Bonsiega Project, Burkina Faso
The Bonsiega Permit Group covers nine exploration permits totalling 1,045 km2 in area with approximately 100km of strike length in the same greenstone belt which hosts the Samira Hill Mine in Niger. A tenth permit, Bassieri, which covers an additional 74km2, is close to being granted. Most of the permits contain artisanal workings and/or significant gold geochemical anomalies.
The Bonsiega permits were acquired either by direct application in PDI’s name or through separate agreements with third parties. The Company holds 100% ownership of the core permits which carry almost all of the known, drilled gold mineralisation. It is also earning in either 95% or 100% of three peripheral permits.
In earlier exploration, PDI discovered a series of areally large power auger gold geochemical anomalies some of which were tested them with large reverse circulation (RC) drilling programs. A series of prospects were discovered containing ore grade and width gold intercepts. These included Bongou, Dave, Fouli, Laterite Hill, Tamboana and Prospect 71, all of which are 100% owned by PDI. In 2012-13, PDI focused most of its attention on the higher grade prospects, especially Bongou. Several other areas were also tested during the field season with RC drilling, bedrock sampling and/or ground geophysics in order to enlarge the prospect pipeline.
Bongou Prospect (PDI 100%)
The Bongou Prospect is located within the Laterite Hill Gold Field in Eastern Burkina Faso (Figure 1). It covers artisanal workings in the form of an irregular open pit approximately 150m long and 50m wide. Gold mineralisation is contained within an intensely silicified, quartz veined and pyritic microgranite intrusion (Figure 2).
Earlier exploration by PDI included rock chip sampling, trenching and one RC drill hole in 2011-12 which intersected 54m at 2.1g/t Au from 36m including 20m at 4.8g/t Au. A large program of exploration aimed at following up this result commenced on the Bongou Prospect in November 2012, and consisted of RC drilling, ground geophysical surveys, bedrock drilling using a power auger, soil sampling, trenching and geological mapping.
Figure 1: Geology of the Laterite Hill Gold Field showing prospect locations.
Figure 2: Silicified, quartz-veined, gold-mineralised microgranite in contact with foliated gabbro or mafic volcanics in Bongou open pit. Mr Seye Kote, PDI’s Chief Geologist in Burkina Faso, in the foreground.
Bongou RC Drilling
RC drilling at Bongou in 2011-12 produced a series of excellent gold intercepts including:
- BNGRC010: 48m at 4.3g/t Au from 34m
- BNGRC014: 26m at 6.9g/t Au from111m
- BNGRC004: 10m at 7.4g/t Au from 47m
- BNGRC003: 102m at 1.1g/t Au from 4m
- BNGRC002: 70m at 1.2g/t Au from 62m (stopped in mineralisation)
Nearly all of the gold mineralisation consists of altered microgranite, with higher grades located close its northern contact with gabbro (Figures 3a and 3b). At a 3g/t Au cut-off, there are now four, high grade intercepts, all located in this near-contact position, and apparently correlating with each other:
- BNGRC010: 16m at 9.7g/t Au
- BNGRC014: 16m at 8.9 g/t Au
- BNGRC004: 7m at 10.1g/t Au
- BNGRC001: 6m at 11.8g/t Au
Lower grade gold mineralisation with an average grade of approximately 1g/t Au is located adjacent to and to the south of the high grade zone (Figures 3a and 3b). The total true width of the gold mineralised zone is up to 50m.
Figure 3a and 3b: Bongou Cross Sections (a) Left - through RC drill hole BNGRC010, (b) Right - through RC drill holes BNGRC002 and BNGRC014. No vertical exaggeration. See Figure 4 for drill hole locations.
Figure 4: Plan view of drilling, Bongou Prospect.
Bongou Regional Exploration
PDI’s program of geological mapping, ground geophysics and power auger geochemical sampling generated a new target, approximately 400m north-west of the Bongou artisanal workings, with a peak value of 4.8g/t Au. The anomaly covers a larger area than the Bongou mineralised zone and remains untested by drilling (Figure 5). Testing of two other targets along strike along the major Bongou Fault Zone (Figure 6) is largely incomplete because of the presence of thick, wet alluvium. RAB testing of these targets will be required in the next field season.
Figure 5: Power auger gold geochemistry contour plan. Note size of Bongou gold mineralised zone for comparison with size of the discovered gold anomalies.Power auger samples were collected at the interface between the overlying cover and the weathered bedrock and analysed by for gold by AAS at SGS in Ouagadougou.
Figure 6: Regional geological map of the area near Bongou showing location of two target zones (red dashed line ellipses) 4km and 10km north-east of the Bongou artisanal workings.
Metallurgical Test work - Bongou
A program of preliminary metallurgical test work was carried out with the aim of providing an indication of potential gold recovery by standard CIL treatment. One sample was submitted for metallurgical test work, weighing 20kg, obtained from seven RC drill holes. The test work was carried out at SGS’s Perth laboratories under the supervision of Coffey Mining. A mineralogical study was also carried out by Roger Townend and Associates.
All of the sampled intervals in the Bongou composite sample were of primary (not oxidised) mineralisation. A 500g screen fire assay of the composite sample at SGS in Perth gave a head grade of 2.92g/t Au and a multi-element ICP analysis indicated low levels of potentially deleterious elements (e.g. arsenic and antimony).
The sample was ground to 75 microns and subjected to a standard cyanide leach test over 72 hours. Gold recovery was 94% at the end of the test with 90% recovered in the first four hours (Figure 7). Cyanide and lime consumption were 2.0kg/t and 0.3kg/t respectively. Cyanide consumption was not optimised and is expected to decrease considerably in future testing when oxygen levels are increased to the levels expected in a commercial CIP plant.
Figure 7: Graph of gold recovery vs. time – Bongou Prospect composite sample.