-cemented gravelly sand, about 15 m thick, which is underlain by variably carbonate cemented gravel and conglomerate. Surfaces were modeled for the surface topography, the loose alluvial sand cover, and the base of the conglomerate or top of the unconformity surface.

Disequilibrium

A small number of samples from Rössing South zones 1 and 2 were submitted to ANSTO Minerals for a disequilibrium study. Samples were taken from downhole depths of 50 to 60, 150 to 160, and 285 to 295 m. Concentrations ranged from 360 to 830 ppm U3O8. The study was undertaken to check that the radionuclides at Rössing South were in secular equilibrium, and that the use of downhole gamma logging was a reliable method of grade determination at the deposit.

Gamma radiation measurements are often used when exploring for and evaluating uranium deposits. The assumption is made that the gamma value measured is proportional to the presence of uranium in the sample. This can be incorrect because the source of the gamma can be from other naturally occurring radionuclides, notably the 232Th decay chain radionuclides and/or the 238U decay chain is in disequilibrium.

Secular equilibrium exists when the members of a decay chain are each decaying at the same rate, i.e., each has the same concentration of radioactivity. Secular equilibrium is normally the case in a relatively long geologic time frame However, depending on the local geochemical conditions, such as oxidation potential or presence of chloride, the major uranium radionuclides can be separated from the daughter products due to dissolution, migration, or reprecipitation of either the uranium or the daughter products.

Most of the gamma energy associated with the 238U decay chain that is measured by downhole gamma logging arises from the short-lived 226Ra progeny. The gamma signal associated with the separated uranium radionuclides can be relatively low. In relatively young uranium deposits, where there has been mobilization of the uranium or daughter products, in rollfront sedimentary-type deposits, for example, there can be uranium with very little gamma activity and/or radium with high gamma but low associated uranium. This has resulted in the limited use of gamma logging for the ultimate establishment of a uranium resource unless more is known about the state of secular equilibrium in the deposit.

The testing by ANSTO resulted in the conclusion that for the three samples in this study, using gamma radiation, delayed neutron activation, and neutron activation analyses, both the 238U and 232Th decay chains are in secular equilibrium, within analytical error (±10%; Prince and Kelly, 2009) Furthermore, disequilibrium would not be expected in a primary uranium deposit such as Rössing South (ANSTO Minerals, writ. commun., 2009). The testwork confirmed this opinion and indicates that gamma logging is an appropriate method with which to collect uranium- information about the deposit.

Assaying and radiometric data collection

All diamond core and reverse circulation drill holes within the project are logged using a hand-held spectrometer. The spectral logs are generally only used as a guide for the occurrence of mineralized intervals within the drill hole. The main analytical technique used for uranium is a four-acid digestion and measurement by inductively coupled plasma with mass-spectrometer analysis (ICP-MS). Some samples have also been analyzed for uranium by pressed pellet X-ray diffraction (PP-XRF). Only chemical assaying, PP-XRF, or ICP-MS, and, to a lesser degree, downhole spectrometer readings are used in resource estimation.

Downhole radiometric data are collected by a Gamma Ray Spectrometer 42 (GRS) tool operated by Terratec Geophysical Services of Namibia. The downhole tool utilizes a 250 or 500 channel unit in conjunction with a thallium activated NaI crystal with dimensions of 25 by 50 mm. Data in log ASCII standard format (LAS) contain information on hole ID, location, date, counts per second (total, U, K, and Th channels) U3O8 (calculated from the U channel) and eU3O8 (calculated from the total count). Based on advice from Terratec, the total count (eU3O8) values have been used in estimation studies. The data from the uranium channel alone were considered too noisy due to the lower sample count. Downhole spectrometer data have been used as a fall-back option for holes drilled immediately prior to compilation of the database for use in resource estimation and for which there have not been chemical assays.

Fig. 10.

Generalized geologic cross section across Rössing South zone 1. The Rössing South anticline in the vicinity of zone 2 becomes more open and somewhat better preserved.

Fig. 10.

Generalized geologic cross section across Rössing South zone 1. The Rössing South anticline in the vicinity of zone 2 becomes more open and somewhat better preserved.

Fig. 11.

General geologic longitudinal section covering zones 1 and 2. Note the plunge reversals along the axis of the Rössing South anticline.

Fig. 11.

General geologic longitudinal section covering zones 1 and 2. Note the plunge reversals along the axis of the Rössing South anticline.

Prior to their use in resource estimation studies, it is necessary to adjust and factor the spectrometer data. To do so it is necessary to have both spectral and chemical assay data for some of the drill holes, so that appropriate factors can be estimated and checked. A water correction factor is applied to samples lying below the water table to account for the different survey responses when surveying dry compared to wet.

All downhole spectrometer surveys show a background value, possibly due to radon in the drill hole. This background value, typically about 30 ppm eU3O8, is subtracted from the readings. Plots and summary statistics of chemical assays versus spectrometer readings before and after adjustment are compared, to help confirm that appropriate and defendable correction factors have been applied to the GRS data used for resource estimation. Throughout the life of the Rössing South project, chemical assay data have been given precedence over radiometric assays during the resource estimation process.

Statistical Analysis of Composites and Top Cuts

The data captured within the mineralization wire frames were composited to a regular 3-m downhole composite length. The composites were used for all statistical, geostatistical, and grade estimations.

A statistical analysis was carried out on the composited data for each separate unit of the mineralization wire-frame model to determine appropriate top cuts to apply to the data The method of top cutting was to look at grade-distribution histograms and the change in coefficient of variation with the progressive removal of high grades This results in the cutting back of a small number of outlier high-grade samples that can have a disproportionately large effect on the estimated grade. Top cuts ranged from 1,200 to 3,500 ppm U3O8.

Bulk Density Data

Several hundred density readings taken from water immersion of whole drill core have been collected for Rössing South. Readings are grouped by lithology, and an average bulk density is calculated for each rock type, as shown in Table 5. Appropriate densities for the sand and conglomerate material were taken from the AusIMM Field Geologists' Manual (1995).

Variography

Traditional semivariograms were used to analyze the spatial variability of the 3-m composites. Given the broad-spaced drilling undertaken for the current resource estimates for Rössing South, generally 100 by 100 m, the variable orientations of the mineralized units, and the somewhat nugget-like nature of the uranium mineralization, variograms for the individual mineralized domains tended to be poorly structured. The best structured variogram was obtained from the anisotropic variography of the combined zones. Values derived from the combined zones variography were used as inputs for the ordinary kriging estimation for each of the mineralized zones.

Block Model and Grade Estimation

Separate block models were created for the zone 1 and 2 resource areas. The U3O8 grade estimation into the block model used ordinary kriging.

Sample neighborhood testing was conducted to determine an appropriate search strategy for the ordinary kriging estimation. The neighborhood testing included investigations into the minimum and maximum number of samples used for estimation, mean sample distance, negative kriging weights, and the slope of regression.

The resulting estimates were checked by a variety of methods to ensure that a robust result had been achieved. Checks included comparison plots of the informing composites and the whole-block estimate reported by elevation and northing; a comparison of the average composite, declustered and naïve, and block-model grade for each mineralized body; and visual inspection of the estimated blocks against the informing composites in three-dimension. Overall, the grade estimate showed a good reproduction of the composite datasets with internal grade zonation within larger blocks being appropriately delineated.

Table 5.

Summary of Rössing South Bulk Density Data Utilized for Resource Estimation1

LithologyNumber of samplesMinMaxAverage density
Alaskite4422.222.992.63
Calc-silicate1022.513.392.84
Metasediment1592.243.322.77
Gneiss1002.303.232.73
Marble152.633.042.75
Schist2962.333.372.71
Loose alluvial sand1.80
Conglomerate2.20
LithologyNumber of samplesMinMaxAverage density
Alaskite4422.222.992.63
Calc-silicate1022.513.392.84
Metasediment1592.243.322.77
Gneiss1002.303.232.73
Marble152.633.042.75
Schist2962.333.372.71
Loose alluvial sand1.80
Conglomerate2.20

Density readings taken from drill core at Rössing South zone 1

Classification and Resource

The resource estimates for zones 1 and 2 at Rössing South have been categorized in accordance with the criteria laid out in the Canadian National Instrument 43-101 (Ontario Securities Commission Board, 2005) and the Australasian Code for Reporting of Exploration Results, Mineral Resources, and Ore Reserves (Joint Ore Reserves Committee, 2004) Indicated and inferred resources were defined using definitive criteria determined during the validation of the grade estimates. The classification of the resources was based on the confidence level of the key criteria that were considered during resource classification (Table 6).

Resource Distribution

Average grades tend to increase with depth at both zones 1 and 2. Average grades in the upper 50 m of the deposit are in the 250- to 400-ppm U3O8 range, whereas below this the typical grade range is 450 to 600 ppm U3O8. This is probably due to the effects of recent weathering and some remobilization and/or leaching of uranium in the upper ~100 m of the deposit. Secondary uranium minerals (e.g., boltwoodite) are frequently observed in drill core.

The mineralization at zone 2 has a flatter, broader geometry than at zone 1, reflecting the underlying dome geometries at each zone The best mineralized areas at both zones 1 and 2 coincide with sites of dilation, particularly on the northern and southern ends of the domes and surrounding faults and flexures on the flanks of the domes. These areas of dilation have formed favorable sites for alaskite intrusion. Both thicknesses of mineralization and overall grade of the mineralization tend to be higher in these "hot spots." Figure 12 shows a plan view of metal accumulation (grade x thickness) within the current resource models and the location of hot spots within the model.

The summary of the resources that have been estimated to date at Rössing South, zones 1 and 2, reported above a 100 ppm U3O8 lower cut-off, are listed in Table 7.

Conclusions

The Rössing South uranium deposit was discovered early in 2008 by drill testing a conceptual exploration target. The deposit is concealed by transported overburden and has no discernible radiometric expression. During the exploration process, emphasis was given to understanding the Damaran stratigraphy of an extensive alluvium-covered area at the northern end of the Husab project, principally using aero-magnetic data, and interpreting the results in the context of a growing understanding of the lithostratigraphic and structural models important for the formation of Rössing-style deposits. In the two years since the Rössing South discovery was announced, the deposit has been subjected to an intensive resource definition and evaluation program which, by January 2010, totals approximately 200,000 m of drill advance. Current resources for zones 1 and 2 at Rössing South total 121,000 t of uranium oxide, and these are expected to increase with further work. Ultimately, it is expected that Rössing South will be elevated into the top five global uranium deposits in terms of metal endowment.

Table 6.

Classification Criteria for Resource Estimates Carried Out at Rössing South

ItemsDiscussionConfidence zone 1Confidence zone 2
Drilling techniquesRC/diamond—industry standard approachHighHigh
LoggingStandard nomenclature applied with recording and apparent high qualityHighHigh
Drill sample recoveryRecorded as goodHighHigh
Subsampling techniquesIndustry standard for both RC and diamond drillingHighHigh
and sample preparation
Quality of assay dataGood internal laboratory and external quality control data available for the majority of the chemical assaying; factored radiometric data is considered to be globally equivalent to chemical assaying but can show local differencesHighModerate to high
Verification of samplingQAQC analysis is within industry acceptable standardsHighHigh
and assaying
Location of sampling pointsMost drill hole collars surveyed by DGPS surveyed and most drill holes have been downhole surveyedHighHigh
Data density and distributionNominal 100- by 100-m drill hole collar spacingLow to highLow to moderate
Audits or reviewsCoffey Mining has reviewed the site drilling and sampling proceduresHighHigh
Database integrityNo material errors identifiedHighHigh
Geologic interpretationInfill drilling is likely to change the mineralization shapes and understanding of structural and grade continuityModerateLow to moderate
Estimation andEstimates based on detailed statistical and geostatistical analysisModerateModerate
modeling techniques
Cutoff gradesRange of cutoff grades reportedHighHigh
Mining factors or assumptionsWhole-block estimates for all mineralized regions completed; the effect of emulating smaller mining blocks has not been investigatedN/AN/A
ItemsDiscussionConfidence zone 1Confidence zone 2
Drilling techniquesRC/diamond—industry standard approachHighHigh
LoggingStandard nomenclature applied with recording and apparent high qualityHighHigh
Drill sample recoveryRecorded as goodHighHigh
Subsampling techniquesIndustry standard for both RC and diamond drillingHighHigh
and sample preparation
Quality of assay dataGood internal laboratory and external quality control data available for the majority of the chemical assaying; factored radiometric data is considered to be globally equivalent to chemical assaying but can show local differencesHighModerate to high
Verification of samplingQAQC analysis is within industry acceptable standardsHighHigh
and assaying
Location of sampling pointsMost drill hole collars surveyed by DGPS surveyed and most drill holes have been downhole surveyedHighHigh
Data density and distributionNominal 100- by 100-m drill hole collar spacingLow to highLow to moderate
Audits or reviewsCoffey Mining has reviewed the site drilling and sampling proceduresHighHigh
Database integrityNo material errors identifiedHighHigh
Geologic interpretationInfill drilling is likely to change the mineralization shapes and understanding of structural and grade continuityModerateLow to moderate
Estimation andEstimates based on detailed statistical and geostatistical analysisModerateModerate
modeling techniques
Cutoff gradesRange of cutoff grades reportedHighHigh
Mining factors or assumptionsWhole-block estimates for all mineralized regions completed; the effect of emulating smaller mining blocks has not been investigatedN/AN/A
Fig. 12.

Metal accumulation (grade × thickness) in the current zone 1 and 2 resource models and the location of the zone 1 and 2 domes.

Fig. 12.

Metal accumulation (grade × thickness) in the current zone 1 and 2 resource models and the location of the zone 1 and 2 domes.

Table 7.

Rössing South Resource Estimates as Classified (current from July 2009)

IndicatedInferred
ContainedContained
Tons aboveU3O8U3O8Tons aboveU3O8U3O8
cutoff (Mt)(ppm)(t)cutoff (Mt)(ppm)(t)
Rossing South zone 1
20.752711,000126.343655,000
Rossing South zone 2
10254355,000
Rossing South zone 1 + zone 2
20.752711,000228484110,000
IndicatedInferred
ContainedContained
Tons aboveU3O8U3O8Tons aboveU3O8U3O8
cutoff (Mt)(ppm)(t)cutoff (Mt)(ppm)(t)
Rossing South zone 1
20.752711,000126.343655,000
Rossing South zone 2
10254355,000
Rossing South zone 1 + zone 2
20.752711,000228484110,000

A feasibility study examining the potential to establish a globally significant uranium mining operation based on Rössing South zones 1 and 2 is currently in progress, with the results scheduled for release in the third quarter of 2010. Results indicate very good potential to establish a mine and processing operation based on current and anticipated future resources. Evaluation drilling is continuing at a rate of >20,000 m/month, and this level of activity will continue for much of 2010. Exploration drilling is expected to continue for several years to quantify the full potential of the Rössing South area for primary granite-hosted uranium mineralization.

References

Anderson
,
H.
Nash
,
C.
,
1997
,
Integrated lithostructural mapping of the Rössing area, Namibia, using high resolution aeromagnetic, radiometric, Landsat data and aerial photographs
:
Exploration Geophysics
 , v.
28
, p.
185
191
.
Berkman
,
D.A.
,
1995
,
Field geologists manual
:
Australian Institute of Mining and Metallurgy Monograph 9
 ,
390
p.
Brown
,
S.
,
February
2009
,
Uranium disequilibrium study—Namibia
:
Lucas Heights, NSW
 ,
Australia Sydney
,
ANSTO Minerals
,
Technical Note AM/TN/2008_12_12
,
11
p.
Core
,
D.
February
2010
,
Interpretation of the Rössing South airborne survey data
:
Houston, Louisiana, United States
,
Unpublished Technical Report or Extract Resources Ltd
 ,
30
p.
Corner
,
B.
,
1982
,
An interpretation of the aeromagnetic data covering a portion of the Damara orogenic belt with special reference to the occurrence of uraniferous granite, NUCOR PER-95
:
Unpublished Ph.D. thesis
 ,
Johannesburg, South Africa
,
University of the Witswatersrand
.
Corner
,
B.
Sinclair
,
H.
Verran
,
D.
,
2009
,
Radon emanometry in Namibia: Case studies of the Tumas and Rössing South deposits
:
South African Geophysical Conference
 ,
2009
,
5
p., http://www.sagaonline.co.za/2009Confer ence/CD%20Handout/SAGA%202009/PDFs/Abstracts_and_Papers/corne r_paper2.pdf
Freemantle
,
G.
June
2009
,
Preliminary report to Extract Resources (Swakop Uranium) of mineralogical results from QemSCAN analyses of selected surface and core samples of the Rössing South deposits
 :
Johannesburg, South Africa
,
School of Geosciences University of Witwatersrand
,
24
p.
Google Earth
,
2010
,
http://earth.google.com/
Inwood
,
N.
Corley
,
D.
Hill
,
M.
Boyce
,
A.
Culpan
,
N.
,
24 August
2009
,
Husab project
,
Namibia National Instrument 43-101 Technical Report
 
Rössing South, August 2009 Resource Update
,
127
p.
http://www.sedar.com/GetFile.do?lang=EN&docClass=24&issuerNo=00026090&fileName=/csfsprod/data101/filings/01463411/00000004/z%3A%5CPUBLIC%5CExtract%5C2009%5CRössingSouthTechRpt%5CRössingSouthTechReportOct22.pdf
Joint Ore Reserves Committee
,
2004
,
Australasian code for reporting of exploration results, mineral resources and ore reserves
:
Joint Ore Reserves Committee of the Australasian Institute of Mining and Metallurgy
 ,
Australian Institute of Geoscientists and Minerals Council of Australia (JORC)
,
20
p.
http://www.jorc.org/pdforExtractResourcesLtdf/jorc2004print_v2.pdf
Kinnaird
,
J.A.
Nex
,
P.A.M.
,
2007
,
A review of geological controls on uranium mineralization in sheeted leucogranites within the Damara orogen, Namibia
:
Transactions of the Society of Mining and Metallury, Applied Earth Science
 ,
sec. B
, v.
116
, p.
68
85
.
Kinnaird
,
J.A.
Nex
,
P.
Freemantle
,
G.
,
2009a
,
Uranium in Africa [abs.]
:
Geological Society of Namibia Uranium Conference
 ,
Witwatersrand
,
22–23 October 2009, Abstracts
,
12
p.
Kinnaird
,
J.A.
Freemantle
,
G.
Nex
,
P.A.M.
,
2009b
,
Uranium deposits in Central Namibia
:
Field Excursion Guide
 ,
June 2009
,
66
p.
Nash
,
C.R.
,
1971
,
Metamorphic petrology of the SJ area, Namibia
:
Precambrian Research Unit
 ,
University of Cape Town
,
Bulletin 9
,
77
p.
Nex
,
P.A.M
Kinnaird
,
J.A.
Oliver
,
G.J.H.
,
2001
,
Petrology, geochemistry and uranium mineralization of post-collisional magmatism around Goanikontes, southern Central zone, Damaran orogen, Namibia
:
Journal of African Earth Sciences
 , v.
33
,
nos. 3-4
, p.
481
502
.
Ontario Securities Commission Board
,
December
2005
,
National Instrument 43-101
:
Standards of disclosure for mineral projects
 ,
Chapter 5
,
13
p.
Prince
,
K.E.
Kelly
,
I.J.
,
May
2009
,
Rössing South ore mineralogy
:
Lucas Heights, NSW
 ,
Australia Sydney
,
ANSTO Minerals
,
Technical Memorandum AM/TM2009_14_05
,
5
p.
Roessener
,
H.
Schreuder
,
C.P.
,
1992
,
The mineral resources of Namibia—uranium
:
Geological Survey, Ministry of Mines and Energy, Republic of Namibia
 ,
chapter 7.1
,
62
p.
http://www.mme.gov.na/gsn/pdf/ura nium.pdf
Townend
,
R.
November
2009
,
Preparation of one polished thin section of one drill core and examination (optical/SEM) for uranium minerals. Concentration of heavy minerals from part crushed drill core in TBE liquid and XRD identification (RDD 23 362m): Our reference 22600
,
Unpublished technical report for Extract Resources Ltd
 ,
7
p.
WNA
,
2010
,
World uranium mining information sheet
  (
update April 2010): http://www.world-nuclear.org/info/inf23.html www.bannerman.com.au; www.extractresources.com; www.forsysmetals.com; www.Rössing.com

Figures & Tables

Fig. 1.

Rössing South project—general location plan, showing the location within Namibia of the Husab project lease boundaries and the location of the Rössing South deposit. (Google Earth, 2010).

Fig. 1.

Rössing South project—general location plan, showing the location within Namibia of the Husab project lease boundaries and the location of the Rössing South deposit. (Google Earth, 2010).

Fig. 2.

Geology of the Rössing South project area from a lithostructural interpretation of aeromagnetic data (Core, 2010).

Fig. 2.

Geology of the Rössing South project area from a lithostructural interpretation of aeromagnetic data (Core, 2010).

Fig. 3.

Granite-hosted uranium deposits of the Erongo region and their location within the southern central zone of the Damara orogen.

Fig. 3.

Granite-hosted uranium deposits of the Erongo region and their location within the southern central zone of the Damara orogen.

Fig. 4.

Husab project total magnetic intensity image. Note the magnetic low associated with the Khan Formation in the Rössing South inset area.

Fig. 4.

Husab project total magnetic intensity image. Note the magnetic low associated with the Khan Formation in the Rössing South inset area.

Fig. 5.

Examples of mineralized leucogranite from RDD002. Note the variable grain size, smoky quartz, and biotite.

Fig. 5.

Examples of mineralized leucogranite from RDD002. Note the variable grain size, smoky quartz, and biotite.

Fig. 6.

Rössing South total magnetic intensity image with drill hole collar positions colored by maximum downhole interval of continuous uranium mineralization as detected by hand held spectrometer (eU). Areas viewed as being prospective for hosting uraniferous leucogranites are shown within the dashed white lines. Original exploration lines are shown on 1,600-m line spacings.

Fig. 6.

Rössing South total magnetic intensity image with drill hole collar positions colored by maximum downhole interval of continuous uranium mineralization as detected by hand held spectrometer (eU). Areas viewed as being prospective for hosting uraniferous leucogranites are shown within the dashed white lines. Original exploration lines are shown on 1,600-m line spacings.

Fig. 7.

Well-mineralized leucogranite dike from the northern section of Rössing South zone 2. Note the semiconformable contact with the enclosing metasedimentary rocks and the enhanced level of oxidation close to the contact.

Fig. 7.

Well-mineralized leucogranite dike from the northern section of Rössing South zone 2. Note the semiconformable contact with the enclosing metasedimentary rocks and the enhanced level of oxidation close to the contact.

Fig. 8.

Radon map of the Rössing South gravel plain compiled from RadonX™ data. The current Rössing South zones 1 and 2 outlines are shown at the northern end of the survey area. Note the enhanced radon flux elsewhere within the area surveyed. Subsequent drilling has shown that some of the targets have potential to host economic uranium mineralization.

Fig. 8.

Radon map of the Rössing South gravel plain compiled from RadonX™ data. The current Rössing South zones 1 and 2 outlines are shown at the northern end of the survey area. Note the enhanced radon flux elsewhere within the area surveyed. Subsequent drilling has shown that some of the targets have potential to host economic uranium mineralization.

Fig. 9.

Mineralization outlines from Rössing South projected to the surface of the gravel plain. A generalized geologic cross section (A-A') is shown below as Figure 10, and a generalized longitudinal section (B-B') is shown as Figure 11.

Fig. 9.

Mineralization outlines from Rössing South projected to the surface of the gravel plain. A generalized geologic cross section (A-A') is shown below as Figure 10, and a generalized longitudinal section (B-B') is shown as Figure 11.

Fig. 10.

Generalized geologic cross section across Rössing South zone 1. The Rössing South anticline in the vicinity of zone 2 becomes more open and somewhat better preserved.

Fig. 10.

Generalized geologic cross section across Rössing South zone 1. The Rössing South anticline in the vicinity of zone 2 becomes more open and somewhat better preserved.

Fig. 11.

General geologic longitudinal section covering zones 1 and 2. Note the plunge reversals along the axis of the Rössing South anticline.

Fig. 11.

General geologic longitudinal section covering zones 1 and 2. Note the plunge reversals along the axis of the Rössing South anticline.

Fig. 12.

Metal accumulation (grade × thickness) in the current zone 1 and 2 resource models and the location of the zone 1 and 2 domes.

Fig. 12.

Metal accumulation (grade × thickness) in the current zone 1 and 2 resource models and the location of the zone 1 and 2 domes.

Table 1.

Generalized Stratigraphy of the Rössing South Area (after Nash, 1971); Nex, 1997; and Kinnaird and Nex, 2008)

SequenceGroupSubgroupFormationDescriptionAge (Ma)
KuisebSchist, minor quartzite~650
KhomasKaribibMarble, calc-silicate, schist
ChuosDiamictite, pelitic schist, biotite gneiss, pebble gneiss~710
SwakopRössingMinor marble, calc-silicate, quartzite, biotite schist, gneiss
DamaraUgabUraniferous granite sheets~510
NosibKhanAmphibole-pyroxene gneiss, schist
EtusisQuartzite, psammitic gneiss752 ± 7
Abbabis Metamorphic ComplexRed granite gneiss, metasediment, amphibolite~2000
SequenceGroupSubgroupFormationDescriptionAge (Ma)
KuisebSchist, minor quartzite~650
KhomasKaribibMarble, calc-silicate, schist
ChuosDiamictite, pelitic schist, biotite gneiss, pebble gneiss~710
SwakopRössingMinor marble, calc-silicate, quartzite, biotite schist, gneiss
DamaraUgabUraniferous granite sheets~510
NosibKhanAmphibole-pyroxene gneiss, schist
EtusisQuartzite, psammitic gneiss752 ± 7
Abbabis Metamorphic ComplexRed granite gneiss, metasediment, amphibolite~2000
Table 2.

Tonnages, Grades and Contained U3O8 for Granite-Hosted Uranium Deposits of the Erongo Region, Namibia

DepositMillion metric tons (Mt)Grade ppm U3O8Tons U3O8
Rössing (resource and reserves)130526179,700
Rössing1 (historic production)?350-40097,800
Rössing (total)177,500
Rössing South (zone 1 + 2)2249488121,000
Etango333122273,500
Valencia427114639,000
ida dome25321311,000
DepositMillion metric tons (Mt)Grade ppm U3O8Tons U3O8
Rössing (resource and reserves)130526179,700
Rössing1 (historic production)?350-40097,800
Rössing (total)177,500
Rössing South (zone 1 + 2)2249488121,000
Etango333122273,500
Valencia427114639,000
ida dome25321311,000
1

www.Rössing.com

2

www.extractresources.com

3

www.bannerman.com.au

4

www.forsysmetals.com

Table 3.

Rössing South Crystalline Phase Components from Selected Samples as Determined by XRD (after Prince and Kelly, 2009)

Sample nameCrystalline phaseEmpirical mineral formula
Ext120309-3
AlaskiteMicrocline (intermediate)KNaAlSi3O8
MuscoviteKAl2 (Si3Al)O3(OH)2
Albite(NaCa)(AlSi3O8)
Ferroan diopside(MgFe)(CaMg)(Si2O6)
QuartzSiO2
Clinochlore(Mg3 Fe Al)(Si3 Al O3)(OH),
Ext120309-2
Calc-silicateMicrocline (intermediate)KNaAlSi3O8
Ferroan diopside(MgFe)(CaMg)(Si2O6)
MuscoviteKAl2(Si3Al)O3(OH)2
Albite(NaCa)(AlSi3O8)
QuartzSiO2
Ext120309-1
Biotite schistMicrocline (intermediate)KNaAlSi3O8
MuscoviteKAl (Si Al)O3(OH)2
QuartzSiO2
Clinochlore(Mg3FeAl)(Si3AlO3)(OH)8
Albite(NaCa)(AlSi3O8)
Ferroan phlogopiteKMg3 (FeSi3O10)(OH)2
Sample nameCrystalline phaseEmpirical mineral formula
Ext120309-3
AlaskiteMicrocline (intermediate)KNaAlSi3O8
MuscoviteKAl2 (Si3Al)O3(OH)2
Albite(NaCa)(AlSi3O8)
Ferroan diopside(MgFe)(CaMg)(Si2O6)
QuartzSiO2
Clinochlore(Mg3 Fe Al)(Si3 Al O3)(OH),
Ext120309-2
Calc-silicateMicrocline (intermediate)KNaAlSi3O8
Ferroan diopside(MgFe)(CaMg)(Si2O6)
MuscoviteKAl2(Si3Al)O3(OH)2
Albite(NaCa)(AlSi3O8)
QuartzSiO2
Ext120309-1
Biotite schistMicrocline (intermediate)KNaAlSi3O8
MuscoviteKAl (Si Al)O3(OH)2
QuartzSiO2
Clinochlore(Mg3FeAl)(Si3AlO3)(OH)8
Albite(NaCa)(AlSi3O8)
Ferroan phlogopiteKMg3 (FeSi3O10)(OH)2
Table 4.

Uranium-Bearing Minerals Identified during Rössing South Test Work

NameFormulaU (%)MetallurgyRelative abundanceComments
UraniniteUO288Oxidant and acid for leachingMajorTends to be present as variably sized anhedral grains; observed both as free particles and as inclusions within other minerals
CoffiniteU(SiO4)1-X(OH)4X70Easy to leachSignificantCoffinite tends to be present as tiny particles (<10 µm) adjacent to quartz and alkali feldspar grain boundaries; it often forms discontinuous rims to much larger quartz grains
Boltwoodite(H3O) K(UO2)SiO455Relatively easy to leachPresentObserved in RC chips and drill core as a fine-grained yellow secondary uranium mineral
Brannerite(U,Ca,Ce)(Ti, Fe)2O6OH10RefractoryMinorCan be leached at higher temperature with increased acid addition
Thorite(Th,U)SiO42Relatively easy to leachTrace
Betafite(Ca,U)2(Ti,Nb,Ta)2O6OH17RefractoryTraceRare occurrences of isolated single grains
NameFormulaU (%)MetallurgyRelative abundanceComments
UraniniteUO288Oxidant and acid for leachingMajorTends to be present as variably sized anhedral grains; observed both as free particles and as inclusions within other minerals
CoffiniteU(SiO4)1-X(OH)4X70Easy to leachSignificantCoffinite tends to be present as tiny particles (<10 µm) adjacent to quartz and alkali feldspar grain boundaries; it often forms discontinuous rims to much larger quartz grains
Boltwoodite(H3O) K(UO2)SiO455Relatively easy to leachPresentObserved in RC chips and drill core as a fine-grained yellow secondary uranium mineral
Brannerite(U,Ca,Ce)(Ti, Fe)2O6OH10RefractoryMinorCan be leached at higher temperature with increased acid addition
Thorite(Th,U)SiO42Relatively easy to leachTrace
Betafite(Ca,U)2(Ti,Nb,Ta)2O6OH17RefractoryTraceRare occurrences of isolated single grains
Table 5.

Summary of Rössing South Bulk Density Data Utilized for Resource Estimation1

LithologyNumber of samplesMinMaxAverage density
Alaskite4422.222.992.63
Calc-silicate1022.513.392.84
Metasediment1592.243.322.77
Gneiss1002.303.232.73
Marble152.633.042.75
Schist2962.333.372.71
Loose alluvial sand1.80
Conglomerate2.20
LithologyNumber of samplesMinMaxAverage density
Alaskite4422.222.992.63
Calc-silicate1022.513.392.84
Metasediment1592.243.322.77
Gneiss1002.303.232.73
Marble152.633.042.75
Schist2962.333.372.71
Loose alluvial sand1.80
Conglomerate2.20

Density readings taken from drill core at Rössing South zone 1

Table 6.

Classification Criteria for Resource Estimates Carried Out at Rössing South

ItemsDiscussionConfidence zone 1Confidence zone 2
Drilling techniquesRC/diamond—industry standard approachHighHigh
LoggingStandard nomenclature applied with recording and apparent high qualityHighHigh
Drill sample recoveryRecorded as goodHighHigh
Subsampling techniquesIndustry standard for both RC and diamond drillingHighHigh
and sample preparation
Quality of assay dataGood internal laboratory and external quality control data available for the majority of the chemical assaying; factored radiometric data is considered to be globally equivalent to chemical assaying but can show local differencesHighModerate to high
Verification of samplingQAQC analysis is within industry acceptable standardsHighHigh
and assaying
Location of sampling pointsMost drill hole collars surveyed by DGPS surveyed and most drill holes have been downhole surveyedHighHigh
Data density and distributionNominal 100- by 100-m drill hole collar spacingLow to highLow to moderate
Audits or reviewsCoffey Mining has reviewed the site drilling and sampling proceduresHighHigh
Database integrityNo material errors identifiedHighHigh
Geologic interpretationInfill drilling is likely to change the mineralization shapes and understanding of structural and grade continuityModerateLow to moderate
Estimation andEstimates based on detailed statistical and geostatistical analysisModerateModerate
modeling techniques
Cutoff gradesRange of cutoff grades reportedHighHigh
Mining factors or assumptionsWhole-block estimates for all mineralized regions completed; the effect of emulating smaller mining blocks has not been investigatedN/AN/A
ItemsDiscussionConfidence zone 1Confidence zone 2
Drilling techniquesRC/diamond—industry standard approachHighHigh
LoggingStandard nomenclature applied with recording and apparent high qualityHighHigh
Drill sample recoveryRecorded as goodHighHigh
Subsampling techniquesIndustry standard for both RC and diamond drillingHighHigh
and sample preparation
Quality of assay dataGood internal laboratory and external quality control data available for the majority of the chemical assaying; factored radiometric data is considered to be globally equivalent to chemical assaying but can show local differencesHighModerate to high
Verification of samplingQAQC analysis is within industry acceptable standardsHighHigh
and assaying
Location of sampling pointsMost drill hole collars surveyed by DGPS surveyed and most drill holes have been downhole surveyedHighHigh
Data density and distributionNominal 100- by 100-m drill hole collar spacingLow to highLow to moderate
Audits or reviewsCoffey Mining has reviewed the site drilling and sampling proceduresHighHigh
Database integrityNo material errors identifiedHighHigh
Geologic interpretationInfill drilling is likely to change the mineralization shapes and understanding of structural and grade continuityModerateLow to moderate
Estimation andEstimates based on detailed statistical and geostatistical analysisModerateModerate
modeling techniques
Cutoff gradesRange of cutoff grades reportedHighHigh
Mining factors or assumptionsWhole-block estimates for all mineralized regions completed; the effect of emulating smaller mining blocks has not been investigatedN/AN/A
Table 7.

Rössing South Resource Estimates as Classified (current from July 2009)

IndicatedInferred
ContainedContained
Tons aboveU3O8U3O8Tons aboveU3O8U3O8
cutoff (Mt)(ppm)(t)cutoff (Mt)(ppm)(t)
Rossing South zone 1
20.752711,000126.343655,000
Rossing South zone 2
10254355,000
Rossing South zone 1 + zone 2
20.752711,000228484110,000
IndicatedInferred
ContainedContained
Tons aboveU3O8U3O8Tons aboveU3O8U3O8
cutoff (Mt)(ppm)(t)cutoff (Mt)(ppm)(t)
Rossing South zone 1
20.752711,000126.343655,000
Rossing South zone 2
10254355,000
Rossing South zone 1 + zone 2
20.752711,000228484110,000

Contents

GeoRef

References

References

Anderson
,
H.
Nash
,
C.
,
1997
,
Integrated lithostructural mapping of the Rössing area, Namibia, using high resolution aeromagnetic, radiometric, Landsat data and aerial photographs
:
Exploration Geophysics
 , v.
28
, p.
185
191
.
Berkman
,
D.A.
,
1995
,
Field geologists manual
:
Australian Institute of Mining and Metallurgy Monograph 9
 ,
390
p.
Brown
,
S.
,
February
2009
,
Uranium disequilibrium study—Namibia
:
Lucas Heights, NSW
 ,
Australia Sydney
,
ANSTO Minerals
,
Technical Note AM/TN/2008_12_12
,
11
p.
Core
,
D.
February
2010
,
Interpretation of the Rössing South airborne survey data
:
Houston, Louisiana, United States
,
Unpublished Technical Report or Extract Resources Ltd
 ,
30
p.
Corner
,
B.
,
1982
,
An interpretation of the aeromagnetic data covering a portion of the Damara orogenic belt with special reference to the occurrence of uraniferous granite, NUCOR PER-95
:
Unpublished Ph.D. thesis
 ,
Johannesburg, South Africa
,
University of the Witswatersrand
.
Corner
,
B.
Sinclair
,
H.
Verran
,
D.
,
2009
,
Radon emanometry in Namibia: Case studies of the Tumas and Rössing South deposits
:
South African Geophysical Conference
 ,
2009
,
5
p., http://www.sagaonline.co.za/2009Confer ence/CD%20Handout/SAGA%202009/PDFs/Abstracts_and_Papers/corne r_paper2.pdf
Freemantle
,
G.
June
2009
,
Preliminary report to Extract Resources (Swakop Uranium) of mineralogical results from QemSCAN analyses of selected surface and core samples of the Rössing South deposits
 :
Johannesburg, South Africa
,
School of Geosciences University of Witwatersrand
,
24
p.
Google Earth
,
2010
,
http://earth.google.com/
Inwood
,
N.
Corley
,
D.
Hill
,
M.
Boyce
,
A.
Culpan
,
N.
,
24 August
2009
,
Husab project
,
Namibia National Instrument 43-101 Technical Report
 
Rössing South, August 2009 Resource Update
,
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