Goldkuppe and Extensions
The Goldkuppe and related targets at Oasis, Wedge and others, are part of the Karibib Gold Project. The Karibib Goild Project is made up of 12 licenses and additional details are given in the Regional Exploration – Karibib Gold Project section.
Osino’s Goldkuppe prospect is located in central Namibia, approximately 135 km to the northwest of the capital city of Windhoek. Goldkuppe lies within Exclusive Prospecting License 3739, 20km northeast the company’s flagship Twin Hills project.
Goldkuppe is a relatively advanced exploration project which has seen detailed exploration and several drill programs since the 1980’s by four different license holders, totalling over 20,000m. The historically known mineralization is associated with massive sulphide and skarn within a dolomitic marble unit in the carbonate dominated Karibib Formation.
The Osino team started exploration at Goldkuppe in late 2016 and since then has completed detailed mapping, structural interpretation, a detailed aeromagnetic survey, soil and rock chip sampling to the south of Goldkuppe Hill as well as three short drill programs. This work has resulted in remodelling of mineralization and the structural setting and extending the mineralised strike from 2km to 4.5km. In late 2018, an area of sheeted quartz veins was discovered at Oasis, stratigraphically below the dolomites in banded marbles and schists. This discovery is an important step forward for the Goldkuppe project, as it raises the potential for a bulk minable deposit.
See Regional Geology and Stratigraphy under the Regional Exploration – Karibib Gold Project section tab.
At Goldkuppe, the Karibib rocks are folded into an overturned isoclinal antiform, plunging shallowly to the north east with limbs dipping southeast. This antiform was later refolded along north – south axial planes with fold axes plunging steeply to the south. See Figure 1 below.
Goldkuppe was first discovered during the German colonial period but no formal exploitation took place. After the discovery of the Navachab gold deposit in 1984, Anglo American carried out a rapid regional exploration programme using primarily stream sampling and targeting similar stratigraphic horizons and basement domes as at Navachab. The known gold occurrence at Goldkuppe was drilled by Anglo American in 1988 and again in 2003.
Helio Resources was granted the license in 2007 and signed a Joint Venture deal with Desert Minerals to carry out exploration. Desert Minerals drilled 18 RC and 3 diamond holes in early 2008 but were forced to close down in October of 2008 due to the Global Financial Crisis. Helio restarted exploration in 2011 with a detailed soil programme over Goldkuppe at a spacing of 100 x 25m and then an extension grid to the northwest at 200 x 25m. These results were used as the basis for the later drill programmes. They also carried out detailed geophysics including ground magnetics, electromagnetics and IP.
Between 2010 and 2013, Helio carried out programmes of RC and diamond drilling. The RC programme focussed on extensions of the known mineralization as well as a series of 200m line spacing east – west traverses. The collars were located at 50m intervals with scissor holes drilled east and west at each collar. Helio also drilled twin holes of the best Anglo intercepts in the central part of the target. See Figure 1.
Highlights of the Helio drilling are as follows:
OJD001 22m @ 3.4g/t,
OJD001a 8m @ 2.8 and 12m @ 2.3g/t
OJD005 6m @ 5.6g/t
OJD007 1m @ 32g/t
OJD012 27m @ 1.8g/t (incl 8m @ 4.1g/t)
OJD016 9m @ 2.3
OJR024 7m @ 3.1
OJR072 10m @ 4.3g/t (incl 1m @ 38g/t)
OJD009 18m of 1.0 g/t
OJD008 6m at 5.3 g/t Au
The higher-grade mineralization is primarily associated with massive sulphides (pyrite and chalcopyrite) on or adjacent to the contact between dolomite and underlying white marble. The high Ag – Au ratio as well as the copper association in the massive sulphide is an indicator that the gold is not of orogenic origin. The mineralization is strongly structurally controlled with the massive sulphide zones occurring in the north – south orientated fold noses as saddle reefs and foliation parallel boudins. Lower-grade disseminated mineralization occurs within the skarn alteration zones, which are often magnetic due to the presence of pyrrhotite. These zones can be 20 or 30m wide but are generally less than 1g/t Au and can be less than 0.5g/t Au. Gold also occurs in quartz – sulphide veins which are 1 – 10cm wide.
Work Completed by Osino to Date
Osino started work on the Goldkuppe project towards the end of 2016. When the project was acquired from Helio Resources, there was a proposed drill programme in place to drill out the central portion of the target with a view to assembling an initial resource – see Figure 1. After 25 holes, Osino decided to curtail the drill programme, as it became apparent that the historical understanding of the mineralization and structure was poor, and that further work was required before an effective drill-out could take place.
During 2017, all historical core and chips were re-logged, and a simpler more coherent geological model was put in place. Structural interpretation was carried out on the core and at surface. Detailed surface mapping was carried out (Figure 2) and a first-pass 3-dimensional geological model produced.
In Q4 2017, the Goldkuppe extensions were drilled at North End, Calidus, Spang, Oasis and Wedge with a total of 28 RC holes for 2991m. These targets were all located on anomalous surface geochemistry and rock chip sampling of gossans at surface. See Figure 2.
A new zone of gold mineralization was discovered at Oasis and occurs within a broad unit of banded marble consisting of alternating layers of marble and calc-silicate. The best hole at Oasis was OJR210 which intersected several high-grade quartz-sulphide veins occurring within or adjacent to narrow calc-silicate layers. Metre assays of 9.45 and 6.95g/t Au are contained within a lower grade halo of 49m @ 0.7g/t Au. The gold mineralization at Wedge North, 1000m to the south west of Oasis, is similar in style to Oasis and is possibly the strike continuation of the same large-scale system. See Figure 2.
At Wedge South two holes were drilled to intersect gold mineralized quartz veins which had returned assays of 5.48 and 1.84g/t in rock grab sampling at surface. These veins occur within biotite schist just below the contact with the banded marble. The best drill intercept was in hole OJR215 which returned 10m @ 2.00g/t Au within intensive (diopside – garnet) skarn altered schist. The stratigraphic position and style of mineralization at Wedge South is similar to Navachab Gold Mine 30km to the southwest, which has a global resource of >5moz.
Narrow, low grade gold mineralization was intersected at Calidus, North End and Spang occurring in boudinaged, massive sulphide (pyrrhotite) zones within dolomitic marble, and associated with skarn.
During H1 2018, follow-up work was carried out at Oasis and Wedge including a detailed airborne magnetic survey, in-fill soil sampling, rock chip sampling and mapping.
During Q4 2018, Osino drilled a further 14 core holes for a total of 2,550m at Oasis and Wedge (see Figure 2).
The 2018 drilling was a step-out program from the initial scout drilling conducted during December 2017. The 2018 program was aimed at delineating strike extensions and obtaining data on the structural and lithological controls on mineralization.
Wide zones of low-grade gold mineralization were intersected in several holes at Oasis, with best intercepts of 77m @ 0.4g/t Au (OJD031), 37m @ 0.5g/t Au (OJD028), and 37m @ 0.4g/t Au (OJD027). This mineralization is contained within sheeted quartz – pyrite veins associated with faulting and folding in the banded marble host lithology. These sheeted veins, which have a fairly consistent distribution and grade throughout the mineralized package, strike north – south and dip moderately to the east. This sheeted vein style of gold mineralization is typical of the 5Moz Navachab Gold Deposit 30km to the southwest.
The 2018 results extend the Goldkuppe mineralization by 2.5km to the southwest, adding scale and proving that the gold mineralization extends into the banded marble which forms the footwall to the dolomitic marble. The low-grade sheeted vein mineralization in the banded marble footwall indicates potential for a larger scale bulk deposit upgraded with the Goldkuppe style high-grade shoots.
An updated structural interpretation of the ground and airborne magnetics along with satellite images was carried out in January 2019. The areas of better mineralization are associated with north-south or north-north-east faults which appear to be acting as pathways for hydrothermal fluids – see Figure 1. The most prominent of the north-south structures forms the Goldkuppe Hill, characterized by intense iron and silica alteration, which has seen very little drilling in the programs to date.
Future drilling will focus on the north-south structures, including deeper drilling under Goldkuppe Hill and the area between Oasis and Goldkuppe Hill.