Karibib Regional Exploration
Osino’s Karibib Gold Project consists of 11 licences covering a total area of approximately 2115km2 in central Namibia near the towns of Usakos, Karibib and Omaruru. This gold bearing district hosts the multi-million ounce Navachab Gold Mine as well as the historical Onguati copper-gold and Goldkuppe small scale gold diggings. Much of the area has never been systemically explored as it is covered by calcrete and/or wind-blown sand.
Regional mapping and re-interpretation of the aeromagnetic data by Osino identified a large, previously unmapped, deep regional structure – now named the Karibib Fault. This structure can be traced over 70km and has several gold-in-soil anomalies along it and on splays leading off it. Osino’s exploration activities since 2017 have been focussed along this major structure between the company’s Twin Hills project in the northeast and the Navachab Gold Mine. Additional licences were recently added to the west and south west of Navachab which will be explored during 2019.
The Karibib Project is situated within the Southern Central Zone of the Neo-Proterozoic aged Damara Supergroup, which is comprised of continental margin carbonates and silts which grade into turbidite sequences representing continental shelf and basin deposits. The Damara underwent a major orogenic event at 550–500Ma when the basin closed along a series of major ENE structures. Hydrothermal fluid movement produced widespread gold mineralisation within the carbonates and schists. There are two major producing gold mines within the Damara (Navachab and Otjikoto) as well as several other smaller deposits which have been mined or evaluated in the past including Ondundu, Onguati, Sandamap and Epako.
Stratigraphic Column for Damara Lithologies in Karibib Project Area:
After the discovery of the Navachab gold deposit in 1984, Anglo American carried out a rapid regional exploration programme primarily using stream sampling and targeting similar stratigraphic horizons and basement domes. Known gold occurrences in marbles at Goldkuppe, Albrechtshöhe and Dobbelsberg were followed up with soil sampling as well as limited drilling. Detailed follow-up at Goldkuppe (see separate summary) and Albrechtshöhe was carried out by Helio Resources in 2013. No further regional work was done.
Work Completed by Osino to Date
The eastern portion of the Karibib Fault Trend (20km in length) was soil sampled during 2017 and a number of significant soil anomalies including Twin Hills, OJW and Okapawe were discovered along the fault zone, which appears to be mineralized throughout its length. The soil anomalies over outcropping rock are in the range of 100 to 400ppb gold against a background of less than 5ppb and follow the regional northeast trend. The mineralized prospects occur in association with splays, bends and syn-tectonic granite intrusions, typical of fertile orogenic belts.
Initial Drilling at Twin Hills
A short scout drill program (RC and DD) was undertaken during April and May of 2018 with 23 holes at the Twin Hills prospect and 6 at Okapawe. The drill results at Twin Hills confirmed the presence of gold within a large-scale hydrothermal alteration system along splays from the Karibib fault. The mineralization is present at surface for 3km in strike length before disappearing beneath calcrete cover to the south west. The gold mineralization is contained within a package of quartz biotite schists and is associated with quartz, sericite, arsenopyrite and pyrite alteration. Gold grades and the intensity of the hydrothermal system appear to increase with depth and towards the south west.
In the second half of 2018, exploration was focussed on the south west strike of the hydrothermal system where it is covered by calcrete and wind-blown sand. The work program included calcrete sampling, detailed ground magnetics and RAB drilling to test the bedrock under the calcrete cover.
Calcrete Sampling at Twin Hills
The use of surface calcrete as a sample medium was pioneered in Namibia by Osino following the success of the technique for gold exploration in Western Australia. Calcrete sampling and analysis by ultra-low detection assay has proven to be successful and the Twin Hills Gold anomaly was increased in size from 3km to 11km in strike length using this method. A large scale, well-definedcore of high grade calcrete samples has been outlined at Twin Hills Central measuring 3km x 300m. The Twin Hills Central gold results coincide with a strong magnetic anomaly in the bedrock due to the presence of pyrrhotite, a magnetic sulphide which is associated with the gold mineralization. Anomalous gold assays and magnetic anomalism are present over the entire 11km strike length.
Surface calcrete sampling to the south west of Twin Hills also identified two additional anomalies as follows:
Quarry – Gold anomaly in marble over 1200m in strike length
Main Road– Gold anomaly in marble over 2000m.
The Main Road anomaly has a highly prospective structural setting as it coincides with a zone of brecciation several hundred metres wide, associated with a set of north-south faults which displace the Karibib Fault and continue for several kilometers northwards into the schists.
Bedrock Drilling to Confirm Calcrete Results at Twin Hills
Bedrock drilling was carried out on two fence lines with holes 20m apart for a total of 49 holes. The holes were drilled vertically through calcrete to test the top of the weathered bedrock with the objective of confirming that gold anomalies at surface correlate with gold in the bedrock. The average thickness of the calcrete in this area is 19m and the bedrock lithology in all holes is biotite schist, similar to the lithology outcropping at Twin Hills. The maximum gold assay value was 2.3g/t and a further seven bedrock samples had values between 0.3g/t and 1.1g/t gold.
Shallow Drill Program Along Karibib Fault South West of Twin
A program of shallow vertical holes, consisting of fence lines spaced at 800m apart and 100m hole spacing along the fences, was completed towards the end of 2018. This drilling was designed to sample the top of the calcrete layer below wind-blown sand cover up to 3m thick. Several deeper holes were also drilled to determine the calcrete thickness along the Karibib Fault and initial indications are that the thickness increases from Twin Hills towards the southwest.
Calcrete assays from the shallow drill program along the Karibib Fault indicate potential for further gold targets with priorities as follows:
Karibib Jog – Gold anomaly in calcrete over schists near jog on Karibib Fault
West End – Anomaly in calcrete over schists just to north of Navachab mining licence. These anomalies look like they continue to the north and further sampling will be carried out in that direction.
Acquisition of Ground Magnetic Data Along Karibib Fault
Ground magnetic data has been collected on a grid of 50m spaced lines from Twin Hills to the Navachab Gold Mine property. This data provides lithological and structural detail in an area that is completely covered by calcrete and sand. The detailed magnetic data is of particular value in defining prospective structures under the thick cover to support the geochemical data collected at surface.
Work Planned for 2019
During 2019 the following work is planned
- Twin Hills Central – Diamond and RC drilling
- Twin Hills West – Bedrock sampling using a RAB rig to delineate drill targets, RC drilling depending on results
- Follow-up sampling and bedrock drilling of gold anomalies southwest of Twin Hills
- Calcrete sampling of Airfield Grid
- Sampling and Bedrock drilling around newly acquired Kranzberg Dome