Twin Hills Discovery
The Twin Hills Discovery forms part of Osino’s Karibib Gold Project, which is made up of 12 contiguous licenses to the northeast of Karibib town. Additional details on the project area and regional setting are outlined in the section “Karibib Gold Project – Regional Exploration”.
Twin Hills lies within the Kuiseb Formation, a sequence of turbiditic marine sediments several kilometres thick, which was folded during the neo-Proterozoic Damaran orogen. The gold mineralization is hosted within a meta-greywacke unit, which has been tightly folded into an overturned syncline, underlain by biotite schist and cordierite schist.
During 2018 and 2019, regional sampling on the Karibib Gold Project outlined several gold in soil anomalies along the Karibib Fault Zone. An initial scout drilling program using Reverse Circulation (RC) and Diamond Drilling (DD) was undertaken on hydrothermally altered outcrop at Twin Hills East. This initial drill program confirmed the presence of anomalous gold within a large-scale hydrothermal alteration system, with gold grades increasing down dip and towards the southwest, where the outcrop is covered by calcrete.
A subsequent surface calcrete sampling program indicated that the gold mineralization continued to the southwest of Twin Hills East and this was later confirmed by a percussion drill program to test the bedrock under the calcrete (see additional detail in the Karibib Gold Project – Regional Exploration section).
Work to Date
Phase 1 Diamond Drilling at Twin Hills Central
The initial diamond drill program consisted of seven diamond holes planned to test bedrock gold anomalies covered by a thick layer of calcrete. This initial program was a resounding success with five of the seven holes intersecting significant mineralization open in all directions. The seven diamond holes (for a total of 1,475m) were drilled to a depth of approximately 200m each at an inclination of 60 degrees towards south-southeast. The drill collars were located along three fences about 400m apart with 100m hole spacing. OKD001 and OKD002 both ended in mineralization at 1.11 and 1.43 g/t Au respectively. Initial logging and structural interpretation indicated that the higher-grade mineralization, which was intersected in holes OKD004 and OKD007, is focussed on the southern margin of Twin Hills surrounded by a lower grade envelope over 100m wide in places. See Figure 1 below for the location of the drill holes and assay results.
The best gold intercepts from Phase 1 include:
- OKD001 – 104m @ 0.70 g/t Au (from 115m), incl. 10m @ 1.27 g/t and 20m @ 1.11 g/t
- OKD002 – 189m @ 0.69 g/t Au (from 21m), incl. 14m @ 1.14g/t, 7m @ 1.42g/t and 5m @ 1.43g/t
- OKD003 – 78m @ 0.64 g/t Au (from 91m) incl. 23m @ 1.01g/t
- OKD004 – 65m @ 1.37 g/t Au (16 – 81m), incl. 31m @ 2.2g/t (42-73m)
- OKD007 – 17m @ 2.17g/t Au (116 – 133m), 11m @ 1.76g/t Au (165 – 176m), 6m @ 1.29g/t Au (182 – 188m), 7m @ 1.10g/t Au (16 – 23m) and 3m @ 2.73g/t Au (87 – 90m)
Highest individual meter assays include:
- 08 and 2.84g/t (OKD001)
- 70 and 4.76g/t (OKD002)
- 29g/t (OKD003)
- 36, 4.40 and 4.31g/t (OKD004)
Phase 2 Reverse Circulation and Diamond Drilling
The objective of the second phase was to further define the Twin Hills Discovery and drill test the other newly defined gold prospects within the Twin Hills Cluster.
The planning of Phase 2 included the following priorities:
- Twin Hills Central: Approximately 5,500m of in-fill and step-out drilling aimed at expanding the mineralized horizon along strike and down dip. This drilling consisted of 23 diamond & RC holes along 7 fence lines spaced 200m apart with 100m borehole spacing. Together with the seven Phase 1 boreholes this drilling tested a strike length of 2000m at Twin Hills Central
- Twin Hills West: Approximately 2,000m of first pass diamond & RC drilling of recently defined bedrock gold and arsenic anomalies. This drilling comprised of 9 diamond & RC holes along 3 fence lines over 600m of strike length on the coincident gold and arsenic anomaly. Twin Hills West has by far the largest arsenic anomaly in the Twin Hills Cluster and also has the highest bedrock gold value to date of 2.69g/t
- Barking Dog and Clouds: Approximately 2,500m of first pass diamond & RC drilling of recently defined bedrock gold and arsenic anomalies. This drilling comprised of 13 diamond & RC holes along 4 fence lines, with two lines each for Barking Dog and Clouds respectively.
All the Phase 2 holes were drilled at an azimuth of 160 degrees (SSE) with the exception of OKD022 (at Twin Hills Central), which was drilled in the opposite direction (340 degrees) in order to check the down-dip continuity.
Assay Results for Phase 2 Drilling at Twin Hills Central
A total of 17 RC and 9 DD holes were drilled at Twin Hills Central during the Phase 2 program which ended in early December 2019 (refer to Figure 2 below). The results outlined a wide zone of gold mineralization as well as plunging high-grade shoots on the southern side of the greywacke package at Twin Hills Central.
Highlights from Phase 2:
- OKRD024 – 92m @ 1.40g/t (20 – 112m), incl. 35m @ 2.54g/t
- OKD022 – 37m @ 2.58g/t (173 – 200m), incl. 8m @ 7.50g/t
- OKR017 – 68m @ 0.99g/t (8 – 76m), incl. 24m @ 2.07g/t
- OKR007 – 49m @ 1.04g/t (57 – 106m), incl. 16m @ 1.58 and 16m @ 1.23g/t
- OKR019 – 54m @ 0.89g/t (90 – 144m), incl. 13m @ 1.44g/t and 5m @ 2.03g/t
Highest individual meter assays include:
- 0g/t, 18.3 g/t, 15.8g/t and 15.2g/t
The mineralized zone appears to have been faulted and displaced by a series of northeast striking structures as indicated on Figure 2. The dip of these structures and the amount of displacement is not fully understood at this time and the 2020 drill program will provide further information.
The gold mineralization at Twin Hills Central is associated with shears and parasitic folds in a meta-greywacke unit, which has been tightly to isoclinally folded at the southern margin of the Karibib Basin. The strike of confirmed gold mineralization is now 1200m and remains open to the east, west and at depth. After two phases of drilling, 26 of 33 holes have intersected significant gold mineralization including wide zones of up to 241m in hole OKD002 with high-grade shoots.
Preliminary Twin Hills Central Modelling
Initial qualitative 3-D modelling carried out on the Twin Hills data indicates a mineralization outline to date of at least 1200m in strike and open at both ends (refer to Figure 2 below). The mineralization is up to 200m wide (apparent) and open down dip.
In Figure 2 below, borehole collars have been colour-coded according to a commonly used shorthand method of ranking gold intercepts: multiplying intercept average grade (g/t) by width (meters) resulting in a “g/t x meter” intercept measure (combining both average gold grade and intercept with into a single metric known as “Gram-Meter” or GM). On this basis, Osino considers any intercept of more than 50GM as “very good” and any intercept of more than 100GM as “exceptional”. Using this metric, Osino has a total of 9 exceptional and very good intercepts out of 33 holes drilled so far (since Jan 2019). By way of comparison, during early drilling at the Otjikoto Mine further northeast along the Damara Belt, a total of 7 exceptional and very good intercepts were achieved in the initial 33 boreholes drilled between 1999 and 2004.
At least two high-grade shoots have been located to date which will be better defined in the 2020 round of in-fill and step-out drilling. The western high-grade shoot was intersected by OKRD024 and the eastern high grade shoot by holes OKD004, OKR007 and OKR017 – see Figure 2. The eastern shoot appears to plunge gently to the east and be related to the dominant fold axis measured on the core, which plunges in a similar orientation in this area.
Twin Hills West, Clouds and Barking Dog Targets
See Figure 3 for location of the Twin Hills West, Clouds and Barking Dog Targets, which were all defined by surface calcrete gold anomalies coincident with magnetic highs defined by a ground magnetic survey conducted in 2019.
Twin Hills West is a 1500m gold-in-calcrete anomaly coincident with a magnetic anomaly along an interpreted splay structure. This area is covered by 20 – 40m of calcrete and produced the highest bedrock assay value (2.63 g/t Au) in the 2019 Twin Hills percussion drill program. Eight diamond holes were drilled on two fence lines at Twin Hills West based on the bedrock gold and arsenic assays from the percussion drill program. The initial Twin Hills West
assay results are promising as they provide a clear indication that gold mineralization is present in greywackes similar in style to Twin Hills Central.
Four of the eight holes at Twin Hills West intersected significant mineralization including 28m @ 0.83 g/t (incl. 11m @ 1.16 g/t) (OKD011) and 11m @ 1.08 g/t (OKD019) with grade and width of mineralization appearing to increase to the south and west. Hole OKD017 on the western fence line also intersected zones of low-grade anomalous gold including 9m @ 0.91 g/t and 4m @ 0.78 g/t. See Figure 4 below.
Although the initial intersections are of modest grade and width, the system is open and improving to the west and south with the best-looking mineralization in the southern most hole OKD011, which ended in mineralization at 4.13g/t – see Figure 4. Further drilling at Twin Hills West will therefore focus on chasing the mineralized system to the south and west.
Clouds is a calcrete covered target, approximately 1200m in strike length, that was scout drilled on the strength of its magnetic signature and surface gold anomaly. No bedrock sampling was carried out at Clouds and hence only two speculative holes were drilled in the 2019 campaign.
The two holes intersected the greywacke target horizon and the southern hole intersected zones of weak mineralization associated with folding and shearing. Further drilling will be carried out at Clouds during the 2020 program as this zone may be a satellite or easterly continuation of the Twin Hills Central mineralization. Refer to Figure 3 for the location of the Clouds drill holes.
A fence line of six RC and diamond holes drilled at Barking Dog did not produce any significant gold assays. Much of the drilling at Barking Dog intercepted fine-grained laminated sediments (biotite and muscovite schists) and not the target greywacke unit which hosts the mineralization further west. Future drilling at Barking Dog during the 2020 campaign will focus on locating the greywacke package further to the south.
Geology and Structure of Twin Hills Central
The Twin Hills Central mineralization is hosted by a meta-greywacke unit, which has been tightly folded into a syncline and slightly overturned towards the south. The meta-greywacke core of the syncline is approximately 100m wide but has been thickened to over 200m by thrusting and repetition in the western portion of Twin Hills Central.
Thrusts and shears have developed along the axial planar foliation along the southern limb of the syncline. The meta-greywacke is underlain by a thin unit of biotite schists and then by cordierite schists which are unmineralized. The early drilling at Twin Hills West indicates a similar structural and lithological setting.
The presence of magnetic pyrrhotite within the greywacke unit allowed the use of ground magnetics as a targeting tool. However, we now know that the gold mineralization is more closely associated with arsenopyrite than pyrrhotite and future targeting will include favourable structural settings which are non-magnetic.
The western fence line of drill holes at Twin Hills Central intersected a very wide zone of gold mineralization at > 1 g/t which dips to the north parallel to foliation and the overturned limb (refer to Figure 5 below). This zone will be followed down dip and along strike as the top priority in the 2020 drill program.
Work Planned for 2020
The 2020 work program will focus on the following:
- 20,000m of diamond and RC drilling in two phases of work (in H1 and H2). Two diamond/RC drill rigs will commence in mid-March with the aim of carrying out targeted drilling to define the high-grade shoots, extend the Twin Hills Central mineralization at depth and along strike, and to carry out in-fill drilling. H2 drilling will be similar, but with the aim of completing the in-fill drilling to a nominal 100m x 50m grid, and sufficient to allow a maiden resource estimate to be completed. In addition, further drilling will be carried out at Twin Hills West, Clouds and Barking Dog as well as a number of new targets defined by surface sampling and IP.
- A gradient array IP (induced polarization) survey will commence in March covering Twin Hills Central and Twin Hills West, as well as prospective areas along strike and to the south of both areas. The IP will help identify non-magnetic targets (i.e. pyrrhotite-poor and arsenopyrite dominant) and concealed structural targets.
- An independent structural geology review of Twin Hills Central drill core aiming to supplement the in-house interpretations and assist in targeting high-grade shoots and further mineralization.
- Preliminary metallurgical test-work and gold deportment studies. These are first pass studies aimed at determining the expected gold recovery with a simple mill and leach circuit, and guiding future study design.