Boschhoek

Locality, infrastructure and tenure

The Boschhoek Project is located on the farms Boschhoek 752KS and Rooibokkop 744KS, approximately 180 kilometres north-east of Johannesburg and just 20 kilometres north-east of the town of Marble Hall at the Limpopo-Mpumalanga provincial boundary. The project area is reached by primary and secondary tar roads, accessing the farms on farm roads. Existing infrastructure is good and would be classified as rural-farmland within South Africa having access to a road, rail, power and communication infrastructure. The project area is close to perennial water.

The Boschhoek prospect is represented on the surface as a well exposed gossanous body forming a prominent hill rising above the surrounding undulating farm land. It is cut by the OlifantsRiver with the major part (>80%) of the mineralized-body occurring to the east of the river. A smaller section of the Boschhoek prospect occurs to the west of the OlifantsRiver.

Lerama Resources (Pty) Ltd holds a prospecting right, granted for 5 years in terms of the Mineral and Petroleum Resources Development Act, no 28 of 2002 (MPRDA). The right, including the approved Prospecting Work Programme and Environmental Management Plan, was executed on 14 November 2006. The right has been registered at Mining Titles office as PR212/2007.

Lerama is currently in the process renewing this right and also applying for additional rights on the adjacent farm, Loskop Noord.

Geological and existing resource summary of the Boschhoek Project

The fundamental premise that drives Lerama’s exploration initiatives in the granitic terrane of the Bushveld Complex is encapsulated in a new geological model (Figure 1) that explains the nature and occurrence of polymetallic deposits in these rocks. This model provides guidelines as to where polymetallic deposits in the Bushveld granites are likely to be located.

Polymetallic deposits in the Bushveld granites are now recognized as having affinities with the so-called Fe oxide-copper-gold (IOCG) class of mineralization which form attractive bulk mineable targets around the world and are represented by several world-class mines such as Olympic Dam and Ernest Henry (Australia), Candelaria (Chile), Kansanshi (Zambia) and Guelb Moghrein (Mauritania). The Bushveld granites host numerous small-to-medium sized polymetallic deposits made up of the following metal assemblage: Sn-W-Cu-Pb-Zn-Au-Ag-U-F-Fe-REE.

Boschhoek Figure 1

Figure 1: Simplified geological model illustrating the nature and location of polymetallic (Sn-W-Cu-Pb-Zn-Au-Ag-U-F-Fe-REE) mineral deposits in the granites of the Bushveld Complex .

The numerous polymetallic, IOCG-like, mineralized deposits that are located throughout the Bushveld granites are believed to be derived from hydrothermal fluids that originate from the cooling granite magma and are focused and trapped in the upper portions of the magma chamber, usually along the contacts with the overlying roof of the intrusive body (Figure 1). This model has been developed from detailed research into the origin, nature and location of several of the known polymetallic deposits in the Bushveld granite terrane and provides a useful guide to the location of these deposit types.

Application of this model has provided Lerama with ‘first mover’ advantage in the acquisition of ground in the eastern Bushveld, and also provides it with exploration vectors that enable the company to identify prospective targets. It is pertinent to note that the world-class Vergenoeg F-Fe-(Cu) mine is now recognized as an example of a large IOCG deposit and emphasizes the highly prospective nature of the Bushveld granites for the latter deposit type. The Boschhoek occurrence is considered to represent an example of an unevaluated IOCG-like deposit.

 BOSCHHOEK -  geological appraisal and nature of target

The Rooibokkop-Boschhoek Cu-Pb-Zn-Ag deposit (Figure 2) has been known since the early 20th Century and comprises an array of north-northeast trending, steeply dipping, gossanous veins and breccias bodies hosted in granites of the Bushveld Complex. Base metal sulphides (chalcopyrite-sphalerite-galena) are located predominantly in the veins although alteration and disseminated mineralization surround the veins.

Boschhoek Figure 2

Figure 2: The Marble Hall license block showing the extent of mineralization in the area. The yellow block on Boschhoek 752KS shows the main northern mineralized zone and the area recommended for drilling. The four Loskop Noord blocks outlined are still under application. Mission Exploration drill collars are shown as stars.

The best developed concentration of veins/breccias, and also the area drilled previously (see below), occurs in the northern section of the mineralized zone. It is this area that has been the object of diamond drilling during 2010-2011 by Lerama. The mineralized footprint in this northern zone is at least 1200m long by 300m wide – with mineralization known, from previous drilling, to extend to at least 150m depth.

The geological setting of the Boschhoek prospect is illustrated in Figure 3. Mineralization occurs within a medium- to coarse-grained phase of the Bushveld granite that is overlain some 2km to the west by the Marble Hall fragment, the latter being an outlier of Transvaal Supergroup sediments. The Marble Hall fragment represents a roof pendant to the Bushveld granite and the mineralization is likely, therefore, to occur close to the upper parts of the batholith, a feature that is consistent with Lerama’s exploration guidelines and geological model.

BOSCHHOEK -  the mineralized body and previous exploration activity

The Boschhoek prospect has never been mined although the occurrence of base metal mineralization at this location has been known for several decades. At least one phase of exploration in the region has been well documented and was carried out in the 1970s. A small adit driven approximately 5m into a prominent gossanous ridge on portion 1152 of Loskop Noord is the only direct evidence for early prospecting at the site.

Boschhoek Figure 3

Figure 3: Geology of the Boschhoek prospect (arrowed), underlain by Bushveld granite (pink), and the Marble Hall outlier, underlain by sediments of the Transvaal Supergroup to the west of Boschhoek (after Hartzer, 2000).

In 1977, seven inclined diamond boreholes were drilled by Mission Exploration Company (Table 1). Most of the boreholes were drilled at a inclinations of 50-60o along the western edge of the prominent gossanous ridges that clearly define the mineralized footprint on Boschhoek 752KS and to a lesser extent on Loskop Noord 12JS. The deepest hole was 191.2 m long, corresponding to an actual depth of 165.6 m. Six of these boreholes explored the outer gossanous ridge along the western side of the mineralized body and only one the eastern boundary ridge of the vein deposit (Smits, 1986). Mission Exploration Company also undertook a geochemical survey.

In 1979 Mission Exploration relinquished their option on the properties and donated the core and core logs to the Geology Department, University of Pretoria. These data and cores subsequently underwent detailed mineralogical study and formed the topic of a Masters thesis by Georgette Smits (1979).

 

Table 1
Description of boreholes drilled by Mission Exploration Company in 1977

 

Borehole no.

D/DH

Location

(Farm)

Inclination of

borehole

Azimuth

Total inclined

depth (m)

1

Loskop Noord

60o

128o

70.77

2

Boschhoek

60o

128o

177.40

3

Boschhoek

60o

136o

190.45

4

Boschhoek

50o

132o

191.25

5

Boschhoek

60o

137o

108.50

6

Boschhoek

60o

136o

102.30

7

Loskop Noord

60o

134o

100.00

 

The Smits (1979) study, together with work carried out by Lerama, have concluded that:

    • Gossanous quartz veins and breccias bodies are prominently displayed over a large area on Boschhoek and point to a sizeable zone of mineralization that is almost certainly structurally controlled. The mineralized zone is deeply weathered and is largely oxidized to depths of several tens of metres, as suggested by the Mission Exploration drilling. Despite widespread oxidation, the previous drilling programme nevertheless revealed the existence of sporadic, remnant hypogene (i.e. fresh sulphidic) mineralization. A deeper and more consistent drill programme is recommended as necessary to evaluate the lower, unoxidized hypogene portions of the Boschhoek mineralized body and test the possibility of higher grade ores at depth.
    • The Boschhoek mineralized body formed within a prominent NNE trending fracture zone that initially played a significant role in the localization of the primary mineralization concentrations, and at a later stage was responsible for extensive leaching and oxidation by meteoric waters. It is possible that the upper, oxidized, 100 to 150m of the Boschhoek mineralized body has been partially leached of metals and that richer, supergene ores at depths below 100-150m might yet be encountered. Again, a deeper and more consistent drill programme is required to test the possibility of higher grade supergene ores at depth.
    • The Boschhoek mineralized body is zoned and exhibits lateral and vertical changes in its Cu to Zn+Pb ratio. Chalcopyrite decreases in importance relative to sphalerite and galena away from a westerly copper-rich zone, the latter possibly representing the focus of hydrothermal fluid flow. The mineralogy of Ni-Co sulpharsenide minerals, and also possibly their Ag contents, is also zoned and emphasizes the necessity to drill the Boschhoek mineralized body more comprehensively and to greater depths.

2.3 BOSCHHOEK -  existing resource information

The Boschhoek prospect was drilled by Mission Exploration in the late 1970s. A total of 7 boreholes was drilled to depths of between 71 and 191m (Table 1), mainly along the western edge of the mineralized zone (Figure 2). The details of mineralized intersections encountered in these boreholes are summarized in Table 2. The holes were inclined at between 50o to 60o  on a southeasterly azimuth and encountered sporadic copper mineralization ranging between 0.5% to 2.25% Cu over mineralized intervals up to 13m wide (true depth). Minor Ag mineralization occurs throughout the mineralized zones. Minor Zn mineralization was encountered in one hole drilled on the eastern margin of the prospect, suggesting that the mineralized body may be regionally zoned. There are no formal resource estimations for the Boschhoek mineralized body and the analytical results presented in Table 2 cannot be regarded as being SAMREC compliant.

Boschhoek table 2

Table 2: Published analytical data for drilling carried out by Mission Exploration in the late 1970s (after Smits, 1986).

Assays carried out in the 1970s exploration programme appear to have been obtained only on selected intersections (possibly selected on the basis of sporadic remnant sulphide minerals) and there is no indication of grade continuity along the length of the entire core. These features render it impossible to obtain any meaningful resource estimation, even at an exploration level, for the upper 150m of the Boschhoek mineralized body.

Despite these limitations, it is possible to gain an impression of the size and extent of the mineralized footprint at Boschhoek form the early work. In addition, Figure 4 illustrates the positions of trenches dug on the Boschhoek and Loskop Noord properties and again reveals that Cu mineralization is consistently developed along a strike length that is some 2000m in length over both the Boschhoek and Loskop Noord properties.

Boschhoek Figure 6

Figure 4: Distribution of trenches and Cu assay grades (ppm) of trenches dug along the western edge of the Boschhoek mineralized body by Mission Exploration.

Additional information relevant to the nature and volume of mineralization at Boschhoek is available from the detailed borehole sections that have recently been re-logged by Lerama. Figure 5 is a log of Mission Exploration’s diamond drillhole DH1 drilled to 70m depth; the log shows that the entire core is made up of gossan comprising quartz-hematite-siderite veins and brecciated granite with minor remnant sulphide bearing zones that were assayed for their Cu, Zn and Ag contents. The core log confirms the extensively oxidized nature of the Boschhoek mineralized body, but clearly indicates that the latter was originally made up of primary sulphide minerals that are likely to be better developed at depth below the gossan cap.

Boschhoek Figure 7

Figure 5: Digitized log of borehole DH1 drilled by Mission Exploration into the western edge of the Boschhoek mineralized body.

 

BOSCHHOEK PROJECT – Phase 1 drilling campaign – 2010/2011

The Boschhoek mineralized body is regarded as a potentially open-pittable, bulk mineable, polymetallic target – this summary below provides a summary of Phase 1 of a work programme carried out in partnership with the Anglo American Khula Mining Fund that is designed to evaluate this resource.

2.1 Preparatory work and drill collar selection

Mineralization at Boschhoek is manifest by ferruginous ridges which represent the topographic expression of a set of well-defined copper-bearing lodes dipping at 60 to 80o north-west, comprising mainly siderite and lesser quartz, both containing sulphide minerals. The width of individual veins range from 0.03 to 7 m. On Boschoek the mineralized fracture system bulges towards the north-west attaining a maximum width of about 700 m. From here it narrows to a mere 100 m at the north-eastern tip of the zone where the ridges appear to terminate abruptly. Southwest of the Olifants River, the width of the zone averages 400 m. Veins linking the eastern with western boundary ridge trend between N600E and N90oE. The boundary ridges occupy 2 km of a lineament that is well defined as a GoogleTM image (Figure 6), and is parallel to that of the Wonderkop Fault, 10 km north of Boschoek, as well as the mineralized fissures of the Stavoren-Mutue Fides tin field, situated 10 to 25 km north-northwest of the prospect.

Boschhoek Figure 8

Figure 6: The Boschhoek lineament trending across the Olifants River onto Loskop Noord and the target area selected for Phase 1 drilling.

Examination of the Boschhoek structure on the satellite image in Figure 6 reveals that the main mineralized zone on the Farm Boschhoek itself occurs as a well defined sigmoidal structure that is demarcated on surface as quartz-siderite-hematite vein sets. This was validated prior to drilling by detailed GPS mapping of the target zone. The shape and orientation of the structure suggests that it may be the result of an E-W oriented sinistral strike-slip shear system active at the time of mineralization. Sinistral strike-slip of this type would result in the formation of conjugate Riedel vein sets at 15o and 75o from the shear orientation, somewhat similar to the orientation of the major vein sets at Boschoek.

Based on the mapping described above, drill collars were selected to cut the main ore body along 4 section lines, with holes drilled on an azimuth of 135o ,inclined at 55-60 o and on heel-to-toe transects – drill specifications are outlined in Figure 7.

Boschhoek Figure 10

Figure 7: Phase 1 of the Boschhoek project – Phase 2 of the prospecting programme which includes geochemical sampling and drilling is planned for execution in 2014.

PHASE 1 – DRILL SPECIFICATIONS

4 section lines; 300m line spacing

Holes drilled heel-to-toe or scissored

Holes inclined at 55o to 60 o on 135o to 200m depth

8 holes – circa 2000m of diamond drilling

 

1.2   Drill collar specifications and layout

Final drill collar location was based on logistical as well as geological constraints, with topography and water access playing important roles in the layout of collars. Drill depths were also subject to constraints related to fissuring and water loss. Drill hole dimensions are presented in Table 3 and a plan view of drill hole orientations projected to the surface presented in Figure 8.

Boschhoek Table 3

Table 3 : Diamond drill hole specifications as drilled in Phase 1.

Boschhoek Figure 11

Figure 8 : Diamond drill hole traces projected to the surface.

Core drilling commenced on 1 October 2010 and ended on 30 November 2010.  A total of eight NQ sized holes were drilled for a total length of 2004 metres (Table 3).

Boschhoek Figure 12

Figure 9 : Diamond drilling at Boschhoek in October 2010.

 
css.php